explanation blue bibcodes open ADS page with paths to full text
Author name code: nelson-chris
ADS astronomy entries on 2022-09-14
author:"Nelson, Christopher J." OR "Nelson, Chris J."
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Title: IRIS burst properties in active regions
Authors: Nelson, C. J.; Kleint, L.
2022arXiv220811013N Altcode:
Interface Region Imaging Spectrograph (IRIS) bursts are localised
features thought to be driven by magnetic reconnection. Although
these events are well-studied, it remains unknown whether their
properties vary as their host active regions (ARs) evolve. Here, we
aim to understand whether the measurable properties of IRIS bursts
are consistent during the evolution of their host ARs. We study 42
dense 400-step rasters sampled by IRIS. These rasters each covered
one of seven ARs, with each AR being sampled at least four times over
a minimum of 48 hours. An automated detection algorithm is used to
identify IRIS burst profiles. Data from the Solar Dynamics Observatory's
Helioseismic and Magnetic Imager are also used to provide context about
the co-spatial line-of-sight magnetic field. Of the rasters studied,
36 were found to contain IRIS burst profiles. Five ARs (11850, 11909,
11916, 12104, and 12139) contained IRIS burst profiles in each raster
that sampled them whilst one AR (11871) was found to contain no such
spectra at any time. A total of 4019 IRIS burst profiles belonging
to 752 connected objects, which we define as parent IRIS bursts,
were identified. IRIS burst profiles were only detected within compact
regions in each raster, with these regions appearing to increase in size
as the host ARs aged. No systematic changes in the frequency of IRIS
burst profiles or the spectral characteristic of IRIS burst profiles
through time were found for these ARs. Finally, 93 % of parent IRIS
bursts with areas between 1 arcsec^2 and 4 arcsec^2 occurred co-spatial
to bi-poles in the photosphere. Overall, IRIS bursts have remarkably
consistent spectral and spatial properties throughout the evolution of
ARs. These events predominantly form within the cores of larger and
more complex ARs, with the regions containing these events appearing
to increase in size as the host region itself evolves.
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Title: The European Solar Telescope
Authors: Quintero Noda, C.; Schlichenmaier, R.; Bellot Rubio, L. R.;
Löfdahl, M. G.; Khomenko, E.; Jurcak, J.; Leenaarts, J.; Kuckein,
C.; González Manrique, S. J.; Gunar, S.; Nelson, C. J.; de la Cruz
Rodríguez, J.; Tziotziou, K.; Tsiropoula, G.; Aulanier, G.; Collados,
M.; the EST team
2022arXiv220710905Q Altcode:
The European Solar Telescope (EST) is a project aimed at studying
the magnetic connectivity of the solar atmosphere, from the deep
photosphere to the upper chromosphere. Its design combines the knowledge
and expertise gathered by the European solar physics community during
the construction and operation of state-of-the-art solar telescopes
operating in visible and near-infrared wavelengths: the Swedish 1m Solar
Telescope (SST), the German Vacuum Tower Telescope (VTT) and GREGOR,
the French Télescope Héliographique pour l'Étude du Magnétisme
et des Instabilités Solaires (THÉMIS), and the Dutch Open Telescope
(DOT). With its 4.2 m primary mirror and an open configuration, EST will
become the most powerful European ground-based facility to study the Sun
in the coming decades in the visible and near-infrared bands. EST uses
the most innovative technological advances: the first adaptive secondary
mirror ever used in a solar telescope, a complex multi-conjugate
adaptive optics with deformable mirrors that form part of the optical
design in a natural way, a polarimetrically compensated telescope design
that eliminates the complex temporal variation and wavelength dependence
of the telescope Mueller matrix, and an instrument suite containing
several (etalon-based) tunable imaging spectropolarimeters and several
integral field unit spectropolarimeters. This publication summarises
some fundamental science questions that can be addressed with the
telescope, together with a complete description of its major subsystems.
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Title: Polymeric jets throw light on the origin and nature of the
forest of solar spicules
Authors: Dey, Sahel; Chatterjee, Piyali; Murthy, O. V. S. N.; Korsós,
Marianna B.; Liu, Jiajia; Nelson, Christopher J.; Erdélyi, Robertus
2022NatPh..18..595D Altcode:
Spicules are plasma jets that are observed in the dynamic interface
region between the visible solar surface and the hot corona. At any
given time, it is estimated that about 3 million spicules are present
on the Sun. We find an intriguing parallel between the simulated
spicular forest in a solar-like atmosphere and the numerous jets of
polymeric fluids when both are subjected to harmonic forcing. In a
radiative magnetohydrodynamic numerical simulation with sub-surface
convection, solar global surface oscillations are excited similarly to
those harmonic vibrations. The jets thus produced match remarkably well
with the forests of spicules detected in observations of the Sun. Taken
together, the numerical simulations of the Sun and the laboratory fluid
dynamics experiments provide insights into the mechanism underlying
the ubiquity of jets. The non-linear focusing of quasi-periodic waves
in anisotropic media of magnetized plasma as well as polymeric fluids
under gravity is sufficient to generate a forest of jets.
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Title: Oscillations in the line-of-sight magnetic field strength in
a pore observed by the GREGOR Infrared Spectrograph (GRIS)
Authors: Nelson, C. J.; Campbell, R. J.; Mathioudakis, M.
2021A&A...654A..50N Altcode: 2021arXiv210710183N
Context. Numerous magnetohydrodynamic oscillations have been reported
within solar pores over the past few decades, including in line-of-sight
(LOS) velocities, intensities, and magnetic field strengths. <BR />
Aims: Our aim is to identify whether high-amplitude oscillations in the
LOS magnetic field strength can be detected within a pore located in
Active Region 12748 and to investigate which physical mechanisms could
be responsible for them. <BR /> Methods: A solar pore was observed on
1 September 2019 using the GREGOR Infrared Spectrograph instrument for
around one hour. Full-Stokes vectors were sampled in a 37 Å window
containing the Fe I 15 648.52 Å line (effective Landé g factor of
3). The LOS magnetic field strength was inferred using the strong-field
approximation. Additionally, the Stokes Inversion based on Response
functions code was used to gain a more complete understanding of the
physical properties of the solar atmosphere at the locations of these
oscillations. <BR /> Results: Oscillations of more than 100 G are
observed in the LOS magnetic field in the period window between 600
and 1272 s at three localised (> 1″<SUP>2</SUP>) regions. These
oscillations have coherence across individual regions, indicating that
jitter cannot account for their occurrence. Longer-period amplitude
variations, amplitudes over 200 G, are also detected, but they
have periods outside of the cone-of-influence. Numerical inversions
confirm both oscillations in the LOS magnetic field strength at optical
depths of around log τ<SUB>5000</SUB> = −0.5 (potentially caused by
compression) and other effects (e.g. changes in the optical depth or the
inclination of the magnetic field) may account for these changes. <BR />
Conclusions: The oscillations in the separations of the Stokes-V lobes
of the 15 648.52 Å line appear to be solar in nature. Future work will
be required to understand whether these are truly oscillations in the
magnetic field strength at a specific depth in the solar atmosphere
or whether other effects are responsible for these signatures.
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Title: Flare-induced Sunquake Signatures in the Ultraviolet as
Observed by the Atmospheric Imaging Assembly
Authors: Quinn, Sean; Mathioudakis, Mihalis; Nelson, Christopher J.;
Milligan, Ryan O.; Reid, Aaron; Jess, David B.
2021ApJ...920...25Q Altcode: 2021arXiv210505704Q
Sunquakes (SQs) have been routinely observed in the solar photosphere,
but it is only recently that signatures of these events have been
detected in the chromosphere. We investigate whether signatures of
SQs are common in ultraviolet (UV) continua that sample the solar
plasma several hundred km above where SQs are typically detected. We
analyze observations from the Solar Dynamics Observatory's Atmospheric
Imaging Assembly (SDO/AIA) 1600 and 1700 Å passbands, for SQ signatures
induced by the flares of Solar Cycle 24. We base our analysis on the
62 SQs detected in the recent statistical study presented by Sharykin
& Kosovichev. We find that 9 out of 62 SQ candidates produced a
response that is clearly detected in running-difference images from
the AIA 1600 and 1700 Å channels. A binary frequency filter with a
width of 2 mHz, centered on 6 mHz, was applied to the data. The first
signature of each SQ was detected at distances between 5.2 and 25.7
Mm from the associated flare ribbon. Time-distance and regression
analysis allowed us to calculate the apparent transverse velocities
of the SQs in the UV data sets and found maximum velocities as high
as 41 km s<SUP>-1</SUP>, 87 Mm away from the SQ source. Our analysis
shows that flare-induced SQ signatures can be detected in the SDO/AIA
1600 and 1700 Å passbands, hinting at their presence in the lower
chromosphere. There was no apparent correlation between GOES flare
classification and the appearance of the SQ at these heights.
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Title: Temporal evolution of small-scale internetwork magnetic fields
in the solar photosphere (Corrigendum)
Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.;
Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A.
2021A&A...652C...2C Altcode:
No abstract at ADS
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Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope
(DKIST)
Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio,
Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart;
Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa,
Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez
Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler,
Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun,
Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres,
Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.;
Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini,
Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena;
Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor;
Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael;
Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli,
Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys,
Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.;
Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis,
Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David
E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson,
Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.;
Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.;
Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava,
Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas
A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas,
Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST
Instrument Scientists; DKIST Science Working Group; DKIST Critical
Science Plan Community
2021SoPh..296...70R Altcode: 2020arXiv200808203R
The National Science Foundation's Daniel K. Inouye Solar Telescope
(DKIST) will revolutionize our ability to measure, understand,
and model the basic physical processes that control the structure
and dynamics of the Sun and its atmosphere. The first-light DKIST
images, released publicly on 29 January 2020, only hint at the
extraordinary capabilities that will accompany full commissioning of
the five facility instruments. With this Critical Science Plan (CSP)
we attempt to anticipate some of what those capabilities will enable,
providing a snapshot of some of the scientific pursuits that the DKIST
hopes to engage as start-of-operations nears. The work builds on the
combined contributions of the DKIST Science Working Group (SWG) and
CSP Community members, who generously shared their experiences, plans,
knowledge, and dreams. Discussion is primarily focused on those issues
to which DKIST will uniquely contribute.
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Title: Temporal evolution of small-scale internetwork magnetic fields
in the solar photosphere
Authors: Campbell, R. J.; Mathioudakis, M.; Collados, M.; Keys, P. H.;
Asensio Ramos, A.; Nelson, C. J.; Kuridze, D.; Reid, A.
2021A&A...647A.182C Altcode: 2021arXiv210200942C
Context. While the longitudinal field that dominates in photospheric
network regions has been studied extensively, small-scale transverse
fields have recently been found to be ubiquitous in the quiet
internetwork photosphere and this merits further study. Furthermore,
few observations have been able to capture how this field evolves. <BR
/> Aims: We aim to statistically characterize the magnetic vector in
a quiet Sun internetwork region and observe the temporal evolution of
specific small-scale magnetic features. <BR /> Methods: We present
two high spatio-temporal resolution observations that reveal the
dynamics of two disk-centre internetwork regions taken by the new GREGOR
Infrared Spectrograph Integral Field Unit with the highly magnetically
sensitive photospheric Fe I line pair at 15648.52 Å and 15652.87
Å. We record the full Stokes vector and apply inversions with the
Stokes inversions based on response functions code to retrieve the
parameters characterizing the atmosphere. We consider two inversion
schemes: scheme 1 (S1), where a magnetic atmosphere is embedded in
a field free medium, and scheme 2 (S2), with two magnetic models
and a fixed 30% stray light component. <BR /> Results: The magnetic
properties produced from S1 inversions returned a median magnetic
field strength of 200 and 240 G for the two datasets, respectively. We
consider the median transverse (horizontal) component, among pixels
with Stokes Q or U, and the median unsigned longitudinal (vertical)
component, among pixels with Stokes V, above a noise threshold. We
determined the former to be 263 G and 267 G, and the latter to be 131
G and 145 G, for the two datasets, respectively. Finally, we present
three regions of interest, tracking the dynamics of small-scale magnetic
features. We apply S1 and S2 inversions to specific profiles of interest
and find that the latter produces better approximations when there is
evidence of mixed polarities. We find patches of linear polarization
with magnetic flux density of the order of 130−150 G and find that
linear polarization appears preferentially at granule-intergranular
lane boundaries. The weak magnetic field appears to be organized in
terms of complex `loop-like' structures, with transverse fields often
flanked by opposite polarity longitudinal fields.
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Title: Significance of Cooling Effect On Comprehension of Kink
Oscillations of Coronal Loops
Authors: Shukhobodskaia, Daria; Shukhobodskiy, Alexander A.; Nelson,
Chris J.; Ruderman, Michael S.; Erdélyi, Robert
2021FrASS...7..106S Altcode:
Kink oscillations of coronal loops have been widely studied, both
observationally and theoretically, over the past few decades. It
has been shown that the majority of observed driven coronal loop
oscillations appear to damp with either exponential or Gaussian
profiles and a range of mechanisms have been proposed to account for
this. However, some driven oscillations seem to evolve in manners which
cannot be modelled with purely Gaussian or exponential profiles, with
amplification of oscillations even being observed on occasions. Recent
research has shown that incorporating the combined effects of coronal
loop expansion, resonant absorption, and cooling can cause significant
deviations from Gaussian and exponential profiles in damping profiles,
potentially explaining increases in oscillation amplitude through time
in some cases. In this article, we analyse 10 driven kink oscillations
in coronal loops to further investigate the ability of expansion and
cooling to explain complex damping profiles. Our results do not rely
on fitting a periodicity to the oscillations meaning complexities in
both temporal (period changes) and spatial (amplitude changes) can be
accounted for in an elegant and simple way. Furthermore, this approach
could also allow us to infer some important diagnostic information
(such as, for example, the density ratio at the loop foot-points)
from the oscillation profile alone, without detailed measurements
of the loop and without complex numerical methods. Our results imply
the existence of correlations between the density ratio at the loop
foot-points and the amplitudes and periods of the oscillations. Finally,
we compare our results to previous models, namely purely Gaussian and
purely exponential damping profiles, through the calculation of chi^2
values, finding the inclusion of cooling can produce better fits in
some cases. The current study indicates that thermal evolution should
be included in kink-mode oscillation models in the future to help
us to better understand oscillations that are not purely Gaussian
or exponential.
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Title: Torsional oscillations within a magnetic pore in the solar
photosphere
Authors: Stangalini, Marco; Erdélyi, Robertus; Boocock, Callum;
Tsiklauri, David; Nelson, Christopher J.; Del Moro, Dario; Berrilli,
Francesco; Korsós, Marianna B.
2021NatAs...5..691S Altcode: 2021NatAs.tmp...82S
Alfvén waves have proven to be important in a range of physical
systems due to their ability to transport non-thermal energy over long
distances in a magnetized plasma. This property is of specific interest
in solar physics, where the extreme heating of the atmosphere of the
Sun remains unexplained. In an inhomogeneous plasma such as a flux
tube in the solar atmosphere, they manifest as incompressible torsional
perturbations. However, despite evidence in the upper atmosphere, they
have not been directly observed in the photosphere. Here, we report the
detection of antiphase incompressible torsional oscillations observed in
a magnetic pore in the photosphere by the Interferometric Bidimensional
Spectropolarimeter. State-of-the-art numerical simulations suggest that
a kink mode is a possible excitation mechanism of these waves. The
excitation of torsional waves in photospheric magnetic structures
can substantially contribute to the energy transport in the solar
atmosphere and the acceleration of the solar wind, especially if such
signatures will be ubiquitously detected in even smaller structures
with the forthcoming next generation of solar telescopes.
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Title: Power-law energy distributions of small-scale impulsive events
on the active Sun: results from IRIS
Authors: Vilangot Nhalil, Nived; Nelson, Chris J.; Mathioudakis,
Mihalis; Doyle, J. Gerry; Ramsay, Gavin
2020MNRAS.499.1385V Altcode: 2020MNRAS.tmp.2719N; 2020arXiv200903123V
Numerous studies have analysed inferred power-law distributions
between frequency and energy of impulsive events in the outer solar
atmosphere in an attempt to understand the predominant energy supply
mechanism in the corona. Here, we apply a burst detection algorithm to
high-resolution imaging data obtained by the Interface Region Imaging
Spectrograph to further investigate the derived power-law index, γ,
of bright impulsive events in the transition region. Applying the
algorithm with a constant minimum event lifetime (of either 60 s or
110 s) indicated that the target under investigation, such as Plage
and Sunspot, has an influence on the observed power-law index. For
regions dominated by sunspots, we always find γ < 2; however,
for data sets where the target is a plage region, we often find that
γ > 2 in the energy range (~10<SUP>23</SUP>, ~10<SUP>26</SUP>)
erg. Applying the algorithm with a minimum event lifetime of three
time-steps indicated that cadence was another important factor, with
the highest cadence data sets returning γ > 2 values. The estimated
total radiative power obtained for the observed energy distributions
is typically 10-25 per cent of what would be required to sustain the
corona indicating that impulsive events in this energy range are not
sufficient to solve coronal heating. If we were to extend the power-law
distribution down to an energy of 10<SUP>21</SUP> erg, and assume parity
between radiative energy release and the deposition of thermal energy,
then such bursts could provide 25-50 per cent of the required energy
to account for the coronal heating problem.
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Title: Umbral chromospheric fine structure and umbral flashes modelled
as one: The corrugated umbra
Authors: Henriques, Vasco M. J.; Nelson, Chris J.; Rouppe van der
Voort, Luc H. M.; Mathioudakis, Mihalis
2020A&A...642A.215H Altcode: 2020arXiv200805482H
Context. The chromosphere of the umbra of sunspots features an
assortment of dynamic fine structures that are poorly understood and
often studied separately. Small-scale umbral brightenings (SSUBs),
umbral microjets, spikes or short dynamic fibrils (SDFs), and umbral
dark fibrils are found in any observation of the chromosphere with
sufficient spatial resolution performed at the correct umbral flash
stage and passband. Understanding these features means understanding
the dynamics of the umbral chromosphere. <BR /> Aims: We aim to fully
understand the dynamics of umbral chromosphere through analysis of the
relationships between distinct observed fine features and to produce
complete models that explain both spectral profiles and the temporal
evolution of the features. We seek to relate such understanding to
umbral flashes. <BR /> Methods: We studied the spatial and spectral
co-evolution of SDFs, SSUBs, and umbral flashes in Ca II 8542 Å
spectral profiles. We produced models that generate the spectral
profiles for all classes of features using non-local thermodynamic
equilibrium radiative transfer with a recent version of the NICOLE
inversion code. <BR /> Results: We find that both bright SSUBs and dark
SDF structures are described with a continuous feature in the parameter
space that is distinct from the surroundings even in pixel-by-pixel
inversions. We find a phase difference between such features and
umbral flashes in both inverted line-of-sight velocities and timing
of the brightenings. For umbral flashes themselves we resolve,
for the first time in inversion-based semi-empirical modelling,
the pre-flash downflows, post-flash upflows, and the counter-flows
present during the umbral flash phase. We further present a simple
time-dependent cartoon model that explains the dynamics and spectral
profiles of both fine structure, dark and bright, and umbral flashes
in umbral chromospheres. <BR /> Conclusions: The similarity of the
profiles between the brightenings and umbral flashes, the pattern of
velocities obtained from the inversions, and the phase relationships
between the structures all lead us to put forward that all dynamic
umbral chromospheric structures observed to this date are a locally
delayed or locally early portion of the oscillatory flow pattern that
generates flashes, secondary to the steepening large-scale acoustic
waves at its source. Essentially, SSUBs are part of the same shock or
merely compression front responsible for the spatially larger umbral
flash phenomenon, but out of phase with the broader oscillation.
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Title: Evolution of downflows in the transition region above a
sunspot over short time-scales
Authors: Nelson, C. J.; Krishna Prasad, S.; Mathioudakis, M.
2020A&A...640A.120N Altcode: 2020arXiv200613617N
Context. Downflows with potentially super-sonic velocities have been
reported to occur in the transition region above many sunspots; however,
how these signatures evolve over short time-scales in both spatial and
spectral terms is still unknown and requires further research. <BR
/> Aims: In this article, we investigate the evolution of downflows
detected within spectral lines sampling the transition region on
time-scales of the order of minutes and we search for clues as to
the formation mechanisms of these features in co-temporal imaging
data. <BR /> Methods: For the purposes of this article, we used
high-resolution spectral and imaging data sampled by the Interface
Region Imaging Spectrograph on the 20 and 21 May 2015 to identify and
analyse downflows. Additionally, photospheric and coronal imaging data
from the Hinode and Solar Dynamics Observatory satellites were studied
to provide context about the wider solar atmosphere. <BR /> Results:
Four downflows were identified and analysed through time. The potential
super-sonic components of these downflows had widths of around 2″ and
were observed to evolve over time-scales of the order of minutes. The
measured apparent downflow velocities were structured both in time and
space, with the highest apparent velocities occurring above a bright
region detected in Si IV 1400 Å images. Downflows with apparent
velocities below the super-sonic threshold that was assumed here
were observed to extend a few arcseconds away from the foot-points,
suggesting that the potential super-sonic components are linked to
larger-scale flows. The electron density and mass flux for these events
were found to be within the ranges of 10<SUP>9.6</SUP>-10<SUP>10.2</SUP>
cm<SUP>-3</SUP> and 10<SUP>-6.81</SUP>-10<SUP>-7.48</SUP> g
cm<SUP>-2</SUP> s<SUP>-1</SUP>, respectively. Finally, each downflow
formed at the foot-point of thin "fingers", extending out around
3-5″ in Si IV 1400 Å data with smaller widths (< 1″) than
the super-sonic downflow components. <BR /> Conclusions: Downflows
can appear, disappear, and recur within time-scales of less than one
hour in sunspots. As the potential super-sonic downflow signatures
were detected at the foot-points of both extended fingers in Si IV
1400 SJI data and sub-sonic downflows in Si IV 1394 Å spectra, it
is likely that these events are linked to larger-scale flows within
structures such as coronal loops.
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Title: Solar Flare Prediction Using Magnetic Field Diagnostics above
the Photosphere
Authors: Korsós, M. B.; Georgoulis, M. K.; Gyenge, N.; Bisoi, S. K.;
Yu, S.; Poedts, S.; Nelson, C. J.; Liu, J.; Yan, Y.; Erdélyi, R.
2020ApJ...896..119K Altcode: 2020arXiv200512180K
In this article, we present the application of the weighted horizontal
gradient of magnetic field (WG<SUB>M</SUB>) flare prediction method
to three-dimensional (3D) extrapolated magnetic configurations of
13 flaring solar active regions (ARs). The main aim is to identify
an optimal height range, if any, in the interface region between the
photosphere and lower corona, where the flare onset time prediction
capability of WG<SUB>M</SUB> is best exploited. The optimal height
is where flare prediction, by means of the WG<SUB>M</SUB> method, is
achieved earlier than at the photospheric level. 3D magnetic structures,
based on potential and nonlinear force-free field extrapolations, are
constructed to study a vertical range from the photosphere up to the
low corona with a 45 km step size. The WG<SUB>M</SUB> method is applied
as a function of height to all 13 flaring AR cases that are subject to
certain selection criteria. We found that applying the WG<SUB>M</SUB>
method between 1000 and 1800 km above the solar surface would improve
the prediction of the flare onset time by around 2-8 hr. Certain caveats
and an outlook for future work along these lines are also discussed.
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Title: Evolution of supersonic downflows in a sunspot
Authors: Nelson, C. J.; Krishna Prasad, S.; Mathioudakis, M.
2020A&A...636A..35N Altcode: 2020arXiv200302489N
Context. Supersonic downflows have been observed in transition
region spectra above numerous sunspots, however, little research
has been conducted to date into how persistent these signatures
are within sunspots on timescales longer than a few hours. <BR />
Aims: We aim to analyse the lead sunspot of AR 12526 to infer the
properties and evolution of supersonic downflows occurring within
it using high-spatial and spectral resolution data. <BR /> Methods:
We analysed 16 large, dense raster scans sampled by the Interface
Region Imaging Spectrograph. These rasters tracked the lead sunspot
of AR 12526 across the solar disc at discrete times between 27 March
2016 and 2 April 2016, providing spectral profiles from the Si IV, O
IV, Mg II, and C II lines. Additionally, we studied one sit-and-stare
observation acquired on 1 April 2016 centred on the sunspot to analyse
the evolution of supersonic downflows on shorter timescales. <BR />
Results: Supersonic downflows are variable within this sunspot both
in terms of spatial structuring and velocities. Thirteen of the 16
raster scans display some evidence of supersonic downflows in the Si
IV 1394 Å line co-spatial to a sustained bright structure detected
in the 1400 Å slit-jaw imaging channel; a peak velocity of 112 km
s<SUP>-1</SUP> is recorded on 29 March 2016. Evidence for supersonic
downflows in the O IV 1401 Å line is found in 14 of these rasters; the
spatial structuring in this line often differs from that inferred from
the Si IV 1394 Å line. Only one example of a supersonic downflow is
detected in the C II 1335 Å line and no downflows are found in the Mg
II 2796 Å lines at these locations. In the sit-and-stare observations,
no dual flow is initially detected, however, a supersonic downflow
develops after approximately 60 min. This downflow accelerates from 73
km s<SUP>-1</SUP> to close to 80 km s<SUP>-1</SUP> in both the Si IV
1394 Å and O IV 1401 Å lines over the course of 20 min before the
end of the observation. <BR /> Conclusions: Supersonic downflows are
found in the Si IV 1394 Å line in 13 of the 16 rasters studied in this
work. The morphology of these downflows evolved over the course of both
hours and days and was often different in the Si IV 1394 Å and O IV
1401 Å lines. These events were found co-spatial to a bright region
in the core of the Si IV 1394 Å line, which appeared to form at the
footpoints of coronal fan loops. Our results indicate that one raster
is not enough to conclusively draw inferences about the properties of
supersonic downflows within a sunspot during its lifetime.
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Title: Multipoint Observations of Solar Wind Conditions and
Magnetopause Motion
Authors: Bagheri, F.; Lopez, R. E.; Dredger, P. M.; Bonde, R. E. F.;
Bui, M.; Chapagain, N.; Nelson, C.; Xing, C.
2019AGUFMSM51C3198B Altcode:
We study the magnetopause motion and structure based on observation
from multiple crossings of the magnetopause of THEMIS A, D and E with
simultaneous solar wind observations from Wind, ACE, THEMIS B, and
THEMIS C. The solar wind data shows the IMF was radial and the velocity
of solar wind was almost constant. The THEMIS A, D and E observations
are consistent with the classic picture of pressure balance across the
magnetopause. The thickness of the Chapman-Ferraro current layer is
about one gyro diameter. The average magnetopause speeds were in the low
10's of km/s, however, speeds up to 100km/s were observed. During this
period there is no evidence of hot flow anomalies in the magnetosheath
near the magnetopause. Although the orientation of the IMF during the
observations would have been predicted to cause wavy motions of the
magnetopause boundary, in our study there is no evidence of such kind
of motion.
---------------------------------------------------------
Title: Co-spatial velocity and magnetic swirls in the simulated
solar photosphere
Authors: Liu, Jiajia; Carlsson, Mats; Nelson, Chris J.; Erdélyi,
Robert
2019A&A...632A..97L Altcode: 2019arXiv191110923L
Context. Velocity or intensity swirls have now been shown to be
widely present throughout the photosphere and chromosphere. It has
been suggested that these events could contribute to the heating
of the upper solar atmosphere, via exciting Alfvén pulses, which
could carry significant amounts of energy. However, the conjectured
necessary physical conditions for their excitation, that the magnetic
field rotates co-spatially and co-temporally with the velocity field,
has not been verified. <BR /> Aims: We aim to understand whether
photospheric velocity swirls exist co-spatially and co-temporally with
photospheric magnetic swirls, in order to demonstrate the link between
swirls and pulses. <BR /> Methods: The automated swirl detection
algorithm (ASDA) is applied to the photospheric horizontal velocity
and vertical magnetic fields obtained from a series of realistic
numerical simulations using the radiative magnetohydrodynamics (RMHD)
code Bifrost. The spatial relationship between the detected velocity
and magnetic swirls is further investigated via a well-defined
correlation index (CI) study. <BR /> Results: On average, there are
∼63 short-lived photospheric velocity swirls (with lifetimes mostly
less than 20 s, and average radius of ∼37 km and rotating speeds of
∼2.5 km s<SUP>-1</SUP>) detected in a field of view (FOV) of 6 ×
6 Mm<SUP>-2</SUP>, implying a total population of velocity swirls of
∼1.06 × 10<SUP>7</SUP> in the solar photosphere. More than 80% of the
detected velocity swirls are found to be accompanied by local magnetic
concentrations in intergranular lanes. On average, ∼71% of the
detected velocity swirls have been found to co-exist with photospheric
magnetic swirls with the same rotating direction. <BR /> Conclusions:
The co-temporal and co-spatial rotation in the photospheric velocity
and magnetic fields provide evidence that the conjectured condition for
the excitation of Alfvén pulses by photospheric swirls is fulfilled.
---------------------------------------------------------
Title: Investigation of light ion fusion reactions with plasma
discharges
Authors: Schenkel, T.; Persaud, A.; Wang, H.; Seidl, P. A.; MacFadyen,
R.; Nelson, C.; Waldron, W. L.; Vay, J. -L.; Deblonde, G.; Wen, B.;
Chiang, Y. -M.; MacLeod, B. P.; Ji, Q.
2019JAP...126t3302S Altcode: 2019arXiv190503400S
The scaling of reaction yields in light ion fusion to low reaction
energies is important for our understanding of stellar fuel chains
and the development of future energy technologies. Experiments become
progressively more challenging at lower reaction energies due to the
exponential drop of fusion cross sections below the Coulomb barrier. We
report on experiments where deuterium-deuterium (D-D) fusion reactions
are studied in a pulsed plasma in the glow discharge regime using a
benchtop apparatus. We model plasma conditions using particle-in-cell
codes. Advantages of this approach are relatively high peak ion currents
and current densities (0.1 to several A/cm<SUP>2</SUP>) that can be
applied to metal wire cathodes for several days. We detect neutrons from
D-D reactions with scintillator-based detectors. For palladium targets,
we find neutron yields as a function of cathode voltage that are over
100 times higher than yields expected for bare nuclei fusion at ion
energies below 2 keV (center of mass frame). A possible explanation is a
correction to the ion energy due to an electron screening potential of
1000 ± 250 eV, which increases the probability for tunneling through
the repulsive Coulomb barrier. Our compact, robust setup enables
parametric studies of this effect at relatively low reaction energies.
---------------------------------------------------------
Title: Spatially Resolved Signatures of Bidirectional Flows Observed
in Inverted-Y Shaped Jets
Authors: Nelson, C. J.; Freij, N.; Bennett, S.; Erdélyi, R.;
Mathioudakis, M.
2019ApJ...883..115N Altcode: 2019arXiv190805132N
Numerous apparent signatures of magnetic reconnection have been
reported in the solar photosphere, including inverted-Y shaped jets. The
reconnection at these sites is expected to cause localized bidirectional
flows and extended shock waves; however, these signatures are rarely
observed as extremely high spatial-resolution data are required. Here,
we use Hα imaging data sampled by the Swedish Solar Telescope’s CRisp
Imaging SpectroPolarimeter to investigate whether bidirectional flows
can be detected within inverted-Y shaped jets near the solar limb. These
jets are apparent in the Hα line wings, while no signature of either
jet is observed in the Hα line core, implying reconnection took place
below the chromospheric canopy. Asymmetries in the Hα line profiles
along the legs of the jets indicate the presence of bidirectional flows,
consistent with cartoon models of reconnection in chromospheric anemone
jets. These asymmetries are present for over two minutes, longer than
the lifetimes of Rapid Blue Excursions, and beyond ±1 Å into the wings
of the line indicating that flows within the inverted-Y shaped jets
are responsible for the imbalance in the profiles, rather than motions
in the foreground. Additionally, surges form following the occurrence
of the inverted-Y shaped jets. This surge formation is consistent with
models, which suggests such events could be caused by the propagation
of shock waves from reconnection sites in the photosphere to the
upper atmosphere. Overall, our results provide evidence that magnetic
reconnection in the photosphere can cause bidirectional flows within
inverted-Y shaped jets and could be the driver of surges.
---------------------------------------------------------
Title: Evidence of ubiquitous Alfvén pulses transporting energy
from the photosphere to the upper chromosphere
Authors: Liu, Jiajia; Nelson, Chris J.; Snow, Ben; Wang, Yuming;
Erdélyi, Robert
2019NatCo..10.3504L Altcode:
The multi-million degree temperature increase from the middle to
the upper solar atmosphere is one of the most fascinating puzzles
in plasma-astrophysics. Although magnetic waves might transport
enough energy from the photosphere to heat up the local chromosphere
and corona, observationally validating their ubiquity has proved
challenging. Here, we show observational evidence that ubiquitous
Alfvén pulses are excited by prevalent intensity swirls in the
solar photosphere. Correlation analysis between swirls detected at
different heights in the solar atmosphere, together with realistic
numerical simulations, show that these Alfvén pulses propagate upwards
and reach chromospheric layers. We found that Alfvén pulses carry
sufficient energy flux (1.9 to 7.7 kW m<SUP>-2</SUP>) to balance the
local upper chromospheric energy losses ( 0.1 kW m<SUP>-2</SUP>) in
quiet regions. Whether this wave energy flux is actually dissipated
in the chromosphere and can lead to heating that balances the losses
is still an open question.
---------------------------------------------------------
Title: The Effect Of Cooling On Driven Kink Oscillations Of Coronal
Loops
Authors: Nelson, Chris J.; Shukhobodskiy, Alexander A.; Erdélyi,
Robertus; Mathioudakis, Mihalis
2019FrASS...6...45N Altcode: 2019arXiv190513137N
Ever since their detection two decades ago, standing kink oscillations
in coronal loops have been extensively studied both observationally
and theoretically. Almost all driven coronal loop oscillations
(e.g., by flares) are observed to damp through time often with
Gaussian or exponential profiles. Intriguingly, however, it has
been shown theoretically that the amplitudes of some oscillations
could be modified from Gaussian or exponential profiles if cooling
is present in the coronal loop systems. Indeed, in some cases the
oscillation amplitude can even increase through time. In this article,
we analyse a flare-driven coronal loop oscillation observed by the
Solar Dynamics Observatory's Atmospheric Imaging Assembly (SDO/AIA)
in order to investigate whether models of cooling can explain the
amplitude profile of the oscillation and whether hints of cooling can
be found in the intensity evolution of several SDO/AIA filters. During
the oscillation of this loop system, the kink mode amplitude appears to
differ from a typical Gaussian or exponential profile with some hints
being present that the amplitude increases. The application of cooling
coronal loop modelling allowed us to estimate the density ratio between
the loop and the background plasma, with a ratio of between 2.05-2.35
being returned. Overall, our results indicate that consideration of
the thermal evolution of coronal loop systems can allow us to better
describe oscillations in these structures and return more accurate
estimates of the physical properties of the loops (e.g., density,
scale height, magnetic field strength).
---------------------------------------------------------
Title: Automated Swirl Detection Algorithm (ASDA) and Its Application
to Simulation and Observational Data
Authors: Liu, Jiajia; Nelson, Chris J.; Erdélyi, Robertus
2019ApJ...872...22L Altcode: 2018arXiv180402931L
Swirling motions in the solar atmosphere have been widely observed in
recent years and suggested to play a key role in channeling energy
from the photosphere into the corona. Here, we present a newly
developed Automated Swirl Detection Algorithm (ASDA) and discuss
its applications. ASDA is found to be very proficient at detecting
swirls in a variety of synthetic data with various levels of noise,
implying our subsequent scientific results are astute. Applying ASDA
to photospheric observations with a pixel size of 39.2 km sampled by
the Solar Optical Telescope on board Hinode suggests a total number
of 1.62 × 10<SUP>5</SUP> swirls in the photosphere, with an average
radius and rotating speed of ∼290 km and <1.0 km s<SUP>-1</SUP>,
respectively. Comparisons between swirls detected in Bifrost numerical
MHD simulations and both ground-based and space-borne observations
suggest that (1) the spatial resolution of data plays a vital role in
the total number and radii of swirls detected, and (2) noise introduced
by seeing effects could decrease the detection rate of swirls, but has
no significant influences in determining their inferred properties. All
results have shown that there is no significant difference in the
analyzed properties between counterclockwise or clockwise rotating
swirls. About 70% of swirls are located in intergranular lanes. Most
of the swirls have lifetimes of less than twice the cadences, meaning
future research should aim to use data with much higher cadences than
6 s. In the conclusions, we propose some promising future research
applications where ASDA may provide useful insight.
---------------------------------------------------------
Title: Solar Ultraviolet Bursts
Authors: Young, Peter R.; Tian, Hui; Peter, Hardi; Rutten, Robert J.;
Nelson, Chris J.; Huang, Zhenghua; Schmieder, Brigitte; Vissers, Gregal
J. M.; Toriumi, Shin; Rouppe van der Voort, Luc H. M.; Madjarska, Maria
S.; Danilovic, Sanja; Berlicki, Arkadiusz; Chitta, L. P.; Cheung, Mark
C. M.; Madsen, Chad; Reardon, Kevin P.; Katsukawa, Yukio; Heinzel, Petr
2018SSRv..214..120Y Altcode: 2018arXiv180505850Y
The term "ultraviolet (UV) burst" is introduced to describe small,
intense, transient brightenings in ultraviolet images of solar active
regions. We inventorize their properties and provide a definition
based on image sequences in transition-region lines. Coronal signatures
are rare, and most bursts are associated with small-scale, canceling
opposite-polarity fields in the photosphere that occur in emerging flux
regions, moving magnetic features in sunspot moats, and sunspot light
bridges. We also compare UV bursts with similar transition-region
phenomena found previously in solar ultraviolet spectrometry and
with similar phenomena at optical wavelengths, in particular Ellerman
bombs. Akin to the latter, UV bursts are probably small-scale magnetic
reconnection events occurring in the low atmosphere, at photospheric
and/or chromospheric heights. Their intense emission in lines with
optically thin formation gives unique diagnostic opportunities
for studying the physics of magnetic reconnection in the low solar
atmosphere. This paper is a review report from an International Space
Science Institute team that met in 2016-2017.
---------------------------------------------------------
Title: Magnetic Braids in Eruptions of a Spiral Structure in the
Solar Atmosphere
Authors: Huang, Zhenghua; Xia, Lidong; Nelson, Chris J.; Liu, Jiajia;
Wiegelmann, Thomas; Tian, Hui; Klimchuk, James A.; Chen, Yao; Li, Bo
2018ApJ...854...80H Altcode: 2018arXiv180105967H
We report on high-resolution imaging and spectral observations of
eruptions of a spiral structure in the transition region, which
were taken with the Interface Region Imaging Spectrograph, and the
Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic
Imager (HMI) onboard the Solar Dynamics Observatory (SDO). The eruption
coincided with the appearance of two series of jets, with velocities
comparable to the Alfvén speeds in their footpoints. Several pieces of
evidence of magnetic braiding in the eruption are revealed, including
localized bright knots, multiple well-separated jet threads, transition
region explosive events, and the fact that all three of these are
falling into the same locations within the eruptive structures. Through
analysis of the extrapolated 3D magnetic field in the region, we found
that the eruptive spiral structure corresponded well to locations
of twisted magnetic flux tubes with varying curl values along their
lengths. The eruption occurred where strong parallel currents,
high squashing factors, and large twist numbers were obtained. The
electron number density of the eruptive structure is found to be ∼3 ×
10<SUP>12</SUP> cm<SUP>-3</SUP>, indicating that a significant amount
of mass could be pumped into the corona by the jets. Following the
eruption, the extrapolations revealed a set of seemingly relaxed loops,
which were visible in the AIA 94 Å channel, indicating temperatures
of around 6.3 MK. With these observations, we suggest that magnetic
braiding could be part of the mechanisms explaining the formation of
solar eruption and the mass and energy supplement to the corona.
---------------------------------------------------------
Title: The formation of small-scale umbral brightenings in sunspot
atmospheres
Authors: Nelson, C. J.; Henriques, V. M. J.; Mathioudakis, M.; Keenan,
F. P.
2017A&A...605A..14N Altcode: 2017arXiv170505617N
Context. Sunspot atmospheres have been shown to be highly inhomogeneous
hosting both quasi-stable and transient features, such as small-scale
umbral brightenings (previously named "umbral micro-jets") and dark
fibril-like events. <BR /> Aims: We seek to understand the morphological
properties and formation mechanisms of small-scale umbral brightenings
(analogous to umbral micro-jets). In addition, we aim to understand
whether links between these events and short dynamic fibrils,
umbral flashes, and umbral dots can be established. <BR /> Methods:
A Swedish 1 m Solar Telescope (SST) filtergram time-series sampling
the Ca II H line and a CRisp Imaging Spectro-Polarimeter (SST/CRISP)
full-Stokes 15-point Ca II 8542 Å line scan dataset were used. The
spatial resolutions of these datasets are close to 0.1” and 0.18”
with cadences of 1.4 s and 29 s, respectively. These data allowed
us to construct light-curves, plot line profiles, and to perform
a weak-field approximation in order to infer the magnetic field
strength. <BR /> Results: The average lifetime and lengths of the 54
small-scale brightenings identified in the sunspot umbra are found
to be 44.2 s (σ = 20 s) and 0.56” (σ = 0.14”), respectively. The
spatial positioning and morphological evolution of these events in
Ca II H filtergrams was investigated finding no evidence of parabolic
or ballistic profiles nor a preference for co-spatial formation with
umbral flashes. Line scans in Ca II 8542 Å and the presence of Stokes
V profile reversals provided evidence that these events could form in a
similar manner to umbral flashes in the chromosphere (I.e. through the
formation of shocks either due to the steepening of localised wavefronts
or due to the impact of returning material from short dynamic fibrils,
a scenario we find evidence for). The application of the weak-field
approximation indicated that changes in the line-of-sight magnetic
field were not responsible for the modifications to the line profile
and suggested that thermodynamic effects are, in fact, the actual
cause of the increased emission. Finally, a sub-set of small-scale
brightenings were observed to form at the foot-points of short dynamic
fibrils. <BR /> Conclusions: The small-scale umbral brightenings studied
here do not appear to be jet-like in nature. Instead they appear to be
evidence of shock formation in the lower solar atmosphere. We found
no correlation between the spatial locations where these events were
observed and the occurrence of umbral dots and umbral flashes. These
events have lifetimes and spectral signatures comparable to umbral
flashes and are located at the footpoints of short dynamic fibrils,
during or at the end of the red-shifted stage. It is possible that
these features form due to the shocking of fibrilar material in the
lower atmosphere upon its return under gravity.
---------------------------------------------------------
Title: IRIS Burst Spectra Co-spatial to a Quiet-Sun Ellerman-like
Brightening
Authors: Nelson, C. J.; Freij, N.; Reid, A.; Oliver, R.; Mathioudakis,
M.; Erdélyi, R.
2017ApJ...845...16N Altcode: 2017arXiv170705080N
Ellerman bombs (EBs) have been widely studied over the past two
decades; however, only recently have the counterparts of these events
been observed in the quiet-Sun. The aim of this article is to further
understand small-scale quiet-Sun Ellerman-like brightenings (QSEBs)
through research into their spectral signatures, including investigating
whether the hot signatures associated with some EBs are also visible
co-spatial to any QSEBs. We combine Hα and Ca II 8542 Å line scans at
the solar limb with spectral and imaging data sampled by the Interface
Region Imaging Spectrograph (IRIS). Twenty-one QSEBs were identified
with average lifetimes, lengths, and widths measured to be around 120 s,
0.″63, and 0.″35, respectively. Three of these QSEBs displayed clear
repetitive flaring through their lifetimes, comparable to the behavior
of EBs in active regions. Two QSEBs in this sample occurred co-spatial
to increased emission in SDO/AIA 1600 Å and IRIS slit-jaw imager 1400
Å data; however, these intensity increases were smaller than those
reported co-spatially with EBs. One QSEB was also sampled by the IRIS
slit during its lifetime, displaying increases in intensity in the
Si IV 1393 Å and Si IV 1403 Å cores, as well as the C II and Mg II
line wings, analogous to IRIS bursts (IBs). Using RADYN simulations,
we are unable to reproduce the observed QSEB Hα and Ca II 8542 Å
line profiles, leaving the question of the temperature stratification
of QSEBs open. Our results imply that some QSEBs could be heated to
transition region temperatures, suggesting that IB profiles should be
observed throughout the quiet-Sun.
---------------------------------------------------------
Title: On the relationship between magnetic cancellation and UV
burst formation
Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.
2016MNRAS.463.2190N Altcode: 2016arXiv160806505N; 2016MNRAS.tmp.1156N
Burst-like events with signatures in the UV are often observed
co-spatial to strong line-of-sight photospheric magnetic fields. Several
authors, for example, have noted the spatial relationship between
Ellerman bombs (EBs) and moving magnetic features (MMFs), regions of
flux which disconnect from a sunspot or pore before propagating away
in the moat flow and often displaying evidence of cancellation. In
this article, data collected by the Solar Dynamics Observatory's
Helioseismic and Magnetic Imager and Atmospheric Imaging Assembly
are analysed in an attempt to understand the potential links between
such cancellation and UV burst formation. Two MMFs from AR 11579,
three bi-poles from AR 11765, and six bi-poles (four of which were
co-spatial to Interface Region Imaging Spectrograph bursts) in AR 11850
were identified for analysis. All of these cancellation features were
found to have lifetimes of the order hours and cancellation rates of
the order 10<SUP>14</SUP>-10<SUP>15</SUP> Mx s<SUP>-1</SUP>. Hα line
wing data from the Dunn Solar Telescope's Interferometric BIdimensional
Spectrometer were also available for AR 11579 facilitating a discussion
of links between MMFs and EBs. Using an algebraic model of photospheric
magnetic reconnection, the measured cancellation rates are then used
to ascertain estimates of certain quantities (such as upflow speeds,
jet extents, and potential energy releases), which compared reasonably
to the properties of EBs reported within the literature. Our results
suggest that cancellation rates of the order measured here are capable
of supplying enough energy to drive certain UV bursts (including EBs),
however, they are not a guaranteeing condition for burst formation.
---------------------------------------------------------
Title: Magnetic Flux Cancellation in Ellerman Bombs
Authors: Reid, A.; Mathioudakis, M.; Doyle, J. G.; Scullion, E.;
Nelson, C. J.; Henriques, V.; Ray, T.
2016ApJ...823..110R Altcode: 2016arXiv160307100R
Ellerman Bombs (EBs) are often found to be co-spatial with bipolar
photospheric magnetic fields. We use Hα imaging spectroscopy along with
Fe I 6302.5 Å spectropolarimetry from the Swedish 1 m Solar Telescope
(SST), combined with data from the Solar Dynamic Observatory, to study
EBs and the evolution of the local magnetic fields at EB locations. EBs
are found via an EB detection and tracking algorithm. Using NICOLE
inversions of the spectropolarimetric data, we find that, on average,
(3.43 ± 0.49) × 10<SUP>24</SUP> erg of stored magnetic energy
disappears from the bipolar region during EB burning. The inversions
also show flux cancellation rates of 10<SUP>14</SUP>-10<SUP>15</SUP>
Mx s<SUP>-1</SUP> and temperature enhancements of 200 K at the detection
footpoints. We investigate the near-simultaneous flaring of EBs due to
co-temporal flux emergence from a sunspot, which shows a decrease in
transverse velocity when interacting with an existing, stationary area
of opposite polarity magnetic flux, resulting in the formation of the
EBs. We also show that these EBs can be fueled further by additional,
faster moving, negative magnetic flux regions.
---------------------------------------------------------
Title: High-cadence observations of spicular-type events on the Sun
Authors: Shetye, J.; Doyle, J. G.; Scullion, E.; Nelson, C. J.;
Kuridze, D.; Henriques, V.; Woeger, F.; Ray, T.
2016A&A...589A...3S Altcode: 2016arXiv160108087S
Context. Chromospheric observations taken at high-cadence and
high-spatial resolution show a range of spicule-like features,
including Type-I, Type-II (as well as rapid blue-shifted excursions
(RBEs) and rapid red-shifted excursions (RREs) which are thought to
be on-disk counterparts of Type-II spicules) and those which seem to
appear within a few seconds, which if interpreted as flows would imply
mass flow velocities in excess of 1000 km s<SUP>-1</SUP>. <BR /> Aims:
This article seeks to quantify and study rapidly appearing spicular-type
events. We also compare the multi-object multi-frame blind deconvolution
(MOMFBD) and speckle reconstruction techniques to understand if
these spicules are more favourably observed using a particular
technique. <BR /> Methods: We use spectral imaging observations taken
with the CRisp Imaging SpectroPolarimeter (CRISP) on the Swedish 1-m
Solar Telescope. Data was sampled at multiple positions within the Hα
line profile for both an on-disk and limb location. <BR /> Results: The
data is host to numerous rapidly appearing features which are observed
at different locations within the Hα line profile. The feature's
durations vary between 10-20 s and lengths around 3500 km. Sometimes,
a time delay in their appearance between the blue and red wings of
3-5 s is evident, whereas, sometimes they are near simultaneous. In
some instances, features are observed to fade and then re-emerge at
the same location several tens of seconds later. <BR /> Conclusions:
We provide the first statistical analysis of these spicules and suggest
that these observations can be interpreted as the line-of-sight (LOS)
movement of highly dynamic spicules moving in and out of the narrow 60
mÅ transmission filter that is used to observe in different parts of
the Hα line profile. The LOS velocity component of the observed fast
chromospheric features, manifested as Doppler shifts, are responsible
for their appearance in the red and blue wings of Hα line. Additional
work involving data at other wavelengths is required to investigate
the nature of their possible wave-like activity.
---------------------------------------------------------
Title: High Cadence Observations and Analysis of Spicular-type Events
Using CRISP Onboard SST
Authors: Shetye, J.; Doyle, J. G.; Scullion, E.; Nelson, C. J.;
Kuridze, D.
2016ASPC..504..115S Altcode:
We present spectroscopic and imaging observations of apparent ultra-fast
spicule-like features observed with CRisp Imaging SpectroPolarimeter
(CRISP) at the Swedish 1-m Solar Telescope (SST). The data shows
spicules with an apparent velocity above 500 km s<SUP>-1</SUP>,
very short lifetimes of up to 20 s and length/height around 3500
km. The spicules are seen as dark absorption structures in the Hα
wings ±516 mÅ, ±774 mÅ and ±1032 mÅ which suddenly appear and
disappear from the FOV. These features show a time delay in their
appearance in the blue and red wings by 3-5 s. We suggest that their
appearance/disappearance is due to their Doppler motion in and out of
the 60 mÅ filter. See Fig. 1 for the evolution of the event at two
line positions.
---------------------------------------------------------
Title: On The Role of MHD Waves in Heating Localised Magnetic
Structures
Authors: Erdélyi, R.; Nelson, C. J.
2016ASPC..504..153E Altcode:
Satellite and ground-based observations from e.g. SOHO, TRACE, STEREO,
Hinode, SDO and IRIS to DST/ROSA, IBIS, CoMP, STT/CRISP have provided
a wealth of evidence of waves and oscillations present in a wide range
of spatial scales of the magnetised solar atmosphere. Our understanding
about localised solar structures has been considerably changed in light
of these high spatial and time resolution observations. However, MHD
waves not only enable us to perform sub-resolution magneto-seismology of
magnetic waveguides but are also potential candidates to carry and damp
the necessary non-thermal energy in these localised waveguides. First,
we will briefly outline the basic recent developments in MHD wave
theory focussing on linear waves. Next, we discuss the role of
the most frequently studied wave classes, including the Alfven, and
magneto-acoustic kink and sausage waves. The current theoretical (and
often difficult) interpretations of the detected solar atmospheric
wave and oscillatory phenomena within the framework of MHD will be
shown. Last, the latest reported observational findings of potential MHD
wave flux, in terms of localised plasma heating, in the solar atmosphere
is discussed, bringing us closer to solve the coronal heating problem.
---------------------------------------------------------
Title: Small-scale Structuring of Ellerman Bombs at the Solar Limb
Authors: Nelson, C. J.; Scullion, E. M.; Doyle, J. G.; Freij, N.;
Erdélyi, R.
2015ApJ...798...19N Altcode: 2014arXiv1410.5715N
Ellerman bombs (EBs) have been widely studied in recent years due to
their dynamic, explosive nature and apparent links to the underlying
photospheric magnetic field implying that they may be formed by
magnetic reconnection in the photosphere. Despite a plethora of
researches discussing the morphologies of EBs, there has been a limited
investigation of how these events appear at the limb, specifically,
whether they manifest as vertical extensions away from the disk. In
this article, we make use of high-resolution, high-cadence observations
of an Active Region at the solar limb, collected by the CRisp Imaging
SpectroPolarimeter (CRISP) instrument, to identify EBs and infer their
physical properties. The upper atmosphere is also probed using the
Solar Dynamic Observatory's Atmospheric Imaging Assembly (SDO/AIA). We
analyze 22 EB events evident within these data, finding that 20 appear
to follow a parabolic path away from the solar surface at an average
speed of 9 km s<SUP>-1</SUP>, extending away from their source by 580
km, before retreating back at a similar speed. These results show strong
evidence of vertical motions associated with EBs, possibly explaining
the dynamical "flaring" (changing in area and intensity) observed
in on-disk events. Two in-depth case studies are also presented that
highlight the unique dynamical nature of EBs within the lower solar
atmosphere. The viewing angle of these observations allows for a direct
linkage between these EBs and other small-scale events in the Hα line
wings, including a potential flux emergence scenario. The findings
presented here suggest that EBs could have a wider-reaching influence
on the solar atmosphere than previously thought, as we reveal a direct
linkage between EBs and an emerging small-scale loop, and other near-by
small-scale explosive events. However, as previous research found,
these extensions do not appear to impact upon the Hα line core,
and are not observed by the SDO/AIA EUV filters.
---------------------------------------------------------
Title: The Detection of Upwardly Propagating Waves Channeling Energy
from the Chromosphere to the Low Corona
Authors: Freij, N.; Scullion, E. M.; Nelson, C. J.; Mumford, S.;
Wedemeyer, S.; Erdélyi, R.
2014ApJ...791...61F Altcode: 2014arXiv1408.4621F
There have been ubiquitous observations of wave-like motions in
the solar atmosphere for decades. Recent improvements to space- and
ground-based observatories have allowed the focus to shift to smaller
magnetic structures on the solar surface. In this paper, high-resolution
ground-based data taken using the Swedish 1 m Solar Telescope is
combined with co-spatial and co-temporal data from the Atmospheric
Imaging Assembly (AIA) on board the Solar Dynamics Observatory
(SDO) satellite to analyze running penumbral waves (RPWs). RPWs
have always been thought to be radial wave propagation that occurs
within sunspots. Recent research has suggested that they are in fact
upwardly propagating field-aligned waves (UPWs). Here, RPWs within a
solar pore are observed for the first time and are interpreted as UPWs
due to the lack of a penumbra that is required to support RPWs. These
UPWs are also observed co-spatially and co-temporally within several
SDO/AIA elemental lines that sample the transition region and low
corona. The observed UPWs are traveling at a horizontal velocity of
around 17 ± 0.5 km s<SUP>-1</SUP> and a minimum vertical velocity
of 42 ± 21 km s<SUP>-1</SUP>. The estimated energy of the waves is
around 150 W m<SUP>-2</SUP>, which is on the lower bound required to
heat the quiet-Sun corona. This is a new, yet unconsidered source of
wave energy within the solar chromosphere and low corona.
---------------------------------------------------------
Title: Effects of Stratification and Flows on P <SUB>1</SUB>/ P
<SUB>2</SUB> Ratios and Anti-node Shifts Within Closed Loop Structures
Authors: Erdélyi, R.; Hague, A.; Nelson, C. J.
2014SoPh..289..167E Altcode: 2013arXiv1306.1051E
The solar atmosphere is a dynamic environment, constantly evolving
to form a wide range of magnetically dominated structures (coronal
loops, spicules, prominences, etc.) which cover a significant
percentage of the surface at any one time. Oscillations and waves
in many of these structures are now widely observed and have led
to the new analytic technique of solar magneto-seismology, where
inferences of the background conditions of the plasma can be deduced
by studying magneto-hydrodynamic (MHD) waves. Here, we generalise
a novel magneto-seismological method designed to infer the density
distribution of a bounded plasma structure from the relationship of
its fundamental and subsequent harmonics. Observations of the solar
atmosphere have emphatically shown that stratification, leading to
complex density profiles within plasma structures, is common thereby
rendering this work instantly accessible to solar physics. We show,
in a dynamic waveguide, how the period ratio differs from the idealised
harmonic ratios prevalent in homogeneous structures. These ratios show
strong agreement with recent observational work. Next, anti-node shifts
are also analysed. Using typical scaling parameters for bulk flows
within atmospheric waveguides, e.g., coronal loops, it is found that
significant anti-node shifts can be predicted, even to the order of 10
Mm. It would be highly encouraged to design specific observations to
confirm the predicted anti-node shifts and apply the developed theory
of solar magneto-seismology to gain more accurate waveguide diagnostics
of the solar atmosphere.
---------------------------------------------------------
Title: Excitation of an outflow from the lower solar atmosphere and
a co-temporal EUV transient brightening
Authors: Nelson, C. J.; Doyle, J. G.
2013A&A...560A..31N Altcode: 2013arXiv1310.8490N
<BR /> Aims: We analyse an absorption event within the Hα line wings,
which has been identified as a surge, and the co-spatial evolution
of an EUV brightening, with spatial and temporal scales analogous
to a small blinker. <BR /> Methods: We conduct a multi-wavelength,
multi-instrument analysis using high-cadence, high-resolution data,
collected by the Interferometric BIdimensional Spectrometer on the
Dunn Solar Telescope, as well as the space-borne Atmospheric Imaging
Assembly and Helioseismic and Magnetic Imager instruments on board
the Solar Dynamics Observatory. <BR /> Results: One large absorption
event situated within the plage region trailing the lead sunspot of
AR 11579 is identified within the Hα line wings. This event is found
to be co-spatially linked to a medium-scale (around 4” in diameter)
brightening within the transition region and corona. This ejection
appears to have a parabolic evolution, first forming in the Hα blue
wing before fading and reappearing in the Hα red wing, and comprises a
number of smaller fibril events. The line-of-sight photospheric magnetic
field shows no evidence of cancellation leading to this event. <BR />
Conclusions: Our research has identified clear evidence that at least
a subset of transient brightening events in the transition region is
linked to the influx of cooler plasma from the lower solar atmosphere
during large eruptive events, such as surges. These observations agree
with previous numerical researches on the nature of blinkers and,
therefore, suggest that magnetic reconnection is the driver of the
analysed surge events; however, further research is required to confirm
this. <P />A movie attached to Fig. 2 is available in electronic form
at <A href="http://www.aanda.org">http://www.aanda.org</A>
---------------------------------------------------------
Title: Ellerman Bombs—Evidence for Magnetic Reconnection in the
Lower Solar Atmosphere
Authors: Nelson, C. J.; Shelyag, S.; Mathioudakis, M.; Doyle, J. G.;
Madjarska, M. S.; Uitenbroek, H.; Erdélyi, R.
2013ApJ...779..125N Altcode: 2013arXiv1310.7756N
The presence of photospheric magnetic reconnection has long been thought
to give rise to short and impulsive events, such as Ellerman bombs (EBs)
and Type II spicules. In this article, we combine high-resolution,
high-cadence observations from the Interferometric BIdimensional
Spectrometer and Rapid Oscillations in the Solar Atmosphere instruments
at the Dunn Solar Telescope, National Solar Observatory, New Mexico,
with co-aligned Solar Dynamics Observatory Atmospheric Imaging Assembly
and Hinode Solar Optical Telescope (SOT) data to observe small-scale
events situated within an active region. These data are then compared
with state-of-the-art numerical simulations of the lower atmosphere
made using the MURaM code. It is found that brightenings, in both the
observations and the simulations, of the wings of the Hα line profile,
interpreted as EBs, are often spatially correlated with increases in
the intensity of the Fe I λ6302.5 line core. Bipolar regions inferred
from Hinode/SOT magnetic field data show evidence of flux cancellation
associated, co-spatially, with these EBs, suggesting that magnetic
reconnection could be a driver of these high-energy events. Through
the analysis of similar events in the simulated lower atmosphere,
we are able to infer that line profiles analogous to the observations
occur co-spatially with regions of strong opposite-polarity magnetic
flux. These observed events and their simulated counterparts are
interpreted as evidence of photospheric magnetic reconnection at scales
observable using current observational instrumentation.
---------------------------------------------------------
Title: Statistical Analysis of Small Ellerman Bomb Events
Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.; Huang, Z.;
Madjarska, M. S.; Mathioudakis, M.; Mumford, S. J.; Reardon, K.
2013SoPh..283..307N Altcode: 2013arXiv1301.1351N
The properties of Ellerman bombs (EBs), small-scale brightenings in
the Hα line wings, have proved difficult to establish because their
size is close to the spatial resolution of even the most advanced
telescopes. Here, we aim to infer the size and lifetime of EBs using
high-resolution data of an emerging active region collected using
the Interferometric BIdimensional Spectrometer (IBIS) and Rapid
Oscillations of the Solar Atmosphere (ROSA) instruments as well as
the Helioseismic and Magnetic Imager (HMI) onboard the Solar Dynamics
Observatory (SDO). We develop an algorithm to track EBs through their
evolution, finding that EBs can often be much smaller (around 0.3″)
and shorter-lived (less than one minute) than previous estimates. A
correlation between G-band magnetic bright points and EBs is also
found. Combining SDO/HMI and G-band data gives a good proxy of the
polarity for the vertical magnetic field. It is found that EBs often
occur both over regions of opposite polarity flux and strong unipolar
fields, possibly hinting at magnetic reconnection as a driver of these
events.The energetics of EB events is found to follow a power-law
distribution in the range of a nanoflare (10<SUP>22−25</SUP> ergs).
---------------------------------------------------------
Title: Ellerman bombs: small-scale brightenings in the photosphere
Authors: Nelson, C. J.; Doyle, J. G.; Erdélyi, R.; Madjarska, M.;
Mumford, S. J.
2013MmSAI..84..436N Altcode:
Observations of small-scale events in the solar atmosphere are
limited by the spatial and temporal resolutions of the current crop
of observational instruments. Both high-cadence and high-resolution
observations of the photosphere have shown the continued dynamics to
extremely small-scales. Ellerman bombs, brightening events in the
wings of the Halpha line profile, are one example of small-scale,
short-lived events which have been widely studied due to their fast
dynamics in recent years. By combining the Interferometric BIdimensional
Spectrometer (IBIS) instrument with the Helioseismic and Magnetic Imager
(HMI/SDO), we show the small-scale nature of these events, as well as
their link to the background magnetic field. It is found that EBs can
be much smaller and shorter-lived than previous estimates have stated,
implying the continued dynamics of the solar atmosphere below current
observational limits.
---------------------------------------------------------
Title: Microlensing Binaries with Candidate Brown Dwarf Companions
Authors: Shin, I. -G.; Han, C.; Gould, A.; Udalski, A.; Sumi, T.;
Dominik, M.; Beaulieu, J. -P.; Tsapras, Y.; Bozza, V.; Szymański,
M. K.; Kubiak, M.; Soszyński, I.; Pietrzyński, G.; Poleski,
R.; Ulaczyk, K.; Pietrukowicz, P.; Kozłowski, S.; Skowron, J.;
Wyrzykowski, Ł.; OGLE Collaboration; Abe, F.; Bennett, D. P.;
Bond, I. A.; Botzler, C. S.; Freeman, M.; Fukui, A.; Furusawa, K.;
Hayashi, F.; Hearnshaw, J. B.; Hosaka, S.; Itow, Y.; Kamiya, K.;
Kilmartin, P. M.; Kobara, S.; Korpela, A.; Lin, W.; Ling, C. H.;
Makita, S.; Masuda, K.; Matsubara, Y.; Miyake, N.; Muraki, Y.;
Nagaya, M.; Nishimoto, K.; Ohnishi, K.; Okumura, T.; Omori, K.;
Perrott, Y. C.; Rattenbury, N.; Saito, To.; Skuljan, L.; Sullivan,
D. J.; Suzuki, D.; Sweatman, W. L.; Tristram, P. J.; Wada, K.; Yock,
P. C. M.; MOA Collaboration; Christie, G. W.; Depoy, D. L.; Dong,
S.; Gal-Yam, A.; Gaudi, B. S.; Hung, L. -W.; Janczak, J.; Kaspi, S.;
Maoz, D.; McCormick, J.; McGregor, D.; Moorhouse, D.; Muñoz, J. A.;
Natusch, T.; Nelson, C.; Pogge, R. W.; Tan, T. -G.; Polishook, D.;
Shvartzvald, Y.; Shporer, A.; Thornley, G.; Malamud, U.; Yee, J. C.;
Choi, J. -Y.; Jung, Y. -K.; Park, H.; Lee, C. -U.; Park, B. -G.; Koo,
J. -R.; μFUN Collaboration; Bajek, D.; Bramich, D. M.; Browne, P.;
Horne, K.; Ipatov, S.; Snodgrass, C.; Steele, I.; Street, R.; Alsubai,
K. A.; Burgdorf, M. J.; Calchi Novati, S.; Dodds, P.; Dreizler, S.;
Fang, X. -S.; Grundahl, F.; Gu, C. -H.; Hardis, S.; Harpsøe, K.;
Hinse, T. C.; Hundertmark, M.; Jessen-Hansen, J.; Jørgensen, U. G.;
Kains, N.; Kerins, E.; Liebig, C.; Lund, M.; Lundkvist, M.; Mancini,
L.; Mathiasen, M.; Hornstrup, A.; Penny, M. T.; Proft, S.; Rahvar, S.;
Ricci, D.; Scarpetta, G.; Skottfelt, J.; Southworth, J.; Surdej, J.;
Tregloan-Reed, J.; Wertz, O.; Zimmer, F.; Albrow, M. D.; Batista, V.;
Brillant, S.; Caldwell, J. A. R.; Calitz, J. J.; Cassan, A.; Cole,
A.; Cook, K. H.; Corrales, E.; Coutures, Ch.; Dieters, S.; Dominis
Prester, D.; Donatowicz, J.; Fouqué, P.; Greenhill, J.; Hill, K.;
Hoffman, M.; Kane, S. R.; Kubas, D.; Marquette, J. -B.; Martin, R.;
Meintjes, P.; Menzies, J.; Pollard, K. R.; Sahu, K. C.; Wambsganss,
J.; Williams, A.; Vinter, C.; Zub, M.
2012ApJ...760..116S Altcode: 2012arXiv1208.2323S
Brown dwarfs are important objects because they may provide a missing
link between stars and planets, two populations that have dramatically
different formation histories. In this paper, we present the candidate
binaries with brown dwarf companions that are found by analyzing
binary microlensing events discovered during the 2004-2011 observation
seasons. Based on the low mass ratio criterion of q < 0.2, we
found seven candidate events: OGLE-2004-BLG-035, OGLE-2004-BLG-039,
OGLE-2007-BLG-006, OGLE-2007-BLG-399/MOA-2007-BLG-334,
MOA-2011-BLG-104/OGLE-2011-BLG-0172, MOA-2011-BLG-149, and
MOA-201-BLG-278/OGLE-2011-BLG-012N. Among them, we are able to confirm
that the companions of the lenses of MOA-2011-BLG-104/OGLE-2011-BLG-0172
and MOA-2011-BLG-149 are brown dwarfs by determining the mass of the
lens based on the simultaneous measurement of the Einstein radius and
the lens parallax. The measured masses of the brown dwarf companions are
0.02 ± 0.01 M <SUB>⊙</SUB> and 0.019 ± 0.002 M <SUB>⊙</SUB> for
MOA-2011-BLG-104/OGLE-2011-BLG-0172 and MOA-2011-BLG-149, respectively,
and both companions are orbiting low-mass M dwarf host stars. More
microlensing brown dwarfs are expected to be detected as the number
of lensing events with well-covered light curves increases with
new-generation searches.
---------------------------------------------------------
Title: Characterizing Lenses and Lensed Stars of High-magnification
Single-lens Gravitational Microlensing Events with Lenses Passing
over Source Stars
Authors: Choi, J. -Y.; Shin, I. -G.; Park, S. -Y.; Han, C.; Gould,
A.; Sumi, T.; Udalski, A.; Beaulieu, J. -P.; Street, R.; Dominik, M.;
Allen, W.; Almeida, L. A.; Bos, M.; Christie, G. W.; Depoy, D. L.;
Dong, S.; Drummond, J.; Gal-Yam, A.; Gaudi, B. S.; Henderson, C. B.;
Hung, L. -W.; Jablonski, F.; Janczak, J.; Lee, C. -U.; Mallia, F.;
Maury, A.; McCormick, J.; McGregor, D.; Monard, L. A. G.; Moorhouse,
D.; Muñoz, J. A.; Natusch, T.; Nelson, C.; Park, B. -G.; Pogge, R. W.;
"TG" Tan, T. -G.; Thornley, G.; Yee, J. C.; μFUN Collaboration; Abe,
F.; Barnard, E.; Baudry, J.; Bennett, D. P.; Bond, I. A.; Botzler,
C. S.; Freeman, M.; Fukui, A.; Furusawa, K.; Hayashi, F.; Hearnshaw,
J. B.; Hosaka, S.; Itow, Y.; Kamiya, K.; Kilmartin, P. M.; Kobara, S.;
Korpela, A.; Lin, W.; Ling, C. H.; Makita, S.; Masuda, K.; Matsubara,
Y.; Miyake, N.; Muraki, Y.; Nagaya, M.; Nishimoto, K.; Ohnishi, K.;
Okumura, T.; Omori, K.; Perrott, Y. C.; Rattenbury, N.; Saito, To.;
Skuljan, L.; Sullivan, D. J.; Suzuki, D.; Suzuki, K.; Sweatman,
W. L.; Takino, S.; Tristram, P. J.; Wada, K.; Yock, P. C. M.;
MOA Collaboration; Szymański, M. K.; Kubiak, M.; Pietrzyński,
G.; Soszyński, I.; Poleski, R.; Ulaczyk, K.; Wyrzykowski, Ł.;
Kozłowski, S.; Pietrukowicz, P.; OGLE Collaboration; Albrow, M. D.;
Bachelet, E.; Batista, V.; Bennett, C. S.; Bowens-Rubin, R.; Brillant,
S.; Cassan, A.; Cole, A.; Corrales, E.; Coutures, Ch.; Dieters, S.;
Dominis Prester, D.; Donatowicz, J.; Fouqué, P.; Greenhill, J.;
Kane, S. R.; Menzies, J.; Sahu, K. C.; Wambsganss, J.; Williams, A.;
Zub, M.; PLANET Collaboration; Allan, A.; Bramich, D. M.; Browne, P.;
Clay, N.; Fraser, S.; Horne, K.; Kains, N.; Mottram, C.; Snodgrass,
C.; Steele, I.; Tsapras, Y.; RoboNet Collaboration; Alsubai, K. A.;
Bozza, V.; Burgdorf, M. J.; Calchi Novati, S.; Dodds, P.; Dreizler,
S.; Finet, F.; Gerner, T.; Glitrup, M.; Grundahl, F.; Hardis, S.;
Harpsøe, K.; Hinse, T. C.; Hundertmark, M.; Jørgensen, U. G.;
Kerins, E.; Liebig, C.; Maier, G.; Mancini, L.; Mathiasen, M.; Penny,
M. T.; Proft, S.; Rahvar, S.; Ricci, D.; Scarpetta, G.; Schäfer, S.;
Schönebeck, F.; Skottfelt, J.; Surdej, J.; Southworth, J.; Zimmer,
F.; MiNDSTEp Consortium
2012ApJ...751...41C Altcode: 2011arXiv1111.4032C
We present the analysis of the light curves of nine high-magnification
single-lens gravitational microlensing events with lenses passing
over source stars, including OGLE-2004-BLG-254, MOA-2007-BLG-176,
MOA-2007-BLG-233/OGLE-2007-BLG-302, MOA-2009-BLG-174, MOA-2010-BLG-436,
MOA-2011-BLG-093, MOA-2011-BLG-274, OGLE-2011-BLG-0990/MOA-2011-BLG-300,
and OGLE-2011-BLG-1101/MOA-2011-BLG-325. For all of the events, we
measure the linear limb-darkening coefficients of the surface brightness
profile of source stars by measuring the deviation of the light curves
near the peak affected by the finite-source effect. For seven events,
we measure the Einstein radii and the lens-source relative proper
motions. Among them, five events are found to have Einstein radii
of less than 0.2 mas, making the lenses very low mass star or brown
dwarf candidates. For MOA-2011-BLG-274, especially, the small Einstein
radius of θ<SUB>E</SUB> ~ 0.08 mas combined with the short timescale
of t <SUB>E</SUB> ~ 2.7 days suggests the possibility that the lens
is a free-floating planet. For MOA-2009-BLG-174, we measure the lens
parallax and thus uniquely determine the physical parameters of the
lens. We also find that the measured lens mass of ~0.84 M <SUB>⊙</SUB>
is consistent with that of a star blended with the source, suggesting
that the blend is likely to be the lens. Although we did not find
planetary signals for any of the events, we provide exclusion diagrams
showing the confidence levels excluding the existence of a planet as
a function of the separation and mass ratio.
---------------------------------------------------------
Title: Microlensing Binaries Discovered through High-magnification
Channel
Authors: Shin, I. -G.; Choi, J. -Y.; Park, S. -Y.; Han, C.; Gould, A.;
Sumi, T.; Udalski, A.; Beaulieu, J. -P.; Dominik, M.; Allen, W.; Bos,
M.; Christie, G. W.; Depoy, D. L.; Dong, S.; Drummond, J.; Gal-Yam,
A.; Gaudi, B. S.; Hung, L. -W.; Janczak, J.; Kaspi, S.; Lee, C. -U.;
Mallia, F.; Maoz, D.; Maury, A.; McCormick, J.; Monard, L. A. G.;
Moorhouse, D.; Muñoz, J. A.; Natusch, T.; Nelson, C.; Park, B. -G.;
Pogge, R. W.; Polishook, D.; Shvartzvald, Y.; Shporer, A.; Thornley,
G.; Yee, J. C.; μFUN Collaboration; Abe, F.; Bennett, D. P.; Bond,
I. A.; Botzler, C. S.; Fukui, A.; Furusawa, K.; Hayashi, F.; Hearnshaw,
J. B.; Hosaka, S.; Itow, Y.; Kamiya, K.; Kilmartin, P. M.; Kobara, S.;
Korpela, A.; Lin, W.; Ling, C. H.; Makita, S.; Masuda, K.; Matsubara,
Y.; Miyake, N.; Muraki, Y.; Nagaya, M.; Nishimoto, K.; Ohnishi, K.;
Okumura, T.; Omori, K.; Perrott, Y. C.; Rattenbury, N.; Saito, To.;
Skuljan, L.; Sullivan, D. J.; Suzuki, D.; Sweatman, W. L.; Tristram,
P. J.; Wada, K.; Yock, P. C. M.; MOA Collaboration; Szymański,
M. K.; Kubiak, M.; Pietrzyński, G.; Soszyński, I.; Poleski, R.;
Ulaczyk, K.; Wyrzykowski, Ł.; Kozłowski, S.; Pietrukowicz, P.; OGLE
Collaboration; Albrow, M. D.; Batista, V.; Bramich, D. M.; Brillant,
S.; Caldwell, J. A. R.; Calitz, J. J.; Cassan, A.; Cole, A.; Cook,
K. H.; Corrales, E.; Coutures, Ch.; Dieters, S.; Dominis Prester, D.;
Donatowicz, J.; Fouqué, P.; Greenhill, J.; Hoffman, M.; Jørgensen,
U. G.; Kane, S. R.; Kubas, D.; Marquette, J. -B.; Martin, R.; Meintjes,
P.; Menzies, J.; Pollard, K. R.; Sahu, K. C.; Wambsganss, J.; Williams,
A.; Vinter, C.; Zub, M.; PLANET Collaboration; Allan, A.; Browne, P.;
Horne, K.; Snodgrass, C.; Steele, I.; Street, R.; Tsapras, Y.; RoboNet
Collaboration; Alsubai, K. A.; Bozza, V.; Browne, P.; Burgdorf, M. J.;
Calchi Novati, S.; Dodds, P.; Dreizler, S.; Finet, F.; Gerner, T.;
Glitrup, M.; Grundahl, F.; Hardis, S.; Harpsøe, K.; Hessman, F. V.;
Hinse, T. C.; Hundertmark, M.; Kains, N.; Kerins, E.; Liebig, C.;
Maier, G.; Mancini, L.; Mathiasen, M.; Penny, M. T.; Proft, S.; Rahvar,
S.; Ricci, D.; Scarpetta, G.; Schäfer, S.; Schönebeck, F.; Skottfelt,
J.; Surdej, J.; Southworth, J.; Zimmer, F.; MiNDSTEp Consortium
2012ApJ...746..127S Altcode: 2011arXiv1109.3295S
Microlensing can provide a useful tool to probe binary distributions
down to low-mass limits of binary companions. In this paper, we analyze
the light curves of eight binary-lensing events detected through the
channel of high-magnification events during the seasons from 2007 to
2010. The perturbations, which are confined near the peak of the light
curves, can be easily distinguished from the central perturbations
caused by planets. However, the degeneracy between close and wide binary
solutions cannot be resolved with a 3σ confidence level for three
events, implying that the degeneracy would be an important obstacle
in studying binary distributions. The dependence of the degeneracy on
the lensing parameters is consistent with a theoretical prediction
that the degeneracy becomes severe as the binary separation and the
mass ratio deviate from the values of resonant caustics. The measured
mass ratio of the event OGLE-2008-BLG-510/MOA-2008-BLG-369 is q ~ 0.1,
making the companion of the lens a strong brown dwarf candidate.
---------------------------------------------------------
Title: Minor Planet Observations [H21 Astronomical Research
Observatory, Westfield]
Authors: Holmes, R.; Vorobjov, T.; Foglia, S.; Buzzi, L.; Johnson,
L.; Nelson, C.; Smith, A.; Friel, M.; Hernandez, J.; Fulmore, C.;
Bowden, R.; Linder, T.; Haithcock, J.; Yan, Y.; Mobley, D.; Allen,
S.; Bell, C.; Urbanski, J.; Devore, H.; Bradshaw, A.; Colby, C.;
Price, C.; Battles, E.; Lucas, M.
2012MPC..77794...2H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Minor Planet Observations [H21 Astronomical Research
Observatory, Westfield]
Authors: Holmes, R.; Linder, T.; Mobley, D.; Bowden, R.; Vorobjov, T.;
Buzzi, L.; Foglia, S.; Devore, H.; Bell, C.; Urbanski, J.; Friel, M.;
Hernandez, J.; Colby, C.; Price, C.; Spell, K.; Battles, E.; Johnson,
L.; Nelson, C.; Allen, S.; Trayah, K.; Yan, Y.; Trotman, A.; Lucas,
M.; Owens, H.
2011MPC..77396...2H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Minor Planet Observations [H21 Astronomical Research
Observatory, Westfield]
Authors: Holmes, R.; Vorobjov, T.; Buzzi, L.; Foglia, S.; Bell, C.;
Urbanski, J.; Tombelli, M.; Mobley, D.; Bowden, R.; Owens, T.; Friel,
M.; Lucas, M.; Haithcock, J.; Battles, E.; Colby, C.; Bradshaw, A.;
Smith, A.; Trotman, A.; Fulmore, C.; Linder, T.; Yan, Y.; Devore,
H.; Vorobjov, M. T.; Johnson, L.; Hernandez, J.; Nelson, C.; Mugrage,
M.; Price, C.; Allen, S.; Trayah, K.; Owens, H.; Spell, K.
2011MPC..77006...1H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Minor Planet Observations [H21 Astronomical Research
Observatory, Westfield]
Authors: Holmes, R.; Linder, T.; Vorobjov, T.; Urbanski, J.; Foglia,
S.; Buzzi, L.; Dankov, K.; Vorobjov, M. T.; Bone, J.; Faircloth,
S.; Yan, Y.; Devore, H.; Bowden, R.; Fulmore, C.; Hernandez, J.;
Friel, M.; Battles, E.; Lucas, M.; Owens, T.; Mobley, D.; Bradshaw,
A.; Spell, K.; Smith, A.; Johnson, L.; Allen, S.; Colby, C.; Rozier,
K.; Price, C.; Nelson, C.; Trayah, K.
2011MPC..76018...1H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Vibration-Induced PM Noise in Oscillators and Measurements
of Correlation with Vibration Sensors
Authors: Howe, D. A.; Lanfranchi, J. L.; Cutsinger, L.; Hati, A.;
Nelson, C.
2005ptti.conf..494H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: [OIII] Emission Line Profiles in PG Quasars
Authors: Nelson, C.; Plasek, A.; Thompson, A.; Gelderman, R.;
Monroe, T.
2004ASPC..311...83N Altcode: 2004apsd.conf...83N
We have obtained high S/N, high resolution profiles of the [OIII]
5007 emission line for all PG quasars with z<0.5. Previous studies
have shown that the kinematics of the narrow line region gas (NLR)
in active galaxies are predominantly due to gravitational motion in
the host bulge potential. Thus, using the well established correlation
between bulge velocity dispersion, σ<SUB>*</SUB>, and nuclear black
hole mass, M<SUB>⊙</SUB>, we can use the widths of the [OIII] line
profiles to estimate M<SUB>⊙</SUB> for the entire sample. If the
[OIII] kinematics are in fact virial, this technique could provide
independent estimates for M<SUB>⊙</SUB> from SDSS quasar spectra.
---------------------------------------------------------
Title: Search for Kaluza-Klein Graviton Emission in pp¯ Collisions
at √(s)=1.8 TeV Using the Missing Energy Signature
Authors: Acosta, D.; Affolder, T.; Akimoto, H.; Albrow, M. G.; Ambrose,
D.; Amidei, D.; Anikeev, K.; Antos, J.; Apollinari, G.; Arisawa, T.;
Artikov, A.; Asakawa, T.; Ashmanskas, W.; Azfar, F.; Azzi-Bacchetta,
P.; Bacchetta, N.; Bachacou, H.; Badgett, W.; Bailey, S.; de Barbaro,
P.; Barbaro-Galtieri, A.; Barnes, V. E.; Barnett, B. A.; Baroiant,
S.; Barone, M.; Bauer, G.; Bedeschi, F.; Behari, S.; Belforte, S.;
Bell, W. H.; Bellettini, G.; Bellinger, J.; Benjamin, D.; Bensinger,
J.; Beretvas, A.; Berryhill, J.; Bhatti, A.; Binkley, M.; Bisello,
D.; Bishai, M.; Blair, R. E.; Blocker, C.; Bloom, K.; Blumenfeld, B.;
Blusk, S. R.; Bocci, A.; Bodek, A.; Bolla, G.; Bolshov, A.; Bonushkin,
Y.; Bortoletto, D.; Boudreau, J.; Brandl, A.; Bromberg, C.; Brozovic,
M.; Brubaker, E.; Bruner, N.; Budagov, J.; Budd, H. S.; Burkett, K.;
Busetto, G.; Byrum, K. L.; Cabrera, S.; Calafiura, P.; Campbell, M.;
Carithers, W.; Carlson, J.; Carlsmith, D.; Caskey, W.; Castro, A.;
Cauz, D.; Cerri, A.; Cerrito, L.; Chan, A. W.; Chang, P. S.; Chang,
P. T.; Chapman, J.; Chen, C.; Chen, Y. C.; Cheng, M. -T.; Chertok,
M.; Chiarelli, G.; Chirikov-Zorin, I.; Chlachidze, G.; Chlebana, F.;
Christofek, L.; Chu, M. L.; Chung, J. Y.; Chung, W. -H.; Chung, Y. S.;
Ciobanu, C. I.; Clark, A. G.; Coca, M.; Connolly, A.; Convery, M.;
Conway, J.; Cordelli, M.; Cranshaw, J.; Culbertson, R.; Dagenhart, D.;
D'Auria, S.; de Cecco, S.; Dejongh, F.; dell'Agnello, S.; dell'Orso,
M.; Demers, S.; Demortier, L.; Deninno, M.; de Pedis, D.; Derwent,
P. F.; Devlin, T.; Dionisi, C.; Dittmann, J. R.; Dominguez, A.;
Donati, S.; D'Onofrio, M.; Dorigo, T.; Eddy, N.; Einsweiler, K.;
Engels, E.; Erbacher, R.; Errede, D.; Errede, S.; Eusebi, R.; Fan,
Q.; Farrington, S.; Feild, R. G.; Fernandez, J. P.; Ferretti, C.;
Field, R. D.; Fiori, I.; Flaugher, B.; Flores-Castillo, L. R.; Foster,
G. W.; Franklin, M.; Freeman, J.; Friedman, J.; Fukui, Y.; Furic, I.;
Galeotti, S.; Gallas, A.; Gallinaro, M.; Gao, T.; Garcia-Sciveres,
M.; Garfinkel, A. F.; Gatti, P.; Gay, C.; Gerdes, D. W.; Gerstein,
E.; Giagu, S.; Giannetti, P.; Giolo, K.; Giordani, M.; Giromini, P.;
Glagolev, V.; Glenzinski, D.; Gold, M.; Goldschmidt, N.; Goldstein,
J.; Gomez, G.; Goncharov, M.; Gorelov, I.; Goshaw, A. T.; Gotra, Y.;
Goulianos, K.; Green, C.; Gresele, A.; Grim, G.; Grosso-Pilcher, C.;
Guenther, M.; Guillian, G.; da Costa, J. Guimaraes; Haas, R. M.; Haber,
C.; Hahn, S. R.; Halkiadakis, E.; Hall, C.; Handa, T.; Handler, R.;
Happacher, F.; Hara, K.; Hardman, A. D.; Harris, R. M.; Hartmann,
F.; Hatakeyama, K.; Hauser, J.; Heinrich, J.; Heiss, A.; Hennecke,
M.; Herndon, M.; Hill, C.; Hocker, A.; Hoffman, K. D.; Hollebeek,
R.; Holloway, L.; Hou, S.; Huffman, B. T.; Hughes, R.; Huston, J.;
Huth, J.; Ikeda, H.; Issever, C.; Incandela, J.; Introzzi, G.; Iori,
M.; Ivanov, A.; Iwai, J.; Iwata, Y.; Iyutin, B.; James, E.; Jones,
M.; Joshi, U.; Kambara, H.; Kamon, T.; Kaneko, T.; Kang, J.; Unel,
M. Karagoz; Karr, K.; Kartal, S.; Kasha, H.; Kato, Y.; Keaffaber,
T. A.; Kelley, K.; Kelly, M.; Kennedy, R. D.; Kephart, R.; Khazins,
D.; Kikuchi, T.; Kilminster, B.; Kim, B. J.; Kim, D. H.; Kim, H. S.;
Kim, M. J.; Kim, S. B.; Kim, S. H.; Kim, T. H.; Kim, Y. K.; Kirby, M.;
Kirk, M.; Kirsch, L.; Klimenko, S.; Koehn, P.; Kondo, K.; Konigsberg,
J.; Korn, A.; Korytov, A.; Kotelnikov, K.; Kovacs, E.; Kroll, J.;
Kruse, M.; Krutelyov, V.; Kuhlmann, S. E.; Kurino, K.; Kuwabara,
T.; Kuznetsova, N.; Laasanen, A. T.; Lai, N.; Lami, S.; Lammel, S.;
Lancaster, J.; Lannon, K.; Lancaster, M.; Lander, R.; Lath, A.; Latino,
G.; Lecompte, T.; Le, Y.; Lee, J.; Lee, S. W.; Leonardo, N.; Leone,
S.; Lewis, J. D.; Li, K.; Lin, C. S.; Lindgren, M.; Liss, T. M.; Liu,
J. B.; Liu, T.; Liu, Y. C.; Litvintsev, D. O.; Lobban, O.; Lockyer,
N. S.; Loginov, A.; Loken, J.; Loreti, M.; Lucchesi, D.; Lukens, P.;
Lusin, S.; Lyons, L.; Lys, J.; Madrak, R.; Maeshima, K.; Maksimovic,
P.; Malferrari, L.; Mangano, M.; Manca, G.; Mariotti, M.; Martignon,
G.; Martin, M.; Martin, A.; Martin, V.; Martínez, M.; Matthews,
J. A.; Mazzanti, P.; McFarland, K. S.; McIntyre, P.; Menguzzato,
M.; Menzione, A.; Merkel, P.; Mesropian, C.; Meyer, A.; Miao, T.;
Miller, R.; Miller, J. S.; Minato, H.; Miscetti, S.; Mishina, M.;
Mitselmakher, G.; Miyazaki, Y.; Moggi, N.; Moore, E.; Moore, R.;
Morita, Y.; Moulik, T.; Mulhearn, M.; Mukherjee, A.; Muller, T.;
Munar, A.; Murat, P.; Murgia, S.; Nachtman, J.; Nagaslaev, V.; Nahn,
S.; Nakada, H.; Nakano, I.; Napora, R.; Niell, F.; Nelson, C.; Nelson,
T.; Neu, C.; Neubauer, M. S.; Neuberger, D.; Newman-Holmes, C.; Ngan,
C. -Y. P.; Nigmanov, T.; Niu, H.; Nodulman, L.; Nomerotski, A.; Oh,
S. H.; Oh, Y. D.; Ohmoto, T.; Ohsugi, T.; Oishi, R.; Okusawa, T.;
Olsen, J.; Orejudos, W.; Pagliarone, C.; Palmonari, F.; Paoletti, R.;
Papadimitriou, V.; Partos, D.; Patrick, J.; Pauletta, G.; Paulini, M.;
Pauly, T.; Paus, C.; Pellett, D.; Penzo, A.; Pescara, L.; Phillips,
T. J.; Piacentino, G.; Piedra, J.; Pitts, K. T.; Pompoš, A.; Pondrom,
L.; Pope, G.; Pratt, T.; Prokoshin, F.; Proudfoot, J.; Ptohos, F.;
Pukhov, O.; Punzi, G.; Rademacker, J.; Rakitine, A.; Ratnikov, F.;
Ray, H.; Reher, D.; Reichold, A.; Renton, P.; Rescigno, M.; Ribon,
A.; Riegler, W.; Rimondi, F.; Ristori, L.; Riveline, M.; Robertson,
W. J.; Rodrigo, T.; Rolli, S.; Rosenson, L.; Roser, R.; Rossin, R.;
Rott, C.; Roy, A.; Ruiz, A.; Ryan, D.; Safonov, A.; Denis, R. St.;
Sakumoto, W. K.; Saltzberg, D.; Sanchez, C.; Sansoni, A.; Santi, L.;
Sarkar, S.; Sato, H.; Savard, P.; Savoy-Navarro, A.; Schlabach, P.;
Schmidt, E. E.; Schmidt, M. P.; Schmitt, M.; Scodellaro, L.; Scott,
A.; Scribano, A.; Sedov, A.; Seidel, S.; Seiya, Y.; Semenov, A.;
Semeria, F.; Shah, T.; Shapiro, M. D.; Shepard, P. F.; Shibayama,
T.; Shimojima, M.; Shochet, M.; Sidoti, A.; Siegrist, J.; Sill, A.;
Sinervo, P.; Singh, P.; Slaughter, A. J.; Sliwa, K.; Snider, F. D.;
Snihur, R.; Solodsky, A.; Speer, T.; Spezziga, M.; Sphicas, P.;
Spinella, F.; Spiropulu, M.; Spiegel, L.; Steele, J.; Stefanini,
A.; Strologas, J.; Strumia, F.; Stuart, D.; Sukhanov, A.; Sumorok,
K.; Suzuki, T.; Takano, T.; Takashima, R.; Takikawa, K.; Tamburello,
P.; Tanaka, M.; Tannenbaum, B.; Tecchio, M.; Tesarek, R. J.; Teng,
P. K.; Terashi, K.; Tether, S.; Thom, J.; Thompson, A. S.; Thomson, E.;
Thurman-Keup, R.; Tipton, P.; Tkaczyk, S.; Toback, D.; Tollefson, K.;
Tonelli, D.; Tonnesmann, M.; Toyoda, H.; Trischuk, W.; de Troconiz,
J. F.; Tseng, J.; Tsybychev, D.; Turini, N.; Ukegawa, F.; Unverhau,
T.; Vaiciulis, T.; Varganov, A.; Vataga, E.; Vejcik, S.; Velev, G.;
Veramendi, G.; Vidal, R.; Vila, I.; Vilar, R.; Volobouev, I.; von
der Mey, M.; Vucinic, D.; Wagner, R. G.; Wagner, R. L.; Wagner, W.;
Wan, Z.; Wang, C.; Wang, M. J.; Wang, S. M.; Ward, B.; Waschke, S.;
Watanabe, T.; Waters, D.; Watts, T.; Weber, M.; Wenzel, H.; Wester,
W. C.; Whitehouse, B.; Wicklund, A. B.; Wicklund, E.; Wilkes, T.;
Williams, H. H.; Wilson, P.; Winer, B. L.; Winn, D.; Wolbers, S.;
Wolinski, D.; Wolinski, J.; Wolinski, S.; Wolter, M.; Worm, S.; Wu,
X.; Würthwein, F.; Wyss, J.; Yang, U. K.; Yao, W.; Yeh, G. P.; Yeh,
P.; Yi, K.; Yoh, J.; Yosef, C.; Yoshida, T.; Yu, I.; Yu, S.; Yu, Z.;
Yun, J. C.; Zanello, L.; Zanetti, A.; Zetti, F.; Zucchelli, S.
2004PhRvL..92l1802A Altcode: 2003hep.ex....9051A
We report on a search for direct Kaluza-Klein graviton production in
a data sample of 84 pb<SUP>-1</SUP> of pp¯ collisions at √(s)=1.8
TeV, recorded by the Collider Detector at Fermilab. We investigate
the final state of large missing transverse energy and one or two
high energy jets. We compare the data with the predictions from a
(3+1+n)-dimensional Kaluza-Klein scenario in which gravity becomes
strong at the TeV scale. At 95% confidence level (C.L.) for n=2,
4, and 6 we exclude an effective Planck scale below 1.0, 0.77, and
0.71TeV, respectively.
---------------------------------------------------------
Title: The MACHO Project Large Magellanic Cloud Variable Star
Inventory. XI. Frequency Analysis of the Fundamental-Mode RR Lyrae
Stars
Authors: Alcock, C.; Alves, D. R.; Becker, A.; Bennett, D.; Cook,
K. H.; Drake, A.; Freeman, K.; Geha, M.; Griest, K.; Kovács,
G.; Lehner, M.; Marshall, S.; Minniti, D.; Nelson, C.; Peterson,
B.; Popowski, P.; Pratt, M.; Quinn, P.; Rodgers, A.; Stubbs, C.;
Sutherland, W.; Vandehei, T.; Welch, D. L.
2003ApJ...598..597A Altcode: 2003astro.ph..8019A
We have frequency-analyzed 6391 variables classified earlier as
fundamental-mode RR Lyrae (RR0) stars in the MACHO database on the
Large Magellanic Cloud (LMC). The overwhelming majority (i.e., 96%)
of these variables have been proved to be indeed RR0 stars, whereas the
remaining ones have fallen into one of the following categories: single-
and double-mode Cepheids, binaries, first-overtone and double-mode RR
Lyrae stars, and nonclassified variables. Special attention has been
paid to the properties of the amplitude- and phase-modulated RR0 stars
(the Blazhko stars). We found altogether 731 Blazhko variables showing
either a doublet or an equidistant triplet pattern at the main pulsation
component in their frequency spectra. This sample overwhelmingly exceeds
the number of Blazhko stars known in all other systems combined. The
incidence rate of the Blazhko variables among the RR0 stars in the
LMC is 11.9%, which is 3 times higher than their rate among the
first-overtone RR Lyrae stars. No difference is found in the average
brightness between the single-mode and Blazhko variables. However,
the latter ones show a somewhat lower degree of skewness in their
average light curves and a concomitant lower total amplitude in their
modulation-free light curves. From the frequency spectra we found that
variables with larger modulation amplitudes at the higher frequency
side of the main pulsation component are 3 times more common than the
ones showing the opposite amplitude pattern. A search for a modulation
component with the Blazhko period in the average brightness of the
individual variables showed the existence of such a modulation with
an overall amplitude of ~0.006 mag. On the other hand, a similar
search for quadruple modulation patterns around the main pulsation
component has failed to clearly detect such components at the ~0.004
mag level. This means that the amplitudes of the quadruple components
(if they exist) should be, on average, at least 10 times smaller than
those of the triplet components. This finding and the existence of
Blazhko variables with highly asymmetric modulation amplitudes not only
question the validity of the magnetic oblique rotator model but also
put stringent constraints on models based on mode-coupling theories.
---------------------------------------------------------
Title: [OIII] Emission Line Profiles in PG Quasars
Authors: Nelson, C.; Gelderman, R.; Plasek, A.; Thompson, A.; Monroe,
T.; Lamb, D. A.
2002AAS...20111404N Altcode: 2002BAAS...34.1286N
We have obtained high S/N, high resolution profiles of the [OIII] λ
5007 emission line for nearly all of the PG quasars.Previous studies
have shown that the kinematics of the narrow line region gas (NLR) in
active galaxies are predominantly due to gravitational motion in the
host bulge potential. Thus, using the now well established correlation
between bulge velocity dispersion, σ , and nuclear black hole mass,
M<SUB></SUB> , we can use the widths of the [OIII] line profiles
to estimate M<SUB></SUB> for the entire sample. These values are
independent of results from reverberation mapping techniques which rely
on the assumption of Keplerian motion in the broad line region. The
M<SUB></SUB> values can be used to estimate the Eddington ratio,
and to test the idea that L/L<SUB>E</SUB> is the primary influence on
the group of AGN correlations known as eigenvector 1. We present the
preliminary results of our analysis in this poster. This project has
been supported by the Iowa Space Grant Consortium.
---------------------------------------------------------
Title: Frequency Analysis of a Subset of Fundamental Mode RR Lyrae
Stars from the MACHO Project Large Magellanic Cloud Database
Authors: Welch, D. L.; Kovács, G.; Cook, K. H.; Alcock, C.;
Allsman, R.; Alves, D. R.; Axelrod, T.; Becker, A.; Bennett, D.;
Drake, A.; Freeman, K.; Geha, M.; Griest, K.; Lehner, M.; Marshall,
S.; Minniti, D.; Nelson, C.; Peterson, B.; Popowski, P.; Pratt, M.;
Quinn, P.; Rodgers, A.; Stubbs, C.; Sutherland, W.; Vandehei, T.;
MACHO Collaboration
2002ASPC..259..412W Altcode: 2002IAUCo.185..412W; 2002rnpp.conf..412W
No abstract at ADS
---------------------------------------------------------
Title: Mass-losing Semiregular Variable Stars in Baade's Windows
Authors: Alard, C.; Blommaert, J. A. D. L.; Cesarsky, C.; Epchtein,
N.; Felli, M.; Fouque, P.; Ganesh, S.; Genzel, R.; Gilmore, G.;
Glass, I. S.; Habing, H.; Omont, A.; Perault, M.; Price, S.; Robin,
A.; Schultheis, M.; Simon, G.; van Loon, J. Th.; Alcock, C.; Allsman,
R. A.; Alves, D. R.; Axelrod, T. S.; Becker, A. C.; Bennett, D. P.;
Cook, K. H.; Drake, A. J.; Freeman, K. C.; Geha, M.; Griest, K.;
Lehner, M. J.; Marshall, S. L.; Minniti, D.; Nelson, C.; Peterson,
B. A.; Popowski, P.; Pratt, M. R.; Quinn, P. J.; Sutherland, W.;
Tomaney, A. B.; Vandehei, T.; Welch, D. L.
2001ApJ...552..289A Altcode: 2001astro.ph..1094A
By cross-correlating the results of two recent large-scale surveys,
the general properties of a well-defined sample of semiregular
variable stars have been determined. ISOGAL mid-infrared photometry
(7 and 15 μm) and MACHO V and R light curves are assembled for
approximately 300 stars in the Baade's windows of low extinction
toward the Galactic bulge. These stars are mainly giants of late M
spectral type, evolving along the asymptotic giant branch (AGB). They
are found to possess a wide and continuous distribution of pulsation
periods and to obey an approximate logP-M<SUB>bol</SUB> relation or
set of such relations. Approximate mass-loss rates M in the range
of ~1×10<SUP>-8</SUP> to 5×10<SUP>-7</SUP> M<SUB>solar</SUB>
yr<SUP>-1</SUP> are derived from ISOGAL mid-infrared photometry and
models of stellar spectra adjusted for the presence of optically thin
circumstellar silicate dust. Mass-loss rates depend on luminosity and
pulsation period. Some stars lose mass as rapidly as short-period Mira
variables but do not show Mira-like amplitudes. A period of 70 days
or longer is a necessary but not sufficient condition for mass loss
to occur. For AGB stars in the mass-loss ranges that we observe,
the functional dependence of mass-loss rate on temperature and
luminosity can be expressed as M~T<SUP>α</SUP>L<SUP>β</SUP>,
where α=-8.80<SUP>+0.96</SUP><SUB>-0.24</SUB> and
β=+1.74<SUP>+0.16</SUP><SUB>-0.24</SUB>, in agreement with
recent theoretical predictions. If we include our mass-loss
rates with a sample of extreme mass-losing AGB stars in the Large
Magellanic Cloud and ignore T as a variable, we get the general
result for AGB stars that M~L<SUP>2.7</SUP>, valid for AGB stars
with 10<SUP>-8</SUP><M<10<SUP>-4</SUP> M<SUB>solar</SUB>
yr<SUP>-1</SUP>.
---------------------------------------------------------
Title: The Nuclear Dynamics of M32. I. Data and Stellar Kinematics
Authors: Joseph, C. L.; Merritt, D.; Olling, R.; Valluri, M.; Bender,
R.; Bower, G.; Danks, A.; Gull, T.; Hutchings, J.; Kaiser, M. E.;
Maran, S.; Weistrop, D.; Woodgate, B.; Malumuth, E.; Nelson, C.;
Plait, P.; Lindler, D.
2001ApJ...550..668J Altcode: 2000astro.ph..5530J
We have obtained optical long-slit spectroscopy of the nucleus of M32
using the Space Telescope Imaging Spectrograph aboard the Hubble Space
Telescope. The stellar rotation velocity and velocity dispersion,
as well as the full line-of-sight velocity distribution (LOSVD),
were determined as a function of position along the slit using two
independent spectral deconvolution algorithms. We see three clear
kinematical signatures of the nuclear black hole: a sudden upturn,
at ~0.3" from the center, in the stellar velocity dispersions; a flat
or rising rotation curve into the center; and strong, non-Gaussian
wings on the central LOSVD. The central velocity dispersion is ~130 km
s<SUP>-1</SUP> (Gaussian fit) or >~175 km s<SUP>-1</SUP> (corrected
for the wings). The central kinematics are consistent with the presence
of a supermassive compact object in M32 with a mass in the range
(2-4)×10<SUP>6</SUP> M<SUB>solar</SUB>. Based on observations with
the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope
Science Institute, which is operated by the Association of Universities
for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.
---------------------------------------------------------
Title: Evidence of a Supermassive Black Hole in the Galaxy NGC 1023
from the Nuclear Stellar Dynamics
Authors: Bower, G. A.; Green, R. F.; Bender, R.; Gebhardt, K.; Lauer,
T. R.; Magorrian, J.; Richstone, D. O.; Danks, A.; Gull, T.; Hutchings,
J.; Joseph, C.; Kaiser, M. E.; Weistrop, D.; Woodgate, B.; Nelson,
C.; Malumuth, E. M.
2001ApJ...550...75B Altcode: 2000astro.ph.11204B
We analyze the nuclear stellar dynamics of the SB0 galaxy NGC 1023,
utilizing observational data both from the Space Telescope Imaging
Spectrograph aboard the Hubble Space Telescope and from the ground. The
stellar kinematics measured from these long-slit spectra show rapid
rotation (V~70 km s<SUP>-1</SUP> at a distance of 0.1"=4.9 pc from
the nucleus) and increasing velocity dispersion toward the nucleus
(where σ=295+/-30 km s<SUP>-1</SUP>). We model the observed stellar
kinematics assuming an axisymmetric mass distribution with both two
and three integrals of motion. Both modeling techniques point to
the presence of a central dark compact mass (which presumably is
a supermassive black hole) with confidence greater than 99%. The
isotropic two-integral models yield a best-fitting black hole mass
of (6.0+/-1.4)×10<SUP>7</SUP> M<SUB>solar</SUB> and mass-to-light
ratio (M/L<SUB>V</SUB>) of 5.38+/-0.08, and the goodness of fit
(χ<SUP>2</SUP>) is insensitive to reasonable values for the galaxy's
inclination. The three-integral models, which nonparametrically fit the
observed line-of-sight velocity distribution as a function of position
in the galaxy, suggest a black hole mass of (3.9+/-0.4)×10<SUP>7</SUP>
M<SUB>solar</SUB> and M/L<SUB>V</SUB> of 5.56+/-0.02 (internal errors),
and the edge-on models are vastly superior fits over models at other
inclinations. The internal dynamics in NGC 1023 as suggested by our
best-fit three-integral model shows that the velocity distribution
function at the nucleus is tangentially anisotropic, suggesting the
presence of a nuclear stellar disk. The nuclear line-of-sight velocity
distribution has enhanced wings at velocities >=600 km s<SUP>-1</SUP>
from systemic, suggesting that perhaps we have detected a group of
stars very close to the central dark mass. Based on observations with
the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope
Science Institute, which is operated by the Association of Universities
for Research in Astronomy, Inc. (AURA), under NASA contract NAS 5-26555.
---------------------------------------------------------
Title: MACHO Bulge Microlensing: Spectroscopy Needed
Authors: Minniti, D.; Alcock, C.; Cook, K.; Geha, M.; Marshall, S.;
Nelson, C.; Popowski, P.; Axelrod, T.; Allsman, R.; Drake, A.; Freeman,
K. C.; Peterson, B.; Becker, A.; Pratt, M.; Stubbs, C.; Tomaney, A.;
Alves, D. R.; Bennett, D.; Quinn, P.; Welch, D.; Sutherland, W.
2001ASPC..230...39M Altcode: 2001gddg.conf...39M
We discuss the analysis of MACHO bulge microlensing. New results
that give a smaller optical depth [τ = (2-3) 10<SUP>-6</SUP>] are
encouragingly closer to current models of the inner Milky Way. Although
hundreds of bulge events are now available and much progress has
occurred, there is still a need for spectroscopic characterization of
the microlensing events.
---------------------------------------------------------
Title: HST Observations of IRAS 15179+3956, an Interacting Galaxy
Pair in the Bootes Void
Authors: Cruzen, S.; Wehr, T.; Weistrop, D.; Nelson, C.; Angione, R.
2000AAS...197.7904C Altcode: 2000BAAS...32.1532C
We present analysis of broadband (U, V, I) images of the asymmetric
Bootes Void galaxy IRAS 15179+3956, taken with the Hubble Space
Telescope's WFPC2 camera. We also include a discussion of optical
spectroscopy from Mount Laguna Observatory. Ground-based optical
(Cruzen, et. al. 1997) and radio observations (Sage et. al. 1997) have
suggested that this system is an interacting pair. It exhibits very
blue broadband colors, a strong emission-line spectrum, and is reported
to be an OH megamaser (Bottinelli, et. al. 1989, Baan et. al. 1998),
all suggesting violent star formation. Our WFPC2 images clearly
confirm that this system is an interacting pair, with the southern-most
galaxy exhibiting a greatly disturbed morphology and an extended tidal
tail. The broadband colors identify regions of enhanced star-formation
within the two galaxies. The starburst models of Leitherer et al. (1999)
are compared with the colors and equivalent widths of emission lines
to place constraints on the age of the star-formation episodes. We
describe the morphologies of both galaxies and discuss the effects of
the tidal interaction. The cosmological implications of interacting
galaxies in low-density environments are also discussed. This work has
been supported in part by NASA under contract NAS5-31231, and through
the Nevada Space Grant Consortium. Mount Laguna Observatory is operated
jointly by San Diego State University and the University of Illinois.
---------------------------------------------------------
Title: The MACHO Project Large Magellanic Cloud Variable-Star
Inventory. IX. Frequency Analysis of the First-Overtone RR Lyrae
Stars and the Indication for Nonradial Pulsations
Authors: Alcock, C.; Allsman, R.; Alves, D. R.; Axelrod, T.; Becker,
A.; Bennett, D.; Clement, C.; Cook, K. H.; Drake, A.; Freeman, K.;
Geha, M.; Griest, K.; Kovács, G.; Kurtz, D. W.; Lehner, M.; Marshall,
S.; Minniti, D.; Nelson, C.; Peterson, B.; Popowski, P.; Pratt, M.;
Quinn, P.; Rodgers, A.; Rowe, J.; Stubbs, C.; Sutherland, W.; Tomaney,
A.; Vandehei, T.; Welch, D. L.
2000ApJ...542..257A Altcode: 2000astro.ph..5361A
More than 1300 variables classified provisionally as first-overtone
RR Lyrae pulsators in the MACHO variable-star database of the Large
Magellanic Cloud (LMC) have been subjected to standard frequency
analysis. Based on the remnant power in the prewhitened spectra, we
found 70% of the total population to be monoperiodic. The remaining 30%
(411 stars) are classified as one of nine types according to their
frequency spectra. Several types of RR Lyrae pulsational behavior
are clearly identified here for the first time. Together with the
earlier discovered double-mode (fundamental and first-overtone)
variables, this study increased the number of known double-mode stars
in the LMC to 181. During the total 6.5 yr time span of the data, 10%
of the stars showed strong period changes. The size, and in general
also the patterns of the period changes, exclude a simple evolutionary
explanation. We also discovered two additional types of multifrequency
pulsators with low occurrence rates of 2% for each. In the first type,
there remains one closely spaced component after prewhitening by the
main pulsation frequency. In the second type, the number of remnant
components is two; they are also closely spaced, and are symmetric
in their frequency spacing relative to the central component. This
latter type of variables are associated with their relatives among the
fundamental pulsators, known as Blazhko variables. Their high frequency
(~20%) among the fundamental-mode variables versus the low occurrence
rate of their first-overtone counterparts makes it more difficult to
explain the Blazhko phenomenon by any theory depending mainly on the
role of aspect angle or magnetic field. None of the current theoretical
models are able to explain the observed close frequency components
without invoking nonradial pulsation components in these stars.
---------------------------------------------------------
Title: Binary Microlensing Events from the MACHO Project
Authors: Alcock, C.; Allsman, R. A.; Alves, D.; Axelrod, T. S.;
Baines, D.; Becker, A. C.; Bennett, D. P.; Bourke, A.; Brakel, A.;
Cook, K. H.; Crook, B.; Crouch, A.; Dan, J.; Drake, A. J.; Fragile,
P. C.; Freeman, K. C.; Gal-Yam, A.; Geha, M.; Gray, J.; Griest, K.;
Gurtierrez, A.; Heller, A.; Howard, J.; Johnson, B. R.; Kaspi, S.;
Keane, M.; Kovo, O.; Leach, C.; Leach, T.; Leibowitz, E. M.; Lehner,
M. J.; Lipkin, Y.; Maoz, D.; Marshall, S. L.; McDowell, D.; McKeown,
S.; Mendelson, H.; Messenger, B.; Minniti, D.; Nelson, C.; Peterson,
B. A.; Popowski, P.; Pozza, E.; Purcell, P.; Pratt, M. R.; Quinn,
J.; Quinn, P. J.; Rhie, S. H.; Rodgers, A. W.; Salmon, A.; Shemmer,
O.; Stetson, P.; Stubbs, C. W.; Sutherland, W.; Thomson, S.; Tomaney,
A.; Vandehei, T.; Walker, A.; Ward, K.; Wyper, G.
2000ApJ...541..270A Altcode: 1999astro.ph..7369M
We present the light curves of 21 gravitational microlensing events from
the first six years of the MACHO Project gravitational microlensing
survey that are likely examples of lensing by binary systems. These
events were manually selected from a total sample of ~350 candidate
microlensing events that were either detected by the MACHO Alert
System or discovered through retrospective analyses of the MACHO
database. At least 14 of these 21 events exhibit strong (caustic)
features, and four of the events are well fit with lensing by large
mass ratio (brown dwarf or planetary) systems, although these fits
are not necessarily unique. The total binary event rate is roughly
consistent with predictions based upon our knowledge of the properties
of binary stars, but a precise comparison cannot be made without a
determination of our binary lens event detection efficiency. Toward
the Galactic bulge, we find a ratio of caustic crossing to noncaustic
crossing binary lensing events of 12:4, excluding one event for which
we present two fits. This suggests significant incompleteness in
our ability to detect and characterize noncaustic crossing binary
lensing. The distribution of mass ratios, N(q), for these binary
lenses appears relatively flat. We are also able to reliably measure
source-face crossing times in four of the bulge caustic crossing events,
and recover from them a distribution of lens proper motions, masses,
and distances consistent with a population of Galactic bulge lenses
at a distance of 7+/-1 kpc. This analysis yields two systems with
companions of ~0.05 M<SUB>solar</SUB>.
---------------------------------------------------------
Title: The MACHO Project Sample of Galactic Bulge High-Amplitude δ
Scuti Stars: Pulsation Behavior and Stellar Properties
Authors: Alcock, C.; Allsman, R. A.; Alves, D. R.; Axelrod, T. S.;
Becker, A. C.; Bennett, D. P.; Cook, K. H.; Freeman, K. C.; Geha, M.;
Griest, K.; Lehner, M. J.; Marshall, S. L.; McNamara, B. J.; Minniti,
D.; Nelson, C.; Peterson, B. A.; Popowski, P.; Pratt, M. R.; Quinn,
P. J.; Rodgers, A. W.; Sutherland, W.; Templeton, M. R.; Vandehei,
T.; Welch, D. L.
2000ApJ...536..798A Altcode:
We have detected 90 objects with periods and light-curve structures
similar to those of field δ Scuti stars using the Massive Compact
Halo Object (MACHO) Project database of Galactic bulge photometry. If
we assume similar extinction values for all candidates and absolute
magnitudes similar to those of other field high-amplitude δ Scuti
stars (HADS), the majority of these objects lie in or near the Galactic
bulge. At least two of these objects are likely foreground δ Scuti
stars, one of which may be an evolved nonradial pulsator, similar to
other evolved, disk-population δ Scuti stars. We have analyzed the
light curves of these objects and find that they are similar to the
light curves of field δ Scuti stars and the δ Scuti stars found
by the Optical Gravitational Lens Experiment (OGLE). However, the
amplitude distribution of these sources lies between those of low-
and high-amplitude δ Scuti stars, which suggests that they may be
an intermediate population. We have found nine double-mode HADS with
frequency ratios ranging from 0.75 to 0.79, four probable double- and
multiple-mode objects, and another four objects with marginal detections
of secondary modes. The low frequencies (5-14 cycles day<SUP>-1</SUP>)
and the observed period ratios of ~0.77 suggest that the majority
of these objects are evolved stars pulsating in fundamental or first
overtone radial modes.
---------------------------------------------------------
Title: The Ionization Source in the Nucleus of M84
Authors: Bower, G. A.; Green, R. F.; Quillen, A. C.; Danks, A.; Gull,
T.; Hutchings, J.; Joseph, C.; Kaiser, M. E.; Weistrop, D.; Woodgate,
B.; Malumuth, E. M.; Nelson, C.
2000ApJ...534..189B Altcode: 1999astro.ph.12393B
We have obtained new Hubble Space Telescope observations of
M84, a nearby massive elliptical galaxy whose nucleus contains a
~1.5×10<SUP>9</SUP> M<SUB>solar</SUB> dark compact object, which
presumably is a supermassive black hole. Our Space Telescope Imaging
Spectrograph spectrum provides the first clear detection of emission
lines in the blue (e.g., [O II] λ3727, Hβ, and [O III] λλ4959,
5007), which arise from a compact region ~0.28" across centered on
the nucleus. Our Near-Infrared Camera and Multiobject Spectrometer
images exhibit the best view through the prominent dust lanes evident
at optical wavelengths and provide a more accurate correction for
the internal extinction. The relative fluxes of the emission lines we
have detected in the blue together with those recently detected in the
wavelength range 6295-6867 Å by Bower et al. indicate that the gas
at the nucleus is photoionized by a nonstellar process instead of hot
stars. Stellar absorption features from cool stars at the nucleus are
very weak. We update the spectral energy distribution of the nuclear
point source and find that although it is roughly flat in most bands,
the optical-to-UV continuum is very red, similar to the spectral
energy distribution of BL Lac. Thus, the nuclear point source seen in
high-resolution optical images by Bower et al. is not a star cluster
but is instead a nonstellar source. Assuming isotropic emission from
this source, we estimate that the ratio of bolometric luminosity to
Eddington luminosity is ~5×10<SUP>-7</SUP>. However, this could be
underestimated if this source is a misaligned BL Lac object, which is
a possibility suggested by the spectral energy distribution and the
evidence of optical variability we describe. Based on observations with
the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope
Science Institute, which is operated by the Association of Universities
for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.
---------------------------------------------------------
Title: Frequency Analysis of the RRc Variables of the MACHO Database
for the LMC
Authors: Kovács, G.; Alcock, C.; Allsman, R.; Alves, D.; Axelrod,
T.; Becker, A.; Bennett, D.; Clement, C.; Cook, K. H.; Drake, A.;
Freeman, K.; Geha, M.; Griest, K.; Kurtz, D. W.; Lehner, M.; Marshall,
S.; Minniti, D.; Nelson, C.; Peterson, B.; Popowski, P.; Pratt, M.;
Quinn, P.; Rodgers, A.; Rowe, J.; Stubbs, C.; Sutherland, W.; Tomaney,
A.; Vandehei, T.; Welch, D. L.; MACHO Collaboration
2000ASPC..203..313K Altcode: 2000ilss.conf..313K; 2000IAUCo.176..313K
We present the first massive frequency analysis of the 1200 first
overtone RR Lyrae stars in the Large Magellanic Cloud observed
in the first 4.3 yr of the MACHO project. Besides the many new
double-mode variables, we also discovered stars with closely spaced
frequencies. These variables are most probably nonradial pulsators.
---------------------------------------------------------
Title: Kinematics and Dynamics of the Narrow Line Region of NGC4151
Authors: Kaiser, M. E.; Bradley, L. D., II; Hutchings, J. B.; Weistrop,
D.; Nelson, C.; Kraemer, S. B.; Crenshaw, D. M.; Ruiz, J.; Gull, T. R.
1999ASPC..182...51K Altcode: 1999gady.conf...51K
No abstract at ADS
---------------------------------------------------------
Title: Kinematic Mapping of the Narrow Line Region of NGC4151
Authors: Kaiser, Mary E.; Bradley, L. D., II; Hutchings, J. B.;
Kraemer, S. B.; Crenshaw, D. M.; Ruiz, J.; Weistrop, D.; Nelson, C.;
Gull, T. R.
1999IAUS..194...79K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Spatially Resolved Spectra of 3C Galaxy Nuclei
Authors: Hutchings, J. B.; Baum, S. A.; Weistrop, D.; Nelson, C.;
Kaiser, M. E.; Gelderman, R. F.
1998AJ....116..634H Altcode: 1998astro.ph..5177H
We present and discuss visible-wavelength long-slit spectra of four
low-redshift 3C galaxies obtained with the Space Telescope Imaging
Spectrograph on the Hubble Space Telescope (HST). The slit was aligned
with near-nuclear jetlike structure seen in HST images of the galaxies,
to give unprecedented spatial resolution of their inner regions. In
3C 135 and 3C 171, the spectra reveal clumpy emission-line structures
that indicate outward motions of a few hundred kilometers per second
within a centrally illuminated and ionized biconical region. There may
also be some low-ionization, high-velocity material associated with
3C 135. In 3C 264 and 3C 78, the jets have blue featureless spectra
consistent with their proposed synchrotron origin. There is weak
associated line emission in the innermost part of the jets with mild
outflow velocity. These jets are bright and highly collimated only
within a circumnuclear region of lower galaxy luminosity, which is
not dusty. We discuss the origins of these central regions and their
connection with relativistic jets.
---------------------------------------------------------
Title: The MACHO Project: Status Report on the Magellanic Clouds.
Authors: Vandehei, T.; Griest, K.; Alcock, C.; Alves, D.; Cook, K.;
Minniti, D.; Marshall, S.; Allsman, R.; Axelrod, T.; Freeman, K.;
Peterson, B.; Rodgers, A.; Pratt, M.; Becker, A.; Stubbs, C.; Tomaney,
A. B.; Lehner, M.; Bennett, D.; Nelson, C.; Quinn, P.; Sutherland,
W.; Welch, D.
1998AAS...192.0703V Altcode: 1998BAAS...30..825V
The MACHO Project is a search for dark matter in the form of massive
compact halo objects (MACHOs). Photometric monitoring of tens of
millions of stars in the Large Magellanic Cloud (LMC), Small Magellanic
Cloud (SMC), and Galactic bulge is used to search for these rare
gravitational microlensing events caused by these otherwise invisible
objects. An analysis of 4 years of LMC data on 12 million stars and 5
years of SMC data on 3 million stars is currently underway. We present
preliminary results of this analysis which reveal about 15 candidate
microlensing events in the LMC and 1 event in the SMC. We also present
our microlensing detection efficiency calculation pipeline. The accurate
determination of our detection efficiency is key in estimating the MACHO
contribution to the dark matter in the halo. The efficiency pipeline
uses data from the MACHO Project's ground based survey and from HST
observations of MACHO fields to determine the true color and luminosity
distribution of LMC source stars. Artificial microlensing events are
then inserted into the underlying source distribution, image sequences
are created from a wide sample of real image conditions and detection
efficiencies are determined using our standard reduction pipeline. The
full calculation of our efficiencies requires the creation, reduction
and analysis of 322 Gbytes of artificial image data and is currently
underway.
---------------------------------------------------------
Title: Long-Slit Spectroscopy of the Star-forming Regions in the
Interacting Galaxies NGC 3991, NGC 3994 and NGC 3995
Authors: Nelson, C.; Weistrop, D.; Angione, R.
1998AAS...192.6912N Altcode: 1998BAAS...30..925N
We have obtained long-slit spectroscopy with the Kitt Peak 2.1-meter
telescope of the interacting galaxies NGC 3991, NGC 3994 and NGC
3995 to study how star formation propagates in tidally disturbed
systems. UBVR imaging of these galaxies has shown they contain bright,
blue star-forming knots, with a range of ages and reddening. Our
apertures were chosen to examine a number of these knots in various
galaxy environments. Preliminary analysis of the spectra reveals
evidence for population differences through a variety of emission and
absorption features of varying strengths. The strength of the nebular
emission lines confirms that many regions are undergoing high rates
of star formation. These data will used to determine the age of each
knot as a function of location in the galaxy, to address a series
of questions. Does the star formation occur first in the nucleus or
outer regions of the galaxies? Are there differences in the stellar
populations of the star forming regions related to the local gas
density, disk dynamics, or other environmental factors? Does star
formation triggered by galaxy interactions produce an initial mass
function biased toward massive stars? These results are part of an
ongoing study of star formation in interacting galaxies that will
include HST imaging and spectroscopy with the Space Telescope Imaging
Spectrograph. This research has been supported in part by NASA, under
contract NAS5-31231.
---------------------------------------------------------
Title: Long-slit Spectroscopy of the Star-forming Regions in the
Interacting Galaxies NGC 3395/3396
Authors: Weistrop, D.; Nelson, C.; Angione, R.
1998AAS...192.6911W Altcode: 1998BAAS...30Q.925W
We have obtained long-slit spectroscopy of the interacting galaxies
NGC 3395, NGC 3396 to investigate the propagation of star formation in
tidally disturbed systems. UBVR imaging of these galaxies has shown that
they contain bright, blue star-forming knots, with a range of ages and
reddening. The NOAO 2.1 meter telescope was used to obtain spectroscopy
of several of the knots in various galaxy environments. Preliminary
analysis of the spectra reveals a variety of emission and absorption
features of varying strengths, defining population differences across
the galaxies. The strength of the nebular emission lines confirms that
regions undergoing high rates of star formation are present. These
data will be used to investigate the amount of reddening in the
knots, and to determine the ages of the youngest stars as a function
of location in the galaxy. Questions to be addressed include: Does
the star formation occur first in the nucleus or outer regions of the
galaxies? Are there differences in the stellar populations of the star
forming regions related to the local gas density, disk dynamics, or
other environmental factors? Does star formation triggered by galaxy
interactions produce an initial mass function biased toward massive
stars? These results are part of an ongoing study of star formation
in interacting galaxies that will include HST imaging and spectroscopy
with the Space Telescope Imaging Spectrograph. This research has been
supported in part by NASA, under contract NAS5-31231.
---------------------------------------------------------
Title: Characterization of Magnetite Within Carbonate in ALH 84001
Authors: Blake, D. F.; Treiman, A. H.; Cady, S.; Nelson, C.;
Krishnan, K.
1998LPI....29.1347B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An improved, optically-pumped, primary frequency standard.
Authors: Hasegawa, A.; Fukuda, K.; Kotake, N.; Kajita, M.; Morikawa,
T.; Lee, W. D.; Nelson, C.; Jennings, D. A.; Mullen, L.; Shiriey,
J. H.; Drullinger, R.
1998pemd.conf..177H Altcode:
An improved primary frequency standard based on an optically-pumped,
thermal, atomic-beam has been jointly developed by CRL and NIST. The
design details along with the first evaluation and comparison with
NIST's existing standard are presented.
---------------------------------------------------------
Title: The MACHO Project: Preliminary Results from 4 years of LMC
observations.
Authors: Cook, K.; Alcock, C.; Alves, D.; Minniti, D.; Marshall,
S.; Vandehei, T.; Griest, K.; Allsman, R.; Axelrod, T.; Freeman, K.;
Peterson, B.; Rodgers, A.; Pratt, M.; Becker, A.; Stubbs, C.; Tomaney,
A.; Lehner, M.; Bennett, D.; Nelson, C.; Quinn, P.; Sutherland, W.;
Welch, D.
1997AAS...191.8301C Altcode: 1997BAAS...29.1346C
The MACHO Project is a search for dark matter in the form of massive
compact halo objects (MACHOs). Photometric monitoring of tens of
millions of stars in the Large Magellanic Cloud (LMC), Small Magellanic
Cloud (SMC), and Galactic bulge is used to search for gravitational
microlensing events caused by these otherwise invisible objects. An
analysis of 4 years of LMC data on 12.5 million stars is currently
underway. We present preliminary results of this analysis which reveal
about 15 candidate microlensing events. We also present our microlensing
detection efficiency calculation pipeline. The accurate determination
of our detection efficiency is key in estimating the MACHO contribution
to the dark matter halo. The efficiency pipeline uses data from the
MACHO Project's ground based survey and from HST observations of MACHO
fields to determine the true color and luminosity distribution of LMC
source stars. Artificial microlensing events are then inserted into
the underlying source distribution, image sequences are created from
a wide sample of real image conditions and detection efficiencies are
determined using our standard reduction pipeline. The full calculation
of our efficiencies requires the creation, reduction and analysis of
322 Gbytes of artificial image data and is currently underway. The MACHO
Project dedicates this work to one of its key founders, Alex Rodgers.
---------------------------------------------------------
Title: The MACHO Project 9 Million Star Color-Magnitude Diagram of
the Large Magellanic Cloud Bar
Authors: Alves, D.; Alcock, C.; Cook, K.; Marshall, S.; Minniti,
D.; Allsman, R.; Axelrod, T.; Freeman, K.; Peterson, B.; Rodgers,
A.; Becker, A.; Stubbs, C.; Tomaney, A.; Griest, K.; Vandehei, T.;
Bennett, D.; Lehner, M.; Nelson, C.; Pratt, M.; Quinn, P.; Sutherland,
W.; Welch, D.
1997AAS...19111501A Altcode: 1997BAAS...29.1398A
We present a composite 9 million star color-magnitude diagram (9M CMD)
of the LMC bar using calibrated MACHO project photometry. The large
number of stars reveal numerous low-level features, many of which can
be attributed to short-lived stages of stellar evolution. The star
formation and chemical enrichment history of the LMC is investigated,
with additional discussion of the ~ 10(5) LMC variable stars in the
MACHO database. Example features are intermediate mass supergiant
sequences, multiple sequences of AGB stars, a bump on the RGB, and
possible evidence for extended HB evolution. The 9M CMD is interpreted
with theoretical isochrones, CMDs of LMC clusters, an HST CMD,
and artificial CMDs. The latter include the effects of differential
reddening and blending. The intermediate mass supergiants, including
Cepheids, suggest a variable recent star formation history. The
RGB and multiple AGB sequences are consistent with two superposed
populations; an ancient population with [Fe/H] ~ -1.6 dex, and a few
Gyr-old population with [Fe/H] ~ -0.7 dex. The location of the bump on
the RGB constrains the age and metallicity of the younger population;
no other RGB bump is observed. The possibility of an intervening
stellar population in the Galactic halo is probed with the 9M CMD and
archival data. Galactic star count model predictions agree well with
foreground stars observed in the 9M CMD. We predict the planetary
nebulae and carbon stars associated with an hypothetical intervening
population. Lastly, we discuss the 9M CMD and MACHO microlensing
detection efficiencies. Alves dedicates this paper to Alex Rodgers,
who greatly influenced this work and will be fondly remembered.
