explanation blue bibcodes open ADS page with paths to full text
Author name code: vaiana
ADS astronomy entries on 2022-09-14
author:Vaiana, G.S.
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Title: B-MINE The Balloon-Borne Microcalorimeter Nuclear Line
Explorer Mission
Authors: Silver, E.; Vaiana, G. S.
2000HEAD....5.4325S Altcode: 2000BAAS...32.1263S
B-MINE will probe the deepest regions of a supernova explosion by
detecting <SUP>44</SUP>Ti emission at 68 keV with spatial and spectral
resolutions that are sufficient to determine the spatial extent and
velocity distribution of the <SUP>44</SUP>Ti emitting region. The
payload introduces the concept of focusing optics and microcalorimeter
spectroscopy to nuclear line emission astrophysics. B-MINE has a thin,
plastic foil telescope multilayered to maximize the reflectivity in a 20
keV band centered at 68 keV and a microcalorimeter array optimized for
the same energy band. This combination provides a reduced background
and allows an energy resolution of 50 eV and a 3 σ sensitivity
in 10<SUP>6</SUP> s of 3.3 x 10<SUP>-7</SUP> ph cm<SUP>-2</SUP>
s<SUP>-1</SUP> at 68 keV. During the course of a long duration balloon
flight, B-MINE will carry out a detailed study of the <SUP>44</SUP>Ti
emission line centroid and width in CAS A.
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Title: An Einstein Observatory SAO-based Catalog of B-Type Stars
Authors: Grillo, F.; Sciortino, S.; Micela, G.; Vaiana, G. S.; Harnden,
F. R., Jr.
1992ApJS...81..795G Altcode:
About 4000 X-ray images obtained with the Einstein Observatory are used
to measure the 0.16-4.0 keV emission from 1545 B-type SAO stars falling
in the about 10 percent of the sky surveyed with the IPC. Seventy-four
detected X-ray sources with B-type stars are identified, and it is
estimated that no more than 15 can be misidentified. Upper limits
to the X-ray emission of the remaining stars are presented. In
addition to summarizing the X-ray measurements and giving other
relevant optical data, the present extensive catalog discusses the
reduction process and analyzes selection effects associated with both
SAO catalog completeness and IPC target selection procedures. It is
concluded that X-ray emission, at the level of Lx not less than 10 exp
30 ergs/s, is quite common in B stars of early spectral types (B0-B3),
regardless of luminosity class, but that emission, at the same level,
becomes less common, or nonexistent, in later B-type stars.
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Title: Modeling the Stellar Contribution to the Galactic Component
of the Diffuse Soft X-Ray Background. I. Background Fluxes and
Number Counts
Authors: Kashyap, V.; Rosner, R.; Micela, G.; Sciortino, S.; Vaiana,
G. S.; Harnden, F. R., Jr.
1992ApJ...391..667K Altcode:
A combination of a stellar Galaxy model based on optical data,
stellar X-ray luminosity functions derived from the full Einstein
base, and a model for X-ray absorption derived from hydrogen column
densities are used to estimate the contribution to the diffuse soft
X-ray background flux from the main-sequence A, F, G, K, and M stars,
and RS CVn stars, at various energies ranging from 0.1 to about 5
keV. Previous discrepancies between earlier estimates of the stellar
contribution to the diffuse soft X-ray background are resolved; this
stellar contribution to the diffuse soft X-ray background is found to
be under 3 percent for photon energies less than energy I and J bands
(about 0.8-2 keV), at a threshold sensitivity for point source detection
about 10 exp -10 ergs/s sq cm. At low latitudes, stellar contribution
estimates are less than 3 percent below 0.3 keV, 7-40 percent in the
medium-energy bands, and 27-70 percent in the I and J bands. It is
shown that while dM stars are the major contributors to the diffuse
stellar flux, other stellar types contribute as much as 40 percent of
this flux at the higher energies in the passband studied.
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Title: X-Ray Activity as Statistical Age Indicator: The Disk G--K
Giants
Authors: Micela, G.; Maggio, A.; Vaiana, G. S.
1992ApJ...388..171M Altcode:
For a sample of late-type disk giant stars, the dependence of coronal
emission on age as defined by metallicity and kinematics indicators has
been studied. It is found that the mean level of X-ray emission for
stars with strong metallic lines and/or small peculiar velocities is
larger by about one order of magnitude than the mean level of emission
for stars with weak lines and/or high peculiar velocities. Hence, it
is suggested that the X-ray activity can be used as a statistical age
indicator for late-type giants, as well as the classical metallicity
or kinematics indicators. It is found that the spread in metallicity
typical of the Galactic disk accounts for less than 50 percent of the
observed difference in X-ray emission. To explain the observations
it is argued that other effects should be invoked, such as changes
in the efficiency of the stellar magnetic dynamo or the influence of
metallicity itself on the coronal heating processes.
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Title: The stellar coronal component of the Galaxy. I. The X-COUNT
numerical model.
Authors: Favata, F.; Micela, G.; Sciortino, S.; Vaiana, G. S.
1992A&A...256...86F Altcode:
The authors present a computational model for the prediction and
analysis of the distribution of galactic X-ray stellar coronal
source counts, based on models for the distribution of stars and of
interstellar hydrogen in the Galaxy and on known properties of stellar
X-ray emission in the solar neighborhood. The model can be, and has
been used, for comparisons with unbiased X-ray surveys (equivalent to
the deep source counts conducted in the optical), for predictions of
stellar X-ray observations with new instruments and to estimate the
stellar contribution to the X-ray background.
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Title: Results from an extensive Einstein Observatory survey of
B-type stars
Authors: Grillo, F.; Sciortino, S.; Micela, G.; Vaiana, G. S.; Harnden,
F. R., Jr.
1992MmSAI..63..739G Altcode:
A summary is presented of the results of an analysis of a recently
compiled catalog of the 0.16-4.0 keV emission from 1545 B-type stars,
taken from the Smithsonian-Astrophysical-Observatory Star Catalog
(Roman and Warren, 1984), falling in the about 10-percent of the
sky surveyed with the Einstein Observatory imaging proportional
counter. The available information made it possible to identify a
pseudovolume-limited sample containing about 54 percent of the surveyed
stars and 87.5 percent of the detected ones.
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Title: X-ray emission at low-mass end of the MS - Results from an
extensive Einstein Observatory survey
Authors: Barbera, M.; Micela, G.; Sciortino, S.; Vaiana, G. S.;
Harnden, F. R., Jr.; Rosner, R.
1992MmSAI..63..743B Altcode:
The 0.16-4.0 keV X-ray emission from K and M stars of luminosity
classes IV, V, and VI within 25 parsec of the sun was measured using
all available Einstein Observatory IPC data and a critical compilation
of catalogued optical data. Fifty four of 88 stars were detected,
70 of 138 M stars with Mv less than 13.4 (corresponding to M6) and 15
or 31 fainter M stars. The surveyed stars were grouped, on the basis
of U, V, W space velocity components, into old-disk, young-disk,
and halo population stars. Then, a subsample was selected which is
statistically representative of the population of K and M stars in the
solar neighborhood, on the basis of which unbiased Maximum Likelihood
X-ray luminosity functions were constructed for K, early M, and late M
stars. The investigation revealed a decrease of X-ray luminosity with
increasing stellar age in the range of ages of disk population stars.
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Title: Coronal emission and stellar evolution
Authors: Vaiana, G. S.
1992HiA.....9..651V Altcode:
No abstract at ADS
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Title: A Comparisons Between Model Predicted and Observed Coronal
Stellar Counts from the X-Ray Flux-Limited EMSS
Authors: Favata, F.; Micela, G.; Sciortino, S.; Vaiana, G.
1992fxra.conf..273F Altcode:
No abstract at ADS
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Title: Coronal emission and stellar evolution.
Authors: Vaiana, G. S.; Maggio, A.; Micela, G.; Sciortino, S.
1992MmSAI..63..545V Altcode:
Results of stellar X-ray astronomy based on the Einstein and Exosat
observations are reviewed together with preliminary results from
Rosat. Attention is given to the influence of stellar evolution on the
X-ray emission from normal stars, the contribution of normal star X-ray
emission to the X-ray makeup of the Galaxy, the stellar contribution
to the diffuse soft X-ray background, and the origin of the Galactic
Ridge. Particular consideration is given to methods for predicting
the stellar coronal source number counts.
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Title: The Diffuse Soft X-Ray Background As Seen with the Einstein
Observatory
Authors: Micela, G.; Harnden, F. R., Jr.; Rosner, R.; Sciortino, S.;
Vaiana, G. S.
1991ApJ...380..495M Altcode:
A systematic survey of the diffuse soft X-ray background as seen
directly with the Einstein Observatory is presented. With the aid of
1633 selected 1 x 1 deg fields of view obtained by the IPC to provide
about 5-percent sky coverage, with some bias toward the Galactic
plane, the background in the 0.16-3.5 keV spectral region was spatially
resolved on this angular scale. Maps of the background are characterized
and produced at different energies within the Einstein passband. It
is confirmed that the Galactic ridge is not present at energies below
0.33 keV and it is demonstrated that the appearance of the ridge above
this energy is not due to hard Galactic sources with a flux above 10
exp -13 ergs/sq cm/s. A southern Galactic region is identified, with l
between 80 and 180 deg and b less than -5 deg, where the mean background
intensity has the lowest value and is homogeneous within better than 9
percent. The implications of these results for the Galactic structure
and for the nature of the extragalactic X-ray background are discussed.
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Title: An Einstein Observatory Catalog of B-Type Stars
Authors: Harnden, F. R., Jr.; Grillo, F.; Sciortino, S.; Micela, G.;
Vaiana, G. S.
1991BAAS...23..913H Altcode:
No abstract at ADS
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Title: The X-Ray Emission from Pre-Main Sequence Stars in
Taurus-Auriga and the Relationship with Other Diagnostics of Activity
Authors: Damiani, F.; Micela, G.; Vaiana, G. S.
1991ASIC..340...89D Altcode: 1991amey.conf...89D
No abstract at ADS
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Title: Einstein Observatory Coronal Temperatures of Late-Type Stars
Authors: Schmitt, J. H. M. M.; Collura, A.; Sciortino, S.; Vaiana,
G. S.; Harnden, F. R., Jr.; Rosner, R.
1990ApJ...365..704S Altcode:
The results are presented of a survey of the coronal temperatures
of late-type stars using the Einstein Observatory IPC. The spectral
analysis shows that the frequently found one- and two-temperature
descriptions are mainly influenced by the SNR of the data and that
models using continuous emission measure distributions can provide
equally adequate and physically more meaningful and more plausible
descriptions. Intrinsic differences in differential emission
measure distributions are found for four groups of stars. M dwarfs
generally show evidence for high-temperature gas in conjunction with
lower-temperature material, while main-sequence stars of types F and
G have the high-temperature component either absent or very weak. Very
hot coronae without the lower-temperature component appearing in dwarf
stars are evident in most of the giant stars studied. RS CVn systems
show evidence for extremely hot coronae, sometimes with no accompanying
lower-temperature material.
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Title: European Photon Imaging Camera (EPIC) for X-ray astronomy.
Authors: Bignami, G. F.; Villa, G. E.; Boella, G.; Bonelli, G.;
Caraveo, P.; Chiappetti, L.; Quadrini, M. E.; Di Cocco, G.; Trifoglio,
M.; Ubertini, P.; Peres, G.; Sciortino, S.; Serio, S.; Vaiana, G.;
Rothenflug, R.; Vigroux, L.; Koch, L.; Rio, Y.; Pigot, C.; Cretolle,
J.; Gabriel, A.; Foing, B.; Atteia, J. L.; Roques, J. P.; Bräuninger,
H.; Pietsch, W.; Predehl, P.; Reppin, C.; Struder, L.; Trümper, J.;
Lutz, G.; Kendziorra, E.; Staubert, R.; Holland, A. D.; Cole, R. E.;
Wells, A.; Pounds, K.; Lumb, D. A.; Pye, J.; Turner, M. J. L.; Goodall,
C. V.; Ponman, T. J.; Skinner, G. K.; Willmore, A. P.
1990SPIE.1344..144B Altcode: 1990exrg.conf..144B
ESA has selected the final payload for its "Cornerstone" mission
in X-Ray astronomy with multiple mirrors (XMM), to be flown in the
late nineties in the context of the "Horizon 2000" long term science
plan. EPIC represents the main instrument of the mission, to include
three CCD arrays in the focal planes of the three telescopes of the
spacecraft. They will be dedicated to source imaging, photometry,
spectroscopy and timing. The goals of EPIC are described.
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Title: Relationship between Optical and X-Ray Properties of O-Type
Stars Surveyed with the Einstein Observatory
Authors: Sciortino, S.; Vaiana, G. S.; Harnden, F. R., Jr.; Ramella,
M.; Morossi, C.; Rosner, R.; Schmitt, J. H. M. M.
1990ApJ...361..621S Altcode:
An X-ray luminosity function is derived for a representative
volume-limited sample of O-type stars selected from the catalog
of Galactic O stars surveyed with the Einstein Observatory. It was
found that, for the stars of this sample which is ten times larger
than any previously analyzed, the level of X-ray emission is strongly
correlated with bolometric luminosity, confirming previous findings of
an Lx-L(bol) relationship (e.g., Harnden et al., 1979; Pallavicini et
al., 1981). Correlations between the Lx and the mass loss rate with the
wind terminal velocity or with the rotation rate were weak. However,
there was a strong correlation with wind momentum flux as well as with
the wind kinetic energy flux.
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Title: IUE and Einstein Survey of Late-Type Giant and Supergiant
Stars and the Dividing Line
Authors: Haisch, Bernhard M.; Bookbinder, Jay A.; Maggio, A.; Vaiana,
G. S.; Bennett, Jeffrey O.
1990ApJ...361..570H Altcode:
Results are presented on an IUE UV survey of 255 late-type G, K, and M
stars, complementing the Maggio et al. (1990) Einstein X-ray survey of
380 late-type stars. The large data sample of X-ray and UV detections
make it possible to examine the activity relationship between the X-ray
and the UV emissions. The results confirm previous finding of a trend
involving a steeply-dropping upper envelope of the transition region
line fluxes, f(line)/f(V), as the dividing line is approached. This
suggests that a sharp decrease in maximum activity accompanies the
advancing spectral type, with the dividing line corresponding to
this steep gradient region. The results confirm the rotation-activity
connection for stars in this region of the H-R diagram.
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Title: Coronal Temperatures of Late-type Stars
Authors: Harnden, F. R., Jr.; Schmitt, J. H. M. M.; Rosner, R.;
Collura, A.; Vaiana, G. S.
1990BAAS...22..858H Altcode:
No abstract at ADS
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Title: X-ray studies of coeval star samples. III. X-ray emission in
the UrsaMajor stream.
Authors: Schmitt, J. H. M. M.; Micela, G.; Sciortino, S.; Vaiana,
G. S.; Harnden, F. R., Jr.; Rosner, R.
1990ApJ...351..492S Altcode:
Results are reported from a comprehensive survey of X-ray emission
from stars known or suspected to be members of the UMa cluster and/or
stream. Of the 42 UMa member stars surveyed, 18 were detected as
X-ray sources, and spectral analysis was performed for 10 stars
with sufficient X-ray counts. Consideration is given to relations
between X-ray luminosity, color, and kinematics of the sample
stars, and the X-ray spectra of the UMa stars are discussed in the
context of the general problem of stellar X-ray temperatures. Also
confirmed is the lack of X-ray-emitting A dwarfs among UMa members;
among stars of later spectra type there is a rather large dispersion
in X-ray luminosity. This dispersion cannot readily be explained by
contamination with field star interlopers and appears rather to be a
property of the UMa X-ray luminosity distribution function.
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Title: The X-Ray Emission of Late Type Evolved Stars
Authors: Maggio, A.; Vaiana, G. S.; Haisch, B. M.; Stern, R. A.;
Harnden, F. R., Jr.; Rosner, R.
1990ixra.conf..233M Altcode:
No abstract at ADS
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Title: The Einstein Survey of O-Stars
Authors: Sciortino, S.; Vaiana, G. S.; Harnden, F. R., Jr.; Ramella,
M.; Morossi, C.; Rosner, R.; Schmitt, J. H. M. M.
1990ixra.conf..227S Altcode: 1990ixra.symp..227S
The authors give a brief account of some of the main results of a
detailed analysis of a sample of 288 X-ray surveyed O stars.
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Title: The Einstein Observatory Stella X-Ray Database
Authors: Harnden, F. R., Jr.; Sciortino, S.; Micela, G.; Maggio, A.;
Vaiana, G. S.; Schmitt, J. H. M. M.
1990ixra.conf..313H Altcode: 1990ixra.symp..313H
The authors present the motivation for and methodology followed in
constructing the Einstin Observatory Stellar X-ray Database from a
uniform analysis of nearly 4000 Imaging Proportional Counter fields
obtained during the life of this mission. This project has been
implemented using the INGRES<SUP>TM</SUP> database system, so that
statistical analyses of the properties of detected X-ray sources are
relatively easy and flexibly accomplished.
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Title: Einstein Observatory Magnitude-limited X-Ray Survey of
Late-Type Giant and Supergiant Stars
Authors: Maggio, A.; Vaiana, G. S.; Haisch, B. M.; Stern, R. A.;
Bookbinder, J.; Harnden, F. R., Jr.; Rosner, R.
1990ApJ...348..253M Altcode:
Results are presented of an extensive X-ray survey of 380 giant and
supergiant stars of spectral types from F to M, carried out with
the Einstein Observatory. It was found that the observed F giants
or subgiants (slightly evolved stars with a mass M less than about 2
solar masses) are X-ray emitters at the same level of main-sequence
stars of similar spectral type. The G giants show a range of emissions
more than 3 orders of magnitude wide; some single G giants exist with
X-ray luminosities comparable to RS CVn systems, while some nearby
large G giants have upper limits on the X-ray emission below typical
solar values. The K giants have an observed X-ray emission level
significantly lower than F and F giants. None of the 29 M giants were
detected, except for one spectroscopic binary.
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Title: X-Ray Emission from Stars - a Sharper and Deeper View of
Our Galaxy
Authors: Vaiana, G. S.
1990ixra.conf...61V Altcode: 1990ixra.symp...61V
Contents: Introduction from early days to the present. The
X-ray selected source data base. The stellar X-ray source
identifications. Sorting the X-ray sources by optical catalog. X-ray
flux limited surveys: their impact on stellar astronomy. The soft X-ray
background. The stellar X-ray content of galaxy and the contribution
of stellar sources to the soft x-ray background.
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Title: Largescale Structures of the Soft X-Ray Background
Authors: Micela, G.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R.,
Jr.; Rosner, R.
1990ixra.conf..247M Altcode: 1990ixra.symp..247M
The Imaging Proportional Counter on board the Einstein Observatory
has measured the soft (0.15 - 3.5) keV X-ray background in ≡4000
directions unevenly spaced on the sky. The authors summarize the main
results of this survey.
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Title: X-Ray Studies of Coeval Star Samples. II. The Pleiades Cluster
as Observed with the Einstein Observatory
Authors: Micela, G.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R.,
Jr.; Rosner, R.; Schmitt, J. H. M. M.
1990ApJ...348..557M Altcode:
Coronal X-ray emission of the Pleiades stars is investigated, and
maximum likelihood, integral X-ray luminosity functions are computed
for Pleiades members in selected color-index ranges. A detailed
search is conducted for long-term variability in the X-ray emission
of those stars observed more than once. An overall comparison of the
survey results with those of previous surveys confirms the ubiquity
of X-ray emission in the Pleiades cluster stars and its higher rate
of emission with respect to older stars. It is found that the X-ray
emission from dA and early dF stars cannot be proven to be dissimilar to
that of Hyades and field stars of the same spectral type. The Pleiades
cluster members show a real rise of the X-ray luminosity from dA stars
to early dF stars. X-ray emission for the young, solarlike Pleiades
stars is about two orders of magnitude more intense than for the nearby
solarlike stars.
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Title: X-ray observations, scaling laws and magnetic fields
Authors: Peres, G.; Vaiana, G. S.
1990MmSAI..61..401P Altcode:
Sounding-rocket, satellite, and Skylab X-ray observations of the sun,
obtained at high spatial resolution using grazing-incidence-telescopes
during the period 1963-1975, are reviewed, with an emphasis on their
astrophysical implications. The history of the observation programs is
discussed; sample images and tables of numerical data are presented;
and it is shown how the X-ray data revealed the magnetic confinement
of the hot coronal plasma and permitted the formulation of scaling
laws, which relate the loop length to the maximum plasma temperature
and pressure at the base of the corona and account for gravitational
effects and magnetic-field heating. More recent Einstein Observatory,
Exosat, and Rosat X-ray observations of stellar coronae are briefly
described, and the applicability of the solar coronal-loop models to
late-type stars is considered.
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Title: Spatial and spectral features of soft diffuse X-ray background
seen by the Einstein Observatory.
Authors: Micela, G.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R.;
Rosner, R., Jr.
1989ESASP.296.1005M Altcode: 1989ttxa.symp.1005M
The authors present the first systematic survey of the diffuse soft
X-ray background as seen directly by the Einstein Observatory Imaging
Proportional Counter (IPC). Using a source free region of the detector
with a 1°×1° field of view they are able to view the background
in the 0.16 - 3.5 keV spectral region with unprecedented spatial
resolution. The data cover roughly 5% of the sky, with some bias in
coverage towards the galactic plane. The moderate energy resolution
of the IPC enables to characterize and produce maps of the background
as a function of energy within the Einstein passband. The authors
compare their results with previous observations of the diffuse X-ray
background, and discuss implications for galactic structure and for
the soft component of the extragalactic X-ray background.
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Title: Variability of X-Ray Emission from OB Stars
Authors: Collura, A.; Sciortino, S.; Serio, S.; Vaiana, G. S.; Harnden,
F. R., Jr.; Rosner, R.
1989ApJ...338..296C Altcode:
The variability in soft X-ray emission of 12 OB stars is studied. Two
different methods of analysis, one more suitable for detecting
short-term variations, the other aimed at detecting long time-scale
variations, are applied to all stars in the sample. The long-term
variability analysis shows that Cyg-OB2 8A Zeta Pup and Delta Ori
exhibit significant count rate variations between different data
sections. Similar variations are marginally detected in 15 Mon; the
count rate variations for the other eight stars are consistent with
statistical fluctuations. The light curve of Cyg-OB2 8A suggests the
existence of two different emission levels. The short-term variability
analysis detects marginal variability in Tau Sco with an effective
amplitude of about 30 percent and a time scale of about 50 s. The
upper limits to the effective short-term variability amplitude for
all other sample stars are in the 10-30 percent range.
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Title: An Einstein Observatory view of large-scale (equal to or
greater than 1 deg) soft X-ray background structures - A status report
Authors: Micela, G.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R.,
Jr.; Rosner, R.
1989MmSAI..60..239M Altcode:
The status report of an ongoing study of both spectral and intensity
structures of X-ray background in the band (0.03-3.5) keV as observed by
the Imaging Proportional Counter (IPC) on board the Einstein Observatory
is presented. Preliminary results indicate the existence of very large
scale (much larger than 1 deg) structures and suggest the presence of
large-scale variation (greater than 1 deg) both in background spectrum
and intensity.
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Title: A magnitude limited X-ray survey of late-type evolved stars
with the Einstein Observatory
Authors: Maggio, A.; Vaiana, G. S.; Harnden, F. R., Jr.; Rosner, R.
1989MmSAI..60..217M Altcode:
A survey establishing the X-ray emission regime of giant and supergiant
stars is used to obtain insight into the relationship between the
stellar evolution and the stellar magnetic dynamo mechanism, as well
as the existence of a dividing line in the H-R diagram separating
solar-type and non-solar-type stars from the point of view of the
X-ray activity. Extensive analyses are performed on 429 star images,
taking advantage of the final REV-1 data processing and the Einstein
Observatory Stellar X-ray database.
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Title: Osservatorio Astronomico di Palermo. Report 1988 - 1989.
Authors: Vaiana, G. S.
1989MmSAI..60..619V Altcode:
No abstract at ADS
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Title: Nearby and bright star samples from the Einstein Observatory
stellar X-ray catalog
Authors: Sciortino, S.; Favata, F.; Micela, G.; Vaiana, G. S.; Harnden,
F. R., Jr.
1989MmSAI..60..125S Altcode:
Results from the study of nearby and/or bright star samples are
presented based on the finalized catalog of identified stellar
X-ray sources observed with the Imaging Proportional Counter (IPC)
onboard the Einstein Observatory. Out of a total of about 10,000 X-ray
sources whose data are organized in a relational database for easily
accomplishing their analysis, data of X-ray sources identified with
bright or nearby optical counterparts are presented. A brief summary of
the major results known to date is presented, relevant properties of
the optical catalogs used for the identifications are discussed, some
new spectral results are shown, and a hint is given on expectations
of future X-ray observations based on present best knowledge of X-ray
emission from stellar sources.
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Title: An Einstein Observatory View of Large-Scale Soft X-ray
Background Structures: A Status Report
Authors: Micela, G.; Sciortino, S.; Vaiana, G. S.; Harnden, F. R.,
Jr.; Rosner, R.; Schmitt, J. H. M. M.
1988feta.conf...28M Altcode:
No abstract at ADS
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Title: Coronal Temperatures of late-type stars
Authors: Collura, A.; Schmitt, J. H. M. M.; Sciortino, S.; Vaiana,
G. S.; Harnden, F. R., Jr.; Rosner, R.
1988feta.conf...14C Altcode:
No abstract at ADS
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Title: The X-ray Emission of Late-Type Giant and Supergiant Stars:
Results of the Einstein Observatory Magnitude-Limited X-ray Survey
Authors: Maggio, A.; Vaiana, G. S.; Haisch, B. M.; Stern, R. A.;
Harnden, F. R.; Rosner, R.
1988feta.conf...12M Altcode:
No abstract at ADS
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Title: Relationship between Optical and X-ray Properties of O-type
Stars Surveyed by Einstein
Authors: Sciortino, S.; Harnden, F. R., Jr.; Ramella, M.; Morossi,
C.; Rosner, R.; Schmitt, J. H. M. M.; Vaiana, G. S.
1988feta.conf...13S Altcode:
No abstract at ADS
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Title: The Einstein Observatory Stellar X-ray Database
Authors: Harnden, F. R., Jr.; Sciortino, S.; Micela, G.; Maggio, A.;
Vaiana, G. S.; Schmitt, J. H. M. M.
1988feta.conf....2H Altcode:
No abstract at ADS
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Title: A Survey of the X-ray Spectra of Stars
Authors: Harnden, F. R., Jr.; Schmitt, J. H. M. M.; Collura, A.;
Vaiana, G. S.
1988BAAS...20.1101H Altcode:
No abstract at ADS
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Title: The Einstein Observatory Survey of Stars in the Hyades
Cluster Region
Authors: Micela, G.; Sciortino, S.; Vaiana, G. S.; Schmitt,
J. H. M. M.; Stern, R. A.; Harnden, F. R., Jr.; Rosner, R.
1988ApJ...325..798M Altcode:
The authors report the results of an extensive X-ray investigation of
the Hyades region and improve upon previous studies by using refined
X-ray source detection algorithms and the complete set of Einstein
Observatory IPC exposures covering the Hyades cluster region (a total
of 63 1°×1° images). Using a somewhat more extensive and complete
compilation of optical candidates, the authors have detected 66 out
of 121 Hyades members falling in the combined fields of view. The
authors have also computed 3σ upper limits for all the nondetected
Hyades members and have derived maximum-likelihood X-ray luminosity
functions for the Hyades stars in selected spectral type ranges,
using both detections and upper limits.
---------------------------------------------------------
Title: The Stellar X-Ray Data Base of Einstein Image Observations
Authors: Micela, G.; Maggio, A.; Sciortino, S.; Vaiana, G. S.; Rosner,
R.; Harnden, F. R., Jr.; Schmitt, J. H. H. M.
1988MmSAI..59..465M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Einstein Observatory Stellar X-ray Database: an overview.
Authors: Sciortino, S.; Harnden, F. R., Jr.; Maggio, A.; Micela, G.;
Vaiana, G. S.; Schmitt, J.; Rosner, R.
1988ESOC...28..483S Altcode: 1988alds.proc..483S
The authors present the motivations for and the methodology followed
in building the "Einstein Observatory Stellar X-ray Database" based on
the uniform analysis of all Einstein Observatory Imaging Proportional
Counter fields obtained during the life of the HEAO-2 mission. The
database has been implemented using the INGRES<SUP>TM</SUP> database
system, so that statistical analyses of the properties of the full
detection catalog are relatively easily and flexibly accomplished. Some
illustrative examples will furnish a general view both of the kind
and the amount of the archived information, and of the statistical
approach used in analyzing the global properties of the data.
---------------------------------------------------------
Title: The Stellar Composition of X-Ray Surveys from the Einstein
Observatory
Authors: Favata, F.; Rosner, R.; Sciortino, S.; Vaiana, G. S.
1988ApJ...324.1010F Altcode:
A new class of X-ray-luminous 'yellow' stellar objects which contributes
significantly to the stellar log N-log S distribution, but which
cannot be reconciled with normal G and K main-sequence stars. This
identification results from a new analysis of the stellar content
of three samples of X-ray-selected X-ray sources observed with the
Einstein Observatory, namely the 'Medium Sensitivity Survey', the 'High
Sensitivity Survey', and the 'Hyades Region Survey'. In this paper, both
X-ray and optical properties of the stellar samples in these surveys
are reported. The actual stellar content of the surveys is compared
with predictions based on current knowledge of stellar X-ray luminosity
functions and the stellar composition and spatial distribution in the
Galaxy. It is shown that a plausible identification for the excess
population of 'yellow' stars is with the active, RS CVn-like binaries.
---------------------------------------------------------
Title: An Einstein Observatory Stellar X-ray Catalog
Authors: Harnden, F. R., Jr.; Rosner, R.; Sciortino, S.; Maggio, A.;
Micela, G.; Vaiana, G. S.; Schmitt, J.
1987BAAS...19.1040H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Variability Analysis in Low Count Rate Sources
Authors: Collura, A.; Maggio, A.; Sciortino, S.; Serio, S.; Vaiana,
G. S.; Rosner, R.
1987ApJ...315..340C Altcode:
A method, based on the chi-square statistics, is described for detecting
pulselike time variability in low count rate sources observed with
photon-counting instruments. This method can be used even in the
presence of observational gaps, takes full advantage of the filtering
effect due to binning with different bin sizes, and takes into account
the arbitrariness introduced by the binning phase. The procedure
developed to limit the dependence of the results on the binning phase
and ensure statistically correct results is described along with
the application of the proposed procedure to a model of a variable
source. Monte Carlo simulations are used to show how the method can
be used to derive the characteristic variability time scales and that
the method is more sensitive than the nonparametric Kolmogorov-Smirnov
test in detecting variability to a given confidence level.
---------------------------------------------------------
Title: Einstein Observatory Survey of X-Ray Emission from Solar-Type
Stars: The Late F and G Dwarf Stars
Authors: Maggio, A.; Sciortino, S.; Vaiana, G. S.; Majer, P.;
Bookbinder, J.; Golub, L.; Harnden, F. R., Jr.; Rosner, R.
1987ApJ...315..687M Altcode:
Results of a volume-limited X-ray survey of stars of luminosity classes
IV and V in the spectral range F7-G9 observed with the Einstein
Observatory are presented. Using survival analysis techniques, the
stellar X-ray luminosity function in the 0.15-4.0 keV energy band for
both single and multiple sources. It is shown that the difference in
X-ray luminosity between these two classes of sources is consistent
with the superposition of individual components in multiple-component
systems, whose X-ray properties are similar to those of the
single-component sources. The X-ray emission of the stars in our sample
is well correlated with their chromospheric CA II H-K line emission
and with their projected equatorial rotational velocity. Comparison
of the X-ray luminosity function constructed for the sample of the dG
stars of the local population with the corresponding functions derived
elsewhere for the Hyades, the Pleiades, and the Orion Ic open cluster
confirms that the level of X-ray emission decreases with stellar age.
---------------------------------------------------------
Title: Observations of stellar coronae.
Authors: Vaiana, G. S.; Sciortino, S.
1987IAUS..122..333V Altcode:
The authors present an overview of recent stellar X-ray observations,
with some discussion of the requirements for future observations. They
argue that solar observations indicate that coronal X-ray emission is
strongly related to surface magnetic field activity; they show that
the interpretation of X-ray stellar coronal emission from late-type
stars within the framework of models analogous to those developed for
the solar corona is viable, and it is supported by many experimental
results. The extension of this solar analogy to the early-type stars
is quite questionable and remains an unsolved problem, while the
working hypothesis of an X-ray phase, related to phenomena of magnetic
field-related activity, as contrasted to a wind phase during the PMS
evolutionary stage is suggested by the present status of observations.
---------------------------------------------------------
Title: The AXAF High Resolution Camera (HRC) and its Use for
Observations of Distant Clusters of Galaxies
Authors: Murray, S. S.; Chappell, J. H.; Elvis, M. S.; Forman, W. R.;
Grindlay, J. E.; Harnden, F. R., Jr.; Jones, C. F.; Maccacaro, T.;
Tananbaum, H. D.; Vaiana, G. S.; Pounds, K. A.; Fraser, G. W.; Henry,
J. P.
1987ApL&C..26..113M Altcode: 1987ApL....26..113M
The High Resolution Camera being developed for AXAF is briefly
described, comparing it with its predecessor, the Einstein HRI,
and providing preliminary performance data. The HRC is a 10 cm x 10
cm detector with CsI coated microchannel plates providing a large
field of view device with high X-ray quantum efficiency. The overall
sensitivity of the HRC on AXAF is about 50 times that of the Einstein
HRI. An example of the power of this instrument is discussed in the
context of studies of distant clusters of galaxies. The HRC can detect
individual galaxies in a cluster of redshift 1, if they are similar to
the early-type galaxies in nearby clusters that have been observed by
the Einstein instruments. The HRC will be used to measure the luminosity
function for clusters of galaxies as a function of their distance up to
a redshift of 1. This will allow observation of evolutionary effects
in clusters as a whole, while the detection of individual galaxies
will permit studies of galaxy evolution in a cluster environment.
---------------------------------------------------------
Title: X-ray activity
Authors: Vaiana, G. S.; Sciortino, S.
1986AdSpR...6h..99V Altcode: 1986AdSpR...6...99V
We review recent observational results related to phenomena of stellar
X-ray activity, and extensively discuss the experimental data for the
activity from late-type stars in the context of solar coronal modelling
analogy. The evidence for a relation between X-ray activity and stellar
surface rotational rate, stellar age and the onset of convection along
the main sequence are extensively discussed, with some emphasis on the
possible changes of X-ray activity manifestation with stellar evolution.
---------------------------------------------------------
Title: The AXAF High Resolution Camera and Its Use For Observations
of Distant Clusters of Galaxies
Authors: Murray, S. S.; Chappell, J. H.; Elvis, M. S.; Forman, W. R.;
Grindlay, J. E.; Harnden, F. R., Jr.; Maccacaro, T.; Tananbaum, H. D.;
Vaiana, G. S.; Pounds, K. A.; Fraser, G. W.; Henry, J. P.
1985BAAS...17R.888M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Einstein X-ray survey of the Pleiades : the dependence of
X-ray emission on stellar age.
Authors: Micela, G.; Sciortino, S.; Serio, S.; Vaiana, G. S.;
Bookbinder, J.; Golub, L.; Harnden, F. R., Jr.; Rosner, R.
1985ApJ...292..172M Altcode:
The data obtained with two pointed observations of 1 deg by 1 deg
fields of the Pleiades region have been analyzed, and the results are
presented. The maximum-likelihood X-ray luminosity functions for the
Pleiades G and K stars in the cluster are derived, and it is shown that,
for the G stars, the Pleiades X-ray luminosity function is significantly
brighter than the corresponding function for Hyades G dwarf stars. This
finding indicates a dependence of X-ray luminosity on stellar age,
which is confirmed by comparison of the same data with median X-ray
luminosities of pre-main sequence and local disk population dwarf G
stars. It is suggested that the significantly larger number of bright
X-ray sources associated with G stars than with K stars, the lack
of detection of M stars, and the relatively rapid rotation of the
Pleiades K stars can be explained in terms of the onset of internal
differential rotation near the convective envelope-radidative core
interface after the spin-up phase during evolution to the main sequence.
---------------------------------------------------------
Title: Magnetohydrodynamic thermal instabilities in cool inhomogeneous
atmospheres
Authors: Bodo, G.; Ferrari, A.; Massaglia, S.; Rosner, R.; Vaiana,
G. S.
1985ApJ...291..798B Altcode:
The stability of magnetic loops to current-driven filamentation
instabilities is investigated. The unperturbed atmosphere is assumed to
be composed of an (upper) isothermal optically thin low-density portion
and a (lower) higher-density portion which is in radiative equilibrium;
in both cases, the atmosphere is in hydrostatic equilibrium, so
that gravitational stratification is taken into account. In order to
provide specific equilibrium conditions for evaluation of the dispersion
relation, conditions appropriate for the surface of a solar-type star
are adopted; i.e., a fairly low temperature (T = 5000 K) appropriate
for a 'precoronal' state associated, for example, with magnetic
flux emerging from photospheric levels under the action of magnetic
buoyancy. A linear stability analysis is performed, and numerical
results show that physically plausible current densities, which would be
generated by typical loop-footpoint motions, are effective in driving
MHD instabilities in such a plasma. The instability growth rates are
strongly dependent on the assumed current density distribution and on
the density scale height.
---------------------------------------------------------
Title: An Einstein Observatory X-ray survey of main-sequence stars
with shallow convection zones.
Authors: Schmitt, J. H. M. M.; Golub, L.; Harnden, F. R., Jr.; Maxson,
C. W.; Rosner, R.; Vaiana, G. S.
1985ApJ...290..307S Altcode:
The results of an X-ray survey of bright late A and early F stars
on the main B-V sequence between 0.1 and 0.5 are presented. All the
stars were observed with the Einstein Observatory for a period of at
least 500 seconds. The survey results show significantly larger X-ray
luminosities for the sample binaries than for the single stars. It
is suggested that the difference is due to the presence of multiple
X-ray sources in binaries. It is shown that the X-ray luminosities
for single stars increase rapidly with increasing color, and that
the relation Lx/Lbol is equal to about 10 to the -7th does not hold
for A stars. No correlation was found between X-ray luminosity and
projected equatorial rotation velocity. It is argued on the basis of
the observations that X-ray emission in the sample stars originated
from coronae. The available observational evidence supporting this
view is discussed.
---------------------------------------------------------
Title: Closed coronal structures. VI. Far-ultraviolet and X-ray
emission from active late-type stars and the applicability of coronal
loop models.
Authors: Giampapa, M. S.; Golub, L.; Peres, G.; Serio, S.; Vaiana,
G. S.
1985ApJ...289..203G Altcode:
We present far-ultraviolet line fluxes of prominent transition region
emission lines, as obtained with the International Ultraviolet
Explorer satellite, for a sample of solar-type stars. We combine
the ultraviolet observations with existing soft X-ray measurements
obtained by the Einstein Observatory (HEAO 2). We utilize the resulting
data set and a new coronal loop model numerical code developed at the
Harvard-Smithsonian Center for Astrophysics to perform a preliminary
investigation of the applicability of coronal loop models to solar-type
stars. In a few cases, reasonable agreement between the predictions of
single-component, coronal loop model atmospheres and the observational
data is achieved for a relatively well-defined, plausible range
of values in the pressure-filling factor (p, f) plane. In general,
however, we find that the addition of non- simultaneous ultraviolet
observations to a previously acquired soft X-ray data set does
not provide a sufficient constraint on the range of possible loop
filling factors and pressures for loop model atmospheres that may
be producing the observed X-ray and transition region emissions. We
discuss the origins of the discrepancies between the model results
and the observations within the context of (1) stellar variability,
(2) multiple coronal components, and (3) the presence of relatively
low temperature loops that give rise to far-ultraviolet emission
but not to coronal X-ray emission. We suggest on the basis of the
results presented in this investigation that in order to verify the
applicability of coronal loop models to solar-type stars, simultaneous
far-ultraviolet and moderate spectral resolution X-ray observations
will eventually have to be obtained.
---------------------------------------------------------
Title: On stellar X-ray emission.
Authors: Rosner, R.; Golub, L.; Vaiana, G. S.
1985ARA&A..23..413R Altcode:
Stellar X-ray astronomy represents an entirely new astronomical
discipline which has emerged during the past five years. It lies
at the crossroads of solar physics, stellar physics, and general
astrophysics. The present review is concerned with the main physical
problems which arise in connection with a study of the stellar X-ray
data. A central issue is the extent to which the extrapolation from
solar physics is justified and the definition (if possible) of the
limits to such extrapolation. The observational properties of X-ray
emission from stars are considered along with the solar analogy and the
modeling of X-ray emission from late-type stars, the modeling of X-ray
emission from early-type stars, the physics of stellar X-ray emission,
stellar X-ray emission in the more general astrophysical context,
and future prospects.
---------------------------------------------------------
Title: X-ray emission from solar-type stars: X-ray luminosity function
of late F and G stars.
Authors: Maggio, A.; Bookbinder, J.; Harnden, F. R., Jr.; Golub, L.;
Majer, P.; Rosner, R.; Vaiana, G. S.
1985xra..conf...39M Altcode: 1984xra..conf...39M
The authors present preliminary results from a volume-limited survey
of X-ray emission from late F and G dwarf stars. They have obtained
count rates or upper limits at the locations of catalogued stars
within 25 parsecs for which an observation of the Einstein Imaging
Proportional Counter was available. They have constructed X-ray
luminosity functions for the whole sample and for selected subsamples
of binary and non-binary sources.
---------------------------------------------------------
Title: Active late-type stars and the applicability of coronal
loop models.
Authors: Giampapa, M. S.; Golub, L.; Peres, G.; Serio, S.; Vaiana,
G. S.
1984NASCP2349..454G Altcode: 1984fiue.rept..454G; 1984IUE84......454G
Far ultraviolet IUE observations of a sample of solar type stars
were combined with existing soft X-ray measurements obtained by HEAO
B. The resulting data set was utilized and a new coronal loop model
numerical code was developed to perform a preliminary investigation of
the applicability of coronal loop models to solar-type stars. Reasonable
agreement was found to exist between the predictions of single-component
coronal loop model atmospheres. It was demonstrated that semi-empirical,
coronal loop models can be applied to account for observed stellar
transition region and coronal emission. This result is corroborative
evidence for the presence of magnetic field structures analogous to
solar coronal loops on the surfaces of solar-type stars. It is suggested
that stellar transition region emission arises predominantly from the
base of quiescent coronal loop configurations.
---------------------------------------------------------
Title: Stellar chromospheres and coronae in the Ursa Major cluster
stars.
Authors: Walter, F. M.; Linsky, J. L.; Simon, T.; Golub, L.; Vaiana,
G. S.
1984ApJ...281..815W Altcode:
IUE spectra of 18 proposed members of the Ursa Major Cluster and
Einstein X-ray images of 11 of these stars are discussed. Thirteen
stars, six in the nucleus and seven in the extended comoving stream,
are probably true members of the UMa Cluster in that their bright
ultraviolet and X-ray surface fluxes indicate youth. Four stars, one in
the nucleus and three in the stream, exhibit weak ultraviolet and/or
X-ray emission suggesting that they are old field stars that have
the same space motion as the UMa Cluster. The X-ray surface fluxes of
the UMa Cluster stars appear to be brighter than those of the Hyades
Cluster stars, consistent with their relative ages. It is argued that
chromospheres and transition regions could be present in dwarf stars
hotter than B-V of about 0.30, but are unobservable in IUE spectra
due to the rapid increase in photospheric flux in hotter stars.
---------------------------------------------------------
Title: Erratum - Einstein Observations of X-Ray Emission from A-Stars
Authors: Golub, L.; Harnden, F. R.; Maxson, C. W.; Rosner, R.; Vaiana,
G. S.; Cash, W., Jr.; Snow, T. P., Jr.
1984ApJ...278..456G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-Ray Survey of the Pleiades - Dependence of X-Ray Luminosity
on Stellar Age
Authors: Micela, G.; Sciortino, S.; Serio, S.; Vaiana, G. S.; Golub,
L.; Harnden, F. R.; Rosner, R.
1984IAUS..105..101M Altcode:
The authors report preliminary results from an Einstein X-ray survey
of the Pleiades. They have analysed a 1°×1° exposure centered over
one of the more luminous stars of the cluster (20 Tau, [B7 III]). This
field contains ≡62 cluster members out of a total of ≡270 stars with
magnitude lower than 14<SUP>m</SUP>. (Hertzsprung, 1947). The authors
have detected 17 distinct X-ray sources; 16 sources are identified
with cluster stars within a distance less than 1arcmin.
---------------------------------------------------------
Title: X-Ray Variable Stars in the Pleiades
Authors: Sciortino, S.; Micela, G.; Serio, S.; Vaiana, G. S.; Golub,
L.; Harnden, F. R., Jr.; Rosner, R.
1983IBVS.2449....1S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Einstein observations of X-ray emission from A stars.
Authors: Golub, L.; Harnden, F. R., Jr.; Maxson, C. W.; Rosner, R.;
Vaiana, G. S.; Cash, W., Jr.; Snow, T. P., Jr.
1983ApJ...271..264G Altcode:
Results are reported from the combined CfA Stellar Survey of selected
bright A stars and an Einstein Guest Observer program for Ap and Am
stars. In an initial report of results from the CfA Stellar Surveys
by Vaiana et al. (1981) it was noted that the spread in observed X-ray
luminosities among the few A stars observed was quite large. The reasons
for this large spread was studied by Pallavicini et al. (1981). It was
found that the X-ray emission from normal stars is related very strongly
to bolometric luminosity for early-type stars and to rotation rate
for late-type stars. However, an exception to this rule has been the
apparently anomalous behavior of A star X-ray emission, for which the
large spread in luminosity showed no apparent correlation with either
bolometric luminosity or stellar rotation rate. In the present study,
it is shown that the level of emission from normal A stars agrees with
the correlation observed for O and B stars.
---------------------------------------------------------
Title: Closed coronal structures. V - Gasdynamic models of flaring
loops and comparison with SMM observations
Authors: Pallavicini, R.; Peres, G.; Serio, S.; Vaiana, G.; Acton,
L.; Leibacher, J.; Rosner, R.
1983ApJ...270..270P Altcode:
The hydrodynamic response of confined magnetic structures to strong
heating perturbations is investigated by means of a time-dependent
one-dimensional colde which incorporates the energy, momentum, and
mass conservation equations. The entire atmospheric structure from the
chromosphere to the corona is taken into account. Models with different
energy input, heating time dependence, preflare conditions and heating
location have been examined in the numerical simulations. <P />The
result of model calculations are compared with observations of flares
obtained with the X-ray Polychromator experiment on the Solar Maximum
Mission. These include light curves of spectral lines formed over a
wide range of coronal flare temperatures, as well as determinations
of Doppler shifts for the high temperature plasma. Several examples
are used to illustrate the range of the observational variation. <P
/>It is shown that the predictions of the numerical simulations
are in good overall agreement with the observed evolution of the
flare coronal plasma. The model reproduces correctly the temporal
profile of X-ray spectral lines and -- to first order at least --
their relative intensities. The upflow velocities predicted by
model calculations are in agreement with the observed blueshifts,
supporting the interpretation of the blueshifts as due to evaporation
of chromospheric material. The possibility of using the comparison
of model predictions with observations to derive information on the
processes of energy release and transfer in solar flares is discussed.
---------------------------------------------------------
Title: Coordinated Einstein and IUE observations of a disparitions
brusques type flare event and quiescent emission from Proxima
Centauri.
Authors: Haisch, B. M.; Linsky, J. L.; Bornmann, P. L.; Stencel,
R. E.; Antiochos, S. K.; Golub, L.; Vaiana, G. S.
1983ApJ...267..280H Altcode:
The Einstein Imaging Particle Counter observed a major X-ray flare
in its entirety during a 5-hr period of simultaneous observations,
with the IUE, of the dM5e flare star Proxima Centauri in August,
1980. The detailed X-ray light curve, temperature determinations
during various intervals, and UV line fluxes obtained before, during,
and after the flare indirectly indicate a 'two-ribbon flare' prominence
eruption. The calculated ratio of coronal to bolometric luminosity for
the event is about 100 times the solar ratio. The Proxima Cen corona
is analyzed in the context of static loop models, in light of which
it is concluded that less than 6% of the stellar surface seems to be
covered by X-ray emitting active regions.
---------------------------------------------------------
Title: An X-ray Survey of Main Sequence Stars with Shallow Convection
Zones
Authors: Schmitt, J. H. M.; Golub, L.; Harnden, F. R., Jr.; Maxson,
C. W.; Vaiana, G. S.
1983BAAS...15..673S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Outlook for Ground-Based and Space Observations - Solar and
Stellar Magnetic Fields
Authors: Vaiana, G. S.
1983IAUS..102..505V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observational Approach and Perspective
Authors: Vaiana, G. S.
1983ASSL..102..651V Altcode: 1983IAUCo..71..651V; 1983ards.proc..651V
No abstract at ADS
---------------------------------------------------------
Title: The Palermo-Harvard numerical code for the dynamics of confined
coronal plasma.
Authors: Peres, G.; Serio, S.; Vaiana, G. S.; Rosner, R.
1983pig..conf...96P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar X-ray emission as an indicator of stellar magnetic
activity
Authors: Vaiana, G. S.
1983IAUS..102..165V Altcode:
The role of recent Einstein Observatory observations and theoretical
models of stellar X-ray emission in furthering current understanding
of stellar magnetic activity is discussed. It is suggested that
solar observations can be used to show that coronal emission is
morphologically related to surface magnetic field activity, as well
as to establish a quantitative link between observed soft X-ray flux
and the mean surface magnetic flux. It is demonstrated that soft
X-ray emission is a sensitive diagnostic for the presence of surface
magnetic fields, since it is unaffected by radiative transfer effects
and the resulting coupling to the underlying atmosphere. Stellar
coronal emissions are therefore an excellent probe for the study of
stellar magnetic activity over a wide dynamic range.
---------------------------------------------------------
Title: Magnetic field-related heating instabilities in the surface
layers of the sun and stars
Authors: Ferrari, A.; Rosner, R.; Vaiana, G. S.
1982ApJ...263..944F Altcode:
The stability of a magnetized low-density plasma to current-driven
filamentation instabilities is investigated and the results are applied
to the surface layers of stars. Unlike previous studies, the initial
(i.e., precoronal) state of the stellar surface atmosphere is taken
to be a low-density, optically thin magnetized plasma in radiative
equilibrium. The linear analysis shows that the surface layers of
main-sequence stars (including the sun) which are threaded by magnetic
fields are unstable; the instabilities considered lead to structuring
perpendicular to the ambient magnetic fields. These results suggest that
relatively modest surface motions, in conjunction with the presence of
magnetic fields, suffice to account for the presence of inhomogeneous
chromospheric and coronal plasma overlying a star's surface.
---------------------------------------------------------
Title: The Temperature-Luminosity Dependence of Stellar X-ray Sources
Authors: Vaiana, G. S.; Serio, S.; Sciortino, S.; Golub, L.; Maxson,
C.; Rosner, R.
1982BAAS...14..945V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray Sources in the Pleiades
Authors: Micela, G.; Serio, S.; Vaiana, G. S.; Golub, L.
1982BAAS...14..891M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Normal Incidence X-ray Telescope for Solar Studies
Authors: Golub, L.; Rosner, R.; Vaiana, G. S.; Zombeck, M. V.; Spiller,
E.; Wilczynski, J.
1982BAAS...14..976G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Variable X-ray Emission from Early-type Stars
Authors: Collura, A.; Serio, S.; Sciortino, S.; Vaiana, G. S.; Harnden,
F. R., Jr.; Maxson, C. W.; Rosner, R.
1982BAAS...14Q.945C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray Variability of Late-type Stars
Authors: Maggio, A.; Serio, S.; Vaiana, G. S.; Golub, L.
1982BAAS...14R.945M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Active region coronal evolution
Authors: Golub, L.; Noci, G.; Poletto, G.; Vaiana, G. S.
1982ApJ...259..359G Altcode:
Scaling relations between coronal base pressure and longitudinal
photospheric magnetic field strength are tested for the case of a
single active region observed for five solar rotations from Skylab. The
evolution of measureable quantities, such as coronal thermal energy
content, total longitudinal photospheric magnetic flux, region scale
size, and peak energy density, is traced throughout the five rotations
observed. The theoretically derived scaling law of Golub et al. (1980)
is found to provide an acceptable fit to the data throughout the entire
evolutionary history of the region from an age of about 3 days to
the fully evolved state in which the mature active region merges into
the general large-scale structure of the quiet corona. An alternative
scaling law obtained by including the results of Galeev et al. (1981),
however, is found to provide a somewhat better fit to the data. The
study is seen as providing additional justification for the belief
that magnetic field-related heating is the operative mechanism in the
solar corona.
---------------------------------------------------------
Title: A magnitude limited stellar X-ray survey and the F star X-ray
luminosity function.
Authors: Topka, K.; Golub, L.; Gorenstein, P.; Harnden, F. R., Jr.;
Vaiana, G. S.; Avni, Y.; Rosner, R.
1982ApJ...259..677T Altcode:
An X-ray survey has been conducted of stars brighter than visual
magnitude 8.5 that have serendipitously fallen into the fields of view
of the Imaging Proportional Counter of the Einstein Observatory. The
survey includes 227 separate 1 x 1 deg fields, containing 274 stars
with a visual magnitude of no more than 8.5 and covering a wide range
of spectral types and luminosity classes. X-ray emission was detected
from 33 stars, and upper limits have been determined for the remainder
of the sample. F type stars dominate the detected sample, and most of
these are shown to be dwarfs. An X-ray luminosity function for dF stars
has been deduced, and reveals that the average 0.2-4.0 keV luminosity
of these stars is around 10 to the 29th erg/sec. Constraints have been
placed on the high luminosity tails and medians of the X-ray luminosity
functions for other types of stars.
---------------------------------------------------------
Title: STCOEX: The stellar X-ray coronal Explorer.
Authors: Vaiana, G. S.; Golub, L.; Maxson, C. W.; Rosner, R.; Zombeck,
M. V.
1982SAOSR.392B.253V Altcode: 1982csss....2..253V
No abstract at ADS
---------------------------------------------------------
Title: A heating mechanism for the chromospheres of M dwarf stars.
Authors: Giampapa, M. S.; Golub, L.; Rosner, R.; Vaiana, G. S.;
Linsky, J. L.; Worden, S. P.
1982SAOSR.392A..73G Altcode: 1982csss....2...73G
The atmospheric structure of the dwarf M-stars which is especially
important to the general field of stellar chromospheres and coronae
was investigated. The M-dwarf stars constitute a class of objects
for which the discrepancy between the predictions of the acoustic
wave chromospheric/coronal heating hypothesis and the observations is
most vivid. It is assumed that they represent a class of stars where
alternative atmospheric heating mechanisms, presumably magnetically
related, are most clearly manifested. Ascertainment of the validity
of a hypothesis to account for the origin of the chromospheric and
transition region line emission in M-dwarf stars is proposed.
---------------------------------------------------------
Title: Chromospheric emission, stellar rotation and X-ray coronae.
Authors: Pallavicini, R.; Golub, L.; Rosner, R.; Vaiana, G.
1982SAOSR.392B..77P Altcode: 1982csss....2...77P
No abstract at ADS
---------------------------------------------------------
Title: Einstein detection of X-rays from the alf CEN system.
Authors: Golub, L.; Harnden, F. R., Jr.; Pallavicini, R.; Rosner,
R.; Vaiana, G. S.
1982ApJ...253..242G Altcode:
Detection of quiescent X-ray emission from the stellar components
of the Alpha Cen system: Alpha Cen A (G2 V) and Alpha Cen B (K1 V)
is reported. Contrary to previous theoretical expectations, both
stars are found to be X-ray emitters and at about the same level:
L<SUB>x</SUB> = 1.2 x 10 to the 27th and 2.8 x 10 to the 27th ergs/s
for A and B, respectively; the sum of these values is in agreement
with the emission level previously reported for Alpha Cen by Nugent and
Garmire (1978). Comparison with previous chromospheric and transition
region measurements suggests that Alpha Cen A and B may have changed
in relative strength in recent years. The coronal temperature of the
combined Cen AB source, which is dominated (approximately 2/3 of the
total) by the K star is (2.1 + or - 0.4) x 10 to the 6th K, similar to
that of the average solar corona; it is noted that this value is not
consistent with the estimate of 5 x 10 to the 5th K quoted by Nugent
and Garmire.
---------------------------------------------------------
Title: Stellar contribution to the diffuse soft X-ray background.
Authors: Bookbinder, J.; Avni, Y.; Golub, L.; Rosner, R.; Vaiana, G.
1982SAOSR.392A.201B Altcode: 1982csss....2..201B
One of the results of the EINSTEIN/C.f.A. X-ray stellar survey was
a determination of the contribution of the disk stellar population
to the galactic component of the diffuse soft (0.28 - 1.0 keV)
X-ray background. This analysis employed both binned and unbinned
nonparametric statistical methods that have been developed by Avni, et
al. (1980). These methods permitted the use of the information contained
in both the 22 detections and 4 upper bounds on the luminosities of
26 dM stars in order to derive their luminosity function. Luminosity
functions for earlier stellar types are not yet developed. For these
earlier stellar types, the median luminosities as determined by Vaiana,
et al., are used (1981), which underestimates their contribution to
the background. We find that it is the M dwarfs that dominate the disk
population stellar contribution to this background. To calculate the
contribution of the stellar sources to the background, simple models
both for the spatial distribution of the stars and for the properties
of the intervening interstellar medium are used. A model is chosen
in which all stellar classes have the same functional form for their
spatial distribution: an exponentially decreasing distribution above
the galactic equatorial plane, and a uniform distribution within the
galactic plane for a region of several kiloparsecs centered on the Sun.
---------------------------------------------------------
Title: Coronal closed structures. IV - Hydrodynamical stability and
response to heating perturbations
Authors: Peres, G.; Serio, S.; Vaiana, G. S.; Rosner, R.
1982ApJ...252..791P Altcode:
The response of magnetically confined atmospheres to perturbations in
the temperature and density distribution, and the local heating rate
by means of a one-dimensional time-dependent hydrodynamical code,
which incorporates the full energy, momentum and mass conservation
equations is studied. These studies extend the linear instability
analysis of Habbal and Rosner (1979) into the finite-amplitude regime,
and generalize the confined atmosphere models of Serio et al., to the
time-dependent domain. The results show that closed coronal atmospheres
are stable against finite-amplitude perturbations if the chromospheric
response is taken into account; and observed correlated increases in
coronal density and temperature can only be achieved under quiescent
conditions by increasing the heat deposition rate relatively more in
the chromosphere than in the corona.
---------------------------------------------------------
Title: Il sistema di trattamento di immagini presso l'Osservatorio
Astronomico di Palermo.
Authors: Sciortino, S.; Peres, G.; Serio, S.; Vaiana, G. S.
1982MmSAI..53..115S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coordinated X-ray, optical and radio observations of flaring
activityon YZ Canis Minoris.
Authors: Kahler, S.; Golub, L.; Harnden, F. R.; Liller, W.; Seward,
F.; Vaiana, G.; Lovell, B.; Davis, R. J.; Spencer, R. E.; Whitehouse,
D. R.; Feldman, P. A.; Viner, M. R.; Leslie, B.; Kahn, S. M.; Mason,
K. O.; Davis, M. M.; Crannell, C. J.; Hobbs, R. W.; Schneeberger,
T. J.; Worden, S. P.; Schommer, R. A.; Vogt, S. S.; Pettersen, B. R.;
Coleman, G. D.; Karpen, J. T.; Giampapa, M. S.; Hege, E. K.; Pazzani,
V.; Rodono, M.; Romeo, G.; Chugainov, P. F.
1982ApJ...252..239K Altcode:
The YZ Canis Minoris (Gliese 285), a late-type dwarf star with
Balmer emission (dM4.5e), is a member of the UV Ceti class of flare
stars. Obtaining good X-ray observations of a dMe star flare is
important not only for understanding the physics of flares but also for
testing current ideas regarding the similarity between stellar and solar
flares. The Einstein X-ray Observatory has made it possible to conduct
X-ray observations of dMe stars with unprecedented sensitivity. A
description is presented of the results of a program of ground-based
optical and radio observations of YZ CMi coordinated with those of
the Einstein Observatory. The observations were carried out as part
of a coordinated program on October 25, 26, and 27, 1979, when YZ CMi
was on the dawn side of the earth. Comprehensive observational data
were obtained of an event detected in all three wavelength regions on
October 25, 1979.
---------------------------------------------------------
Title: Solar corona at high resolution
Authors: Golub, L.; Rosner, R.; Zombeck, M. V. Z.; Vaiana, G. S.
1982SPIE..316..149G Altcode:
The earth's surface is shielded from solar X rays almost completely by
the atmosphere. It is, therefore, necessary to place X-ray detectors
on rockets or orbiting satellites. Solar rays were detected for the
first time in the late 1940's, using V-2 rockets. In 1960, the first
true X-ray images of the sun were obtained with the aid of a simple
pinhole camera. The spatial resolution of the X-ray images could be
considerably improved by making use of reflective optics, operating at
grazing incidence. Aspects of X-ray mirror developments are discussed
along with the results obtained in coronal studies utilizing the new
devices for the observation of solar X-ray emission. It is pointed
out that the major achievements of the Skylab missions were due
primarily to the unique opportunity to obtain data over an extended
period of time. Attention is given to normal incidence X-ray optics,
achievements possible by making use of high spatial resolution optics,
and details of improved mirror design.
---------------------------------------------------------
Title: Short-term UV line profile variation in 59 Cyg.
Authors: Grady, C. A.; Doazan, V.; Peters, G. J.; Willis, A. J.; Snow,
T. P.; Aitken, D. K.; Barker, P. K.; Bolton, C. T.; Henrichs, H. F.;
Kitchen, C. R.; Kuhi, L. V.; Marlborough, J. M.; Meikle, W. P. S.;
Mendzies, J.; Oegerle, W.; Polidan, R. S.; Rosner, R.; Selvelli, P. L.;
Stalio, R.; Thomas, R. N.; Vaiana, G.; Whitelock, P. A.; Wilson, R.;
Wu, C. -C.
1982NASCP2238..425G Altcode: 1982NASCP2338..425G; 1982auva.nasa..425G
The International ultraviolet Explorer high dispersion spectra of 59
Cyg obtained as part of the long term monitoring program have shown that
noticeable variation can occur in C 5 and N 5 on timescales 3 hours t24
to 28 hours. In order to begin to resolve whether these changes occur
continuously or sporadically, 48 hours were devoted to monitoring this
star in January 1982. The January spectra show no short term variation,
which may be consistent with sporadic rather than continuous variation.
---------------------------------------------------------
Title: X-Ray Flare Spectroscopy: SMM Observations and Loop Modeling.
Authors: Acton, L.; Pallavicini, R.; Peres, G.; Vaiana, G.
1982uxsa.coll....1A Altcode: 1982IAUCo..73....1A
No abstract at ADS
---------------------------------------------------------
Title: X-ray emission from Of stars and OB supergiants.
Authors: Cassinelli, J. P.; Waldron, W. L.; Sanders, W. T.; Harnden,
F. R., Jr.; Rosner, R.; Vaiana, G. S.
1981ApJ...250..677C Altcode:
The result of a survey of X-ray emission from luminous early-type
stars is reported in which observations were made using the imaging
proportional counter on the Einstein Observatory. The survey suggests
that all Of stars and OB supergiants earlier than B1 I are X-ray
sources with luminosities not less than 10 to the 32nd ergs/s and that
some later B supergiants have X-ray luminosities not less than 10 to
the 31st ergs/s. The X-ray luminosities are roughly 10 to the -7.2nd
of the bolometric luminosities for supergiants earlier than B1 and
perhaps a factor of 3 less for later B supergiants. Spectral analysis
of the X-rays in conjunction with information on anomalous ionization
in the wind from four of the strongest sources implies that the data
are not consistent with a model in which the X-rays originate in a thin
slab coronal zone at the base of the wind. Constraints on the source
of X-rays from B supergiants are derived by combining the X-ray flux
information with that on ultraviolet line anomalies.
---------------------------------------------------------
Title: The cool Half of the H-R diagram in soft X-rays.
Authors: Ayres, T. R.; Linsky, J. L.; Vaiana, G. S.; Golub, L.;
Rosner, R.
1981ApJ...250..293A Altcode:
The results of an Einstein Observatory program to map the occurrence
of hot coronae (T greater than 1 million K) in the cool half of the
Hertzsprung-Russell diagram are reported. F-M dwarfs, and late F
through early K star giants characterized by 10,000 K chromospheric
and 20,000-200,000 K FUV emission lines were studied in one region,
while a second region study included red giants later than K2 III and
supergiants later than G5 Ib with weaker chromospheric emission and
no high temperature species. Program goals comprised determination of
the C IV division as seen in soft X-rays, and identification of stellar
parameters which distinguish strong from weak coronal X-ray sources. A
summary of target stars, X-ray fluxes, and UV emission profiles
is provided, and coronal emissions, comparisons of C IV and wind
boundaries, hybrid-spectrum supergiants, the energy balance of stellar
outer atmospheres, stellar rotation and coronae, and evolutionary
considerations are discussed, along with lines of future research.
---------------------------------------------------------
Title: The Einstein/CFA stellar survey - Overview of the data and
interpretation of results
Authors: Vaiana, G. S.
1981ASSL...87....1V Altcode: 1981xaes.proc....1V
Results are presented from an extensive survey of stellar X-ray
emission, using the Einstein Observatory. Over 140 stars have been
detected to date, throughout the H-R diagram, thus showing that soft
X-ray emission is the norm rather than the exception for stars in
general. This finding is strongly at odds with pre-Einstein expectations
based on standard acoustic theories of coronal heating. Typical
examples of stellar X-ray detections and an overview of the survey
data are presented. In combination with recent results from solar X-ray
observations, the new Einstein data argue for the general applicability
of magnetic field-related coronal heating mechanisms.
---------------------------------------------------------
Title: X-ray emission from stars
Authors: Vaiana, G. S.
1981STIA...8231574V Altcode:
Data from the Einstein Observatory are examined to discover
the processes which lead to the appearance of stellar surface
activity. Previous astrophysical observations are reviewed,
including stellar X ray, UV, Ca II, H, and K emissions observations,
and monitoring of the solar corona. All stars have been observed to
emit X rays at one time or another, and the Einstein spacecraft has
furnished data on X ray emission and stellar rotation, Ca II, H, and
K emission from late-type stars, X ray emission from early-type stars
and pre-main-sequence stars, and has provided evidence that X rays are
not emitted by stellar winds. Stellar coronae have been identified
as the source of the X ray emission in pre-main-sequence stars, and
correlations have been found between the level of X ray emission and
the rotation rate in late-type stars. Further attention is given to
the capture of the energy of infalling and outgassing material by the
stellar magnetic fields, and purposes of the AXAF orbiting instrument
to be launched by the Shuttle are discussed, specifically for stellar
X ray spectrographic observations.
---------------------------------------------------------
Title: The stellar coronal X-ray Explorer: STCOEX
Authors: Vaiana, G. S.
1981xras.nasa..371V Altcode:
The status of the newly born field of stellar X-ray astronomy is
considered. The need for further observational capability, the
study of stellar surface activity and the development of design
criteria for a follow-up mission, with primary emphasis on stellar
observations and with general capabilities within the scope of the
Explorer program are examined. The criteria which lead to the desired
instrumental capabilities are reviewed; and an overview of the proposed
instrument and some of its capabilities, as indicated by simulations is
presented. Two versions of a trial payload the stellar coronal. Explorer
(STCOEX) which meet the observational desirable are developed.
---------------------------------------------------------
Title: The stellar contribution to the galactic soft X-ray background
Authors: Rosner, R.; Avni, Y.; Bookbinder, J.; Giacconi, R.; Golub,
L.; Harnden, F. R., Jr.; Maxson, C. W.; Topka, K.; Vaiana, G. S.
1981ApJ...249L...5R Altcode:
Log N-log S relations for stars are constructed based on median
X-ray luminosities for dF, dG, and dK stars previously reported for
the Einstein Observatory/Center for Astrophysics stellar survey and
on a detailed X-ray luminosity function derived here for dM stars,
and the stellar contribution to the diffuse soft X-ray background is
investigated. The principal results are that stars provide approximately
20% of the soft X-ray background in the 0.28-1.0 keV passband and
therefore contribute significantly to the soft X-ray background in this
energy range (with dM stars constituting the dominant contributing
class), and that the stellar contribution to the diffuse X-ray
background in the 0.15-0.28 keV passband is less than approximately 3%.
---------------------------------------------------------
Title: Erratum - Dynamics of Coronal Structures - Magnetic Field
Related Heating and Loop Energy Balance
Authors: Galeev, A. A.; Rosner, R.; Serio, S.; Vaiana, G. S.
1981ApJ...248..882G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Relations among stellar X-ray emission observed from Einstein,
stellar rotation and bolometric luminosity.
Authors: Pallavicini, R.; Golub, L.; Rosner, R.; Vaiana, G. S.; Ayres,
T.; Linsky, J. L.
1981ApJ...248..279P Altcode:
The correlation between observed stellar X-ray luminosities, bolometric
luminosities, and projected rotational velocities for stars of various
spectral types and luminosity classes are determined. Early type
stars (O3 to A5) have X-ray luminosities independent of rotational
velocities, and correlating with bolometric luminosities. Late type
stars of spectral type G to M have luminosities well correlated to
equatorial rotational velocities, and are independent of luminosity
class. The dependence of late type stars is found to be equivalent
to a relation between the X-ray surface flux and the stellar angular
velocity. F stars are intermediate with X-ray luminosities higher
than would be predicted on the basis of the early type star relation,
although lower than expected from the late type velocity dependence. The
location of RS CVn stars as a class is also discussed, and it is found
that the heating of late type stellar coronas does not result from
direct conversion of ratational energy.
---------------------------------------------------------
Title: Closed coronal structures. III - Comparison of static models
with X-ray, EUV, and radio observations
Authors: Pallavicini, R.; Peres, G.; Serio, S.; Vaiana, G. S.; Golub,
L.; Rosner, R.
1981ApJ...247..692P Altcode:
Numerical models of static coronal loops in energy balance are compared
with high spatial resolution observations of extreme ultraviolet lines,
broad-band X-ray emission, and interferometric observations at 2.8 cm
of a solar active region. Difficulties of using scaling laws to test
static models of coronal loops are reviewed. The theoretical model
used for the comparison is summarized; the detailed X-ray, EUV, and
microwave observations of the selected active region are presented;
and the comparison of the model with the observations is performed. It
is shown that simple static models with conductive flux vanishing at the
loop base reproduce satisfactorily the observed properties in the upper
portion of loop structures from compact, high-pressure loops in the
core of the region to more extended, fainter loops and to large-scale
loops interconnecting different active regions. Effects of changing
loop parameters are investigated, and it is argued, that in contrast
to the present approach, scaling laws cannot be used to discriminate
between different static energy balance models. Some discrepancy is
found between model predictions and observations for the lower sections
of loop structures. Possible causes of the discrepancy are discussed.
---------------------------------------------------------
Title: X-ray, EUV, and centimetric observations of solar active
regions - an empirical model for bright radio sources
Authors: Pallavicini, R.; Sakurai, T.; Vaiana, G. S.
1981A&A....98..316P Altcode:
Coordinated observations of solar active regions in X-rays, EUV, and
2.8 cm radio waves, and current-free extrapolations of the photospheric
magnetic field to coronal levels are used to determine the emission
mechanism of bright radio sources. High spatial resolution X-ray and
EUV observations of the active regions show that the temperature and
density structure of the atmosphere above the sunspots differs greatly
from that above the plages. Extended low brightness temperature
radio sources, associated with plage areas, are consistent with
thermal free-free emission from the transition region and the corona
above the active centers. High brightness temperature radio sources,
associated with sunspots, cannot be explained by thermal free-free
emissions either in hot, dense loops or in the cooler, lower pressure
loops, observed emanating from sunspot umbrae. There is evidence that
thermal gyroresonance absorption at the second and third harmonics of
the gyrofrequency can produce sunspots associated with bright radio
sources. The empirical models of the coronal loops, based on energy
balance, and the effects of electric currents flowing in the corona
above the sunspots are discussed.
---------------------------------------------------------
Title: Results from an extensive Einstein stellar survey.
Authors: Vaiana, G. S.; Cassinelli, J. P.; Fabbiano, G.; Giacconi,
R.; Golub, L.; Gorenstein, P.; Haisch, B. M.; Harnden, F. R., Jr.;
Johnson, H. M.; Linsky, J. L.; Maxson, C. W.; Mewe, R.; Rosner, R.;
Seward, F.; Topka, K.; Zwaan, C.
1981ApJ...245..163V Altcode:
The preliminary results of the Einstein Observatory stellar X-ray survey
are presented. To date, 143 soft X-ray sources have been identified with
stellar counterparts, leaving no doubt that stars in general constitute
a pervasive class of low-luminosity galactic X-ray sources. Stars along
the entire main sequence, of all luminosity classes, pre-main sequence
stars as well as very evolved stars have been detected. Early type
OB stars have X-ray luminosities in the range 10 to the 31st to 10 to
the 34th ergs/s; late type stars show a somewhat lower range of X-ray
emission levels, from 10 to the 26th to 10 to the 31st ergs/s. Late type
main-sequence stars show little dependence of X-ray emission levels upon
stellar effective temperature; similarly, the observations suggest weak,
if any, dependence of X-ray luminosity upon effective gravity. Instead,
the data show a broad range of emission levels (about three orders of
magnitude) throughout the main sequence later than F0.
---------------------------------------------------------
Title: Low Luminosity Galactic X-Ray Sources
Authors: Vaiana, G. S.
1981SSRv...30..151V Altcode:
Models of soft X-ray emission from low-luminosity galactic X-ray
sources are compared with currently available data. Emphasis is
placed on disk population stars, irrespective of source temperatures
spectral type, luminosity class, and age; and predictions of source
temperatures and variability have been used to distinguish between
the various models. It is tentatively found that the X-ray emission
characteristics of late and early spectral types, and young and old
stars, share many similarities; an economical explanation for this is
the manifestation of coronal surface activity modulated by the stellar
parameters that govern stellar magnetic activity (e.g., rotation). In
some cases (such as for OB stars), a proper theory accounting for the
heating of the coronal plasma does not exist.
---------------------------------------------------------
Title: Solar corona at high resolution.
Authors: Golub, L.; Rosner, R.; Vaiana, G. S.; Zombeck, M. V.
1981SPIE..316..149G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar magnetic fields - The generation of emerging flux
Authors: Golub, L.; Rosner, R.; Vaiana, G. S.; Weiss, N. O.
1981ApJ...243..309G Altcode:
X-ray observations have provided information about magnetic fields on
the sun, and the implications of these observations are discussed. The
pattern of small-scale flux emergence is quite different from that of
active regions. It is inferred that the small-scale fields originate
fairly high in the convective zone, while the fields in active regions
have a deeper origin. The small-scale turbulent fields are only loosely
related to the fields that define the normal solar cycle. The way in
which dynamo models must be modified in the light of these results
is indicated.
---------------------------------------------------------
Title: Closed coronal structures. II - Generalized hydrostatic model
Authors: Serio, S.; Peres, G.; Vaiana, G. S.; Golub, L.; Rosner, R.
1981ApJ...243..288S Altcode:
Numerical computations of stationary solar coronal loop atmospheres
are used to extend earlier analytical work. Two classes of loops are
examined, namely symmetric loops with a temperature maximum at the
top but now having a length greater than the pressure scale height and
loops which have a local temperature minimum at the top. For the first
class, new scaling laws are found which relate the base pressure and
loop length to the base heating, the heating deposition scale height,
and the pressure scale height. It is found that loops for which the
length is greater than about two to three times the pressure scale
height do not have stable solutions unless they have a temperature
minimum at the top. Computed models with a temperature inversion at the
top are permitted in a wider range of heating deposition scale height
values than are loops with a temperature maximum at the top. These
results are discussed in relation to observations showing a dependence
of prominence formation and stability on the state of evolution of
magnetic structures, and a general scenario is suggested for the
understanding of loop evolution from emergence in active regions
through the large-scale structure phase to opening in coronal holes.
---------------------------------------------------------
Title: Dynamics of coronal structures - Magnetic field-related
heating and loop energy balance
Authors: Galeev, A. A.; Rosner, R.; Serio, S.; Vaiana, G. S.
1981ApJ...243..301G Altcode:
The heating of the inhomogeneous solar corona is discussed in the
context of local coronal magnetic field energy release and associated
plasma heating. Expressions of general applicability relating the
parameters characterizing heated and confined atmospheres to heating
processes involving magnetic field reconnection are derived and then
evaluated for a specific heating process. This work is thought to
extend and refine previous models for the heating of confined coronal
plasma structures. A theory for steady energy release is developed, and
scaling laws are derived for the average coronal loop temperature and
energy-release rate which are compared with similar (but parameter-free)
scaling laws; this comparison makes it possible to determine the plasma
beta and nonpotential magnetic field within coronal loop structures in
the context of the model. Constraints on the applicability of static
coronal loop atmosphere models are developed, and the close correlation
between the thermal conductive loss and radiative loss for quasi-static
confined loop atmospheres is shown.
---------------------------------------------------------
Title: X-Ray Emission from Stars
Authors: Vaiana, G. S.
1981isas.rept....1V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal Explorer
Authors: Vaiana, G.
1981uhur.symp...96V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Einstein observations of X-ray emission from variable stars
Authors: Serio, G.; Vaiana, G. S.
1980MmSAI..51..713S Altcode:
Planned observations and preliminary results of recent observations of
the X-ray emission from variable stars made by the Einstein Observatory
are reviewed. The cataclysmic variables detected in the X-ray by
Einstein, which has a sensitivity three orders of magnitude greater than
previous instruments, are indicated, together with detections of Orion
and other pre-main sequence stars within nebulae, including T Tauri
stars. Observations of high X-ray luminosities from OB stars, Wolf-Rayet
stars and searches for X-ray emission in the regions of molecular
clouds, H II regions and COS-B gamma ray sources are considered, and
X-ray emission detected from late-type main sequence stars is then
discussed, with particular attention given to RS CVn-type and dwarf
M and UV Ceti/flare stars. Conclusions that may be derived from the
observations concerning the prevalence of X-ray emission from stars
of practically all spectral types and luminosity classes are summarized.
---------------------------------------------------------
Title: Einstein X-ray observations of Proxima Centauri and the
surrounding region
Authors: Haisch, B. M.; Harnden, F. R., Jr.; Seward, F. D.; Vaiana,
G. S.; Linsky, J. L.; Rosner, R.
1980ApJ...242L..99H Altcode:
The first detection of both quiescent and flaring soft X-ray emission
from a dMe flare star, Proxima Centauri (dM5e) is reported. The data
are analyzed for temporal variability and spectral characteristics. The
quiescent state is characterized by a mean X-ray luminosity of 1.5 x 10
to the 27th erg s/s, corresponding to a mean surface flux of 700,000
erg s/sq cm-s, and an inferred temperature of 4-million K. The flare
that is detected has a peak flux of 7.4 x 10 to the 27th erg s/s and
a peak temperature of 17-million K. The implications of these data for
models of the quiescent and flare coronae of dMe stars are discussed.
---------------------------------------------------------
Title: The Cool Half of the HR Diagram in Soft X-Rays
Authors: Ayres, T. R.; Linsky, J. L.; Vaiana, G. S.; Golub, L.;
Rosner, R.
1980BAAS...12..870A Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Einstein Observations of A-Stars
Authors: Golub, L.; Vaiana, G. S.; Snow, T. P.; Cash, W. C.
1980BAAS...12..872G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Magnetic Field Extrapolations, XUV Observations and the Nature
of Microwave Emission from Sunspots
Authors: Pallavicini, R.; Sakurai, T.; Vaiana, G. S.
1980BAAS...12..896P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Stellar Contribution to Galactic Component of Diffuse Soft
X-ray Background
Authors: Bookbinder, J. A.; Rosner, R.; Vaiana, G. S.
1980BAAS...12..871B Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transition Region and Corona in Solar Active Regions:
Observations and Numerical Modeling
Authors: Golub, L.; Pallavicini, R.; Peres, G.; Rosner, R.; Serio,
S.; Vaiana, G. S.
1980BAAS...12..908G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: INVITED TALK Stellar X-ray Astronomy Saul Rappaport
Authors: Vaiana, Giuseppe S.
1980BAAS...12..870V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The flare of September 7, 1973: A typical example of a newly
recognized class of solar transients
Authors: Pallavicini, R.; Vaiana, G. S.
1980SoPh...67..127P Altcode:
X-ray, extreme-ultraviolet and optical observations of a solar flare are
discussed. It is shown that the flare exemplifies a class of transient
events characterized by long duration and long decay time and by the
development of high systems of loops, generally brighter at the top.
---------------------------------------------------------
Title: Magnetic fields and coronal heating
Authors: Golub, L.; Maxson, C.; Rosner, R.; Vaiana, G. S.; Serio, S.
1980ApJ...238..343G Altcode:
General considerations concerning the scaling properties of
magnetic-field-related coronal heating mechanisms are used to build
a two-parameter model for the heating of closed coronal regions. The
model predicts the way in which coronal temperature and electron density
are related to photospheric magnetic field strength and the size of the
region, using the additional constraint provided by the scaling law of
Rosner, Tucker, and Vaiana. The model duplicates the observed scaling
of total thermal energy content with total longitudinal flux; it also
predicts a relation between the coronal energy density (or pressure)
and the longitudinal field strength modified by the region scale size.
---------------------------------------------------------
Title: Coordinated X-Ray, Optical, and Radio Observations of Flares
from the dMe Star YZ Canis Minoris
Authors: Kahler, S. W.; Golub, L.; Harnden, F. R.; Seward, F. D.;
Vaiana, G. S.
1980BAAS...12..526K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-Ray Bright Points and the Solar Cycle
Authors: Golub, L.; Vaiana, G. S.
1980NASCP2098...75G Altcode: 1980sscs.nasa...75G
The shape of the Sun's activity spectrum is such that the majority of
all magnetic flux emerging at the surface comes in the form of bright
points, i.e., regions living less than two days. Examination of soft
X-ray data obtained from 1970 to 1978 shows that the number of bright
points appears to be anticorrelated with traditional activity indices,
such as sunspot number; the anticorrelation persists after corrections
are made for obscuration by active regions. Comparison of X-ray data
with KPNO magnetograms shows that to within a factor of two, the average
total amount of magnetic flux emerging over the full Sun is constant
through the entire period of observation. The Solar cycle therefore
appears to be more an oscillation in the wavenumber distribution of
emerging flux than of the total quantity of magnetic flux produced.
---------------------------------------------------------
Title: Stellar coronae.
Authors: Vaiana, G. S.
1980HiA.....5..419V Altcode:
The physics of stellar coronae are discussed on the basis of recent
observations of the solar corona and stellar X-ray emission. The
standard scenario of stellar coronal formation and dynamics, which
predicts that the level of coronal emission should follow the level of
acoustic flux generation rather than rotation rate and that mass loss
will vary with coronal activity level, is outlined. Results are then
reviewed of solar observations, which indicate that high mass loss
rates are associated with regions of low activity and that coronal
activity levels correlate with surface magnetic fields, and of Einstein
X-ray observations, which have demonstrated that X-ray emission is
associated with stars throughout the H-R diagram. On the basis of
these observations, a model of stellar corona formation is suggested
in which stellar magnetic fields play the key role in determining the
level of coronal emission, and the modulation of the surface magnetic
flux level and the level of surface magnetic field stressing essentially
determine the variation of mean coronal activity in the H-R diagram
---------------------------------------------------------
Title: Rotational Variations in the Nonflaring Optical and X-Ray
Fluxes of Yz-Canis
Authors: Pettersen, B. R.; Kahler, S.; Golub, L.; Vaiana, G. S.
1980SAOSR.389..113P Altcode: 1980csss....1..113P
No abstract at ADS
---------------------------------------------------------
Title: Evidence for globally coherent variability in solar magnetic
flux emergence
Authors: Golub, L.; Vaiana, G. S.
1980ApJ...235L.119G Altcode:
We examine the large-scale spatial and temporal variations in the
emergence of X-ray bright points on the sun, in order to study the
global properties of magnetic flux emergence. Major variations in the
rate of flux emergence are observed at all solar latitudes, on a time
scale of 3-5 months. The most economical explanation of the observations
is that the full sun participated in a single large eruptive event
during the available 8 month observing period from Skylab in 1973. The
peak of this global event corresponds in time to the eruption of a
major complex of activity. Moreover, it appears that the only portion
of the solar surface which deviates from the above pattern of behavior
is the low latitude region in the vicinity of the AR complex; this area
shows a temporary depletion immediately following the AR outburst. The
high-latitude regions in both hemispheres show the same variation and
appear to lead the low-latitude emergence by approximately 1 month.
---------------------------------------------------------
Title: Stellar Coronae - Overview of the Einstein / CFA Stellar Survey
Authors: Vaiana, G. S.
1980SAOSR.389..195V Altcode: 1980csss....1..195V
No abstract at ADS
---------------------------------------------------------
Title: Stellar Coronae from Einstein: Observations and Theory
Authors: Rosner, R.; Vaiana, G. S.
1980ASIC...60..129R Altcode: 1980xras.proc..129R
Einstein Observatory observations of stellar X-ray emission are
presented and their implications for the formation of stellar coronae
and the problem of stellar angular momentum loss are discussed. Solar
coronal X-ray observations and observations of stellar coronae made
prior to Einstein are reviewed, and it is noted that they already
suggest that the standard theory of acoustic coronal heating is
inadequate. The principal results of the Einstein/CfA stellar survey
are summarized, with attention given to variations of the level of
X-ray flux detected along the main sequence, the decline of X-ray flux
with increasing age of giants and supergiants, and indications of a
large range of X-ray emission levels within a given type, which are
clearly incompatible with models for acoustic flux generation. A new
theory to explain stellar coronae and hence X-ray emission from them
is then proposed in which stellar magnetic fields play the key role
in determining the level of coronal emission, and the modulation of
the surface magnetic flux level and the level of stressing of surface
magnetic fields essentially determine the variation of mean coronal
activity in the H-R diagram.
---------------------------------------------------------
Title: Discovery of an X-ray star association in VI Cygni (Cyg OB2).
Authors: Harnden, F. R., Jr.; Branduardi, G.; Elvis, M.; Gorenstein,
P.; Grindlay, J.; Pye, J. P.; Rosner, R.; Topka, K.; Vaiana, G. S.
1979ApJ...234L..51H Altcode:
A group of six X-ray sources located within 0.4 deg of Cygnus X-3 has
been discovered with the Einstein Observatory. These sources have been
positively identified and five of them correspond to stars in the
heavily obscured OB association VI Cygni. The optical counterparts
include four of the most luminous O stars within the field of view
and a B5 supergiant. These sources are found to have typical X-ray
luminosities of 5 x 10 to the 33rd ergs/s, with temperatures of 10 to
the 6.8th K and hydrogen column densities of 10 to the 22nd/sq cm,
and therefore comprise a new class of low-luminosity galactic X-ray
sources associated with early-type stars.
---------------------------------------------------------
Title: X-ray Observations of the α Cen System from EINSTEIN.
Authors: Golub, L.; Harnden, F. R., Jr.; Rosner, R.; Topka, K.;
Vaiana, G. S.
1979BAAS...11..775G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray Observations
Authors: Vaiana, G.
1979BAAS...11Q.770V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal X-Ray Emission from OB Supergiants.
Authors: Cassinelli, J. P.; Waldron, W. L.; Vaiana, G. S.; Rosner, R.
1979BAAS...11..775C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray Observations of Very Late-Type Dwarf Stars from the
EINSTEIN Observatory.
Authors: Rosner, R.; Giacconi, R.; Golub, L.; Harnden, F. R., Jr.;
Topka, K.; Vaiana, G. S.
1979BAAS...11..776R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On Stars and OB Associations Observed from EINSTEIN.
Authors: Harnden, F. R., Jr.; Golub, L.; Rosner, R.; Seward, F.;
Topka, K.; Vaiana, G. S.
1979BAAS...11..775H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A Magnitude Limited Stellar Survey with EINSTEIN.
Authors: Topka, K.; Golub, L.; Harnden, F. R., Jr.; Gorenstein, P.;
Rosner, R.; Vaiana, G. S.
1979BAAS...11..781T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Erratum: Cosmic Flare Transients: Constraints upon Models
for Energy Storage and Release Derived from the Event Frequency
Distribution
Authors: Rosner, R.; Vaiana, G. S.
1979ApJ...229.1211R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Structured coronae of accretion disks.
Authors: Galeev, A. A.; Rosner, R.; Vaiana, G. S.
1979ApJ...229..318G Altcode:
A model based on the amplification of magnetic fields by convective
motions and differential rotation within a hot (no less than about
1,000,000 K) accretion disk is developed for the fluctuating hard
component of intense cosmic X-ray sources such as Cyg X-1. It is
shown that field reconnection within the inner portion of the disk
is ineffective in limiting field amplification. Magnetic fields may
therefore reach strengths comparable to the equipartition value, leading
to their emergence through buoyancy in the form of looplike structures
and resulting in a very hot (over 100 million K) magnetically confined
structured corona similar to the observed structure of solar corona. In
particular, the soft X-ray luminosity of the accretion disk determines
the dominant energy loss mechanism in loops.
---------------------------------------------------------
Title: The coronal atmosphere above solar active regions: comparison
of high spatial resolution soft X-ray and centimetric observations.
Authors: Pallavicini, R.; Vaiana, G. S.; Tofani, G.; Felli, M.
1979ApJ...229..375P Altcode:
High spatial resolution observations of solar active regions in soft
X-rays and centimetric wavelengths are compared using X-ray and radio
data obtained during the 1973 Skylab mission. An overall correspondence
in position and size between regions of enhanced X-ray emission and
regions of enhanced microwave emission was noticed. However, a closer
analysis of the findings suggested that substantial differences exist
between the emission properties of the atmosphere over sunspots and
that over plages, with the difference probably related to the average
intensity of the magnetic field, which was found to be higher over
sunspot umbrae than over plage areas.
---------------------------------------------------------
Title: Observational Tests of Magnetic Field-Related Coronal Heating
Theories
Authors: Golub, L.; Maxson, C.; Rosner, R.; Serio, S.; Vaiana, G. S.
1979BAAS...11R.408G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Initial Results from the Einstein Survey of Stellar
Low-Luminosity X-ray Sources
Authors: Vaiana, G.; Forman, W.; Giacconi, R.; Gorenstein, P.; Pye,
J.; Rosner, R.; Seward, F.; Topka, K.
1979BAAS...11..446V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Far-Infrared Observations of Regions Near W42
Authors: Maxson, C. W.; Sciortino, S.; Serio, S.; Vaiana, G. S.;
Fazio, G. G.
1979BAAS...11R.470M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-Ray Sources from O Star Associations
Authors: Rosner, R.; Grindlay, G.; Harnden, R.; Seward, F.; Vaiana, G.
1979BAAS...11..446R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Transienti nella corona solare: determinazione dei parametri
fisici del plasma e leggi di scala.
Authors: Peres, G.; Sciortino, S.; Serio, S.; Vaiana, G. S.
1979RSAI...22..165P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Formation of structured confined coronae on accretion disks.
Authors: Galeev, A. A.; Rosner, R.; Vaiana, G. S.
1979xras.proc..263G Altcode:
The interaction of magnetic fields and flows within accretion disks
and formation of structured confined coronae are discussed. Emphasis
is placed on the evolution of magnetic fields within a convective
disk and the consequences of dissipating erupted fields above the
disk where reconnection processes have substantially shorter time
scales. The key results are that the closed field topology above the
disk, together with plasma heating resulting from reconnection, leads
to the formation of an ensemble of very hot confined plasma structures
whose emission time scales are dictated by the heating process; the
cooling of these plasma structures is strongly influenced by the soft
X-ray luminosity of the underlying accretion disk.
---------------------------------------------------------
Title: Ricerche su fenomeni transitori della corona solare mediante
osservazioni ottiche, ultraviolette ed X.
Authors: Pallavicini, R.; Serio, S.; Vaiana, G. S.
1979RSAI...22..163P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Rivelazione quantica di immagini ad alta risoluzione
spazio-temporale: il progetto Photicon.
Authors: Peres, G.; Sciortino, S.; Serio, S.; Vaiana, G. S.
1979RSAI...22..237P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Sistema analisi dati per fotometria nel lontano infrarosso
della collaborazione Palermo-Harvard. Risultati preliminari per la
regione intorno a W42.
Authors: Peres, G.; Sciortino, S.; Serio, S.; Vaiana, G. S.
1979RSAI...22..190P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An atlas of soft X-ray images of the solar corona from SKYLAB
Authors: Zombeck, M. V.; Vaiana, G. S.; Haggerty, R.; Krieger, A. S.;
Silk, J. K.; Timothy, A.
1978ApJS...38...69Z Altcode:
An atlas is presented which contains daily full-sun photographs of the
soft X-ray solar corona taken in two filters with an X-ray telescope
on the Apollo telescope mount of Skylab for the period from May 29
to November 27, 1973. The passband of the first filter covers the
wavelength regions from 2 to 32 A and 44 to 54 A; the second filter
covers the region from 2 to 17 A. Characteristics of the instrument,
the wavelength response, and sensitivity are described along with the
total data base, of which the atlas represents only 1%. Comparisons
are made with observations of the white-light corona, photospheric
magnetic field, H-alpha radiation from the chromosphere, and 284-A Fe XV
emission from the corona. A complete bibliography of scientific papers
that have used the data base and a bibliography of catalogs and atlases
containing related data for the same observational period are provided.
---------------------------------------------------------
Title: Configuration and gradual dynamics of prominence-related
X-ray coronal cavities.
Authors: Serio, S.; Vaiana, G. S.; Godoli, G.; Motta, S.; Pirronello,
V.; Zappala, R. A.
1978SoPh...59...65S Altcode:
We have analyzed X-ray images of the solar corona obtained by the
S-054 telescope on Skylab, together with Hα filtergrams from the
Catania Astrophysical Observatory and EUV and magnetic data, to study
the morphology and the evolution of the coronal structures associated
with prominences (coronal cavities).
---------------------------------------------------------
Title: Cosmic flare transients: constraints upon models for energy
storage and release derived from the event frequency distribution.
Authors: Rosner, R.; Vaiana, G. S.
1978ApJ...222.1104R Altcode:
Flare behavior for a variety of transient sources, including the Sun,
flare stars, and a transient cosmic X-ray source, is examined. It is
found that, although these sources span an energy release rate of over
10 decades, the flare frequency (v) as a function of energy released
(E) follows a similar power law [v(E) E - J at large energies for
all these sources; the flare frequency distributions at low energies,
however, differ substantially. This result is used to develop a model
for the general flaring phenomenon which allows a unified description
of the flaring process for these diverse sources and which permits
one to infer information concerning the modes of energy storage and
release; specifically, the power-law behavior is shown to follow from
the assumption that flaring is a stochastic relaxation phenomenon and
from the requirements that the e-folding time for energy storage be
constant (independent of the instantaneous free energy accumulated)
and that the energy released be large when compared with the energy
of the unperturbed state. These requirements place constraints upon
physical models for transient sources in addition to those adduced
from the spectral behavior of the transient itself. Subject headings:
plasmas - stars: flare - Sun: flares - X-rays: bursts
---------------------------------------------------------
Title: Heating of coronal plasma by anomalous current dissipation.
Authors: Rosner, R.; Golub, L.; Coppi, B.; Vaiana, G. S.
1978ApJ...222..317R Altcode:
It is shown that there exist heating mechanisms which connect the
observed radiative properties of the inner corona in a simple way to
the underlying solar magnetic field. The mechanisms considered involve
the generation and consequent dissipation of coronal currents. It
is argued that the spatially and temporally inhomogeneous nature
of the erupting solar magnetic field is an essential element of
coronal heating. Unlike heating theories conceived in the context
of the 'homogeneous' corona, this class of current heating models
incorporates the observed stochastic coronal structuring at the onset,
and does not view it as a complication of an otherwise straightforward
model. Attention is given to the generation of coronal currents, the
flux-tube emergence, the gradual growth and decay of active regions,
the energetics of current dissipation, current sheath geometry and
heat transport, and anomalous current dissipation.
---------------------------------------------------------
Title: Coronal Heating and Its Relation to Magnetic Field Evolution.
Authors: Golub, L.; Rosner, R.; Vaiana, G. S.
1978BAAS...10..440G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Palermo four-color far infrared program
Authors: Peres, G.; Serio, S.; Vaiana, G. S.; Cali, C.; Daneu, V.;
Maxson, C.; Steier, M.
1978MmSAI..49...95P Altcode:
A four-channel far-IR photometer designed for use with a balloon-borne
102-cm telescope is described. The data analysis system for this
photometer is discussed, and a typical observational program is
outlined. Possible objects that may be observed with the four-color
far-IR photometer include molecular clouds, the galactic-center region,
H II regions, quasars, Seyfert galaxies, and BL Lacertae objects.
---------------------------------------------------------
Title: Dynamics of the quiescent solar corona.
Authors: Rosner, R.; Tucker, W. H.; Vaiana, G. S.
1978ApJ...220..643R Altcode:
An analytical model for the quiescent inhomogeneous solar corona is
developed on the basis of the hypothesis that looplike structures are
the basic coronal building blocks. By assuming that quiescent loop
structures observed in X-rays are in hydrostatic equilibrium, it is
demonstrated that such loops must have their temperature maximum
located near their apex and that substantial nonradiative energy
deposition must occur along most of their length. The calculations
yield a unique relation among loop temperature, pressure, and size,
which fits the X-ray observations of quiescent structures well and is
consistent with the initial assumption of hydrostatic equilibrium. The
results suggest that the coronal loops visible in X-rays represent a
relatively steady-state equilibrium of the confined plasmas and that
fluctuations in such quantities as the local heating rate can lead to
dynamically unstable states in which the loop plasma does not attain
a temperature sufficient for X-ray emission. A parameterization of
various proposed coronal heating theories is also developed within
the context of the analytical model.
---------------------------------------------------------
Title: Differential rotation rates for short-lived regions of emerging
magnetic flux.
Authors: Golub, L.; Vaiana, G. S.
1978ApJ...219L..55G Altcode:
We have measured the synodic rotation rates of a sample of compact
X-ray emission features lasting from 1 day to 7 days, thus bridging
the transition between X-ray bright points and active regions. The
rotation rate is found to be a function of the lifetime, or size, of
the feature; shorter-lived smaller features rotate more slowly than
long-lived ones. The rotation rate for features lasting 2 days or less
is consistent with that of the photospheric gas. The longest-lived
features rotate at a rate about 5% higher, consistent with the sunspot
rotation rate.
---------------------------------------------------------
Title: Recent advances in coronal physics.
Authors: Vaiana, G. S.; Rosner, R.
1978ARA&A..16..393V Altcode:
The relation between the extended atmosphere of a star, including
the chromosphere and corona, and the dynamics governing the outward
radial energy transport within the star has been considered. In this
connection, coronal activity serves as an indicator for the level
of internal activity and hence as one of the tools for investigating
stellar evolution. The observational framework is examined, taking into
account the structuring of the corona by the solar magnetic field, the
activity of the corona on virtually all spatial and temporal scales,
and the problem of accounting for the physical basis of solar coronal
structure on a variety of distinct levels. The modeling of coronae and
coronal structures is discussed, giving attention to coronal morphology
and magnetic fields, mechanisms for coronal formation, and an analysis
of coronal structures. A description of studies of stellar coronae is
also provided.
---------------------------------------------------------
Title: New instrumentation for space astronomy
Authors: van der Hucht, K. A.; Vaiana, G.
1978nisa.symp.....V Altcode: 1978nisa.conf.....V
These papers deal with the design and operation of present and planned
high-energy instrumentation for space astronomy. The major subject
areas encompass UV instrumentation and related techniques, X-ray
instrumentation and related techniques, miscellaneous instrumentation,
imaging, spectroscopy, and nonimaging instruments. Specific topics
include a deep photographic survey from Spacelab, an integrated UV/X-ray
astronomy facility for Spacelab, a far-UV camera, the space telescope,
the faint-object camera, techniques for UV astrophysical studies from
space vehicles, and the faint-object telescope. Other papers discuss
HEAO-A and -B, the development of a gas scintillation proportional
counter for the first Spacelab mission, solar X-ray spectroscopy with
a bent crystal spectrometer, solar X-ray imaging techniques, imaging
soft and hard X-ray telescopes, X-ray imaging scintillation detectors,
and a hard X-ray camera for the study of gamma-ray burst sources.
---------------------------------------------------------
Title: Solar X-ray imaging techniques, past and future: the sun as
a laboratory plasma.
Authors: Vaiana, G. S.
1978nisa.symp..177V Altcode: 1978nisa.conf..177V
No abstract at ADS
---------------------------------------------------------
Title: Four Color Infrared Bolometer System for One-Meter Telescope
Authors: Daneu, V.; Maxson, C.; Peres, G.; Serio, S.; Vaiana, G.
1978ASIC...38..335D Altcode: 1978infa.proc..335D
A far-infrared photometer has been developed as a focal plane instrument
for a balloon-borne 102-cm telescope. The four gallium-doped Ge
bolometers adopted for the system operate at 1.8 K in a liquid-helium
dewar. Wavelength bands of the four-bolometer system are a narrow
spectrum between 18 and 22 microns, and bands centered at 42, 70,
and 140 microns. The responsivity and Johnson noise of the detectors
limit the performance of the instrument.
---------------------------------------------------------
Title: Solar X-ray transients in magnetically confined plasma:
observational data and hydrodynamic model.
Authors: Peres, G.; Serio, S.; Vaiana, G. S.; Rosner, R.
1978spre.conf..341P Altcode: 1978spre.proc..341P
No abstract at ADS
---------------------------------------------------------
Title: The dynamic X-ray corona.
Authors: Vaiana, G. S.
1978spre.conf..331V Altcode: 1978spre.proc..331V
A series of images of X-rays emitted by the solar corona in
the wavelength range from about 2 to 54 A is discussed. These
images reveal the ubiquitous nature of high-temperature plasma loops
confined by the coronal magnetic field and extending over virtually all
coronal regions. The X-ray bright corona, which consists entirely of
structures in the form of loops, is shown to emphasize the confinement
of high-temperature plasma by the coronal magnetic field. The images
examined also indicate that the intensity of the X-ray emission seems
to be directly related to the magnetic-field configuration and that
coronal heating may well be coupled to convection via the magnetic
field. It is concluded that at least in the sun's case, there is not one
corona but rather many small-scale 'coronae' of differing temperatures
and pressures which can coexist, with the magnetic field providing
the required 'isolation'. An analytical solution for the energy
balance within a hydrostatic, topologically closed loop structure is
summarized which excludes acoustical heating but is consistent with
magnetic-field-related heating.
---------------------------------------------------------
Title: The Palermo four-color far infrared program.
Authors: Peres, G.; Serio, S.; Vaiana, G. S.; Cali', C.; Daneu, V.;
Maxson, C.; Steier, M.
1978ASIC...38...95P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Dynamical behavior of coronal cavities, prominence material
and magnetic field.
Authors: Serio, S.; Vaiana, G. S.; Godoli, G.; Motta, S.; Pirronello,
V.; Zappala, R. A.
1978spre.conf..337S Altcode: 1978spre.proc..337S
Results are reported for a study of the slow modes of solar prominence
dynamics based on examination of daily maps of H-alpha activity, a set
of daily X-ray photographs of the sun, H-alpha pictures taken at 5-min
intervals, and synoptic maps of neutral lines. It is found that both
the presence and the dynamics of prominences related to X-ray cavities
depend on the age of the associated neutral line. Long-lasting and large
prominences are shown to be associated with middle-aged neutral lines,
while transient and small prominences are observed to occur in X-ray
structures that are disturbed either by rapid evolution, as in young
field lines, or by decreasing intensity of the field characterizing
older structures. The results indicate that the lack of material within
an X-ray cavity in no case seems to balance the prominence material, so
that some chromospheric material is necessary for prominence formation.
---------------------------------------------------------
Title: Identificazione di due classi di brillamenti X mediante
osservazioni di eventi al bordo con l'esperimento Skylab S-054.
Authors: Pallavicini, R.; Serio, S.; Vaiana, G.
1977MmSAI..48..760P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A survey of soft X-ray limb flare images: the relation between
their structure in the corona and other physical parameters.
Authors: Pallavicini, R.; Serio, S.; Vaiana, G. S.
1977ApJ...216..108P Altcode:
The data used in the investigation were obtained by the American
Science and Engineering S-054 experiment on board Skylab. The instrument
employed was a grazing incidence X-ray telescope which records images
of the sun on film. The morphology of limb flares is investigated
and the observed spatial structure is related with the other physical
parameters of the region (temperature, density, characteristic times,
and energy density). It is concluded that two physically distinct
classes of flares exist that differ both in their morphology and in
the physical properties which characterize the emitting regions.
---------------------------------------------------------
Title: Determination of plasma parameters from soft X-ray images
for coronal holes (open magnetic field configurations) and coronal
large-scale structures (extended closed-field configurations).
Authors: Maxson, C. W.; Vaiana, G. S.
1977ApJ...215..919M Altcode:
In connection with high-quality solar soft X-ray images the 'quiet'
features of the inner corona have been separated into two sharply
different components, including the strongly reduced emission areas
or coronal holes (CH) and the extended regions of looplike emission
features or large-scale structures (LSS). Particular central meridian
passage observations of the prominent CH1 on August 21, 1973, are
selected for a quantitative study. Histogram photographic density
distributions for full-disk images at other central meridian passages
of CH 1 are also presented, and the techniques of converting low
photographic density data to deposited energy are discussed, with
particular emphasis on the problems associated with the CH data.
---------------------------------------------------------
Title: Hydrostatic and dynamic models of solar coronal holes.
Authors: Rosner, R.; Vaiana, G. S.
1977ApJ...216..141R Altcode:
A description is presented of a sequence of one-dimensional fluid
flow models of the transition zone and the inner corona. A hydrostatic
model atmosphere in reasonable agreement with observations of closed,
large-scale coronal structures found in the quiet sun is considered
and various physical effects are introduced, one at a time, observing
the response of the model. As a result of the investigations, a model
is developed of the plasma flow in a coronal hole. It is shown that
the data severely circumscribe the allowable range of possible models.
---------------------------------------------------------
Title: Magnetic properties of X-ray bright points.
Authors: Golub, L.; Krieger, A. S.; Harvey, J. W.; Vaiana, G. S.
1977SoPh...53..111G Altcode:
Using high resolution KPNO magnetograms and sequences of simultaneous
S-054 soft X-ray solar images we have compared the properties of X-ray
bright points (XBP) and ephemeral active regions (ER). All XBP appear on
the magnetograms as bipolar features, except for very newly emerged or
old and decayed XBP. We find that the separation of the magnetic bipoles
increases with the age of the XBP, with an average emergence growth
rate of 2.2 ± 0.4 km s<SUP>−1</SUP>. The total magnetic flux in a
typical XBP living about 8 hr is found to be ≈ 2 x 10<SUP>19</SUP>
Mx. A proportionality is found between XBP lifetime and total magnetic
flux, equivalent to ≈ 10<SUP>20</SUP> Mx per day of lifetime.
---------------------------------------------------------
Title: Heating of Coronal Plasma by Anomalous Current Dissipation.
Authors: Rosner, R.; Golub, L.; Vaiana, G. S.; Coppi, B.
1977BAAS....9..370R Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The S-054 X-ray telescope experiment on Skylab.
Authors: Vaiana, G. S.; van Speybroeck, L.; Zombeck, M. V.; Krieger,
A. S.; Silk, J. K.; Timothy, A.
1977SSI.....3...19V Altcode:
A description of the S-054 X-ray telescope on Skylab is presented
with a discussion of the experimental objectives, observing program,
data reduction and analysis. Some results from the Skylab mission are
given. The telescope photographically records high-resolution images
of the solar corona in several broadband regions of the soft X-ray
spectrum. It includes an objective grating used to study the line
spectrum. The spatial resolution, sensitivity, dynamic range and time
resolution of the instrument were chosen to survey a wide variety of
solar phenomena. It embodies improvements in design, fabrication, and
calibration techniques which were developed over a ten-year period. The
observing program was devised to optimize the use of the instrument and
to provide studies on a wide range of time scales. The data analysis
program includes morphological studies and quantitative analysis using
digitized images. A small sample of the data obtained in the mission
is presented to demonstrate the type of information that is available
and the kinds of results that can be obtained from it.
---------------------------------------------------------
Title: Spatially-Resolved Observations of Solar Active Regions in
Soft X-Ray and Centimetric WAVELENGTHS."
Authors: Pallavicini, R.; Tofani, G.; Vaiana, G. S.
1977uxsa.coll...44P Altcode: 1977IAUCo..43...44P
No abstract at ADS
---------------------------------------------------------
Title: Observation of spatial and temporal variations in X-ray bright
point emergence patterns
Authors: Golub, L.; Krieger, A. S.; Vaiana, G. S.
1976SoPh...50..311G Altcode:
Observations of X-ray bright points (XBP) over a six-month interval
in 1973 show significant variations in both the number density of XBP
as a function of heliographic longitude and in the full Sun average
number of XBP from one rotation to the next. The observed increases
in XBP emergence are estimated to be quivalent to several large active
regions emerging per day for several months. The number of XBP emerging
at high latitudes also varies, in phase with the low latitude variation
and reaches a maximum approximately simultaneous with a major outbreak
of active regions. The quantity of magnetic flux emerging in the form
of XBP at high latitudes alone is estimated to be as large as the
contribution from all active regions.
---------------------------------------------------------
Title: The spatial structure of a solar flare in soft X-rays and
centimetric wavelengths.
Authors: Pallavicini, R.; Vaiana, G. S.
1976SoPh...49..297P Altcode:
High-resolution images of the decay phase of a soft X-ray flare observed
by the S-054 experiment on Skylab are compared with interferometric
scans of the radio burst obtained simultaneously at 2.8 cm (Felli
et al., 1975). The spatial resulution of the radio instrument in
one direction, although lower than the X-ray telescope resolution,
is high enough for a detailed comparison. The comparison clarifies
the relationship between the sources of soft X-ray and thermal radio
emission in solar flares. The X-ray emission is localized in a loop-like
structure which appears spatially coincident with the rapidly varying
component of the radio burst. The more stable components of the radio
source, which do not appear to contribute substantially to X-ray
emission, are found to be spatially associated with the extremes of
the X-ray loop. A model of plasma-filled loops is suggested which
accounts for the emissions in both spectral ranges and for their
spatial location and temporal development.
---------------------------------------------------------
Title: Distribution of lifetimes for coronal soft X-ray broght points.
Authors: Golub, L.; Krieger, A. S.; Vaiana, G. S.
1976SoPh...49...79G Altcode:
We have measured the lifetimes of all compact emission features
visible on three sets of high time resolution soft X-ray images. The
spectrum of lifetimes is found to be heavily weighted toward short
lifetimes. The number of features present on the disk which live 2-48
hours is at least ten times as great as the number living more than 48
hours. The distribution of lifetimes can be fit in all three cases by
a four-parameter function N(t) = N<SUB>s</SUB> exp(-t/τ<SUB>s</SUB>)
+ N<SUB>L</SUB> exp(-t/τ<SUB>L</SUB>), with τ<SUB>s</SUB> = 8.7±0.2,
τ<SUB>L</SUB> = 35±4 and N<SUB>s</SUB> ≈ 10N<SUB>L</SUB>. Features
living two days or less have a very broad latitude distribution
(Golub et al., 1974, 1975) whereas nearly all longer-lived features
are found within 30° of the equator. The growth rates of long-lived vs
short-lived points are the same to within ≈ 20%, the major difference
being that long-lived points continue to grow and generally reach
larger sizes.
---------------------------------------------------------
Title: Association of X-ray arches with chromospheric neutral lines.
Authors: McIntosh, P. S.; Krieger, A. S.; Nolte, J. T.; Vaiana, G.
1976SoPh...49...57M Altcode:
Daily maps of magnetic neutral lines derived from Hα observations
have been superimposed on solar X-ray images for the period 15-30 June
1973. Nearly all X-ray-emitting structures consist of systems of arches
covering chromospheric neutral lines. Areas of low emissivity, coronal
holes, appear as the areas between arcades of arches. The presence of a
coronal hole, therefore, is determined by the spacing between neutral
lines and the scale of the arches over those neutral lines. X-ray
emissivity on the solar disk extends from neutral lines in proportion
to the vertical and horizontal scale of the arches over those neutral
lines. Increasing scale of arches corresponds with increasing age of
magnetic fields associated with the neutral line. All X-ray filament
cavities coincided with neutral lines, but filaments appeared under
cavities for only part of their length and for only a fraction of the
disk passage.
---------------------------------------------------------
Title: Spectroscopic Studies of the Solar Corona at X-Ray Wavelengths:
Discussion
Authors: Vaiana, G.; Acton, L. W.
1976RSPTA.281..390V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The X-Ray Corona from Skylab
Authors: Vaiana, G. S.
1976RSPTA.281..365V Altcode: 1976RSLPT.281..365V
An overview of the images obtained with the A.S. & E. X-ray
telescope on Skylab shows the low corona to be highly structured. The
plasma is distributed in closed loops shaped by the magnetic field with
sizes ranging from the smallest resolvable structures of a few thousand
kilometres to loops that reach halfway across the solar disk. Relatively
high-temperature and dense plasma loops overlay active regions;
large-scale inter-connections link active regions to their surrounding
fields and in some cases to other active regions. The large-scale
loops, which cover most of the Sun outside of active regions, appear
to be related to old active regions whose magnetic fields have spread
out over the course of several solar rotations. Often at the poles
and occasionally on the disk, large regions display radial field
configurations (coronal holes) from which the plasma preferentially
escapes into high-velocity solar wind streams. A comprehensive view
of the structure and evolution of the X-ray corona is given in terms
of the physical conditions existing in the various coronal loops,
and the importance of active regions is emphasized by examining their
structure and time development over a wide range of scales.
---------------------------------------------------------
Title: Emergence of Small-Scale Magnetic Fields on the Sun
Authors: Golub, L.; Krieger, A. S.; Vaiana, G. S.
1976BAAS....8..333G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Energy and Material Loss in the Decay of an X-ray Flare
Authors: Silk, J. K.; Kahler, S. W.; Krieger, A. S.; Vaiana, G. S.
1976BAAS....8..375S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Morphology and Evolution of Long Decay Soft X-ray Events
Observed with the S-054 X-ray Experiment on Skylab
Authors: Kahler, S.; Krieger, A. S.; Vaiana, G. S.
1976BAAS....8..316K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Evidence for magnetic energy storage in coronal active regions.
Authors: Krieger, A. S.; de Feiter, L. D.; Vaiana, G. S.
1976SoPh...47..117K Altcode:
Examination of X-ray images obtained by the S-054 X-ray spectrographic
telescope on Skylab shows the presence of some atypical X-ray emitting
coronal structures in active regions which are not consistent with
potential extrapolations of photospheric magnetic fields. Analysis
of the observed temporal changes in the X-ray emitting active region
structures demonstrates that the majority of these consist of brightness
changes representing temperature (and perhaps, density) variations of
the material in the loops.
---------------------------------------------------------
Title: AN atlas of coronal hole boundary positions May 28 to November
21, 1973.
Authors: Nolte, J. T.; Krieger, A. S.; Timothy, A. F.; Vaiana, G. S.;
Zombeck, M. V.
1976SoPh...46..291N Altcode:
This atlas shows the boundary locations of the coronal holes observed
in soft X-rays (2-32, 44-54 Å) by the AS & E X-ray spectrographic
telescope on Skylab. The data are presented as tracings of the
boundaries as they appeared when the holes were near central meridian.
---------------------------------------------------------
Title: Coronal holes as sources of solar wind.
Authors: Nolte, J. T.; Krieger, A. S.; Timothy, A. F.; Gold, R. E.;
Roelof, E. C.; Vaiana, G.; Lazarus, A. J.; Sullivan, J. D.; McIntosh,
P. S.
1976SoPh...46..303N Altcode:
We investigate the association of high-speed solar wind with coronal
holes during the Skylab mission by: (1) direct comparison of solar wind
and coronal X-ray data; (2) comparison of near-equatorial coronal hole
area with maximum solar wind velocity in the associated streams; and
(3) examination of the correlation between solar and interplanetary
magnetic polarities. We find that all large near-equatorial coronal
holes seen during the Skylab period were associated with high-velocity
solar wind streams observed at 1 AU.
---------------------------------------------------------
Title: The temperature and density structures of an X-ray flare
during the decay phase.
Authors: Silk, J. K.; Kahler, S. W.; Krieger, A. S.; Vaiana, G. S.
1976spre.conf..911S Altcode: 1976spre.proc..911S
The X-ray flare of 9 August 1973 was characterized by a spatially
small kernel structure which persisted throughout its duration. The
decay phase of this flare was observed in the objective grating mode
of the X-ray telescope aboard the Skylab. Data analysis was carried
out by scanning the images with a microdensitometer, converting the
density arrays to energy using laboratory film calibration data and
taking cross sections of the energy images. The 9 August flare shows
two distinct periods in its decay phase, involving both cooling and
material loss. The objective grating observations reveal that the two
phenomena are separated in time. During the earlier phase of the flare
decay, the distribution of emission measure as a function of temperature
is changing, the high temperature component of the distribution being
depleted relative to the cooler body of plasma. As the decay continues,
the emission measure distribution stabilizes and the flux diminishes
as the amount of material at X-ray emitting temperatures decreases.
---------------------------------------------------------
Title: ATM Observations, X-Ray Results
Authors: Vaiana, G. S.; Krieger, A. S.; Timothy, A. F.; Zombeck, M.
1976Ap&SS..39...75V Altcode:
Preliminary results of the solar X-ray observations from Skylab are
reviewed, indicating a highly structured nature for the corona, with
closed magnetic loop structures over a wide range of size scales. A
description of the S-054 experiments is provided, and values are given
for parameters, including size, density, and temperature, describing
a variety of typical coronal features. The structures and evolutions
of active regions, coronal holes and bright points are discussed.
---------------------------------------------------------
Title: Skylab observations of X-ray loops connecting separate
active regions.
Authors: Chase, R. C.; Krieger, A. S.; Svestka, Z.; Vaiana, G. S.
1976spre.conf..917C Altcode: 1976spre.proc..917C
One hundred loops interconnecting 94 separate active solar
regions detectable in soft X-rays were identified during the Skylab
mission. While close active regions are commonly interconnected with
loops, the number of such interconnections decreases steeply for longer
distances; the longest interconnecting loop observed in the Skylab data
connected regions separated by 37 deg. Several arguments are presented
which support the point of view that this is the actual limit of the
size of magnetic interconnections between active regions. No sympathetic
flares could be found in the interconnected regions. These results cast
doubt on the hypothesis that accelerated particles can be guided in
interconnecting loops from one active region to another over distances
of 100 deg or more and eventually produce sympathetic flares in them.
---------------------------------------------------------
Title: Coronal Bright Points
Authors: Golub, L.; Krieger, A. S.; Vaiana, G. S.
1976IAUS...71..145G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Interpretation of Simultaneous Soft X-Ray Spectroscopic
and Imaging Observations of an Active Region
Authors: Davis, J. M.; Gerassimenko, M.; Krieger, A. S.; Vaiana, G. S.
1975SoPh...45..393D Altcode:
Simultaneous soft X-ray spectroscopic and broad band imaging
observations of an active region have been analyzed together to
determine the parameters which describe the coronal plasma. From the
spectroscopic data, models of temperature-emission measure-elemental
abundance have been constructed which provide acceptable statistical
fits. By folding these possible models through the imaging analysis,
models which are not self-consistent can be rejected. In this way,
only the oxygen, neon and iron abundances of Pottasch (1967), combined
with either an isothermal or exponential temperature-emission measure
model are consistent with both sets of data. Contour maps of electron
temperature and density for the active region have been constructed from
the imaging data. The implications of the analysis to the determination
of coronal abundances and to future satellite experiments are discussed.
---------------------------------------------------------
Title: Spatial Structure and Temporal Development of a Solar X-Ray
Flare Observed from Skylab on June 15, 1973
Authors: Pallavicini, R.; Vaiana, G. S.; Kahler, S. W.; Krieger, A. S.
1975SoPh...45..411P Altcode:
A solar flare on June 15, 1973 has been observed with high spatial and
temporal resolution by the S-054 grazing-incidence X-ray telescope on
Skylab. Both morphological and quantitative analyses are presented. Some
of the main results are: (a) the overall configuration of the flare
is that of a compact region with a characteristic size of the order of
30″ at the intensity peak, (b) this region appears highly structured
inside with complex systems of loops which change during the event, (c)
a brightening over an extended portion of the active region precedes
the flare onset, (d) the impulsive phase indicated by the non-thermal
radio emission is a period during which a rapid brightening occurs in
loop structures, (e) the X-ray emission is centered over the neutral
line of longitudinal magnetic field, and the brightest structures at the
flare onset bridge the neutral line, (f) loop systems at successively
increasing heights form during the decay phase, finally leading to
the large loops observed in the postflare phase, (g) different parts
of the flare show distinctly different light curves, and the temporal
development given by full disk detectors is the result of integrating
the different intensity vs time profiles.
---------------------------------------------------------
Title: A Comparison of Coronal X-Ray Structures of Active Regions
with Magnetic Fields Computed from Photospheric Observations
Authors: Poletto, G.; Vaiana, G. S.; Zombeck, M. V.; Krieger, A. S.;
Timothy, A. F.
1975SoPh...44...83P Altcode:
The appearances of several X-ray active regions observed on March 7,
1970 and June 15, 1973 are compared with the corresponding coronal
magnetic field topology. Coronal fields have been computed from
measurements of the longitudinal component of the underlying magnetic
fields, under the current-free hypothesis. An overall correspondence
between X-ray structures and calculated field lines is established,
and the magnetic counterpart of different X-ray features is also
examined. A correspondence between enhanced X-ray emission and the
location of compact closed field lines is suggested by this study.
---------------------------------------------------------
Title: The Coronal Structure of Active Regions
Authors: Landini, M.; Monsignori Fossi, B. C.; Krieger, A.; Vaiana,
G. S.
1975SoPh...44...69L Altcode:
A four-parameter model which assumes a Gaussian dependence of
both temperature and pressure on distance from center is used
to fit the compact part of coronal active regions as observed in
X-ray photographs from a rocket experiment. The four parameters
are the maximum temperature T<SUB>M</SUB>, the maximum pressure
P<SUB>M</SUB>= 2N<SUB>M</SUB>kT<SUB>M</SUB>, the width of the pressure
distribution σ<SUB>P</SUB>, and the width of the temperature
distribution σ<SUB>T</SUB> = α<SUP>1/2</SUP>σ<SUB>P</SUB>. The
maximum temperature T<SUB>M</SUB> ranges from 2.2 to 2.8 ×
10<SUP>6</SUP>K, and the maximum density N<SUB>M</SUB> from 2 to 9 ×
10<SUP>9</SUP>cm<SUP>−3</SUP>. The range of σ<SUB>P</SUB> is from
2 to 4 × 10<SUP>9</SUP> cm and that of α from 2 to 7.
---------------------------------------------------------
Title: The location of the site of energy release in a solar X-ray
subflare.
Authors: Petrasso, R. D.; Kahler, S. W.; Krieger, A. S.; Silk, J. K.;
Vaiana, G. S.
1975ApJ...199L.127P Altcode:
A rapid sequence of high-resolution X-ray photographs was obtained
by the S-054 X-ray Telescope Experiment on Skylab on 1973 September
1. During the course of this observation, photographs were obtained of
a flarelike brightening in a simple, bipolar active region. Analysis
reveals the following facts. The event had the form of a small,
elongated bright feature whose narrowest dimension was less than seconds
of arc. The brightness peak of the flarelike brightening was located
within seconds of arc of the center of brightness of a preexisting
loop structure that crossed the magnetic neutral line. This loop was
observed to brighten gradually beginning approximately 10 minutes
prior to the flarelike event. During the rise of the event, the 2-17
A X-ray brightness of the center of the subflare core rose by over a
factor of 10 in a time period of 196 seconds or less.
---------------------------------------------------------
Title: Morphological evolution of X-ray flare structures from the
rise through the decay phase.
Authors: Kahler, S. W.; Krieger, A. S.; Vaiana, G. S.
1975ApJ...199L..57K Altcode:
The morphological evolution of 12 solar X-ray subflares from onset
through the decay phase has been studied using photographic X-ray
images obtained from Skylab. The spatial configurations are found
to vary widely from flare to flare, but they appear to be composed
of two basic kinds of structures. The first, termed 'X-ray kernels',
are brightest during the rise phase; the second, looplike structures,
appear during the maximum and decay phases of the event. The X-ray
kernels are small pointlike structures which may be related to the
nonthermal phases of flares.
---------------------------------------------------------
Title: Association of X-ray Arches with Chromospheric Neutral Lines.
Authors: McIntosh, P. S.; Krieger, A. S.; Nolte, J. T.; Vaiana, G.
1975BAAS....7..444M Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal X-ray Transient Events Associated with Hα Filament
Disappearances
Authors: Webb, D.; Krieger, A.; Rust, D.; Vaiana, G.
1975BAAS....7..430W Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Structure and Evolution of Coronal Holes
Authors: Timothy, A. F.; Krieger, A. S.; Vaiana, G. S.
1975SoPh...42..135T Altcode:
When observed at soft X-ray wavelengths coronal holes are seen as
open features, devoid of X-ray emission and bounded by apparently
divergent coronal loop structures. Inspection of the topology of the
photospheric magnetic fields associated with these features suggests
that holes are formed when the remnants of active region fields,
emerging in both hemispheres over a period of several solar rotations,
combine to form a large area of essentially unipolar field. Remnants
of opposite polarity fields surround these features resulting in a
divergent magnetic configuration at the hole boundaries. Holes are seen
to form and evolve while the large scale divergent field pattern is
reinforced and to close when large scale remnants occur which disrupt
the general field pattern. Two types of holes are observed in the
early Skylab observations. The first are elongated features which are
aligned approximately north-south extending from one solar pole to a
polar filament channel in the opposite hemisphere. The polar holes and
somewhat lower latitude holes appear to lie in unipolar areas which
are completely confined by opposite polarity fields.
---------------------------------------------------------
Title: Observation of a Non-Uniform Component in the Distribution
of Coronal Bright Points
Authors: Golub, L.; Krieger, A. S.; Vaiana, G. S.
1975SoPh...42..131G Altcode:
The longitude distribution of X-ray bright points shows very strong
variations when plotted in a heliocentric (Carrington) coordinate
system. In addition, the latitude distribution can be interpreted as
having two components : a uniformly distributed component and one
having a distribution similar to that of active regions, occurring
mostly within ±30° of the equator.
---------------------------------------------------------
Title: Comparison of Skylab X-Ray and Ground-Based Helium Observations
Authors: Harvey, J. W.; Krieger, A. S.; Davis, J. M.; Timothy, A. F.;
Vaiana, G. S.
1975BAAS....7..358H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Simultaneous X-ray Spectra and X-ray Images of an Active Region
Authors: Gerassimenko, M.; Davis, J. M.; Chase, R. C.; Krieger, A. S.;
Silk, J. K.; Vaiana, G. S.
1975BAAS....7..347G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Time Changes in the Structure and Spectrum of an X-ray Flare
Authors: Silk, J. K.; Kahler, S. W.; Krieger, A. S.; Vaiana, G. S.
1975BAAS....7..355S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Coronal Source of Recurrent, High Speed Solar Wind Streams
Authors: Nolte, J.; Krieger, A. S.; Webb, D.; Vaiana, G. S.; Lazarus,
A. J.; Sullivan, J.; Timothy, A. F.
1975BAAS....7..358N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: General Properties of Soft X-ray Flare Images
Authors: Kahler, S. W.; Krieger, A. S.; Vaiana, G. S.
1975BAAS....7..355K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Location of the Site of Energy Release in an X-ray
Sub-flare
Authors: Petrasso, R. D.; Kahler, S. W.; Krieger, A. S.; Silk, J. K.;
Vaiana, G. S.
1975BAAS....7..352P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Temperature and Density Measurements of Coronal Loops
Authors: Chase, R. C.; Golub, L.; Krieger, A.; Silk, J. K.; Vaiana,
G. S.; Zombeck, M.; Timothy, A. F.
1975BAAS....7..346C Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Temporal and Spatial Properties of Coronal Bright Points
Authors: Golub, L.; Krieger, A.; Simon, R.; Vaiana, G.; Timothy, A. F.
1975BAAS....7Q.350G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Studies of the Dynamic Structure and Spectra of Solar X-Ray
Flares
Authors: Kaahler, S. W.; Krieger, A. S.; Silk, J. K.; Simon, R. W.;
Timothy, A. F.; Vaiana, G. S.
1975IAUS...68..185K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The long term development of the large scale corona and the
evolution of coronal holes
Authors: Timothy, A. F.; Gerassimenko, M.; Golub, L.; Krieger, A. S.;
Petrasso, R.; Vaiana, G. S.
1975xtcg.work...93T Altcode:
The evolution of coronal holes and the typical coronal configurations
that result in the formation of a hole are investigated using
results obtained by the X-ray telescope experiment on the Apollo
Telescope Mount. The evolution of one particular hole is traced,
the magnetic-field configuration associated with it is examined,
and its rotational characteristics between 20 deg S and 50 deg N are
analyzed. It is found that coronal holes form in bands of unipolar
magnetic field bounded by areas of opposite polarity when patterns of
emerging active-region flux produce the appropriate large-scale field
pattern. The holes are shown to have lifetime in excess of five solar
rotations and to die when the large-scale field pattern is distorted. It
is suggested that the observed rigid rotation of a hole, which is in
contrast to the differential rotation of the field associated with it,
may be explained by the fact that the hole is a source of a recurrent
high-velocity solar-wind stream.
---------------------------------------------------------
Title: Time Variations of Solar X-Ray Bright Points
Authors: Golub, L.; Kriegher, A. S.; Silk, J. K.; Timothy, A. F.;
Vaiana, G. S.
1975IAUS...68...23G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Skylab and the ASE X-ray telescope experiment - A new view
of the X-ray corona
Authors: Vaiana, G. S.; Chase, R.; Davis, J.; Gerassimenko, M.; Golub,
L.; Kahler, S.; Krieger, A. S.; Petrasso, R.; Silk, J. K.; Simon, R.
1975xtcg.work....3V Altcode:
A broad description of the Skylab X-ray telescope experiment is
given. The design and development of the S-054 X-ray telescope and
the X-ray imaging system are reviewed, and the primary telescope is
described along with its spectral characteristics, imaging optics,
camera, and film. The technique for determining the temperature and
emission integral of the coronal plasma from X-ray photographs is
outlined. Data are presented on the long-term variation of large-scale
coronal structures, the evolution of active regions, and observations
of coronal holes and bright points. It is shown that active regions
undergo short-term changes related to changes in the photospheric
magnetic fields as well as long-term changes in large-scale structure,
that the decay of active regions probably contributes to the formation
of coronal holes, and that bright points are a distinct class of flaring
active regions which seem to be distributed uniformly over the sun.
---------------------------------------------------------
Title: Comparison of SKYLAB X-ray and ground-based helium observations
Authors: Harvey, J.; Krieger, A. S.; Timothy, A. F.; Vaiana, G. S.
1975xtcg.work...50H Altcode:
Comparison of soft X-ray images of the sun obtained with the
S-054 experiment aboard Skylab and photoelectric helium D3
(5876 A) spectroheliograms obtained at Kitt Peak yields a good
agreement. Distinctively coronal features such as coronal holes
and bright points are identified in helium pictures with sufficient
confidence that ground-based helium observations should be valuable for
the study of the evolution of these primarily coronal features. The
reason low-temperature helium lines show coronal structures is
probably due to strong radiative control of the excited levels by
coronal radiation at wavelengths of less than 504 A.
---------------------------------------------------------
Title: Time Variations in Coronal Active Regions
Authors: Krieger, A. S.; Chase, R. C.; Gerassimenko, M.; Kahler,
S. W.; Timothy, A. F.; Vaiana, G. S.
1975IAUS...68..103K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Objective grating studies of X-ray flare spectra
Authors: Silk, J. K.; Kahler, S.; Krieger, A. S.; Timothy, A. F.;
Vaiana, G. S.
1975xtcg.work..143S Altcode:
The objective-grating mode of the X-ray telescope on Skylab provides
dispersed and zero-order images of coronal features which can be
employed to determine the temperature of the emitting plasma. Variations
of temperature with time and position in the flaring region are
studied. The M2 flare of August 9, 1973, is used to illustrate the
data obtained with the objective grating. Preliminary analysis of the
data suggests a two-temperature model for the flare.
---------------------------------------------------------
Title: X-ray and radio emission for the June 15, 1973 solar flare.
Authors: Pallavicini, R.; Kahler, S.; Krieger, A. S.; Silk, J. K.;
Vaiana, G. S.
1975MmArc.104..157P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Objective grating studies of X-ray flare spectra.
Authors: Silk, J. K.; Kahler, S.; Krieger, A. S.; Timothy, A. F.;
Vaiana, G. S.
1975MmArc.104..143S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Skylab and the ASE X-ray telescope experiment: a new view of
the X-ray corona.
Authors: Vaiana, G. S.; Chase, R.; Davis, J.; Gerassimenko, M.;
Golub, L.; Kahler, S.; Krieger, A. S.; Petrasso, R.; Silk, J. K.;
Simon, R.; Timothy, A. F.; Zombeck, M.; Webb, D.
1975MmArc.104....3V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray and radio emission for the June 15, 1973 solar flare
Authors: Pallavicini, R.; Kahler, S.; Krieger, A. S.; Silk, J. K.;
Vaiana, G. S.
1975xtcg.work..157P Altcode:
Results are summarized for observations of a solar flare by the
grazing-incidence X-ray telescope on the Apollo Telescope Mount
which were made with high spatial and temporal resolution. The
X-ray observations are compared with ground-based radio, optical,
and magnetogram observations as well as with X-ray data from other
satellite instruments. The temporal development of the flare as shown
by X-ray pictures is outlined, and an X-ray picture taken at the
flare peak is compared with a magnetogram obtained at the end of the
flare and an H-alpha picture taken during its decay. Other data used
in the analysis include satellite measurements of hard and soft X-ray
fluxes, and radio fluxes measured at several frequencies between 245
and 15,400 MHz. The volume, temperature, density, and emission measure
of the flare region are determined along with the temporal evolution
of these parameters. It is shown that the soft X-ray and microwave
emissions originated from a thermal plasma whose temperature and
density increased during the rising part of the event and decreased
during the decay phase. It is suggested that plasma heating was due
to collisional losses of nonthermal electrons accelerated during the
rising phase and that conductive and radiative cooling contributed
equally to the flare's decay.
---------------------------------------------------------
Title: Coronal X-ray structures and coronal magnetic fields
Authors: Poletto, G.; Timothy, A. F.; Krieger, A. S.; Vaiana, G. S.
1975xtcg.work..175P Altcode:
Coronal X-ray structures are compared with corresponding current-free
coronal magnetic fields, particularly with regard to compact structures
where potential fields are expected to be strong enough to correspond
to energy densities well above the plasma densities. The comparison
is conducted using X-ray images of several active regions obtained
by five different days and ground-based magnetograms for the same
days. Images of the active regions are superposed on extrapolated
potential field lines, and qualitative agreement is found between
the two configurations. It is noted that this agreement is limited
to compact structures and is especially apparent in the absence of
flare activity or large structural changes. Since the extrapolated
potential fields seem to represent well the general topology outlined
by the X-ray structures, it is concluded that current fields make a
minor contribution to the total coronal field.
---------------------------------------------------------
Title: Models of coronal active regions
Authors: Landini, M.; Monsignori Fossi, B. C.; Krieger, A. S.; Vaiana,
G. S.
1975xtcg.work...59L Altcode:
The intensity distribution of a coronal active region observed by means
of an X-ray telescope similar to that of the Apollo Telescope Mount is
simulated, assuming that temperature and pressure are radially symmetric
and follow a Gaussian distribution. A simple technique is described
for taking account of the instrumental function and evaluating the
temperature and pressure comparing two pictures taken with different
filters. Some preliminary results are presented, and an evaluation of
the magnetic field necessary to confine the structure is given.
---------------------------------------------------------
Title: Comparison of Skylab X-ray and Ground-Based Helium Observations
Authors: Harvey, J. W.; Krieger, A. S.; Timothy, A. F.; Vaiana, G. S.
1975OMOAA.104...50H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal X-ray structures and coronal magnetic fields.
Authors: Poletto, G.; Timothy, A. F.; Krieger, A. S.; Vaiana, G. S.
1975MmArc.104..175P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Comparison of Skylab X-ray and ground-based helium
observations.
Authors: Harvey, J.; Krieger, A. S.; Timothy, A. F.; Vaiana, G. S.
1975MmArc.104...50H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Models of coronal active region.
Authors: Landini, M.; Monsignori Fossi, B. C.; Krieger, A. S.; Vaiana,
G. S.
1975MmArc.104...59L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The long term development of the large scale corona and the
evolution of coronal holes.
Authors: Timothy, A. F.; Gerassimenko, M.; Golub, L.; Krieger, A. S.;
Petrasso, R.; Vaiana, G. S.
1975MmArc.104...93T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Soft X-ray imaging on photographic film.
Authors: Haggerty, R.; Simon, R.; Golub, L.; Silk, J. K.; Timothy,
A. F.; Krieger, A. S.; Vaiana, G. S.
1975AASPB..10....8H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar X-Ray Bright Points
Authors: Golub, L.; Krieger, A. S.; Silk, J. K.; Timothy, A. F.;
Vaiana, G. S.
1974ApJ...189L..93G Altcode:
Preliminary analysis of photographs from the 8-054 X-ray telescope
aboard Skylab has shown that bright points have a statistical
distribution of lifetimes with a mean of eight hours. The lifetime
of a bright point is approximately proportional to its maximum area,
which is typically 2 X 108 km2. A small bright core generally develops
during the middle part of the bright-point lifetime with area 10
km2. A small fraction of bright points are seen to increase their
surface brightness by several orders of magnitude on a time scale of
minutes. These "flares" occur at all latitudes from the equator to the
poles. To first order, bright points are uniformly distributed across
the solar surface. An estimated 1500 X-ray bright points emerge per
day, possibly bringing more new magnetic flux to the surface than is
contributed by the major active regions. Sukiect headings: X-rays, solar
---------------------------------------------------------
Title: Temporal Behavior of the Coronal Structure of Active Regions
Authors: Krieger, A.; Golub, L.; Silk, J. K.; Timothy, A.; Vaiana,
G.; Webb, D.
1974BAAS....6..290K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An X-ray flare from Skylab: results and interpretations.
Authors: Vaiana, G. S.; Kahler, S.; Krieger, A.; Pallavicini, R.;
Silk, J. K.
1974BAAS....6..265V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Extrapolation of Photospheric Magnetic Fields into the Corona
Authors: Poletto, G.; Krieger, A.; Silk, J. K.; Timothy, A.; Vaiana, G.
1974BAAS....6..292P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An Experimental Model of Solar Flares in the Corona
Authors: Silk, J. K.; Kahler, S.; Krieger, A.; Timothy, A.; Vaiana,
G.; Pallavicini, R.
1974BAAS....6T.294S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal Loop Structures Associated with Active Filaments
Authors: Davis, J.; Chase, R.; Krieger, A.; Simon, R.; Timothy, A.;
Vaiana, G.
1974BAAS....6Q.286D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The evolution of the coronal structure of an active region.
Authors: Krieger, A.; Gerassimenko, M.; Petrasso, R.; Timothy, A.;
Vaiana, G.
1974BAAS....6..265K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal Bright Points
Authors: Golub, L.; Chase, R.; Krieger, A.; Silk, J. K.; Timothy,
A.; Vaiana, G.
1974BAAS....6R.287G Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar X-ray bright points.
Authors: Timothy, A.; Golub, L.; Krieger, A.; Silk, J. K.; Vaiana, G.
1974BAAS....6..265T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal loops associated with active filaments.
Authors: Davis, J.; Chase, R.; Krieger, A.; Timothy, A.; Vaiana, G.
1974BAAS....6..265D Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Temperature and Density of the Coronal Portion of an Active
Region
Authors: Vaiana, G.; Gerassimenko, M.; Krieger, A.; Timothy, A.;
Landini, M.; Monsignori-Fossi, B. C.
1974BAAS....6Q.296V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Evolution of Coronal Holes
Authors: Timothy, A.; Krieger, A.; Petrasso, R.; Silk, J. K.;
Vaiana, G.
1974BAAS....6S.295T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The X-ray spectrographic telescope
Authors: Vaiana, G. S.; Krieger, A. S.; Petrasso, R.; Silk, J. K.;
Timothy, A. F.
1974SPIE...44..185V Altcode:
The S-054 X-ray telescope, which operated successfully throughout
the eight-month Skylab mission, is a grazing incidence instrument
with a spatial resolution of the order of 2 arc sec on axis. The
total wavelength range observed by the instrument is 2 to 60 A. Crude
spectral resolution within this range is achieved by means of a series
of six X-ray filter materials. A spectrographic mode of operation,
employing an objective grating, is used to obtain spectra of flare
events and selected coronal features.
---------------------------------------------------------
Title: Solar X-Ray Emission
Authors: Vaiana, Giuseppe; Tucker, Wallace H.
1974ASSL...43..169V Altcode: 1974xras.conf..169V
No abstract at ADS
---------------------------------------------------------
Title: X-ray and Radio Emission for the June 1. 1973 Solar Flare
Authors: Pallavicini, R.; Kahler, S.; Krieger, A. S.; Silk, J. K.;
Vaiana, G. S.
1974OMOAA.104..157P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Dynamic events in the X-ray corona. (A progress report from
the AS&E X-ray telescope on Skylab).
Authors: Vaiana, G. S.; Krieger, A. S.; Silk, J. K.; Timothy, A. F.;
Chase, R. C.; Davis, J.; Gerassimenko, M.; Golub, L.; Kahler, S.;
Petrasso, R.
1974IAUS...57..501V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Coronal X-ray Structures and Coronal Magnetic Fields
Authors: Poletto, G.; Timothy, A. F.; Krieger, A. S.; Vaiana, G. S.
1974OMOAA.104..175P Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Skylab and the ASE X-ray Telescope Experiment: A New View of
the X-ray Corona
Authors: Vaiana, G. S.; et al.
1974OMOAA.104....3V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The X-ray spectrographic telescope.
Authors: Vaiana, G. S.; Krieger, A. S.; Petrasso, R.; Silk, J. K.;
Timothy, A. F.
1974inas.conf..185V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Long Term Development of the Large Scale Corona and the
Evolution of Coronal Holes
Authors: Timothy, A. F.; Gerassimenko, M.; Golub, L.; Krieger, A. S.;
Petrasso, R.; Vaiana, G. S.
1974OMOAA.104...93T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray observations of coronal holes and their relation to
high velocity solar wind streams.
Authors: Krieger, A. S.; Timothy, A. F.; Vaiana, G. S.; Lazarus,
A. J.; Sullivan, J. D.
1974sowi.conf..132K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Methods of imaging X-Ray astronomy and the X-Ray
spectroheliograph on ATM
Authors: Vaiana, G.
1974spop.conf..295V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The AS&E X-ray telescope on Skylab.
Authors: Vaiana, G. S.; Krieger, A. S.; Petrasso, R. D.; Silk, K.
1974JOSA...64..524V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-Ray Observations of Characteristic Structures and Time
Variations from the Solar Corona: Preliminary Results from SKYLAB
Authors: Vaiana, G. S.; Davis, J. M.; Giacconi, R.; Krieger, A. S.;
Silk, J. K.; Timothy, A. F.; Zombeck, M.
1973ApJ...185L..47V Altcode:
Examples taken from the 5-054 X-ray telescope observations made
during the first Skylab mission show the hot coronal plasma tracing
the configuration of the magnetic fields. The high spectral resolution
and sensitivity of the instrument has enabled the following two facts
to be more firmly established: (a) that the "quiet homogeneous corona"
is in fact highly structured and that the structures observed appear
to be the results of dispersed active region magnetic fields; and (b)
that numerous bright points are distributed randomly on the disk. Their
presence at high latitudes may play a role in solar cycle models. In
addition, the capability of Skylab for studying time evolution has
enabled the restructuring of coronal features to be seen at times
of high activity, indicating a restructuring of the coronal magnetic
fields. Subject headings:corona, solar - X-rays, solar
---------------------------------------------------------
Title: Identification and Analysis of Structures in the Corona from
X-Ray Photography
Authors: Vaiana, G. S.; Krieger, A. S.; Timothy, A. F.
1973SoPh...32...81V Altcode:
This paper summarizes the results of a program of rocket observations
of the solar corona with grazing incidence X-ray telescopes. A series
of five flights of a Kanigen-surfaced telescope with a few arc seconds
resolution, together with the first flight of a newer telescope have
resulted in the identification of six classes of coronal structures
observable in the X-ray photographs. These are: active regions,
active region interconnections, large loop structures associated with
unipolar magnetic regions, coronal holes, coronal bright points, and
the structures surrounding filament cavities. Two solar flares have
been observed. The methods involved in deriving coronal temperature
and density information from X-ray photographs are described and
the analysis of a bright active region (McMath plage 11035) observed
at the west limb on November 24, 1970 is presented as an example of
these techniques.
---------------------------------------------------------
Title: A View of the X-Ray Corona.
Authors: Vaiana, G.
1973BAAS....5..419V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: A High Resolution Imaging Rocket X-Ray Telescope for Celestial
Observations.
Authors: Kellogg, E.; Murray, S.; van Speybroeck, L.; Vaiana, G.;
Giacconi, R.; Gursky, H.
1973BAAS....5..342K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Large Scale Coronal X ray Structures
Authors: Krieger, A.; Barrett, T.; Timothy, A. F.; Vaiana, G. S.;
van Speybroeck, L.
1972BAAS....4..386K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Structure of the X ray Corona Surrounding Quiescent
Filaments
Authors: Timothy, A. F.; Barrett, T.; Krieger, A.; Vaiana, G. S.;
van Speybroeck, L.
1972BAAS....4T.393T Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Results from OSO-IV: the Long Term Behavior of X-Ray Emitting
Regions
Authors: Krieger, A.; Paolini, F.; Vaiana, G. S.; Webb, D.
1972SoPh...22..150K Altcode:
A grazing incidence X-ray telescope on board the OSO-IV spacecraft
obtained images of the Sun in the 2.5 to 12 Å waveband nearly
continuously from 27 October 1967 to 12 May 1968. The instrument had
sufficient spatial resolution (one and four arc minutes) and temporal
resolution (5 to 20 min) to estimate the spatial characteristics
of X-ray emitting regions and to monitor the temporal behavior of
individual active regions. Variations in the absence of flares of as
much as a factor of 10 in the X-ray output of individual regions were
observed, with typical durations ranging from several hours to several
days. The X-ray time variations are related to observations at optical
and radio wavelengths. The results are interpreted under the assumption
that the X-ray time variations are caused by temperature changes in
the coronal portions of active regions. The contribution of radiative
losses to the energy budget of the coronal active region is estimated.
---------------------------------------------------------
Title: The Structure of Coronal X-ray Features.
Authors: Krieger, A. S.; Timothy, A. F.; Vaiana, G. S.
1971BAAS....3..439K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The X-Ray Corona and the Photospheric Magnetic Field
Authors: Krieger, A. S.; Vaiana, G. S.; van Speybroeck, L. P.
1971IAUS...43..397K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray Photographs of the Sun on March 7, 1970
Authors: van Speybroeck, L. P.; Krieger, A. S.; Vaiana, G. S.
1970Natur.227..818V Altcode:
The Sun was photographed from an Aerobee rocket by means of equipment
responding to the wavelength interval 3-60 Å, revealing interesting
relationships between structures in the corona.
---------------------------------------------------------
Title: Analysis of High-Resolution x-Ray Photographs. I. An Importance
1N Flare
Authors: Vaiana, G. S.; Zehnpfennig, T.
1969BAAS....1Q.294V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Results from the AS and E x-Ray Telescope on OSO-IV
Authors: Krieger, A. S.; Vaiana, G. S.
1969BAAS....1T.283K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Grazing-Incidence Telescopes for X-Ray Astronomy
Authors: Giacconi, R.; Reidy, W. P.; Vaiana, G. S.; van Speybroeck,
L. P.; Zehnpfennig, T. F.
1969SSRv....9....3G Altcode:
We review the progress made at our laboratory over the past several
years in developing grazing-incidence imaging X-ray optics. Mirrors,
detection systems and dispersion techniques are discussed and
experimental results are given. We discuss the application of two
telescope systems to a number of experimental observations in X-ray
astronomy.
---------------------------------------------------------
Title: Observations of an x-ray flare: Spatial distribution and
physical parameters
Authors: Vaiana, G. S.; Giacconi, R.
1969pia..conf...91V Altcode:
No abstract at ADS
---------------------------------------------------------
Title: X-ray Structures of the Sun during the Importance 1N Flare
of 8 June 1968
Authors: Vaiana, G. S.; Reidy, W. P.; Zehnpfennig, T.; van Speybroeck,
L.; Giacconi, R.
1968Sci...161..564V Altcode:
High-resolution solar x-ray images were obtained with a rocket-borne
grazing incidence telescope. The x-ray flare is large in extent, has
fine structure, and follows a neutral magnetic line. X-ray emitting
coronal links interconnect active regions. The general coronal emission
at the limb and several faint regions on the disc are observed.
---------------------------------------------------------
Title: Preliminary Results from the AS+/-E X-Ray Spectroheliograph
on OSO-IV.
Authors: Paolini, F. R.; Giacconi, R.; Manley, O.; Reidy, W. P.;
Vaiana, G. S.; Zehnpfennig, T.
1968AJS....73...73P Altcode:
The ASE x-ray spectroheliograph on OSO-I V uses image-forming grazing
optics in a system which enables sustained observation of the sun with
an angular resolution of 1 min of arc. This makes possible, for the
first time, observations on the evolution of flares in x-rays with a
resolution commensurate with the optical size of a flare. Data on six
flares which occurred on 27, 28, 29 October and 16 November 1967 are
presented. The data include maps of the flares in various phases of
progress, curves of x-ray intensity and spectral hardness as functions
of time, and x-ray brightness profiles along lines of scan through
sites of maximum flare brightness. We observe that x-rays are produced
about 4X 10~ km above the photosphere; that sizes in x radiation
tend to correlate with sizes in Ha; that x-ray spectra tend to soften
as the flares decay; and that flares are observable in x rays after
they are no longer so in Ha. We also present data, including maps,
on observations of some dozen x-ray plages for the period 25 October
to 3 December 1967, mostly obtained in an instrument mode having 4 min
of arc resolution. We find that x-ray emitting regions of plages, too,
are about 4 X 10~ km above the photosphere; that plages are of the
order of min of arc in diameter; and that x-ray brightness of plages
tend to correlate with 9.1 cm radiation brightness temperatures.
---------------------------------------------------------
Title: The ATM Soft X-Ray Slitless Spectrograph.
Authors: Zehnpfennig, T.; Reidy, W.; Vaiana, G.; Wiza, J.
1968AJS....73...85Z Altcode:
The design of a soft x-ray slitless spectrograph to be flown on the
first Apollo telescope mount is presented. The spectrograph consists of
an x-ray transmission grating and an image-forming x-ray telescope. The
transmission gratings investigated to date consist of thin film plastic
replica gratings shadowed with gold. Grating constants of 0.8 microns
are feasible; grating constants as small as 0.35 microns have been used,
but at low efficiency. The x-ray telescope consists of two con focal
mirror systems working at grazing incidence. The combined collecting
area is 42 cm2 the focal length is 213 cm. Laboratory tests which
demonstrate an angular resolution of better ~han 5 sec of arc and a
spectral resolution of 0.2 A at 7 A will be discussed.
---------------------------------------------------------
Title: Study of X-Ray Images of the Sun at Solar Minimum
Authors: Reidy, W. P.; Vaiana, G. S.; Zehnpfennig, T.; Giacconi, R.
1968ApJ...151..333R Altcode:
A set of solar X-ray photographs obtained using grazing-incidence
optics at solar minimum is analyzed. The spatial distribution of the
X-ray radiation above 20 A is shown to be consistent with models of the
general coronal emission by Elwert A model for the X-ray emission from
a plage is constructed by use of the experimental data on temperature,
volume, and density of the emitting regions The results obtained in
X-rays are compared to the 9.1 cm spectroheliogram, the Ha spectrohelio-
gram, and the magnetogram of the Sun obtained simultaneously by ground
observation. It is shown that the ionized plasma which produces the
observed X-ray emission also accounts for the observed radio emission
at 9.1 cm. Thus, we conclude that the correlation between enhanced
radio emission and X-rays from this plage region is due to a common
physical process which is responsible for both. The lifetime and the
mode of confinement of such an ionized plasma are discussed. It is
shown that energy injection must occur during the life of the plage
to account for the observed persistence. It is also shown that the
observed magnetic field would be capable of containing the plasma if
it extends to the coronal heights in which the plasma is maintained
