Author name code: rosner
ADS astronomy entries on 2022-09-14
author:"Rosner, Robert"
------------------------------------------------------------------------
Title: Research Opportunities in Plasma Astrophysics
Authors: Bale, Stuart; Bhattacharjee, Amitava; Cattaneo, Fausto; Drake,
Jemes; Ji, Hantao; Lee, Marty; Li, Hui; Liang, Edison; Pound, Marc;
Prager, Stewart; Quataert, Eliot; Remington, Bruce; Rosner, Robert;
Ryutov, Dmitri; Thomas, Edward, Jr; Zweibel, Ellen
Bibcode: 2022arXiv220302406B
Altcode:
Major scientific questions and research opportunities are described
on 10 unprioritized plasma astrophysics topics: (1) magnetic
reconnection, (2) collisionless shocks and particle acceleration, (3)
waves and turbulence, (4) magnetic dynamos, (5) interface and shear
instabilities, (6) angular momentum transport, (7) dusty plasmas,
(8) radiative hydrodynamics, (9) relativistic, pair-dominated and
strongly magnetized plasmas, (10) jets and outflows. Note that this
is a conference report from a Workshop on Opportunities in Plasma
Astrophysics (WOPA, https://w3.pppl.gov/conferences/2010/WOPA/) in
January 2010, that attracted broad representation from the community
and was supported by the U.S. Department of Energy, National Aeronautics
and Space Administration, National Science Foundation, American Physical
Society's Topical Group for Plasma Astrophysics and Division of Plasma
Physics, and Center for Magnetic Self-Organization in Laboratory and
Astrophysical Plasmas. Although there has been much planning and many
developments in both science and infrastructure since the report was
written, most of the motivation, priorities, problems and technical
challenges discussed therein remain unaddressed and are relevant at
the time of posting.
Title: Cryogenic spectrometer for measuring the far-IR to
millimeter-wave absorptivity of cosmic analog dusts
Authors: Perera, T. A.; Zhang, R.; Liu, L. -J.; Schonert, R. K.;
Phan, B.; Nam, S. M.; Dorsey, R.; Lopez, K.; North, K. C.; Ussery,
C.; Roesner, R. A.
Bibcode: 2021ApOpt..60.5880P
Altcode:
No abstract at ADS
Title: The National Science Foundation's Daniel K. Inouye Solar
Telescope — Status Update
Authors: Rimmele, T.; Woeger, F.; Tritschler, A.; Casini, R.; de Wijn,
A.; Fehlmann, A.; Harrington, D.; Jaeggli, S.; Anan, T.; Beck, C.;
Cauzzi, G.; Schad, T.; Criscuoli, S.; Davey, A.; Lin, H.; Kuhn, J.;
Rast, M.; Goode, P.; Knoelker, M.; Rosner, R.; von der Luehe, O.;
Mathioudakis, M.; Dkist Team
Bibcode: 2021AAS...23810601R
Altcode:
The National Science Foundation's 4m Daniel K. Inouye Solar Telescope
(DKIST) on Haleakala, Maui is now the largest solar telescope in the
world. DKIST's superb resolution and polarimetric sensitivity will
enable astronomers to unravel many of the mysteries the Sun presents,
including the origin of solar magnetism, the mechanisms of coronal
heating and drivers of flares and coronal mass ejections. Five
instruments, four of which provide highly sensitive measurements
of solar magnetic fields, including the illusive magnetic field of
the faint solar corona. The DKIST instruments will produce large and
complex data sets, which will be distributed through the NSO/DKIST Data
Center. DKIST has achieved first engineering solar light in December
of 2019. Due to COVID the start of the operations commissioning phase
is delayed and is now expected for fall of 2021. We present a status
update for the construction effort and progress with the operations
commissioning phase.
Title: The Daniel K. Inouye Solar Telescope - Observatory Overview
Authors: Rimmele, Thomas R.; Warner, Mark; Keil, Stephen L.; Goode,
Philip R.; Knölker, Michael; Kuhn, Jeffrey R.; Rosner, Robert R.;
McMullin, Joseph P.; Casini, Roberto; Lin, Haosheng; Wöger, Friedrich;
von der Lühe, Oskar; Tritschler, Alexandra; Davey, Alisdair; de Wijn,
Alfred; Elmore, David F.; Fehlmann, André; Harrington, David M.;
Jaeggli, Sarah A.; Rast, Mark P.; Schad, Thomas A.; Schmidt, Wolfgang;
Mathioudakis, Mihalis; Mickey, Donald L.; Anan, Tetsu; Beck, Christian;
Marshall, Heather K.; Jeffers, Paul F.; Oschmann, Jacobus M.; Beard,
Andrew; Berst, David C.; Cowan, Bruce A.; Craig, Simon C.; Cross,
Eric; Cummings, Bryan K.; Donnelly, Colleen; de Vanssay, Jean-Benoit;
Eigenbrot, Arthur D.; Ferayorni, Andrew; Foster, Christopher; Galapon,
Chriselle Ann; Gedrites, Christopher; Gonzales, Kerry; Goodrich, Bret
D.; Gregory, Brian S.; Guzman, Stephanie S.; Guzzo, Stephen; Hegwer,
Steve; Hubbard, Robert P.; Hubbard, John R.; Johansson, Erik M.;
Johnson, Luke C.; Liang, Chen; Liang, Mary; McQuillen, Isaac; Mayer,
Christopher; Newman, Karl; Onodera, Brialyn; Phelps, LeEllen; Puentes,
Myles M.; Richards, Christopher; Rimmele, Lukas M.; Sekulic, Predrag;
Shimko, Stephan R.; Simison, Brett E.; Smith, Brett; Starman, Erik;
Sueoka, Stacey R.; Summers, Richard T.; Szabo, Aimee; Szabo, Louis;
Wampler, Stephen B.; Williams, Timothy R.; White, Charles
Bibcode: 2020SoPh..295..172R
Altcode:
We present an overview of the National Science Foundation's Daniel
K. Inouye Solar Telescope (DKIST), its instruments, and support
facilities. The 4 m aperture DKIST provides the highest-resolution
observations of the Sun ever achieved. The large aperture of
DKIST combined with state-of-the-art instrumentation provide the
sensitivity to measure the vector magnetic field in the chromosphere
and in the faint corona, i.e. for the first time with DKIST we will
be able to measure and study the most important free-energy source
in the outer solar atmosphere - the coronal magnetic field. Over its
operational lifetime DKIST will advance our knowledge of fundamental
astronomical processes, including highly dynamic solar eruptions
that are at the source of space-weather events that impact our
technological society. Design and construction of DKIST took over two
decades. DKIST implements a fast (f/2), off-axis Gregorian optical
design. The maximum available field-of-view is 5 arcmin. A complex
thermal-control system was implemented in order to remove at prime
focus the majority of the 13 kW collected by the primary mirror and
to keep optical surfaces and structures at ambient temperature, thus
avoiding self-induced local seeing. A high-order adaptive-optics
system with 1600 actuators corrects atmospheric seeing enabling
diffraction limited imaging and spectroscopy. Five instruments, four
of which are polarimeters, provide powerful diagnostic capability
over a broad wavelength range covering the visible, near-infrared,
and mid-infrared spectrum. New polarization-calibration strategies
were developed to achieve the stringent polarization accuracy
requirement of 5×10−4. Instruments can be combined and
operated simultaneously in order to obtain a maximum of observational
information. Observing time on DKIST is allocated through an open,
merit-based proposal process. DKIST will be operated primarily in
"service mode" and is expected to on average produce 3 PB of raw
data per year. A newly developed data center located at the NSO
Headquarters in Boulder will initially serve fully calibrated data to
the international users community. Higher-level data products, such as
physical parameters obtained from inversions of spectro-polarimetric
data will be added as resources allow.
Title: Major Scientific Challenges and Opportunities in Understanding
Magnetic Reconnection and Related Explosive Phenomena in Solar and
Heliospheric Plasmas
Authors: Ji, H.; Karpen, J.; Alt, A.; Antiochos, S.; Baalrud, S.;
Bale, S.; Bellan, P. M.; Begelman, M.; Beresnyak, A.; Bhattacharjee,
A.; Blackman, E. G.; Brennan, D.; Brown, M.; Buechner, J.; Burch, J.;
Cassak, P.; Chen, B.; Chen, L. -J.; Chen, Y.; Chien, A.; Comisso,
L.; Craig, D.; Dahlin, J.; Daughton, W.; DeLuca, E.; Dong, C. F.;
Dorfman, S.; Drake, J.; Ebrahimi, F.; Egedal, J.; Ergun, R.; Eyink,
G.; Fan, Y.; Fiksel, G.; Forest, C.; Fox, W.; Froula, D.; Fujimoto,
K.; Gao, L.; Genestreti, K.; Gibson, S.; Goldstein, M.; Guo, F.; Hare,
J.; Hesse, M.; Hoshino, M.; Hu, Q.; Huang, Y. -M.; Jara-Almonte, J.;
Karimabadi, H.; Klimchuk, J.; Kunz, M.; Kusano, K.; Lazarian, A.; Le,
A.; Lebedev, S.; Li, H.; Li, X.; Lin, Y.; Linton, M.; Liu, Y. -H.;
Liu, W.; Longcope, D.; Loureiro, N.; Lu, Q. -M.; Ma, Z-W.; Matthaeus,
W. H.; Meyerhofer, D.; Mozer, F.; Munsat, T.; Murphy, N. A.; Nilson,
P.; Ono, Y.; Opher, M.; Park, H.; Parker, S.; Petropoulou, M.; Phan,
T.; Prager, S.; Rempel, M.; Ren, C.; Ren, Y.; Rosner, R.; Roytershteyn,
V.; Sarff, J.; Savcheva, A.; Schaffner, D.; Schoeffier, K.; Scime, E.;
Shay, M.; Sironi, L.; Sitnov, M.; Stanier, A.; Swisdak, M.; TenBarge,
J.; Tharp, T.; Uzdensky, D.; Vaivads, A.; Velli, M.; Vishniac, E.;
Wang, H.; Werner, G.; Xiao, C.; Yamada, M.; Yokoyama, T.; Yoo, J.;
Zenitani, S.; Zweibel, E.
Bibcode: 2020arXiv200908779J
Altcode:
Magnetic reconnection underlies many explosive phenomena in the
heliosphere and in laboratory plasmas. The new research capabilities in
theory/simulations, observations, and laboratory experiments provide the
opportunity to solve the grand scientific challenges summarized in this
whitepaper. Success will require enhanced and sustained investments
from relevant funding agencies, increased interagency/international
partnerships, and close collaborations of the solar, heliospheric,
and laboratory plasma communities. These investments will deliver
transformative progress in understanding magnetic reconnection and
related explosive phenomena including space weather events.
Title: Major Scientific Challenges and Opportunities in Understanding
Magnetic Reconnection and Related Explosive Phenomena throughout
the Universe
Authors: Ji, H.; Alt, A.; Antiochos, S.; Baalrud, S.; Bale, S.;
Bellan, P. M.; Begelman, M.; Beresnyak, A.; Blackman, E. G.; Brennan,
D.; Brown, M.; Buechner, J.; Burch, J.; Cassak, P.; Chen, L. -J.;
Chen, Y.; Chien, A.; Craig, D.; Dahlin, J.; Daughton, W.; DeLuca, E.;
Dong, C. F.; Dorfman, S.; Drake, J.; Ebrahimi, F.; Egedal, J.; Ergun,
R.; Eyink, G.; Fan, Y.; Fiksel, G.; Forest, C.; Fox, W.; Froula, D.;
Fujimoto, K.; Gao, L.; Genestreti, K.; Gibson, S.; Goldstein, M.; Guo,
F.; Hesse, M.; Hoshino, M.; Hu, Q.; Huang, Y. -M.; Jara-Almonte, J.;
Karimabadi, H.; Klimchuk, J.; Kunz, M.; Kusano, K.; Lazarian, A.;
Le, A.; Li, H.; Li, X.; Lin, Y.; Linton, M.; Liu, Y. -H.; Liu, W.;
Longcope, D.; Loureiro, N.; Lu, Q. -M.; Ma, Z-W.; Matthaeus, W. H.;
Meyerhofer, D.; Mozer, F.; Munsat, T.; Murphy, N. A.; Nilson, P.;
Ono, Y.; Opher, M.; Park, H.; Parker, S.; Petropoulou, M.; Phan, T.;
Prager, S.; Rempel, M.; Ren, C.; Ren, Y.; Rosner, R.; Roytershteyn,
V.; Sarff, J.; Savcheva, A.; Schaffner, D.; Schoeffier, K.; Scime, E.;
Shay, M.; Sitnov, M.; Stanier, A.; TenBarge, J.; Tharp, T.; Uzdensky,
D.; Vaivads, A.; Velli, M.; Vishniac, E.; Wang, H.; Werner, G.; Xiao,
C.; Yamada, M.; Yokoyama, T.; Yoo, J.; Zenitani, S.; Zweibel, E.
Bibcode: 2020arXiv200400079J
Altcode:
This white paper summarizes major scientific challenges and
opportunities in understanding magnetic reconnection and related
explosive phenomena as a fundamental plasma process.
Title: Major Scientific Challenges and Opportunities in Understanding
Magnetic Reconnection and Related Explosive Phenomena throughout
the Universe
Authors: Ji, Hantao; Alt, A.; Antiochos, S.; Baalrud, S.; Bale, S.;
Bellan, P. M.; Begelman, M.; Beresnyak, A.; Blackman, E. G.; Brennan,
D.; Brown, M.; Buechner, J.; Burch, J.; Cassak, P.; Chen, L. -J.;
Chen, Y.; Chien, A.; Craig, D.; Dahlin, J.; Daughton, W.; DeLuca, E.;
Dong, C. F.; Dorfman, S.; Drake, J.; Ebrahimi, F.; Egedal, J.; Ergun,
R.; Eyink, G.; Fan, Y.; Fiksel, G.; Forest, C.; Fox, W.; Froula, D.;
Fujimoto, K.; Gao, L.; Genestreti, K.; Gibson, S.; Goldstein, M.;
Guo, F.; Hesse, M.; Hoshino, M.; Hu, Q.; Huang, Y. -M.; Jara-Almonte,
J.; Karimabadi, H.; Klimchuk, J.; Kunz, M.; Kusano, K.; Lazarian,
A.; Le, A.; Li, H.; Li, X.; Lin, Y.; Linton, M.; Liu, Y. -H.; Liu,
W.; Longcope, D.; Louriero, N.; Lu, Q. -M.; Ma, Z. -W.; Matthaeus,
W. H.; Meyerhofer, D.; Mozer, F.; Munsat, T.; Murphy, N. A.; Nilson,
P.; Ono, Y.; Opher, M.; Park, H.; Parker, S.; Petropoulou, M.; Phan,
T.; Prager, S.; Rempel, M.; Ren, C.; Ren, Y.; Rosner, R.; Roytershteyn,
V.; Sarff, J.; Savcheva, A.; Schaffner, D.; Schoeffier, K.; Scime, E.;
Shay, M.; Sitnov, M.; Stanier, A.; TenBarge, J.; Tharp, T.; Uzdensky,
D.; Vaivads, A.; Velli, M.; Vishniac, E.; Wang, H.; Werner, G.; Xiao,
C.; Yamada, M.; Yokoyama, T.; Yoo, J.; Zenitani, S.; Zweibel, E.
Bibcode: 2019BAAS...51c...5J
Altcode: 2019astro2020T...5J
This is a group white paper of 100 authors (each with explicit
permission via email) from 51 institutions on the topic of magnetic
reconnection which is relevant to 6 thematic areas. Grand challenges
and research opportunities are described in observations, numerical
modeling and laboratory experiments in the upcoming decade.
Title: Status of the Daniel K. Inouye Solar Telescope: unraveling
the mysteries the Sun.
Authors: Rimmele, Thomas R.; Martinez Pillet, Valentin; Goode, Philip
R.; Knoelker, Michael; Kuhn, Jeffrey Richard; Rosner, Robert; Casini,
Roberto; Lin, Haosheng; von der Luehe, Oskar; Woeger, Friedrich;
Tritschler, Alexandra; Fehlmann, Andre; Jaeggli, Sarah A.; Schmidt,
Wolfgang; De Wijn, Alfred; Rast, Mark; Harrington, David M.; Sueoka,
Stacey R.; Beck, Christian; Schad, Thomas A.; Warner, Mark; McMullin,
Joseph P.; Berukoff, Steven J.; Mathioudakis, Mihalis; DKIST Team
Bibcode: 2018AAS...23231601R
Altcode:
The 4m Daniel K. Inouye Solar Telescope (DKIST) currently under
construction on Haleakala, Maui will be the world’s largest solar
telescope. Designed to meet the needs of critical high resolution and
high sensitivity spectral and polarimetric observations of the sun,
this facility will perform key observations of our nearest star that
matters most to humankind. DKIST’s superb resolution and sensitivity
will enable astronomers to address many of the fundamental problems
in solar and stellar astrophysics, including the origin of stellar
magnetism, the mechanisms of coronal heating and drivers of the
solar wind, flares, coronal mass ejections and variability in solar
and stellar output. DKIST will also address basic research aspects of
Space Weather and help improve predictive capabilities. In combination
with synoptic observations and theoretical modeling DKIST will unravel
the many remaining mysteries of the Sun.The construction of DKIST is
progressing on schedule with 80% of the facility complete. Operations
are scheduled to begin early 2020. DKIST will replace the NSO
facilities on Kitt Peak and Sac Peak with a national facility with
worldwide unique capabilities. The design allows DKIST to operate as
a coronagraph. Taking advantage of its large aperture and infrared
polarimeters DKIST will be capable to routinely measure the currently
illusive coronal magnetic fields. The state-of-the-art adaptive optics
system provides diffraction limited imaging and the ability to resolve
features approximately 20 km on the Sun. Achieving this resolution
is critical for the ability to observe magnetic structures at their
intrinsic, fundamental scales. Five instruments will be available at
the start of operations, four of which will provide highly sensitive
measurements of solar magnetic fields throughout the solar atmosphere
- from the photosphere to the corona. The data from these instruments
will be distributed to the world wide community via the NSO/DKIST data
center located in Boulder. We present examples of science objectives
and provide an overview of the facility and project status, including
the ongoing efforts of the community to develop the critical science
plan for the first 2-3 years of operations.
Title: Construction Status and Early Science with the Daniel K. Inouye
Solar Telescope
Authors: McMullin, Joseph P.; Rimmele, Thomas R.; Warner, Mark;
Martinez Pillet, Valentin; Craig, Simon; Woeger, Friedrich; Tritschler,
Alexandra; Berukoff, Steven J.; Casini, Roberto; Goode, Philip R.;
Knoelker, Michael; Kuhn, Jeffrey Richard; Lin, Haosheng; Mathioudakis,
Mihalis; Reardon, Kevin P.; Rosner, Robert; Schmidt, Wolfgang
Bibcode: 2016SPD....4720101M
Altcode:
The 4-m Daniel K. Inouye Solar Telescope (DKIST) is in its seventh
year of overall development and its fourth year of site construction
on the summit of Haleakala, Maui. The Site Facilities (Utility
Building and Support & Operations Building) are in place with
ongoing construction of the Telescope Mount Assembly within. Off-site
the fabrication of the component systems is completing with early
integration testing and verification starting.Once complete this
facility will provide the highest sensitivity and resolution for study
of solar magnetism and the drivers of key processes impacting Earth
(solar wind, flares, coronal mass ejections, and variability in solar
output). The DKIST will be equipped initially with a battery of first
light instruments which cover a spectral range from the UV (380 nm)
to the near IR (5000 nm), and capable of providing both imaging and
spectro-polarimetric measurements throughout the solar atmosphere
(photosphere, chromosphere, and corona); these instruments are being
developed by the National Solar Observatory (Visible Broadband Imager),
High Altitude Observatory (Visible Spectro-Polarimeter), Kiepenheuer
Institute (Visible Tunable Filter) and the University of Hawaii
(Cryogenic Near-Infrared Spectro-Polarimeter and the Diffraction-Limited
Near-Infrared Spectro-Polarimeter). Further, a United Kingdom consortium
led by Queen's University Belfast is driving the development of high
speed cameras essential for capturing the highly dynamic processes
measured by these instruments. Finally, a state-of-the-art adaptive
optics system will support diffraction limited imaging capable of
resolving features approximately 20 km in scale on the Sun.We present
the overall status of the construction phase along with the current
challenges as well as a review of the planned science testing and the
transition into early science operations.
Title: Daniel K. Inouye Solar Telescope: Overview and Status
Authors: Rimmele, Thomas; McMullin, Joseph; Warner, Mark; Craig,
Simon; Woeger, Friedrich; Tritschler, Alexandra; Cassini, Roberto;
Kuhn, Jeff; Lin, Haosheng; Schmidt, Wolfgang; Berukoff, Steve; Reardon,
Kevin; Goode, Phil; Knoelker, Michael; Rosner, Robert; Mathioudakis,
Mihalis; DKIST TEAM
Bibcode: 2015IAUGA..2255176R
Altcode:
The 4m Daniel K. Inouye Solar Telescope (DKIST) currently under
construction on Haleakala, Maui will be the world’s largest solar
telescope. Designed to meet the needs of critical high resolution and
high sensitivity spectral and polarimetric observations of the sun,
this facility will perform key observations of our nearest star that
matters most to humankind. DKIST’s superb resolution and sensitivity
will enable astronomers to unravel many of the mysteries the Sun
presents, including the origin of solar magnetism, the mechanisms of
coronal heating and drivers of the solar wind, flares, coronal mass
ejections and variability in solar output. The all-reflecting, off-axis
design allows the facility to observe over a broad wavelength range and
enables DKIST to operate as a coronagraph. In addition, the photon flux
provided by its large aperture will be capable of routine and precise
measurements of the currently elusive coronal magnetic fields. The
state-of-the-art adaptive optics system provides diffraction limited
imaging and the ability to resolve features approximately 20 km on
the Sun. Five first light instruments, representing a broad community
effort, will be available at the start of operations: Visible Broadband
Imager (National Solar Observatory), Visible Spectro-Polarimeter (High
Altitude Observatory), Visible Tunable Filter (Kiepenheuer Institute,
Germany), Diffraction Limited NIR Spectro-Polarimeter (University
of Hawaii) and the Cryogenic NIR Spectro-Polarimeter (University of
Hawaii). High speed cameras for capturing highly dynamic processes
in the solar atmosphere are being developed by a UK consortium. Site
construction on Haleakala began in December 2012 and is progressing
on schedule. Operations are scheduled to begin in 2019. We provide an
overview of the facility, discuss the construction status, and present
progress with DKIST operations planning.
Title: Gravitationally Unstable Flames: Rayleigh-Taylor Stretching
versus Turbulent Wrinkling
Authors: Hicks, E. P.; Rosner, R.
Bibcode: 2013ApJ...771..135H
Altcode:
In this paper, we provide support for the Rayleigh-Taylor-(RT)-based
subgrid model used in full-star simulations of deflagrations in Type
Ia supernovae explosions. We use the results of a parameter study of
two-dimensional direct numerical simulations of an RT unstable model
flame to distinguish between the two main types of subgrid models (RT or
turbulence dominated) in the flamelet regime. First, we give scalings
for the turbulent flame speed, the Reynolds number, the viscous scale,
and the size of the burning region as the non-dimensional gravity (G)
is varied. The flame speed is well predicted by an RT-based flame speed
model. Next, the above scalings are used to calculate the Karlovitz
number (Ka) and to discuss appropriate combustion regimes. No transition
to thin reaction zones is seen at Ka = 1, although such a transition is
expected by turbulence-dominated subgrid models. Finally, we confirm
a basic physical premise of the RT subgrid model, namely, that the
flame is fractal, and thus self-similar. By modeling the turbulent
flame speed, we demonstrate that it is affected more by large-scale RT
stretching than by small-scale turbulent wrinkling. In this way, the RT
instability controls the flame directly from the large scales. Overall,
these results support the RT subgrid model.
Title: Computation as a Bridge between the Laboratory and Astrophysics
Authors: Rosner, Robert; Cattaneo, F.
Bibcode: 2013AAS...22221201R
Altcode:
Over the past decade, the many deep connections between terrestrial
laboratory studies and astrophysics have been powerfully supported
by modern numerical simulation: These calculations are able to make
contact with modeling of both physically complex astrophysical phenomena
and related phenomena observed in far greater detail in terrestrial
laboratories. We will describe several examples that illustrate the
power of numerical simulations to bridge laboratory and astrophysical
studies.
Title: The Advanced Technology Solar Telescope: Science Drivers and
Construction Status
Authors: Rimmele, Thomas; Berger, Thomas; McMullin, Joseph; Keil,
Stephen; Goode, Phil; Knoelker, Michael; Kuhn, Jeff; Rosner, Robert;
Casini, Roberto; Lin, Haosheng; Woeger, Friedrich; von der Luehe,
Oskar; Tritschler, Alexandra; Atst Team
Bibcode: 2013EGUGA..15.6305R
Altcode:
The 4-meter Advance Technology Solar Telescope (ATST) currently
under construction on the 3000 meter peak of Haleakala on Maui,
Hawaii will be the world's most powerful solar telescope and the
leading ground-based resource for studying solar magnetism. The
solar atmosphere is permeated by a 'magnetic carpet' that constantly
reweaves itself to control solar irradiance and its effects on Earth's
climate, the solar wind, and space weather phenomena such as flares and
coronal mass ejections. Precise measurement of solar magnetic fields
requires a large-aperture solar telescope capable of resolving a few
tens of kilometers on the solar surface. With its 4 meter aperture,
the ATST will for the first time resolve magnetic structure at the
intrinsic scales of plasma convection and turbulence. The ATST's
ability to perform accurate and precise spectroscopic and polarimetric
measurements of magnetic fields in all layers of the solar atmosphere,
including accurate mapping of the elusive coronal magnetic fields,
will be transformative in advancing our understanding of the magnetic
solar atmosphere. The ATST will utilize the Sun as an important astro-
and plasma-physics "laboratory" demonstrating key aspects of omnipresent
cosmic magnetic fields. The ATST construction effort is led by the US
National Solar Observatory. State-of-the-art instrumentation will be
constructed by US and international partner institutions. The technical
challenges the ATST is facing are numerous and include the design of the
off-axis main telescope, the development of a high order adaptive optics
system that delivers a corrected beam to the instrument laboratory,
effective handling of the solar heat load on optical and structural
elements, and minimizing scattered light to enable observations
of the faint corona. The ATST project has transitioned from design
and development to its construction phase. The project has awarded
design and fabrication contracts for major telescope subsystems. Site
construction has commenced following the successful conclusion of
the site permitting process. Science goals and construction status of
telescope and instrument systems will be discussed.
Title: Construction of the Advanced Technology Solar Telescope -
A Progress Report.
Authors: Rimmele, T. R.; Keil, S.; McMullin, J.; Goode, P. R.;
Knoelker, M.; Kuhn, J. R.; Rosner, R.; ATST Team
Bibcode: 2012IAUSS...6E.206R
Altcode:
The 4m Advance Technology Solar Telescope (ATST) will be the most
powerful solar telescope and the world's leading ground-based resource
for studying solar magnetism that controls the solar wind, flares,
coronal mass ejections and variability in the Sun's output. The ATST
will provide high resolution and high sensitivity observations of the
dynamic solar magnetic fields throughout the solar atmosphere, including
the corona at infrared wavelengths. With its 4 m aperture, ATST will
resolve magnetic features at their intrinsic scales. A high order
adaptive optics system delivers a corrected beam to the initial set of
five state-of-the-art, facility class instrumentation located in the
coude laboratory facility. Photopheric and chromospheric magnetometry
is part of the key mission of four of these instruments. Coronal
magnetometry and spectroscopy will be performed by two of these
instruments at infrared wavelengths. The ATST project has transitioned
from design and development to its construction phase. Site construction
is expected to begin in the first half of 2012. The project has awarded
design and fabrication contracts for major telescope subsystems. A
robust instrument program has been established and all instruments
have passed preliminary design reviews or critical design reviews. A
brief summary of the science goals and observational requirements of
the ATST will be given, followed by a summary of the project status of
the telescope and discussion of the approach to integrating instruments
into the facility.
Title: Construction of the Advanced Technology Solar Telescope
Authors: Rimmele, T. R.; Keil, S.; McMullin, J.; Knölker, M.; Kuhn,
J. R.; Goode, P. R.; Rosner, R.; Casini, R.; Lin, H.; Tritschler,
A.; Wöger, F.; ATST Team
Bibcode: 2012ASPC..463..377R
Altcode:
The 4m Advance Technology Solar Telescope (ATST) will be the most
powerful solar telescope and the world's leading ground-based resource
for studying solar magnetism that controls the solar wind, flares,
coronal mass ejections and variability in the Sun's output. The
project has entered its construction phase. Major subsystems have
been contracted. As its highest priority science driver ATST shall
provide high resolution and high sensitivity observations of the
dynamic solar magnetic fields throughout the solar atmosphere,
including the corona at infrared wavelengths. With its 4m aperture,
ATST will resolve features at 0.″03 at visible wavelengths and
obtain 0.″1 resolution at the magnetically highly sensitive near
infrared wavelengths. A high order adaptive optics system delivers a
corrected beam to the initial set of state-of-the-art, facility class
instrumentation located in the Coudé laboratory facility. The initial
set of first generation instruments consists of five facility class
instruments, including imagers and spectro-polarimeters. The high
polarimetric sensitivity and accuracy required for measurements of
the illusive solar magnetic fields place strong constraints on the
polarization analysis and calibration. Development and construction
of a four-meter solar telescope presents many technical challenges,
including thermal control of the enclosure, telescope structure and
optics and wavefront control. A brief overview of the science goals
and observational requirements of the ATST will be given, followed by a
summary of the design status of the telescope and its instrumentation,
including design status of major subsystems, such as the telescope
mount assembly, enclosure, mirror assemblies, and wavefront correction
Title: The Solar Tachocline
Authors: Hughes, D. W.; Rosner, R.; Weiss, N. O.
Bibcode: 2012sota.book.....H
Altcode:
Preface; Part I. Setting the Scene: 1. An introduction to the solar
tachocline D. O. Gough; 2. Reflections on the solar tachocline
E. A. Spiegel; Part II. Observations: 3. Observational results
and issues concerning the tachocline J. Christensen-Dalsgaard and
M. J. Thompson; Part III. Hydrodynamic Models: 4. Hydrodynamic models of
the tachocline J.-P. Zahn; 5. Turbulence in the tachocline M. S. Miesch;
6. Mean field modelling of differential rotation G. Rudiger and
L. L. Kitchatinov; Part IV. Hydromagnetic Properties: 7. Magnetic
confinement of the solar tachocline P. Garaud; 8. Magnetic confinement
and the sharp tachopause M. E. McIntyre; 9. ß-Plane MHD turbulence
and dissipation in the solar tachocline P. H. Diamond, K. Itoh,
S.-I. Itoh and L. J. Silvers; Part V. Instabilities: 10. Global
MHD instabilities of the tachocline P. A. Gilman and P. S. Cally;
11. Magnetic buoyancy instabilities in the tachocline D. W. Hughes;
12. Instabilities, angular momentum transport and magnetohydrodynamic
turbulence G. I. Ogilvie; Part VI. Dynamo Action: 13. The solar dynamo
and the tachocline S. M. Tobias and N. O. Weiss; Part VII. Overview:
14. On studying the rotating solar interior R. Rosner; Index.
Title: Advanced Technology Solar Telescope Construction: Progress
Report
Authors: Rimmele, Thomas R.; McMullin, J.; Keil, S.; Goode, P.;
Knoelker, M.; Kuhn, J.; Rosner, R.; ATST Team
Bibcode: 2012AAS...22012202R
Altcode:
The 4m Advance Technology Solar Telescope (ATST) on Haleakala will be
the most powerful solar telescope and the world’s leading ground-based
resource for studying solar magnetism that controls the solar wind,
flares, coronal mass ejections and variability in the Sun’s
output. The ATST will provide high resolution and high sensitivity
observations of the dynamic solar magnetic fields throughout the solar
atmosphere, including the corona at infrared wavelengths. With its 4
m aperture, ATST will resolve magnetic features at their intrinsic
scales. A high order adaptive optics system delivers a corrected
beam to the initial set of five state-of-the-art, facility class
instrumentation located in the coude laboratory facility. Photopheric
and chromospheric magnetometry is part of the key mission of four
of these instruments. Coronal magnetometry and spectroscopy will be
performed by two of these instruments at infrared wavelengths. The
ATST project has transitioned from design and development to its
construction phase. Site construction is expected to begin in April
2012. The project has awarded design and fabrication contracts for major
telescope subsystems. A robust instrument program has been established
and all instruments have passed preliminary design reviews or critical
design reviews. A brief overview of the science goals and observational
requirements of the ATST will be given, followed by a summary of the
project status of the telescope and discussion of the approach to
integrating instruments into the facility. The National Science
Foundation (NSF) through the National Solar Observatory (NSO) funds
the ATST Project. The NSO is operated under a cooperative agreement
between the Association of Universities for Research in Astronomy,
Inc. (AURA) and NSF.
Title: The Transition to Turbulence of Rayleigh-Taylor Unstable Flames
Authors: Hicks, Elizabeth P.; Rosner, R.
Bibcode: 2011AAS...21730803H
Altcode: 2011BAAS...4330803H
Part of the uncertainty surrounding the explosion mechanism of
Type 1A supernovae is the extent to which the turbulence created
by the flame front can speed the flame up. A premixed flame moving
against a sufficiently strong gravitational field becomes deformed
and creates vorticity. If gravity is strong enough, this vorticity
is shed and deposited behind the flame front. We have completed some
two-dimensional direct numerical simulations of this shedding process
for various values of the gravitational force. If gravity is weak
enough, the flame front remains flat and no vorticity is created. If
gravity is slightly stronger, the flame front becomes cusped and
creates vorticity; long vortices attach to the flame front and extend
behind it. For even larger values of gravity, the far end of these
vortices becomes unstable and sheds more vortices. For simulations
with increased gravity, the position of the shedding instability
moves closer to the flame front. Next, the vortex shedding disturbs
the flame front, causing the flame to pulsate. These pulsations lose
their left/right symmetry and the period of oscillation doubles. For
even higher values of gravity, an additional frequency is introduced
into the system as the Rayleigh-Taylor instability begins to dominate
over burning. Eventually, the pulsations of the flame become quite
complex and the interaction between the flame front and the vortices
can't be simply described. We have measured the subsequent wrinkling
of the flame front by computing its fractal dimension and the energy
spectra behind the flame front. Measurements of the fractal dimension
suggest that it saturates, implying that any additional speed up of
the flame must be due to large-scale stretching or disruption of the
flame front. Our simulations were performed at NERSC which is supported
by the Department of Energy.
Title: FLASH: Adaptive Mesh Hydrodynamics Code for Modeling
Astrophysical Thermonuclear Flashes
Authors: Fryxell, B.; Olson, K.; Ricker, P.; Timmes, F. X.; Zingale,
M.; Lamb, D. Q.; MacNeice, P.; Rosner, R.; Truran, J. W.; Tufo, H.
Bibcode: 2010ascl.soft10082F
Altcode:
The FLASH code, currently in its 4th version, is a publicly available
high performance application code which has evolved into a modular,
extensible software system from a collection of unconnected legacy
codes. FLASH consists of inter-operable modules that can be combined
to generate different applications. The FLASH architecture allows
arbitrarily many alternative implementations of its components
to co-exist and interchange with each other. A simple and elegant
mechanism exists for customization of code functionality without the
need to modify the core implementation of the source. A built-in unit
test framework combined with regression tests that run nightly on
multiple platforms verify the code.
Title: X-Ray Studies of Stars and Planets with Ultrahigh Sensitivity
and Resolution
Authors: Wolk, Scott; Brickhouse, Nancy; Brissenden, Roger; Drake,
Jeremy; Dupree, Andrea; Elvis, Martin; Evans, Nancy; Fabbiano,
Guiseppina; Feigelson, Eric; Gange, Marc; Güdel, Manuel; Kashyap,
Vinay; Linsky, Jeffery; Osten, Rachel; Rosner, Robert; Smith, Randall;
Townsley, Leisa; Walter, Frederick; Wargelin, Bradford
Bibcode: 2009astro2010S.318W
Altcode:
No abstract at ADS
Title: PREFACE: Turbulent Mixing and Beyond Turbulent Mixing and
Beyond
Authors: Abarzhi, Snezhana I.; Gauthier, Serge; Rosner, Robert
Bibcode: 2008PhST..132a1001A
Altcode:
The goals of the International Conference `Turbulent Mixing and
Beyond' are to expose the generic problem of Turbulence and Turbulent
Mixing in Unsteady Flows to a wide scientific community, to promote
the development of new ideas in tackling the fundamental aspects
of the problem, to assist in the application of novel approaches
in a broad range of phenomena, where the non-canonical turbulent
processes occur, and to have a potential impact on technology. The Conference provides the opportunity to bring together
scientists from the areas which include, but are not limited to,
high energy density physics, plasmas, fluid dynamics, turbulence,
combustion, material science, geophysics, astrophysics, optics and
telecommunications, applied mathematics, probability and statistics,
and to have their attention focused on the long-standing formidable
task. The Turbulent Mixing and Turbulence in Unsteady Flows,
including multiphase flows, plays a key role in a wide variety of
phenomena, ranging from astrophysical to nano-scales, under either
high or low energy density conditions. Inertial confinement and
magnetic fusion, light-matter interaction and non-equilibrium heat
transfer, properties of materials under high strain rates, strong
shocks, explosions, blast waves, supernovae and accretion disks,
stellar non-Boussinesq and magneto-convection, planetary interiors and
mantle-lithosphere tectonics, premixed and non-premixed combustion,
oceanography, atmospheric flows, unsteady boundary layers, hypersonic
and supersonic flows, are a few examples to list. A grip on unsteady
turbulent processes is crucial for cutting-edge technology such as
laser-micromachining and free-space optical telecommunications,
and for industrial applications in aeronautics. Unsteady
Turbulent Processes are anisotropic, non-local and multi-scale, and
their fundamental scaling, spectral and invariant properties depart
from the classical Kolmogorov scenario. The singular aspects and
similarity of the mixing dynamics are interplayed with fundamental
properties of the Euler and compressible Navier-Stokes equations,
with the problem sensitivity to the initial conditions and to the
boundary conditions at the discontinuities, and with its stochastic
description. The state-of-the-art numerical simulations of the
multi-phase non-equilibrium dynamics suggest new methods for capturing
discontinuities and singularities and shock-interface interaction, for
predictive modeling of the multi-scale dynamics in fluids and plasmas,
for error estimate and uncertainty quantification as well as for novel
data assimilation techniques. The First International Conference
`Turbulent Mixing and Beyond' (TMB-2007), was held on 18-26 August
2007 at the Abdus Salam International Centre for Theoretical Physics,
Trieste, Italy. This was a highly informative and exciting meeting,
by all the standards a major success. The Conference brought together
120 participants (307 authors) from five continents, ranging from
students to members of National Academies of Sciences and Engineering
and including researchers from the Universities, National Laboratories,
Leading Scientific Institutions and Industry. TMB-2007 covered
16 different topics, maintaining the scope and the interdisciplinary
character of the meeting, and kept the focus on a fundamental fluid
dynamic problem of unsteady turbulent processes and the Conference
Objectives. The success of the TMB-07 was a result of the
successful work of all the participants, who were serious and
professional people, caring for the quality of their research and
sharing their scientific vision. The level of presentations was high,
and the presentations included 87 oral contributions, 32 invited
lectures and 5 tutorials and over 30 poster contributions. The round
table discussions held at TMB-2007 investigated the organization of
a Collaborative Computing Environment for the Turbulent Mixing and
Beyond Community. The abstracts of the 150 accepted Conference
presentations were published in the Book of Abstracts, International
Conference `Turbulent Mixing and Beyond', August 18-26, 2007, Copyright
2007 Abdus Salam International Centre for Theoretical Physics, Trieste,
Italy, ISBN 92-95003-36-5. This Topical Issue consists of nearly
60 articles accepted for publication in the Conference Proceedings
and reflects a substantial part of the Conference contributions. The
articles cover a broad variety of TMB-2007 themes and are sorted
alphabetically by the last name of the first author within each
of the following topics: Canonical Turbulence and Turbulent
Mixing (invariant, scaling, spectral properties, scalar transports)
Wall-bounded Flows (structure and fundamentals, unsteady boundary
layers, super-sonic flows, shock - boundary layer interaction)
Interfacial Dynamics (Rayleigh-Taylor, Richtmyer-Meshkov and
Kelvin-Helmholtz instabilities) Unsteady Turbulent Processes (turbulence
and turbulent mixing in unsteady, multiphase and anisotropic flows)
High Energy Density Physics (laser-material interaction, Z-pinches,
laser-driven, heavy-ion and magnetic fusion) Astrophysics (supernovae,
interstellar medium, star formation, stellar interiors, early Universe,
cosmic micro-wave background) Magneto-hydrodynamics (magneto-convection,
magneto-rotational instability, accretion disks, dynamo) Plasmas in
Ionosphere (coupled plasmas, anomalous resistance, ionosphere) Physics
of Atmosphere (environmental fluid dynamics, forecasting, data analysis,
error estimate) Geophysics (turbulent convection in stratified, rotating
and active flows) Combustion (dynamics of flames, fires, blast waves
and explosions) Mathematical Aspects of Multi-Scale Dynamics (vortex
dynamics, singularities, discontinuities, asymptotic dynamics, weak
solutions, well- and ill-posedness) Statistical Approaches, Stochastic
Processes and Probabilistic Description (uncertainty quantification,
anomalous diffusion, long-tail distributions, wavelets) Advanced
Numerical Simulations (continuous DNS/LES/RANS, Molecular dynamics,
Monte-Carlo, predictive modeling) New Experimental Diagnostics (novel
methods for flow visualization and control, high-tech) The First
International Conference `Turbulent Mixing and Beyond' was organized
by the following members of the Organizing Committee: Snezhana
I Abarzhi (chairperson, Chicago, USA) Malcolm J Andrews (Los Alamos
National Laboratory, USA) Sergei I Anisimov (Landau Institute for
Theoretical Physics, Russia) Serge Gauthier (Commissariat à l'Energie
Atomique, France) Donald Q Lamb (The University of Chicago, USA)
Katsunobu Nishihara (Institute for Laser Engineering, Osaka, Japan)
Bruce A Remington (Lawrence Livermore National Laboratory, USA)
Robert Rosner (Argonne National Laboratory, USA) Katepalli R
Sreenivasan (International Centre for Theoretical Physics, Italy)
Alexander L Velikovich (Naval Research Laboratory, USA) The
Organizing Committee gratefully acknowledges the financial support of
the Conference Sponsors: National Science Foundation (NSF), USA
(Divisions and Programs Directors: Drs A G Detwiler, L M Jameson,
E L Lomon, P E Phelan, G A Prentice, J A Raper, W Schultz, P R
Westmoreland; PI: Dr S I Abarzhi) Air Force Office of Scientific
Research (AFOSR), USA (Program Director: Dr J D Schmisseur; PI: Dr S I
Abarzhi) European Office of Aerospace Research and Development (EOARD)
of the AFOSR, UK (Program Chief: Dr S Surampudi; PI: Dr S I Abarzhi)
International Centre for Theoretical Physics (ICTP), Trieste, Italy
(Centre's Director: Dr K R Sreenivasan) The University of Chicago and
The Argonne National Laboratory (ANL), USA (Laboratory's Director: Dr R
Rosner) Commissariat à l'Energie Atomique (CEA), France (Directeur de
Recherche: Dr S Gauthier) Department of Energy, Los Alamos National
Laboratory (LANL), USA (Program manager: Dr R J Hanrahan; Group
Leader: Dr M J Andrew) The DOE ASC Alliance Center for Astrophysical
Thermonuclear Flashes, The University of Chicago, USA (Center's
Director: Dr D Q Lamb) Institute for Laser Engineering (ILE), Osaka,
Japan (Division Head: Dr K Nishihara) Illinois Institute of Technology
(IIT), Chicago, USA (College of Science and Letters, Department of
Applied Mathematics: Dr S I Abarji) and thanks them for making
this event possible. The Organizing Committee appreciates the
assistance of Suzie Radosic (administrator and assistant, ICTP)
Daniil Ilyin (web-master, Chicago) Elena Magnus (assistant, Chicago)
We express our gratitude for the help with the Conference Program
to the members of the Scientific Advisory Committee S I Abarzhi
(The University of Chicago, Illinois Institute of Technology, USA)
G Ahlers (University of California at Santa Barbara, USA) M J Andrews
(Los Alamos National Laboratory, Texas A & M University, USA)
S I Anisimov (Landau Institute for Theoretical Physics, Russia)
E Bodenschatz (Max Plank Institute, Gottingen, Germany) S Dalziel
(DAMTP, University of Cambridge, UK) R Ecke (Los Alamos National
Laboratory, USA) H J Fernando (Arizona State University, USA) S Gauthier
(Commissariat à l'Energie Atomique, France) G A Glatzmaier (University
of California at Santa Cruz, USA) W A Goddard III (California Institute
of Technology, USA) L P Kadanoff (The University of Chicago, USA)
D Q Lamb (The University of Chicago, USA) D P Lathrop (University of
Maryland, USA) S Lebedev (Imperial College, UK) P Manneville (Ecole
Polytechnique, France) D I Meiron (California Institute of Technology,
USA) H Nagib (Illinois Institute of Technology, Chicago, USA) J Niemela
(International Center for Theoretical Physics, Italy) K Nishihara
(Institute for Laser Engineering, Osaka, Japan) S A Orszag (Yale
University, USA) E Ott (University of Maryland, USA) N Peters (RWTS,
Aachen, Germany) S B Pope (Cornell, USA) B A Remington (Lawrence
Livermore National Laboratory, USA) R Rosner (Argonne National
Laboratory and The University of Chicago, USA) A Schmidt (Naval
Research Laboratory, USA) K R Sreenivasan (International Centre for
Theoretical Physics, Italy) V Steinberg (Weiznmann Institute, Israel)
A L Velikovich (Naval Research Laboratory, USA) P K Yeung (Georgia
Institute of Technology, USA) F A Williams (University of California
at San Diego, USA) We would like to thank all the authors and the
referees for their contributions to this Topical Issue and for offering
their expertise, time and effort We cordially invite the reader to
take a look at this Topical Issue for information on the frontiers of
theoretical, numerical and experimental research and technology The
Organizing Committee hopes the TMB Conference will serve to advance the
state-of-the-art in understanding of fundamental physical properties
of turbulent mixing and turbulence in unsteady flows and will have an
impact on predictive modeling capabilities, physical description and,
ultimately, control of these complex processes Snezhana I Abarzhi,
Serge Gauthier, Robert Rosner Chicago, 20 Nov 2008
Title: Strongly compressible current sheets under gravitation
Authors: Vainshtein, S. I.; Mikic, Z.; Rosner, R.; Sagdeev, R. Z.
Bibcode: 2008arXiv0804.3789V
Altcode:
Many stormy events in astrophysics occur due to the sudden magnetic
energy release. This is possible if a magnetic configuration abruptly
changes its topology, an event usually referred to as magnetic
reconnection. It is known that pure Ohmic decay is inefficient,
occurring during cosmological times (due to the huge characteristic
scales $L$). It is recognized that the presence of current sheets speeds
up the process, but still insufficiently$^{1,2,3,4,5}$. We show that,
in highly compressible and substantially gravitational media, the
reconnection is fast enough to account for stormy events. Thus, highly
compressible situations offer exiting opportunities in explanations
of violent events, although full-scale compressible and gravitational
simulations proved to be quite challenging.
Title: Some Things I Wished I Understood Better (or at all...)
Authors: Rosner, Robert
Bibcode: 2008APS..APR.H5003R
Altcode:
Astrophysics has, since its very beginnings, sought to build our
understanding of astronomical phenomena on the solid foundation of
our understanding of physical phenomena in the terrestrial context. In
areas such as spectroscopy, this approach has had outstanding success;
but in other areas, making this connection in an intellectually rigorous
way has proved to be very challenging. I will discuss some of the most
troublesome examples, and offer some guidelines on how the resulting
uncertainties in our understanding of the astrophysical phenomena can
be circumscribed.
Title: An Estimate of P-Mode Damping by Wave Leakage
Authors: De Moortel, I.; Rosner, R.
Bibcode: 2007SoPh..246...53D
Altcode:
High-cadence TRACE observations show that outward-propagating
intensity disturbances are a common feature in large, quiescent coronal
loops. Analysis of the frequency distribution of these modes shows
peaks at both three- and five-minute periods, indicating that they may
be driven by the solar surface oscillations (p modes). The energy flux
contained within the coronal intensity disturbances is of the order of
(1.1±0.4)×103 ergs cm−2 s−1. A
simple order-of-magnitude estimate of the damping rate of the relevant
p modes allows us to put an observational constraint on the damping of
p modes and shows that leakage into the overlying coronal atmosphere
might be able to account for a significant fraction of p-mode damping.
Title: MHD simulations of jet acceleration from Keplerian accretion
disks. The effects of disk resistivity
Authors: Zanni, C.; Ferrari, A.; Rosner, R.; Bodo, G.; Massaglia, S.
Bibcode: 2007A&A...469..811Z
Altcode: 2007astro.ph..3064Z
Context: Accretion disks and astrophysical jets are used to model
many active astrophysical objects, such as young stars, relativistic
stars, and active galactic nuclei. However, existing proposals for
how these structures may transfer angular momentum and energy from
disks to jets through viscous or magnetic torques do not yet provide
a full understanding of the physical mechanisms involved. Thus,
global stationary solutions have not explained the stability of these
structures; and global numerical simulations that include both the
disk and jet physics have so far been limited to relatively short time
scales and narrow (and possibly astrophysically unlikely) ranges of
viscosity and resistivity parameters that may be crucial to defining
the coupling of the inflow-outflow dynamics.
Aims: We present
self-consistent, time-dependent simulations of supersonic jets launched
from magnetized accretion disks, using high-resolution numerical
techniques. In particular we study the effects of the disk's magnetic
resistivity, parametrized through an α-prescription, in determining
the properties of the inflow-outflow system. Moreover we analyze
under which conditions steady state solutions of the type proposed
in the self-similar models of Blandford & Payne can be reached
and maintained in a self-consistent nonlinear stage.
Methods:
We used the resistive MHD FLASH code with adaptive mesh refinement
(AMR), allowing us to follow the evolution of the structure on a long
enough time scale to reach steady state. A detailed analysis of the
initial configuration state is given.
Results: We obtain the
expected solutions within the axisymmetric (2.5 D) limit. Assuming
a magnetic field around equipartition with the thermal pressure of
the disk, we show how the characteristics of the disk-jet system,
such as the ejection efficiency and the energetics, are affected by
the anomalous resistivity acting inside the disk.
Title: The Solar Tachocline
Authors: Hughes, D. W.; Rosner, R.; Weiss, N. O.
Bibcode: 2007sota.book.....H
Altcode:
Preface; Part I. Setting the Scene: 1. An introduction to the solar
tachocline D. O. Gough; 2. Reflections on the solar tachocline
E. A. Spiegel; Part II. Observations: 3. Observational results
and issues concerning the tachocline J. Christensen-Dalsgaard and
M. J. Thompson; Part III. Hydrodynamic Models: 4. Hydrodynamic models of
the tachocline J.-P. Zahn; 5. Turbulence in the tachocline M. S. Miesch;
6. Mean field modelling of differential rotation G. Rudiger and
L. L. Kitchatinov; Part IV. Hydromagnetic Properties: 7. Magnetic
confinement of the solar tachocline P. Garaud; 8. Magnetic confinement
and the sharp tachopause M. E. McIntyre; 9. ß-Plane MHD turbulence
and dissipation in the solar tachocline P. H. Diamond, K. Itoh,
S.-I. Itoh and L. J. Silvers; Part V. Instabilities: 10. Global
MHD instabilities of the tachocline P. A. Gilman and P. S. Cally;
11. Magnetic buoyancy instabilities in the tachocline D. W. Hughes;
12. Instabilities, angular momentum transport and magnetohydrodynamic
turbulence G. I. Ogilvie; Part VI. Dynamo Action: 13. The solar dynamo
and the tachocline S. M. Tobias and N. O. Weiss; Part VII. Overview:
14. On studying the rotating solar interior R. Rosner; Index.
Title: X-rays from protostellar jets: emission from continuous flows
Authors: Bonito, R.; Orlando, S.; Peres, G.; Favata, F.; Rosner, R.
Bibcode: 2007A&A...462..645B
Altcode: 2006astro.ph.10507B
Context: Recently X-ray emission from protostellar jets has been
detected with both XMM-Newton and Chandra satellites, but the physical
mechanism which can give rise to this emission is still unclear.
Aims: We performed an extensive exploration of the parameter space for
the main parameters influencing the jet/ambient medium interaction. Aims
include: 1) to constrain the jet/ambient medium interaction regimes
leading to the X-ray emission observed in Herbig-Haro objects in
terms of the emission by a shock forming at the interaction front
between a continuous supersonic jet and the surrounding medium;
2) to derive detailed predictions to be compared with optical and
X-ray observations of protostellar jets; 3) to get insight into the
protostellar jet's physical conditions.
Methods: We performed
a set of two-dimensional hydrodynamic numerical simulations, in
cylindrical coordinates, modeling supersonic jets ramming into a uniform
ambient medium. The model takes into account the most relevant physical
effects, namely thermal conduction and radiative losses.
Results:
Our model explains the observed X-ray emission from protostellar
jets in a natural way. In particular, we find that a protostellar
jet that is less dense than the ambient medium well reproduces the
observations of the nearest Herbig-Haro object, HH 154, and allows us
to make detailed predictions of a possible X-ray source proper motion
(v_sh ≈500 km s-1) detectable with Chandra. Furthermore,
our results suggest that the simulated protostellar jets which best
reproduce the X-rays observations cannot drive molecular outflows.
Title: On studying the rotating solar interior
Authors: Rosner, Robert
Bibcode: 2007sota.conf..353R
Altcode:
No abstract at ADS
Title: The Solar Tachocline
Authors: Hughes, David W.; Rosner, Robert; Weiss, Nigel O.
Bibcode: 2007sota.conf.....H
Altcode:
No abstract at ADS
Title: Crushing of interstellar gas clouds in supernova
remnants. II. X-ray emission
Authors: Orlando, S.; Bocchino, F.; Peres, G.; Reale, F.; Plewa, T.;
Rosner, R.
Bibcode: 2006A&A...457..545O
Altcode: 2006astro.ph..7252O
Context: .X-ray observations of evolved supernova remnants (e.g. the
Cygnus loop and the Vela SNRs) reveal emission originating from the
interaction of shock waves with small interstellar gas clouds.
Aims: .We study and discuss the time-dependent X-ray emission
predicted by hydrodynamic modeling of the interaction of a SNR shock
wave with an interstellar gas cloud. The scope includes: 1) to study
the correspondence between modeled and X-ray emitting structures, 2)
to explore two different physical regimes in which either thermal
conduction or radiative cooling plays a dominant role, and 3) to
investigate the effects of the physical processes at work on the
emission of the shocked cloud in the two different regimes.
Methods: .We use a detailed hydrodynamic model, including thermal
conduction and radiation, and explore two cases characterized
by different Mach numbers of the primary shock: M= 30 (post-shock
temperature T_psh ≈ 1.7 MK) in which the cloud dynamics is dominated
by radiative cooling and M= 50 (T_psh ≈ 4.7 MK) dominated by thermal
conduction. From the simulations, we synthesize the expected X-ray
emission, using available spectral codes.
Results: .The morphology
of the X-ray emitting structures is significantly different from that of
the flow structures originating from the shock-cloud interaction. The
hydrodynamic instabilities are never clearly visible in the X-ray
band. Shocked clouds are preferentially visible during the early phases
of their evolution. Thermal conduction and radiative cooling lead to
two different phases of the shocked cloud: a cold cooling dominated
core emitting at low energies and a hot thermally conducting corona
emitting in the X-ray band. The thermal conduction makes the X-ray
image of the cloud smaller, more diffuse, and shorter-lived than that
observed when thermal conduction is neglected.
Title: The Traveling-Wave MRI in Cylindrical Taylor-Couette Flow:
Comparing Wavelengths and Speeds in Theory and Experiment
Authors: Rüdiger, Günther; Hollerbach, Rainer; Stefani, Frank;
Gundrum, Thomas; Gerbeth, Gunter; Rosner, Robert
Bibcode: 2006ApJ...649L.145R
Altcode: 2006astro.ph..7041R
We study experimentally the flow of a liquid metal confined between
differentially rotating cylinders, in the presence of externally imposed
axial and azimuthal magnetic fields. For increasingly large azimuthal
fields a wavelike disturbance arises, traveling along the axis of the
cylinders. The wavelengths and speeds of these structures, as well
as the field strengths and rotation rates at which they arise, are
broadly consistent with theoretical predictions of such a traveling-wave
magnetorotational instability.
Title: X-ray Emission Mechanisms in Herbig - Haro objects .
Authors: Bonito, R.; Orlando, S.; Peres, G.; Favata, F.; Rosner, R.
Bibcode: 2006MSAIS...9..226B
Altcode:
X-ray emission in Herbig - Haro objects is a quite recent and uncommon
finding still waiting full explanation. With the scope of explaining
this X-ray emission, our project is devoted to model the interaction
between a supersonic jet originating from a young stellar object
and the ambient medium. We have performed a wide exploration of the
parameter space to infer the configuration(s) which can give rise to
X-ray emission very similar to what recently observed.
Title: Hydrodynamic interaction of SNR shocks with thermally
conducting, radiative clouds .
Authors: Orlando, S.; Peres, G.; Reale, F.; Bocchino, F.; Plewa, T.;
Rosner, R.
Bibcode: 2006MSAIS...9..208O
Altcode:
Supernova remnants (SNRs) are privileged laboratories to investigate
the physical and chemical evolution of the galactic interstellar
medium (ISM) and the mass distribution of the plasma in the Galaxy. Here, we study the interaction of an evolved SNR shock front with
on a small interstellar gas cloud. Our model takes into account the
hydrodynamics and the effects of the radiative losses and of the
thermal conduction. We study the interplay between the radiative
cooling and the thermal conduction during the cloud evolution and
their effect on the mass and energy exchange between the cloud and the
surrounding medium. We find that in cases dominated by the radiative
losses the cloud fragments into cold, dense, and compact filaments
surrounded by a hot corona which is ablated by the thermal conduction;
instead, in cases dominated by the thermal conduction, the shocked
cloud evaporates into the ISM in a few dynamical time-scales. In all
the cases analyzed we find that the thermal conduction suppresses the
hydrodynamic instabilities at the cloud boundaries.
Title: Crushing of interstellar gas clouds in supernova
remnants. I. The role of thermal conduction and radiative losses
Authors: Orlando, S.; Peres, G.; Reale, F.; Bocchino, F.; Rosner,
R.; Plewa, T.; Siegel, A.
Bibcode: 2005A&A...444..505O
Altcode: 2005astro.ph..8638O
We model the hydrodynamic interaction of a shock wave of an evolved
supernova remnant with a small interstellar gas cloud like the ones
observed in the Cygnus loop and in the Vela SNR. We investigate the
interplay between radiative cooling and thermal conduction during cloud
evolution and their effect on the mass and energy exchange between
the cloud and the surrounding medium. Through the study of two cases
characterized by different Mach numbers of the primary shock (M= 30 and
50, corresponding to a post-shock temperature T≈ 1.7× 106
K and ≈ 4.7× 106 K, respectively), we explore two very
different physical regimes: for M= 30, the radiative losses dominate
the evolution of the shocked cloud which fragments into cold, dense,
and compact filaments surrounded by a hot corona which is ablated by
the thermal conduction; instead, for M= 50, the thermal conduction
dominates the evolution of the shocked cloud, which evaporates in a few
dynamical time-scales. In both cases we find that the thermal conduction
is very effective in suppressing the hydrodynamic instabilities that
would develop at the cloud boundaries.
Title: Magnetic-Field Generation in Helical Turbulence
Authors: Boldyrev, Stanislav; Cattaneo, Fausto; Rosner, Robert
Bibcode: 2005PhRvL..95y5001B
Altcode: 2005astro.ph..4588B
We investigate analytically the amplification of a weak magnetic
field in a homogeneous and isotropic turbulent flow lacking
reflectional symmetry (helical turbulence). We propose that the
spectral distributions of magnetic energy and magnetic helicity can
be found as eigenmodes of a self-adjoint, Schrödinger-type system of
evolution equations. We argue that large-scale and small-scale magnetic
fluctuations cannot be effectively separated, and that the conventional
α model is, in general, not an adequate description of the large-scale
dynamo mechanism. As a consequence, the correct numerical modeling of
such processes should resolve magnetic fluctuations down to the very
small, resistive scales.
Title: What does Astrophysics want to know about (Astrophysical)
Reconnection?
Authors: Rosner, R.
Bibcode: 2005AGUFMSH51D..02R
Altcode:
Magnetic reconnection is commonly invoked as a plasma energization and
particle acceleration process in astrophysics, but the levels of detail
regarding the underlying physics that are required are generally far
demanding than what is typically encountered in laboratory or space
plasma physics. Naively, one would therefore expect it to be far easier
to answer questions regarding reconnection in the astrophysical context
as opposed to the laboratory or space plasma physics contexts. My
talk will focus on why this naive expectation is not correct, and
will discuss the specifics of such astrophysics-motivated questions,
as well as some possible answers.
Title: Hughes, Rosner, Weiss: Stellar MHD: Magnetohydrodynamics of
stellar interiors
Authors: Hughes, David; Rosner, Robert; Weiss, Nigel
Bibcode: 2005A&G....46d..35H
Altcode:
David Hughes, Robert Rosner and Nigel Weiss describe what was
achieved during a programme on stellar magnetic fields at the Isaac
Newton Institute in Cambridge. Over a four-month period more than
90 participants visited the Institute for a mixture of structured
workshops and informal collaboration.
Title: X-ray emission mechanisms in protostellar jets
Authors: Bonito, R.; Orlando, S.; Peres, G.; Favata, F.; Rosner, R.
Bibcode: 2005ESASP.560..185B
Altcode: 2005csss...13..185B
No abstract at ADS
Title: Mixing at the surface of white dwarf stars
Authors: Rosner, R.; Alexakis, A.
Bibcode: 2005fdda.conf...63R
Altcode:
No abstract at ADS
Title: Magneto-Couette Instabilities - Astrophysics, Theory and
Experiments
Authors: Rosner, Robert
Bibcode: 2004AIPC..733....3R
Altcode:
No abstract at ADS
Title: On the non-linear evolution of wind driven gravity waves
Authors: Alexakis, Alexandros; Calder, Alan; Dursi, Jonathan; Rosner,
Robert
Bibcode: 2004APS..DFD.JM002A
Altcode:
We present a study of wind-driven nonlinear interfacial gravity waves
using numerical simulations in two dimensions. We consider a case
relevant to mixing phenomenon in astrophysical events such as novae
in which the density ratio is approximately 1:10. Our physical setup
follows the proposed mechanism of Miles [J. Fluid Mech. 3, 185 (1957)]
for the amplification of such waves. We explore how the wind strength
affects the wave dynamics and the resulting mixing in the nonlinear
stage. We identify two regimes of mixing, namely, the overturning and
the cusp-breaking regimes. The former occurs when the wind is strong
enough to overcome the gravitational potential barrier and overturn the
wave. This result is in agreement with the common notion of turbulent
mixing in which density gradients are increased to diffusion scales
by the stretching of a series of vortices. In the latter case, mixing
is the result of cusp instabilities. Although the wind is not strong
enough to overturn the wave in this case, it can drive the wave up to
a maximum amplitude where a singular structure at the cusp of the wave
forms. Such structures are subject to various instabilities near the
cusp that result in breaking the cusp. Mixing then results from these
secondary instabilities and the spray-like structures that appear as
a consequence of the breaking. [Phys. Fluid v.16 p.3256]
Title: The X-ray emission mechanism in the protostellar jet HH 154
Authors: Bonito, R.; Orlando, S.; Peres, G.; Favata, F.; Rosner, R.
Bibcode: 2004A&A...424L...1B
Altcode:
We study the mechanism causing the X-ray emission recently detected in
protostellar jets, by performing a detailed modeling of the interaction
between a supersonic jet originating from a young stellar object and the
ambient medium, for various values of density contrast, ν, between the
ambient density and the jet, and of Mach number, M; radiative losses
and thermal conduction have been taken into account. Here we report a
representative case which reproduces, without any ad hoc assumption,
the characteristics of the X-ray emission recently observed in the
protostellar jet HH 154. We find that the X-ray emission originates
from a localized blob, consistent with observations, which moves with
velocity v ∼ 500 km s-1; we therefore predict the X-ray
source to have a detectable proper motion.
Title: Kelvin-Helmholtz instability for relativistic fluids
Authors: Bodo, G.; Mignone, A.; Rosner, R.
Bibcode: 2004PhRvE..70c6304B
Altcode:
We reexamine the stability of an interface separating two nonmagnetized
relativistic fluids in relative motion, showing that, in an appropriate
reference frame, it is possible to find analytic solutions to the
dispersion relation. Moreover, we show that the critical value
of the Mach number, introduced by compressibility, is unchanged
from the nonrelativistic case if we redefine the Mach number as
M=[β/(1-β2)1/2][βs/(1-βs2)1/2]-1
, where β and βs are, respectively, the speed of the
fluid and the speed of sound (in units of the speed of light).
Title: On the nonlinear evolution of wind-driven gravity waves
Authors: Alexakis, A.; Calder, A. C.; Dursi, L. J.; Rosner, R.; Truran,
J. W.; Fryxell, B.; Zingale, M.; Timmes, F. X.; Olson, K.; Ricker, P.
Bibcode: 2004PhFl...16.3256A
Altcode:
We present a study of wind-driven nonlinear interfacial gravity waves
using numerical simulations in two dimensions. We consider a case
relevant to mixing phenomenon in astrophysical events such as novae
in which the density ratio is approximately 1:10. Our physical setup
follows the proposed mechanism of Miles [J. Fluid Mech. 3, 185 (1957)]
for the amplification of such waves. Our results show good agreement
with linear predictions for the growth of the waves. We explore how
the wind strength affects the wave dynamics and the resulting mixing
in the nonlinear stage. We identify two regimes of mixing, namely, the
overturning and the cusp-breaking regimes. The former occurs when the
wind is strong enough to overcome the gravitational potential barrier
and overturn the wave. This result is in agreement with the common
notion of turbulent mixing in which density gradients are increased
to diffusion scales by the stretching of a series of vortices. In the
latter case, mixing is the result of cusp instabilities. Although the
wind is not strong enough to overturn the wave in this case, it can
drive the wave up to a maximum amplitude where a singular structure
at the cusp of the wave forms. Such structures are subject to various
instabilities near the cusp that result in breaking the cusp. Mixing
then results from these secondary instabilities and the spray-like
structures that appear as a consequence of the breaking.
Title: Crushing of Interstellar Gas Clouds in Supernova Remnants:
the Role of Thermal Conduction and Radiative Losses
Authors: Peres, G.; Orlando, S.; Reale, F.; Rosner, R.; Plewa, T.;
Siegel, A.
Bibcode: 2004AIPC..703..326P
Altcode:
We model hydrodynamic interactions of an old supernova remnant shock
wave with a small interstellar gas cloud, taking into account the
effects of thermal conduction and radiative losses. In particular,
we consider a representative case of a Mach 30 shock impacting on an
isolated cloud with density contrast χ = 10 with respect to the ambient
medium. Thermal conduction appears to be effective in suppressing the
Kelvin-Helmholtz and Rayleigh-Taylor instabilities which would develop
at the cloud boundaries. We demonstrate that the radiative losses
play a crucial role in the dynamics of the shock-cloud interaction,
dominating evolution of the shocked cloud medium.
Title: Morphology of Rising Hydrodynamic and Magnetohydrodynamic
Bubbles from Numerical Simulations
Authors: Robinson, K.; Dursi, L. J.; Ricker, P. M.; Rosner, R.;
Calder, A. C.; Zingale, M.; Truran, J. W.; Linde, T.; Caceres, A.;
Fryxell, B.; Olson, K.; Riley, K.; Siegel, A.; Vladimirova, N.
Bibcode: 2004ApJ...601..621R
Altcode: 2003astro.ph.10517R
Recent Chandra and XMM-Newton observations of galaxy cluster cooling
flows have revealed X-ray emission voids of up to 30 kpc in size that
have been identified with buoyant, magnetized bubbles. Motivated
by these observations, we have investigated the behavior of rising
bubbles in stratified atmospheres using the FLASH9 adaptive-mesh
simulation code. We present results from two-dimensional simulations
with and without the effects of magnetic fields and with varying bubble
sizes and background stratifications. We find purely hydrodynamic
bubbles to be unstable; a dynamically important magnetic field is
required to maintain a bubble's integrity. This suggests that, even
absent thermal conduction, for bubbles to be persistent enough to be
regularly observed, they must be supported in large part by magnetic
fields. Thermal conduction unmitigated by magnetic fields can dissipate
the bubbles even faster. We also observe that the bubbles leave a tail
as they rise; the structure of these tails can indicate the history
of the dynamics of the rising bubble.
Title: On Heavy Element Enrichment in Classical Novae
Authors: Alexakis, A.; Calder, A. C.; Heger, A.; Brown, E. F.; Dursi,
L. J.; Truran, J. W.; Rosner, R.; Lamb, D. Q.; Timmes, F. X.; Fryxell,
B.; Zingale, M.; Ricker, P. M.; Olson, K.
Bibcode: 2004ApJ...602..931A
Altcode: 2003astro.ph..7126A
Many classical nova ejecta are enriched in CNO and Ne. Rosner and
coworkers recently suggested that the enrichment might originate
in the resonant interaction between large-scale shear flows in the
accreted H/He envelope and gravity waves at the interface between
the envelope and the underlying C/O white dwarf (WD). The shear flow
amplifies the waves, which eventually form cusps and break. This wave
breaking injects a spray of C/O into the superincumbent H/He. Using
two-dimensional simulations, we formulate a quantitative expression for
the amount of C/O per unit area that can be entrained, at saturation,
into the H/He. The fraction of the envelope that is enriched depends on
the horizontal distribution of shear velocity and the density contrast
between the C/O WD and the H/He layer but is roughly independent of
the vertical shape of the shear profile. Using this parameterization
for the mixed mass, we then perform several one-dimensional Lagrangian
calculations of an accreting WD envelope and consider two scenarios:
that the wave breaking and mixing is driven by the convective flows and
that the mixing occurs prior to the onset of convection. In the absence
of enrichment prior to ignition, the base of the convective zone,
as calculated from mixing-length theory with the Ledoux instability
criterion, does not reach the C/O interface. As a result, there is no
additional mixing, and the runaway is slow. In contrast, the formation
of a mixed layer during the accretion of H/He, prior to ignition, causes
a more violent runaway. The envelope can be enriched by <~25% of
C/O by mass (consistent with that observed in some ejecta) for shear
velocities, over the surface, with Mach numbers <~0.4.
Title: Photospheric Variability and the Solar Atmosphere
Authors: Rosner, R.
Bibcode: 2004cosp...35.4522R
Altcode: 2004cosp.meet.4522R
Variations in the bolometric luminosity of the Sun (due to photospheric
variability) have for some time been related to solar magnetic
activity. Such variations are observed on both the solar rotational
period and on much longer time scales; I will review the current work
in this area, and discuss related work in observations of stellar
photospheric variability tied to stellar magnetic activity.
Title: Using AMR to Simulate the 3-D Hydrodynamic Interaction of
Supernova Shocks with Interstellar Gas Clouds
Authors: Orlando, S.; Peres, G.; Reale, F.; Plewa, T.; Rosner, R.;
Siegel, A.
Bibcode: 2004MSAIS...4...82O
Altcode:
We study the 3-D hydrodynamic interaction of supernova shock fronts
with interstellar clouds to investigate the evolution, the morphology
and the deviations from equilibrium of ionization. To this end, we
use the FLASH code including PARAMESH, an advanced and versatile
parallel adaptive mesh refinement package. We present here the
preliminary results obtained modeling a representative case of a Mach
50 shock impacting on an isolated cloud with density contrast chi =
10 with respect to the ambient medium. The preliminary analysis of the
non-equilibrium ionization (NEI) effects on the ionization stages of
oxygen, and iron is discussed.
Title: Simulations of Rising Hydrodynamic and Magnetohydrodynamic
Bubbles
Authors: Ricker, P. M.; Robinson, K.; Dursi, L. J.; Rosner, R.;
Calder, A. C.; Zingale, M.; Truran, J. W.; Linde, T.; Caceres, A.;
Fryxell, B.; Olson, K.; Riley, K.; Siegel, A.; Vladimirova, N.
Bibcode: 2004rcfg.proc...95R
Altcode: 2004rcfg.procE..36R
Motivated by recent Chandra and XMM-Newton observations of X-ray
emission voids in galaxy cluster cooling flows, we have investigated
the behavior of rising bubbles in stratified atmospheres using the FLASH
adaptive-mesh simulation code. We present results from two-dimensional
simulations with and without the effects of magnetic fields, and with
varying bubble sizes and background stratifications. We find purely
hydrodynamic bubbles to be unstable; a dynamically important magnetic
field is required to maintain a bubble's integrity. This suggests that,
even absent thermal conduction, for bubbles to be persistent enough
to be regularly observed, they must be supported in large part by
magnetic fields. We also observe that magnetically supported bubbles
leave a tail as they rise. The structure of these tails may provide
clues to the bubble's dynamical history.
Title: MHD Couette Flows: Experiments and Models
Authors: Rosner, Robert; Rüdiger, Günther; Bonanno, Alfio
Bibcode: 2004AIPC..733.....R
Altcode:
No abstract at ADS
Title: Microphysical Effects on the Instabilities of Astrophysical
Flames
Authors: Dursi, L. J.; Rosner, R.; Zingale, M.; Calder, A. C.; Fryxell,
B.; Timmes, F. X.; Vladimirova, N.; Caceres, A.; Lamb, D. Q.; Olson,
K.; Ricker, P. M.; Riley, K.; Siegel, A.; Truran, J. W.
Bibcode: 2003AAS...20312502D
Altcode: 2003BAAS...35.1412D
Large-scale simulations of supernovae of Type Ia, which are essential
for the ultimate understanding of the supernovae mechanism, need flame
physics input at three stages: Ignition and early flame propagation,
Large scale burning in a turbulent medium, and a transition to
detonation, should one occur. One aspect of our investigation
of flame physics has been to examine the behavior of well-known flame
instabilities such as Landau-Darrieus in the context of astrophysical
flames and degenerate matter. These instabilities can distort and
wrinkle the flame surface, increasing the amount of burning and
thus the rate of energy input. We have examined both the effects of
magnetic fields, and flame curvature and strain in degenerate material,
on the growth rate of these instabilities. LJD was supported by
the Department of Energy Computational Science Graduate Fellowship
Program of the Office of Scientific Computing and Office of Defense
Programs in the Department of Energy under contract DE-FG02-97ER25308.
Title: On Heavy Element Enrichment in Classical Novae
Authors: Alexakis, A.; Calder, A. C.; Heger, A.; Brown, E. F.; Dursi,
L. J.; Truran, J. W.; Rosner, R.; Lamb, D. Q.; Timmes, F. X.; Fryxel,
B.; Zingale, M.; Ricker, P.; Olson, K.; ASCI/Flash Center Team
Bibcode: 2003AAS...20312504A
Altcode: 2003BAAS...35.1412A
Many classical nova ejecta are enriched in CNO and Ne. Rosner et
al. recently suggested that the enrichment might originate in the
resonant interaction between large-scale shear flows in the accreted
H/He envelope and gravity waves at the interface between the envelope
and the underlying C/O white dwarf. The shear flow amplifies the waves,
which eventually form cusps and break. This wave breaking injects
a spray of C/O into the superincumbent H/He. Using two-dimensional
simulations, we formulate a quantitative expression for the amount
of C/O per unit area that can be entrained, at saturation, into the
H/He. The fraction of the envelope that is enriched depends on the
horizontal distribution of shear velocity and the density contrast
between the C/O white dwarf and the H/He layer but is roughly
independent of the vertical shape of the shear profile. Using
this parameterization for the mixed mass, we then perform several
one-dimensional Lagrangian calculations of an accreting white dwarf
envelope and consider two scenarios: that the wave breaking and
mixing is driven by the convective flows; and that the mixing occurs
prior to the onset of convection. In the absence of enrichment prior
to ignition, the base of the convective zone, as calculated from
mixing-length theory with the Ledoux instability criterion, does not
reach the C/O interface. As a result, there is no additional mixing,
and the runaway is slow. In contrast, the formation of a mixed layer
during the accretion of H/He, prior to ignition, causes a more violent
runaway. The envelope can be enriched by < 25% of C/O by mass
(consistent with that observed in some ejecta) for shear velocities,
over the surface, with Mach numbers < 0.4.
Title: New frontiers in bridging astrophysics and the laboratory
Authors: Rosner, Robert
Bibcode: 2003APS..DPPCI1001R
Altcode:
While the deep connections between terrestrial laboratory studies
and astrophysics have been long appreciated - atomic physics and
spectroscopy being the classic example of the possible synergies that
can arise - there has been a recent powerful revival of efforts in
this direction. This revival has been led in part by the fact that
modern simulation capabilities of particle and continuum fluid systems
are able to make contact with modeling of both physically complex
astrophysical phenomena and related phenomena observed in far greater
detail in terrestrial laboratories. These connections now offer new
possibilities for studying - and understanding - phenomena as diverse as
the cosmic origins of magnetic fields, energy transport in magnetized
galaxy cluster gas, and radiation transport in supernovae. This review
will provide an overview of progress in this exciting field.
Title: Solar physics: Heat exposure
Authors: Rosner, Robert
Bibcode: 2003Natur.425..672R
Altcode:
The outermost layers of the Sun are hotter than expected. Observation
and analysis now confirm that magnetic fields are involved in the
heating process, and also signal the existence of a long-sought
'current sheet'.
Title: The Response of Model and Astrophysical Thermonuclear Flames
to Curvature and Stretch
Authors: Dursi, L. J.; Zingale, M.; Calder, A. C.; Fryxell, B.; Timmes,
F. X.; Vladimirova, N.; Rosner, R.; Caceres, A.; Lamb, D. Q.; Olson,
K.; Ricker, P. M.; Riley, K.; Siegel, A.; Truran, J. W.
Bibcode: 2003ApJ...595..955D
Altcode: 2003astro.ph..6176D
Critically understanding the standard candle-like behavior of Type
Ia supernovae requires understanding their explosion mechanism. One
family of models for Type Ia supernovae begins with a deflagration
in a carbon-oxygen white dwarf that greatly accelerates through
wrinkling and flame instabilities. While the planar speed and behavior
of astrophysically relevant flames is increasingly well understood,
more complex behavior, such as the flame's response to stretch and
curvature, has not been extensively explored in the astrophysical
literature; this behavior can greatly enhance or suppress instabilities
and local flame-wrinkling, which in turn can increase or decrease the
bulk burning rate. In this paper, we explore the effects of curvature
on both nuclear flames and simpler model flames to understand the
effect of curvature on the flame structure and speed.
Title: Starting Models in FLASH for Calculations of Type Ia Supernovae
Authors: Lamb, D. Q.; Caceres, A.; Calder, A. C.; Dursi, L. J.;
Fryxell, B.; MacNeice, P.; Olson, K.; Plewa, T.; Ricker, P.; Riley,
K.; Rosner, R.; Siegel, A.; Timmes, F. X.; Truran, J. W.; Vladimirova,
N.; Wiers, G.; Zingale, M.
Bibcode: 2003HEAD....7.1810L
Altcode: 2003BAAS...35..865L
Type Ia supernovae are thought to be the result of a thermonuclear
explosion in a white dwarf that is approaching the Chandrasekhar mass
limit. The properties of the supernova explosion, including its energy,
depends significantly on the way in which the thermonuclear runaway
begins. Where in the white dwarf ignition takes place, and how many
ignition points there are, are important unsolved questions. We
discuss the challenges of modeling Type Ia supernova during the
several hours before thermonuclear runaway using the FLASH code. In
three-dimensional hydrodynamic codes, the pre-supernova white dwarf
can exhibit ``ringing'' at the fundamental frequency of the star that
is driven by numerical noise. These solutions manifest themselves
as undamped velocity waves (the white dwarf "breathes in and out")
that reach peak amplitudes of about 200 km s-1. We show the
results of several methods aimed at reducing the amplitude of these
undamped waves in FLASH. We also discuss some of our experiments
in mapping spherically symmetric models, which suggest large scale
convective motions of 50 km s-1 a few hours prior to
ignition, onto a three-dimensional mesh. This work was supported in
part by the DOE under the ASCI/Alliance program.
Title: Microphysics of Astrophysical Flames
Authors: Dursi, L. J.; Zingale, M.; Caceres, A.; Calder, A. C.; Timmes,
F. X.; Truran, J. W.; Rosner, R.; Lamb, D. Q.; Brown, E.; Ricker,
P.; Fryxell, B.; Olson, K.; Riley, K.; Siegel, A.; Vladimirova, N.
Bibcode: 2003HEAD....7.1803D
Altcode: 2003BAAS...35..630D
Type Ia supernovae are thought to begin with a deflagration phase,
where burning occurs as a subsonic flame which accelerates and
possibly undergoes a transition to a supersonic detonation. Both the
acceleration and possible transition will depend on the microphysics of
astrophysical flames, and their interaction with a turbulent flow in
degenerate material. Here we present recent progress in studying the
interactions of astrophysical flames and curvature and strain at the
FLASH center; in particular, we discuss quantitative measurements of the
effects of strain on burning rate of these flames, and implications for
instability growth and quenching. This work was supported by the
DOE ASCI/Alliances program at the University of Chicago under grant
No. B341495 and the Scientific through Advanced Computing (SciDAC)
program of the DOE, grant number DE-FC02-01ER41176 to the Supernova
Science Center/UCSC.
Title: Shear mixing in classical Novae
Authors: Alexakis, A.; Calder, A. C.; Dursi, L. J.; Times, F. X.;
Truran, J. W.; Rosner, R.; Lamb, D. M.; Mignone, A.; Fryxel, B.;
Zingale, M.; Olson, K.; Ricker, P.
Bibcode: 2003HEAD....7.1808A
Altcode: 2003BAAS...35..631A
The mixing of white dwarf material with the accretion envelope in
classical novae scenarios is essential for the later evolution and the
outburst. One of the plausible mechanisms for the enrichment involves
the coupling of large scale flows like convection or accretion with the
breaking interfacial waves at the white dwarf surface. We examine how
the interaction of accretion wind with a white dwarf surface can lead to
a substantial C/O enrichment that can power a novae. We use the FLASH
code to perform two and three dimensional simulations of wind driven
gravity waves and investigate their growth and non-linear development
for a variety of wind profiles. Our results show that even weak winds
generate gravity waves through a resonant mechanism with the wind that
grow nonlinear and break leading to spray formation and mixing. The
total amount of white dwarf material mixed at late times, is shown to
be proportional to the square of the maximum wind velocity, inversely
proportional to gravity and independent of the functional form of the
wind profile. This work has been supported by the DOE ASCI/Alliances
program at the University of Chicago under grant No. B341495.
Title: Progress in Modeling Classical Nova Outbursts
Authors: Calder, A. C.; Alexakis, A.; Dursi, L. J.; Mignone, A.;
Timmes, F. X.; Truran, J. W.; Rosner, R.; Lamb, D. Q.; Brown, E.;
Fryxell, B.; Zingale, M.; Ricker, P.; Olson, K.
Bibcode: 2003HEAD....7.1802C
Altcode: 2003BAAS...35..630C
We report on progress in modeling many facets of Classical Novae. These
include magnetohydrodynamical simulations of the accretion phase (for
the case of magnetic white dwarfs) and hydrodynamical simulations of
the mixing of white dwarf material into the hydrogen-rich envelope
by resonant gravity wave breaking at the surface of the white dwarf
(See also Alexakis, et al.). We also report on initial efforts at
the development of a sub-grid enrichment model based on these results
as well as results of one-dimensional simulations with mixing length
convection of the enrichment process exploring the long-term behavior
of the enriched region. Finally, we present two-dimensional simulations
of the onset and development of convection in nova precursor models
and during the runaway. This work was supported by the DOE
ASCI/Alliances program at the University of Chicago under grant
No. B341495.
Title: Development and Application of Numerical Modules for FLASH
in Palermo: Two Astrophysical Examples
Authors: Orlando, S.; Peres, G.; Reale, F.; Rosner, R.; Plewa, T.;
Siegel, A.
Bibcode: 2003MSAIS...1...45O
Altcode:
We collaborate with the Flash Center at the University of Chicago to
help upgrading and to apply extensively the FLASH code to astrophysical
problems. In particular, we have developed new modules for FLASH
which extend the field of applicability of the code to some areas
in astrophysics, like solar and stellar coronae, and supernova
remnants. The new modules so far developed and tested describe:
the non-equilibrium ionization effects of the most abundant elements
in astrophysical plasmas, the thermal conduction and the viscosity
according to the formulation of Spitzer (1962), and the radiative losses
from an optically thin plasma according to the Raymond spectral code,
and to Peres et al. (1982) for the chromosphere. We show some selected
results for a coronal flare and for a supernova remnant, obtained with
the version of FLASH 2.0 code including the new modules.
Title: Non-Equilibrium Ionization Effects Induced During Coronal
Flares
Authors: Orlando, S.; Peres, G.; Reale, F.; Rosner, R.; Siegel, A.
Bibcode: 2003MmSAI..74..643O
Altcode:
We present preliminary results of hydrodynamic modeling of flares
occurring in plasma confined in coronal loops. Our analysis focuses on
the deviations from ionization equilibrium on the population fractions
of the most abundant elements in astrophysical plasmas, and on the
possible implications for plasma diagnostics.
Title: Issues in Advanced Computing: A US Perspective
Authors: Rosner, Robert
Bibcode: 2003MSAIS...1..220R
Altcode:
I give a review of the situation in USA in the field of
supercomputing. After the necessary distinction between advanced- and
high-performance computing, I sketch both the various program areas
(networking, grid computing, scalable numerical tools, etc.) and the
major advanced computing science initiatives, from the data-intensive
science (virtual observatories, digital sky surveys, bioinformatics,
etc.) to complex systems science (multi-physics/multi-scale numerical
simulations with related problems of code verification and validation).
Title: Investigations of Pointwise Ignition of Helium Deflagrations
on Neutron Stars
Authors: Zingale, M.; Woosley, S. E.; Cumming, A.; Calder, A.; Dursi,
L. J.; Fryxell, B.; Olson, K.; Ricker, P.; Rosner, R.; Timmes, F. X.
Bibcode: 2003ASPC..293..329Z
Altcode: 2002astro.ph.11336Z; 2003tdse.conf..329Z
We look at the spreading of localized temperature perturbations in
the accreted fuel layer of a non-rotating neutron star. The pressure
at the base of the accreted fuel layer is large and the material is
only partially degenerate. Any temperature perturbations and resulting
pressure gradients will lead to enormous accelerations (both laterally
and vertically) of the material in the fuel layer. If the burning
of this fuel cannot proceed more rapidly than the spreading of this
perturbation, then localized burning cannot take place, and it is likely
that the ignition would have to proceed simultaneously throughout the
envelope. We present some multidimensional simulations of the spreading
of temperature perturbations in a helium atmosphere on a neutron star.
Title: The statistical challenges of wavelet-based source detection
Authors: Freeman, Peter E.; Kashyap, V.; Rosner, R.; Lamb, D. Q.
Bibcode: 2003sca..book..365F
Altcode:
Wavelet functions are proving extremely useful for detecting sources
in binned, two-dimensional photon counts images. In this chapter, we
describe the mission-independent source detection algorithm WAVDETECT,
part of the Chandra Interactive Analysis of Observations (CIAO)
softwave package, and discuss the statistical challenges we have
faced in its development, such as: what is the best way to estimate
the local background in each pixel, if it is a priori unknown? What
is the best way to eliminate false detections caused by instrumental
variations? And what is the significance of a detected source?
Title: Mapping Initial Hydrostatic Models in Godunov Codes
Authors: Zingale, M.; Dursi, L. J.; ZuHone, J.; Calder, A. C.; Fryxell,
B.; Plewa, T.; Truran, J. W.; Caceres, A.; Olson, K.; Ricker, P. M.;
Riley, K.; Rosner, R.; Siegel, A.; Timmes, F. X.; Vladimirova, N.
Bibcode: 2002ApJS..143..539Z
Altcode: 2002astro.ph..8031Z
We look in detail at the process of mapping an astrophysical initial
model from a stellar evolution code onto the computational grid
of an explicit, Godunov-type code while maintaining hydrostatic
equilibrium. This mapping process is common in astrophysical
simulations, when it is necessary to follow short-timescale dynamics
after a period of long-timescale buildup. We look at the effects
of spatial resolution, boundary conditions, the treatment of the
gravitational source terms in the hydrodynamics solver, and the
initialization process itself. We conclude with a summary detailing
the mapping process that yields the lowest ambient velocities in the
mapped model.
Title: Connections between laser hydrodynamics experiments and
astrophysics
Authors: Drake, R. P.; Robey, H. A.; Remington, B. A.; Ryutov, D. D.;
Calder, A.; Rosner, R.; Fryxell, B.; Arnett, D.; Zhang, Y.; Glimm,
J.; Knauer, J.
Bibcode: 2002APS..DPPGP1055D
Altcode:
Recent and ongoing experiments have studied mechanisms that affect the
evolution of supernovae, supernova remnants, and related systems. These
experiments are designed to be well scaled from astrophysical systems to
the laboratory. The experiments and some of the astrophysical systems
involve time-dependent flows with very large Reynolds number. In
contrast, numerical viscosity limits computer simulations of these
phenomena to a Reynolds number of order 1000. Using our own experiments
and other work in fluid dynamics as a guide, we will explore the
implications for astrophysical systems. The key question is whether
the astrophysical systems might evolve into a turbulent state that the
computer simulations cannot reproduce. The US DOE and NASA supported
this work.
Title: Nonlinear Rayleigh Taylor Hydrodynamics on the Omega laser
Authors: Harding, E. C.; Drake, R. P.; Keiter, P.; Korreck, K. E.;
Blackburn, M.; Leibrandt, D.; Grosskopf, M.; Robey, H. A.; Perry,
T. S.; Remington, B. A.; Wallace, R. J.; Louis, H.; Ryutov, D. D.;
Hansen, F.; Edwards, J.; Miles, A.; Knauer, J.; Calder, A.; Rosner,
R.; Fryxell, B.; Arnett, D.; Zhang, Y.; Glimm, J.
Bibcode: 2002APS..DPPGP1056H
Altcode:
We will show calibrated images from experiments to study the development
of the Rayleigh Taylor instability at a decelerating interface, a
mechanism that affects the evolution of supernovae, supernova remnants,
and related systems. These experiments are designed to be well scaled
from astrophysical systems to the laboratory. They begin by using the
laser to drive a strong shock into a target material. After the laser
ends, a rarefaction overtakes the shock, forming a blast wave. The
blast wave shocks a structured interface, which then decelerates. We
have explored the development of Rayleigh Taylor from initial 2D
perturbations with one, two, or 8 modes present, and from initial 3D,
single-mode perturbations. There are indications in the data of bubble
merger and possibly of the onset of turbulence.
Title: Mixing by Non-linear Gravity Wave Breaking on a White Dwarf
Surface
Authors: Calder, A. C.; Alexakis, A.; Dursi, L. J.; Rosner, R.; Truran,
J. W.; Fryxell, B.; Ricker, P.; Zingale, M.; Olson, K.; Timmes, F. X.;
MacNeice, P.
Bibcode: 2002AIPC..637..134C
Altcode: 2002astro.ph..7248C; 2002cne..conf..134C
We present the results of a simulation of a wind-driven non-linear
gravity wave breaking on the surface of a white dwarf. The ``wind''
consists of H/He from an accreted envelope, and the simulation
demonstrates that this breaking wave mechanism can produce a well-mixed
layer of H/He with C/O from the white dwarf above the surface. Material
from this mixed layer may then be transported throughout the accreted
envelope by convection, which would enrich the C/O abundance of the
envelope as is expected from observations of novae.
Title: On Validating an Astrophysical Simulation Code
Authors: Calder, A. C.; Fryxell, B.; Plewa, T.; Rosner, R.; Dursi,
L. J.; Weirs, V. G.; Dupont, T.; Robey, H. F.; Kane, J. O.; Remington,
B. A.; Drake, R. P.; Dimonte, G.; Zingale, M.; Timmes, F. X.; Olson,
K.; Ricker, P.; MacNeice, P.; Tufo, H. M.
Bibcode: 2002ApJS..143..201C
Altcode: 2002astro.ph..6251C
We present a case study of validating an astrophysical simulation
code. Our study focuses on validating FLASH, a parallel, adaptive-mesh
hydrodynamics code for studying the compressible, reactive flows found
in many astrophysical environments. We describe the astrophysics
problems of interest and the challenges associated with simulating
these problems. We describe methodology and discuss solutions to
difficulties encountered in verification and validation. We describe
verification tests regularly administered to the code, present the
results of new verification tests, and outline a method for testing
general equations of state. We present the results of two validation
tests in which we compared simulations to experimental data. The first
is of a laser-driven shock propagating through a multilayer target,
a configuration subject to both Rayleigh-Taylor and Richtmyer-Meshkov
instabilities. The second test is a classic Rayleigh-Taylor instability,
where a heavy fluid is supported against the force of gravity by a light
fluid. Our simulations of the multilayer target experiments showed good
agreement with the experimental results, but our simulations of the
Rayleigh-Taylor instability did not agree well with the experimental
results. We discuss our findings and present results of additional
simulations undertaken to further investigate the Rayleigh-Taylor
instability.
Title: Non-equilibrium ionization effects during flares in coronal
loops
Authors: Orlando, Salvatore; Peres, Giovanni; Reale, Fabio; Rosner,
Robert
Bibcode: 2002ESASP.505..517O
Altcode: 2002solm.conf..517O; 2002IAUCo.188..517O
We present preliminary results of hydrodynamic modeling of flares
occurring in plasma magnetically confined in coronal loops, using the
adaptive-mesh astrophysical hydrodynamic code FLASH. We also investigate
the deviations from ionization equilibrium on the population fractions
of the most abundant elements in astrophysical plasmas and the relevant
consequences on observed spectra.
Title: Simulating Astrophysical Thermonuclear Flashes
Authors: Rosner, Robert
Bibcode: 2002APS..CCP.A1003R
Altcode:
not available at this time.
Title: On the Generation of Flux-Tube Waves in Stellar Convection
Zones. IV. Longitudinal Wave Energy Spectra and Fluxes for Stars
with Nonsolar Metallicities
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.
Bibcode: 2002ApJ...573..418M
Altcode:
In the previous papers of this series, we developed an analytical
method describing the generation of longitudinal tube waves in
stellar convection zones and used it to compute the wave energy
spectra and fluxes for late-type stars with the solar metal abundance
(Population I). We now extend these calculations to Population II
stars with effective temperatures ranging from Teff=2500
to 10,000 K, gravities logg=3-5, and with three different metal
abundances: 1/10, 1/100, and 1/1000 of solar metallicity. The obtained
results are valid for a single magnetic flux, and they show that
the effects of metallicity are important only for cool stars with
Teff<6000 K and that the amount of the generated wave
energy decreases roughly by an order of magnitude for every decrease
of the metallicity by an order of magnitude. The maximum wave energy
flux generated in Population II stars is 7×108 ergs
cm-2 s-1, and it is practically the same for
stars of different gravities and metallicities. The computed spectra
and fluxes can be used to construct theoretical models of magnetic
regions in chromospheres of Population II stars.
Title: Convection and Mixing in Classical Novae Precursors
Authors: Dursi, L. J.; Calder, A. C.; Alexakis, A.; Truran, J. W.;
Zingale, M.; Times, F. X.; Ricker, P. M.; Fryxell, B.; Olson, K.;
Rosner, R.; MacNeice, P.
Bibcode: 2002AAS...200.9502D
Altcode: 2002BAAS...34..955D
To explain observed abundances from classical nova outbursts, and to
help explain their energetics, nova models must incorporate a mechanism
that will dredge up the heavier white dwarf material into the lighter
accreted atmosphere. One proposed mechanism relies on the fluid
motions from an early convective phase to do the mixing. We present
recent work investigating two aspects of this mechanism. We examine
results from two-dimensional simulations of classical nova precursor
models that demonstrate the beginning of a convective phase during the
`simmering' of a nova precursor. We use a new hydrostatic equilibrium
hydrodynamics module recently developed for the adaptive-mesh code
FLASH. The two-dimensional models are based on the one-dimensional
models of Ami Glasner (Glasner et al. 1997), and were evolved with FLASH
from a pre-convective state to the onset of convection. The onset of
convection induces a velocity field near the C,O/H,He interface, which
can then cause mixing through interactions with gravity waves. We show
results from simulations of these wind-wave interactions, and estimate
whether the `wind' caused by the convection could induce sufficient
dredge-up to power a classical novae. This research has been supported
by the US. Department of Energy under grant no. B341495 to the ASCI
Flash Center at the University of Chicago
Title: Investigations of Pointwise Ignition of Helium Deflagrations
on Neutron Stars
Authors: Zingale, M.; Woosley, S. E.; Cumming, A.; Calder, A. C.;
Dursi, L. J.; Fryxell, B. A.; Olson, K.; Ricker, P. M.; Rosner, R.;
Timmes, F. X.
Bibcode: 2002AAS...200.9403Z
Altcode: 2002BAAS...34..955Z
We look at localized helium burning in the accreted fuel layer of a
non-rotating neutron star. The pressure at the base of the accreted
fuel layer is large and the material is only partially degenerate. Any
temperature perturbations and resulting pressure gradients will lead to
enormous accelerations (both laterally and vertically) of the material
in the fuel layer. If the burning cannot proceed more rapidly than the
spreading of this temperature perturbation, then localized burning
cannot take place, and it is likely that the ignition would have
to proceed simultaneously throughout the envelope. We present some
initial multidimensional simulations of pointwise burning in a helium
atmosphere on a neutron star. Support for this work was provided by
the Scientific Discovery through Advanced Computing (SciDAC) program
of the DOE, grant number DE-FC02-01ER41176.
Title: Erratum: Shear instability of fluid interfaces: Stability
analysis [Phys. Rev. E 65, 026313 (2002)]
Authors: Alexakis, A.; Young, Y.; Rosner, R.
Bibcode: 2002PhRvE..65e9904A
Altcode:
No abstract at ADS
Title: Mixing by wave breaking at the surface of a white dwarf
Authors: Truran, J. W.; Alexakis, A.; Calder, A. C.; Dursi, L. J.;
Zingale, M.; Fryxell, B.; Ricker, P.; Timmes, F. X.; Olson, K.;
Rosner, R.
Bibcode: 2002nuas.conf..186T
Altcode:
No abstract at ADS
Title: Explosive energy release in magnetic shocks
Authors: Vainshtein, S. I.; Rosner, R.; Sagdeev, R. Z.
Bibcode: 2002PhRvE..65c5401V
Altcode:
We show that a magnetic shock whose initial density and/or magnetic
perturbation exceeds the Hugoniot limit may lead to substantial
and rapid energy release in low β plasmas (such as occur in the
magnetospheres of neutron stars). We illustrate this effect for a
fast Magnetohydrodynamic perturbation, as well as for large density
perturbations which can be naturally created in low β plasmas. Using
the Riemann solution and simulations, we show that slow modes of finite
magnitudes and Alfvénic perturbations can generate strong density
perturbations. These perturbations develop into shocks, resulting in
efficient energy release.
Title: Shear instability of fluid interfaces: Stability analysis
Authors: Alexakis, A.; Young, Y.; Rosner, R.
Bibcode: 2002PhRvE..65b6313A
Altcode:
We examine the linear stability of fluid interfaces subjected to
a shear flow. Our main object is to generalize previous work to an
arbitrary Atwood number, and to allow for surface tension and weak
compressibility. The motivation derives from instances in astrophysical
systems where mixing across material interfaces driven by shear flows
may significantly affect the dynamical evolution of these systems.
Title: Sloan Digital Sky Survey: Early Data Release
Authors: Stoughton, Chris; Lupton, Robert H.; Bernardi, Mariangela;
Blanton, Michael R.; Burles, Scott; Castander, Francisco J.; Connolly,
A. J.; Eisenstein, Daniel J.; Frieman, Joshua A.; Hennessy, G. S.;
Hindsley, Robert B.; Ivezić, Željko; Kent, Stephen; Kunszt,
Peter Z.; Lee, Brian C.; Meiksin, Avery; Munn, Jeffrey A.; Newberg,
Heidi Jo; Nichol, R. C.; Nicinski, Tom; Pier, Jeffrey R.; Richards,
Gordon T.; Richmond, Michael W.; Schlegel, David J.; Smith, J. Allyn;
Strauss, Michael A.; SubbaRao, Mark; Szalay, Alexander S.; Thakar,
Aniruddha R.; Tucker, Douglas L.; Vanden Berk, Daniel E.; Yanny,
Brian; Adelman, Jennifer K.; Anderson, John E., Jr.; Anderson,
Scott F.; Annis, James; Bahcall, Neta A.; Bakken, J. A.; Bartelmann,
Matthias; Bastian, Steven; Bauer, Amanda; Berman, Eileen; Böhringer,
Hans; Boroski, William N.; Bracker, Steve; Briegel, Charlie; Briggs,
John W.; Brinkmann, J.; Brunner, Robert; Carey, Larry; Carr, Michael
A.; Chen, Bing; Christian, Damian; Colestock, Patrick L.; Crocker,
J. H.; Csabai, István; Czarapata, Paul C.; Dalcanton, Julianne;
Davidsen, Arthur F.; Davis, John Eric; Dehnen, Walter; Dodelson,
Scott; Doi, Mamoru; Dombeck, Tom; Donahue, Megan; Ellman, Nancy; Elms,
Brian R.; Evans, Michael L.; Eyer, Laurent; Fan, Xiaohui; Federwitz,
Glenn R.; Friedman, Scott; Fukugita, Masataka; Gal, Roy; Gillespie,
Bruce; Glazebrook, Karl; Gray, Jim; Grebel, Eva K.; Greenawalt,
Bruce; Greene, Gretchen; Gunn, James E.; de Haas, Ernst; Haiman,
Zoltán; Haldeman, Merle; Hall, Patrick B.; Hamabe, Masaru; Hansen,
Brad; Harris, Frederick H.; Harris, Hugh; Harvanek, Michael; Hawley,
Suzanne L.; Hayes, J. J. E.; Heckman, Timothy M.; Helmi, Amina; Henden,
Arne; Hogan, Craig J.; Hogg, David W.; Holmgren, Donald J.; Holtzman,
Jon; Huang, Chih-Hao; Hull, Charles; Ichikawa, Shin-Ichi; Ichikawa,
Takashi; Johnston, David E.; Kauffmann, Guinevere; Kim, Rita S. J.;
Kimball, Tim; Kinney, E.; Klaene, Mark; Kleinman, S. J.; Klypin,
Anatoly; Knapp, G. R.; Korienek, John; Krolik, Julian; Kron, Richard
G.; Krzesiński, Jurek; Lamb, D. Q.; Leger, R. French; Limmongkol,
Siriluk; Lindenmeyer, Carl; Long, Daniel C.; Loomis, Craig; Loveday,
Jon; MacKinnon, Bryan; Mannery, Edward J.; Mantsch, P. M.; Margon,
Bruce; McGehee, Peregrine; McKay, Timothy A.; McLean, Brian; Menou,
Kristen; Merelli, Aronne; Mo, H. J.; Monet, David G.; Nakamura, Osamu;
Narayanan, Vijay K.; Nash, Thomas; Neilsen, Eric H., Jr.; Newman,
Peter R.; Nitta, Atsuko; Odenkirchen, Michael; Okada, Norio; Okamura,
Sadanori; Ostriker, Jeremiah P.; Owen, Russell; Pauls, A. George;
Peoples, John; Peterson, R. S.; Petravick, Donald; Pope, Adrian;
Pordes, Ruth; Postman, Marc; Prosapio, Angela; Quinn, Thomas R.;
Rechenmacher, Ron; Rivetta, Claudio H.; Rix, Hans-Walter; Rockosi,
Constance M.; Rosner, Robert; Ruthmansdorfer, Kurt; Sandford, Dale;
Schneider, Donald P.; Scranton, Ryan; Sekiguchi, Maki; Sergey, Gary;
Sheth, Ravi; Shimasaku, Kazuhiro; Smee, Stephen; Snedden, Stephanie A.;
Stebbins, Albert; Stubbs, Christopher; Szapudi, István; Szkody, Paula;
Szokoly, Gyula P.; Tabachnik, Serge; Tsvetanov, Zlatan; Uomoto, Alan;
Vogeley, Michael S.; Voges, Wolfgang; Waddell, Patrick; Walterbos,
René; Wang, Shu-i.; Watanabe, Masaru; Weinberg, David H.; White,
Richard L.; White, Simon D. M.; Wilhite, Brian; Wolfe, David; Yasuda,
Naoki; York, Donald G.; Zehavi, Idit; Zheng, Wei
Bibcode: 2002AJ....123..485S
Altcode:
The Sloan Digital Sky Survey (SDSS) is an imaging and spectroscopic
survey that will eventually cover approximately one-quarter of the
celestial sphere and collect spectra of ~106 galaxies,
100,000 quasars, 30,000 stars, and 30,000 serendipity targets. In 2001
June, the SDSS released to the general astronomical community its early
data release, roughly 462 deg2 of imaging data including
almost 14 million detected objects and 54,008 follow-up spectra. The
imaging data were collected in drift-scan mode in five bandpasses (u,
g, r, i, and z); our 95% completeness limits for stars are 22.0, 22.2,
22.2, 21.3, and 20.5, respectively. The photometric calibration is
reproducible to 5%, 3%, 3%, 3%, and 5%, respectively. The spectra are
flux- and wavelength-calibrated, with 4096 pixels from 3800 to 9200 Å
at R~1800. We present the means by which these data are distributed
to the astronomical community, descriptions of the hardware used
to obtain the data, the software used for processing the data, the
measured quantities for each observed object, and an overview of the
properties of this data set.
Title: A Wavelet-Based Algorithm for the Spatial Analysis of
Poisson Data
Authors: Freeman, P. E.; Kashyap, V.; Rosner, R.; Lamb, D. Q.
Bibcode: 2002ApJS..138..185F
Altcode: 2001astro.ph..8429F
Wavelets are scalable, oscillatory functions that deviate from zero
only within a limited spatial regime and have average value zero, and
thus may be used to simultaneously characterize the shape, location, and
strength of astronomical sources. But in addition to their use as source
characterizers, wavelet functions are rapidly gaining currency within
the source detection field. Wavelet-based source detection involves the
correlation of scaled wavelet functions with binned, two-dimensional
image data. If the chosen wavelet function exhibits the property of
vanishing moments, significantly nonzero correlation coefficients will
be observed only where there are high-order variations in the data;
e.g., they will be observed in the vicinity of sources. Source pixels
are identified by comparing each correlation coefficient with its
probability sampling distribution, which is a function of the (estimated
or a priori known) background amplitude. In this paper, we describe
the mission-independent, wavelet-based source detection algorithm
``WAVDETECT,'' part of the freely available Chandra Interactive Analysis
of Observations (CIAO) software package. Our algorithm uses the Marr,
or ``Mexican Hat'' wavelet function, but may be adapted for use with
other wavelet functions. Aspects of our algorithm include: (1) the
computation of local, exposure-corrected normalized (i.e., flat-fielded)
background maps; (2) the correction for exposure variations within
the field of view (due to, e.g., telescope support ribs or the edge
of the field); (3) its applicability within the low-counts regime,
as it does not require a minimum number of background counts per
pixel for the accurate computation of source detection thresholds;
(4) the generation of a source list in a manner that does not depend
upon a detailed knowledge of the point spread function (PSF) shape; and
(5) error analysis. These features make our algorithm considerably more
general than previous methods developed for the analysis of X-ray image
data, especially in the low count regime. We demonstrate the robustness
of WAVDETECT by applying it to an image from an idealized detector with
a spatially invariant Gaussian PSF and an exposure map similar to that
of the Einstein IPC; to Pleiades Cluster data collected by the ROSAT
PSPC; and to simulated Chandra ACIS-I image of the Lockman Hole region.
Title: The Distribution of the Emission Measure, and of the Heating
Budget, among the Loops in the Corona
Authors: Peres, G.; Orlando, S.; Reale, F.; Rosner, R.
Bibcode: 2001ApJ...563.1045P
Altcode: 2001astro.ph.11192P
The aim of this paper is to validate a methodology for connecting the
emission measure of individual solar coronal loops to the integrated
emission measure of the entire solar corona and using this connection
to deduce the energetic properties of the corona; we then show how
this methodology can be applied to observations of solar-like stellar
coronae. The solar validation is carried out by using spatially resolved
X-ray observations of the Sun obtained from the Yohkoh satellite. This
work is a further step in our effort to place the ``solar-stellar
connection'' on a quantitative footing. In particular, we show how this
analysis procedure can be used in the context of archival Einstein,
ROSAT, and EUVE data, as well as for Chandra and XMM-Newton data, as
a complementary analysis tool to existing multithermal component models.
Title: Initiation of Convection in a Classical Nova Precursor
Authors: Dursi, L. J.; Calder, A. C.; Ricker, P. M.; Truran, J. W.;
Zingale, M.; Fryxell, B.; Olson, K.; Rosner, R.; Timmes, F. X.; Tufo,
H.; MacNeice, P.
Bibcode: 2001AAS...199.6213D
Altcode: 2001BAAS...33.1402D
Classical Novae result from the explosive thermonuclear burning of
material accreted from a companion star onto the surface of a white
dwarf. Observed abundances and explosion energies estimated from
observations indicate that there must be significant mixing of the
heavier material of the white dwarf (C/O) into the lighter accreted
material (H/He). Accordingly, nova models must incorporate a mechanism
that will dredge up the heavier white dwarf material, and fluid motions
from an early convection phase is one proposed mechanism. We present
results from two-dimensional simulations of classical nova precursor
models that demonstrate the beginning of a convective phase during the
`simmering' of a Nova precursor. We use a new hydrostatic equilibrium
hydrodynamics module recently developed for the adaptive-mesh code
FLASH. The two-dimensional models are based on the one-dimensional
models of Ami Glasner (Glasner et al. 1997), and were evolved with FLASH
from a pre-convective state to the onset of convection. In addition,
we present the details of the hydrostatic equilibrium module and
the hydrostatic boundary conditions used in the simulations. This
research has been supported by the U.S. Department of Energy under
grant no. B341495 to the ASCI Flash Center at the University of Chicago.
Title: On the C/O Enrichment of Nova Ejecta
Authors: Rosner, R.; Alexakis, A.; Young, Y. -N.; Truran, J. W.;
Hillebrandt, W.
Bibcode: 2001ApJ...562L.177R
Altcode: 2001astro.ph.10684R
Using the results of recent work in shear instabilities in stratified
fluids, we show that the resonant interaction between large-scale flows
in the accreted H/He envelope of white dwarf stars and interfacial
gravity waves can mix the star's envelope with the white dwarf's
surface material, leading to the enhancement of the envelope's C/O
abundance to levels required by extant models for nova outbursts.
Title: Gas Stripping, Turbulence, and Wake Formation in Cluster
Mergers
Authors: Ricker, P. M.; Sarazin, C. L.; Kempner, J. C.; Calder, A. C.;
Dursi, L. J.; Fryxell, B.; Lamb, D. Q.; Olson, K.; Rosner, R.; Timmes,
F. X.; Truran, J. W.; Tufo, H.; Zingale, M.
Bibcode: 2001AAS...19910016R
Altcode: 2001BAAS...33.1460R
We present results from high-resolution (sub-kpc) hydro + dark matter
simulations of the interaction of subclusters with the intracluster
medium during the initial stages of a galaxy cluster merger. Using
the adaptive-mesh code FLASH, we study the development of fluid
instabilities along the contact surface and in the wake produced by this
interaction. We examine the role of shock waves and instability-induced
turbulence in the stripping of gas from the dense subcluster core. We
discuss the observability of merger-induced turbulence, and we compare
our results to the observed clusters Abell 85 and Abell 3667. This
research has been supported by the U.S. Department of Energy under
grant no. B341495 to the ASCI Flash Center at the University of Chicago.
Title: Multidimensional Simulations of Type Ia Supernovae
Authors: Calder, A. C.; Ricker, P. M.; Dursi, L. J.; Truran, J. W.;
Fryxell, B.; Rosner, R.; Timmes, F. X.; Tufo, H. M.; Zingale, M.;
Olson, K.; MacNeice, P.
Bibcode: 2001AAS...199.4706C
Altcode: 2001BAAS...33Q1371C
We present results from two- and three-dimensional simulations
of Type Ia supernovae carried out from first principles using the
adaptive-mesh code FLASH. Considering off-center prompt detonations in
Chandrasekhar-mass carbon-oxygen white dwarfs, we observe temperature
and abundance inhomogeneities with a cell-like structure behind the
detonation front. We discuss these results in light of the commonly
accepted view that prompt detonation models cannot reproduce the
abundances of intermediate-mass elements observed in Type Ia supernovae,
considering in general the observability of multidimensional structure
in carbon detonations under conditions present in a white dwarf. This
research has been supported by the U.S. Department of Energy under
grant no. B341495 to the ASCI Flash Center at the University of Chicago.
Title: Linear and Weakly Non-Linear Analysis of Wind Driven Gravity
Waves
Authors: Alexakis, Alexandros; Young, Yuan-Nan; Rosner, Robert
Bibcode: 2001APS..DFD.AJ004A
Altcode:
We generalize the formulation for the generation of gravity waves
by Miles('57) for air over water case to arbitrary density ratio and
wind strength. The motivation comes from an astrophysical problem in
which mixing at the material interface between two fluids becomes
essential to the stellar evolution. Using different wind profiles
we provide the instability boundaries in the parameter space of
density ratio, potential to kinetic energy ratio and wave number. We
compare with the classical Kelvin Helmholtz instability and explore
their differences. Also, assuming small but finite amplitude for
the perturbation we derive the amplitude equations in the weakly
nonlinear regime. The nonlinearity first appears inside the critical
layer and this leads to a weakly non-linear development of a critical
layer coupled to a linear gravity wave. Long time evolution and
supercriticality can then be determined.
Title: Supernova hydrodynamics on the Omega laser
Authors: Drake, R. P.; Keiter, P.; Korreck, K. E.; Dannenberg, K. K.;
Robey, H. A.; Perry, T. S.; Kane, J. O.; Remington, B. A.; Wallace,
R. J.; Hurricane, O. A.; Ryutov, D. D.; Knauer, J.; Teyssier, R.;
Calder, A.; Rosner, R.; Fryxell, B.; Arnett, D.; Zhang, Y.; Glimm,
J.; Turner, N.; Stone, J.; McCray, R.; Grove, J.
Bibcode: 2001APS..DPPRP1087D
Altcode:
Our experiments study mechanisms that affect the evolution
of supernovae, supernova remnants, and related systems. These
experiments are designed to be well scaled from astrophysical
systems to the laboratory. This overview of our work will highlight
our most recent results. Our work is motivated by the specific
fact that numerical simulations have proven unable to reproduce
certain aspects of astrophysical observations, and by the general
need to provide experimental tests of modeling of hydrodynamic and
radiation-hydrodynamic systems. The experiments use the Omega Laser
at the Lab. for Laser Energetics, Univ. of Rochester. We have recently
explored the comparison of 2D and 3D systems, the comparison of single
mode and multimode systems, and the production and diagnosis of a
radiative-precursor shock.
Title: On a mechanism of highest-energy cosmic ray acceleration
Authors: Litwin, C.; Rosner, R.
Bibcode: 2001AIPC..586..856L
Altcode: 2001tsra.conf..856L; 2001astro.ph..4093L
A recently proposed mechanism of acceleration of highest energy cosmic
rays by polarization electric fields arising in plasmoids injected
into neutron star magnetospheres is discussed. .
Title: On the shear instability of fluid interfaces
Authors: Alexakis, A.; Young, Y.; Rosner, R.
Bibcode: 2001astro.ph.10686A
Altcode:
We examine the linear stability of fluid interfaces subjected to a shear
flow. Our main object is to generalize previous work to arbitrary Atwood
number, and to allow for surface tension and weak compressibility. The
motivation derives from instances in astrophysical systems where mixing
across material interfaces driven by shear flows may significantly
affect the dynamical evolution of these systems.
Title: Simulations of Astrophysical fluid instabilities
Authors: Calder, A. C.; Fryxell, B.; Rosner, R.; Dursi, L. J.; Olson,
K.; Ricker, P. M.; Timmes, F. X.; Zingale, M.; MacNeice, P.; Tufo,
H. M.
Bibcode: 2001AIPC..586..484C
Altcode: 2001tsra.conf..484C; 2001astro.ph..2239C
We present direct numerical simulations of mixing at Rayleigh-Taylor
unstable interfaces performed with the FLASH code, developed at the
ASCI/Alliances Center for Astrophysical Thermonuclear Flashes at the
University of Chicago. We present initial results of single-mode
studies in two and three dimensions. Our results indicate that
three-dimensional instabilities grow significantly faster than
two-dimensional instabilities and that grid resolution can have a
significant effect on instability growth rates. We also find that
unphysical diffusive mixing occurs at the fluid interface, particularly
in poorly resolved simulations. .
Title: Quenching processes in flame-vortex interactions
Authors: Zingale, M.; Niemeyer, J. C.; Timmes, F. X.; Dursi, L. J.;
Calder, A. C.; Fryxell, B.; Lamb, D. Q.; MacNeice, P.; Olson, K.;
Ricker, P. M.; Rosner, R.; Truran, J. W.; Tufo, H. M.
Bibcode: 2001AIPC..586..490Z
Altcode: 2001tsra.conf..490Z
We show direct numerical simulations of flame-vortex interactions
in order to understand quenching of thermonuclear flames. The
key question is-can a thermonuclear flame be quenched? If not,
the deflagration-detonation transition mechanisms that demand a
finely tuned preconditioned region in the interior of a white dwarf
are unlikely to work. In these simulations, we pass a steady-state
laminar flame through a vortex pair. The vortex pair represents the
most severe strain the flame front will encounter inside the white
dwarf. We perform a parameter study, varying the speed and size of
the vortex pair, in order to understand the quenching process. No
quenching is observed in any of the calculations performed to date. .
Title: Summary: Panel discussion on large-scale Astrophysical
calculations
Authors: Rosner, Robert
Bibcode: 2001AIPC..583..351R
Altcode:
I summarize the key points of the discussion following the astrophysics
presentations in the panel discussion sessions covering large-scale
simulations in high energy, accelerator and astrophysics. .
Title: Large-scale simulations of clusters of galaxies
Authors: Ricker, P. M.; Calder, A. C.; Dursi, L. J.; Fryxell, B.;
Lamb, D. Q.; MacNeice, P.; Olson, K.; Rosner, R.; Timmes, F. X.;
Truran, J. W.; Tufo, H. M.; Zingale, M.
Bibcode: 2001AIPC..583..316R
Altcode: 2000astro.ph.11502R
We discuss some of the computational challenges encountered in
simulating the evolution of clusters of galaxies. Eulerian adaptive mesh
refinement (AMR) techniques can successfully address these challenges
but are currently being used by only a few groups. We describe our
publicly available AMR code, FLASH, which uses an object-oriented
framework to manage its AMR library, physics modules, and automated
verification. We outline the development of the FLASH framework to
include collisionless particles, permitting it to be used for cluster
simulation. .
Title: Adaptive mesh simulations of astrophysical detonations using
the ASCI flash code
Authors: Fryxell, B.; Calder, A. C.; Dursi, L. J.; Lamb, D. Q.;
MacNeice, P.; Olson, K.; Ricker, P.; Rosner, R.; Timmes, F. X.;
Truran, J. W.; Tufo, H. M.; Zingale, M.
Bibcode: 2001AIPC..583..223F
Altcode:
The Flash code was developed at the University of Chicago as part of
the Department of Energy's Accelerated Strategic Computing Initiative
(ASCI). The code was designed specifically to simulate thermonuclear
flashes in compact stars (white dwarfs and neutron stars). This paper
will give a brief introduction to the astrophysics problems we wish
to address, followed by a description of the current version of the
Flash code. Finally, we discuss two simulations of astrophysical
detonations that we have carried out with the code. The first is of
a helium detonation in an X-ray burst. The other simulation models a
carbon detonation in a Type Ia supernova explosion. .
Title: Ballooning Instability in Polar Caps of Accreting Neutron Stars
Authors: Litwin, C.; Brown, Edward F.; Rosner, R.
Bibcode: 2001ApJ...553..788L
Altcode: 2001astro.ph..1168L
We assess the stability of Kruskal-Schwarzschild (magnetic
Rayleigh-Taylor) type modes for accreted matter on the surface of a
neutron star confined by a strong (>~1012 G) magnetic
field. Employing the energy principle to analyze the stability of
short-wavelength ballooning modes, we find that line-tying to the
neutron star crust stabilizes these modes until the overpressure at
the top of the neutron star crust exceeds the magnetic pressure by a
factor ~8(a/h), where a and h are, respectively, the lateral extent of
the accretion region and the density scale height. The most unstable
modes are localized within a density scale height above the crust. We
calculate the amount of mass that can be accumulated at the polar cap
before the onset of instability.
Title: Plasmoid Impacts on Neutron Stars and Highest Energy Cosmic
Rays
Authors: Litwin, C.; Rosner, R.
Bibcode: 2001PhRvL..86.4745L
Altcode: 2001astro.ph..4090L
Particle acceleration by electrostatic polarization fields that arise
in plasmas streaming across magnetic fields is discussed as a possible
acceleration mechanism of highest energy \(>~1020 eV\)
cosmic rays. Specifically, plasmoids arising in planetoid impacts onto
neutron star magnetospheres are considered. We find that such impacts
at plausible rates may account for the observed flux and energy spectrum
of the highest energy cosmic rays.
Title: Code Validation With Laser Astrophysics Experiments
Authors: Calder, A. C.; Fryxell, B.; Rosner, R.; Dursi, L. J.; Ricker,
P. M.; Timmes, F. X.; Zingale, M.; Kane, J. O.; Remington, B. A.;
Drake, R. P.; Olson, K.; MacNeice, P.; Tufo, H. M.
Bibcode: 2001AAS...198.6401C
Altcode: 2001BAAS...33..882C
An essential part of numerical modeling is validating simulation
codes with laboratory experiments that capture many of the physical
processes of interest. Validation is difficult in astrophysics because
the problems of interest typically encompass complex physics and
involve conditions that are difficult to reproduce in a terrestrial
laboratory. Laboratory astrophysics with intense lasers serves as an
invaluable validation tool by providing the chance to experimentally
probe environments similar to those in which complex astrophysical
phenomena occur. We describe the process of validating FLASH,
an adaptive mesh astrophysical simulation code for compressible,
reactive flows. We present the results of validation simulations,
principally simulations of laser experiments involving shock propagation
through multi-layer targets performed at the Omega laser facility
at the University of Rochester. This work was supported by the DOE
ASCI/Alliances program at the University of Chicago under grant
No. B341495.
Title: Helium Detonations on Neutron Stars
Authors: Zingale, M.; Timmes, F. X.; Fryxell, B.; Lamb, D. Q.; Olson,
K.; Calder, A. C.; Dursi, L. J.; Ricker, P.; Rosner, R.; MacNeice,
P.; Tufo, H. M.
Bibcode: 2001ApJS..133..195Z
Altcode:
We present the results of a numerical study of helium detonations on
the surfaces of neutron stars. We describe two-dimensional simulations
of the evolution of a detonation as it breaks through the accreted
envelope of the neutron star and propagates laterally through the
accreted material. The detonation front propagates laterally at nearly
the Chapman-Jouguet velocity, v=1.3×109 cm s-1. A
series of surface waves propagate across the pool of hot ash behind
the detonation front with the same speed, matching the speed expected
from shallow water wave theory. The entire envelope oscillates in the
gravitational potential well of the neutron star with a period of ~50
μs. The photosphere reaches an estimated height of 10 km above the
surface of the neutron star. Our study confirms that such a detonation
can insure the spread of burning over the entire neutron star surface
on a timescale consistent with burst rise times. We analyze the
sensitivity of the results to the spatial resolution and the assumed
initial conditions. We conclude by presenting a comparison of this
model to type I X-ray bursts.
Title: Theory and the Solar-Stellar Connection
Authors: Rosner, R.
Bibcode: 2001ASPC..248..671R
Altcode: 2001mfah.conf..671R
No abstract at ADS
Title: Simulating Thermonuclear Runaway in Novae
Authors: Dursi, L. J.; Truran, J.; Zingale, M.; Calder, A. C.; Fryxell,
B.; Olson, K.; Ricker, P.; Rosner, R.; Timmes, F. X.; Tufo, H. M.;
MacNeice, P.
Bibcode: 2000AAS...197.8105D
Altcode: 2000BAAS...32.1538D
A nova is a thought to result from a partially degenerate thermonuclear
runaway on the surface of a white dwarf. Material from the underlying
white dwarf must be dredged up into the atmosphere in order to
produce an explosion with the observed energies; the carbon and
oxygen serve as catalysts for the hydrogen burning, allowing the
much more temperature-sensitive CNO burning to occur. In order to
understand this dredge-up problem, we are running two different
types of simulations. The first are large-scale simulations with
the FLASH code (Fryxell et al., 2000), using a one-dimensional
set of initial conditions of a nova about to undergo runaway
created by Ami Glasner. These initial conditions have been used in
previous multidimensional simulations (Glasner et al. 1997; Kercek et
al. 1998), but these simulations have given widely different results
because of different mixing behaviors in the two codes. Our set of
simulations will shed some light on this discrepancy; since our code
has adaptive mesh refinement (MacNeice et al., 2000), we can afford
to highly refine the region of the star where the mixing occurs,
without the cost of highly refining the entire region. Because these
large-scale computations are extremely compute-intensive, they are not
appropriate for broad exploration of initial conditions. To do this,
we use a One-Dimensional Turbulence (ODT) model which has been used in
astrophysical models previously (Niemeyer & Kerstein, 1997). This
allows us to use ODT simulations of the nova as experiments to guide
us to interesting regimes to study further with multidimensional FLASH
code simulations. This work was supported in part by the Department of
Energy Grant No. B341495 to the Center for Astrophysical Thermonuclear
Flashes at the University of Chicago under the ASCI Strategic Alliances
Program and by NASA/Goddard Space Flight Center
Title: The Structure of Self-Gravitating Hydrodynamic Turbulence
Authors: Ricker, P. M.; Dursi, L. J.; Rosner, R.; Calder, A. C.;
Fryxell, B.; Olson, K.; Timmes, F. X.; Truran, J.; Tufo, H.; Zingale,
M.; MacNeice, P.
Bibcode: 2000AAS...197.4213R
Altcode: 2000BAAS...32.1467R
The formation of the first stars occurred in an extremely metal-poor
environment in which magnetic fields are believed to have been
dynamically unimportant. Recent cosmological simulations (Abel
et al. 2000) have begun to reach mass scales at which the first
molecular clouds can be identified, but thus far simulation has not
been able to determine the initial mass function of the resulting
stellar population. The fragmentation of these clouds depends upon both
radiative cooling instabilities in the primordial gas and the properties
of turbulence generated by the Jeans instability itself. To investigate
the latter question, we present high-resolution 3D hydrodynamical
simulations of compressible, gravitationally unstable media performed
using the adaptive-mesh code Flash (Fryxell et al. 2000). We study both
turbulence generated by the nonlinear phase of the Jeans instability and
the gravitational stability of a stirred, turbulent medium. We discuss
the evolution of these cases in terms of the structure functions of
the medium, comparing our results to recent calculations by Klessen et
al. (2000). This work is supported by the U. S. Department of Energy
under Contract No. B341495 to the Center for Astrophysical Thermonuclear
Flashes at the University of Chicago.
Title: Thermonuclear Quenching in Flame-Vortex Interactions
Authors: Zingale, M.; Niemeyer, J. C.; Timmes, F. X.; Dursi, L. J.;
Calder, A. C.; Fryxell, B.; Olson, K.; Ricker, P.; Rosner, R.; Truran,
J. W.; Tufo, H.; MacNeice, P.
Bibcode: 2000AAS...197.8104Z
Altcode: 2000BAAS...32.1537Z
A Type Ia supernova begins as a flame, deep in the interior of a white
dwarf. At some point, the burning may undergo a deflagration-detonation
transition (DDT). Some mechanisms for this transition require a
preconditioned region in the star. As the flame propagates down the
temperature gradient, the speed increases, and the transition to
a detonation may occur (see Khokhlov et al. 1997; Niemeyer &
Woosley 1997). For this to happen, the region must be free of any
temperature fluctuations -- any burning must be quenched. We show
direct numerical simulations of flame-vortex interactions in order to
understand quenching of thermonuclear flames. The key question is --
can a thermonuclear flame be quenched? If not, the DDT mechanisms that
demand the finely tuned preconditioned region are unlikely to work. In
these simulations, we pass a steady-state laminar flame through a vortex
pair. The vortex pair represents the most severe strain the flame front
will encounter inside the white dwarf. We perform a parameter study,
varying the speed and size of the vortex pair, in order to understand
the quenching process. These simulations were carried out with the FLASH
Code. This work is supported by the Department of Energy under Grant
No. B341495 to the Center for Astrophysical Thermonuclear Flashes at
the University of Chicago. These calculations were performed on the
Nirvana Cluster at Los Alamos National Laboratory
Title: Pre-nova Mixing at the Surface of White Dwarfs
Authors: Rosner, R.; Young, Y. N.; Alexakis, A.; Dursi, L. J.; Truran,
J.; Calder, A. C.; Fryxell, B.; Olson, K.; Ricker, P. M.; Timmes,
F. X.; Zingale, M.; Tufo, H. M.; MacNeice, P.
Bibcode: 2000AAS...197.8106R
Altcode: 2000BAAS...32.1538R
We report on studies of shear-driven mixing at the interface between
a hydrogen-helium envelope and the carbon-oxygen surface of a pre-nova
outburst white dwarf. Linear theory shows distinct regimes of unstable
gravity surface waves and Kelvin-Helmholtz modes, which we follow
into the weakly nonlinear regime by analytical techniques; we then
follow the fully nonlinear evolution to the point of wave breaking,
using the Chicago Flash Code. We also report on estimates of the
mixing efficiency resulting from the combination of weakly driven
convection and wave breaking; and discuss their implications for nova
outbursts. This work was supported by the DOE ASCI/Alliances program
at the University of Chicago, under grant No. B341495.
Title: Searching for Global oscillations of Jupiter
Authors: Murphy, N.; Smith, E. J.; Rogers, W.; Gillam, S.; Rosner,
R.; Baliunas, S.
Bibcode: 2000DPS....32.6516M
Altcode: 2000BAAS...32.1642M
The detection of global oscillations of Jupiter would lead to
significant advances in our understanding of giant planet internal
structure, analogous to the enormous increase in knowledge of the
sun's interior facilitated by helioseismology. In particular, the
frequencies of p-mode oscillations will be strongly affected by the
presence of density discontinuities and the planet's core size and
structure. While it is clear from previous observations that such
oscillations probably only exist with very small amplitudes, current
instrumentation may still be able to detect them. We will describe a
proposed experiment to detect (or place a firm upper amplitude limit on)
global p-mode oscillations of Jupiter, using a magneto-optical filter
on the Mt Wilson 100" telescope. We will describe the operation of the
instrument, present preliminary data and describe models of instrument
response which show that with 7 nights of data we can expect to detect
signals with amplitudes less than 20 cm/s.
Title: Mixing in Rayleigh-Taylor Instabilities
Authors: Calder, A. C.; Fryxell, B.; Rosner, R.; Dursi, L. J.;
Olson, K.; Ricker, P. M.; Timmes, F. X.; Zingale, M.; Tufo, H. M.;
MacNeice, P.
Bibcode: 2000AAS...197.8102C
Altcode: 2000BAAS...32.1537C
Fluid instabilities and subsequent mixing can play a fundamental role
in many astrophysical processes, including the shock of a core-collapse
supernova propagating through the outer layers of a massive star and the
propagation of a burning front through a white dwarf in a thermonuclear
runaway supernova. We present direct numerical simulations of mixing
at Rayleigh-Taylor unstable interfaces performed with the Flash code,
developed at the ASCI/Alliances Center for Astrophysical Thermonuclear
Flashes at the University of Chicago. We present results of both single-
and multi-mode studies in 2- and 3-dimensions. Our results indicate
that 3-d perturbations grow significantly faster than 2-d perturbations
and that grid resolution can have a significant effect on instability
growth rates. We also find that unphysical diffusive mixing occurs
at the fluid interface, particularly in poorly resolved simulations,
making it difficult to maintain the purity of our fluids. This work
was supported by the U.S Department of Energy under grant No. B341495.
Title: The Structure of Carbon Detonation in Type Ia Supernovae
Authors: Fryxell, B.; Timmes, F. X.; Zingale, M.; Dursi, L. J.; Ricker,
P.; Olson, K.; Calder, A. C.; Tufo, H.; Truran, J. W.; Rosner, R.;
MacNeice, P.
Bibcode: 2000AAS...197.8103F
Altcode: 2000BAAS...32.1537F
Type Ia Supernova explosions are thought to begin as deflagrations
in the center of accreting white dwarfs. Observations suggest that
at some point, the burning undergoes a transition from a deflagration
to a detonation front. We describe high-resolution three-dimensional
simulations of the structure of such a detonation. The pre-detonation
material is assumed to be pure C12 at a density of
107 g cm-3. A cellular structure develops behind
the front, leaving pockets of unburned fuel. The cellular instability is
unlikely to have any observational consequences at this density, since
the cell size is only a few centimeters. However, as the detonation
approaches the surface, the cell size will become comparable to the
radius of the star, leaving a nonspherical distribution of reaction
products and modifying the spectral signature of the explosion. The
calculations were performed on 1000 processors of ASCI Blue Pacific
at Lawrence Livermore National Laboratory using the Flash Code
developed at the Center for Astrophysical Thermonuclear Flashes at the
University of Chicago. They represent by far the largest simulations
ever carried out on the detailed structure of burning fronts in Type
Ia supernovae. This work was supported in part by the Department of
Energy Grant No. B341495 to the Center for Astrophysical Thermonuclear
Flashes at the University of Chicago under the ASCI Strategic Alliances
Program and by NASA/Goddard Space Flight Center.
Title: MHD Stability of Polar Caps of Accreting Neutron Stars
Authors: Litwin, C.; Brown, E. F.; Rosner, R.
Bibcode: 2000AAS...197.8308L
Altcode: 2000BAAS...32.1544L
We assess the stability of magnetic Rayleigh-Taylor type modes driven by
the overpressure of magnetically confined accreted matter on the surface
of a neutron star. We employ the magnetohydrodynamic (MHD) energy
principle to analyze the stability of short-wavelength (ballooning)
modes subject to line-tying in the neutron star crust. Research
supported by ASCI/Alliances Center for Astrophysical Thermonuclear
Flashes at the University of Chicago.
Title: FLASH: An Adaptive Mesh Hydrodynamics Code for Modeling
Astrophysical Thermonuclear Flashes
Authors: Fryxell, B.; Olson, K.; Ricker, P.; Timmes, F. X.; Zingale,
M.; Lamb, D. Q.; MacNeice, P.; Rosner, R.; Truran, J. W.; Tufo, H.
Bibcode: 2000ApJS..131..273F
Altcode:
We report on the completion of the first version of a new-generation
simulation code, FLASH. The FLASH code solves the fully compressible,
reactive hydrodynamic equations and allows for the use of adaptive
mesh refinement. It also contains state-of-the-art modules for the
equations of state and thermonuclear reaction networks. The FLASH code
was developed to study the problems of nuclear flashes on the surfaces
of neutron stars and white dwarfs, as well as in the interior of white
dwarfs. We expect, however, that the FLASH code will be useful for
solving a wide variety of other problems. This first version of the code
has been subjected to a large variety of test cases and is currently
being used for production simulations of X-ray bursts, Rayleigh-Taylor
and Richtmyer-Meshkov instabilities, and thermonuclear flame fronts. The
FLASH code is portable and already runs on a wide variety of massively
parallel machines, including some of the largest machines now extant.
Title: Dynamos: Solar and Stellar
Authors: Rosner, R.
Bibcode: 2000eaa..bookE2220R
Altcode:
The direct observation of magnetic fields on the surface of the Sun
(see SOLAR MAGNETIC FIELD), as well as on the surface of other stars
(see MAGNETIC FIELDS IN STARS), directly raises the question of the
origins of these magnetic fields. The simplest hypothesis is that these
magnetic fields are simply the remnants of magnetic fields carried in
by the accreting gas during the formation phase of s...
Title: On the Cellular Structure of Carbon Detonations
Authors: Timmes, F. X.; Zingale, M.; Olson, K.; Fryxell, B.; Ricker,
P.; Calder, A. C.; Dursi, L. J.; Tufo, H.; MacNeice, P.; Truran,
J. W.; Rosner, R.
Bibcode: 2000ApJ...543..938T
Altcode:
We present the results of a numerical study on two-dimensional
carbon detonations. For an upstream density of 107 g
cm-3 the length-to-width ratio of the detonation cells is
about 1.6 and is not strongly dependent on the spatial resolution of
the simulation. However, the curvature of the weak incident shocks,
strength of the triple points and transverse waves, and sizes of
the underreacted and overreacted regions all depend strongly on the
spatial resolution of the calculation. These resolution studies help
define the minimum resolution required by multidimensional Type Ia
supernovae models where the cellular structure of a detonation front
is a key feature of the model.
Title: Astrophysically Relevant Instabilities at a Decelerating
Interface.
Authors: Calder, A. C.; Fryxell, B.; Rosner, R.; Kane, J.; Remington,
B. A.; Robey, H.; Keiter, P.; Drake, R. P.; Knauer, J.; Dursi,
L. J.; Olson, K.; Ricker, P. M.; Timmes, F. X.; Zingale, M.; Tufo,
H.; MacNeice, P.
Bibcode: 2000APS..DPPBP1078C
Altcode:
Hydrodynamic instabilities play an important role in many astrophysical
phenomena, and modern intense lasers offer the chance to experimentally
investigate these instabilities in similar environments in a
laboratory. In this poster, we report on experimental and theoretical
progress in ongoing research in laser astrophysics. We presents
results of simulations of experiments performed using the University
of Rochester's Omega laser facility. These experiments involve
shock propagation through multi-layer targets, and are designed to
replicate the complex hydrodynamic instabilities thought to arise
during supernovae explosions. The simulations were performed with
the FLASH code, developed by the ASCI/ASAP Center for Astrophysical
Thermonuclear Flashes at the University of Chicago, and we are
planning on a study making use of a realistic equation of state. We
present results of an experimental study of 2-D vs. 3-D perturbation
growth rates also performed at the Omega laser facility. Data from
experiments with nominally identical two-layer targets, but 2-D
or 3-D perturbations, show clear differences between the evolution
of 2-D vs. 3-D perturbations. We also present simulations showing
qualitatively similar features for comparison. This work is supported
by the US Department of Energy.
Title: The Beginnings of Stellar X-Ray Astronomy
Authors: Rosner, R.
Bibcode: 2000exun.conf..243R
Altcode:
I review the beginnings of the field of stellar X-ray astronomy,
concentrating on the period immediately preceeding, and immediately
following, the launch of the Einstein Observatory. The wealth of data
was such that, within the first two years following launch, major
discoveries were made by scientists from both the Einstein Observatory
PI groups and Einstein Observatory Guest Observers which established
stellar X-ray astronomy as a new astronomical discipline: Discovery of
early and late-type stars, as well as young protostars, as soft X-ray
sources; discovery of the "dividing line" separating X-ray emitting
and X-ray quiet giant and supergiant stars; and establishment of the
"solar-stellar connection" as a paradigm for understanding X-ray
emission from late-type stars.
Title: On the Generation of Flux-Tube Waves in Stellar Convection
Zones. III. Longitudinal Tube Wave-Energy Spectra and Fluxes for
Late-Type Stars
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.
Bibcode: 2000ApJ...541..410M
Altcode:
The wave-energy spectra and fluxes for longitudinal tube waves
generated in stellar convection zones are computed by using analytical
methods developed in the two previous papers of this series. The main
physical process responsible for the generation of these waves is the
interaction between a thin and vertically oriented magnetic flux tube
and the external turbulent convection. The spatial component of the
turbulent convection is represented by an extended Kolmogorov turbulent
energy spectrum, and its temporal component by a modified Gaussian
frequency factor. The calculations are performed for Population I
stars with effective temperatures ranging from Teff=2000 K
to 10,000 K, and with gravities logg=3-5. The obtained results can be
used to construct theoretical models of magnetic regions in stellar
chromospheres.
Title: Kelvin-Helmholtz instability in three dimensional radiative
jets
Authors: Micono, M.; Bodo, G.; Massaglia, S.; Rossi, P.; Ferrari,
A.; Rosner, R.
Bibcode: 2000A&A...360..795M
Altcode: 2000astro.ph..6212M
The analysis of the stability properties of astrophysical jets against
Kelvin-Helmholtz (or shear- layer) instabilities plays a basic role
in the understanding of the origin and physical characteristics of
these objects. Numerical simulations by Bodo et al. (1998) have shown
that the three-dimensional non-linear evolution of KH instabilities
in supersonic jets is substantially faster than in the two-dimensional
case, leading to a cascade of modes towards smaller scales and a very
effective mixing and momentum transfer to the ambient medium. On the
other hand, Rossi et al. (1997) and Micono et al. (1998) found, in
two dimensions, that radiative losses tend to reduce and delay mixing
effects and momentum transfer to the ambient medium. In this paper,
as a logical next step, we investigate the effects of radiative losses
on the stability of 3D supersonic jets, assuming that the internal jet
density is initially lower, equal and higher than the ambient medium,
respectively. We find that light and equal-density radiative jets evolve
in a qualitatively similar fashion with respect to the corresponding
adiabatic ones. Conversely, we note substantial differences in the
evolution of heavy jets: they remain more collimated and do not spread
out, while the momentum gained by the ambient medium stays within ~
5 jet radii.
Title: Evidence for topological nonequilibrium in magnetic
configurations
Authors: Vainshtein, S. I.; Mikić, Z.; Rosner, R.; Linker, J. A.
Bibcode: 2000PhRvE..62.1245V
Altcode: 2000astro.ph..3274V
We use direct numerical simulations to study the evolution, or
relaxation, of magnetic configurations to an equilibrium state. We
use the full single-fluid equations of motion for a magnetized,
nonresistive, but viscous fluid; and a Lagrangian approach is used
to obtain exact solutions for the magnetic field. As a result, the
topology of the magnetic field remains unchanged, which makes it
possible to study the case of topological nonequilibrium. We find two
cases for which such nonequilibrium appears, indicating that these
configurations may develop singular current sheets.
Title: Helium Detonations on Neutron Stars
Authors: Zingale, M.; Timmes, F. X.; Fryxell, B.; Lamb, D. Q.; Olson,
K.; Calder, A. C.; Dursi, L. J.; Ricker, P.; Rosner, R.; Truran,
J. W.; MacNeice, P.; Tufo, H.
Bibcode: 2000AAS...196.1703Z
Altcode: 2000BAAS...32..696Z
We present the results of a numerical study of helium detonations on
the surfaces of neutron stars. We analyze the evolution of a detonation
as it breaks through the envelope of the neutron star and propagates
across its surface. A series of surface waves propagate across the pool
of hot ash with a speed of 1.3 x 109 \ cm \ s-1,
matching the speed expected from shallow water wave theory. The entire
envelope bounces in the gravitational potential well of the neutron
star with a period of 50 μ s. The photosphere reaches a height of
15 km above the surface of the neutron star. The sensitivity of the
results to the spatial resolution and assumed initial conditions are
analyzed, and the relevance of this model to Type I X-ray bursts is
discussed. This work is supported by the Department of Energy under
Grant No. B341495 to the Center for Astrophysical Thermonuclear Flashes
at the University of Chicago.
Title: FLASH simulations of multi-layer targets
Authors: Calder, A. C.; Fryxell, B.; Rosner, R.; Kane, J.; Remington,
B. A.; Dursi, L. J.; Olson, K.; Ricker, P. M.; Timmes, F. X.; Zingale,
M.; MacNeice, P.; Tufo, H.
Bibcode: 2000AAS...196.2203C
Altcode: 2000BAAS...32..704C
Modern intense lasers offer the chance to experimentally probe
environments similar to those that exist in complex astrophysical
phenomena. In addition to providing observation of the behavior of
matter in such environments, well-controlled experiments provide
data with which to validate models and simulations. Simulations of
experiments performed using the University of Rochester's Omega laser
facility, which involve shock propagation through a multi-layer target,
are being used as a validation test for the FLASH code, developed
by the ASCI/ASAP Center for Thermonuclear Flashes at the University
of Chicago. These multi-layer target experiments are designed to
replicate the complex hydrodynamic instabilities thought to arise
during supernovae explosions. In addition to validating the FLASH code,
we seek to gain a better understanding of the turbulent mixing that
occurs as a result of instabilities driven by the propagation of the
shock through the layered target. We report on our progress to date on
these simulations. This work is supported by the Department of Energy
under grant B341495.
Title: Dynamo action and the period gap in cataclysmic variables
Authors: Lanza, A. F.; Rodonò, M.; Rosner, R.
Bibcode: 2000MNRAS.314..398L
Altcode:
The conjecture is presented that the gap in the distribution of the
orbital periods of cataclysmic variables is related to a particular kind
of hydromagnetic dynamo, called an interface dynamo, operating near the
base of the convective envelope of their secondary components. Such a
dynamo is characterized by the spatial separation of the regions where
differential rotation and the α effect operate. Unlike conventional
dynamos, the linear growth rate of an interface dynamo becomes negative
for highly supercritical dynamo numbers, leading to the disappearance of
the dynamo action. If such a result, from linear theory, is confirmed
by non-linear calculations, it may provide a physical basis for the
so-called disrupted magnetic braking hypothesis, invoked to explain
the existence of the period gap by several evolutionary models of
cataclysmic variables.
Title: Miscible Rayleigh-Taylor Instability: 2D versus 3D
Authors: Young, Y. -N.; Tufo, H.; Dubey, A.; Rosner, R.
Bibcode: 2000AAS...196.2206Y
Altcode: 2000BAAS...32..704Y
We investigate the miscible Rayleigh-Taylor (RT) instability in both 2
and 3 dimensions using direct numerical simulations, where the working
fluid is assumed incompressible under the Boussinesq approximation. We
first consider the case of randomly perturbed interfaces. With a
variety of diagnostics, we develop a physical picture for the detailed
temporal development of the mixed layer: We identify three distinct
evolutionary phases in the development of the mixed layer, which can be
related to detailed variations in the growth of the mixing zone. Our
analysis provides an explanation for the observed differences between
two and three-dimensional RT instability; the analysis also leads us
to concentrate on the RT models which (1) work equally well for both
laminar and turbulent flows, and (2) do not depend on turbulent scaling
within the mixing layer between fluids. These candidate RT models are
based on point sources within bubbles (or plumes) and interaction with
each other (or the background flow). With this motivation, we examine
the evolution of single plumes, and relate our numerical results
(of single plumes) to a simple analytical model for plume evolution.
Title: The Cellular Structure of Carbon Detonations
Authors: Fryxell, B.; Timmes, F. X.; Zingale, M.; Dursi, L. J.; Ricker,
P.; Olson, K.; Calder, A. C.; Tufo, H.; MacNeice, P.; Truran, J. W.;
Rosner, R.
Bibcode: 2000AAS...196.3902F
Altcode: 2000BAAS...32R.735F
We compare two and three-dimensional simulations of the cellular
structure of carbon detonations. The initial density of the carbon is
taken to be 107 g cm-3. This value has been
suggested as the density at which a deflagration to detonation
transition may occur in Type Ia supernovae. An initial planar
detonation front becomes unstable and develops a complex structure
due to the generation of transverse waves. Differences in the amount
of asymmetry between the 2D and 3D cases, as well as the relative
sizes of individual cells will be discussed. This work was supported
in part by the Department of Energy Grant No. B341495 to the Center
for Astrophysical Thermonuclear Flashes at the University of Chicago
under the ASCI Strategic Alliances Program.
Title: Flash Code: Studying Astrophysical Thermonuclear Flashes
Authors: Rosner, R.; Calder, A. C.; Dursi, L. J.; Fryxell, B.; Lamb,
D. Q.; Niemeyer, J. C.; Olson, K.; Ricker, P.; Timmes, F. X.; Truran,
J. W.; Tufo, H.; Young, Y.; Zingale, M.; Lusk, E.; Stevens, R.
Bibcode: 2000CSE.....2...33R
Altcode:
The Center for Astrophysical Thermonuclear Flashes is constructing
a new generation of codes designed to study runaway thermonuclear
burning on the surface or in the interior of evolved compact stars.
Title: Magnetic fields of stars: using stars as tools for
understanding the origins of cosmic magnetic fields
Authors: Rosner, Robert
Bibcode: 2000RSPTA.358..689R
Altcode:
I survey the status of research on the detection and quantitative
measurement of stellar magnetic fields, and discuss theoretical
ideas which try to account for the origins of these magnetic fields,
consistent with present observations.
Title: High-Performance Reactive Fluid Flow Simulations Using Adaptive
Mesh Refinement on Thousands of Processors
Authors: Calder, A. C.; Curtis, B. C.; Dursi, L. J.; Fryxell, B.;
Henry, G.; MacNeice, P.; Olson, K.; Ricker, P.; Rosner, R.; Timmes,
F. X.; Tufo, H. M.; Truran, J. W.; Zingale, M.
Bibcode: 2000sc00.conf.....C
Altcode:
We present simulations and performance results of nuclear burning
fronts in supernovae on the largest domain and at the finest spatial
resolution studied to date. These simulations were performed on the
Intel ASCI-Red machine at Sandia National Laboratories using FLASH, a
code developed at the Center for Astrophysical Thermonuclear Flashes at
the University of Chicago. FLASH is a modular, adaptive mesh, parallel
simulation code capable of handling compressible, reactive fluid flows
in astrophysical environments. FLASH is written primarily in Fortran
90, uses the Message-Passing Interface library for inter-processor
communication and portability, and employs the PARAMESH package to
manage a block-structured adaptive mesh that places blocks only where
the resolution is required and tracks rapidly changing flow features,
such as detonation fronts, with ease. We describe the key algorithms and
their implementation as well as the optimizations required to achieve
sustained performance of 238 GLOPS on 6420 processors of ASCI-Red in
64-bit arithmetic.
Title: Helium Detonations on Neutron Stars
Authors: Fryxell, B.; Zingale, M.; Timmes, F. X.; Lamb, D. Q.; Olson,
K.; Calder, A. C.; Dursi, L. J.; Ricker, P.; Rosner, R.
Bibcode: 2000nuas.conf...38F
Altcode:
No abstract at ADS
Title: The Sun as an X-Ray Star. II. Using theYohkoh/Soft X-Ray
Telescope-derived Solar Emission Measure versus Temperature to
Interpret Stellar X-Ray Observations
Authors: Peres, G.; Orlando, S.; Reale, F.; Rosner, R.; Hudson, H.
Bibcode: 2000ApJ...528..537P
Altcode:
This paper is the second of a project dedicated to using solar
Yohkoh/SXT data as a guide and a template to interpret data on
stellar coronae. In the light of the large differences in scope
and approach between solar and stellar studies, we have developed a
method to translate Yohkoh/SXT data of the whole solar corona into
stellar-like data, i.e., to put them in the same format and context
as the stellar ones. First from the Yohkoh/SXT images we derive
the whole-Sun X-ray emission measure versus temperature [EM(T)],
in the range 105.5-108 K, during the specific
observation. Then, we synthesize the solar X-ray spectrum; finally,
we fold the spectrum through the instrumental response of nonsolar
X-ray observatories, for instance, ROSAT/PSPC and ASCA/SIS. Finally,
we analyze such solar coronal data in the same band and with the
same methods used for stellar observations, allowing a direct
and homogeneous comparison with them. In this paper we present in
detail our method and, as an example of results, we show and discuss
EM(T) and stellar-like spectra for three phases of the solar cycle:
maximum, intermediate phase, and minimum. The total amount and the
distribution of the emission measure change dramatically during the
cycle, in particular at temperatures above 106 K. We also
show the EM(T) of the whole solar corona during a large flare. The
ROSAT/PSPC- and ASCA/SIS-like X-ray spectra of the Sun as a star
that we obtain are discussed in the context of stellar coronal
physics. The Sun's coronal total luminosity in the ROSAT/PSPC band
ranges from ~2.7×1026 ergs s-1 (at minimum)
to ~4.7×1027 ergs s-1 (at maximum). We discuss
future developments and possible applications of our method.
Title: Structure and dynamics of astrophysical jets
Authors: Massaglia, S.; Ferrari, A.; Micono, M.; Bodo, G.; Rossi,
P.; Rosner, R.; Malagoli, A.
Bibcode: 2000MmSAI..71..945M
Altcode:
No abstract at ADS
Title: 2-dimensional Helium Detonations on the Surface of Neutron
Stars
Authors: Zingale, M.; Timmes, F. X.; Fryxell, B.; Lamb, D. Q.; Olson,
K.; Ricker, P.; Calder, A. C.; Dursi, L. J.; Rosner, R.; Truran, J. W.
Bibcode: 2000arxt.confE..67Z
Altcode:
We present two-dimensional hydrodynamic simulations of helium
detonations on the surfaces of neutron stars performed with the FLASH
Code -- a multidimensional, adaptive hydrodynamics code developed at
the Center for Astrophysical Thermonuclear Flashes at the University
of Chicago. These calculations show the evolution of the detonation as
it breaks through the atmosphere of the neutron star and propagates
across the surface. The calculation shows a series of surface waves
propagating behind the detonation, and the bouncing of the atmosphere
as the detonation evolves. The sensitivity of the results to spatial
resolution and initial conditions are explored. The event is followed
as the detonation travels 2 km across the surface of the neutron
star. The detonation velocity implies a timescale of a few milliseconds
to propagate around the star. The relevance of such a model to observed
X-ray bursts is discussed.
Title: X-ray spectra of the Sun as a star: how different coronal
regions contribute to the observed X-ray spectrum
Authors: Orlando, S.; Peres, G.; Reale, F.; Rosner, R.; Hudson, H.
Bibcode: 2000ASPC..198..479O
Altcode: 2000scac.conf..479O
No abstract at ADS
Title: Accretion streams in magnetic binaries
Authors: Litwin, C.; Rosner, R.; Lamb, D. Q.
Bibcode: 1999PPCF...41B.343L
Altcode: 1999PPCF...41..343L
We review the problem of plasma penetration of astrophysical
magnetospheres, focusing on close binary stellar systems in which the
Roche lobe overflow occurs. We point out that the accretion stream can
penetrate the magnetosphere, even if its ram pressure is smaller than
the magnetic pressure. This can occur without any turbulent mixing
postulated in the past. The particular mechanism of cross-field
penetration is an E × B drift caused by an electric field arising
from polarization currents in the accretion stream. We determine the
criteria for deep magnetosphere penetration; in particular, we find
that deep penetration results for narrow streams (such as suggested
by the previous theoretical analyses), and for reasonably low ambient
plasma densities and temperatures.
Title: FLASH: A Multidimensional Hydrodynamics Code for Modeling
Astrophysical Thermonuclear Flashes
Authors: Ricker, P. M.; Fryxell, B.; Olson, K.; Timmes, F. X.; Zingale,
M.; Lamb, D. Q.; MacNeice, P.; Rosner, R.; Tufo, H.
Bibcode: 1999AAS...195.4205R
Altcode: 1999BAAS...31.1431R
We report on the completion of the first version of a new-generation
simulation code, FLASH. The FLASH code solves the fully-compressible,
reactive hydrodynamic equations, allowing for the use of adaptive mesh
refinement. It also contains state-of-the-art modules for the equation
of state and thermonuclear reaction networks. FLASH was developed to
study the problems of thermonuclear flashes on the surfaces of neutron
stars and white dwarfs and in the interiors of white dwarfs. We expect,
however, that FLASH will be useful for solving other astrophysical
problems. The first version of this code has been subjected to a large
suite of test cases, and it is currently being used for production
simulations of X-ray bursts, the Rayleigh-Taylor and Richtmyer-Meshkov
instabilities, and thermonuclear flame fronts. FLASH is modular,
extensible, and portable, and it already runs on a wide variety of
massively parallel machines, including some of the largest now in
existence. This work is supported by the U.S. Department of Energy
under Grant No. B341495 to the Center for Astrophysical Thermonuclear
Flashes at the University of Chicago.
Title: On accretion flow penetration of magnetospheres
Authors: Litwin, C.; Rosner, R.; Lamb, D. Q.
Bibcode: 1999MNRAS.310..324L
Altcode:
We address the problem of plasma penetration of astrophysical
magnetospheres, an important issue in a wide variety of contexts,
ranging from accretion in cataclysmic variables to flows in
protostellar systems. We point out that under well-defined conditions,
penetration can occur without any turbulent mixing (driven, for
example, by Rayleigh-Taylor or Kelvin-Helmholtz instabilities)
caused by charge polarization effects, if the inflowing plasma is
bounded in the direction transverse to both the flow velocity and the
magnetic field. Depolarization effects limit the penetration depth,
which nevertheless can, under specific circumstances, be comparable
to the size of the magnetosphere. We discuss the effect of ambient
medium on plasma propagation across the stellar magnetic field and
determine the criteria for deep magnetosphere penetration. We show
that, under conditions appropriate to magnetized white dwarfs in AM
Her type cataclysmic variables, charge polarization effects can lead
to deep penetration of the magnetosphere.
Title: Direct Simulations of Thermonuclear Flames with the FLASH Code
Authors: Zingale, M.; Timmes, F. X.; Calder, A.; Dursi, J.; Fryxell,
B.; Lamb, D.; Olson, K.; Ricker, P.; Rosner, R.; Truran, J.; Tufo, H.
Bibcode: 1999AAS...195.4201Z
Altcode: 1999BAAS...31.1430Z
Direct numerical simulations of thermonuclear carbon flames in white
dwarf interiors are presented. These calculations are performed
with the FLASH code, and demonstrate the effectiveness of adaptive
mesh refinement for capturing flame fronts. One-dimensional laminar
flame velocities are verified, and simulations of two-dimensional
flame fronts are presented. This work is supported by the Department
of Energy under Grant No. B341495 to the Center for Astrophysical
Thermonuclear Flashes at the University of Chicago.
Title: Accretion streams in magnetic binaries.
Authors: Litwin, C.; Rosner, R.; Lamb, D. Q.
Bibcode: 1999PPCF...41..343L
Altcode:
The authors review the problem of plasma penetration of astrophysical
magnetospheres, focusing on close binary stellar systems in which
the Roche lobe overflow occurs. They point out that the accretion
stream can penetrate the magnetosphere, even if its ram pressure
is smaller than the magnetic pressure. This can occur without any
turbulent mixing postulated in the past. The particular mechanism
of cross-field penetration is an E×B drift caused by an electric
field arising from polarization currents in the accretion stream. The
authors determine the criteria for deep magnetosphere penetration;
in particular, they find that deep penetration results for narrow
streams (such as suggested by the previous theoretical analyses),
and for reasonably low ambient plasma densities and temperatures.
Title: Long-lived Coronal Loop Profiles from TRACE
Authors: Lenz, Dawn D.; DeLuca, Edward E.; Golub, Leon; Rosner, Robert;
Bookbinder, Jay A.; Litwin, Christof; Reale, Fabio; Peres, Giovanni
Bibcode: 1999SoPh..190..131L
Altcode:
An initial study of long-lived loops observed with TRACE (Lenz et al.,
1999) shows that they have no significant temperature stratification
and that they are denser than the classic loop model predicts. Models
that agree better with the observations include a loop consisting of a
bundle of filaments at different temperatures and a loop with momentum
input by MHD waves. Some implications for coronal heating models and
mechanisms are discussed.
Title: Compressed Reactive Turbulence and Supernovae Ia Recollapse
using the FLASH code
Authors: Dursi, J.; Niemeyer, J.; Calder, A.; Fryxell, B.; Lamb, D.;
Olson, K.; Ricker, P.; Rosner, R.; Timmes, F.; Tufo, H.; Zingale, M.
Bibcode: 1999AAS...195.4202D
Altcode: 1999BAAS...31.1430D
The collapse of turbulent fluid, apart from being interesting for
its own sake, is also of interest to the supernova problem; a failed
ignition can cause a turbulent re-collapse, which might lead to a
subsequent reignition under more favourable circumstances. We use the
FLASH code, developed at the Center on Astrophysical Thermonuclear
Flashes, to run small-scale DNS of the evolution of a compressible,
combustible turbulent fluid under the effect of a forced radial
homogeneous compression. We follow the evolution of density and
temperature fluctuations over the compression history. This work
is supported by the Department of Energy under Grant No. B341495 to
the Center for Astrophysical Thermonuclear Flashes at the University
of Chicago.
Title: Helium Burning on Neutron Stars: 2-dimensional Results
Authors: Fryxell, B.; Zingale, M.; Timmes, F. X.; Olson, K.; Lamb,
D.; Calder, A.; Dursi, J.; Ricker, P.; Rosner, R.; Tufo, H.
Bibcode: 1999AAS...195.4204F
Altcode: 1999BAAS...31.1431F
We present a two dimensional, cylindrically symmetric simulation of
an X-ray burst. The explosion was followed along a 2 km stretch of a
neutron star atmosphere for a total time of 166 μ s. The calculation
was performed using the FLASH code, a parallel, multidimensional,
adaptive mesh refinement (AMR) hydrodynamics code developed by the
Center for Astrophysical Thermonuclear Flashes, an ASCI Alliance
Center. This work is supported by the Department of Energy under Grant
No. B341495.
Title: A mechanism of particle acceleration in astrophysical
magnetospheres
Authors: Litwin, Christof; Rosner, Robert
Bibcode: 1999APS..DPP.FO108L
Altcode:
We discuss particle acceleration by electrostatic polarization
fields arising in plasmoids injected into the magnetic field. In
magnetospheres of compact stellar objects these fields can give rise to
ultra-relativistic voltages in typical accreting plasma streams as well
as in impacting asteroid-size plasma ``blobs''. We focus on limitations
on accelerated particle energies due to curvature and synchrotron
radiation losses and analyze particle motion with radiation reaction
taken into account. Finally we discuss implications of this mechanism
for highest-energy cosmic ray generation in neutron star magnetospheres.
Title: Temperature and Emission-Measure Profiles along Long-lived
Solar Coronal Loops Observed with the Transition Region and Coronal
Explorer
Authors: Lenz, Dawn D.; DeLuca, Edward E.; Golub, Leon; Rosner,
Robert; Bookbinder, Jay A.
Bibcode: 1999ApJ...517L.155L
Altcode: 1999astro.ph..3491L
We report an initial study of temperature and emission-measure
distributions along four steady loops observed with the Transition
Region and Coronal Explorer at the limb of the Sun. The temperature
diagnostic is the filter ratio of the extreme-ultraviolet 171 and 195
Å passbands. The emission-measure diagnostic is the count rate in the
171 Å passband. We find essentially no temperature variation along
the loops. We compare the observed loop structure with theoretical
isothermal and nonisothermal static loop structure.
Title: On stream accretion onto magnetized compact objects
Authors: Litwin, C.; Rosner, R.; Lamb, D. Q.
Bibcode: 1999AAS...194.2909L
Altcode: 1999BAAS...31..867L
The problem of plasma penetration of astrophysical magnetospheres is
an important issue in a wide variety of contexts. We point out that
under well-defined conditions, deep penetration can occur without any
turbulent mixing (driven, e.g., by Rayleigh-Taylor or Kelvin-Helmholtz
instabilities) postulated in the past. Specifically, in binary stellar
systems with the Roche lobe overflow, the accretion stream can penetrate
even if its ram pressure is smaller than the magnetic pressure. The
particular mechanism responsible for cross-field propagation is an
E-cross-B drift caused by an electric field arising from polarization
currents in the accretion stream. Depolarization effects result in a
drag on the plasma flow and limit the penetration depth. Estimating the
drag force resulting from magnetic field-aligned currents, we determine
the criteria for deep magnetosphere penetration; in particular, we
find that deep penetration results for sufficiently narrow streams
(such as suggested by the analysis of Lubov & Shu 1975), and for
sufficiently low ambient plasma densities and temperatures. Research
supported by the U.S. Department of Energy.
Title: Front propagation in pre-mixed material: approaches to modeling
thermonuclear flames
Authors: Young, Y.; Niemeyer, J. C.; Rosner, R.
Bibcode: 1999AAS...194.8613Y
Altcode: 1999BAAS...31..978Y
The interaction of thermonuclear fusion flames with turbulent flows
is studied by means of incompressible DNS with a simplified flame
description. This interaction plays an important role in flame
propagation in Type Ia supernovae. The flame is treated as a single
diffusive scalar field with a nonlinear source term (the nuclear
reaction rate), and is characterized by the Prandtl number (Pr, the
ratio of kinematic viscosity to thermal diffusivity and Pr << 1 in
our cases), and laminar flame speed, S_L. We simulate the propagation of
such a flame through a stirred, turbulent velocity field, and study the
increase of flame propagation speed due to turbulent mixing. A previous
study (J.C. Niemeyer, W.K. Bushe, and G.R. Guetsch) shows that if S_L
>= u(') , where u(') is the rms turbulent velocity fluctuation,
the local flame propagation speed does not significantly deviate from
S_L even in the presence of velocity fluctuations on scales below the
laminar flow thickness. The ratio S_L/u(') in this study is limited
to values greater or closer to 1. In the present study, we perform
the same simulation for S_L/u(') << 1 and compare results to
the previous study.
Title: Deep ROSAT HRI observations of the Pleiades
Authors: Micela, G.; Sciortino, S.; Harnden, F. R., Jr.; Kashyap,
V.; Rosner, R.; Prosser, C. F.; Damiani, F.; Stauffer, J.; Caillault,
J. -P.
Bibcode: 1999A&A...341..751M
Altcode:
In a deep X-ray survey of the Pleiades open cluster, we use the ROSAT
High Resolution Imager to explore a region of the cluster formerly
surveyed with the PSPC. These new observations substantially improve
upon both the sensitivity and the spatial resolution for this region
of the Pleiades, allowing us to detect 18 cluster members not detected
before and 16 members not included in the catalogs used in previous
surveys. The high sensitivity of the present observations permits us
to obtain more stringent upper limits for 72 additional members and
also provides sufficient numbers of stars to enable us to explore
the dependence of L_x on stellar rotation for the slow rotators of
the Pleiades. Using the new high sensitivity X-ray observations and
the recent rotational measurements we discuss the activity-rotation
relationship in the Pleiades solar type stars. We also present new
photometric observations of optical counterparts of a number of X-ray
sources detected in previous surveys but not yet identified. Table~2
is available in electronic form at CDS via ftp 130.79.128.5
Title: The Solar-Stellar Connection in X-rays: How to Take Advantage
of the YOHKOH data
Authors: Peres, G.; Orlando, S.; Reale, F.; Rosner, R.; Hudson, H.
Bibcode: 1999ASPC..158..391P
Altcode: 1999ssa..conf..391P
No abstract at ADS
Title: Photometric Separation of Stellar Properties Using SDSS Filters
Authors: Lenz, Dawn D.; Newberg, Jo; Rosner, Robert; Richards, Gordon
T.; Stoughton, Chris
Bibcode: 1998ApJS..119..121L
Altcode:
Using synthetic photometry of Kurucz model spectra, we explore the
colors of stars as a function of temperature, metallicity, and surface
gravity with Sloan Digital Sky Survey (SDSS) filters, u'g'r'i'z'. The
synthetic colors show qualitative agreement with the few published
observations in these filters. We find that the locus of synthetic
stars is basically two-dimensional for 4500 < T < 8000 K, which
precludes simultaneous color separation of the three basic stellar
characteristics we consider. Colors including u' contain the most
information about normal stellar properties; measurements in this filter
are also important for selecting white dwarfs. We identify two different
subsets of the locus in which the loci separate by either metallicity or
surface gravity. For 0.5 < g' - r' < 0.8 (corresponding roughly
to G stars), the locus separates by metallicity; for photometric
error of a few percent, we estimate metallicity to within ~0.5 dex in
this range. In the range -0.15 < g' - r' < 0.00 (corresponding
roughly to A stars), the locus shows separation by surface gravity. In
both cases, we show that it is advantageous to use more than two colors
when determining stellar properties by color. Strategic observations in
SDSS filters are required to resolve the source of a ~5% discrepancy
between synthetic colors of Gunn-Stryker stars, Kurucz models, and
external determinations of the metallicities and surface gravities. The
synthetic star colors can be used to investigate the properties of any
normal star and to construct analytic expressions for the photometric
prediction of stellar properties in special cases.
Title: Coronal Scale-Height Enhancement by Magnetohydrodynamic Waves
Authors: Litwin, C.; Rosner, R.
Bibcode: 1998ApJ...506L.143L
Altcode:
We discuss the possibility that the transmission of Alfvén waves from
the photosphere into coronal loops can increase the density scale
height in these loops. The mechanism involved is the ponderomotive
force of transmitted waves, which opposes the force of gravity. We
propose that this effect may account for cool coronal loops observed
by the Solar and Heliospheric Observatory (SOHO). We also suggest that
it may be an explanation of the emission measure enhancement found at
the top of coronal X-ray loops observed by Yohkoh.
Title: VizieR Online Data Catalog: ROSAT HRI observations of the
Pleiades (Micela+ 1999)
Authors: Micela, G.; Sciortino, S.; Harnden, F. R., Jr.; Kashyap,
V.; Rosner, R.; Prosser, C. F.; Damiani, F.; Stauffer, J.; Caillault,
J. -P.
Bibcode: 1998yCat..33410751M
Altcode:
In a deep X-ray survey of the Pleiades open cluster, we use the
ROSAT High Resolution Imager to explore a region of the cluster
formerly surveyed with the PSPC. These new observations substantially
improve upon both the sensitivity and the spatial resolution for this
region of the Pleiades, allowing us to detect 18 cluster members not
detected before and 16 members not included in the catalogs used in
previous surveys. The high sensitivity of the present observations
permits us to obtain more stringent upper limits for 72 additional
members and also provides sufficient numbers of stars to enable us to
explore the dependence of Lx on stellar rotation for the
slow rotators of the Pleiades. Using the new high sensitivity X-ray
observations and the recent rotational measurements we discuss the
activity-rotation relationship in the Pleiades solar type stars. We
also present new photometric observations of optical counterparts of
a number of X-ray sources detected in previous surveys but not yet
identified. (2 data files).
Title: Density Structure in a Multicomponent Coronal Loop
Authors: Lenz, Dawn D.; Lou, Yu-Qing; Rosner, Robert
Bibcode: 1998ApJ...504.1020L
Altcode:
We investigate the variation of species densities and electric field
along a static model coronal loop consisting of electrons, protons,
and heavier ions in a gravitationally stratified stellar atmosphere in
an attempt to relate photospheric and coronal loop abundances. The loop
plasma is assumed to be confined along a strong magnetic field line, so
all forces transverse to the magnetic field are taken to be in balance
and the loop can be modeled as a one-dimensional structure. Differential
gravitational stratification of the ion species induces a polarization
electric field E along the loop. By invoking charge quasi-neutrality,
we devise an iteration scheme to compute numerical solutions for
the species densities and E to prescribed accuracy; we also derive
approximate analytic solutions. For confined coronal plasma loops
that are sufficiently long lived for gravitational settling to occur
(e.g., >~1 day), severe reduction in coronal ion densities would
be expected. Our self-consistent, multicomponent treatment predicts
higher loop densities than those predicted by a model that neglects the
effect of the heavy ions on the electric field; the density enhancement
is an increasing function of the distance along the loop and of the
ion charge and ranges from 4% for twice-ionized species to 33% for
14 times-ionized species at the top of an isothermal loop with T =
3 × 106 K and a radius of 109 cm.
Title: Relativistic space-charge-limited bipolar flow
Authors: Litwin, C.; Rosner, R.
Bibcode: 1998PhRvE..58.1163L
Altcode:
Relativistic generalization of the Child-Langmuir law is derived for
flows involving two oppositely charged species. A large enhancement
of the space-charge-limited current in the ultrarelativistic limit,
in which both species are accelerated to energies exceeding their
rest-mass energies, is demonstrated.
Title: VizieR Online Data Catalog: ROSAT Observations of the Pleiades
(Micela+ 1996)
Authors: Micela, G.; Sciortino, S.; Kashyap, V.; Harnden, F. R.;
Rosner, R.
Bibcode: 1998yCat..21020075M
Altcode:
The nucleus of the composite catalog used in this study is the catalog
compiled from the published literature for the Einstein investigations
of the Pleiades (Micela et al. 1990). This list has been extended
by the results of recent surveys to a completeness limit of visual
magnitude about 18. (3 data files).
Title: Orbital period modulation and magnetic cycles in close binaries
Authors: Lanza, A. F.; Rodono, M.; Rosner, R.
Bibcode: 1998MNRAS.296..893L
Altcode:
We discuss the observed orbital period modulations in close binaries,
and focus on the mechanism proposed by Applegate relating the changes of
the stellar internal rotation associated with a magnetic activity cycle
with the variation of the gravitational quadrupole moment of the active
component; the variation of this quadrupole moment in turn forces the
orbital motion of the binary stars to follow the activity level of the
active star. We generalize this approach by considering the details of
this interaction, and develop some illustrative examples in which the
problem can be easily solved in analytical form. Starting from such
results, we consider the interplay between rotation and magnetic field
generation in the framework of different types of dynamo models, which
have been proposed to explain solar and stellar activity. We show how
the observed orbital period modulation in active binaries may provide
new constraints for discriminating between such models. In particular,
we study the case of the prototype active binary RS Canum Venaticorum,
and suggest that torsional oscillations - driven by a stellar magnetic
dynamo - may account for the observed behaviour of this star. Further
possible applications of the relationship between magnetic activity and
orbital period modulation, related to the recent discovery of binary
systems containing a radio pulsar and a convecting upper main-sequence
or a late-type low-mass companion, are discussed.
Title: Alfvén Wave Transmission and Heating of Solar Coronal Loops
Authors: Litwin, C.; Rosner, R.
Bibcode: 1998ApJ...499..945L
Altcode:
We discuss the problem of wave transmission from the solar photosphere
into coronal loops. We conclude that wave energy can be efficiently
transmitted into loops with a sufficiently twisted magnetic field. The
value of the required twist is below but close to the threshold for
kink instability.
Title: Three-dimensional simulations of jets
Authors: Bodo, G.; Rossi, P.; Massaglia, S.; Ferrari, A.; Malagoli,
A.; Rosner, R.
Bibcode: 1998A&A...333.1117B
Altcode:
We present three-dimensional direct numerical simulations of
an hydrodynamical supersonic jet, comparing them to analogous
results obtained in two dimensions. The differences seen between
three-dimensional and two-dimensional jet evolution including
faster evolution, enhanced mixing and larger jet momentum depletion,
are interpreted in terms of specific physical differences between
these two cases. We have identified two main physical differences:
The first is the faster development of small-scale structures in
three dimensions, through either the growth of linearly unstable
non-axisymmetric (three-dimensional) modes or the non-linear cascade
of energy to smaller scales; the second is the different scaling of
volumes in the two cases. Based on our 2-D and 3-D results, we discuss
the limitations of using two-dimensional simulations to capture the
evolution of three-dimensional jets.
Title: Solar-Stellar Connection: Relevance of YOHKOH Data
Authors: Orlando, S.; Peres, G.; Reale, F.; Rosner, R.; Hudson, H.
Bibcode: 1998ASPC..154.1130O
Altcode: 1998csss...10.1130O
The similarity of late-type stars to the Sun is often assumed
when studying the physical conditions in their coronae. In order
to explore better such a ``solar-stellar'' connection we use the
Yohkoh/SXT X-ray images to generate the distribution of the emission
measure vs. temperature of the Sun and, from that, the expected
emission, as it would be observed by non-solar X-ray telescopes
such as ROSAT/PSPC and ASCA/SIS. We discuss the role of the various
solar structures in determining the total distribution of the emission
measure vs. temperature and in determining the stellar-like synthesized
X-ray spectra.
Title: X-ray Variability and Rotation in the Pleiades Cluster
Authors: Micela, G.; Sciortino, S.; Harnden, F. R., Jr.; Rosner, R.
Bibcode: 1998Ap&SS.261..105M
Altcode: 1999Ap&SS.261..105M
No abstract at ADS
Title: The Sun as an X-Ray Star: Overview of the Method
Authors: Peres, G.; Orlando, S.; Reale, F.; Rosner, R.; Hudson, H.
Bibcode: 1998ASSL..229...29P
Altcode: 1998opaf.conf...29P
No abstract at ADS
Title: Thermal Transport and Magnetic Fields in the Diffuse Gas of
Galaxy Clusters
Authors: Rosner, Robert
Bibcode: 1997APS..DPPiTI204R
Altcode:
I will discuss the problem of thermal transport and its effects on
cooling flows in the hot (T > 10 keV) plasmas in halos of clusters
of galaxies. This is an important problem in astrophysics believed
to be connected with the formation of most massive galaxies and the
distribution of mass in the Universe. I will address the question of
the magnetic field effects as well as of the possible origin of these
fields in galactic cluster halos. In particular, I will discuss the
role played by the magnetic fields in modifying thermal transport and
the possible dynamical effects of these fields on cooling flows.
Title: Ultra-relativistic Cosmic Ray Generation in Neutron Star
Magnetospheres
Authors: Litwin, C.; Rosner, R.
Bibcode: 1997APS..DPPgTP108L
Altcode:
We propose a mechanism for particle acceleration that can account for
the highest energy cosmic ray events observed to date, with energies
above 10^20 eV. The acceleration results from electric fields that
arise as a consequence of charge separation in plasmas streaming
across magnetic fields. As specific source of accreting plasma,
we suggest solid body impacts onto the neutron star magnetosphere,
similar to what had been earlier proposed to account for galactic gamma
ray bursts. We find that such solid object impacts at plausible rates
would give rise to the observed flux of highest energy particles. We
conclude that the proposed mechanism is at least a plausible source
of most energetic cosmic rays.
Title: Alfvénic fluctuations in fast and slow solar winds
Authors: Orlando, S.; Lou, Y. -Q.; Peres, G.; Rosner, R.
Bibcode: 1997JGR...10224139O
Altcode:
We compute properties of Alfvénic
fluctuations within a wide frequency range (i.e.,
10-6s-1<~f<~10-2s-1)
in both high- and low-speed magnetized radial solar winds. In
particular, the radial and frequency variations of the
normalized cross helicity σc, the Alfvén ratio
<script>R</script>A, and other relevant
quantities associated with Alfvénic fluctuations are presented and
analyzed. Because of the existence of the Alfvén critical radius
rA and a characteristic frequency fc for a given
magnetized solar wind profile, continuous reflection effects are clearly
manifest at frequencies lower than several times fc. Since
outward propagating fluctuations which many authors consider Alfvénic
fluctuations have been detected in the high-latitude solar wind
(which is fast and steady), such continuous reflection effects in
the low-frequency end of the fluctuation spectrum may be found in
the Ulysses data. In order to strengthen our case, comparisons are
carried out between our theoretical results and previous data analyses
of observations from the Helios 1 and 2 spacecraft in the radial
range of 0.29AU<~r<~1.0AU. Stronger evidence for continuous
reflection effects of low-frequency Alfvénic fluctuations is found
in the high-speed solar wind close to the Sun than in the low-speed
solar wind in general.
Title: The Sun as AN X-Ray Star: Overview of the Method
Authors: Peres, G.; Orlando, S.; Reale, F.; Rosner, R.; Hudson, H.
Bibcode: 1997SoPh..172..239P
Altcode: 1997ESPM....8..239P
We present a method to study the solar-stellar connection, i.e., the
close similarity of the physical phenomena occurring on the Sun and
on late-type active stars, by taking advantage of Yohkoh/SXT X-ray
images. From such images, we first generate distribution functions
of the whole disk differential emission measure, and then synthesize
from these spectra analogous to those collected by X-ray telescope
instruments aimed at stars other than the Sun. Here we illustrate the
application of this method to the ROSAT/PSPC and ASCA/SIS, and discuss
test cases as well as future applications.
Title: Alfven Wave Transmission and Coronal Loop Heating
Authors: Litwin, Christof; Rosner, Robert
Bibcode: 1997SPD....28.0703L
Altcode: 1997BAAS...29..911L
It has been argued (Parker 1994) that Alfven waves excited by
photospheric motions cannot heat coronal loops because their frequency
is much lower than the resonant frequency required for efficient
energy transmission (Hollweg 1984). This conclusion is based on
results of an analysis that was restricted to axisymmetric modes in an
untwisted magnetic field. We examine the question of nonaxisymmetric
mode transmission efficiency from photosphere into coronal loops. We
conclude that wave energy can be efficiently transmitted into loops
with a sufficiently twisted magnetic field. The value of the required
twist is below the threshold for kink instability. REFERENCES Hollweg,
J. V., 1984, ApJ, 277, 392 Parker, E. N. 1994, Spontaneous Current
Sheets in Magnetic Fields (New York: Oxford)
Title: The Sun as an X-ray Star: Overview of the Method
Authors: Peres, G.; Orlando, S.; Reale, F.; Rosner, R.; Hudson, H.
Bibcode: 1997IAUJD..19E..37P
Altcode:
We present a method to study the solar-stellar connection, i.e., the
close similarity of the physical phenomena occurring on the Sun and
on late-type active stars, by taking advantage of Yohkoh/SXT X-ray
images. From such images, we first generate distribution functions
of the whole disk differential emission measure, and then synthesize
from these spectra analogous to those collected by X-ray telescope
instruments aimed at stars other than the Sun. Here we illustrate
the application of this method to the ROSAT/PSPC and ASCA/SIS,
and discuss test cases as well as future applications. For a more
detailed discussion, please refer to a paper, by the same authors in
"OBSERVATIONAL PLASMA ASTROPHYSICS: FIVE YEARS OF YOHKOH AND BEYOND",
T. Watanabe, T. Kosugi, and A. C. Sterling, eds., Kluwer Academic
Publishers, the Proceedings of the Yohkoh 5th Anniversary Symposium,
held in November 1996, in Yoyogi, Tokyo, Japan.
Title: Self-consistent and Time-dependent Solar Wind Models
Authors: Ong, K. K.; Musielak, Z. E.; Rosner, R.; Suess, S. T.;
Sulkanen, M. E.
Bibcode: 1997ApJ...474L.143O
Altcode:
We describe the first results from a self-consistent study of Alfvén
waves for the time-dependent, single-fluid magnetohydrodynamic (MHD)
solar wind equations, using a modified version of the ZEUS MHD code. The
wind models we examine are radially symmetrical and magnetized; the
initial outflow is described by the standard Parker wind solution. Our
study focuses on the effects of Alfvén waves on the outflow and is
based on solving the full set of the ideal nonlinear MHD equations. In
contrast to previous studies, no assumptions regarding wave linearity,
wave damping, and wave-flow interaction are made; thus, the models
naturally account for the back-reaction of the wind on the waves,
as well as for the nonlinear interaction between different types of
MHD waves. Our results clearly demonstrate when momentum deposition
by Alfvén waves in the solar wind can be sufficient to explain the
origin of fast streams in solar coronal holes; we discuss the range
of wave amplitudes required to obtained such fast stream solutions.
Title: Imaging Stellar Surfaces via Matrix Lightcurve Inversion
Authors: Harmon, R. O.; Wild, W. J.; Rosner, R.; Drish, W. F., Jr.
Bibcode: 1996AAS...189.8603H
Altcode: 1996BAAS...28.1389H
Matrix lightcurve inversion (MLI) is a method for deducing the
appearance of a rapidly-rotating star's surface features (in particular
starspots) from its photometric lightcurve. It has the significant
advantage over "spot models" that no a priori assumptions are made
regarding the number of spots on the surface or their shapes. We present
here the results of an extensive set of simulations using synthetic
lightcurves generated from artificial surfaces. These have allowed
us to test the ability of MLI to reconstruct stellar surfaces under
conditions in which the true surface features are known. We demonstrate
that MLI represents a viable alternative to other techniques such as
spot models and Doppler imaging, and is of particular value when used
in conjunction with such techniques.
Title: Propagation of three-dimensional Alfvén waves in a stratified,
thermally conducting solar wind
Authors: Orlando, S.; Lou, Y. -Q.; Rosner, R.; Peres, G.
Bibcode: 1996JGR...10124443O
Altcode: 1996JGR...10124433O
We model the propagation of three-dimensional, adiabatic, linear Alfvén
waves in the solar atmosphere and wind, taking into account relevant
physical effects, including gravity stratification, thermal conduction,
radiative losses, and heating (via a phenomenological term). Our
magnetohydrodynamic solar wind model also accounts for the momentum
deposition by a spectrum of non-WKB Alfvén waves. The transmission
and reflection of such waves has been previously studied by a variety
of techniques, including calculations based on the computation of the
ratio between the wavelength and the scale length of the Alfvén speed
change and based on a globally-computed transmission coefficient. In
this paper we discuss both techniques and show how they are related. We
also discuss the physics underlying the reflection process and the
possible role wave reflection might play in the acceleration of the
solar wind and the winds from other stars.
Title: Accretion Flow Penetration of Compact Object Magnetospheres
Authors: Litwin, Christof; Rosner, Robert
Bibcode: 1996APS..DPP..7E03L
Altcode:
We discuss the problem of plasma penetration of magnetospheres, an
important issue in a wide variety of astrophysical contexts, ranging
from accretion in cataclysmic variables to flows in protostellar
systems. It has been argued that cross-field accretion on strongly
magnetized stars (e.g., white dwarfs and neutron stars) is impeded
when the kinetic energy density of the free-falling plasma becomes
comparable to or smaller than the magnetic field energy density;
consequently, the accretion should occur only in the close vicinity of
magnetic poles. Despite that, accretion is frequently observed in the
vicinity of the magnetic equator (assuming the stellar magnetic field
is dipolar). It is well known that high-permittivity, bounded plasma
can E×B drift across the magnetic field due to the polarization charge
build-up on the plasma stream boundary. We discuss this mechanism in
application to the problem of accretion on AM Her magnetic cataclysmic
variables. For typical parameters, we find that this mechanism can
lead to deep penetration of the accreting matter, if depolarizing
effects are weak. We consider various depolarization mechanisms and
their effects on plasma propagation.
Title: On the Stability of Magnetized Rotating Jets: The
Nonaxisymmetric Modes
Authors: Bodo, G.; Rosner, R.; Ferrari, A.; Knobloch, E.
Bibcode: 1996ApJ...470..797B
Altcode:
We discuss the linear response of a rotating, magnetized jet to shear
instabilities, extending our previous work to the nonaxisymmetric
case. Our focus is on describing both the solutions derived from the
dispersion relation and the physics underlying the changes in behavior
seen as compared with the axisymmetric case. The most interesting new
result is the strong stabilization of the ordinary mode for small
longitudinal wavenumbers and large Mach numbers; this behavior is
particularly pronounced for counterrotating (i.e., negative azimuthal
wavenumber) modes and leads to a predominance of linearly unstable
inertial or intermediate modes for rotating jets at small Mach numbers.
Title: The Origin of Filaments in the Interstellar Medium
Authors: Rosner, R.; Bodo, G.
Bibcode: 1996ApJ...470L..49R
Altcode:
Radio observations of the Milky Way indicate that "filaments,"
or enlongated plasma structures, seen in synchrotron emission from
accelerated electrons, are a common feature within our Galaxy. A number
of theories attempt to explain this spatial structuring; however, we
show that none can account quantitatively for the most striking aspect
of these observations, namely, the observed transverse dimensions of the
filaments. We then describe a new model, which provides both a plausible
source of the accelerated electrons and a physical process that
can explain the filamentation process. In particular, we show that a
particle acceleration process, akin to the acceleration of the anomalous
cosmic-ray component associated with the solar wind termination shock,
can provide an economical explanation both for the acceleration and,
in part, for the filamentation process; the filamentation process
may then be further assisted by radiative instabilities driven by
synchrotron emission. This model connects processes related to star
formation with "activity" observed in the interstellar medium.
Title: Generation of Density Perturbations by Primordial Magnetic
Fields
Authors: Kim, Eun-Jin; Olinto, Angela V.; Rosner, Robert
Bibcode: 1996ApJ...468...28K
Altcode: 1994astro.ph.12070K
We study the generation and evolution of density perturbations and
peculiar velocities due to primordial magnetic fields. We assume that
a random magnetic field was present before recombination and follow
the field's effect on the baryon fluid starting at recombination. We
find that magnetic fields generate growing density perturbations on
length scales larger than the magnetic Jeans length, λ_B_ and damped
oscillations for scales smaller than λ_B_. For small wavenumbers k
(large length scales), We find that the magnetic field-induced density
power spectrum generally scales as k^4^. We derive the magnetic Jeans
length explicitly by including the back-reaction of the velocity field
onto the magnetic field and by decomposing the magnetic field into a
force-free background field and perturbations about it. Depending on
the strength of the magnetic field and the ultraviolet cutoff of its
spectrum, structure can be generated on small or intermediate scales
early in the history of the universe. For a present rms magnetic field
of 10^-10^ G on intergalactic scales, we find that perturbations on
galactic scales could have gone nonlinear at z ~ 6. Finally, we discuss
how primordial magnetic fields affect scenarios of structure formation
with nonbaryonic dark matter.
Title: The Coronae of Low-Mass Dwarf Stars
Authors: Giampapa, M. S.; Rosner, R.; Kashyap, V.; Fleming, T. A.;
Schmitt, J. H. M. M.; Bookbinder, J. A.
Bibcode: 1996ApJ...463..707G
Altcode:
We report the results of our analysis of pointed X-ray observations
of nearby dMe and dM stars using the position sensitive proportional
counter (PSPC) on board the ROSA T satellite (Roentgensatellit). In the
cases of those M dwarf stars where PSPC pulse-height distributions of
sufficient quality for spectral fitting were obtained, we derive key
coronal plasma parameters in order to investigate stellar coronal
structure in more detail. In particular, we utilize temperatures
and emission measures inferred for one or more distinct components
as constraints for the development of semiempirical magnetic loop
models as representations of the coronae of low-mass stars. The
consistency of these static models as adequate descriptions of the
coronae of M dwarfs is then examined. We find that the coronae of
low-mass dwarfs consist of two distinct thermal components: a "soft"
component with T ∼ 2-4 x 106 K and a "hard" component
with T ∼ 107 K. We find that the pulse- height spectra
are systematically fitted better with "depleted" abundances compared to
solar; the high- temperature emission component on dMe stars appears to
contribute a systematically larger fraction of the total flux than the
corresponding component in dM stars; and the high-temperature emission
component on dMe stars is responsible for most of the observed variation
in the count rate. We have modeled the observed temperature
components with hydrostatic coronal loop models, and find that: the
low-temperature components can be modeled with loops of small size (l
≪ R*) and high pressure (Po ); and the high-temperature
components require solutions with either small filling factors (
0.1), large loops (1 > R*), and high base pressure (P0
≳ P0sun), or very small filling factors
(∼0.1), small loops (1 ≳ R*), and very high
pressure (P0 ≫ P0sun)). Based on
these observational and model results, we conclude that coronal emission
in dMe stars can be interpreted as arising from quiescent active regions
(a quiescent, low-temperature component) and compact flaring structures
(variable, high- temperature component). Our conclusion that the
coronal geometry for low-mass dwarf stars is dominated by a combination
of relatively compact, quiescent loop configurations and an unstable
flaring component has implications for both stellar dynamo theory and
for our understanding of stellar angular momentum evolution. With regard
to rotation in late-type stars, which has a direct bearing on dynamo
action, we know from observations that the lowest mass stars spin down
(via magnetic braking) more slowly than the more nearly solar-type
stars. The compact loops we find for the low-temperature component
suggests a natural explanation for the observed mass dependence of
angular momentum evolution in late-type, main-sequence stars.
Title: Fractal properties of the stretch-twist-fold magnetic dynamo
Authors: Vainshtein, Samuel I.; Sagdeev, Roald Z.; Rosner, Robert;
Kim, Eun-Jin
Bibcode: 1996PhRvE..53.4729V
Altcode:
This paper presents direct numerical simulations of the
stretch-twist-fold (STF) dynamo. For more than two decades, this dynamo
has been viewed as the prototype of the fast dynamo process; and because
of its apparently conceptual simplicity, it was generally not thought to
be necessary to investigate its quantitative properties in detail via
numerical simulations. Furthermore, it has been generally assumed that
the STF dynamo is not characterized by small-scale fluctuations, as is
usually the case for many other dynamo processes. Numerical simulations
show, however, that the STF dynamo process is accompanied by the
generation of small-scale fluctuations in the magnetic field. Therefore,
it cannot be taken as an a priori given that the STF dynamo is a
large-scale dynamo; however, our results suggest that the STF dynamo
does generate large-scale magnetic fields. In any eventuality,
the magnetic fields generated by the STF process do not behave as
was previously expected: As we show, these fields become chaotic,
first, in the sense that magnetic field lines acquire multifractal
properties; and, second, because the field itself becomes chaotic
[i.e., the (intermittency) fractal dimensions are no longer trivial].
Title: TRACE: the Transition Region and Coronal Explorer
Authors: Schrijver, C.; Title, A.; Acton, L.; Bruner, M.; Fischer,
R.; Golub, L.; Harrison, R.; Lemen, J.; Rosner, R.; Scharmer, G.;
Scherrer, P.; Strong, K.; Tarbell, T.; Wolfson, J.
Bibcode: 1996AAS...188.6704S
Altcode: 1996BAAS...28..934S
The TRACE mission is designed to obtain images of the solar
transition region and corona of unprecedented quality. With these
images we will be able to explore quantitatively the connections
between the photospheric magnetic field and the associated hot and
tenuous structures in the outer atmosphere. The TRACE telescope has
an aperture of 30 cm, and will observe an 8.5 x 8.5 arcminute field of
view with a resolution of one arcsecond. Finely tuned coatings on four
quadrants on the primary and secondary normal--incidence mirrors will
allow observations in narrow EUV and UV spectral bands. The passbands
are set to Fe IX, XII, and XV lines in the EUV band, while filters
allow observations in C IV, Ly alpha , and the UV continuum using
the UV mirror quadrant. The data thus cover temperatures from 10(4)
K up to 10(7) K. The Sun--synchronous orbit allows long intervals of
uninterrupted viewing. Observations at different wavelengths can be
made in rapid succession with an alignment of 0.1 arcsec. Coordinated
observing with TRACE, SoHO and YOHKOH will give us the first opportunity
to observe all temperature regimes in the solar atmosphere, including
magnetograms, simultaneously from space. TRACE is currently scheduled
to be launched in October 1997. More information can be found on the
web at ``http://pore1.space.lockheed.com/TRACE/welcome.html''.
Title: HRI observations of the Pleiades.
Authors: Harnden, F. R., Jr.; Caillault, J. -P.; Damiani, F.; Kashyap,
V.; Micela, G.; Prosser, C.; Rosner, R.; Sciortino, S.; Stauffer, J.
Bibcode: 1996rftu.proc...43H
Altcode:
Preliminary analysis of data from the first four ROSAT HRI pointings
has provided many new faint Pleiades detections. Completion of the
high-resolution survey of the most source-confused regions of this
open cluster will permit the construction of proper X-ray luminosity
functions and yield a definitive assessment of the coronal emission
of Pleiades members.
Title: Constraining the low-mass stellar mass-function
Authors: Kashyap, V.; Rosner, R.; Harnden, F. R., Jr.; Micela, G.;
Sciortino, S.
Bibcode: 1996ASPC..109..365K
Altcode: 1996csss....9..365K
No abstract at ADS
Title: ROSAT HRI survey of the Pleiades
Authors: Harnden, F. R., Jr.; Caillault, J. -P.; Damiani, F.; Kashyap,
V.; Micela, G.; Prosser, C.; Rosner, R.; Sciortino, S.; Stauffer, J.
Bibcode: 1996ASPC..109..359H
Altcode: 1996csss....9..359H
No abstract at ADS
Title: Detection of Variable Sources
Authors: Kashyap, Vinay; Rosner, Robert
Bibcode: 1996ASPC..101..171K
Altcode: 1996adass...5..171K
We have developed an algorithm to find variable sources in X-ray
data. This algorithm is designed for use as a first-look analysis of the
data to find regions of interest which may then be analyzed in detail by
other means. We detect these `interesting' regions in the data by first
estimating the expected counts in each pixel, and then comparing it to
the actual number of counts observed. We show the results of applying
this algorithm to ROSAT PSPC and HRI data of the Pleiades Cluster.
Title: X-Ray Source Detection Using the Wavelet Transform
Authors: Freeman, P. E.; Kashyap, V.; Rosner, R.; Nichol, R.; Holden,
B.; Lamb, D. Q.
Bibcode: 1996ASPC..101..163F
Altcode: 1996adass...5..163F
We present a new method that uses the Mexican Hat wavelet transform
in a particularly simple manner to detect X-ray sources. We use an
iterative approach to correlate data with the Mexican Hat function and
to cleanse suspected sources from the data. This allows us to estimate
the background and specify a threshold for source detection in the
correlation map of the original (uncleansed) data. This method is valid
in the Gaussian limit of high background counts and assumes that the
background does not vary over the instrument field-of-view. Application
of this method to simulated data of the ROSAT PSPC show it to detect
X-ray sources more sensitively than a method in which we calculate S/N,
and its use with ROSAT PSPC data of the Pleiades Cluster results in
the detection of ~ 30 X-ray sources not detected with the S/N method.
Title: An Analysis of X-ray Flares in Pleiades Stars
Authors: Sciortino, S.; Micela, G.; Reale, F.; Kashyap, V.; Rosner,
R.; Harnden, F. R., Jr.
Bibcode: 1996mpsa.conf..277S
Altcode: 1996IAUCo.153..277S
No abstract at ADS
Title: Coronal Structwre in M Dwarf Stars
Authors: Giampapa, M. S.; Rosner, R.; Kashyap, V.; Fleming, T. A.;
Schmitt, J. H. M. M.; Bookbinder, J. A.
Bibcode: 1996mpsa.conf...81G
Altcode: 1996IAUCo.153...81G
No abstract at ADS
Title: ROSAT Observations of the Pleiades. I. X-Ray Characteristics
of a Coeval Stellar Population
Authors: Micela, G.; Sciortino, S.; Kashyap, V.; Harnden, F. R., Jr.;
Rosner, R.
Bibcode: 1996ApJS..102...75M
Altcode:
We report the results of a deep X-ray survey of the core region
of the Pleiades carried out with ROSA T. In a single PSPC field
(∼1° radius), we detect 99 of 214 Pleiades stars, and we compute
upper limits for the remainder. We have detected all early dM stars
that fell within 20' of the field's center, where the instrument's
sensitivity is highest. We have computed maximum-likelihood integral
X-ray luminosity functions in various B - V intervals and compared the
results with previous studies of the Pleiades. Our results support
the contention that B and dA star "detections" are likely due to
X-ray emission from lower mass companions; we confirm the existence
of a stellar age versus X-ray luminosity relation found with the
Einstein Observatory for dG stars and extend it to dK and dM stars,
and we construct an essentially statistically complete X-ray luminosity
function for Pleiades dG stars and an almost complete X-ray luminosity
function for dK stars. We have verified the stellar rotation versus
X-ray luminosity relation for Pleiades dG stars and also show that a
similar relation does not hold for dK stars. Indeed, it appears that
some stellar parameters other than age and/or rotation rate must affect
the level of X-ray emission of Pleiades dG and dK stars. We demonstrate
the lack of measurable variability in X-ray emission at timescales of
∼6 months (except for flares) and the presence of variability by
a factor of 2 on timescales of ∼10 yr in at least 15% of Pleiades
members. The magnitude of this variability (by a factor of ∼2) is
too small to account for the spread of the X-ray luminosity functions.
Title: Mechanisms of Solar (and Stellar) Mass Loss
Authors: Rosner, R.
Bibcode: 1996mpsa.conf..107R
Altcode: 1996IAUCo.153..107R
No abstract at ADS
Title: Generation of Linear and Nonlinear Magnetic Tube Waves in
the Solar Atmosphere
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.
Bibcode: 1996mpsa.conf..427M
Altcode: 1996IAUCo.153..427M
No abstract at ADS
Title: On the Nonlinear Evolution of Magnetohydrodynamic
Kelvin-Helmholtz Instabilities
Authors: Malagoli, Andrea; Bodo, Gianluigi; Rosner, Robert
Bibcode: 1996ApJ...456..708M
Altcode:
We investigate the physical behavior in the nonlinear regime of
Kelvin-Helmholtz (KH) instabilities in a simple conducting shear flow
in the presence of magnetic fields, based upon the use of numerical
simulations of the ideal magnetofluid equations of motion in two
dimensions. The flow is characterized by three principal control
parameters: the Mach number M of the shear flow, the ratio α of the
Alfvén speed to the sound speed, and the effective diffusivity; we
investigate how these parameters affect the evolution and saturation of
the instability. The key result of our study is that even relatively
small magnetic fields (i.e., small compared to the equipartition
intensity) affect the way the KH instability saturates with respect to
the purely hydrodynamic case. If the magnetic field intensity is not
sufficiently strong to suppress the KH instability entirely, then the
field itself can still mediate the turbulent decay and diffusion of
energy and mass across the layer. We present a detailed study of the
various phases of this process for our simple shear layer configuration.
Title: The long-term evolution and mixing properties of high Mach
number hydrodynamic jets.
Authors: Bodo, G.; Massaglia, S.; Rossi, P.; Rosner, R.; Malagoli,
A.; Ferrari, A.
Bibcode: 1995A&A...303..281B
Altcode:
We present the results of numerical simulations of the long-term
evolution of Kelvin-Helmholtz instabilities of arbitrary symmetry for a
2-D fluid slab jet, focusing on the mechanisms governing the exchange of
mass, momentum, and energy between the jet and its environment. Most
of our novel results emerge from studies of the behavior of the
anti-symmetric mode, which is believed to resemble that of the m=1
modes for a cylinder; for this reason, our 2-D results can give some
insight into the computationally far more complex 3-D problem. The
solution space explored by us is defined by the main control parameters
describing our system - the flow Mach number M and the density ratio
between the ambient medium and the jet, ν. Our results show that
the evolution of the slab can be typically divided into four stages
(rather than three stages, as earlier results suggested): An initial
`linear' stage, during which the amplitude of unstable perturbations
grows, leading to the formation of alternating shocks and to a growing
deformation of the jet; an `acoustic' phase, during which the jet
radiates acoustic waves and shock waves into the external medium,
and by this means loses momentum and energy to the external medium; a
`mixing' phase, during which we observe strong mixing between the jet
and external material; and a final `quasi-steady' state. A key tool for
distinguishing these stages is the concept of `tracer entropy', which
we introduce in order to discriminate between turbulent and `molecular'
mixing of the jet and ambient materials. One of the notable results
which then emerges from our study is that a jet's loss of momentum
and energy can be entirely decoupled from its loss of mass, that is,
momentum and energy may be lost substantially before there is any
significant material entrainment; whether this effect is important
depends entirely on the details of the `acoustic' phase, during which
no significant entrainment occurs. The characteristics of the ultimate
quasi-steady state strongly depend on the two control parameters M and
ν; which dominates is determined by the precise details characterizing
the initial state. The most distinctive result is that while a light
jet (ν>>1) is virtually disrupted after the `mixing' phase,
the asymptotic state of an initially heavy jet (ν<=1) differs
little in its velocity amplitude from its initial state.
Title: On the Generation of Flux-Tube Waves in Stellar Convection
Zones. II. Improved Treatment of Longitudinal Tube Wave Generation
Authors: Musielak, Z. E.; Rosner, R.; Gail, H. P.; Ulmschneider, P.
Bibcode: 1995ApJ...448..865M
Altcode:
We have previously considered the generation of purely longitudinal
magnetohydrodynamic tube waves by external turbulent convection and
derived general formulas for the source function and for the wave
energy fluxes. In this paper, we present an improved treatment of the
generation of such tube waves, based on a more sophisticated description
of the turbulence and more refined calculations. These improvements
allow us to compute and discuss in greater detail the spectra and fluxes
of longitudinal tube waves generated in the solar convective zone.
Title: On the Possibility of Coherently Stimulated Recombination
and Cosmological Structure Generation: Recombination Instability
Authors: Klemperer, William; Luo, Xiaochun; Rosner, Robert; Schramm,
David N.
Bibcode: 1995PNAS...92.6166K
Altcode:
Possible instabilities during cosmological recombination may produce an
epoch of nonlinear density growth and fractal-like structural patterns
out to the horizon scale at that epoch (≈200 Mpc today). With this
motivation, we examine the consequences of the change in effective
radiative recombination reaction rate coefficients produced by intense
stimulated emission. The proton-electron recombination is considered
as a natural laser, leading to the formation of spatially nonuniform
distributions of neutral matter earlier than the recombination epoch.
Title: On the Possibility of Coherently Stimulated Recombination
and Cosmological Structure Generation: Cosmological Consequences
Authors: Schramm, David N.; Rosner, Robert; Luo, Xiaochun; Klemperer,
William
Bibcode: 1995PNAS...92.6171S
Altcode:
Given a specific physical mechanism for instabilities during
cosmological recombination discussed in an earlier paper, we examine the
nonlinear growth of density structures to form fractal-like structural
patterns out to the horizon scale at that epoch (~ 200 Mpc today). A
model for such fractal patterns is presented. Such effects could
explain observed large-scale structure patterns and the formation of
objects at high z, while keeping microwave background anisotropies
at the observed minimal levels. We also discuss possible microwave
background implications of such a transition and note a potentially
observable spectral signature at λ~ 0.18 mm as well as a weak line
near the peak in the microwave background.
Title: An Objective Multicolor Method for the Characterization of
Low-Resolution X-Ray Spectra
Authors: Collura, A.; Micela, G.; Sciortino, S.; Harnden, F. R., Jr.;
Rosner, R.
Bibcode: 1995ApJ...446..108C
Altcode:
We describe a new technique for the characterization of low-resolution
X-ray spectra, based on generalized colors defined by means of a
principal component analysis. Application of the method to a sample
of optically and radio-selected Einstein Observatory X-ray sources
yields groups that are dominated either by stars or by extragalactic
sources. The method thereby provides an immediate interpretation in
terms of differences in the physics of the emission processes dominating
the objects studied. The principal advantages of the method are that it
provides an objective means of classifying source spectra and that it
provides an objective means of obtaining the minimal set of spectral
classification parameters. Though the method does not significantly
improve results obtained with previously employed techniques when
applied to Einstein data, its objective operation should prove powerful
in aiding source classification in the more recent medium spectral
resolution X-ray surveys based on the ROSAT and ASCA mission.
Title: On the Spatial Distribution of Magnetic Fields on the Solar
Surface
Authors: Tao, L.; Du, Y.; Rosner, R.; Cattaneo, F.
Bibcode: 1995ApJ...443..434T
Altcode:
Recent measurements of solar surface magnetic fields suggest that the
spatial distribution of these fields is fractal. In order to understand
the physical basis for such geometric complexity, we study here the
advection of magnetic flux tubes relatively simple random motions on
the surface of a fluid and investigate the spatial statistics of the
resulting surface field. While this study does not directly address
the question of why solar surface fields have the observed spatial
structure, it is designed to build our intuition about how surface
flows lead to complex spatial structuring of magnetic fields. As part
of our study, we discuss the various methods by which one can describe
the spatial distribution of the surface magnetic flux and relate them
mathematically; this turns out to be a crucial point of our work since,
as we show, a number of previous analyses have misinterpreted the
analysis procedures for determining fractal dimensions. Our principal
result is the explicit demonstration that simple random flows lead
to magnetic flux spatial distributions with a multifractal dimension
spectrum. Furthermore, we demonstrate that this magnetic spatial
structure is generic, i.e., is characteristic of a very large class
of random flows.
Title: On the Origin of ``Dividing Lines'' for Late-Type Giants
and Supergiants
Authors: Rosner, R.; Musielak, Z. E.; Cattaneo, F.; Moore, R. L.;
Suess, S. T.
Bibcode: 1995ApJ...442L..25R
Altcode:
We show how a change in the nature of the stellar dyanmo can lead to
a transition in the topological character of stellar magnetic fields
of evolved stars, from being mainly closed on the blueward side of the
giant tracks in the Hertzsprung-Russell (H-R) diagram to being mainly
open on their redward side. If such a topological transition occurs,
then these stars naturally segregate into two classes: those having hot
coronae on the blueward side, and those having massive cool winds on the
redward side, thus leading naturally to the so-called dividing lines.
Title: Structuring in the Solar Corona
Authors: Rosner, R.
Bibcode: 1995SPD....26..611R
Altcode: 1995BAAS...27..963R
No abstract at ADS
Title: The evolution of helicity in the presence of turbulence
Authors: Berger, M.; Rosner, R.
Bibcode: 1995GApFD..81...73B
Altcode:
In this paper, the turbulent diffusion of a magnetic field in the
kinematic approximation, i.e., kinematic dynamo theory, is studied
in the context of spectral densities rather than mean fields. In
particular, we derive the evolution equations for the magnetic energy
and helicity spectra, given the corresponding kinetic energy and
helicity spectra. We verify that for the kinematic turbulent diffusion
problem, the total magnetic helicity remains an exact invariant -
as it must for ideal magnetohydrodynamics; and that with the use of
inequalities connecting the magnetic energy and helicity spectra,
one can place bounds on the magnetic energy spectrum which depend on
the field topology.
Title: Coronal Loop Model Atmospheres for Low Mass Stars
Authors: Giampapa, M.; Rosner, R.; Kashyap, V.; Fleming, T.; Schmitt,
J.; Bookbinder, J.
Bibcode: 1994AAS...185.9807G
Altcode: 1994BAAS...26Q1480G
We have constructed semi-empirical loop models that best fit key
coronal parameters derived from ROSAT PSPC observations of selected
low mass stars. The X-ray pulse-height distributions are represented
by two dominant components. These include a soft component that is
characterized by compact loop configurations with loop lengths that are
one or more orders of magnitude smaller than the stellar radius. By
contrast, two types of stable solutions can be found for the hard
component, namely very long loops (much larger than a pressure scale
height) with large filling factors, and very compact loops with very
small filling factors. The ``long" solutions are physically excluded
since they violate stability criteria. We identify the ``small"
solutions with compact loop flares. The implications of these results
for coronal structure and angular momentum evolution in low mass dwarfs
will be discussed.
Title: X-Ray Emission on Hybrid Stars: ROSAT Observations of alpha
Trianguli Australis and IOTA Aurigae
Authors: Kashyap, V.; Rosner, R.; Harnden, F. R., Jr.; Maggio, A.;
Micela, G.; Sciortino, S.
Bibcode: 1994ApJ...431..402K
Altcode:
We report on deep ROSAT observations of two Hybrid atmosphere stars,
alpha TrA and iota Aur, and our analysis of these observations. We
detect high-energy transient phenomena on alpha TrA and consider the
implications of this discovery to the atmospheres of Hybrid stars. We
detect iota Aur in the high-energy passband of ROSAT, implying the
existence of multimillion degree plasma on the star. Our major results
include the following: discovery of two large flare events, detected
during pointed observations of alpha TrA; the demonstration that the
flare emission most likely comes from the giant itself, rather than
from a previously unseen low-mass companion star; the demonstration
that the plasma characteristics associated with the flares and with the
'quiescent' component are essentially indistinguishable; and that the
geometric dimensions of the emitting plasma are considerably smaller
than the critical dimension characterizing stable 'hot' coronal loop
structures. Our results suggest that alpha TrA does not have any steady
X-ray emission consistent with theoretical expectations, and support
the argument that Hybrid stars constitute a transitional type of object
in which large-scale magnetic dynamo activity ceases, and the dominant
spatial scales characterizing coronal structure rapidly decline as
such stars evolve across the X-ray 'Dividing Line' in the H-R diagram.
Title: MACHOs and the Diffuse X-Ray Background
Authors: Kashyap, V.; Rosner, R.; Schramm, D.; Truran, J.
Bibcode: 1994ApJ...431L..87K
Altcode:
The possible contribution of X-ray emission from massive compact
objects in the Galactic halo (MACHOs) to the diffuse X-ray background
is explored. We show that such emission cannot be responsible for
the shadowing seen in soft X-ray observations by ROSAT but that these
objects may indeed contribute significantly (at levels greater than 10%)
to the diffuse background at higher (greater than or approximately
0.5 keV) energies. Thus, X-ray observations may well be able to
significantly constrain the spatial distribution of MACHOs.
Title: Diffuse X-Ray Shadow in the Pleiades
Authors: Kashyap, V.; Rosner, R.; Harnden, F. R., Jr.; Micela, G.;
Sciortino, S.
Bibcode: 1994AAS...184.2913K
Altcode: 1994BAAS...26..903K
We report the results of our analysis of the diffuse X-ray background
present in the ROSAT PSPC observations of the core of the Pleiades
Cluster. We detect the existence of an X-ray shadow in the 0.2-0.41
keV passband coinciding with IRAS emission. However, the depth of
this shadow is significantly less than expected, casting doubts on
the generality of the X-ray shadowing observed previously with ROSAT.
Title: Possible role of massive black holes in the generation of
galactic magnetic fields
Authors: Chakrabarti, Sandip K.; Rosner, R.; Vainshtein, S. I.
Bibcode: 1994Natur.368..434C
Altcode:
THE origin of galactic magnetic fields has been a long-standing
puzzle. Models based on standard dynamo theory1-4
encounter several problems, the most fundamental of which is that,
in order to explain the strengths of observed large-scale magnetic
fields5-7, the fluctuating magnetic fields in galaxies
must be unreasonably large8-12: the energy density in
these small-scale fields must far exceed the local kinetic energy
density. Here we propose an alternative mechanism of magnetic-field
generation in galaxies. We show that a seed field can be generated by
the rotation of an aspherical cloud of ionized gas around a central
massive black hole. Strong shear flows in the rotating gas amplify this
seed field, and a relatively slow galactic wind can transport the field
to the outer regions of a galaxy in about 100 million years-a timescale
short enough to meet the constraints imposed by the observation of
strong fields in very young galaxies13,14.
Title: On Sound Generation by Turbulent Convection: A New Look at
Old Results
Authors: Musielak, Z. E.; Rosner, R.; Stein, R. F.; Ulmschneider, P.
Bibcode: 1994ApJ...423..474M
Altcode:
We have revisited the problem of acoustic wave generation by turbulent
convection in stellar atmospheres. The theory of aerodynamically
generated sound, originally developed by Lighthill and later modified
by Stein to include the effects of stratification, has been used
to estimate the acoustic wave energy flux generated in solar and
stellar convection zones. We correct the earlier computations by
incorporating an improved description of the spatial and temporal
spectrum of the turbulent convection. We show the dependence of the
resulting wave fluxes on the nature of the turbulence, and compute the
wave energy spectra and wave energy fluxes generated in the Sun on
the basis of a mixing-length model of the solar convection zone. In
contrast to the previous results, we show that the acoustic energy
generation does not depend very sensitively on the turbulent energy
spectrum. However, typical total acoustic fluxes of order FA
= 5 x 107 ergs/sq cm/s with a peak of the acoustic frequency
spectrum near omega = 100 mHz are found to be comparable to those
previously calculated. The acoustic flux turns out to be strongly
dependent on the solar model, scaling with the mixing-length parameter
alpha as alpha3.8. The computed fluxes most likely constitute
a lower limit on the acoustic energy produced in the solar convection
zone if recent convection simulations suggesting the presence of shocks
near the upper layers of the convection zone apply to the Sun.
Title: Reflection of Alfven Waves in Stellar Atmospheres: The Case
of Open Magnetic Fields
Authors: Lou, Yu-Qing; Rosner, Robert
Bibcode: 1994ApJ...424..429L
Altcode:
We investigate the basic properties of reflection and transmission of
Alfven waves in a radially inhomogeneous, magnetized, and 'open' late
spectral type stellar atmosphere. We have obtained analytic solutions
for the limiting cases of large and small distances above the stellar
surface and have obtained numerical solutions for all radii over the
entire frequency range of interest in such atmospheres. Our key result
is that while Alfven wave trapping in a stratified atmosphere with
open magnetic fields may not be very effective in solar coronal holes,
it can be very effective in the magnetized outer atmospheres of giant
and supergiant stars. This result supports earlier conjectures that
Alfven wave reflection may be in part responsible for the driving of
massive winds in the atmophseres of late-type giants and supergiants.
Title: An X-Ray Study of a Coeval Star Population: A Deep ROSAT
Observation of the Core of the Pleiades Cluster
Authors: Micela, G.; Sciortino, S.; Kashyap, V.; Harnden, F. R., Jr.;
Rosner, R.
Bibcode: 1994ASPC...64..110M
Altcode: 1994csss....8..110M
No abstract at ADS
Title: A Variability Study of X-Ray Emission of Pleiades Stars
Authors: Sciortino, S.; Micela, C.; Kashyap, V.; Harnden, F. R., Jr.;
Rosner, R.
Bibcode: 1994ASPC...64..140S
Altcode: 1994csss....8..140S
No abstract at ADS
Title: Evaluation of Source Counts and Upper Limits in Crowded ROSAT
PSPC Fields
Authors: Kashyap, V.; Micela, G.; Sciortino, S.; Harnden, F. R., Jr.;
Rosner, R.
Bibcode: 1994AIPC..313..239K
Altcode: 1994sxrc.conf..239K
We present a method for determining source counts, S/N, and upper
limits at specified positions in a crowded ROSAT PSPC field using a
combination of publicly available software packages. The algorithm
is based on the so-called `Local DETECT' method of source detection,
and improves upon currently available software, to permit a meaningful
comparison of non-detections with detected sources. We also present
a recipe to obtain source counts and S/N in the case of point sources
which overlap significantly.
Title: Stellar Surface Mapping by Matrix Lightcurve Inversion
(Invited Review)
Authors: Wild, Walter J.; Rosner, Robert; Harmon, Robert; Drish,
William F., Jr.
Bibcode: 1994ASPC...64..628W
Altcode: 1994csss....8..628W
No abstract at ADS
Title: Overview and Future Prospects
Authors: Rosner, R.
Bibcode: 1994xspy.conf..225R
Altcode:
No abstract at ADS
Title: The Coronal Structure above Sunspots and Pores
Authors: Harmon, R.; Rosner, R.; Zirin, H.; Spiller, E.; Golub, L.
Bibcode: 1993ApJ...417L..83H
Altcode:
No abstract at ADS
Title: ROSAT X-Ray Detection of epsilon Taurus: Revisiting the
Coronal and Transition Region Emission of the Hyades Giants
Authors: Collura, A.; Maggio, A.; Micela, G.; Sciortino, S.; Harnden,
F. R., Jr.; Rosner, R.
Bibcode: 1993ApJ...416..204C
Altcode:
We report on a recent pointed X-ray observation of the Hyades giant ɛ
Tau, obtained with the ROSA T PS PC. We confirm at higher significance
the earlier ROSAT all-sky survey detection of this star, with an X-ray
luminosity of ∼1028 ergs s-1. ɛ Tau turns out
to be the X-ray faintest among the four giants of the Hyades cluster,
and the only one with no evidence of binarity. We rediscuss possible
explanations, already put forward in previous studies, for the large
spread in coronal and transition region emission observed among these
stars. We revisit this issue in the light of our most recent knowledge
on X-ray and UV emission properties of other Hyades and field stars.
Title: X-Ray Emission at the Low-Mass End: Results from an Extensive
Einstein Observatory Survey
Authors: Barbera, M.; Micela, G.; Sciortino, S.; Harnden, F. R., Jr.;
Rosner, R.
Bibcode: 1993ApJ...414..846B
Altcode:
We have used available IPC data and a critical compilation of cataloged
optical data to measure the 0.16-3.5 keV X-ray emission from 88 K and
169 M stars of luminosity classes IV, V, and VI within 25 pc from
the Sun. The IPC detected 54 out of the 88 K stars, 70 out of the
138 M stars with M(v) less than 13.4, and 15 out of the 31 fainter
M stars. We have identified a subsample of surveyed stars that is
statistically representative of the population of K and M stars in the
solar neighborhood. On the basis of this subsample (1) we have shown the
occurrence of a drop in the level of X-ray emission for M stars later
than approximately M5; (2) we have built unbiased maximum likelihood
X-ray luminosity functions for the K, early M, and late M stars;
(3) we have confirmed, both for K and M stars, the decrease of X-ray
luminosity with increasing stellar age in the range of ages of disk
population stars: and (4) we have shown that no obvious correlation
is present between X-ray and bolometric luminosities in the entire
representative samples of K and M stars, but only within flare stars
which also seem to mark a saturation in X-ray luminosity level.
Title: On the Structure of Solar and Stellar Coronae: Loops and Loop
Heat Transport
Authors: Litwin, Christof; Rosner, Robert
Bibcode: 1993ApJ...412..375L
Altcode:
We discuss the principal constraints on mechanisms for structuring and
heating the outer atmospheres - the coronae - of stars. We argue that
the essential cause of highly localized heating in the coronae of stars
like the sun is the spatially intermittent nature of stellar surface
magnetic fields, and that the spatial scale of the resulting coronal
structures is related to the spatial structure of the photospheric
fields. We show that significant constraints on coronal heating
mechanisms derive from the observed variations in coronal emission,
and, in addition, show that the observed structuring perpendicular
to coronal magnetic fields imposes severe constraints on mechanisms
for heat dispersal in the low-beta atmosphere. In particular, we find
that most of commonly considered mechanisms for heat dispersal, such
as anomalous diffusion due to plasma turbulence or magnetic field
line stochasticity, are much too slow to account for the observed
rapid heating of coronal loops. The most plausible mechanism appears
to be reconnection at the interface between two adjacent coronal flux
bundles. Based on a model invoking hyperresistivity, we show that such
a mechanism naturally leads to dominance of isolated single bright
coronal loops and to bright coronal plasma structures whose spatial
scale transverse to the local magnetic field is comparable to observed
dimensions of coronal X-ray loops.
Title: X-Ray Emission From Hybrid Stars
Authors: Kashyap, V.; Rosner, R.; Harnden, F. R., Jr.; Maggio, A.
Bibcode: 1993AAS...182.2206K
Altcode: 1993BAAS...25..824K
Hybrid stars are giant stars that exhibit both chromospheric emission
features and signatures of mass outflow, and hence provide a link
between stars on either side of the ``Coronal Dividing Line". We have
obtained long duration ROSAT PSPC exposures of two nearby hybrid stars
(alpha TrA and iota Aur), and here, we compare these observations with
models of X-ray emission on giant stars.
Title: On the Thermal Stability of a Radiating Plasma Subject to
Nonlocal Thermal Conduction. I. Linear Analysis
Authors: Chun, E.; Rosner, R.
Bibcode: 1993ApJ...408..678C
Altcode:
We study the linear stability of an optically thin uniform radiating
plasma subject to nonlocal heat transport. We derive the dispersion
relation appropriate to this problem, and the marginal wavenumbers
for instability. Our analysis indicates that nonlocal heat transport
acts to reduce the stabilizing influence of thermal conduction, and
that there are critical values for the electron mean free path such
that the plasma is always unstable. Our results may be applied to a
number of astrophysical plasmas, one such example being the halos of
clusters of galaxies.
Title: On the Generation of ``Strong'' Magnetic Fields
Authors: Vainshtein, S. I.; Parker, E. N.; Rosner, R.
Bibcode: 1993ApJ...404..773V
Altcode:
We rediscuss the nature of magnetic field generation in astrophysical
systems. We show that as a result of ineffective three-dimensional
turbulent diffusion in the presence of strong azimuthal magnetic fields,
the standard dynamo equations are not likely to provide a reasonable
description of magnetic dynamos in systems such as late-type stars
and galaxies. Instead, we propose a new set of dynamo equations,
which take into account the modifications of turbulent diffusion by
strong magnetic fields.
Title: The ROSAT view of stellar coronae.
Authors: Rosner, R.
Bibcode: 1993BAAS...25..742R
Altcode:
No abstract at ADS
Title: Evolution of stellar activity in early post-main-sequence
phases
Authors: Maggio, A.; Sciortino, S.; Bianchi, L.; Harnden, F. R., Jr.;
Rosner, R.
Bibcode: 1993ASPC...40..648M
Altcode: 1993ist..proc..648M; 1993IAUCo.137..648M
No abstract at ADS
Title: A multi-color method for the classification of low resolution
X-ray spectra
Authors: Collura, A.; Micela, G.; Sciortino, S.; Harnden, F. R., Jr.;
Rosner, R.
Bibcode: 1993MmSAI..64..637C
Altcode:
No abstract at ADS
Title: Wiggled Structure of Herbig-Haro Objects: Helical Kink
Instability of Jets from Young Stellar Objects
Authors: Todo, Yasushi; Uchida, Yutaka; Sato, Tetsuya; Rosner, Robert
Bibcode: 1993ApJ...403..164T
Altcode:
We describe the results of three-dimensional magnetohydrodynamic
numerical simulations, as applied to the behavior of the jets from YSO
jets under circumstances in which the ambient large-scale interstellar
magnetic field is twisted helically by the rotation of the protostar and
the protostellar disk through which this field threads. The calculations
are continued until the bow shock propagates a distance 60 times as
far as the initial jet radius. The specific case we examine involves
a jet with density 100 mH/cu cm and velocity 100 km/s;
we then show that an azimuthal field of strength 70 micro-G drives
a helical kink instability. The growth rate of this instability is
large enough that significant morphological effects are expected to
be visible during the typical lifetime of an HH object; for example,
the observed 'wiggled' appearance of some HH objects may be due to
this helical kink instability.
Title: X-ray and UV Emission from Post-Main-Sequence Stars: The
Connection between Surface Activity and Evolution
Authors: Maggio, A.; Sciortino, S.; Bianchi, L.; Harnden, F. R., Jr.;
Rosner, R.
Bibcode: 1993ASSL..183..291M
Altcode: 1993pssc.symp..291M
No abstract at ADS
Title: Coronal Emission at the Low Mass End: Results from an
Optical-Selected Sample of Nearby K and M Stars Surveyed with the
EINSTEIN Observatory
Authors: Barbera, M.; Micela, G.; Sciortino, S.; Harnden, F. R., Jr.;
Rosner, R.
Bibcode: 1993ASSL..183..279B
Altcode: 1993pssc.symp..279B
No abstract at ADS
Title: Mass Loss and X-ray Emission from Giants and Supergiants
Authors: Rosner, R.
Bibcode: 1993ASSL..183..549R
Altcode: 1993pssc.symp..549R
No abstract at ADS
Title: High sensitivity ROSAT observations of the Pleiades.
Authors: Micela, G.; Sciortino, S.; Harnden, F. R.; Kashyap, V.;
Rosner, R.
Bibcode: 1993MmSAI..64..695M
Altcode:
No abstract at ADS
Title: Turbulent magnetic transport effects and their relation to
magnetic field intermittency.
Authors: Vainshtein, S. I.; Tao, L.; Cattaneo, F.; Rosner, R.
Bibcode: 1993spd..conf..311V
Altcode:
No abstract at ADS
Title: On using a neutrino magnetic moment to attack the solar
neutrino problem.
Authors: Shi, X.; Schramm, D. N.; Rosner, R.; Dearborn, D. S.
Bibcode: 1993CNPPh..21..151S
Altcode:
The matter-enhanced spin-flavor precession of the solar neutrinos as
a possible solution to the solar neutrino problem is revisited. It is
argued that in order to explain the possible anti-correlation between
the neutrino flux and the solar activity in the Homestake experiment,
the neutrino magnetic resonance must occur with substantial amplitude
in the convective zone. The maximal magnetic field inside the solar
convective zone is discussed in detail. Combining these constraints
with the astrophysical constraints on the neutrino magnetic moment, and
data from the 37Cl Homestake experiment, and numerical models
of the Sun, it is shown that, by itself, the spin-flavor precession of
solar neutrinos cannot simultaneously explain the observed neutrino flux
and possible anti-correlations of the Homestake experiment. An Appendix
is devoted to the statistical questions of possible anti-correlations.
Title: ROSAT Observations of alpha TrA and IOTA AUR
Authors: Kashyap, V.; Rosner, R.; Harnden, F. R., Jr.; Maggio, A.
Bibcode: 1992AAS...181.5102K
Altcode: 1992BAAS...24.1205K
We report here on pointed ROSAT observations of the hybrid chromosphere
stars alpha TrA (K4III) and iota Aur (K3II). We detect alpha TrA at
signal-to-noise greater than 50, and iota Aur marginally. The column
density of absorption of X-rays from alpha TrA is consistent with IUE
observations. We also see a flare type event in its lightcurve. Finally,
we find that the X-ray emission from alpha TrA is mostly from plasma
at temperatures greater than 1 keV.
Title: The ROSAT View of Stellar Coronae
Authors: Rosner, R.
Bibcode: 1992AAS...18111910R
Altcode:
The ROSAT mission has proven itself to be a cornucopia of new results
for stellar X-ray astronomy. I will review the major new results,
focussing especially on results which ROSAT has uniquely contributed to,
and on the physical implications of these results. Among other topics,
I will discuss X-ray emission from evolved stars, spectroscopy and
structure of stellar coronae, and the general variation of stellar
X-ray emission in the H-R diagram.
Title: Reducing the Thermal Stability of a Radiating Plasma: The
Effects of Nonlocal Thermal Conduction
Authors: Chun, E.; Rosner, R.
Bibcode: 1992AAS...181.1503C
Altcode: 1992BAAS...24.1143C
No abstract at ADS
Title: On Sound Generation by Turbulent Convection: A New Look at
Old Results
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.; Gail, P.;
Wang, A.
Bibcode: 1992AAS...181.9403M
Altcode: 1992BAAS...24.1269M
No abstract at ADS
Title: Starspot Reconstruction via Matrix Light Curve Inversion
Authors: Harmon, R.; Wild, W.; Rosner, R.; Drish, W.
Bibcode: 1992AAS...181.5114H
Altcode: 1992BAAS...24R1207H
No abstract at ADS
Title: A New Look at Stars from ROSAT
Authors: Rosner, R.
Bibcode: 1992AAS...181.5902R
Altcode: 1992BAAS...24.1216R
No abstract at ADS
Title: Behavior of Jets from Young Stellar Objects in Large-Scale
Interstellar Magnetic Fields: MHD Model of Herbig-Haro Objects in
2.5-D Simulations
Authors: Todo, Yasushi; Uchida, Yutaka; Sato, Tetsuya; Rosner, Robert
Bibcode: 1992PASJ...44..245T
Altcode:
We describe the results of 2.5-D magnetohydrodynamic numerical
simulations of the behavior of YSO (young stellar objects) jets ---
so-called ``optical jets" --- in a magnetized interstellar medium. Our
aim is to understand the behavior of such jets under circumstances in
which the large-scale interstellar magnetic field is twisted helically
by the rotation of the protostar and the protostellar disk through
which these fields thread. Herbig-Haro objects are interpreted by
our magnetic model as being the shocked gas caused by the injection
of YSO jets into an interstellar medium pervaded by a large-scale
helical magnetic field. Our results show that the bow shock and the
jet-terminal shock are both magnetohydrodynamic fast shocks, accompanied
by a slow shock, respectively. For weak magnetic fields, the shocked
gas expands in the lateral direction and forms a cocoon around the
jet by stretching the magnetic field. For strong magnetic fields,
fast shocks are either weak or not formed, and the kinetic energy is
mainly dissipated at slow shocks. In the presence of strong magnetic
fields, the separation between the bow shock and the jet-terminal shock
becomes much larger because of the effect of the magnetic pressure;
further, Kelvin-Helmholtz instability is entirely suppressed. The
cocoon structure in the strong-field case is either very slender, or
not formed at all, because the shocked gas cannot expand perpendicular
to the magnetic field. Although the weak helical magnetic fields in
the ambient medium reduce the propagation velocity of the bow shock,
the bow shock can nevertheless propagate faster in magnetic fields
exceeding a certain critical value. We discuss the relation of our
results to Herbig-Haro objects in general, while focusing particularly
on HH47A and HH47D, which we contend can be explained by a single jet
with a strong helical magnetic field.
Title: A Magnetohydrodynamic Model for Herbig-Haro Objects:
Magnetically Guided Shocked Flows Associated with Optical Jets from
Young Stellar Objects
Authors: Uchida, Yutaka; Todo, Yasushi; Rosner, Robert; Shibata,
Kazunari
Bibcode: 1992PASJ...44..227U
Altcode:
We propose a magnetohydrodynamic (MHD) model for Herbig-Haro (HH)
objects in which a large-scale interstellar magnetic field plays
a basic role. The model contains two essential, distinct elements:
First, we assume that the large-scale interstellar magnetic field is
spatially constricted during the contraction phase of star formation,
and becomes helical due to production of a toroidal field component
by the rotation of the central star + disk system. Second, we assume
that this large-scale field acts as a guide field for the high-velocity
flows associated with the optical jets emanating from the star forming
at the center. In that case, we show that the impinging optical jet
accompanies four distinct shock fronts, namely, MHD fast and slow
shocks ahead, and reverse fast and slow shocks propagating backward
into the moving jet medium behind the contact discontinuity. The result
of our simplified 1.5-D MHD simulations strongly indicate that our
``magnetically-guided stream" picture can account for the high Doppler
and proper-motion velocities of the HH objects, which are generally
different from each other. Our results suggest that the more complex
morphological characteristics of these objects [such as the ``jet with
bright-spot + bow shock" type structures (e.g., HH34) and those with
``wiggled filamentary structures" (e.g., HH46/47) of some HH objects]
could be explained by MHD models in 2.5-D or 3-D.
Title: Modeling the Stellar Contribution to the Galactic Component
of the Diffuse Soft X-Ray Background. I. Background Fluxes and
Number Counts
Authors: Kashyap, V.; Rosner, R.; Micela, G.; Sciortino, S.; Vaiana,
G. S.; Harnden, F. R., Jr.
Bibcode: 1992ApJ...391..667K
Altcode:
A combination of a stellar Galaxy model based on optical data,
stellar X-ray luminosity functions derived from the full Einstein
base, and a model for X-ray absorption derived from hydrogen column
densities are used to estimate the contribution to the diffuse soft
X-ray background flux from the main-sequence A, F, G, K, and M stars,
and RS CVn stars, at various energies ranging from 0.1 to about 5
keV. Previous discrepancies between earlier estimates of the stellar
contribution to the diffuse soft X-ray background are resolved; this
stellar contribution to the diffuse soft X-ray background is found to
be under 3 percent for photon energies less than energy I and J bands
(about 0.8-2 keV), at a threshold sensitivity for point source detection
about 10 exp -10 ergs/s sq cm. At low latitudes, stellar contribution
estimates are less than 3 percent below 0.3 keV, 7-40 percent in the
medium-energy bands, and 27-70 percent in the I and J bands. It is
shown that while dM stars are the major contributors to the diffuse
stellar flux, other stellar types contribute as much as 40 percent of
this flux at the higher energies in the passband studied.
Title: Emergence of Magnetic Flux from the Convection Zone into the
Solar Atmosphere. I. Linear and Nonlinear Adiabatic Evolution of
the Convective-Parker Instability
Authors: Nozawa, S.; Shibata, K.; Matsumoto, R.; Sterling, A. C.;
Tajima, T.; Uchida, Y.; Ferrari, A.; Rosner, R.
Bibcode: 1992ApJS...78..267N
Altcode:
The linear and nonlinear properties of the evolution of emerging
magnetic flux from the solar convection zone into the photosphere,
chromosphere, and corona are studied. A linear stability analysis
of the partially magnetized convection zone is presented. The growth
rate of this combined convective-Parker instability is found to differ
significantly from that of the Parker instability in the absence of
convection. When beta(=pg/pm) is greater than 10 in the initial flux
sheet, the growth rate increases with horizontal wavenumber, and there
is no maximum growth rate. A local maximum can occur when the flux
is initially located near the top of the convection zone. When beta
is less than 10, the convective-Parker instability behaves like the
Parker instability for long-wavelength modes, and like the convective
instability for short-wavelength modes. A 2D MHD code is used to study
the nonlinear evolution of the system. When the initial flux sheet has
beta less than 10, the long-wavelength mode dominates the nonlinear
evolution of the system, independently of the initial perturbation
wavelength.
Title: Why the Winds from Late-Type Giants; Supergiants are Cool
Authors: Moore, R. L.; Musielak, Z. E.; An, C. -H.; Rosner, R.; Suess,
S. T.
Bibcode: 1992ASPC...26..464M
Altcode: 1992csss....7..464M
No abstract at ADS
Title: A Rosat Image of the Pleiades
Authors: Kashyap, V.; Rosner, R.; Harnden, F. R.; Micela, G.;
Sciortino, S.
Bibcode: 1992AAS...179.9410K
Altcode: 1992BAAS...24..689K
No abstract at ADS
Title: X-ray emission at low-mass end of the MS - Results from an
extensive Einstein Observatory survey
Authors: Barbera, M.; Micela, G.; Sciortino, S.; Vaiana, G. S.;
Harnden, F. R., Jr.; Rosner, R.
Bibcode: 1992MmSAI..63..743B
Altcode:
The 0.16-4.0 keV X-ray emission from K and M stars of luminosity
classes IV, V, and VI within 25 parsec of the sun was measured using
all available Einstein Observatory IPC data and a critical compilation
of catalogued optical data. Fifty four of 88 stars were detected,
70 of 138 M stars with Mv less than 13.4 (corresponding to M6) and 15
or 31 fainter M stars. The surveyed stars were grouped, on the basis
of U, V, W space velocity components, into old-disk, young-disk,
and halo population stars. Then, a subsample was selected which is
statistically representative of the population of K and M stars in the
solar neighborhood, on the basis of which unbiased Maximum Likelihood
X-ray luminosity functions were constructed for K, early M, and late M
stars. The investigation revealed a decrease of X-ray luminosity with
increasing stellar age in the range of ages of disk population stars.
Title: The Origin of the Solar Cycle
Authors: Rosner, R.; Weiss, N. O.
Bibcode: 1992ASPC...27..511R
Altcode: 1992socy.work..511R
No abstract at ADS
Title: Development of hard-turbulent convection in two dimensions:
Numerical evidence
Authors: Werne, J.; Deluca, E. E.; Rosner, R.; Cattaneo, F.
Bibcode: 1991PhRvL..67.3519W
Altcode:
New numerical evidence for a transition to hard turbulence in 2D
Boussinesq convection is presented. These 2D simulations agree with
some, but not all, experimental results for the scaling properties of
3D hard turbulence. The transition to 2D hard turbulence, as measured
by a change in the Nusselt-Rayleigh scaling law, coincides with a
gradual change in the velocity probability distribution from Gaussian
to exponential form and with the development of a ``well-mixed''
central region.
Title: The Diffuse Soft X-Ray Background As Seen with the Einstein
Observatory
Authors: Micela, G.; Harnden, F. R., Jr.; Rosner, R.; Sciortino, S.;
Vaiana, G. S.
Bibcode: 1991ApJ...380..495M
Altcode:
A systematic survey of the diffuse soft X-ray background as seen
directly with the Einstein Observatory is presented. With the aid of
1633 selected 1 x 1 deg fields of view obtained by the IPC to provide
about 5-percent sky coverage, with some bias toward the Galactic
plane, the background in the 0.16-3.5 keV spectral region was spatially
resolved on this angular scale. Maps of the background are characterized
and produced at different energies within the Einstein passband. It
is confirmed that the Galactic ridge is not present at energies below
0.33 keV and it is demonstrated that the appearance of the ridge above
this energy is not due to hard Galactic sources with a flux above 10
exp -13 ergs/sq cm/s. A southern Galactic region is identified, with l
between 80 and 180 deg and b less than -5 deg, where the mean background
intensity has the lowest value and is homogeneous within better than 9
percent. The implications of these results for the Galactic structure
and for the nature of the extragalactic X-ray background are discussed.
Title: Why the Winds from Late-Type Giants and Supergiants are Cool
Authors: Moore, R. L.; Musielak, Z. E.; An, C. -H.; Rosner, R.; Suess,
S. T.
Bibcode: 1991BAAS...23Q1385M
Altcode:
No abstract at ADS
Title: On the Generation of Magnetic Tube Waves in the Solar
Convection Zone
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.; Gail, P.
Bibcode: 1991BAAS...23.1442M
Altcode:
No abstract at ADS
Title: Numerical simulations of thermal instabilities in stratified
gases. II - Exploration of the parameter space
Authors: Reale, F.; Rosner, R.; Malagoli, A.; Peres, G.; Serio, S.
Bibcode: 1991MNRAS.251..379R
Altcode:
The temporal evolution of density perturbations in an initially
hydrostatic isothermal atmosphere consisting of an optically thin
radiating compressible plasma is studied. Numerical techniques are
used to describe the nonlinear evolution of the perturbations, and
the relative equilibrium between dynamic and thermal instabilities as
governed by three independent control parameters are examined, namely,
the initial density contrast of the perturbation, the ratio of the
local buoyancy oscillation period to the local radiative cooling time,
and the ratio of the perturbation radius to the local scaleheight. Four
orders of magnitude of initial density contrasts and ratios of buoyancy
and cooling times, and one order of magnitude of the bubble dimensions
are explored. Well-defined oscillations were found to occur in a limited
parameter range, and thermal instability to occur even within secondary
condensations deriving from the bubble fragmentation.
Title: On Turbulent Diffusion of Magnetic Fields and the Loss of
Magnetic Flux from Stars
Authors: Vainshtein, Samuel I.; Rosner, Robert
Bibcode: 1991ApJ...376..199V
Altcode:
The turbulent diffusion of magnetic fields in astrophysical objects,
and the processes leading to magnetic field flux loss from such
objects are discussed with attention to the suppression of turbulent
diffusion by back-reaction of magnetic fields on small spatial scales,
and on the constraint imposed on magnetic flux loss by flux-freezing
within stars. Turbulent magnetic diffusion can be suppressed even for
very weak large-scale magnetic fields, so that 'standard' turbulent
diffusion is incapable of significant magnetic flux destruction within
a star. Finally, magnetic flux loss via winds is shown to be generally
ineffective, no matter what the value of the effective magnetic Reynolds
number is.
Title: Magnetic Confinement, Alfven Wave Reflection, and the Origins
of X-Ray and Mass-Loss ``Dividing Lines'' for Late-Type Giants
and Supergiants
Authors: Rosner, R.; An, C. -H.; Musielak, Z. E.; Moore, R. L.; Suess,
S. T.
Bibcode: 1991ApJ...372L..91R
Altcode:
A simple qualitative model for the origin of the coronal and mass-loss
dividing lines separating late-type giants and supergiants with and
without hot, X-ray-emitting corona, and with and without significant
mass loss is discussed. The basic physical effects considered are
the necessity of magnetic confinement for hot coronal material on the
surface of such stars and the large reflection efficiency for Alfven
waves in cool exponential atmospheres. The model assumes that the
magnetic field geometry of these stars changes across the observed
'dividing lines' from being mostly closed on the high effective
temperature side to being mostly open on the low effective temperature
side.
Title: On Magnetic Diffusion in a Turbulent Fluid
Authors: Vainshtein, S.; Cattaneo, F.; Rosner, R.
Bibcode: 1991BAAS...23.1049V
Altcode:
No abstract at ADS
Title: On the generation of magnetic tube waves in the solar
convection zone.
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.; Gail, P.
Bibcode: 1991BAAS...23.1037M
Altcode:
No abstract at ADS
Title: The Finite-Amplitude Behavior of the Joule Mode under
Astrophysical Conditions
Authors: Bodo, G.; Massaglia, S.; Rosner, R.; Ferrari, A.
Bibcode: 1991ApJ...370..398B
Altcode:
Magnetized astrophysical plasmas reveal a great deal of structure when
spatially resolved. One possible explanation for this structuring
is based on the existence of filamenting instabilities driven by
radiation. In this paper, previous linear calculations are extended
by considering the weakly nonlinear (finite-amplitude) development of
such filamenting instabilities in magnetized unstratified plasmas. It
is shown that under most conditions these instabilities (in particular,
the Jouse model) are unstable at finite amplitude; in particular, in
the temperature and plasma-beta domains characteristic of, for example,
much of the solar transition region, these modes - which can be linearly
stable under these conditions - become unstable to finite-amplitude
perturbations. The relevance of this to the problem of heating the
solar low transition region by current dissipation is discussed.
Title: On the Generation of Magnetic Tube Waves in the Solar
Convection Zone
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.; Gail, P.
Bibcode: 1991BAAS...23Q1037M
Altcode:
No abstract at ADS
Title: Solar astronomy
Authors: Rosner, Robert; Noyes, Robert; Antiochos, Spiro K.; Canfield,
Richard C.; Chupp, Edward L.; Deming, Drake; Doschek, George A.;
Dulk, George A.; Foukal, Peter V.; Gilliland, Ronald L.
Bibcode: 1991aap..reptR....R
Altcode:
An overview is given of modern solar physics. Topics covered include
the solar interior, the solar surface, the solar atmosphere, the Large
Earth-based Solar Telescope (LEST), the Orbiting Solar Laboratory, the
High Energy Solar Physics mission, the Space Exploration Initiative,
solar-terrestrial physics, and adaptive optics. Policy and related
programmatic recommendations are given for university research and
education, facilitating solar research, and integrated support for
solar research.
Title: Mechanisms of Chromospheric and Coronal Heating
Authors: Ulmschneider, Peter; Priest, Eric R.; Rosner, Robert
Bibcode: 1991mcch.conf.....U
Altcode: 1991QB809.M43......
One of the great problems of astrophysics is the unanswered
question about the origin and mechanism of chromospheric and coronal
heating. Just how these outer stellar envelopes are heated is of
fundamental importance, since all stars have hot chromospheric and
coronal shells where the temperature rises to millions of degrees,
comparable to the temperatures in the stars' cores. Here for the first
time is a comprehensive inventory of the proposed chromospheric and
coronal heating theories. The proposed heating processes are critically
compared, and the observational evidence for the various mechanisms
is reviewed. This is essential reading for all those working in such
fields as stellar activity, radio and XUV emission, rotation, and mass
loss, for whom a detailed and consistent presentation of our knowledge
of chromospheric and coronal heating mechanisms is urgently needed.
Title: On the theory of mass loss from late-type stars.
Authors: Rosner, R.
Bibcode: 1991cwlt.conf...81R
Altcode:
The author reviews the theory of mass loss from stars as it applies to
late-type stars, and in particular to giants and supergiants in the
G to K spectral type range. The basic conclusion is that there is as
yet no complete explanation for mass loss from giants and supergiants.
Title: Magnetic Confinement, Alfvén Wave Reflection, and the Origin
of X-ray and Mass Loss "Dividing Lines"
Authors: An, C. -H.; Rosner, R.; Musielak, Z. E.; Moore, R. L.; Suess,
S. T.
Bibcode: 1991mcch.conf..445A
Altcode:
No abstract at ADS
Title: Implications for Coronal Heating Theories from Stellar X-ray
Observations (With 5 Figures)
Authors: Rosner, R.
Bibcode: 1991mcch.conf..287R
Altcode:
No abstract at ADS
Title: Numerical Simulations of Thermal Instabilities in Stratified
Gases
Authors: Malagoli, A.; Rosner, R.; Fryxell, B.
Bibcode: 1990MNRAS.247..367M
Altcode:
We present a set of numerical two-dimensional simulations of initially
isobaric perturbations in a thermally unstable, optically thin,
radiating and gravitationally stratified ionized fluid. Our study
was initially motivated by the problem of the nonlinear evolution of
isobaric perturbations in typical regions of cooling flows in galaxy
clusters, but the results have applicability beyond this particular
physical case. We show that buoyancy effects substantially change
the nature of the thermal instability, as predicted previously by
linear analyses. The final behaviour of the instability, however, does
not resemble previous predictions based on either linear theory or
more qualitative analysis. For example, we find that a bubble-shaped
isobaric perturbation typically undergoes Rayleigh-Taylor and shear
flow instabilities, which can disrupt the bubble on a time comparable
to the oscillation period about its equilibrium position. Even when
completely disrupted, the bubble tends to oscillate about its previous
equilibrium position; there is no sign for a continuing monotonic
thermal instability. Indeed, the simulations strongly suggest that
the perturbation is ultimately dispersed by vortical circulations
triggered by the Rayleigh-Taylor and shear flow instabilities. Thus,
initially isobaric thermal instabilities do not seem to be an efficient
mechanism for removing the gas in the inner region of a cooling flow.
Title: Einstein Observatory Coronal Temperatures of Late-Type Stars
Authors: Schmitt, J. H. M. M.; Collura, A.; Sciortino, S.; Vaiana,
G. S.; Harnden, F. R., Jr.; Rosner, R.
Bibcode: 1990ApJ...365..704S
Altcode:
The results are presented of a survey of the coronal temperatures
of late-type stars using the Einstein Observatory IPC. The spectral
analysis shows that the frequently found one- and two-temperature
descriptions are mainly influenced by the SNR of the data and that
models using continuous emission measure distributions can provide
equally adequate and physically more meaningful and more plausible
descriptions. Intrinsic differences in differential emission
measure distributions are found for four groups of stars. M dwarfs
generally show evidence for high-temperature gas in conjunction with
lower-temperature material, while main-sequence stars of types F and
G have the high-temperature component either absent or very weak. Very
hot coronae without the lower-temperature component appearing in dwarf
stars are evident in most of the giant stars studied. RS CVn systems
show evidence for extremely hot coronae, sometimes with no accompanying
lower-temperature material.
Title: Relationship between Optical and X-Ray Properties of O-Type
Stars Surveyed with the Einstein Observatory
Authors: Sciortino, S.; Vaiana, G. S.; Harnden, F. R., Jr.; Ramella,
M.; Morossi, C.; Rosner, R.; Schmitt, J. H. M. M.
Bibcode: 1990ApJ...361..621S
Altcode:
An X-ray luminosity function is derived for a representative
volume-limited sample of O-type stars selected from the catalog
of Galactic O stars surveyed with the Einstein Observatory. It was
found that, for the stars of this sample which is ten times larger
than any previously analyzed, the level of X-ray emission is strongly
correlated with bolometric luminosity, confirming previous findings of
an Lx-L(bol) relationship (e.g., Harnden et al., 1979; Pallavicini et
al., 1981). Correlations between the Lx and the mass loss rate with the
wind terminal velocity or with the rotation rate were weak. However,
there was a strong correlation with wind momentum flux as well as with
the wind kinetic energy flux.
Title: X-ray emission from normal stars
Authors: Rosner, Robert
Bibcode: 1990AIPC..211...11R
Altcode: 1990heac.work...11R
With the closing of the Einstein and EXOSAT eras, the characteristics
of stellar x-ray emission are now fairly well understood, but the more
fundamental reasons why there is any x-ray emission at all is not at
all well understood. Future x-ray missions will have to play a key
role in unraveling this mystery.
Title: Book Review: Wave phenomena: theoretical, computational,
and practical aspects / Springer-Verlag
Authors: Rosner, R.
Bibcode: 1990SoPh..127..209R
Altcode: 1990SoPh..127..209L
No abstract at ADS
Title: Numerical simulations of soft and hard turbulence: Preliminary
results for two-dimensional convection
Authors: Deluca, E. E.; Werne, J.; Rosner, R.; Cattaneo, F.
Bibcode: 1990PhRvL..64.2370D
Altcode:
We report results on the transition from soft to hard turbulence in
simulations of 2D Boussinesq convection. The computed probability
densities for temperature fluctuations are exponential in form in both
soft and hard turbulence, unlike what is observed in experiments; in
contrast, we obtain a change in the Nusselt number scaling on Rayleigh
number in good agreement with the 3D experiments.
Title: Book reviews
Authors: Bahcall, J. N.; Rosner, R.
Bibcode: 1990SoPh..127..209B
Altcode:
No abstract at ADS
Title: The solar probe mission
Authors: Feldman, W. C.; Anderson, J.; Bohlin, J. D.; Burlaga, L. F.;
Farquhar, R.; Gloeckler, G.; Goldstein, B. E.; Harvey, J. W.; Holzer,
T. E.; Jones, W. V.; Kellogg, P. J.; Krimigis, S. M.; Kundu, M. R.;
Lazarus, A. J.; Mellott, M. M.; Parker, E. N.; Rosner, R.; Rottman,
G. J.; Slavin, J. A.; Suess, S. T.; Tsurutani, B. T.; Woo, R. T.;
Zwickl, R. D.
Bibcode: 1990AIPC..203..101F
Altcode: 1990pacr.rept..101F
The Solar Probe will deliver a 133.5 kg science payload into a 4 Rs
perihelion solar polar orbit (with the first perihelion passage in 2004)
to explore in situ one of the last frontiers in the solar system-the
solar corona. This mission is both affordable and technologically
feasible. Using a payload of 12 (predominantly particles and
fields) scientific experiments, it will be possible to answer many
long-standing, fundamental problems concerning the structure and
dynamics of the outer solar atmosphere, including the acceleration,
storage, and transport of energetic particles near the Sun and in the
inner (<65 Rs) heliosphere.
Title: Coronal Temperatures of Late-type Stars
Authors: Harnden, F. R., Jr.; Schmitt, J. H. M. M.; Rosner, R.;
Collura, A.; Vaiana, G. S.
Bibcode: 1990BAAS...22..858H
Altcode:
No abstract at ADS
Title: X-ray studies of coeval star samples. III. X-ray emission in
the UrsaMajor stream.
Authors: Schmitt, J. H. M. M.; Micela, G.; Sciortino, S.; Vaiana,
G. S.; Harnden, F. R., Jr.; Rosner, R.
Bibcode: 1990ApJ...351..492S
Altcode:
Results are reported from a comprehensive survey of X-ray emission
from stars known or suspected to be members of the UMa cluster and/or
stream. Of the 42 UMa member stars surveyed, 18 were detected as
X-ray sources, and spectral analysis was performed for 10 stars
with sufficient X-ray counts. Consideration is given to relations
between X-ray luminosity, color, and kinematics of the sample
stars, and the X-ray spectra of the UMa stars are discussed in the
context of the general problem of stellar X-ray temperatures. Also
confirmed is the lack of X-ray-emitting A dwarfs among UMa members;
among stars of later spectra type there is a rather large dispersion
in X-ray luminosity. This dispersion cannot readily be explained by
contamination with field star interlopers and appears rather to be a
property of the UMa X-ray luminosity distribution function.
Title: The X-Ray Emission of Late Type Evolved Stars
Authors: Maggio, A.; Vaiana, G. S.; Haisch, B. M.; Stern, R. A.;
Harnden, F. R., Jr.; Rosner, R.
Bibcode: 1990ixra.conf..233M
Altcode:
No abstract at ADS
Title: The Einstein Survey of O-Stars
Authors: Sciortino, S.; Vaiana, G. S.; Harnden, F. R., Jr.; Ramella,
M.; Morossi, C.; Rosner, R.; Schmitt, J. H. M. M.
Bibcode: 1990ixra.conf..227S
Altcode: 1990ixra.symp..227S
The authors give a brief account of some of the main results of a
detailed analysis of a sample of 288 X-ray surveyed O stars.
Title: Einstein Observatory Magnitude-limited X-Ray Survey of
Late-Type Giant and Supergiant Stars
Authors: Maggio, A.; Vaiana, G. S.; Haisch, B. M.; Stern, R. A.;
Bookbinder, J.; Harnden, F. R., Jr.; Rosner, R.
Bibcode: 1990ApJ...348..253M
Altcode:
Results are presented of an extensive X-ray survey of 380 giant and
supergiant stars of spectral types from F to M, carried out with
the Einstein Observatory. It was found that the observed F giants
or subgiants (slightly evolved stars with a mass M less than about 2
solar masses) are X-ray emitters at the same level of main-sequence
stars of similar spectral type. The G giants show a range of emissions
more than 3 orders of magnitude wide; some single G giants exist with
X-ray luminosities comparable to RS CVn systems, while some nearby
large G giants have upper limits on the X-ray emission below typical
solar values. The K giants have an observed X-ray emission level
significantly lower than F and F giants. None of the 29 M giants were
detected, except for one spectroscopic binary.
Title: Largescale Structures of the Soft X-Ray Background
Authors: Micela, G.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R.,
Jr.; Rosner, R.
Bibcode: 1990ixra.conf..247M
Altcode: 1990ixra.symp..247M
The Imaging Proportional Counter on board the Einstein Observatory
has measured the soft (0.15 - 3.5) keV X-ray background in ≡4000
directions unevenly spaced on the sky. The authors summarize the main
results of this survey.
Title: A brief introduction to coronal 'loops'
Authors: Rosner, Robert
Bibcode: 1990GMS....58..189R
Altcode:
A discussion is presented of elementary aspects of the physics of
coronal loops, in order to more securely approach the question of their
existence. It is noted that the time-scales for pressure equilibration
are far shorter than typical cooling times in loop structures, and
that the loop structures are accordingly in pressure balance with
their surroundings. Those surroundings, however, are dark, implying
a decreased density and gas pressure outside the bright loops. It is
deduced that the loop interiors must have a weaker magnetic field than
the gas immediately outside them.
Title: X-Ray Studies of Coeval Star Samples. II. The Pleiades Cluster
as Observed with the Einstein Observatory
Authors: Micela, G.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R.,
Jr.; Rosner, R.; Schmitt, J. H. M. M.
Bibcode: 1990ApJ...348..557M
Altcode:
Coronal X-ray emission of the Pleiades stars is investigated, and
maximum likelihood, integral X-ray luminosity functions are computed
for Pleiades members in selected color-index ranges. A detailed
search is conducted for long-term variability in the X-ray emission
of those stars observed more than once. An overall comparison of the
survey results with those of previous surveys confirms the ubiquity
of X-ray emission in the Pleiades cluster stars and its higher rate
of emission with respect to older stars. It is found that the X-ray
emission from dA and early dF stars cannot be proven to be dissimilar to
that of Hyades and field stars of the same spectral type. The Pleiades
cluster members show a real rise of the X-ray luminosity from dA stars
to early dF stars. X-ray emission for the young, solarlike Pleiades
stars is about two orders of magnitude more intense than for the nearby
solarlike stars.
Title: Generation of Transverse Magnetic Tube Waves and X-Ray
Emissions from Late-Type Dwarfs
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.
Bibcode: 1990ASPC....9...79M
Altcode: 1990csss....6...79M
The X-ray emissions observed in late-type stars are shown to be
associated with transverse magnetic tube waves generated in stellar
convective zones. The heating theory is examined to insure that it
accounts for the mechanical energy flux associated with the wide range
of X-ray emissions for each spectral type, and the inhomogeneous and
locally strong magnetic fields in stellar atmospheres. The values of
the free parameters from the wave-heating model developed agree with
observational data, and the tube waves can account for the observed
X-ray emissions of F, G, and K dwarfs.
Title: A Mechanism for the Increase in Stellar Wind Mass Loss from
Giants across the Dividing Line
Authors: An, C. H.; Musielak, Z. E.; Rosner, R.; Moore, R. L.; Suess,
S. T.
Bibcode: 1990ASPC....9...70A
Altcode: 1990csss....6...70A
No abstract at ADS
Title: Winds from Hot Accretion Disks
Authors: Takahara, Fumio; Rosner, Robert; Kusunose, Masaaki
Bibcode: 1989ApJ...346..122T
Altcode:
Hydrodynamical winds from hot accretion disks around compact objects
are investigated using a simplified model. The flow pattern above the
disk is solved assuming that specific angular momentum is conserved
along a stream line and that the radial component of the gravitational
force balances the centrifugal force everywhere. An isothermal or
polytropic relation is also assumed. It is shown that there exists a
critical solution for which the flow is subsonic at the disk plane
and becomes supersonic beyond the critical point. The mass-loss
rate is calculated for the critical solution, and it turns out to be
comparable to the accretion rate if the temperature is near the virial
temperature. Thus wind loss will significantly affect the properties
of hot two-temperature accretion disks.
Title: The generation of MHD waves by forced turbulence in a weakly
magnetized fluid
Authors: Rosner, R.; Musielak, Z. E.
Bibcode: 1989A&A...219L..27R
Altcode:
The effect of the fluctuating buoyancy force on wave generation in a
weakly magnetized plasma is considered. As expected, the efficiency of
MHD wave generation is enhanced by including this force. However, it
remains true that the observed variation of coronal emission at fixed
spectral type cannot be accounted for by a wave generation process of
the type discussed here.
Title: On the Stability of Magnetized Rotating Jets: The Axisymmetric
Case
Authors: Bodo, G.; Rosner, R.; Ferrari, A.; Knobloch, E.
Bibcode: 1989ApJ...341..631B
Altcode:
The stability of a nonrelativistic, magnetized rotating flow to
Kelvin-Helmholtz modes is discussed, using numerical methods for the
analysis of the dispersion relation which allow complete and systematic
mode classification. In the initial study presented here, attention
is restricted to the axisymmetric case, giving sole attention to the
vortex-sheet approximation. Major results include (1) interpretation of
the reflected modes in terms of negative energy modes; (2) correction
of previous results on the route to destabilization of reflected modes;
(3) explanation of multiple maxima in the reflection mode growth rate
as a function of Mach number; (4) discovery of a new unstable mode for
magnetized, nonrotating beams which can be as important as the ordinary
mode in a limited Mach number regime; and (5) the derivation of new
unstable inertial modes for rotating jets. Some of the astrophysical
implications of this study are noted.
Title: Variability of X-Ray Emission from OB Stars
Authors: Collura, A.; Sciortino, S.; Serio, S.; Vaiana, G. S.; Harnden,
F. R., Jr.; Rosner, R.
Bibcode: 1989ApJ...338..296C
Altcode:
The variability in soft X-ray emission of 12 OB stars is studied. Two
different methods of analysis, one more suitable for detecting
short-term variations, the other aimed at detecting long time-scale
variations, are applied to all stars in the sample. The long-term
variability analysis shows that Cyg-OB2 8A Zeta Pup and Delta Ori
exhibit significant count rate variations between different data
sections. Similar variations are marginally detected in 15 Mon; the
count rate variations for the other eight stars are consistent with
statistical fluctuations. The light curve of Cyg-OB2 8A suggests the
existence of two different emission levels. The short-term variability
analysis detects marginal variability in Tau Sco with an effective
amplitude of about 30 percent and a time scale of about 50 s. The
upper limits to the effective short-term variability amplitude for
all other sample stars are in the 10-30 percent range.
Title: The Role of Alfven Wave Trapping in the Acceleration of
Stellar Winds from Late-Type Giants and Supergiants
Authors: An, C. -H.; Musielak, Z. E.; Rosner, R.; Suess, S. T.; Moore,
R. L.
Bibcode: 1989BAAS...21..792A
Altcode:
No abstract at ADS
Title: Can Magnetic Tube Waves Account for X-ray Emissions Observed
from Late-Type Dwarfs
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.
Bibcode: 1989BAAS...21..796M
Altcode:
No abstract at ADS
Title: Subphotospheric Excitation of Alfven Waves and Their Role in
the Solar Atmosphere
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.; Moore, R. L.
Bibcode: 1989BAAS...21R.830M
Altcode:
No abstract at ADS
Title: Nonlinear Parker Instability of Isolated Magnetic Flux in
a Plasma
Authors: Shibata, K.; Tajima, T.; Matsumoto, R.; Horiuchi, T.; Hanawa,
T.; Rosner, R.; Uchida, Y.
Bibcode: 1989ApJ...338..471S
Altcode:
The nonlinear evolution of the Parker instability in an isolated
horizontal magnetic-flux sheet embedded in a two-temperature layer
atmosphere is studied by using a two-dimensional MHD code. In the solar
case, this two-layer model is regarded as a simplified abstraction
of the sun's photosphere/chromosphere and its overlying much hotter
(coronal) envelope. The horizontal flux sheet is initially located
in the lower temperature atmosphere so as to satisfy magnetostatic
equilibrium under a constant gravitational acceleration. Ideal
MHD is assumed, and only perturbations with k parallel to the
magnetic-field lines are investigated. As the instability develops,
the gas slides down the expanding loop, and the evacuated loop rises as
a result of enhanced magnetic buoyancy. In the nonlinear regime of the
instability, both the rise velocity of a magnetic loop and the local
Alfven velocity at the top of the loop increase linearly with height
and show self-similar behavior with height as long as the wavelength
of the initial perturbation is much smaller than the horizontal size
of the computing domain.
Title: On Magnetic Fields, Heating and Thermal Conduction in Halos,
and the Suppression of Cooling Flows
Authors: Rosner, R.; Tucker, W. H.
Bibcode: 1989ApJ...338..761R
Altcode:
We discuss the physics of thermal heat transport in halos of giant
elliptical galaxies and clusters of galaxies and the consequences for
cooling flows in such halos. We demonstrate that--contrary to widespread
belief-- "tangled" magnetic fields do not reduce the effect of thermal
conduction by an amount sufficient to allow one to ignore conduction
in cooling flows. Thus, when thermal conduction is included, one can
explain the observed density and temperature profiles with the rate of
mass inflow reduced from the values commonly quoted in the literature
by about a factor of 3-10 for M87. This effect, possibly in conjunction
with very modest amounts of heating (possibly as a result of accretion
onto, for example, a central black hole), can regulate the cooling flow
in a thermally stable manner at mass accretion rates of less than 0.1
M_sun_ yr^-1^.
Title: Interaction Between Forced Turbulent Flow Field and Intense
Magnetic Flux Tubes
Authors: Rosner, R.; Musielak, Z. E.; Ulmschneider, P.
Bibcode: 1989BAAS...21..844R
Altcode:
No abstract at ADS
Title: On the Two-Dimensional Inversion of Helioseismology Data to
Obtain the Internal Rotation Curve of the Sun
Authors: Horner, S.; Rosner, R.; Deluca, E. E.; Jeffrey, W.
Bibcode: 1989BAAS...21..842H
Altcode:
No abstract at ADS
Title: On the effects of Cosmions upon the structure and evolution
of very low mass stars
Authors: Deluca, E. E.; Griest, K.; Rosner, R.; Wang, J.
Bibcode: 1989STIN...8920880D
Altcode:
A number of recent studies have suggested that cosmions, or WIMPS,
may play an important role in the energetics of the solar interior;
in particular, it has been argued that these hypothetical particles
may transport sufficient energy within the nuclear-burning solar core
so as to depress the solar core temperature to the point of resolving
the solar neutrino problem. Solutions to the solar neutrino problem
have proven themselves to be quite nonunique, so that it is of some
interest whether the cosmion solution can be tested in some independent
manner. It is argued that if cosmions solve the solar neutrino problem,
then they must also play an important role in the evolution of low mass
main sequence stars; and, second, that if they do so, then a simple
(long mean free path) model for the interaction of cosmions with
baryons leads to changes in the structure of the nuclear-burning core
which may be in principal observable. Such changes include suppression
of a fully-convective core in very low mass main sequence stars; and a
possible thermal runaway in the core of the nuclear burning region. Some
of these changes may be directly observable, and hence may provide
independent constraints on the properties of the cosmions required to
solve the solar neutrino problem, perhaps even ruling them out.
Title: On the Generation of Flux Tube Waves in Stellar Convection
Zones. I. Longitudinal Tube Waves Driven by External Turbulence
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.
Bibcode: 1989ApJ...337..470M
Altcode:
The source functions and the energy fluxes for wave generation in
magnetic flux tubes embedded in an otherwise magnetic field-free,
turbulent, and compressible fluid are derived. The calculations
presented here assume that the tube interior is not itself turbulent,
e.g., that motions within the flux tube are due simply to external
excitation. Specific results for the generation of longitudinal tube
waves are presented.
Title: Numerical simulations of thermal instabilities in galactic
and cluster halos
Authors: Peres, G.; Rosner, R.; Bodo, G.
Bibcode: 1989MmSAI..60..139P
Altcode:
X-ray observations have shown the presence of diffuse hot gas in
many clusters of galaxies and around some elliptical galaxies. It is
typically expected that radiative cooling in the central region of
these halos drives significant subsonic inflow of gas to the center
of the system. Steady infall models of such flows typically predict
that the gas will 'drop out' of the flow, so that the mass accretion
rate is a function of radius. The plausible mechanism that removes
some fraction of the gas from the flow at various radii is thermal
instability in the cooling flow itself. Here, results are reported of
a fully nonlinear analysis of the monotonic radial modes in a cooling
flow which uses physical parameters appropriate to the cooling flow
of M87. A case of spontaneous formation of the radiative instability
at the center of the halo is described and the relevance of thermal
conductivity in determining the stability is shown.
Title: An Einstein Observatory view of large-scale (equal to or
greater than 1 deg) soft X-ray background structures - A status report
Authors: Micela, G.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R.,
Jr.; Rosner, R.
Bibcode: 1989MmSAI..60..239M
Altcode:
The status report of an ongoing study of both spectral and intensity
structures of X-ray background in the band (0.03-3.5) keV as observed by
the Imaging Proportional Counter (IPC) on board the Einstein Observatory
is presented. Preliminary results indicate the existence of very large
scale (much larger than 1 deg) structures and suggest the presence of
large-scale variation (greater than 1 deg) both in background spectrum
and intensity.
Title: On the Galactic Dynamo
Authors: Rosner, R.; Deluca, E.
Bibcode: 1989IAUS..136..319R
Altcode:
No abstract at ADS
Title: An update on X-ray emission from stars
Authors: Rosner, R.
Bibcode: 1989HiA.....8..521R
Altcode:
No abstract at ADS
Title: A magnitude limited X-ray survey of late-type evolved stars
with the Einstein Observatory
Authors: Maggio, A.; Vaiana, G. S.; Harnden, F. R., Jr.; Rosner, R.
Bibcode: 1989MmSAI..60..217M
Altcode:
A survey establishing the X-ray emission regime of giant and supergiant
stars is used to obtain insight into the relationship between the
stellar evolution and the stellar magnetic dynamo mechanism, as well
as the existence of a dividing line in the H-R diagram separating
solar-type and non-solar-type stars from the point of view of the
X-ray activity. Extensive analyses are performed on 429 star images,
taking advantage of the final REV-1 data processing and the Einstein
Observatory Stellar X-ray database.
Title: On the relationship between the topology of magnetic field
lines and flux surfaces
Authors: Rosner, R.; Low, B. C.; Tsinganos, K.; Berger, M. A.
Bibcode: 1989GApFD..48..251R
Altcode:
We consider the topological relationship between magnetic field
lines and magnetic flux surfaces. Magnetic helicity provides the
most elementary description of the topology of magnetic field lines
in terms of their linkage. In a simply-connected volume, a sufficient
but not necessary condition for the total magnetic helicity to vanish
is that there exist two independent families of globally-extendable
flux surfaces (given by the level surfaces of Euler potentials). In
contrast, the existence of two distinct global Euler potentials for
multiply-connected volumes is insufficient to guarantee that the total
magnetic helicity vanishes. These well-known results are discussed
in the context of Frobenius' theorem as applied to the differential
equations describing magnetic lines of force; and the notion of Euler
potentials is extended by introducing an analogy to the Hopf map
between the three-sphere and the two-sphere.
Title: An Einstein Observatory View of Large-Scale Soft X-ray
Background Structures: A Status Report
Authors: Micela, G.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R.,
Jr.; Rosner, R.; Schmitt, J. H. M. M.
Bibcode: 1988feta.conf...28M
Altcode:
No abstract at ADS
Title: Coronal Temperatures of late-type stars
Authors: Collura, A.; Schmitt, J. H. M. M.; Sciortino, S.; Vaiana,
G. S.; Harnden, F. R., Jr.; Rosner, R.
Bibcode: 1988feta.conf...14C
Altcode:
No abstract at ADS
Title: The X-ray Emission of Late-Type Giant and Supergiant Stars:
Results of the Einstein Observatory Magnitude-Limited X-ray Survey
Authors: Maggio, A.; Vaiana, G. S.; Haisch, B. M.; Stern, R. A.;
Harnden, F. R.; Rosner, R.
Bibcode: 1988feta.conf...12M
Altcode:
No abstract at ADS
Title: Relationship between Optical and X-ray Properties of O-type
Stars Surveyed by Einstein
Authors: Sciortino, S.; Harnden, F. R., Jr.; Ramella, M.; Morossi,
C.; Rosner, R.; Schmitt, J. H. M. M.; Vaiana, G. S.
Bibcode: 1988feta.conf...13S
Altcode:
No abstract at ADS
Title: The Equilibrium Structure of a Thin Magnetic Flux
Tube. III. The Effects of Molecular CO Absorption
Authors: Massaglia, S.; Bodo, G.; Kalkofen, W.; Rosner, R.
Bibcode: 1988ApJ...333..925M
Altcode:
The authors determine the structure of a stellar atmosphere and
of a thin magnetic flux tube embedded in it, taking the opacity by
H- and carbon monoxide into account. It is found that CO
has a strong cooling effect on the external atmosphere. For effective
temperatures below ≡5900K, the surface temperature of the atmosphere
with H- and CO opacity is much lower than with H-
alone. In the interior of the flux tube the equations can have multiple
solutions. Thus hot flux tubes can exist in a cool atmosphere even in
the absence of nonradiative heating.
Title: X-ray Emission from Stellar Coronae
Authors: Rosner, R.
Bibcode: 1988BAAS...20.1025R
Altcode:
No abstract at ADS
Title: On the Generation of Magnetohydrodynamic Waves in a Stratified
and Magnetized Fluid. II. Magnetohydromagnetic Energy Fluxes for
Late-Type Stars
Authors: Musielak, Z. E.; Rosner, R.
Bibcode: 1988ApJ...329..376M
Altcode:
Magnetohydrodynamic (MHD) wave energy fluxes for late-type stars are
calculated, using previously obtained formulae for the source functions
for the generation of MHD waves in a stratified, but otherwise uniform,
turbulent atmosphere; the magnetic fields in the wave generation
region are assumed to be homogeneous. In contradiction to previous
results, it is shown that in this uniform magnetic field case there is
no significant increase in the efficiency of MHD wave generation, at
least within the theory's limits of applicability. The major results are
that the MHD energy fluxes calculated for late-type stars are less than
those obtained for compressible modes in the magnetic field-free case,
and that these MHD energy fluxes do not vary enough for a given spectral
type to explain the observed range of UV and X-ray fluxes from such
stars. It is therefore concluded that MHD waves in stellar atmospheres
with homogeneous magnetic fields in the wave generation region cannot
explain the observed stellar coronal emissions; if such MHD waves are
responsible for a significant component of stellar coronal heating,
then nonuniform fields within the generation region must be appealed to.
Title: Hydrodynamic Modeling of an X-Ray Flare on Proxima Centauri
Observed by the Einstein Telescope
Authors: Reale, F.; Peres, G.; Serio, S.; Rosner, R.; Schmitt,
J. H. M. M.
Bibcode: 1988ApJ...328..256R
Altcode:
Hydrodynamic numerical calculations of a flare which occurred on Proxima
Centauri and was observed by the Einstein satellite on August 20, 1980
at 12:50 UT are presented. The highlights of the hydrodynamic code
are reviewed, and the physical and geometrical parameters necessary
for the calculations are derived and compared with observations. The
results are consistent with the stellar flare being caused by the
rapid dissipation of 5.9 x 10 to the 31st ergs, within a magnetic loop
structure whose semilength is 7 x 10 to the 9th cm and cross-sectional
radius is 7.3 x 10 to the 8th cm. The results provide evidence that
flares on late-type stars can be described by a hydrodynamic model
with a relatively simple geometry, similar to solar compact flares.
Title: Nonlinear Filamentation Instability
Authors: Steinolfson, R. S.; Rosner, R.
Bibcode: 1988BAAS...20Q.714S
Altcode:
No abstract at ADS
Title: Generation of MHD Waves by Convective Turbulence
Authors: Rosner, R.; Musielak, Z. E.
Bibcode: 1988BAAS...20..715R
Altcode:
No abstract at ADS
Title: The Einstein Observatory Survey of Stars in the Hyades
Cluster Region
Authors: Micela, G.; Sciortino, S.; Vaiana, G. S.; Schmitt,
J. H. M. M.; Stern, R. A.; Harnden, F. R., Jr.; Rosner, R.
Bibcode: 1988ApJ...325..798M
Altcode:
The authors report the results of an extensive X-ray investigation of
the Hyades region and improve upon previous studies by using refined
X-ray source detection algorithms and the complete set of Einstein
Observatory IPC exposures covering the Hyades cluster region (a total
of 63 1°×1° images). Using a somewhat more extensive and complete
compilation of optical candidates, the authors have detected 66 out
of 121 Hyades members falling in the combined fields of view. The
authors have also computed 3σ upper limits for all the nondetected
Hyades members and have derived maximum-likelihood X-ray luminosity
functions for the Hyades stars in selected spectral type ranges,
using both detections and upper limits.
Title: On Wind-Type Flows in Astrophysical Jets. III. Temporal
Evolution of Perturbations and the Formation of Shocks
Authors: Trussoni, E.; Ferrari, A.; Rosner, R.; Tsinganos, K.
Bibcode: 1988ApJ...325..417T
Altcode:
The temporal evolution of disturbances in a spherically symmetric
polytropic wind from a central object is studied. Such disturbances
may be due to localized momentum addition/subtraction, as, for example,
by MHD waves, heating/cooling mechanisms in the outflow, or localized
deviations from spherical symmetric expansion. The evolution of
an initial perturbed state to a continuous or discontinuous final
equilibrium state, as predicted by previous analytic calculations for
stationary flows, is followed. It is shown that some of the predicted
discontinuous equilibrium states are not physically accessible, while
the attainment of the remaining equilibrium states depends on both the
temporal and the spatial parameters characterizing the perturbation. The
results are derived for solar conditions, but in fact can be applied
to outflows in other astrophysical systems. In particular, applications
to the solar wind and flows in astrophysical jets are discussed.
Title: An Optimal Approach to the Inverse Problem
Authors: Jeffrey, W.; Rosner, R.
Bibcode: 1988IAUS..123..129J
Altcode:
The authors describe how remote sensing problems can be reformulated
within the framework of optimization theory. The inversion problem then
reduces to a search for the global extremum in the possible presence
of local extrema. Two algorithms are presented that can be used to
solve this global optimization problem, and their application to the
helioseismology inverse problem is detailed.
Title: The Stellar X-Ray Data Base of Einstein Image Observations
Authors: Micela, G.; Maggio, A.; Sciortino, S.; Vaiana, G. S.; Rosner,
R.; Harnden, F. R., Jr.; Schmitt, J. H. H. M.
Bibcode: 1988MmSAI..59..465M
Altcode:
No abstract at ADS
Title: The Einstein Observatory Stellar X-ray Database: an overview.
Authors: Sciortino, S.; Harnden, F. R., Jr.; Maggio, A.; Micela, G.;
Vaiana, G. S.; Schmitt, J.; Rosner, R.
Bibcode: 1988ESOC...28..483S
Altcode: 1988alds.proc..483S
The authors present the motivations for and the methodology followed
in building the "Einstein Observatory Stellar X-ray Database" based on
the uniform analysis of all Einstein Observatory Imaging Proportional
Counter fields obtained during the life of the HEAO-2 mission. The
database has been implemented using the INGRESTM database
system, so that statistical analyses of the properties of the full
detection catalog are relatively easily and flexibly accomplished. Some
illustrative examples will furnish a general view both of the kind
and the amount of the archived information, and of the statistical
approach used in analyzing the global properties of the data.
Title: The Stellar Composition of X-Ray Surveys from the Einstein
Observatory
Authors: Favata, F.; Rosner, R.; Sciortino, S.; Vaiana, G. S.
Bibcode: 1988ApJ...324.1010F
Altcode:
A new class of X-ray-luminous 'yellow' stellar objects which contributes
significantly to the stellar log N-log S distribution, but which
cannot be reconciled with normal G and K main-sequence stars. This
identification results from a new analysis of the stellar content
of three samples of X-ray-selected X-ray sources observed with the
Einstein Observatory, namely the 'Medium Sensitivity Survey', the 'High
Sensitivity Survey', and the 'Hyades Region Survey'. In this paper, both
X-ray and optical properties of the stellar samples in these surveys
are reported. The actual stellar content of the surveys is compared
with predictions based on current knowledge of stellar X-ray luminosity
functions and the stellar composition and spatial distribution in the
Galaxy. It is shown that a plausible identification for the excess
population of 'yellow' stars is with the active, RS CVn-like binaries.
Title: Finite amplitude stability of a plane shear layer
Authors: Bodo, G.; Rosner, R.; Ferrari, A.
Bibcode: 1988GApFD..43..333B
Altcode:
We analyze the finite amplitude stability of a planar shear layer
near the marginal stability point in the limit of large wavelengths
and small Reynolds numbers. We find a subcritical bifurcation and
therefore instability to finite amplitude perturbations where linear
analysis predicts stability. This result is opposite to that found
by previous analyses done in the high Reynolds number regime, where
a supercritical bifurcation was found.
Title: Quasi-Steady Outflows from Astrophysical Objects: Complementary
Views from Different Experiences.
Authors: Ferrari, Attilio; Rosner, Robert
Bibcode: 1988ASSL..142....3F
Altcode: 1988mosg.proc....3F
As a general introduction to the present workshop, the motivation
for joining the perspectives of solar, stellar, and extragalactic
astronomers, both theorists and experimentalists, on the problem of
mass outflows from astrophysical objects is discussed. Some of the
principal physical similarities and differences between outflows in
various astrophysical systems are illustrated, and it is shown that
experiences derived from different subject areas can help to build a
complete picture of the wind phenomenon.
Title: Evolution of Perturbations and Shock Formation in Stellar
Winds and Jets.
Authors: Trussoni, E.; Ferrari, A.; Rosner, R.; Tsinganos, K.
Bibcode: 1988ASSL..142..397T
Altcode: 1988mosg.proc..397T
The authors study the temporal evolution of disturbances in spherically
symmetric and polytropic winds from a central source. Such disturbances
may be due to localized momentum addition in the outflow, or localized
deviation from spherically symmetric expansion. The authors follow the
evolution of an initial steady state which is perturbed to a continuous
or discontinuous final equilibrium state, as predicted by previous
calculations of stationary flows. They show that some of the predicted
discontinuous equilibrium solutions are not physically accessible,
while the attainment of the other equilibrium solutions depends on
both temporal and spatial parameters characterizing the perturbation.
Title: Models of Solar-type coronae
Authors: Hartquist, T. W.; Rosner, R.
Bibcode: 1988ASSL..143..183H
Altcode: 1988acse.conf..183H
Simple models for the thermal and ionization structure of "closed"
stellar coronal structures (loops) are desdribed, for which the
heating rates are specified a priori. The authors discuss thermal
and MHD instabilities of such structures, as well as possible heating
mechanisms which have been considered.
Title: Simulations of the CA XIX Spectral Emission from a Flaring
Solar Crornal Loop. I. Thermal Case
Authors: Antonucci, E.; Dodero, M. A.; Peres, G.; Serio, S.; Rosner, R.
Bibcode: 1987ApJ...322..522A
Altcode:
Spectral profiles synthesized from the results of numerical simulations
of solar coronal loop plasma are compared with the observed line
profiles, and the sensitivity of this comparison to variations in
the parameter values is tested. The comparison allows the procedures
commonly adopted for obtaining temperatures and velocities directly
from the bent crystal spectrometer observations, as well as the
interpretation of parameters obtained from hydrodynamical calculations,
to be independently validated. The characteristic spectral signatures
of different models for the deposition of impulsive thermal energy
in the loop are derived assuming two distinct spatial distributions
of thermal heating: in one case, the heating function peaks near the
apex of the loop, while in the second, energy is deposited directly
in the lower atmosphere.
Title: An Einstein Observatory Stellar X-ray Catalog
Authors: Harnden, F. R., Jr.; Rosner, R.; Sciortino, S.; Maggio, A.;
Micela, G.; Vaiana, G. S.; Schmitt, J.
Bibcode: 1987BAAS...19.1040H
Altcode:
No abstract at ADS
Title: Nonlinear Parker Instability of an Isolated Magnetic Flux
Sheet in Astrophysical Plasmas
Authors: Shibata, K.; Tajima, T.; Matsuomoto, R.; Horiuchi, T.;
Hanawa, T.; Rosner, R.; Uchida, Y.
Bibcode: 1987BAAS...19.1030S
Altcode:
No abstract at ADS
Title: On the Thermal Instability of Galactic and Cluster Halos
Authors: Malagoli, A.; Rosner, R.; Bodo, G.
Bibcode: 1987ApJ...319..632M
Altcode:
The paper presents a detailed study of thermal instabilities in
cooling flows associated with galaxies and clusters of galaxies. In
the case of purely radiation-driven accretion onto a central object
such as the cD galaxy M87, it is found that the gas is largely subject
to overstability, rather than to monotonic instability. If thermal
conductivity is taken into account, the flow is stabilized on scales of
several kiloparsecs, even if the conductivity is appreciably reduced
(e.g., about 1 percent) with respect to the Spitzer value. In no case
are the globular perturbations (i.e., perturbations with comparable
radial and azimuthal dimensions) found to be monotonically unstable. The
paper presents numerical solutions of the local dispersion relation
for the cooling flow in M87 and discusses the possible consequences
of the results for a correct understanding of cooling flows.
Title: The Influence of a Magnetic Flux Tube on its Environment
Authors: Kalkofen, W.; Rosner, R.; Bodo, G.; Massaglia, S.
Bibcode: 1987BAAS...19..939K
Altcode:
No abstract at ADS
Title: A Computational Code for Two-dimensional Unsteady
Magnetohydrodynamics by the Method of Characteristics
Authors: Lou, Y. Q.; Rosner, R.; Ulmschneider, P.
Bibcode: 1987ApJ...315..349L
Altcode:
The authors present a computational code for solving two-dimensional,
time-dependent magnetohydrodynamic (MHD) equations by the method
of characteristics. The physical system under consideration is
axisymmetric, with vφ = 0 and Bφ = 0. The
numerical scheme is described in detail, and the results of calculations
are compared with two analytic solutions of the MHD equations: (1)
linearized, standing MHD wave motions in a magnetized cylindrical
plasma; (2) nonlinear self-similar expansion of a magnetized plasma
ball. In addition, the authors have studied the nonlinear development
of standing MHD wave solutions in a cylindrical plasma.
Title: On the Generation of Magnetohydrodynamic Waves in a Stratified
and Magnetized Fluid. I. Vertical Propagation
Authors: Musielak, Z. E.; Rosner, R.
Bibcode: 1987ApJ...315..371M
Altcode:
The generation of MHD waves by turbulent motions in a stratified medium
with an embedded uniform magnetic field, a topic which is relevant to
the study of the solar atmosphere, is considered. Both compressible
and incompressible MHD waves are treated in a one-dimensional approach;
however, the direction of the background magnetic field is permitted to
vary in an arbitrary direction. Theoretical expressions for MHD energy
fluxes are obtained as a function of wave frequency and multipole
coefficients. It is shown that monopole, dipole, and quadrupole
emissions are responsible for the generation of the compressible
components of the fast and slow modes. However, the incompressible
components and the Alfven modes can be generated by the dipole emission
only. Specific results obtained for special magnetic field geometries
are discussed for the fast and slow modes.
Title: Variability Analysis in Low Count Rate Sources
Authors: Collura, A.; Maggio, A.; Sciortino, S.; Serio, S.; Vaiana,
G. S.; Rosner, R.
Bibcode: 1987ApJ...315..340C
Altcode:
A method, based on the chi-square statistics, is described for detecting
pulselike time variability in low count rate sources observed with
photon-counting instruments. This method can be used even in the
presence of observational gaps, takes full advantage of the filtering
effect due to binning with different bin sizes, and takes into account
the arbitrariness introduced by the binning phase. The procedure
developed to limit the dependence of the results on the binning phase
and ensure statistically correct results is described along with
the application of the proposed procedure to a model of a variable
source. Monte Carlo simulations are used to show how the method can
be used to derive the characteristic variability time scales and that
the method is more sensitive than the nonparametric Kolmogorov-Smirnov
test in detecting variability to a given confidence level.
Title: Einstein Observatory Survey of X-Ray Emission from Solar-Type
Stars: The Late F and G Dwarf Stars
Authors: Maggio, A.; Sciortino, S.; Vaiana, G. S.; Majer, P.;
Bookbinder, J.; Golub, L.; Harnden, F. R., Jr.; Rosner, R.
Bibcode: 1987ApJ...315..687M
Altcode:
Results of a volume-limited X-ray survey of stars of luminosity classes
IV and V in the spectral range F7-G9 observed with the Einstein
Observatory are presented. Using survival analysis techniques, the
stellar X-ray luminosity function in the 0.15-4.0 keV energy band for
both single and multiple sources. It is shown that the difference in
X-ray luminosity between these two classes of sources is consistent
with the superposition of individual components in multiple-component
systems, whose X-ray properties are similar to those of the
single-component sources. The X-ray emission of the stars in our sample
is well correlated with their chromospheric CA II H-K line emission
and with their projected equatorial rotational velocity. Comparison
of the X-ray luminosity function constructed for the sample of the dG
stars of the local population with the corresponding functions derived
elsewhere for the Hyades, the Pleiades, and the Orion Ic open cluster
confirms that the level of X-ray emission decreases with stellar age.
Title: Current-driven Magnetohydrodynamic Thermal Instabilities in
Sheared Fields
Authors: Bodo, G.; Ferrari, A.; Massaglia, S.; Rosner, R.
Bibcode: 1987ApJ...313..432B
Altcode:
Approximate analytic solutions are sought for the dispersion
relation for the MHD stability of magnetized medium in current-driven
filamentation modes such as those observed in the solar atmosphere. The
magnetic field is assumed to have a self-consistent sheared equilibrium
structure. The analysis is carried out in the small wavenumber regime,
where shear length is similar to the mode wavelength. Instability
is found to depend on the ratio between the thermal and magnetic
diffusivities, i.e., the Prandtl number, which identifies the unstable
transverse wavenumbers. The instability conditions are expressed in
an algebraic equation amenable to numerical solution. Results are
provided from use of the model to determine the maximum growth rate
and typical scale lengths of instabilities in a precoronal atmosphere
and the lower transition region.
Title: Hydrodynamics of an X-Ray Flare on Proxima Centauri
Authors: Reale, F.; Peres, G.; Serio, S.; Rosner, R.; Schmitt,
J. H. M. M.
Bibcode: 1987LNP...291..179R
Altcode: 1987csss....5..179R; 1987LNP87.291..179R
We apply the Palermo-Harvard hydrodynamic numerical code to compute
the evolution of temperature, density, pressure and velocity in
a semicircular symmetric rigid loop to reproduce the Einstein IPC
observations of the 20 August 1980 flare on Proxima Centauri.
Title: Kelvin-Helmholtz instability of magnetized rotating jets.
Authors: Bodo, G.; Rosner, R.; Ferrari, A.; Knobloch, E.
Bibcode: 1987txra.symp..353B
Altcode:
No abstract at ADS
Title: MHD Wave Energy Fluxes for Late-Type Dwarfs
Authors: Rosner, R.; Musielak, Z. E.
Bibcode: 1987LNP...291...69R
Altcode: 1987csss....5...69R
We calculate the efficiency of MHD wave generation by turbulent motions
in the stratified stellar atmospheres of late-type main sequence
stars, under the assumption that the embedded magnetic fields are
uniform. In contradiction with previous results, we show that there is
no significant increase in the efficiency of wave generation because of
the presence of magnetic fields, at least within the theory's limits
of applicability. Thus, we show that MHD energy fluxes for late-type
stars whose surface magnetic fields are uniform are less than those
obtained for acoustic waves in a magnetic field-free atmosphere,
and do not vary enough for a given spectral type in order to explain
observed UV and X-ray fluxes. Thus, our results show that MHD energy
fluxes obtained if stellar surface magnetic fields are uniform cannot
explain the observed stellar coronal emissions.
Title: Explosive chromospheric instability in hydrodynamic loopflare
models:the problem and its cure.
Authors: Peres, G.; Serio, S.; Rosner, R.
Bibcode: 1987NCimB..99...15P
Altcode:
No abstract at ADS
Title: Nonlocal thermal conduction in hydrodynamic loop flare models.
Authors: Peres, G.; Rosner, R.; Serio, S.
Bibcode: 1987NCimB..99...29P
Altcode:
No abstract at ADS
Title: Line Broadening and Magnetic Reconnection at Flare Onset
Authors: Antonucci, E.; Rosner, R.; Tsinganos, K.
Bibcode: 1987sman.work...37A
Altcode:
The onset of solar flares is characterized by large non-thermal
soft X-ray line broadening, which can be attributed to isotropic
plasma flows within localized regions of reconnecting magnetic
fields; the reconnection in turn reflects structural instability
of the quasi-equilibrium magnetohydrodynamic structure in the flare
region. The authors show these hypotheses to be consistent with solar
flare data obtained with the Solar Maximum Mission (SMM) instruments.
Title: Magnetic Flux Tubes as Sources of Wave Generation
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.
Bibcode: 1987LNP...291...66M
Altcode: 1987csss....5...66M
Because solar (and, most likely, stellar) surface magnetic fields
are highly inhomogeneous, and show concentration into `flux tube'
structures, the wave energy generated in stellar convection zones
may be largely carried away by flux tube waves, which then become
important sources for the heating of the outer atmospheric layers. We
report calculations for longitudinal tube waves generated in magnetic
flux tubes embedded in an otherwise magnetic field-free, turbulent,
and stratified medium; we find that such waves are generated by dipole
emission, and that the generation efficiency is a strong function of
the magnetic field strength. We also present wave flux calculations
for magnetic flux tubes embedded in the solar convective zone; the
main result is that the longitudinal tube wave fluxes are at least 2
orders of magnitude too low to play a significant role in the heating
of the solar chromosphere.
Title: Generation of flux tube waves in stellar convection zones. 1:
Longitudinal tube waves
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.
Bibcode: 1987STIN...8824561M
Altcode:
The source functions and the energy fluxes are derived for wave
generation in magnetic flux tubes embedded in an otherwise magnetic-
field free, turbulent, and compressible fluid. Specific results for
the generation of longitudinal tube waves are presented.
Title: Joint Discussion on Topics of Sessions 1 and 2
Authors: Roca Cortés, T.; Rosner, R.
Bibcode: 1987rfsm.conf...61R
Altcode:
No abstract at ADS
Title: A model for collimated outflows in molecular clouds and the
case of HH 7-11
Authors: Silvestro, G.; Ferrari, A.; Rosner, R.; Trussoni, E.;
Tsinganos, K.
Bibcode: 1987Natur.325..228S
Altcode:
Collimated outflows of high-velocity gas, with typical scale lengths
of 0.01-0.2 pc, are often observed to be associated with linear chains
of optical emission knots1, sometimes connected by faint
nebulosities. The flows have been ascribed to the interaction between
an energetic wind ejected by a young stellar object and circumstellar
material. However, none of the acceleration and collimation mechanisms
proposed so far can easily account for the most peculiar properties
of the outflows, namely the almost constant spacing between the
knots, their radial motion and the abrupt velocity changes along the
flow, well illustrated by the prototype we use for our modelling,
HH 7-11. We suggest here a new interpretation of the phenomenon,
based on flows in a channel of variable cross-sectional area due to
Kelvin-Helmholtz instabilities between the flow and the ambient medium;
and present solutions of the Mach number equation for such a channel,
which possess multiple critical points and shocks identified with the
observed optical knots.
Title: Optimization Algorithms: Simulated Annealing and Neural
Network Processing
Authors: Jeffrey, W.; Rosner, R.
Bibcode: 1986ApJ...310..473J
Altcode:
Two algorithms which have been previously used for discrete
optimization, simulated annealing and neural network processing, are
developed and compared. It is demonstrated how these algorithms can be
used to find global extrema of functions, while avoiding trapping in
local extrema. In the standard treatment of neural network processors,
only quadratic and linear terms in the function variables are included
in the objective function. This traditional approach is extended to show
how constraints not expressible in quadratic and linear terms (e.g.,
entropy) can be incorporated into the function to be minimized. The
efficiency of the implementation of neural net processing is also
demonstrated, and it is shown how its speed advantage over more
traditional optimization techniques (even when implemented on serial
processors) is related to its convergence properties. An important
application of the results is in the interpretation of remote sensing
data, since typical indirect sensing problems can be readily cast into
the language of optimization theory; the methods presented here have the
particular ability to solve severely ill posed inversion problems. The
algorithms described here have been implemented on a serial processor
but are cast in a form which is ideally suited for parallel processing.
Title: On Strategies for Inverting Remote Sensing Data
Authors: Jeffrey, W.; Rosner, R.
Bibcode: 1986ApJ...310..463J
Altcode:
Attention is given to a number of methods for inverting remote sensing
data obtained in a variety of astronomical applications. Applications
include image restoration, inversion of helioseismological data to
obtain the internal rotation rate of stars such as the sun, fitting
of spectra (especially thermal line spectra) to grating or other
dispersed observed spectra, differential emission measure analysis, and
reconstruction of images derived from interferometric observations. The
results consider the tradeoff between resolution and variance and the
stability properties for each method and propose an inversion stragegy
using the available techniques.
Title: The Damping of the Alven Mode in Stochastic Astrophysical
Fluids
Authors: Lou, Y. Q.; Rosner, R.
Bibcode: 1986ApJ...309..874L
Altcode:
The properties of coherent small-amplitude Alfven waves propagating in
the presence of a strong mean background magnetic field in an infinitely
conducting, inviscid, cold, incompressible, and turbulent plasma are
investigated by using projection operator techniques. The coherent
Alfven mode is shown to be damped owing to the background fluctuations,
and the damping decrement is estimated for cases of relevence to MHD
wave propagation in the solar corona. One significant consequence
of these results is that long-wavelength Alfven modes may in fact be
effectively damped on time scales of the order of the Alfven crossing
time if the background atmosphere is only weakly unsteady.
Title: Efficiency of Flux Tube Wave Generation in Late Type Stars
Authors: Musielak, Z. E.; Rosner, R.; Ulmschneider, P.; Bohn, H. U.
Bibcode: 1986BAAS...18.1002M
Altcode:
No abstract at ADS
Title: Intermittent Stellar Wind Acceleration and the Long-Term
Activity of Population I Binary Systems Containing an X-Ray Pulsar
Authors: Stella, L.; White, N. E.; Rosner, R.
Bibcode: 1986ApJ...308..669S
Altcode:
The full range of possible regimes for a magnetized neutron star that
interacts with the stellar wind of an OB star is investigated, and the
results are compared with observational data. The observed properties
and system parameters for all the currently known OB stars systems
are summarized, and a search for a correlation between pulse periods,
orbital periods, and X-ray luminosities is made. Four different regimes
where a magnetized neutron star can interact with the stellar wind are
identified, and the regime where centrifugal inhibition of accretion
becomes important is discussed in the context of a strong correlation
found between the maximum observed luminosity from a pulsar and its
pulse frequency.
Title: The Equilibrium Structure of Thin Magnetic Flux Tubes. II.
Authors: Kalkofen, W.; Rosner, R.; Ferrari, A.; Massaglia, S.
Bibcode: 1986ApJ...304..519K
Altcode:
The thermal structure of the medium inside thin, vertical magnetic flux
tubes embedded in a given external atmosphere is investigated, assuming
cylindrical symmetry and a depth-independent plasma beta. The variation
with tube radius of the temperature on the tube axis is computed and the
temperature on the tube wall is estimated. The temperature variation
across the flux tube is found to be due to the depth variation of the
intensity and to the density stratification of the atmosphere. Since
the temperature difference between the axis and the wall is small in
thin flux tubes (of the order of 10 percent), the horizontal temperature
gradient may often be neglected and the temperature in a tube of given
radius may be described by a single function of depth. Thus, a more
detailed numerical treatment of the radiative transfer within thin
flux tubes can be substantially simplified by neglecting horizontal
temperature differences within the flux tube proper.
Title: The Sun at high spatial resolution: The physics of small
spatial structures in a magnetized medium
Authors: Rosner, R. T.
Bibcode: 1986sfcp.nasa...14R
Altcode:
An attempt is made to provide a perspective on the problem of spatial
structuring on scales smaller than can presently be directly and
regularly observed from the ground or with which current space-based
instrumentation can be anticipated. There is abundant evidence from both
observations and theory that such spatial structuring of the solar outer
atmosphere is ubiquitous not only on the observed scales, but also on
spatial scales down to (at least) the subarcsecond range. This is not
to say that the results to be obtained from observations on these small
scales can be anticipated: quite the opposite. What is clear instead
is that many of the classic problems of coronal and chromospheric
activity - involving the basic dissipative nature of magnetized
plasmas - will be seen from a novel perspective at these scales,
and that there are reasons for believing that dynamical processes of
importance to activity on presently-resolved scales will themselves
begin to be resolved on the sub-arcsecond level. Since the Sun is the
only astrophysical laboratory for which there is any hope of studying
these processes in any detail, this observatioinal opportunity is an
exciting prospect for any student of magnetic activity in astrophysics.
Title: Dynamics of Coronal Plasmas
Authors: Rosner, R.
Bibcode: 1986BAAS...18..686R
Altcode:
No abstract at ADS
Title: On Magnetic Field Stochasticity and Nonthermal Line Broadening
in Solar Flares
Authors: Antonucci, E.; Rosner, R.; Tsinganos, K.
Bibcode: 1986ApJ...301..975A
Altcode:
Observations of nonthermal line broadening seen in solar flares by the
Solar Maximum Mission satellite are discussed in light of recent results
on the generation of magnetic field stochasticity. It is shown that a
consistent model for the data can be constructed by assuming that the
observations signal the destruction of an ambient magnetohydrodynamic
equilibrium.
Title: On the Long Term Activity of Pop. I Binary Systems Containing
an X-ray Pulsar
Authors: Stella, L.; White, N. E.; Rosner, R.
Bibcode: 1986LNP...266...77S
Altcode: 1986paco.conf...77S
The authors review the observed properties of the population I binaries
containing X-ray pulsars. They point out that many of the pulsing
X-ray transients in OB star systems with pulse periods of 1 - 10 s,
when in outburst, lie close to the critical equilibrium point where the
corotation radius equals the magnetospheric radius. This suggests that
many of these systems usually are dormant because of the centrifugal
drag exerted by the pulsar magnetosphere which inhibits accretion and
that a small increase in the mass accretion rate can turn them into
very luminous transient X-ray sources. If a system lies close to the
equilibrium point and it is in an eccentric orbit, luminous outbursts
may occur around the time of periastron passage. A correlation between
the X-ray luminosity and the pulsar frequency is found and interpreted
as the result of centrifugal inhibition of accretion preventing low
luminosity, fast spin period magnetised neutron stars accreting.
Title: Some Aspects of the Physics of Stellar X-Ray Emission
Authors: Rosner, R.
Bibcode: 1986MitAG..65...79R
Altcode:
No abstract at ADS
Title: On Wind-Type Flows in Astrophysical Jets. II. Propagation
outside the Nucleus and the Case of M87
Authors: Ferrari, A.; Trussoni, E.; Rosner, R.; Tsinganos, K.
Bibcode: 1986ApJ...300..577F
Altcode:
Solutions of the basic polytropic flow equations appropriate to the
physical conditions of extragalactic jets well outside the acceleration
region within their parent active galactic nuclei are presented. The
solutions are based on observationally determined galactic mass
distributions and quasi-periodic brightness enhancements along the
jets. It is demonstrated that such a model is able to connect the
observed morphology of jets to processes (including shocks or density
condensations) which can give rise to the brightness enhancements,
as well as to provide estimates for the jet flow speeds which are
consistent with values implied by observations.
Title: X-Ray Spectra and the Rotation-Activity Connection of RS
Canum Venaticorum Binaries
Authors: Majer, P.; Schmitt, J. H. M. M.; Golub, L.; Harnden, F. R.,
Jr.; Rosner, R.
Bibcode: 1986ApJ...300..360M
Altcode:
Results are presented from a survey of RS CVn binaries which were
observed with the imaging proportional counter (IPC) on board the
Einstein Observatory. Spectral analyses of the IPC pulse height spectra
show that the coronae of RS CVn binaries always contain hot gas with
temperatures in excess of 10 to the 7th K, similar to active late-type
main-sequence stars, and that at least two temperature components
are necessary to account for the higher quality IPC spectra (when
absorption is unimportant). It is argued that these bimodal temperature
distributions found by the IPC are indicative of true distributions
of emission measure versus temperature that are continuous (just as
is the case of magnetically confined coronal plasma loops observed
on the sun). It is further shown that none of the derivable X-ray
characteristics of RS CVn binaries depend on rotation period, implying
that previous claims of period-activity relationships in RS CVn binaries
were unfounded.
Title: On the Origins and Dynamics of Spatial Structure in the Outer
Solar Atmosphere
Authors: Rosner, R.
Bibcode: 1986hmps.conf...37R
Altcode:
The author discusses some of the observational and theoretical reasons
for believing that significant physical processes take place on spatial
scales which have not as yet been directly observed, but which do
occur on spatial scales which are in principle observable. He also
illustrates that such structuring on presently unresolved scales
can have very significant impact on the interpretation of physical
phenomena occurring on resolved spatial scales by considering the
"damping" of coherent Alfvén waves by small-scale irregularities in
the background plasma.
Title: The sun at high spatial resolution: the physics of small
spatial structures in a magnetized medium.
Authors: Rosner, R. T.
Bibcode: 1986NASCP2421...14R
Altcode:
The author reviews some of the reasons for thinking that there do
exist structures in the solar outer atmosphere with spatial scales
smaller than those typically accessible to present-day instrumentation.
Title: Physical processes in the solar corona.
Authors: Rosner, R.; Low, B. C.; Holzer, T. E.
Bibcode: 1986psun....2..135R
Altcode:
Contents: Transport theory (fundamental parameter regimes, the "ideal"
problem, viscosity, parallel thermal energy transport, perpendicular
transport, some comments on model building). Magnetohydrodynamic
processes in the corona (equilibrium magnetic fields, linear stability
and nonequilibrium, time-dependent phenomena). Energy and momentum
balance of open and closed coronal structures (coronal holes and
high-speed streams, Alfvén waves in the lower solar atmosphere,
energy supply to magnetically closed coronal regions).
Title: Highlights of the Einstein Survey of Cool Stars
Authors: Bookbinder, J.; Golub, L.; Rosner, R.
Bibcode: 1986LNP...254...97B
Altcode: 1986csss....4...97B
No abstract at ADS
Title: Collimated Winds from Active Galactic Nuclei
Authors: Ferrari, A.; Trussoni, E.; Rosner, R.; Tsinganos, K.
Bibcode: 1986ASSL..121..543F
Altcode: 1986seag.proc..543F; 1986seag.conf..543F
The authors present a wind-type model for the modulation of jet
brightness (knots) on kpc scale. It is shown that the mass distribution
of the parent galaxy and the development of unstable modes on the
surface of the beam can lead to the periodic formation of internal
shocks that can be associated with enhanced particle acceleration. The
results are compared specifically with the data of the jet of M87.
Title: On magnetohydrodynamic thermal instabilities in magnetic
flux tubes
Authors: Massaglia, S.; Ferrari, A.; Bodo, G.; Kalkofen, W.; Rosner, R.
Bibcode: 1985ApJ...299..769M
Altcode:
The authors discuss the stability of current-driven filamentary modes
in magnetic flux tubes embedded in a plane-parallel atmosphere in LTE
and in hydrostatic equilibrium. Within the tube only energy transport
by radiation is considered. The dominant contribution to the opacity is
due to H- ions and H atoms (in the Paschen continuum). The
authors delimit a region in the parameter space of the equilibrium
configuration in which the instability is effective, and they discuss
the relevance of this process for the formation of structured coronae
in late-type stars and accretion disks.
Title: The equilibrium structure of thin magnetic flux tubes. I
Authors: Ferrari, A.; Massaglia, S.; Kalkofen, W.; Rosner, R.; Bodo, G.
Bibcode: 1985ApJ...298..181F
Altcode:
A model atmosphere within a thin magnetic flux tube that is embedded in
an arbitrarily stratified medium is presently constructed by solving the
radiative transfer equation in the two-stream approximation for gray
opacity, under the assumption that the magnetic field is sufficiently
strong to warrant the neglect of both thermal conduction and convective
diffusion; energy inside the flux tube therefore being transported
solely by radiation. The structure of the internal atmosphere is
determined on the basis of the hydrostatic and radiative equilibrium
conditions of the tube embedded in an external atmosphere. The gas
temperature along the axis of the tube is computed, and the geometry of
the flux tube is determined on the basis of magnetic flux conservation
and total pressure equilibrium.
Title: Differential rotation and magnetic torques in the interior
of the Sun
Authors: Rosner, R.; Weiss, N. O.
Bibcode: 1985Natur.317..790R
Altcode:
The frequencies of solar oscillations can be measured with extreme
precision and 5-min oscillations reveal the internal structure of
the Sun1-5. In particular, measurements of rotational
splitting4 have provided the first reliable indications of
the variation of angular velocity with radius6, while recent
observations5 have yielded information on the variation
with depth of latitudinal differential rotation. These results confirm
theoretical predictions that the angular velocity decreases inwards in
the convective zone7,8 but raise problems for dynamo models
of the solar cycle. The suggestion that the core rotates with roughly
twice the surface angular velocity has important implications both
for the rotational history of the Sun and for other late-type stars,
whose magnetic activity is closely correlated with rotation. Such a
rapidly rotating core is hard to reconcile with the presence of any
significant magnetic field pervading the entire radiative interior. We
can only explain it by suggesting that the core contains a fossil
field, unaffected by turbulence in the pre-main sequence Hayashi phase,
that is decoupled from the rest of the star.
Title: The Atmosphere in a Thin Magnetic Flux Tube
Authors: Bodo, G.; Ferrari, A.; Kalkofen, W.; Massaglia, S.; Rosner, R.
Bibcode: 1985tphr.conf..192B
Altcode:
No abstract at ADS
Title: On the Properties of Well-studied, Early Type Stars Observed
with the Einstein X-ray Observatory
Authors: Harnden, F. R., Jr.; Rosner, R.; Ramella, M.; Morossi, C.
Bibcode: 1985BAAS...17R.862H
Altcode:
No abstract at ADS
Title: Inverting Remote Sensing Data by Simulated Annealing
Authors: Jeffrey, W.; Rosner, R.
Bibcode: 1985BAAS...17..901J
Altcode:
No abstract at ADS
Title: On the solution topologies of polytropic winds
Authors: Bailyn, C.; Rosner, R.; Tsinganos, K.
Bibcode: 1985ApJ...296..696B
Altcode:
Steady polytropic wind flows are studied by examining their solution
topologies. The problem of whether the degeneracy of the continuous and
standing shocked solutions in the isothermal case persist in the more
general case of a polytropic expanding atmosphere is addressed. The
effects of departures from spherical symmetry and nonthermal
momentum addition are considered within the context of the new class
of magnetospheric models proposed by Low and Tsinganos (1985). The
flow near the boundary of a polar coronal hole is considered for the
specific case of a magnetosphere in which this boundary asymptotically
approaches the equator at large heliocentric distances.
Title: Standing Waves in Stratified finite-radius Magnetic Flux Tubes
Authors: Lou, Y. Q.; Rosner, R.
Bibcode: 1985BAAS...17..833L
Altcode:
No abstract at ADS
Title: X-ray spectra and the rotation-activity connection of RS
CVn binaries.
Authors: Majer, P.; Schmitt, J. H. M. M.; Golub, L.; Harnden, F. R.;
Rosner, R.
Bibcode: 1985ESASP.239..141M
Altcode: 1985cxrs.work..141M
Results from a survey of RS CVn binaries which were observed with the
Imaging Proportional Counter (IPC) on board the Einstein Observatory are
presented. Spectral analyses of the IPC pulse height spectra show that
the coronae of RS CVn binaries always contain hot gas with temperatures
10 million K, similar to active late-type main sequence stars, and
that at least 2 temperature components are necessary to account for
the higher quality IPC spectra (when absorption is unimportant). It
is argued that these bimodal temperature distributions indicate true
distributions of emission measure vs temperature that are continuous
(just as is the case for magnetically-confined coronal plasma loops
observed on the Sun). It is shown that none of the derivable X-ray
characteristics of RS CVn binaries depend on rotation period, implying
that claims of period-activity relationships in RS CVn binaries are
unfounded.
Title: On wind-type flows in astrophysical jets. I - The initial
relativistic acceleration
Authors: Ferrari, A.; Trussoni, E.; Rosner, R.; Tsinganos, K.
Bibcode: 1985ApJ...294..397F
Altcode:
The initial acceleration of jet plasma emerging from the funnel of an
accretion disk in orbit about a compact central object is investigated
analytically, extending the treatment of Ferrari et al. (1984),
based on the quasi-two-dimensional Navier-Stokes equations, to the
relativistic case for an optically thin jet. The transonic wind-type
solutions are shown to depend strongly on the geometry of the funnel
and the radiation field within it, with the possibility of multiple
critical points, supersonic flow in the vicinity of the central object,
and multiple transonic solutions (connected by shock transitions) for
a single set of input parameters. Numerical results are presented in
diagrams, tables, and graphs.
Title: Einstein X-ray survey of the Pleiades : the dependence of
X-ray emission on stellar age.
Authors: Micela, G.; Sciortino, S.; Serio, S.; Vaiana, G. S.;
Bookbinder, J.; Golub, L.; Harnden, F. R., Jr.; Rosner, R.
Bibcode: 1985ApJ...292..172M
Altcode:
The data obtained with two pointed observations of 1 deg by 1 deg
fields of the Pleiades region have been analyzed, and the results are
presented. The maximum-likelihood X-ray luminosity functions for the
Pleiades G and K stars in the cluster are derived, and it is shown that,
for the G stars, the Pleiades X-ray luminosity function is significantly
brighter than the corresponding function for Hyades G dwarf stars. This
finding indicates a dependence of X-ray luminosity on stellar age,
which is confirmed by comparison of the same data with median X-ray
luminosities of pre-main sequence and local disk population dwarf G
stars. It is suggested that the significantly larger number of bright
X-ray sources associated with G stars than with K stars, the lack
of detection of M stars, and the relatively rapid rotation of the
Pleiades K stars can be explained in terms of the onset of internal
differential rotation near the convective envelope-radidative core
interface after the spin-up phase during evolution to the main sequence.
Title: Propagation of nonlinear, radiatively damped longitudinal
waves along magnetic flux tubes in the solar atmosphere
Authors: Herbold, G.; Ulmschneider, P.; Spruit, H. C.; Rosner, R.
Bibcode: 1985A&A...145..157H
Altcode:
For solar magnetic flux tubes the authors compare three types of
waves: longitudinal MHD tube waves, acoustic tube waves propagating
in the same tube geometry but with rigid walls and ordinary acoustic
waves in plane geometry. They find that the effect of distensibility
of the tube is small and that longitudinal waves are essentially
acoustic tube waves. Due to the tube geometry there is considerable
difference between longitudinal waves or acoustic tube waves and
ordinary acoustic waves. Longitudinal waves as well as acoustic tube
waves show a smaller amplitude growth, larger shock formation heights,
smaller mean chromospheric temperature but a steeper dependence of
the temperature gradient on wave period.
Title: Intermittent stellar wind accretion in Pop. I binary systems
containing an X-ray pulsar
Authors: Stella, L.; White, N. E.; Rosner, R.
Bibcode: 1985SSRv...40..399S
Altcode:
We review the long term variability properties of accretion powered
X-ray pulsars in massive Pop. I binary systems and discuss how their
characteristics, in particular the large dynamic range in luminosity of
the transient pulsars, can be understood in terms of the interaction of
the accreting material with the neutron star magnetosphere. We point
out that the X-ray pulsar transient activity in general can be due to
the transition between direct wind accretion and a regime in which
the centrifugal drag exerted by the pulsar magnetosphere inhibits
accretion onto the neutron star surface.
Title: Magnetohydrodynamic thermal instabilities in cool inhomogeneous
atmospheres
Authors: Bodo, G.; Ferrari, A.; Massaglia, S.; Rosner, R.; Vaiana,
G. S.
Bibcode: 1985ApJ...291..798B
Altcode:
The stability of magnetic loops to current-driven filamentation
instabilities is investigated. The unperturbed atmosphere is assumed to
be composed of an (upper) isothermal optically thin low-density portion
and a (lower) higher-density portion which is in radiative equilibrium;
in both cases, the atmosphere is in hydrostatic equilibrium, so
that gravitational stratification is taken into account. In order to
provide specific equilibrium conditions for evaluation of the dispersion
relation, conditions appropriate for the surface of a solar-type star
are adopted; i.e., a fairly low temperature (T = 5000 K) appropriate
for a 'precoronal' state associated, for example, with magnetic
flux emerging from photospheric levels under the action of magnetic
buoyancy. A linear stability analysis is performed, and numerical
results show that physically plausible current densities, which would be
generated by typical loop-footpoint motions, are effective in driving
MHD instabilities in such a plasma. The instability growth rates are
strongly dependent on the assumed current density distribution and on
the density scale height.
Title: Mass Accretion Rates for Giant Elliptical Galaxies
Authors: Tucker, W.; Rosner, R.
Bibcode: 1985BAAS...17..600T
Altcode:
No abstract at ADS
Title: An Einstein Observatory X-ray survey of main-sequence stars
with shallow convection zones.
Authors: Schmitt, J. H. M. M.; Golub, L.; Harnden, F. R., Jr.; Maxson,
C. W.; Rosner, R.; Vaiana, G. S.
Bibcode: 1985ApJ...290..307S
Altcode:
The results of an X-ray survey of bright late A and early F stars
on the main B-V sequence between 0.1 and 0.5 are presented. All the
stars were observed with the Einstein Observatory for a period of at
least 500 seconds. The survey results show significantly larger X-ray
luminosities for the sample binaries than for the single stars. It
is suggested that the difference is due to the presence of multiple
X-ray sources in binaries. It is shown that the X-ray luminosities
for single stars increase rapidly with increasing color, and that
the relation Lx/Lbol is equal to about 10 to the -7th does not hold
for A stars. No correlation was found between X-ray luminosity and
projected equatorial rotation velocity. It is argued on the basis of
the observations that X-ray emission in the sample stars originated
from coronae. The available observational evidence supporting this
view is discussed.
Title: Inversion Techniques for Helioseismology
Authors: Jeffrey, W.; Rosner, R.
Bibcode: 1985BAAS...17..639J
Altcode:
No abstract at ADS
Title: The X-ray corona of Procyon.
Authors: Schmitt, J. H. M. M.; Harnden, F. R., Jr.; Rosner, R.; Peres,
G.; Serio, S.
Bibcode: 1985ApJ...288..751S
Altcode:
X-ray emission from the nearby system Procyon A/B (F5 IV + DF) was
detected, using the IPC (Imaging Proportional Counter) on board the
Einstein Observatory. Analysis of the X-ray pulse height spectrum
suggests that the observed X-ray emission originates in Procyon A
rather than in the white dwarf companion Procyon B, since the derived
X-ray temperature, log T = 6.2, agrees well with temperatures found
for quiescent solar X-ray emission. Modeling Procyon's corona with
loops characterized by some apex temperature Tmax and emission
length scale L, it is found that Tmax is well constrained, but L,
and consequently the filling factor of the X-ray emitting gas, are
essentially unconstrained even when EUV emission from the transition
region is included in the analysis.
Title: Optimized variability analysis in non periodic sources:
application to X-ray emission from normal stars.
Authors: Collura, A.; Sciortino, S.; Maggio, A.; Serio, S.; Rosner, R.
Bibcode: 1985xra..conf...47C
Altcode: 1984xra..conf...47C
The authors discuss the application of a χ2 method for
variability analysis of aperiodic sources. By binning photon arrival
times, they consider the deviation of the values of χ2 from
those expected under the hypothesis of a constant source with Poisson
noise, and its dependence on the binning rate and phase. They determine
from this dependence an "effective" fractional variability and the
dominant time scale of the variable component (if any). They use Monte
Carlo simulations to check the validity of the method employed. They
show applications of this method to X-ray emission from normal stars.
Title: On stellar X-ray emission.
Authors: Rosner, R.; Golub, L.; Vaiana, G. S.
Bibcode: 1985ARA&A..23..413R
Altcode:
Stellar X-ray astronomy represents an entirely new astronomical
discipline which has emerged during the past five years. It lies
at the crossroads of solar physics, stellar physics, and general
astrophysics. The present review is concerned with the main physical
problems which arise in connection with a study of the stellar X-ray
data. A central issue is the extent to which the extrapolation from
solar physics is justified and the definition (if possible) of the
limits to such extrapolation. The observational properties of X-ray
emission from stars are considered along with the solar analogy and the
modeling of X-ray emission from late-type stars, the modeling of X-ray
emission from early-type stars, the physics of stellar X-ray emission,
stellar X-ray emission in the more general astrophysical context,
and future prospects.
Title: X-ray emission from solar-type stars: X-ray luminosity function
of late F and G stars.
Authors: Maggio, A.; Bookbinder, J.; Harnden, F. R., Jr.; Golub, L.;
Majer, P.; Rosner, R.; Vaiana, G. S.
Bibcode: 1985xra..conf...39M
Altcode: 1984xra..conf...39M
The authors present preliminary results from a volume-limited survey
of X-ray emission from late F and G dwarf stars. They have obtained
count rates or upper limits at the locations of catalogued stars
within 25 parsecs for which an observation of the Einstein Imaging
Proportional Counter was available. They have constructed X-ray
luminosity functions for the whole sample and for selected subsamples
of binary and non-binary sources.
Title: The atmosphere in a thin magnetic flux tube.
Authors: Bodo, G.; Ferrari, A.; Kalkofen, W.; Massaglia, S.; Rosner, R.
Bibcode: 1985MPARp.212..192B
Altcode:
The authors construct the equilibrium atmosphere inside a thin, vertical
magnetic flux tube embedded in a grey external atmosphere in radiative
and convective equilibrium.
Title: Quasi-two-dimensional cosmic jets
Authors: Tsinganos, K.; Rosner, R.; Ferrari, A.
Bibcode: 1985IAUS..107..497T
Altcode:
Insights gained from observations of the nearest known astrophysical
jet, the high-speed solar wind stream, are used to describe the
mechanisms of jet acceleration and collimation in star-forming
molecular clouds, galaxies, and quasars. The time-dependent
second-order partial differential equations governing the motion of
the solar wind are applied to a jet originating in the central mass
surrounded by an accretion disk. The structure of the jet is shown,
and the characteristics of momentum deposition in the funnel of the
accretion disk are described. The propagation of the jet outside the
'power source' of the central mass is also considered.
Title: The appearance of magnetic flux on the surfaces of the early
main-sequence F stars
Authors: Giampapa, M. S.; Rosner, R.
Bibcode: 1984ApJ...286L..19G
Altcode:
Available chromospheric, transition region, and coronal observations
of the early main-sequence F stars are examined in order to find that
while these objects exhibit enhanced levels of magnetic field-related
radiative emissions, significant inhomogeneities in surface activity
are not present. This phenomenon is discussed within the context of the
calculations published by Schmitt and Rosner (1983) for the production
of flux ropes of various spatial scales at a given rotation rate at
the bottom of a stellar convection zone. It is found that the spatial
scales and area contrast of emergent magnetic flux in these stars that,
as a class, are characterized by rapid rotation and thin convection
zones are substantially reduced relative to that of the sun.
Title: Equilibrium Model of Thin Magnetic Flux Tubes
Authors: Bodo, G.; Ferrari, A.; Massaglia, S.; Kalkofen, W.; Rosner, R.
Bibcode: 1984ESASP.207..277B
Altcode: 1984plap.rept..277B
The existence of a physically realizable domain in which approximations
that lead to a self consistent solution for flux tube stratification
in the solar atmosphere, without ad hoc hypotheses, is proved. The
transfer equation is solved assuming that no energy transport other
than radiative is present. Convective motions inside the tube are
assumed to be suppressed by magnetic forces. Only one parameter, the
plasma beta at tau = 0, must be specified, and this can be estimated
from observations of spatially resolved flux tubes.
Title: Collimated winds from active galactic nuclei
Authors: Ferrari, A.; Rosner, R.; Trussoni, E.; Tsinganos, K.
Bibcode: 1984xue..conf..200F
Altcode: 1984xue..conf..200T
A mechanism of astronomical jet-acceleration via radiation pressure
momentum addition and the hydrodynamic approach in the twin-exhaust
model are proposed. Expansion of the gas at the exit of the accretion
funnel may synergistically interact with the funnel's intense radiation
field to act as a nozzle against the gravitational field of the central
object. The model shows that wind theory can be suitably scaled to
explain the presence of supersonic flows from the inner core of radio
galaxies; in contrast to jets emerging from quasars, it is not clear
if jets emerging from the center of radio galaxies are relativistic
in their inner part. Propagation of jets out of the potential well of
the parent galaxy may lead to peculiar and observable features related
to the physical conditions in the jet itself and in the central engine.
Title: An X-ray Survey of Solar-Type Stars
Authors: Bookbinder, J. A.; Majer, P.; Golub, L.; Rosner, R.
Bibcode: 1984BAAS...16Q.940B
Altcode:
No abstract at ADS
Title: The overshoot region at the bottom of the solar convection
zone.
Authors: Schmitt, J. H. M. M.; Rosner, R.; Bohn, H. U.
Bibcode: 1984ApJ...282..316S
Altcode:
The extent and thermal stratification of the region of
convective overshoot underneath the convection zone of the sun are
investigated. The phenomenon of convective overshoot in general is
discussed, and some of the modal and model approaches to studying it are
briefly reviewed. A detailed theoretical description of the motion of
plumes in a stably stratified medium is given, leading to a 'derivation'
of the plume equations from the hydrodynamic equations. Entrainment
is discussed, and it is shown how the plume equations can be used
to compute convective overshoot in the sun. The limitations of the
plume model are addressed, arguing that a thin boundary layer must
exist which separates convective and radiative regions. The results
of numerical integrations of the plume equations, as applied to the
region of convective overshoot underneath the solar convective zone,
are discussed.
Title: Erratum - Einstein Observations of X-Ray Emission from A-Stars
Authors: Golub, L.; Harnden, F. R.; Maxson, C. W.; Rosner, R.; Vaiana,
G. S.; Cash, W., Jr.; Snow, T. P., Jr.
Bibcode: 1984ApJ...278..456G
Altcode:
No abstract at ADS
Title: X-ray Spectra of RS CVn Binaries
Authors: Majer, P.; Schmitt, J. H. M.; Golub, L.; Harnden, F. R.,
Jr.; Rosner, R.
Bibcode: 1984BAAS...16..514M
Altcode:
No abstract at ADS
Title: An X-ray Survey of Late-Type Dwarf Stars
Authors: Bookbinder, J. A.; Schmitt, J. H. M.; Golub, L.; Rosner, R.
Bibcode: 1984BAAS...16..515B
Altcode:
No abstract at ADS
Title: On the topological stability of magnetostatic equilibria
Authors: Tsinganos, K. C.; Rosner, R.; Distler, J.
Bibcode: 1984ApJ...278..409T
Altcode:
The topological stability of MHD equilibria is investigated by exploring
the formal analogy, in the ideal MHD limit, between the topology
of magnetic lines of force in coordinate space and the topology of
integral surfaces of one- and two-dimensional Hamiltonian systems
in phase space. It is demonstrated that in an astrophysical setting,
symmetric magnetostatic equilibria satisfying the ideal MHD equations
are exceptional. The principal result of the study is that previous
infinitesimal perturbation theory calculations can be generalized to
include finite-amplitude and symmetry-breaking effects. The effect of
the ergodicity of perturbed symmetric equilibria on heat dispersal in
magnetically dominated plasmas is discussed.
Title: A wind-type model for the generation of astrophysical jets
Authors: Ferrari, A.; Habbal, S. R.; Rosner, R.; Tsinganos, K.
Bibcode: 1984ApJ...277L..35F
Altcode:
Wind-type solutions are discussed for the generation of astrophysical
jets from active galactic nuclei and stellar sources such as
those associated with SS433 and protostellar objects. Acceleration,
collimation, and morphology are consistently interpreted in terms of
a flow starting from the galactic or stellar core inside the "throat"
of a thick accretion disk.
Title: Magnetic field instabilities in accretion disks
Authors: Stella, L.; Rosner, R.
Bibcode: 1984ApJ...277..312S
Altcode:
The stability of magnetic fields within the accretion disks is examined,
including the effects of magnetic buoyancy, Rayleigh-Taylor, and
Kelvin-Helmholtz instabilities. The purpose of the study is to
examine the efficacy of turbulent accretion (alpha-)disk models
which depend upon 'magnetic viscosity' to provide the dissipation
necessary to account for radial infall. Estimates are provided
for the time scales of the dominant instabilities in both the gas
pressure-dominated and radiation pressure-dominated regions of a thin
accretion disk. Constraints are provided on dynamo processes such
that 'magnetic viscosity' operates to permit stationary accretion. It
is shown that field amplification may take place even in vertically
stably stratified regions of a thin disk by the action of 'magnetic
buoyancy-driven' convection. It is demonstrated that the turbulent
Reynolds stress responsible for accretion is proportional to the gas
pressure even in the radiation-dominated portion of the disk.
Title: A Relativistic Wind Type Model for the Generation of VLBI Jets
Authors: Ferrari, A.; Rosner, R.; Trussoni, E.; Tsinganos, K.
Bibcode: 1984IAUS..110..233F
Altcode:
The authors discuss wind-type solutions for flows from accretion
funnels, and show under what physical conditions such flows can become
supersonic and relativistic very close to the stagnation point within
the funnel. The acceleration is due to radiation emitted by the funnel
walls, while the location of the transonic points is also affected by
the geometrical shape of the funnel's cross-section.
Title: Particle acceleration.
Authors: Rosner, R.; Chupp, E. L.; Gloeckler, G.; Gorney, D. J.;
Krimigis, S. M.; Mok, Y.; Ramaty, R.; Swift, D. W.; Vlahos, L.;
Zweibel, E. G.
Bibcode: 1984NASRP1120....2R
Altcode:
Contents: 1. Introduction. 2. Phenomenology: Solar flares. Acceleration
processes in the interplanetary medium. Magnetospheric and
ionospheric observations. Particle acceleration outside the solar
system. 3. Theoretical particle acceleration mechanisms: Adiabatic
compression, magnetic pumping, and diffusion. Acceleration in
direct electric fields. Stochastic acceleration. Shock particle
acceleration. Coherent wave acceleration. Injection. 4. The remaining
questions.
Title: X-Ray Survey of the Pleiades - Dependence of X-Ray Luminosity
on Stellar Age
Authors: Micela, G.; Sciortino, S.; Serio, S.; Vaiana, G. S.; Golub,
L.; Harnden, F. R.; Rosner, R.
Bibcode: 1984IAUS..105..101M
Altcode:
The authors report preliminary results from an Einstein X-ray survey
of the Pleiades. They have analysed a 1°×1° exposure centered over
one of the more luminous stars of the cluster (20 Tau, [B7 III]). This
field contains ≡62 cluster members out of a total of ≡270 stars with
magnitude lower than 14m. (Hertzsprung, 1947). The authors
have detected 17 distinct X-ray sources; 16 sources are identified
with cluster stars within a distance less than 1arcmin.
Title: Collimated winds from active galactic nuclei.
Authors: Ferrari, A.; Rosner, R.; Trussoni, E.; Tsinganos, K.
Bibcode: 1984MPERp.184..200F
Altcode:
No abstract at ADS
Title: Temporal evolution of the solar wind and the formation of a
standing shock
Authors: Habbal, Shadia Rifai; Rosner, Robert
Bibcode: 1984JGR....8910645H
Altcode: 1984JGR....8910645R
The temporal evolution of the solar wind from one steady state to
another is explored when momentum deposition produces multiple critical
points in the flow. We show that the wind always evolves in time to
a new steady state compatible with the solution of the steady state
equation of motion. However, for the same initial state and identical
asymptotic momentum deposition rate the temporal evolution pattern of
the wind depends on the detailed time history of momentum addition
and is therefore not unique. This feature plays an important role
in the particular case when multiple (three in this study) steady
states exist for identical boundary conditions; each one of these
solutions is thus shown to be physically accessible. The details
of the temporal evolution pattern of the wind reveal the formation
of a shock discontinuity whenever the flow becomes supersonic at a
critical point upstream from the initial critical point. If the flow
remains supersonic at that inner critical point, the shock can become
a standing one, depending on the strength and the temporal history of
momentum addition. The results of this study indicate that the time
scale required for the solar wind to evolve between steady states
is of the order of 30-60 hours. Furthermore, the results also reveal
the interesting and novel phenomenon that a standing shock is likely
to develop in the inner solar wind flow within this time frame, in
particular, in coronal hole regions with rapidly diverging geometries.
Title: X-Ray Variable Stars in the Pleiades
Authors: Sciortino, S.; Micela, G.; Serio, S.; Vaiana, G. S.; Golub,
L.; Harnden, F. R., Jr.; Rosner, R.
Bibcode: 1983IBVS.2449....1S
Altcode:
No abstract at ADS
Title: Multiple transonic solutions and a new class of shock
transitions in solar and stellar winds.
Authors: Habbal, S. R.; Tsinganos, K.; Rosner, R.
Bibcode: 1983NASCP.2280.213H
Altcode: 1983sowi.conf..213H
The steady isothermal solar wind equations are shown to admit,
under certain circumstances, mutliple transonic solutions when,
for example, momentum deposition gives rise to multiplee critical
points in the flow. These multiple solutions consist of a continuous
solution and solutions which involve shock transitions between critical
solutions. The ambiguity arising from the multiplicity of the solutions
can be resolved by following the time evolution of a wind profile
with one critical point. Results of the numerical integration of the
time-dependent equations with momentum addition show that each of these
multiple solutions is physically accessible and depends on the rate
of change of momentum deposition. These results suggest that standing
shocks are likely to be present in the inner solar wind flow.
Title: Formation of standing shocks in stellar winds and related
astrophysical flows.
Authors: Tsinganos, K.; Habbal, S. R.; Rosner, R.
Bibcode: 1983NASCP.2280.289T
Altcode: 1983sowi.conf..289T
Stellar winds and other analogous astrophysical flows can be described,
to lowest order, by the familiar one dimensional hydrodynamic equations
which, being nonlinear, admit in some instances discontinuous as
well as continuous transonic solutions for identical inner boundary
conditions. The characteristics of the time dependent differential
equations of motion are described to show how a perturbation changes
profile in time and, under well defined conditions, develops into a
stationary shock discontinuity. The formation of standing shocks in
wind type astrophysical flows depends on the fulfillment of appropriate
necessary conditions, which are determined by the conservation of mass,
momentum and energy across the discontinuity, and certain sufficient
conditions, which are determined by the flow's history.
Title: X-ray Emission from A and F Stars - What Do We Learn About
Convection and Dynamos?
Authors: Schmitt, J. H. M.; Golub, L.; Harnden, F. R., Jr.; Maxson,
C. W.; Rosner, R.
Bibcode: 1983BAAS...15Q.948S
Altcode:
No abstract at ADS
Title: Einstein observations of X-ray emission from A stars.
Authors: Golub, L.; Harnden, F. R., Jr.; Maxson, C. W.; Rosner, R.;
Vaiana, G. S.; Cash, W., Jr.; Snow, T. P., Jr.
Bibcode: 1983ApJ...271..264G
Altcode:
Results are reported from the combined CfA Stellar Survey of selected
bright A stars and an Einstein Guest Observer program for Ap and Am
stars. In an initial report of results from the CfA Stellar Surveys
by Vaiana et al. (1981) it was noted that the spread in observed X-ray
luminosities among the few A stars observed was quite large. The reasons
for this large spread was studied by Pallavicini et al. (1981). It was
found that the X-ray emission from normal stars is related very strongly
to bolometric luminosity for early-type stars and to rotation rate
for late-type stars. However, an exception to this rule has been the
apparently anomalous behavior of A star X-ray emission, for which the
large spread in luminosity showed no apparent correlation with either
bolometric luminosity or stellar rotation rate. In the present study,
it is shown that the level of emission from normal A stars agrees with
the correlation observed for O and B stars.
Title: Closed coronal structures. V - Gasdynamic models of flaring
loops and comparison with SMM observations
Authors: Pallavicini, R.; Peres, G.; Serio, S.; Vaiana, G.; Acton,
L.; Leibacher, J.; Rosner, R.
Bibcode: 1983ApJ...270..270P
Altcode:
The hydrodynamic response of confined magnetic structures to strong
heating perturbations is investigated by means of a time-dependent
one-dimensional colde which incorporates the energy, momentum, and
mass conservation equations. The entire atmospheric structure from the
chromosphere to the corona is taken into account. Models with different
energy input, heating time dependence, preflare conditions and heating
location have been examined in the numerical simulations. The
result of model calculations are compared with observations of flares
obtained with the X-ray Polychromator experiment on the Solar Maximum
Mission. These include light curves of spectral lines formed over a
wide range of coronal flare temperatures, as well as determinations
of Doppler shifts for the high temperature plasma. Several examples
are used to illustrate the range of the observational variation. It is shown that the predictions of the numerical simulations
are in good overall agreement with the observed evolution of the
flare coronal plasma. The model reproduces correctly the temporal
profile of X-ray spectral lines and -- to first order at least --
their relative intensities. The upflow velocities predicted by
model calculations are in agreement with the observed blueshifts,
supporting the interpretation of the blueshifts as due to evaporation
of chromospheric material. The possibility of using the comparison
of model predictions with observations to derive information on the
processes of energy release and transfer in solar flares is discussed.
Title: The Sun as a Star
Authors: Jordan, S.; Rosner, R.
Bibcode: 1983Natur.303...92J
Altcode:
No abstract at ADS
Title: Thermal conduction and heating by nonthermal electrons in
the X-ray halo of M87.
Authors: Tucker, W. H.; Rosner, R.
Bibcode: 1983ApJ...267..547T
Altcode:
A hydrostatic model for the X-ray halo around the giant elliptical
galaxy M87 is presented. The authors show that by taking into
account the processes of thermal conduction, and nonthermal heating by
relativistic electrons in the radio lobes, a self-consistent hydrostatic
model can be constructed. There is no need to invoke radiative accretion
or the suppression of thermal conductivity.
Title: Doubly diffusive magnetic buoyancy instability in the solar
interior
Authors: Schmitt, J. H. M. M.; Rosner, R.
Bibcode: 1983ApJ...265..901S
Altcode:
An investigation of the buoyancy of diffuse magnetic fields has shown
that in the presence of rotation, static equilibrium configurations
of the toroidal magnetic field and ambient plasma can exist. In that
case, the escape of toroidal magnetic flux from the solar interior may
be determined by the growth of instabilities which the equilibrium
configuration may be subject to. In connection with the present
investigation, it is assumed that in the region of toroidal magnetic
flux amplification, the magnetic field has not as yet filamented into
flux ropes, and is therefore 'diffuse'. A study is conducted of the
MHD stability of an electrically conducting and differentially rotating
gas in the presence of a toroidal magnetic field, an external constant
gravitational field, and radiance pressure. The full dispersion relation
for the magnetic buoyancy problem is developed, and the solutions of
the dispersion relation are discussed.
Title: The Palermo-Harvard numerical code for the dynamics of confined
coronal plasma.
Authors: Peres, G.; Serio, S.; Vaiana, G. S.; Rosner, R.
Bibcode: 1983pig..conf...96P
Altcode:
No abstract at ADS
Title: Magnetic fields and activity of the sun and stars - an overview
Authors: Rosner, R.
Bibcode: 1983ASSL..102....5R
Altcode: 1983IAUCo..71....5R; 1983ards.proc....5R
Recent work on the observation and theory of solar and stellar magnetic
field activity and its relation to stellar activity is reviewed,
emphasizing those aspects relevant to the problem of activity of red
dwarf stars. New observational facts relevant to understanding the
root cause of stellar surface activity are summarized and theoretical
questions concerning the underlying physical basis for the observed
correlations between stellar activity, rotation, and magnetic fields
are addressed. These include dyanamo theory and the rotation-activity
connection as well as flux tube dynamics and plasma heating.
Title: MHD thermal instabilities in cool inhomogeneous atmospheres
Authors: Bodo, G.; Ferrari, A.; Massaglia, S.; Rosner, R.
Bibcode: 1983ASSL..102..621B
Altcode: 1983IAUCo..71..621B; 1983ards.proc..621B
The formation of a coronal state in a stellar atmosphere is
investigated. A numerical code is used to study the effects of
atmospheric gradients and finite loop dimension on the scale of unstable
perturbations, solving for oscillatory perturbations as eigenfunctions
of a boundary value problem. The atmosphere is considered as initially
isothermal, with density and pressure having scale heights fixed by
the hydrostatic equations. Joule mode instability is found to be an
efficient mechanism for current filamentation and subsequent heating
in initially cool atmospheres. This instability is mainly effective at
the top of magnetic loops and is not suppressed by thermal conduction.
Title: On the stellar rotation-activity connection
Authors: Rosner, R.
Bibcode: 1983IAUS..102..279R
Altcode:
The relationship between rotation rates and surface activity
in late-type dwarf stars is explored in a survey of recent
theoretical and observational studies. Current theoretical models of
stellar-magnetic-field production and coronal activity are examined,
including linear kinematic dynamo theory, nonlinear dynamos using
approximations, and full numerical simulations of the MHD equations;
and some typical results are presented graphically. The limitations of
the modeling procedures and the constraints imposed by the physics are
indicated. The statistical techniques used in establishing correlations
between various observational parameters are analyzed critically,
and the methods developed for quasar luminosity functions by Avni et
al. (1980) are used to evaluate the effects of upper detection bounds,
incomplete samples, and missing data for the case of rotation and
X-ray flux data.
Title: Solar wind five. Proceedings of a conference held in Woodstock,
Vermont, November 1 - 5, 1982.
Authors: Neugebauer, M.; Hollweg, J. V.; Barnes, A.; MacQueen, R.;
Rosner, R.; Eddy, J. A.
Bibcode: 1983swfp.book.....N
Altcode:
No abstract at ADS
Title: Magnetic field-related heating instabilities in the surface
layers of the sun and stars
Authors: Ferrari, A.; Rosner, R.; Vaiana, G. S.
Bibcode: 1982ApJ...263..944F
Altcode:
The stability of a magnetized low-density plasma to current-driven
filamentation instabilities is investigated and the results are applied
to the surface layers of stars. Unlike previous studies, the initial
(i.e., precoronal) state of the stellar surface atmosphere is taken
to be a low-density, optically thin magnetized plasma in radiative
equilibrium. The linear analysis shows that the surface layers of
main-sequence stars (including the sun) which are threaded by magnetic
fields are unstable; the instabilities considered lead to structuring
perpendicular to the ambient magnetic fields. These results suggest that
relatively modest surface motions, in conjunction with the presence of
magnetic fields, suffice to account for the presence of inhomogeneous
chromospheric and coronal plasma overlying a star's surface.
Title: On perturbations of magnetic field configurations
Authors: Rosner, R.; Knobloch, E.
Bibcode: 1982ApJ...262..349R
Altcode:
The behavior of stationary equilibrium solutions to the MHD equations
possessing a well-defined symmetry to perturbations lacking that
symmetry is explored. Two distinct situations of astrophysical interest
are considered: solutions of the magnetostatic equations and of the
magnetoconvection equations. The results show that in these cases
changes in solution topology are not accessible to small-parameter
(epsilon) expansions, so that such expansions do not describe the full
range of behavior. In particular, finite-amplitude perturbations can
lead to new stationary solutions possessing different symmetries from
the initial solution.
Title: Plasma astrophysics at Santa Barbara
Authors: Rosner, R.; Zweibel, E.; Trimble, V.
Bibcode: 1982Natur.299..579R
Altcode:
Discussions at the Space and Astrophysical Plasmas workshop held
in Santa Barbara, CA in the summer of 1982 are reviewed. Attention
was given mainly to hydromagnetic shocks and particle acceleration,
interactions between cold and hot plasmas, and hydromagnetic flows. The
structure of collisionless shocks was examined, with attention given
to the terrestrial bowshock. Numerical simulations of collisionless
shocks were presented, including details of ion dynamics in studies
of internal shock structure. Shock acceleration was explored on a
basis of a steady-state model showing cosmic rays to diffuse near a
high Mach number quasi-parallel shock approximated a discontinuity in
the flow speed. Problems needing further study were indicated, e.g.,
the efficiency of a shock wave, energy transfer between plasmas of
differing temperatures, and heat transport in laser-irradiated plasmas.
Title: Activity in red-dwarf stars
Authors: Rosner, Robert
Bibcode: 1982Natur.299..680R
Altcode:
No abstract at ADS
Title: Chromospheres and Coronae of Cool Stars
Authors: Dupree, A. K.; Rosner, R.
Bibcode: 1982BAAS...14..864D
Altcode:
No abstract at ADS
Title: Time Evolution of the Solar Wind Flow with Momentum Addition
and the Formation of Standing Shocks
Authors: Habbal, S. R.; Tsinganos, K.; Rosner, R.
Bibcode: 1982BAAS...14R.939H
Altcode:
No abstract at ADS
Title: A New Class of Standing Shocks in Astrophysical Jets and
Accretion Flows
Authors: Tsinganos, K.; Habbal, S.; Rosner, R.
Bibcode: 1982BAAS...14..871T
Altcode:
No abstract at ADS
Title: The Temperature-Luminosity Dependence of Stellar X-ray Sources
Authors: Vaiana, G. S.; Serio, S.; Sciortino, S.; Golub, L.; Maxson,
C.; Rosner, R.
Bibcode: 1982BAAS...14..945V
Altcode:
No abstract at ADS
Title: A Normal Incidence X-ray Telescope for Solar Studies
Authors: Golub, L.; Rosner, R.; Vaiana, G. S.; Zombeck, M. V.; Spiller,
E.; Wilczynski, J.
Bibcode: 1982BAAS...14..976G
Altcode:
No abstract at ADS
Title: Variable X-ray Emission from Early-type Stars
Authors: Collura, A.; Serio, S.; Sciortino, S.; Vaiana, G. S.; Harnden,
F. R., Jr.; Maxson, C. W.; Rosner, R.
Bibcode: 1982BAAS...14Q.945C
Altcode:
No abstract at ADS
Title: Search for Effects of an Intergalactic Medium Upon the Hot
Intracluster Gas of A2256
Authors: Gorenstein, P.; Fabricant, D.; Rosner, R.
Bibcode: 1982BAAS...14R.905G
Altcode:
No abstract at ADS
Title: Book-Review - Solar Flare Magnetohydrodynamics
Authors: Priest, E. R.; Rosner, R.
Bibcode: 1982Natur.298..691P
Altcode:
No abstract at ADS
Title: A magnitude limited stellar X-ray survey and the F star X-ray
luminosity function.
Authors: Topka, K.; Golub, L.; Gorenstein, P.; Harnden, F. R., Jr.;
Vaiana, G. S.; Avni, Y.; Rosner, R.
Bibcode: 1982ApJ...259..677T
Altcode:
An X-ray survey has been conducted of stars brighter than visual
magnitude 8.5 that have serendipitously fallen into the fields of view
of the Imaging Proportional Counter of the Einstein Observatory. The
survey includes 227 separate 1 x 1 deg fields, containing 274 stars
with a visual magnitude of no more than 8.5 and covering a wide range
of spectral types and luminosity classes. X-ray emission was detected
from 33 stars, and upper limits have been determined for the remainder
of the sample. F type stars dominate the detected sample, and most of
these are shown to be dwarfs. An X-ray luminosity function for dF stars
has been deduced, and reveals that the average 0.2-4.0 keV luminosity
of these stars is around 10 to the 29th erg/sec. Constraints have been
placed on the high luminosity tails and medians of the X-ray luminosity
functions for other types of stars.
Title: The Solar Outer Atmosphere. (Book Reviews: Solar Active
Regions)
Authors: Rosner, Robert
Bibcode: 1982Sci...215.1606O
Altcode:
No abstract at ADS
Title: STCOEX: The stellar X-ray coronal Explorer.
Authors: Vaiana, G. S.; Golub, L.; Maxson, C. W.; Rosner, R.; Zombeck,
M. V.
Bibcode: 1982SAOSR.392B.253V
Altcode: 1982csss....2..253V
No abstract at ADS
Title: A heating mechanism for the chromospheres of M dwarf stars.
Authors: Giampapa, M. S.; Golub, L.; Rosner, R.; Vaiana, G. S.;
Linsky, J. L.; Worden, S. P.
Bibcode: 1982SAOSR.392A..73G
Altcode: 1982csss....2...73G
The atmospheric structure of the dwarf M-stars which is especially
important to the general field of stellar chromospheres and coronae
was investigated. The M-dwarf stars constitute a class of objects
for which the discrepancy between the predictions of the acoustic
wave chromospheric/coronal heating hypothesis and the observations is
most vivid. It is assumed that they represent a class of stars where
alternative atmospheric heating mechanisms, presumably magnetically
related, are most clearly manifested. Ascertainment of the validity
of a hypothesis to account for the origin of the chromospheric and
transition region line emission in M-dwarf stars is proposed.
Title: Chromospheric emission, stellar rotation and X-ray coronae.
Authors: Pallavicini, R.; Golub, L.; Rosner, R.; Vaiana, G.
Bibcode: 1982SAOSR.392B..77P
Altcode: 1982csss....2...77P
No abstract at ADS
Title: Einstein detection of X-rays from the alf CEN system.
Authors: Golub, L.; Harnden, F. R., Jr.; Pallavicini, R.; Rosner,
R.; Vaiana, G. S.
Bibcode: 1982ApJ...253..242G
Altcode:
Detection of quiescent X-ray emission from the stellar components
of the Alpha Cen system: Alpha Cen A (G2 V) and Alpha Cen B (K1 V)
is reported. Contrary to previous theoretical expectations, both
stars are found to be X-ray emitters and at about the same level:
Lx = 1.2 x 10 to the 27th and 2.8 x 10 to the 27th ergs/s
for A and B, respectively; the sum of these values is in agreement
with the emission level previously reported for Alpha Cen by Nugent and
Garmire (1978). Comparison with previous chromospheric and transition
region measurements suggests that Alpha Cen A and B may have changed
in relative strength in recent years. The coronal temperature of the
combined Cen AB source, which is dominated (approximately 2/3 of the
total) by the K star is (2.1 + or - 0.4) x 10 to the 6th K, similar to
that of the average solar corona; it is noted that this value is not
consistent with the estimate of 5 x 10 to the 5th K quoted by Nugent
and Garmire.
Title: Stellar contribution to the diffuse soft X-ray background.
Authors: Bookbinder, J.; Avni, Y.; Golub, L.; Rosner, R.; Vaiana, G.
Bibcode: 1982SAOSR.392A.201B
Altcode: 1982csss....2..201B
One of the results of the EINSTEIN/C.f.A. X-ray stellar survey was
a determination of the contribution of the disk stellar population
to the galactic component of the diffuse soft (0.28 - 1.0 keV)
X-ray background. This analysis employed both binned and unbinned
nonparametric statistical methods that have been developed by Avni, et
al. (1980). These methods permitted the use of the information contained
in both the 22 detections and 4 upper bounds on the luminosities of
26 dM stars in order to derive their luminosity function. Luminosity
functions for earlier stellar types are not yet developed. For these
earlier stellar types, the median luminosities as determined by Vaiana,
et al., are used (1981), which underestimates their contribution to
the background. We find that it is the M dwarfs that dominate the disk
population stellar contribution to this background. To calculate the
contribution of the stellar sources to the background, simple models
both for the spatial distribution of the stars and for the properties
of the intervening interstellar medium are used. A model is chosen
in which all stellar classes have the same functional form for their
spatial distribution: an exponentially decreasing distribution above
the galactic equatorial plane, and a uniform distribution within the
galactic plane for a region of several kiloparsecs centered on the Sun.
Title: Models of transition region and coronal plasma in solar
"loop" structures.
Authors: Raymond, J. C.; Rosner, R.
Bibcode: 1982SAOSR.392A..15R
Altcode: 1982csss....2...15R
The theory of coronal loops was developed and the simple version of
the theory and observations are compared. It is shown that the gross
properties of the confined corona can be understood by considering
simple hydrostatic equilibrium models. By observing the corona it
is apparent that hydrostatic models are seriously inadequate. It is
suggested that observations of intensity fluctuations, of persistent up
and down flows, of relatively cool matter residing at coronal heights,
of apparent spatial co-mingling of hot plasmas at quite different
temperatures, need a more sophisticated modeling.
Title: Coronal closed structures. IV - Hydrodynamical stability and
response to heating perturbations
Authors: Peres, G.; Serio, S.; Vaiana, G. S.; Rosner, R.
Bibcode: 1982ApJ...252..791P
Altcode:
The response of magnetically confined atmospheres to perturbations in
the temperature and density distribution, and the local heating rate
by means of a one-dimensional time-dependent hydrodynamical code,
which incorporates the full energy, momentum and mass conservation
equations is studied. These studies extend the linear instability
analysis of Habbal and Rosner (1979) into the finite-amplitude regime,
and generalize the confined atmosphere models of Serio et al., to the
time-dependent domain. The results show that closed coronal atmospheres
are stable against finite-amplitude perturbations if the chromospheric
response is taken into account; and observed correlated increases in
coronal density and temperature can only be achieved under quiescent
conditions by increasing the heat deposition rate relatively more in
the chromosphere than in the corona.
Title: The solar corona: A testing ground for plasma astrophysics
Authors: Rosner, R.
Bibcode: 1982AdSpR...2i...3R
Altcode: 1982AdSpR...2Q...3R
The extension of solar surface activity models to the domain of stellar
activity, and the possibility of testing such extensions, are discussed.
Title: Solar corona at high resolution
Authors: Golub, L.; Rosner, R.; Zombeck, M. V. Z.; Vaiana, G. S.
Bibcode: 1982SPIE..316..149G
Altcode:
The earth's surface is shielded from solar X rays almost completely by
the atmosphere. It is, therefore, necessary to place X-ray detectors
on rockets or orbiting satellites. Solar rays were detected for the
first time in the late 1940's, using V-2 rockets. In 1960, the first
true X-ray images of the sun were obtained with the aid of a simple
pinhole camera. The spatial resolution of the X-ray images could be
considerably improved by making use of reflective optics, operating at
grazing incidence. Aspects of X-ray mirror developments are discussed
along with the results obtained in coronal studies utilizing the new
devices for the observation of solar X-ray emission. It is pointed
out that the major achievements of the Skylab missions were due
primarily to the unique opportunity to obtain data over an extended
period of time. Attention is given to normal incidence X-ray optics,
achievements possible by making use of high spatial resolution optics,
and details of improved mirror design.
Title: Solar scenarios
Authors: Rosner, R.
Bibcode: 1982rupp.book..101R
Altcode:
The employment of empirical observations of the sun and the coronal
structure to form scenarios describing the characteristics of other
stars is presented as a means to test theory against data. Convective
surface forces are thought to be dominant in suns which are smaller
than two solar masses, and the sun is noted to display a higher level
of surface noise than most stars, with noise levels falling off in
stars with larger or smaller masses. Ca II emission from the surface
has become a standard for examining stellar coronal activity, and
further aids in defining the age of a star in terms of evidence of
rotation rates, with slower rotation attributed to older stars. The
IUE spacecraft has provided stellar coronal data and the Einstein
Observatory has allowed X-ray coverage of stars, with the finding that
mass is not the sole indicator of coronal activity. There are stars
the mass of the sun with more powerful X-ray emissions.
Title: Short-term UV line profile variation in 59 Cyg.
Authors: Grady, C. A.; Doazan, V.; Peters, G. J.; Willis, A. J.; Snow,
T. P.; Aitken, D. K.; Barker, P. K.; Bolton, C. T.; Henrichs, H. F.;
Kitchen, C. R.; Kuhi, L. V.; Marlborough, J. M.; Meikle, W. P. S.;
Mendzies, J.; Oegerle, W.; Polidan, R. S.; Rosner, R.; Selvelli, P. L.;
Stalio, R.; Thomas, R. N.; Vaiana, G.; Whitelock, P. A.; Wilson, R.;
Wu, C. -C.
Bibcode: 1982NASCP2238..425G
Altcode: 1982NASCP2338..425G; 1982auva.nasa..425G
The International ultraviolet Explorer high dispersion spectra of 59
Cyg obtained as part of the long term monitoring program have shown that
noticeable variation can occur in C 5 and N 5 on timescales 3 hours t24
to 28 hours. In order to begin to resolve whether these changes occur
continuously or sporadically, 48 hours were devoted to monitoring this
star in January 1982. The January spectra show no short term variation,
which may be consistent with sporadic rather than continuous variation.
Title: Magnetic fields in late-type stars
Authors: Knobloch, E.; Rosner, R.; Weiss, N. O.
Bibcode: 1981MNRAS.197P..45K
Altcode:
Observations show that magnetic activity in late-type stars is
correlated with rotation rates and that there is a discontinuous change
in behavior at a critical rotation period. This can be explained as
a consequence of a transition from convection in rolls parallel to
the rotation axis to normal convection cells as the angular velocity
is decreased.
Title: Thermal instability of solar loop structures
Authors: Rosner, Robert
Bibcode: 1981Natur.294..611R
Altcode:
No abstract at ADS
Title: X-ray emission from Of stars and OB supergiants.
Authors: Cassinelli, J. P.; Waldron, W. L.; Sanders, W. T.; Harnden,
F. R., Jr.; Rosner, R.; Vaiana, G. S.
Bibcode: 1981ApJ...250..677C
Altcode:
The result of a survey of X-ray emission from luminous early-type
stars is reported in which observations were made using the imaging
proportional counter on the Einstein Observatory. The survey suggests
that all Of stars and OB supergiants earlier than B1 I are X-ray
sources with luminosities not less than 10 to the 32nd ergs/s and that
some later B supergiants have X-ray luminosities not less than 10 to
the 31st ergs/s. The X-ray luminosities are roughly 10 to the -7.2nd
of the bolometric luminosities for supergiants earlier than B1 and
perhaps a factor of 3 less for later B supergiants. Spectral analysis
of the X-rays in conjunction with information on anomalous ionization
in the wind from four of the strongest sources implies that the data
are not consistent with a model in which the X-rays originate in a thin
slab coronal zone at the base of the wind. Constraints on the source
of X-rays from B supergiants are derived by combining the X-ray flux
information with that on ultraviolet line anomalies.
Title: The cool Half of the H-R diagram in soft X-rays.
Authors: Ayres, T. R.; Linsky, J. L.; Vaiana, G. S.; Golub, L.;
Rosner, R.
Bibcode: 1981ApJ...250..293A
Altcode:
The results of an Einstein Observatory program to map the occurrence
of hot coronae (T greater than 1 million K) in the cool half of the
Hertzsprung-Russell diagram are reported. F-M dwarfs, and late F
through early K star giants characterized by 10,000 K chromospheric
and 20,000-200,000 K FUV emission lines were studied in one region,
while a second region study included red giants later than K2 III and
supergiants later than G5 Ib with weaker chromospheric emission and
no high temperature species. Program goals comprised determination of
the C IV division as seen in soft X-rays, and identification of stellar
parameters which distinguish strong from weak coronal X-ray sources. A
summary of target stars, X-ray fluxes, and UV emission profiles
is provided, and coronal emissions, comparisons of C IV and wind
boundaries, hybrid-spectrum supergiants, the energy balance of stellar
outer atmospheres, stellar rotation and coronae, and evolutionary
considerations are discussed, along with lines of future research.
Title: The stellar contribution to the galactic soft X-ray background
Authors: Rosner, R.; Avni, Y.; Bookbinder, J.; Giacconi, R.; Golub,
L.; Harnden, F. R., Jr.; Maxson, C. W.; Topka, K.; Vaiana, G. S.
Bibcode: 1981ApJ...249L...5R
Altcode:
Log N-log S relations for stars are constructed based on median
X-ray luminosities for dF, dG, and dK stars previously reported for
the Einstein Observatory/Center for Astrophysics stellar survey and
on a detailed X-ray luminosity function derived here for dM stars,
and the stellar contribution to the diffuse soft X-ray background is
investigated. The principal results are that stars provide approximately
20% of the soft X-ray background in the 0.28-1.0 keV passband and
therefore contribute significantly to the soft X-ray background in this
energy range (with dM stars constituting the dominant contributing
class), and that the stellar contribution to the diffuse X-ray
background in the 0.15-0.28 keV passband is less than approximately 3%.
Title: Erratum - Dynamics of Coronal Structures - Magnetic Field
Related Heating and Loop Energy Balance
Authors: Galeev, A. A.; Rosner, R.; Serio, S.; Vaiana, G. S.
Bibcode: 1981ApJ...248..882G
Altcode:
No abstract at ADS
Title: Relations among stellar X-ray emission observed from Einstein,
stellar rotation and bolometric luminosity.
Authors: Pallavicini, R.; Golub, L.; Rosner, R.; Vaiana, G. S.; Ayres,
T.; Linsky, J. L.
Bibcode: 1981ApJ...248..279P
Altcode:
The correlation between observed stellar X-ray luminosities, bolometric
luminosities, and projected rotational velocities for stars of various
spectral types and luminosity classes are determined. Early type
stars (O3 to A5) have X-ray luminosities independent of rotational
velocities, and correlating with bolometric luminosities. Late type
stars of spectral type G to M have luminosities well correlated to
equatorial rotational velocities, and are independent of luminosity
class. The dependence of late type stars is found to be equivalent
to a relation between the X-ray surface flux and the stellar angular
velocity. F stars are intermediate with X-ray luminosities higher
than would be predicted on the basis of the early type star relation,
although lower than expected from the late type velocity dependence. The
location of RS CVn stars as a class is also discussed, and it is found
that the heating of late type stellar coronas does not result from
direct conversion of ratational energy.
Title: A glimpse of new results: the preliminary Solar Maximum
Mission data
Authors: Rosner, R.
Bibcode: 1981Natur.292..582R
Altcode:
The most significant results of the Solar Maximum Mission
Satellite's seven experiments are presented. These are: (1) the
coronograph/polarimeter, which showed that estimates of total
flare energies based solely on observed radiative fluxes can be
mistaken by up to several orders of magnitude; (2) the ultraviolet
spectrometer and polarimeter, which demonstrated that although the
pre-flare state resembles a small loop of emerging flux rising into
an overlying complex of magnetic loops, the detailed evolution of
loop brightening and plasma motion does not do so; (3) the soft X-ray
polychromator, which showed that line widths are strongly variable
during the course of a flare, starting with rather broad profiles
and narrowing significantly after the hard X-ray impulsive event;
(4) the hard X-ray imaging spectrometer, which showed emission regions
characterized by a hard spectrum to be spatially associated with, and
to overlie, the brightest H-alpha emission patches; (5) the hard X-ray
burst spectrometer, which detected persistent intensity fluctuations
significant down to the 100 msec level and spectral variability down
to a time scale of seconds; (6) the gamma ray spectrometer, whose data
impose a non-trivial constraint on particle acceleration mechanisms
anticipated at the time of the Skylab Solar Flare workshop; and (7)
the active cavity radiometer irradiance monitor, which demonstrated
fluctuations of the total solar irradiance at the 0.05 per cent level.
Title: Closed coronal structures. III - Comparison of static models
with X-ray, EUV, and radio observations
Authors: Pallavicini, R.; Peres, G.; Serio, S.; Vaiana, G. S.; Golub,
L.; Rosner, R.
Bibcode: 1981ApJ...247..692P
Altcode:
Numerical models of static coronal loops in energy balance are compared
with high spatial resolution observations of extreme ultraviolet lines,
broad-band X-ray emission, and interferometric observations at 2.8 cm
of a solar active region. Difficulties of using scaling laws to test
static models of coronal loops are reviewed. The theoretical model
used for the comparison is summarized; the detailed X-ray, EUV, and
microwave observations of the selected active region are presented;
and the comparison of the model with the observations is performed. It
is shown that simple static models with conductive flux vanishing at the
loop base reproduce satisfactorily the observed properties in the upper
portion of loop structures from compact, high-pressure loops in the
core of the region to more extended, fainter loops and to large-scale
loops interconnecting different active regions. Effects of changing
loop parameters are investigated, and it is argued, that in contrast
to the present approach, scaling laws cannot be used to discriminate
between different static energy balance models. Some discrepancy is
found between model predictions and observations for the lower sections
of loop structures. Possible causes of the discrepancy are discussed.
Title: On the spectrum of turbulent magnetic fields
Authors: Knobloch, E.; Rosner, R.
Bibcode: 1981ApJ...247..300K
Altcode:
Theoretical power spectra of magnetic fields subject to turbulent fluid
motions in the kinematic regime are presented, and previous theories
are reviewed, with reference to magnetic fields on the sun. Magnetic
field diffusion in turbulence with persistent eddies is predicted
to be described by an effective negative magnetic diffusivity. It is
found that observations cannot be explained on the basis of turbulent
kinematic theories unless the turbulent motions are three-dimensional,
and the effective diffusivities are larger than the molecular
diffusivities. Lower bounds on the turbulent viscosity are derived,
suggesting that dynamical processes controlling the magnetic field
spectrum occur at least 15,000 km below the surface. The results,
which remain consistent with the assumption that effective diffusivity
is uniform, suggest that surface magnetic field observations can be
used as a diagnostic for subsurface flows.
Title: Results from an extensive Einstein stellar survey.
Authors: Vaiana, G. S.; Cassinelli, J. P.; Fabbiano, G.; Giacconi,
R.; Golub, L.; Gorenstein, P.; Haisch, B. M.; Harnden, F. R., Jr.;
Johnson, H. M.; Linsky, J. L.; Maxson, C. W.; Mewe, R.; Rosner, R.;
Seward, F.; Topka, K.; Zwaan, C.
Bibcode: 1981ApJ...245..163V
Altcode:
The preliminary results of the Einstein Observatory stellar X-ray survey
are presented. To date, 143 soft X-ray sources have been identified with
stellar counterparts, leaving no doubt that stars in general constitute
a pervasive class of low-luminosity galactic X-ray sources. Stars along
the entire main sequence, of all luminosity classes, pre-main sequence
stars as well as very evolved stars have been detected. Early type
OB stars have X-ray luminosities in the range 10 to the 31st to 10 to
the 34th ergs/s; late type stars show a somewhat lower range of X-ray
emission levels, from 10 to the 26th to 10 to the 31st ergs/s. Late type
main-sequence stars show little dependence of X-ray emission levels upon
stellar effective temperature; similarly, the observations suggest weak,
if any, dependence of X-ray luminosity upon effective gravity. Instead,
the data show a broad range of emission levels (about three orders of
magnitude) throughout the main sequence later than F0.
Title: Solar physics at Taos
Authors: Rosner, R.
Bibcode: 1981Natur.290..734R
Altcode:
No abstract at ADS
Title: Buoyancy Instabilities at the Base of the Solar Convection Zone
Authors: Schmitt, J. H. M. M.; Rosner, R.
Bibcode: 1981BAAS...13..907S
Altcode:
No abstract at ADS
Title: Solar corona at high resolution.
Authors: Golub, L.; Rosner, R.; Vaiana, G. S.; Zombeck, M. V.
Bibcode: 1981SPIE..316..149G
Altcode:
No abstract at ADS
Title: Solar magnetic fields - The generation of emerging flux
Authors: Golub, L.; Rosner, R.; Vaiana, G. S.; Weiss, N. O.
Bibcode: 1981ApJ...243..309G
Altcode:
X-ray observations have provided information about magnetic fields on
the sun, and the implications of these observations are discussed. The
pattern of small-scale flux emergence is quite different from that of
active regions. It is inferred that the small-scale fields originate
fairly high in the convective zone, while the fields in active regions
have a deeper origin. The small-scale turbulent fields are only loosely
related to the fields that define the normal solar cycle. The way in
which dynamo models must be modified in the light of these results
is indicated.
Title: Closed coronal structures. II - Generalized hydrostatic model
Authors: Serio, S.; Peres, G.; Vaiana, G. S.; Golub, L.; Rosner, R.
Bibcode: 1981ApJ...243..288S
Altcode:
Numerical computations of stationary solar coronal loop atmospheres
are used to extend earlier analytical work. Two classes of loops are
examined, namely symmetric loops with a temperature maximum at the
top but now having a length greater than the pressure scale height and
loops which have a local temperature minimum at the top. For the first
class, new scaling laws are found which relate the base pressure and
loop length to the base heating, the heating deposition scale height,
and the pressure scale height. It is found that loops for which the
length is greater than about two to three times the pressure scale
height do not have stable solutions unless they have a temperature
minimum at the top. Computed models with a temperature inversion at the
top are permitted in a wider range of heating deposition scale height
values than are loops with a temperature maximum at the top. These
results are discussed in relation to observations showing a dependence
of prominence formation and stability on the state of evolution of
magnetic structures, and a general scenario is suggested for the
understanding of loop evolution from emergence in active regions
through the large-scale structure phase to opening in coronal holes.
Title: Dynamics of coronal structures - Magnetic field-related
heating and loop energy balance
Authors: Galeev, A. A.; Rosner, R.; Serio, S.; Vaiana, G. S.
Bibcode: 1981ApJ...243..301G
Altcode:
The heating of the inhomogeneous solar corona is discussed in the
context of local coronal magnetic field energy release and associated
plasma heating. Expressions of general applicability relating the
parameters characterizing heated and confined atmospheres to heating
processes involving magnetic field reconnection are derived and then
evaluated for a specific heating process. This work is thought to
extend and refine previous models for the heating of confined coronal
plasma structures. A theory for steady energy release is developed, and
scaling laws are derived for the average coronal loop temperature and
energy-release rate which are compared with similar (but parameter-free)
scaling laws; this comparison makes it possible to determine the plasma
beta and nonpotential magnetic field within coronal loop structures in
the context of the model. Constraints on the applicability of static
coronal loop atmosphere models are developed, and the close correlation
between the thermal conductive loss and radiative loss for quasi-static
confined loop atmospheres is shown.
Title: Einstein X-ray observations of Proxima Centauri and the
surrounding region
Authors: Haisch, B. M.; Harnden, F. R., Jr.; Seward, F. D.; Vaiana,
G. S.; Linsky, J. L.; Rosner, R.
Bibcode: 1980ApJ...242L..99H
Altcode:
The first detection of both quiescent and flaring soft X-ray emission
from a dMe flare star, Proxima Centauri (dM5e) is reported. The data
are analyzed for temporal variability and spectral characteristics. The
quiescent state is characterized by a mean X-ray luminosity of 1.5 x 10
to the 27th erg s/s, corresponding to a mean surface flux of 700,000
erg s/sq cm-s, and an inferred temperature of 4-million K. The flare
that is detected has a peak flux of 7.4 x 10 to the 27th erg s/s and
a peak temperature of 17-million K. The implications of these data for
models of the quiescent and flare coronae of dMe stars are discussed.
Title: The Cool Half of the HR Diagram in Soft X-Rays
Authors: Ayres, T. R.; Linsky, J. L.; Vaiana, G. S.; Golub, L.;
Rosner, R.
Bibcode: 1980BAAS...12..870A
Altcode:
No abstract at ADS
Title: Development in EUV, XUV, and X-Ray Astronomy beyond the
Solar System
Authors: Rosner, R.
Bibcode: 1980BAAS...12..897R
Altcode:
No abstract at ADS
Title: Stellar Contribution to Galactic Component of Diffuse Soft
X-ray Background
Authors: Bookbinder, J. A.; Rosner, R.; Vaiana, G. S.
Bibcode: 1980BAAS...12..871B
Altcode:
No abstract at ADS
Title: Transition Region and Corona in Solar Active Regions:
Observations and Numerical Modeling
Authors: Golub, L.; Pallavicini, R.; Peres, G.; Rosner, R.; Serio,
S.; Vaiana, G. S.
Bibcode: 1980BAAS...12..908G
Altcode:
No abstract at ADS
Title: Magnetic fields and coronal heating
Authors: Golub, L.; Maxson, C.; Rosner, R.; Vaiana, G. S.; Serio, S.
Bibcode: 1980ApJ...238..343G
Altcode:
General considerations concerning the scaling properties of
magnetic-field-related coronal heating mechanisms are used to build
a two-parameter model for the heating of closed coronal regions. The
model predicts the way in which coronal temperature and electron density
are related to photospheric magnetic field strength and the size of the
region, using the additional constraint provided by the scaling law of
Rosner, Tucker, and Vaiana. The model duplicates the observed scaling
of total thermal energy content with total longitudinal flux; it also
predicts a relation between the coronal energy density (or pressure)
and the longitudinal field strength modified by the region scale size.
Title: Stellar Coronae from Einstein: Observations and Theory
Authors: Rosner, R.; Vaiana, G. S.
Bibcode: 1980ASIC...60..129R
Altcode: 1980xras.proc..129R
Einstein Observatory observations of stellar X-ray emission are
presented and their implications for the formation of stellar coronae
and the problem of stellar angular momentum loss are discussed. Solar
coronal X-ray observations and observations of stellar coronae made
prior to Einstein are reviewed, and it is noted that they already
suggest that the standard theory of acoustic coronal heating is
inadequate. The principal results of the Einstein/CfA stellar survey
are summarized, with attention given to variations of the level of
X-ray flux detected along the main sequence, the decline of X-ray flux
with increasing age of giants and supergiants, and indications of a
large range of X-ray emission levels within a given type, which are
clearly incompatible with models for acoustic flux generation. A new
theory to explain stellar coronae and hence X-ray emission from them
is then proposed in which stellar magnetic fields play the key role
in determining the level of coronal emission, and the modulation of
the surface magnetic flux level and the level of stressing of surface
magnetic fields essentially determine the variation of mean coronal
activity in the H-R diagram.
Title: Stellar Coronae - Interpretation and Modeling of Stellar
Activity
Authors: Rosner, R.
Bibcode: 1980SAOSR.389...79R
Altcode: 1980csss....1...79R
No abstract at ADS
Title: Thermal instabilities in magnetically confined plasmas -
Solar coronal loops
Authors: Habbal, S. R.; Rosner, R.
Bibcode: 1979ApJ...234.1113H
Altcode:
The thermal stability of confined solar coronal structures ('loops') is
investigated, following both normal mode and a new, global instability
analysis. It is demonstrated that: (1) normal mode analysis shows
modes with size scales comparable to that of loops to be unstable,
but to be strongly affected by the loop boundary conditions; (2) a
global analysis, based upon variation of the total loop energy losses
and gains, yields loop stability conditions for global modes dependent
upon the coronal loop heating process, with magnetically coupled heating
processes giving marginal stability. The connection between the present
analysis and the minimum flux corona of Hearn is also discussed.
Title: Discovery of an X-ray star association in VI Cygni (Cyg OB2).
Authors: Harnden, F. R., Jr.; Branduardi, G.; Elvis, M.; Gorenstein,
P.; Grindlay, J.; Pye, J. P.; Rosner, R.; Topka, K.; Vaiana, G. S.
Bibcode: 1979ApJ...234L..51H
Altcode:
A group of six X-ray sources located within 0.4 deg of Cygnus X-3 has
been discovered with the Einstein Observatory. These sources have been
positively identified and five of them correspond to stars in the
heavily obscured OB association VI Cygni. The optical counterparts
include four of the most luminous O stars within the field of view
and a B5 supergiant. These sources are found to have typical X-ray
luminosities of 5 x 10 to the 33rd ergs/s, with temperatures of 10 to
the 6.8th K and hydrogen column densities of 10 to the 22nd/sq cm,
and therefore comprise a new class of low-luminosity galactic X-ray
sources associated with early-type stars.
Title: X-ray Observations of the α Cen System from EINSTEIN.
Authors: Golub, L.; Harnden, F. R., Jr.; Rosner, R.; Topka, K.;
Vaiana, G. S.
Bibcode: 1979BAAS...11..775G
Altcode:
No abstract at ADS
Title: Coronal X-Ray Emission from OB Supergiants.
Authors: Cassinelli, J. P.; Waldron, W. L.; Vaiana, G. S.; Rosner, R.
Bibcode: 1979BAAS...11..775C
Altcode:
No abstract at ADS
Title: X-ray Observations of Very Late-Type Dwarf Stars from the
EINSTEIN Observatory.
Authors: Rosner, R.; Giacconi, R.; Golub, L.; Harnden, F. R., Jr.;
Topka, K.; Vaiana, G. S.
Bibcode: 1979BAAS...11..776R
Altcode:
No abstract at ADS
Title: On Stars and OB Associations Observed from EINSTEIN.
Authors: Harnden, F. R., Jr.; Golub, L.; Rosner, R.; Seward, F.;
Topka, K.; Vaiana, G. S.
Bibcode: 1979BAAS...11..775H
Altcode:
No abstract at ADS
Title: A Magnitude Limited Stellar Survey with EINSTEIN.
Authors: Topka, K.; Golub, L.; Harnden, F. R., Jr.; Gorenstein, P.;
Rosner, R.; Vaiana, G. S.
Bibcode: 1979BAAS...11..781T
Altcode:
No abstract at ADS
Title: "Coronae! of rotating interstellar clouds.
Authors: Rosner, R.; Hartquist, T. W.
Bibcode: 1979ApJ...231L..83R
Altcode:
This letter considers differential rotation of cool interstellar
clouds in the presence of internal magnetic fields, and shows that
because of the relative ineffectiveness of field dissipation within
the clouds, magnetized gas experiences buoyant forces. The resulting
field loops emerge from the cloud and dissipate their energy by field
reconnection. The consequent heating is sufficient to produce relatively
hot (T approximately 10,000 K) 'coronae' about the clouds.
Title: Stellar luminosity stability: luminosity variations and light
curve period changes in BY Draconis stars.
Authors: Hartmann, L.; Rosner, R.
Bibcode: 1979ApJ...230..802H
Altcode:
The implications for convection in late type stars arising from
the observations of BY Draconis type variability are examined. The
possibility that the total luminosity of such a star is not constant
is emphasized, and further observational tests to better define the
variability are suggested. An alternative to standard spot models is
explored in which the 'missing' flux from 'dark' spots is temporally
redistributed; this model makes definite predictions about the
correlation of mean light and color, and about the quiescent (i.e.,
unspotted) magnitudes of BY Draconis stars. The time scales of the
long-period variability of these stars appear to require secular changes
in convective energy transport. Consideration is given to the evidence
for period changes in the optical light curves, and it is concluded that
the reality of such changes is far less certain than previously claimed.
Title: On the origin of solar magnetic fields.
Authors: Layzer, D.; Rosner, R.; Doyle, H. T.
Bibcode: 1979ApJ...229.1126L
Altcode:
A fresh approach to the theoretical problems raised by observations of
solar magnetic fields is outlined. Tentative conclusions are made that
the large-scale magnetic field from which Cowling's (1953) hypothetical
toroidal field is generated by differential rotation is not itself
regenerated by diffusive processes in the sun's outer layers and that
this field enters the differentially rotating layer from below rather
than from above. Two crucial aspects of turbulent-dynamo theory are
critically examined: turbulent diffusion and the spatial separability
of the alpha and omega regenerative processes. It is argued that the
mathematical difficulties encountered in this theory are rooted in
unrealistic physical assumptions and that there is no physically or
mathematically plausible basis for turbulent-dynamo theories. The
hypothesis is considered that an irregular magnetic field, largely
confined to the convective core, was generated during the Hayashi
phase of pre-main-sequence evolution.
Title: Erratum: Cosmic Flare Transients: Constraints upon Models
for Energy Storage and Release Derived from the Event Frequency
Distribution
Authors: Rosner, R.; Vaiana, G. S.
Bibcode: 1979ApJ...229.1211R
Altcode:
No abstract at ADS
Title: Structured coronae of accretion disks.
Authors: Galeev, A. A.; Rosner, R.; Vaiana, G. S.
Bibcode: 1979ApJ...229..318G
Altcode:
A model based on the amplification of magnetic fields by convective
motions and differential rotation within a hot (no less than about
1,000,000 K) accretion disk is developed for the fluctuating hard
component of intense cosmic X-ray sources such as Cyg X-1. It is
shown that field reconnection within the inner portion of the disk
is ineffective in limiting field amplification. Magnetic fields may
therefore reach strengths comparable to the equipartition value, leading
to their emergence through buoyancy in the form of looplike structures
and resulting in a very hot (over 100 million K) magnetically confined
structured corona similar to the observed structure of solar corona. In
particular, the soft X-ray luminosity of the accretion disk determines
the dominant energy loss mechanism in loops.
Title: Detection of soft X-rays from alpha Lyrae and eta Bootis with
an imaging X-ray telescope.
Authors: Topka, K.; Fabricant, D.; Harnden, F. R., Jr.; Gorenstein,
P.; Rosner, R.
Bibcode: 1979ApJ...229..661T
Altcode:
Results are presented for observations of Alpha Lyr (Vega) and Eta
Boo with an imaging X-ray telescope during two rocket flights. It is
found that Vega and Eta Boo are soft X-ray sources with respective
luminosities of approximately 3 x 10 to the 28th erg/s (0.15-0.8 keV)
and 1 x 10 to the 29th erg/s (0.15-1.5 keV). Surface X-ray luminosities
of about 640,000 erg/sq cm per sec for Vega and 300,000 erg/sq cm
per sec for Eta Boo are estimated and shown to fall within the range
of solar coronal X-ray emission. It is concluded that in view of the
substantially larger surface areas of these stars, the relatively large
total soft X-ray luminosity (as compared with that of the sun) can in
both cases be understood as resulting from a moderately active corona,
although the Vega observation is in severe conflict with simple models
for X-ray emission from single main-sequence stars.
Title: Observational Tests of Magnetic Field-Related Coronal Heating
Theories
Authors: Golub, L.; Maxson, C.; Rosner, R.; Serio, S.; Vaiana, G. S.
Bibcode: 1979BAAS...11R.408G
Altcode:
No abstract at ADS
Title: Initial Results from the Einstein Survey of Stellar
Low-Luminosity X-ray Sources
Authors: Vaiana, G.; Forman, W.; Giacconi, R.; Gorenstein, P.; Pye,
J.; Rosner, R.; Seward, F.; Topka, K.
Bibcode: 1979BAAS...11..446V
Altcode:
No abstract at ADS
Title: X-Ray Sources from O Star Associations
Authors: Rosner, R.; Grindlay, G.; Harnden, R.; Seward, F.; Vaiana, G.
Bibcode: 1979BAAS...11..446R
Altcode:
No abstract at ADS
Title: Formation of structured confined coronae on accretion disks.
Authors: Galeev, A. A.; Rosner, R.; Vaiana, G. S.
Bibcode: 1979xras.proc..263G
Altcode:
The interaction of magnetic fields and flows within accretion disks
and formation of structured confined coronae are discussed. Emphasis
is placed on the evolution of magnetic fields within a convective
disk and the consequences of dissipating erupted fields above the
disk where reconnection processes have substantially shorter time
scales. The key results are that the closed field topology above the
disk, together with plasma heating resulting from reconnection, leads
to the formation of an ensemble of very hot confined plasma structures
whose emission time scales are dictated by the heating process; the
cooling of these plasma structures is strongly influenced by the soft
X-ray luminosity of the underlying accretion disk.
Title: Cosmic flare transients: constraints upon models for energy
storage and release derived from the event frequency distribution.
Authors: Rosner, R.; Vaiana, G. S.
Bibcode: 1978ApJ...222.1104R
Altcode:
Flare behavior for a variety of transient sources, including the Sun,
flare stars, and a transient cosmic X-ray source, is examined. It is
found that, although these sources span an energy release rate of over
10 decades, the flare frequency (v) as a function of energy released
(E) follows a similar power law [v(E) E - J at large energies for
all these sources; the flare frequency distributions at low energies,
however, differ substantially. This result is used to develop a model
for the general flaring phenomenon which allows a unified description
of the flaring process for these diverse sources and which permits
one to infer information concerning the modes of energy storage and
release; specifically, the power-law behavior is shown to follow from
the assumption that flaring is a stochastic relaxation phenomenon and
from the requirements that the e-folding time for energy storage be
constant (independent of the instantaneous free energy accumulated)
and that the energy released be large when compared with the energy
of the unperturbed state. These requirements place constraints upon
physical models for transient sources in addition to those adduced
from the spectral behavior of the transient itself. Subject headings:
plasmas - stars: flare - Sun: flares - X-rays: bursts
Title: Heating of coronal plasma by anomalous current dissipation.
Authors: Rosner, R.; Golub, L.; Coppi, B.; Vaiana, G. S.
Bibcode: 1978ApJ...222..317R
Altcode:
It is shown that there exist heating mechanisms which connect the
observed radiative properties of the inner corona in a simple way to
the underlying solar magnetic field. The mechanisms considered involve
the generation and consequent dissipation of coronal currents. It
is argued that the spatially and temporally inhomogeneous nature
of the erupting solar magnetic field is an essential element of
coronal heating. Unlike heating theories conceived in the context
of the 'homogeneous' corona, this class of current heating models
incorporates the observed stochastic coronal structuring at the onset,
and does not view it as a complication of an otherwise straightforward
model. Attention is given to the generation of coronal currents, the
flux-tube emergence, the gradual growth and decay of active regions,
the energetics of current dissipation, current sheath geometry and
heat transport, and anomalous current dissipation.
Title: Coronal Heating and Its Relation to Magnetic Field Evolution.
Authors: Golub, L.; Rosner, R.; Vaiana, G. S.
Bibcode: 1978BAAS...10..440G
Altcode:
No abstract at ADS
Title: Dynamics of the quiescent solar corona.
Authors: Rosner, R.; Tucker, W. H.; Vaiana, G. S.
Bibcode: 1978ApJ...220..643R
Altcode:
An analytical model for the quiescent inhomogeneous solar corona is
developed on the basis of the hypothesis that looplike structures are
the basic coronal building blocks. By assuming that quiescent loop
structures observed in X-rays are in hydrostatic equilibrium, it is
demonstrated that such loops must have their temperature maximum
located near their apex and that substantial nonradiative energy
deposition must occur along most of their length. The calculations
yield a unique relation among loop temperature, pressure, and size,
which fits the X-ray observations of quiescent structures well and is
consistent with the initial assumption of hydrostatic equilibrium. The
results suggest that the coronal loops visible in X-rays represent a
relatively steady-state equilibrium of the confined plasmas and that
fluctuations in such quantities as the local heating rate can lead to
dynamically unstable states in which the loop plasma does not attain
a temperature sufficient for X-ray emission. A parameterization of
various proposed coronal heating theories is also developed within
the context of the analytical model.
Title: Recent advances in coronal physics.
Authors: Vaiana, G. S.; Rosner, R.
Bibcode: 1978ARA&A..16..393V
Altcode:
The relation between the extended atmosphere of a star, including
the chromosphere and corona, and the dynamics governing the outward
radial energy transport within the star has been considered. In this
connection, coronal activity serves as an indicator for the level
of internal activity and hence as one of the tools for investigating
stellar evolution. The observational framework is examined, taking into
account the structuring of the corona by the solar magnetic field, the
activity of the corona on virtually all spatial and temporal scales,
and the problem of accounting for the physical basis of solar coronal
structure on a variety of distinct levels. The modeling of coronae and
coronal structures is discussed, giving attention to coronal morphology
and magnetic fields, mechanisms for coronal formation, and an analysis
of coronal structures. A description of studies of stellar coronae is
also provided.
Title: Solar X-ray transients in magnetically confined plasma:
observational data and hydrodynamic model.
Authors: Peres, G.; Serio, S.; Vaiana, G. S.; Rosner, R.
Bibcode: 1978spre.conf..341P
Altcode: 1978spre.proc..341P
No abstract at ADS
Title: Hydrostatic and dynamic models of solar coronal holes.
Authors: Rosner, R.; Vaiana, G. S.
Bibcode: 1977ApJ...216..141R
Altcode:
A description is presented of a sequence of one-dimensional fluid
flow models of the transition zone and the inner corona. A hydrostatic
model atmosphere in reasonable agreement with observations of closed,
large-scale coronal structures found in the quiet sun is considered
and various physical effects are introduced, one at a time, observing
the response of the model. As a result of the investigations, a model
is developed of the plasma flow in a coronal hole. It is shown that
the data severely circumscribe the allowable range of possible models.
Title: Heating of Coronal Plasma by Anomalous Current Dissipation.
Authors: Rosner, R.; Golub, L.; Vaiana, G. S.; Coppi, B.
Bibcode: 1977BAAS....9..370R
Altcode:
No abstract at ADS
Title: Some Aspects of Magnetic Field Dynamics in Astrophysical
Plasmas.
Authors: Rosner, Robert
Bibcode: 1976PhDT........78R
Altcode:
No abstract at ADS