Author name code: michalitsanos
ADS astronomy entries on 2022-09-14
author:"Michalitsanos, Andrew G."
------------------------------------------------------------------------
Title: Supernova 1987A in the Large Magellanic Cloud
Authors: Kafatos, Minas; Michalitsianos, Andrew G.
Bibcode: 2006supe.book.....K
Altcode:
Foreword; Acknowledgements; Workshop participants; 1. Images
and spectrograms of Sanduleak - 69º202, the SN 1987a progenitor
N. R. Walborn; 2. The progenitor of SN 1987A G. Sonneborn; 3. Another
supernova with a blue progenitor C. M. Gaskell and W. C. Keel;
4. Optical and infrared observations of SN 1987A from Cerro Tololo
Inter-American Observatory M. M. Phillips; 5. SN 1987A: observational
results obtained at ESO I. J. Danziger, P. Bouchet, R. A. E. Fosbury,
C. Gouiffes, L. B. Lucy, A. F. M. Moorwood, E. Oliva and F. Rufener;
6. Observations of SN 1987A at the South African Astronomical
Observatory (SAAO) M. W. Feast; 7. Observations of SN 1987A at the
Anglo-Australian Telescope W. J. Couch; 8. Linear polarimetric study
of SN 1987A A. Clocchiatti, M. Méndez, O. Benvenuto, C. Feinstein,
H. Marraco, B. García and N. Morrell; 9. Infrared spectroscopy of
SN 1987A from the NASA Kuiper Airborne Observatory H. P. Larson,
S. Drapatz, M. J. Mumma and H. A. Weaver; 10. Radio observations of
SN 1987A N. Bartel et al.; 11. Ultraviolet observations of SN 1987A:
clues to mass loss R. P. Kirshner; 12. On the energetics of SN 1987A
N. Panagia; 13. On the nature and apparent uniqueness of SN 1987A
A. V. Filippenko; 14. A comparison of the SN 1987A light curve with
other type II supernovae, and the detectability of similar supernovae
M. F. Schmitz and C. M. Gaskell; 15. P-Cygni features and photospheric
velocities L. Bildsten and J. C. L. Wang; 16. The Neutrino burst
from SN 1987A detected in the Mont Blanc LSD experiment M. Aglietta
et al.; 17. Toward observational neutrino astrophysics M. Koshiba;
18. The discovery of neutrinos from SN 1987A with the IMB detector
J. Matthews; 19. Peering into the abyss: the neutrinos from SN 1987A
A. Burrows; 20. Phenomenological analysis of neutrino emission from
SN 1987A J. N. Bahcall, D. N. Spergel and W. H. Press; 21. Mass
determination of neutrinos H. Y. Chiu; 22. Neutrino transport in a
type II supernova D. C. Ellison, P. M. Giovanoni and S. W. Bruenn;
23. Neutrino masses from SN 1987A J. Franklin; 24. Supernova neutrinos
and their oscillations T. K. Kuo and J. T. Pantaleone; 25. Neutrinos
from SN 1987A and cooling of the nascent neutron star D. Q. Lamb,
F. Melia and T. J. Loredo; 26. Neutrino Energetics of SN 1987A
J. M. Lattimer and A. Yahil; 27. Neutrino emission from cooling neutron
stars E. S. Myra, J. M. Lattimer and A. Yahil; 28. Statistical analysis
of the time structure of the neutrinos from SN 1987A P. J. Schinder
and S. A. Bludman; 29. Neutrino properties from observations
of SN 1987A A. Dar; 30. SN 1987A and companion C. Papaliolios,
M. Karovska, P. Nisenson, and C. Standley; 31. Supernovae light echoes
B. E. Schaefer; 32. A real light echo: Nova Persei 1901 J. E. Felten;
33. IR speckle- interferometry of SN 1987A A. A. Chalabaev, C. Perrier
and J. M. Mariotti; 34. Infrared opportunities for Supernova 1987A
E. Dwek; 35. The UV interstellar spectrum and environment of SN 1987A
F. C. Bruhweiler; 36. The interstellar spectrum of SN 1987A in the
ultraviolet J. C. Blades, J. M. Wheatley, N. Panagia, M. Grewing,
M. Pettini and W. Wamsteker; 37. The structure and spectrum of SN
1987A J. C. Wheeler, R. P. Harkness, and Z. Barkat; 38. Supernova
1987A: constraints on the theoretical model K. Nomoto and T. Shigeyama;
39. Supernova 1987A: a model and its predictions S. E. Woosley; 40. SN
1987A: circumstellar and interstellar interaction R. A. Chevalier;
41. Theoretical models of Supernova 1987A W. D. Arnett; 42. Evolution of
the stellar progenitor of Supernova 1987A J. W. Truran and A. Weiss;
43.Modelling the atmosphere of SN 1987A L. B. Lucy; 44. SN 1987A:
a stripped asymptotic- branch giant in a binary system P. C. Joss,
Ph. Podsiadlowski, J. J. L. Hsu and S. Rappaport; 45. Pulsar formation
and the fall back mass fraction S. A. Colgate; 46. An unusual hard
X-ray source in the region of SN 19
Title: Ultraviolet Spectral Variability and the Lyα Forest in the
Lensed Quasar Q0957+561
Authors: Dolan, J. F.; Michalitsianos, A. G.; Nguyen, Q. T.; Hill,
R. J.
Bibcode: 2000ApJ...539..111D
Altcode:
Far-ultraviolet spectra of the gravitational lens components
Q0957+561A, B were obtained with the Hubble Space Telescope Faint
Object Spectrograph (FOS) at five equally spaced epochs, one every
2 weeks. We confirm the flux variability of the quasar's Lyα and O
VI λ1037 emission lines in IUE spectra reported in earlier work of
Dolan et al. The fluxes in these lines vary on a timescale of weeks
in the observer's rest frame, independently of each other and of
the surrounding continuum. The individual spectra of each image were
co-added to investigate the properties of the Lyα forest along the
two lines of sight to the quasar. Absorption lines having equivalent
width Wλ>=0.3 Å in the observer's frame not previously
identified by Michalitsianos et al. as interstellar lines, metal lines,
or higher order Lyman lines were taken to be Lyα forest lines. The
existence of each line in this consistently selected set was then
verified by its presence in two archival FOS spectra with ~1.5 times
higher signal to noise than our co-added spectra. Lyα forest lines
with Wλ>=0.3 Å appear at 41 distinct wavelengths in
the spectra of the two images. One absorption line in the spectrum of
image A has no counterpart in the spectrum of image B, and one line in
image B has no counterpart in image A. Based on the separation of the
lines of sight over the redshift range searched for Lyα forest lines,
the density of the absorbing clouds in the direction of Q0957+561 must
change significantly over a distance R=160+120-70
h-150 kpc in the simplified model where the
absorbers are treated as spherical clouds and the characteristic
dimension, R, is the radius. (We adopt H0=50 h50
km s-1 Mpc-1, q0=1/2, and Λ=0
throughout this paper.) The 95% confidence interval on R extends from
50 to 950 h-150 kpc. We show in the Appendix that
the fraction of Lyα forest lines that appear in only one spectrum can
be expressed as a rapidly converging power series in 1/r, where r the
ratio of the radius of the cloud to the separation of the two lines of
sight at the redshift of the cloud. This power series can be rewritten
to give r in terms of the fraction of Lyα forest wavelengths that
appear in the spectrum of only one image. A simple linear approximation
to the solution that everywhere agrees with the power series solution
to better than 0.8% for r>=2 is derived in the Appendix. Based in
part on observations with the Hubble Space Telescope obtained at the
Space Telescope Science Institute, which is operated by AURA, Inc.,
under NASA contract NAS 5-26555.
Title: Overview of the Far Ultraviolet Spectroscopic Explorer Mission
Authors: Moos, H. W.; Cash, W. C.; Cowie, L. L.; Davidsen, A. F.;
Dupree, A. K.; Feldman, P. D.; Friedman, S. D.; Green, J. C.; Green,
R. F.; Gry, C.; Hutchings, J. B.; Jenkins, E. B.; Linsky, J. L.;
Malina, R. F.; Michalitsianos, A. G.; Savage, B. D.; Shull, J. M.;
Siegmund, O. H. W.; Snow, T. P.; Sonneborn, G.; Vidal-Madjar, A.;
Willis, A. J.; Woodgate, B. E.; York, D. G.; Ake, T. B.; Andersson,
B. -G.; Andrews, J. P.; Barkhouser, R. H.; Bianchi, L.; Blair,
W. P.; Brownsberger, K. R.; Cha, A. N.; Chayer, P.; Conard, S. J.;
Fullerton, A. W.; Gaines, G. A.; Grange, R.; Gummin, M. A.; Hebrard,
G.; Kriss, G. A.; Kruk, J. W.; Mark, D.; McCarthy, D. K.; Morbey,
C. L.; Murowinski, R.; Murphy, E. M.; Oegerle, W. R.; Ohl, R. G.;
Oliveira, C.; Osterman, S. N.; Sahnow, D. J.; Saisse, M.; Sembach,
K. R.; Weaver, H. A.; Welsh, B. Y.; Wilkinson, E.; Zheng, W.
Bibcode: 2000ApJ...538L...1M
Altcode: 2000astro.ph..5529M
The Far Ultraviolet Spectroscopic Explorer satellite observes light
in the far-ultraviolet spectral region, 905-1187 Å, with a high
spectral resolution. The instrument consists of four co-aligned
prime-focus telescopes and Rowland spectrographs with microchannel
plate detectors. Two of the telescope channels use Al:LiF coatings
for optimum reflectivity between approximately 1000 and 1187 Å,
and the other two channels use SiC coatings for optimized throughput
between 905 and 1105 Å. The gratings are holographically ruled to
correct largely for astigmatism and to minimize scattered light. The
microchannel plate detectors have KBr photocathodes and use photon
counting to achieve good quantum efficiency with low background
signal. The sensitivity is sufficient to examine reddened lines
of sight within the Milky Way and also sufficient to use as active
galactic nuclei and QSOs for absorption-line studies of both Milky
Way and extragalactic gas clouds. This spectral region contains a
number of key scientific diagnostics, including O VI, H I, D I, and
the strong electronic transitions of H2 and HD.
Title: The Characteristic Dimension of Lyman-α Forest Clouds toward
Q0957+561
Authors: Dolan, J. F.; Michalitsianos, A. G.; Nguyen, Q. T.; Hill,
R. J.
Bibcode: 2000AAS...196.1603D
Altcode: 2000BAAS...32..694D
Far-ultraviolet spectra of the gravitational lens components Q0957+561
A and B were obtained with the Hubble Space Telescope Faint Object
Spectrograph to investigate the characteristic dimension of Ly-α
forest clouds in the direction of the quasar. If one makes the usual
assumption that the absorbing structures are spherical clouds with a
single radius, that radius can be found analytically from the ratio
of the number of Ly-α wavelengths in only one line of sight to the
number in both. A simple power series approximation to this solution,
accurate everywhere to better than 1%, will be presented. Absorption
lines in Q0957+561 having equivalent width > 0.3 Angstroms in
the observer's frame not previously identified by Michalitsianos
et al. (1997) as interstellar lines, metal lines, or higher order
Lyman lines were taken to be Ly-α forest lines. The existence of
each line in this consistently selected set was then verified by its
presence in two archival FOS spectra with ~1.5 times higher signal
to noise than our spectra. Ly-α forest lines appear at 41 distinct
wavelengths in the spectra of the two images. One absorption line in
the spectrum of image A has no counterpart in the spectrum of image B,
and one line in image B has no counterpart in image A. Based on the
separation of the lines of sight over the redshift range searched
for Ly-α forest lines, the density of the absorbing clouds in the
direction of Q0957+561 must change significantly over a radius R =
160 (+120, -70) h50-1 kpc (H0 =
50 h50 km s-1 Mpc-1, q0
= 1/2). The 95% confidence interval on R extends from (50 - 950)
h50-1 kpc. QN acknowledges support from NSF
grant AST-9417035.
Title: NASA's Goddard Space Flight Center, Laboratory for Astronomy
& Solar Physics, Greenbelt, Maryland 20771. Report for the period
1 Jul 1996 - 30 Jun 1997.
Authors: Michalitsianos, A. G.
Bibcode: 1998BAAS...30..315M
Altcode:
No abstract at ADS
Title: HUT Observations of AGN and Prospects for FUSE
Authors: Kriss, G.; Davidsen, A.; Friedman, S.; Oegerle, W.; Sembach,
K.; Green, R.; Hutchings, J.; Michalitsianos, A.; Shull, J. M.
Bibcode: 1997AAS...191.7809K
Altcode: 1997BAAS...29R1334K
During the Astro-1 and Astro-2 missions, the Hopkins Ultraviolet
Telescope (HUT) observed a total of 16 low-redshift active galactic
nuclei (AGN) in the largely unexplored wavelength region shortward of
1200 Angstroms. With this limited number of objects, we can do crude,
but interesting, statistics on the frequency of Lyman limits and warm
absorbers, correlate the strength of O VI line emission with other
emission lines and continuum bands, and correlate far-UV spectral
properties with detailed morphology as observed with the Hubble
Space Telescope. The sensitivity and long mission lifetime of the
Far Ultraviolet Spectroscopic Explorer (FUSE), scheduled for launch
in the fall of 1998, will increase the number of AGN observable in
the 900--1200 Angstroms band by a factor of ~ 5. Prime goals for FUSE
observations are the shape of the far-UV continuum, the strengths of
far-UV emission lines, and the prevalence of intrinsic absorption and
Lyman limits. FUSE observations will resolve velocity structure in
the O VI absorbing gas, and in any neutral hydrogen gas. Observations
of Seyfert 2s (in addition to NGC 1068) will search for strong line
emission in O VI, C III, and N III indicative of shock-heated gas. FUSE
will also be sensitive to any molecular gas (visible as H_2 absorption)
along the line of sight. In BAL QSOs, FUSE will be able to measure the
absorption in the EUV transitions of high ionization ions such as Si
XII. Much of the AGN science with FUSE will be obtained collaterally
from observations used to probe O VI absorption and the D/H ratio in
the Galactic halo. ``Snapshot" observations of ~ 2000 s of ~ 75 AGN
will yield spectra with 1 Angstroms resolution at a S/N of ~ 10. High
S/N, R ~ 30,000 observations will be obtained for ~ 15 of the brightest
targets. Deep integrations ( ~ 100,000 s) on some objects, required for
precision D/H measurements, will provide opportunities for monitoring
intrinsic variability since these will require 10--20 visits per target.
Title: The Detection of the λ2175 Feature and Further Analysis of
the Broad Absorption Line Profile Structure in the Gravitational
Lens Candidate UM 425
Authors: Michalitsianos, Andrew G.; Falco, Emilio E.; Muñoz, José
A.; Kazanas, Demosthenes
Bibcode: 1997ApJ...487L.117M
Altcode: 1997astro.ph..7254M
We obtained Multiple Mirror Telescope spectra of the gravitational lens
candidate UM 425 to compare the redshifts and line profile structures of
lens components A and B, which are separated by approximately 6.5". The
C IV λ1550 emission in both A and B exhibits broad absorption line
(BAL) structure, consistent with the earlier detection of BAL structure
in O VI λ1033 and N V λ1240 that was found with the International
Ultraviolet Explorer in component A. Cross-correlation of the spectra
of A and B using emission lines of C IV λ1550, He II λ1640, N
III λ1750, C III] λ1909, and Mg II λ2800 reveals a difference
in the redshifts of A and B. However, the detailed BAL profile
structure found in the spectra of A and B are strikingly similar to
one another, which suggests the system is lensed. The spectra of A
and B also indicate significant dust extinction, which we base on the
presence of the λ2175 absorption feature in the rest frame of the QSO
(zQSO=1.47). This feature is commonly seen in galactic
sources but is not generally observed in QSO spectra. Our spectra
show the presence of the λ2175 absorption feature in spectra of both
images associated with the gravitational lens UM 425. Based upon the
strong similarity of BAL profile structure exhibited by UM 425A and UM
425B, particularly the presence of the λ2175 dust absorption feature
in spectra of both images, we conclude that UM 425 is a gravitational
lens. Observations reported here were made with the Multiple Mirror
Telescope Observatory, which is operated jointly by the University of
Arizona and the Smithsonian Institution.
Title: NASA/Goddard Space Flight Center, Laboratory for Astronomy
& Solar Physics. Greenbelt, Maryland 20771. Report for the period
1 Jul 1995 - 30 Jun 1996.
Authors: Michalitsianos, A. G.
Bibcode: 1997BAAS...29..326M
Altcode:
No abstract at ADS
Title: MWC 560 - the situation not clear yet!
Authors: Tomov, T.; Mikolajewski, M.; Michalitsianos, A.; Kontizas,
E.; Dapergolas, A.; Bellas-Vellidis, I.; Jones, A.
Bibcode: 1997jena.confE.167T
Altcode:
MWC 560 attracted considerable interest in the beginning of 1990 when,
during the largest outburst observed until now, its optical and UV
spectra were dominated by wide, intensive absorption components,
blue-shifted up to 6000 km/s from their respective emission
components. Large-amplitude, rapid variations (flickering) in the
brightness of the star has always been observed afterwards. We review
here the observational behaviour of MWC 560 since 1990, using our large
collection of visual and photoelectric brightness estimations as well
as optical and UV spectral observations. It is pointed out that the
spectrum and its variations are unique. This object is a good chance
to test the applicability of the propeller/accretor model to magnetic
white dwarfs and the study of discrete mass ejection.
Title: Lyα Absorption-Line Systems in the Gravitational Lens
Q0957+5611
Authors: Michalitsianos, A. G.; Dolan, J. F.; Kazanas, D.; Bruhweiler,
F. C.; Boyd, P. T.; Hill, R. J.; Nelson, M. J.; Percival, J. W.;
van Citters, G. W.
Bibcode: 1997ApJ...474..598M
Altcode:
Far-ultraviolet spectra of the gravitational lens components
Q0957+561A and B were obtained with the Hubble Space Telescope Faint
Object Spectrograph (HST FOS). Two previously known absorption-line
systems were detected at redshifts zdamped = 1.3911 and
zLyα = 1.1249. Their prominent absorption features are
superposed on intense QSO continuum emission between λλ900-1400
in the quasar rest frame. Strong O VI λ1033, Lyα λ1216, and N V
λ1240 line emission found at the QSO redshift (zQSO = 1.41)
accompany the absorption-line systems. Lyα through Lyɛ associated
with the damped absorption system were found in both lensed components,
together with other ionic species of N I, N III, C II, C III, Si II,
Si III, and O I. We tentatively identify O VI λλ1033, 1037 absorption
at the damped Lyα redshift, which, if confirmed, would be the highest
ionization species yet detected in such systems. The equivalent widths
of the Lyman series in Q0957+561A are measurably greater compared with
absorption in 0957+561B, consistent with the narrower and shallower
depth of the Lyman series line profiles in image B. The differences
of the damped Lyman series absorption in the lensed components are
the only significant spectral characteristic that distinguishes the
far-ultraviolet spectra of 0957+561A and B. These results indicate
that the damped Lyα absorber is inhomogeneous over scale lengths of
~200 pc, which corresponds to the beam separation at the damped Lyα
redshift. However, the equivalent widths of neutral and ionized metals
in lens components A and B are correlated, which suggests these spectral
features arise in an extended region. The metal line-absorption strength
is consistent with lower column densities compared with the hydrogen
line-forming region. Thus, the small coherence length scale indicated
by the difference in hydrogen line absorption between the lensed
components suggests the geometric ray paths intercept different regions
of a galactic disk that is viewed pole-on, while the metal absorption
occurs in the halo. Based in part on observations with the Hubble
Space Telescope obtained at the Space Telescope Science Institute,
which is operated by AURA, Inc., under NASA contract NAS5-26555.
Title: Detection of O VI lambda 1033 Emission and Far-Ultraviolet
Spectral Variability in the Gravitational Lens PG 1115+080
Authors: Michalitsianos, A. G.; Oliversen, R. J.; Nichols, J.
Bibcode: 1996ApJ...461..593M
Altcode:
Far-UV spectra acquired with the International Ultraviolet Explorer
(IUE) of the gravitational lens PG 1115+080 and processed with the
NEWSIPS software show the presence of prominent O VI λ1033 resonance
line emission that is superimposed on strong far-UV continuum between
900 and 1100 A (in the z_QSO_ = 1.722 rest frame). A comparison of these
spectra with an IUE Archive spectrum of PG 1115+080 indicates that
O VI emission was not present in 1978, when the only other spectrum
covering this wavelength range was obtained, which showed only far-UV
continuum. The detection of O VI λ1033 resonance line emission in the
brightest component, PG 1115+080A, suggests a high state of ionization
in the broad emission line region (BELR). O VI emission is accompanied
by absorption in the line core and complex absorption features that
truncate the blue wing of the emission profile. The O VI absorption
trough suggests outflow that is characteristic of high- ionization
resonance lines in broad absorption line (BAL) quasars. Both the O
VI emission and BAL absorption decreased significantly in strength
relative to the continuum over a timescale of ~100 days. The equivalent
widths of absorption features within the O VI BAL trough also changed
on timescales of roughly weeks down to ~1 day. Rapid variations
associated with absorption features may reflect ionization changes
that cause column densities in the BAL outflow to fluctuate. These
results emphasize the importance of monitoring emission lines of very
high ionization (>100 eV) because the timescale over which O VI
changes occur is comparable to the gravitational delay time of ~2-3
months estimated for images in PG 1115+080.
Title: Far-UV Spectral Variability in the Gravitational Lens Candidate
UM 425
Authors: Michalitsianos, A. G.; Oliversen, R. J.; Maran, S. P.
Bibcode: 1996ApJ...458...67M
Altcode:
A comparison of recently acquired far-UV spectra with data obtained
nearly 10 months earlier indicates changes have occurred in both
absorption and ionization levels associated with Broad Absorption Line
(BAL) structure in the QSO UM 425, a candidate gravitationally lensed
system. These observations are compared with the initial discovery of
O VI and N V BAL structure previously found with the International
Ultraviolet Explorer (IUE), that suggests outflow of highly ionized
material with speeds up to ∼-12,000 km s-1 in the QSO
(z = 1.471) rest frame. Discrete absorption components in the O VI BAL
trough, occurring at velocity intervals of ∼2100 km s-1
up to the terminal speed, are also evident in the Lyman-α 1216 line
profile, which is affected by similar absorption structures within the
velocity-broadened N V λ1240 BAL trough. The greatest temporal change
in relative optical depth occurs at velocity intervals which correspond
to the BAL absorption components. Significantly, a decrease in O VI BAL
absorption over the entire BAL velocity range was accompanied by both
an increase in ionization level, indicated by enhanced 0 vi emission,
and by a strengthening of other moderate-to high-excitation emission
lines, that include S VI(1) λλ937,945, C III(1) λ977, N III(1)
λ990, and S IV(1) λλ1063,1073. These observations are relevant to
time-delay studies of UM 425 because the temporal changes observed in
intrinsic QSO ionization are small compared with the estimated delay
time between the images in the system.
Title: Detection of O VI lambda 1033 and Far-UV Spectral Variability
in Lenses UM 425 and PGlll5+080
Authors: Michalitsianos, A. G.; Oliversen, R. J.; Maran, S. P.
Bibcode: 1996ASPC...88..241M
Altcode: 1996clfu.conf..241M
No abstract at ADS
Title: Far-UV Spectral Variability In UM425; PG111S+080
Authors: Michalitsianos, A. G.; Oliversen, R. J.
Bibcode: 1996IAUS..173..257M
Altcode:
No abstract at ADS
Title: The Gravitational Lens System Q0957+561 in the Ultraviolet
Authors: Dolan, J. F.; Michalitsianos, A. G.; Thompson, R. W.; Boyd,
P. T.; Wolinski, K. G.; Bless, R. C.; Nelson, M. J.; Percival, J. W.;
Taylor, M. J.; Elliot, J. L.; van Citters, G. W.
Bibcode: 1995ApJ...442...87D
Altcode:
Photometric and polarimetric observations of both images of the
gravitationally lensed quasar Q0957 + 561 (z_em_ = 1.41) were obtained
in the UV in 1993 with the High Speed Photometer on board the Hubble
Space Telescope. The images exhibited no significant polarization
in a bandpass centered on 2770 A (observer's frame); p <= 3.2%
(2 σ upper limit) in each image. The ratio of the flux density in
image A to that in image B in late 1993 had a constant value, 1.021
+/- 0.008, in four different UV bandpasses between 1400 A and 3040 A
(observer's frame). These results are consistent with the prediction
of the gravitational lens interpretation that the photometric ratio
of the images measured simultaneously should be independent of
frequency. Reprocessed archival spectra of the two images obtained
between 1981 and 1983 by the International Ultraviolet Explorer show
that the photometric ratio of A to B varies between 0.96 and 2.0 in
the Lyα emission line, and between 0.77 and 1.8 in the O VI λ1037
emission line (quasar rest frame). The photometric ratio of A to B at
any single epoch is often significantly different in the two emission
lines. Accepting the system as a gravitational lens implies that in
the quasar the flux in the Lyα emission line can vary independently
of the flux in the O VI emission line.
Title: The Ultraviolet Spectrum of the Gravitational Lens Candidate UM
425 = QSO 1120+019: Evidence for Broad Absorption Line (BAL) Structure
Authors: Michalitsianos, A. G.; Oliversen, R. J.
Bibcode: 1995ApJ...439..599M
Altcode:
The UV line profile structure of high-ionization resonance lines found
with the International Ultraviolet Explorer (IUE) in the brightest of
four multiply imaged sources (image-A) in the `candidate gravitational
lens UM 425 = QSO 1120+019 indicates broad absorption line (BAL)
structure. The deep-broad trough associated with the O VI line extends
to velocities ~-12,000 km s^-1^, and contains discrete features that
suggest multicomponent velocity structure. This structure may include
contributions from C IV absorption from the early-type galaxy that is
believed to lens UM 425. A strong absorption feature in the blue wing
of the Lyman-α λ1216 emission line may be a Lyman-α absorption
system at a z_Lya_ = 1.437 +/- 0.003, or it may be formed by the
superposition of the broad N V λλ1238, 1242 absorption trough on the
extended blue emission wing of the QSO Lyman-α line. We obtained a
redshift of z_QSO_ = 1.471 +/- 0.003 from Lyman-α λ1215, consistent
with the redshift found by Meylan and Djorgovski in the optical. The
Lyman-α line appears unusually weak due to the presence of N V
λ1240 BAL absorption. A Lyman-limit absorption system at λ912 was
not observed in the QSO rest frame. The detection of BAL structure
in the other weaker ground-state resonance lines of N II(1) and S IV
(1) was not found, suggesting these lines are formed in a region that
is distinct from the BAL component. Detection of BAL structure in the
other fainter images in this system with HST instrumentation, similar
to structure observed here in image A, could provide evidence that UM
425 is a gravitational lens.
Title: Sanduleak's Star: A Possible Supernova Progenitor in the LMC
Authors: Michalitsianos, Andrew G.
Bibcode: 1995iue..prop.4987M
Altcode:
The pronounced enhancement of nitrogen relative to carbon emission in
the SWP 1200-2000 wavelength range of Sanduleak's Star in the Large
Magellanic Cloud is strikingly similar to the emission line spectrum
which characterizes the SCondensation in -Carinae, and provides one of
the first clear examples of an object which exhibits evidence for CNO
processing in another galaxy. Far-UV spectra obtained previously with
IUE of Sanduleak's Star (LMC Anonymous) provides compelling evidence
that the surface composition of this star contains highly processed
nuclear-synthesized material. LORES-SWP spectra obtained nearly
three years apart indicate that C IV emission is variable, while the
emission lines of N V, N IV] and N III] appear to remain essentially
constant. The progenitor stars of Type II supernova are believed to
undergo a significant phase of mass loss via a high velocity wind,
in which core-envelope mixing results in a significant overabundance
of nitrogen relative to carbon at the stellar surface, prior to core
collapse. Thus, the supernova remnant is expected to contain enhanced
nitrogen. The 14N/12C ratio of LMC Anonymous has been found previously
to lie in the range 70 to 150, which brackets the value determined for
the remnant of the recent supernova in the LMC. The similarity of LMC
Anonymous with Eta-Carinae in the far-UV provides further indications
that Sanduleak's Star could become a Type II supernova. IUE observations
are proposed to further investigate the properties of this unusual
object for possible time-dependent effects in the abundance of carbon.
Title: IUE Remote Observing System
Authors: Michalitsianos, A. G.; Pitts, R. E.; Groebner, A.; Arquilla,
R.
Bibcode: 1994AAS...185.6906M
Altcode: 1994BAAS...26.1423M
No abstract at ADS
Title: A Far-Ultraviolet Atlas of Symbiotic Stars Observed with
IUE. I. The SWP Range
Authors: Meier, S. R.; Kafatos, M.; Fahey, R. P.; Michalitsianos, A. G.
Bibcode: 1994ApJS...94..183M
Altcode:
This atlas contains sample spectra from the far-ultraviolet
observations of 32 symbiotic stars obtained with the International
Ultraviolet Explorer (IUE) satellite. In all, 394 low-resolution
spectra from the short-wavelength primary (SWP) camera covering
the range 1200-2000 A have been extracted from the IUE archive,
calibrated, and measured. Absolute line fluxes and wavelengths for
the prominent emission lines have been tabulated. Tables of both the
general properties of these symbiotics and of features specific to the
spectrum of each are included. The spectra shown are representative
of the different classes of symbiotic stars that are currently in the
IUE archive. These include known eclipsing systems and those that have
been observed in outburst (as well as quiescence).
Title: A Model for the Spectroscopic Variations of the Peculiar
Symbiotic Star MWC 560
Authors: Shore, Steven N.; Aufdenberg, Jason P.; Michalitsianos, A. G.
Bibcode: 1994AJ....108..671S
Altcode:
In this note, we show that the ultraviolet and optical spectroscopic
variability of this unique symbiotic star can be understood in terms of
a time variable collimated stellar wind with a rapid acceleration near
the source. Using the radial velocities observed during the ultraviolet
bright phase, we find that a variation in the mass loss rate of a factor
of ten can explain the ultraviolet spectral changes. The acceleration
is far faster than normally observed in radiatively driven stellar
winds and may be due to mechanical driving of the outflow from the disk.
Title: Evidence Signaling the Start of Enhanced Counterjet Flow in
the Symbiotic System R Aquarii
Authors: Michalitsianos, A. G.; Perez, M.; Kafatos, M.
Bibcode: 1994ApJ...423..441M
Altcode:
The velocity struture of strong far-UV emission lines observed in
the symbiotic variable R Aqr suggests the start of new jet activity
which will probably culminate in the appearance of a series of
intense nebular emission knots within a decade. This is indicated
by a systematic redward wavelength drift of emission lines, which
we have followed with the International Ultraviolet Explorer (IUE)
since the discovery of the brilliant northeast jet emission knots more
than 10 years ago. The C IV wavelengths 1548, 1550 resonance lines,
which previously showed a prominent blue asymmetric wing that extended
to velocities in excess -200 km/s, exhibit red wing asymmetry that
extends to speeds of approximately +200 km/s in late 1992. The C IV
line profile structure is consistent with the model proposed by Solf
(1993), who explains the appearance of the northeast jet knots in
terms of a approximately 300-500 km/s collimated wind that collides
with slower moving material expelled earlier in a nova outburst that
occurred approximately 190 yr ago. Based upon these high-resolution
UV spectra, similar emission structures should appear southwest of the
central star when the counterwind (or stream) interacts with material
in the southwest inner nebula. The apparent change in direction of
flow could result from a precessing accretion disk that alters the
projection angle of collimated flow from the disk poles. The direction
of the collimated wind may be related to the binary orbit, because the
velocity shifts associated with emission lines formed in the flow change
direction on a timescale which is comparable to the binary period.
Title: MCW 560 : an exotic interacting binary system.
Authors: Tomov, T.; Kolev, D.; Michalitsianos, A. G.; Mikolajewski,
M.; Sonneborn, S. N.; Maran, S. P.; Oliversen, R. J.; Sonneborn, G.
Bibcode: 1994MmSAI..65..167T
Altcode:
No abstract at ADS
Title: IUE Observations of a Possible Gravitational
Authors: Michalitsianos, Andrew G.
Bibcode: 1994iue..prop.4895M
Altcode:
No abstract at ADS
Title: Gravitational Lensed Quasar B1422+231
Authors: Michalitsianos, Andrew G.
Bibcode: 1994iue..prop.4904M
Altcode:
No abstract at ADS
Title: The IUE Final Archive: Conception to Completion
Authors: Nichols-Bohlin, J.; de La Peña, M.; Linsky, J.; Kondo, Y.;
Michalitsianos, A.; Ponz, D.; Talavera, A.; González-Riestra, R.;
Wamsteker, W.
Bibcode: 1994ASSL..187..715N
Altcode: 1994fsgb.book..715N
No abstract at ADS
Title: The IUE Final Archive -- Scientific Evaluation and Results
with NEWSIPS Data
Authors: de La Pena, M. D.; Nichols-Bohlin, J.; Levay, K. L.;
Michalitsianos, A.
Bibcode: 1994ASPC...61..127D
Altcode: 1994adass...3..127D
The culmination of the IUE Project will be the creation of a Final
Archive which will contain all scientific and calibration data acquired
during the mission, processed in a consistent and homogenous fashion,
using an enhanced image processing system designed specifically for
this purpose. Fundamental observational and image processing parameters
will be incorporated into the headers of the image data files, and
compiled into an IUE Project Database, further enhancing the utility
of the archival information. Data processed for the Final Archive will
begin to be available during 1993. The Final Archive data reduction
system, NEW Spectral Image Processing System (NEWSIPS), utilizes
innovative image processing techniques in order to achieve an improved
signal-to-noise ratio (S/N) in the extracted spectrum. Specifically,
NEWSIPS employs: an image registration algorithm and a ``raw space''
Intensity Transfer Function (ITF) which yield a more accurate
photometric correction; a flux conserving resampling which maps the
data to a geometric space where the echelle orders are parallel to
an image axis and the wavelength dispersion is linear within each
order; and a signal-weighted extraction method. NEWSIPS achieves
a significant increase in the S/N in the two-dimensional images,
and ultimately, in the extracted spectra. The increase in the S/N for
low-dispersion data ranges from 10 -- 50 percent, with factors of 2 --
4 improvement in some cases. The greatest improvements have been seen
in under-exposed, high radiation, and high sky background images. The
S/N for NEWSIPS data is often better than that of the IUESIPS data
for a single spectrum, and multiple NEWSIPS images can be co-added
to attain further increases in the S/N. Preliminary results from
the high-dispersion system suggest a comparable improvement in S/N
to that obtained for low-dispersion. Examples of the improvements in
the data are presented. The Goddard IUE Project Database will contain
the basic observational parameters for each exposure ( i.e., accurate
coordinates and exposure times, homogeneous names for objects) and the
image processing parameters of NEWSIPS. The observational parameters
for every exposure have been verified in a consistent way to ensure
the accuracy and clarity of the information; the image processing
parameters are statistical indicators of image quality. These database
parameters are potent tools that will allow the archival researcher
to determine in an efficient way the best data available to achieve
specific scientific goals.
Title: The IUE Final Archive: High-Dispersion Processing Algorithms
and Results
Authors: Nichols, J. S.; Smith, M. A.; de La Pena, M. D.; Garhart,
M.; Perez, M. R.; Coulter, B.; England, M.; Michalitsianos, A.
Bibcode: 1993AAS...183.4509N
Altcode: 1993BAAS...25.1361N
The development of new algorithms and techniques for processing high
dispersion IUE data for the creation of the Final Archive is nearly
complete. The techniques are similar to those for low dispersion
through the two-dimensional photometric correction step. However,
the system provides an entirely new high-dispersion output product,
a two-dimensional geometrically rectified image with the echelle orders
horizontal to facilitate custom spectral extraction methods. Wavelengths
are linearized within each order in this new image and small-scale
distortions removed. The global background intensity level is
modeled in two dimensions. The high-dispersion spectral data will
be extracted with a weighted slit technique which includes not only
the modeled background correction, but also an interorder overlap
correction and an error estimate for each extracted point. Results
from processing high-dispersion data with the prototype system are
presented. Improvements in the signal-to-noise ratio of the extracted
data over the original processing are substantial, partially due to
the elimination of over-sampling in the extraction and partially to
the improved photometric correction and extraction technique. This
work has been supported under NASA contract NAS5-31230 to Computer
Sciences Corporation.
Title: The IUE Final Archive: Calibration of the Scientific Instrument
Authors: Garhart, M.; Perez, M. R.; Nichols, J. S.; Gonzalez-Riestra,
R.; Michalitsianos, A.
Bibcode: 1993AAS...183.4501G
Altcode: 1993BAAS...25.1359G
As part of the effort to produce a uniformly processed and calibrated
final archive of IUE data, all aspects of the photometric correction,
image resampling, spectral extraction, wavelength calibration, and
absolute flux calibration have been revised. These new derivations
have significantly reduced the errors in absolutely calibrated spectral
data compared to the originally processed data. To ensure an accurate
detector photometric correction for all images in the archive, full 2-D
calibrations of the detectors were re-acquired in 1992 for both prime
cameras. These new photometric calibrations combined with an improved
raw image registration technique (which correlates the photometric
calibration with the science image) represent a dramatic improvement
over the previous calibrations. Several new image resampling techniques
have been created which also represent an improvement over the original
processing. These include corrections for the spatial deviations
(cross-dispersion ``wiggles''), and the change of scale needed to
linearize the dispersion. The absolute flux scale for Final Archive
data is set from previous UV experiment data of standard stars in the
2100--2300 Angstroms region. However, a notable departure from the
previous flux calibration of IUE data is the use of models of white
dwarf atmospheres to determine the relative flux scale for the entire
IUE spectral region. In addition, flux corrections which compensate
for both time and temperature dependent sensitivity degradations of
the IUE detectors (a step not employed in the original processing)
are included in the final calibration. This work has been supported
under NASA contract NAS5-31230 to Computer Sciences Corporation.
Title: The IUE Final Archive Processing System
Authors: Imhoff, C. L.; Dunn, N.; Fireman, G. F.; Levay, K. L.;
Meylan, T.; Nichols, J.; Michalitsianos, A.
Bibcode: 1993AAS...183.4502I
Altcode: 1993BAAS...25.1359I
The IUE Project has begun the task of reprocessing all IUE data using
significantly enhanced reduction algorithms and calibrations. In
order to perform this task in a timely, reliable manner, we have
developed the IUE Final Archive Processing System. The system runs on a
DECstation 5000, using Fortran software embedded in portable MIDAS. The
processing queue is driven by a commercial relational database. The
database interface allows the system to access the enhanced IUE
database, which is resident on a second DECstation 5000 (see poster
by Levay et al.). The system runs automatically, with little operator
intervention. Built-in quality assurance software detects virtually all
input or processing problems. In addition, a fraction of the images,
including all those with quality assurance warnings, are screened by the
staff. The screening system, known as the Post-Production Verification
(PPV) system, uses a widget-based graphics user interface written in
IDL. It allows one to display and inspect the MIDAS and FITS files,
review the FITS headers and other text files, and record the results
in the IUE database. Images which have passed quality assurance are
then delivered to NASA's National Space Science Data Center, which
makes the data available to the astronomical community. This work has
been supported under NASA contract NAS5-31230 to Computer Sciences Corp.
Title: The IUE Final Archive: Low Dispersion Results
Authors: de La Pena, M. D.; Nichols, J. S.; Garhart, M.; Coulter,
B.; Michalitsianos, A.
Bibcode: 1993AAS...183.4504D
Altcode: 1993BAAS...25.1360D
The IUE Final Archive data reduction system, NEW Spectral Image
Processing System (NEWSIPS), was specifically designed to process the
entire IUE dataset in a consistent and homogenous fashion. The system
is comprised of enhanced image processing techniques which exploit the
inherent characteristics of IUE data in order to achieve ultimately an
improved signal-to-noise ratio (S/N) in the extracted spectrum. All raw
IUE images suffer from: non-linearities due to detector response, fixed
pattern noise, periodic noise, and multiple geometric distortions. In
addition, the dispersion direction lies at an angle with respect to
either image axis, rendering spectral extraction complicated. NEWSIPS
was designed to address each of these challenges by applying rigorous
mathematical and image processing techniques. NEWSIPS includes:
automated raw image characterization; Intensity Transfer Functions
(ITFs) created in their own ``geometric'' space -- eliminating the
need for resampling (and consequent degradation) of calibration data;
an explicit image registration combined with the non-degraded ITFs
yield a more accurate photometric correction; a single flux- and
line-shape preserving resampling to a rectified spatial domain which
incorporates multiple ``geometric corrections'' such that the spectral
orders are parallel to an image axis and the wavelength dispersion is
linear within each order; and a signal-weighted extraction method which
includes an error estimate for each extraction bin. NEWSIPS achieves
a significant increase in the S/N in the two-dimensional images which
ultimately manifests itself in the extracted spectra. The increase in
the S/N ranges from 10 -- 200%; the greatest improvements occurring in
under-exposed, high radiation, and high sky background images. Examples
of the improvements in the low-dispersion data are presented. This
work was supported under NASA contract NAS5-31230 to CSC.
Title: The IUE GSFC IUE Final Archive Production Database
Authors: Levay, K. L.; Crabb, S. B.; Imhoff, C. L.; Wasatonic, R. P.;
Nichols, J.; Michalitsianos, A.
Bibcode: 1993AAS...183.4503L
Altcode: 1993BAAS...25.1359L
A fundamental component of the IUE Final Archive will be a comprehensive
database containing a group of "core data items" to fully and accurately
characterize the IUE dataset and to facilitate future analysis. As
the Final Archive database is being populated, the accuracy of each
of these core data items is verified. The database is housed in a
commercial off-the-shelf (COTS) RDBMS allowing the data to be easily
and flexibly accessed by the IUE Project and ultimately by users. In
addition, the database has become an integral component of the GSFC
Final Archive Processing System. The database drives the processing
pipeline and tracks the progress of each image through all four steps
of the system beginning with core data item verification, through the
pipeline processing and image screening subsystems, and ending with the
archive interface with the National Space Science Data Center (NSSDC)
where the data are made available to the astronomical community. The
database is used effectively to control the queue of images in these
subsystems, allowing the overall system to run with minimal human
interface. This work has been supported under NASA contract NAS5-31230
to Computer Sciences Corporation.
Title: The High Dispersion Background Algorithm in NEWSIPS
Authors: Smith, M. A.; Grady, C. A.; O'Brien, P.; de la Pena, M.;
Nichols, J.; Garhart, M.; Coulter, B.; Michalitsianos, A.
Bibcode: 1993AAS...183.4508S
Altcode: 1993BAAS...25.1360S
A two-dimensional interpolating scheme, followed by modeling of the
point spread function, is outlined for use in the final archiving
NEWSIPS program in removing background fluxes of high dispersion
IUE images. So far our tests have been limited mainly to SWP camera
images. An integral facet of our background removal algorithm, basisiue,
is its execution in a totally automated environment. Toward this end
several conditioning steps are required before the background fluxes can
be sampled. These include the removal of ``wiggles" of echelle orders as
well as rotation of the camera format and removal of order ``splaying"
and avoiding pixels with high fluxes due to permanent image blemishes
and cosmic ray hits. Image-specific pixels with such pathologies are
eliminated, along with on-order pixels, for a sample of pixels along
26 "swaths" (SWP camera) in the cross-dispersion direction. Smoothed,
one-dimensional 7-th degree Chebyshev fits are then computed from
the interpolated fluxes modified by a global point spread function
determined from the interorder overlap pattern in an ensemble of science
images. A second set of continuous Chebyshev functions, perpendicular
to the first, is computed next along the positions of the IUE orders
by interpolating across fluxes determined from the first set. Thus,
this algorithm determines both the of background fluxes at arbitrary
locations on the image and also determines the amount of interorder
flux-overlap among short-wavelength orders, which is necessary to
the final extraction of spectral fluxes. This work has been supported
under NASA Contact NAS5-31230 to the Computer Sciences Corporation.
Title: Analysis of Far-UV High Excitation Line Emission Detected in
the Gravitational Lens Q0957+561 with IUE-NEWSIPS
Authors: Michalitsianos, A. G.; Maran, S. P.; Kazanas, D.; Kondo,
Y.; Bruhweiler, F. C.; Nichols-Bohlin, J.; de La Pena, M.; Meylan,
T.; Perez, M.; Thompson, R.
Bibcode: 1993AAS...183.1201M
Altcode: 1993BAAS...25Q1307M
We have continued analysis of far-UV high excitation emission lines
which were detected in the double lens quasar 0957+561 during
test runs of the New Spectral Image Processing System (NEWSIPS)
of data obtained from the International Ultraviolet Explorer (IUE)
archive (Michalitsianos et al., ApJ. Lett., Nov. 10, 1993). The
significant reduction of fixed-pattern background noise, and the
use of a signal-weighted extraction slit, which was applied to 10
co-added LWP (2000-3200A) spectra, revealed the presence of emission
lines of S VI 933,945A, C III 978A, N III 992A, S IV 1063-1073, N II
1084A, O VI 1031,1037A and Fe III(UV1;1125A), in addition to Ly-alpha
1215A and N V 1240A previously reported. These identifications assume
rest wavelengths consistent with the z = 1.41 redshift of the lensed
quasar. We also found strong Ly-beta 1020A absorption at a redshift
consistent with a previously reported damped Ly-alpha system at z =
1.3911, which is probably associated with an intervening gas near
the quasar. The strong discontinuity in the continuum at 912A is
appropriate to absorption that corresponds to the Ly-alpha and Ly-beta
absorption line system at a z = 1.3911. The expected far-UV emission
lines strengths appropriate for a QSO (assuming solar elemental
abundances) were calculated using the photo-ionization code CLOUDY,
where we assumed a power-law synchrotron flux distribution with slopes
that range from -0.5 to -1.5, and ionization and density parameters
appropriate for the QSO broad line region. These results predict strong
features that correspond to the emission lines identified here. The
relative intensities of emission lines present in the lens images A
and B were obtained to determine if gravitational lensing leads to
flux variations of different ionic species, which sets constraints on
the size of the quasar emitting regions.
Title: Detection of Far-Ultraviolet High-Excitation Line Emission
and Lyman- beta Absorption in the Gravitational Lens Q0957+561
Authors: Michalitsianos, A. G.; Nichols-Bohlin, J.; Bruhweiler, F. C.;
Kazanas, D.; Kondo, Y.; de La Pena, M.; Maran, S. P.; Meylan, T.;
Perez, M.; Thompson, R.
Bibcode: 1993ApJ...417L..57M
Altcode:
Test runs with a new data processing software system on archival
spectra obtained by the International Ultraviolet Explorer (IUE)
reveal high-excitation emission lines in the gravitationally lensed
binary quasar 0957+561. The lines of O VI λλ1031,1037 and S VI
λ2933,945 are readily seen in a single 390 minute, low-dispersion
IUE exposure, when calibrated with the New Spectral Image Processing
System (NEWSIPS). Coaddition of 10 exposures, as processed by NEWSIPS,
followed by the application of a five-point smoothing filter,
allows clear detection of the additional emission of C III λ978, N
II λ992, S IV λλ1063-1073, N II λ1084, Fe III (UV1; λ1125), and
N V λ1238. These identifications assume rest wavelengths consistent
with the z = 1.41 redshift of the lensed quasar. In addition, we find
a strong absorption that can be attributed to H I Lyman-βλ1017 with
a redshift consistent with a previously reported damped Lyman-α
absorption system at z = 1.3911, which is probably associated with
intervening gas near the quasar (Turnshek & Bohlin 1993). Another
absorption feature appears to be due to Si II λλ1190,1193 in the halo
of an intervening galaxy at z = 1.38. Finally, the strong discontinuity
in the continuum at the Lyman limit λ912 is appropriate to absorption
that corresponds to the Lyman-α and Lyman-β absorption line system
at z = 1.3911. These first results suggest that NEWSIPS is capable of
disclosing much previously unrecognized information that is contained
in the nearly 100,000 ultraviolet spectra currently in the IUE Archive,
especially in regions of the spectra that are underexposed.
Title: Evidence for Precession of the R Aquarii Jet
Authors: Hollis, J. M.; Michalitsianos, A. G.
Bibcode: 1993ApJ...411..235H
Altcode:
Several models of the R Aqr northeast jet have been proposed which
attempt to explain the presence of shock excitation, resulting in
a confusing picture of this nearest astrophysical jet. This paper
compares observations of the jet in the R Aqr system with the HST's
Faint Object Camera (FOC) and radio continuum images acquired with
the VLA. The forbidden-O III jet structure is derived from restored
FOC imagery, which has been convolved with an elliptical Gaussian of
the same size as the restoring beam of the 6-cm VLA maps, allowing
image comparison at the same spatial resolution. It is found that,
at increasing distances from the central star, the forbidden O III
emission knots that comprise the optical jet occur at systematically
larger position angles when compared with corresponding features in
the radio images. The angular separation of forbidden O III and radio
continuum emission can be understood in terms of a shock formed when
ejecta in the stream interacts with previously existing circumstellar
material and subsequently cools by nebular line emission.
Title: Ultraviolet Continuum Variability and Visual Flickering in
the Peculiar Object MWC 560
Authors: Michalitsianos, A. G.; Perez, M.; Shore, S. N.; Maran,
S. P.; Karovska, M.; Sonneborn, G.; Webb, J. R.; Barnes, Thomas G.,
III; Frueh, Marian L.; Oliversen, R. J.; Starrfield, S. G.
Bibcode: 1993ApJ...409L..53M
Altcode:
High-speed U-band photometry of the peculiar emission object MWC 560
obtained with the ground-based instrumentation, and V-band photometry
obtained with the International Ultraviolet Explorer-Fine Error Sensor
indicates irregular brightness variations are quasi-periodic. Multiple
peaks of relative brightness power indicate statistically significant
quasi periods existing in a range of 3-35 minutes, that are superposed
on slower hourly varying components. We present a preliminary model
that explains the minute and hourly time-scale variations in MWC 560 in
terms of a velocity-shear instability that arises because a white dwarf
magnetosphere impinges on an accretion disk. We also find evidence for
Fe II multiplet pseudocontinuum absorption opacity in far-UV spectra of
CH Cygni which is also present in MWC 560. Both CH Cyg and MWC 560 may
be in an evolutionary stage that is characterized by strong UV continuum
opacity which changes significantly during outburst, occurring before
they permanently enter the symbiotic nebular emission phase.
Title: Radial distribution of metallicity in the LMC cluster systems.
Authors: Kontizas, M.; Kontizas, E.; Michalitsianos, A. G.
Bibcode: 1993A&A...269..107K
Altcode:
New determinations of the deprojected distances to the galaxy centre
for 94 star clusters and their metal abundances are used to investigate
the variation of metallicity across the two LMC star cluster systems
(Kontizas et al. 1990). A systematic radial trend of metallicity is
observed in the extended outer cluster system, the outermost clusters
being significantly metal poorer than the more central ones, with
the exception of six clusters (which might lie out of the plane of
the cluster system) out of 77. A radial metallicity gradient has
been found, qualitatively comparable to that of the Milky Way for
its system of the old disk clusters. If the six clusters are taken
into consideration then the outer cluster system is well mixed up to
8 kpc. The spatial distribution of metallicities for the inner LMC
cluster system, consisting of very young globulars does not show a
systematic radial trend; they are all metal rich.
Title: UIT Ultraviolet Imaging of 30 Doradus
Authors: Hintzen, P.; Cheng, K. -P.; Michalitsianos, A.; Bohlin,
R.; O'Connell, R.; Cornett, R.; Roberts, M.; Smith, A.; Smith, E.;
Stecher, T.
Bibcode: 1993LNP...416..157H
Altcode: 1993namc.meet..157H
During the Astro-1 mission, near- and far-UV images of the 30
Doradus region were obtained using the Ultraviolet Imaging Telescope
(UIT). These wide-field, 40 min in diameter, high spatial resolution,
2-3 sec, UIT UV images reveal a rich field of luminous UV-bright
stars, clusters, and associations. There are 181 stars brighter than
m2558A = 16.5 and 197 stars brighter than m1615A
= 16.4 within 3 min diameter of the 30 Doradus central cluster. We
have derived UV fluxes emitted from the 30 Doradus central cluster
and from its UV bright core, R136. The region within 5 sec of R136
produces approximately 14% of the far-UV flux (lambda = 1892 A) and
approximately 16% of the near-UV flux (lambda = 2558 A) emitted from
the 3 min diameter central cluster. The derived UV luminosity of R136
at 1892 A is only 7.8 times that of the nearby O6-7 Iaf star, R139,
and the m1892 - mv colors of R136 are similar to
other O or Wolf-Rayet stars in the same region. These UIT data, combined
with other published observations at longer wavelengths, indicate that
there is no observational evidence for a supermassive star in R136.
Title: Indications for common origin and gravitational interaction
in three binary LMC clusters.
Authors: Kontizas, E.; Kontizas, M.; Michalitsianos, A.
Bibcode: 1993A&A...267...59K
Altcode:
Three close pair clusters of the LMC, NGC 2006/SL 538, NGC 2011a/b
and NGC 2042a/b, have been studied in order to establish their
binarity. The stellar content in the outer region of each cluster
has been investigated by means of low resolution objective UK Schmidt
prism spectra, the cores of the clusters have been examined using low
resolution integrated IUE spectra, whereas their density profiles and
their observed dynamical parameters have been derived by means of
star counts. The integrated spectra of their cores and the stellar
content of their outer cluster regions have shown a common origin
and a very young age (< 2 10^7^ yr) for each member of the pairs
whereas their dynamical study has shown that they are gravitationally
interacting. Comparing the age of their stellar content with their
dynamical and relaxation times it has been found that these clusters are
physically associated and had no time to relax by stellar encounters,
no time to merge and no time to be destroyed by dynamical friction.
Title: Flickering in MWC 560 and a comparison with the symbiotic
star CH Cyg.
Authors: Maran, S. P.; Michalitsianos, A. G.; Sonneborn, G.; Oliversen,
R. J.; Karovska, M.; Perez, M.; Shore, S. N.; Webb, J. R.; Starrfield,
S. G.
Bibcode: 1992BAAS...24R1286M
Altcode:
No abstract at ADS
Title: Flickering in MWC 560 and a Comparison with the Symbiotic
Star CH Cyg
Authors: Maran, S. P.; Michalitsianos, A. G.; Sonneborn, G.; Oliversen,
R. J.; Karovska, M.; Perez, M.; Shore, S. N.; Webb, J. R.; Starrfield,
S. G.
Bibcode: 1992AAS...18110214M
Altcode: 1992BAAS...24.1286M
No abstract at ADS
Title: Astro-1 Ultraviolet Imaging of the 30 Doradus and SN 1987A
Fields with the Ultraviolet Imaging Telescope
Authors: Cheng, Kwang-Ping; Michalitsianos, Andrew G.; Hintzen, Paul;
Bohlin, Ralph C.; O'Connell, Robert W.; Cornett, Robert H.; Roberts,
Morton S.; Smith, Andrew M.; Smith, Eric P.; Stecher, Theodore P.
Bibcode: 1992ApJ...395L..29C
Altcode:
During the Astro-1 mission, near- and far-UV images of selected fields
in the Magellanic Clouds were obtained using the Ultraviolet Imaging
Telescope (UIT). These ultraviolet images, centered on SN 1987A, 30
Doradus, supernova remnants N49A + B, and SMC-A, provide the first
wide- field (40' in diameter), high spatial resolution (2"-3") UV
images of these regions. The 30 Doradus data reveal a rich field of
luminous UV- bright stars, clusters, and associations: within the 3'
diameter central cluster, there are 181 stars brighter than m_2558_ =
16.5, and 197 stars brighter than m_1615_ = 16.4. We have derived UV
fluxes from the 30 Doradus central cluster and from its UV-bright core,
R136. A region within 5" of R136 produces ~14% of the far-UV flux (λ =
1892 A) and ~16% of the near-UV flux (λ= 2558 A) emitted from the 3'
diameter central cluster. The derived UV luminosity of R136 at 1892
A is only 7.8 times that of the nearby O6-O7 Iaf star, R139, and the
m_1892_- m_v_ colors of R136 are similar to other O or Wolf-Rayet stars
in the same region. The UIT data, combined with published observations
at longer wavelengths, indicate that there is no observational evidence
for a supermassive star in R136. In the UIT images, we also detect an
extensive dust feature, which extends throughout the 30 Doradus and
SN 1987A fields. Diffuse UV emission at low flux levels runs from
northeast to southwest at the northern boundary of N157A, N157B,
and N157C, corresponding closely to the extended infrared emission
seen in the IRAS 60 micron high-resolution (HiRes) image. The observed
correlation between the UV and the IR emission suggests that the dust
scatters a substantial fraction of the incident UV photons, while
absorbing some of the remainder and reemitting this energy in the
IR. We have compared the UIT images with the Einstein X-ray images,
IRAS HiRes images, and ground- based CCD fields in [O III] λ5007,
Hα, B, R, U, and Stromgren u. This comparison is extremely useful
in identifying and studying large H II regions, stellar windblown
cavities, and extended large-scale filaments which are delineated
largely by the expansion of supernova shells.
Title: Colliding Winds in the Peculiar Emission-Line Star MWC 560
Authors: Maran, S. P.; Michalitsianos, A. G.; Oliversen, R.; Sonneborn,
G.; Bopp, B. W.; Shore, S. N.; Starrfield, S. G.
Bibcode: 1992AAS...180.4412M
Altcode: 1992BAAS...24..801M
No abstract at ADS
Title: Vacuum Ultraviolet Imaging with ASTRO 1-UIT of the 30 Doradus
and SN 1987A Fields
Authors: Cheng, K. -P.; Michalitsianos, A. G.; Hintzen, P.; Bohlin,
R. C.; O'Connell, R. W.; Cornett, R. H.; Roberts, M. S.; Smith, A. M.;
Smith, E. P.; Stecher, T. P.
Bibcode: 1992AAS...180.3903C
Altcode: 1992BAAS...24..790C
No abstract at ADS
Title: Optical Spectroscopy of the Unusual Emission-Line Object
MWC 560
Authors: Bopp, B. W.; Mak, A. T.; Michalitsianos, A.; Maran, S.
Bibcode: 1992AAS...180.4413B
Altcode: 1992BAAS...24..801B
MWC 560, classified Beq in the original Mt. Wilson survey but noted
as type M4ep by Sanduleak and Stephenson (Ap.J. 185, 899), underwent
an outburst in 1990. Between Feb.-Apr. 1990 the star showed dramatic
UV spectral variability, indicating the ejection of a thick shell
(Michalitsianos et al., Ap.J. 371, 761). We have monitored the optical
spectrum of MWC 560 during 1990-92 at Ritter Observatory using a
fiber-coupled spectrograph and CCD, in coordination with IUE. Very
significant spectral changes took place between the 90/91 and 91/92
observing seasons. Compared with 90/91, the data from a year later show:
a broader and more blueshifted (-2200 km/s) absorption component of the
strong Hα emission line; weaker Fe II, O I, and He I emission lines;
much weaker D-line absorption. In the 8000-9000 Angstroms region, the
Ca II infrared triplet lines are strong, narrow emission features,
superimposed on the continuum of an M5 star; TiO bandheads appear
stronger in 91/92 than a year earlier. The visible/red spectrum of MWC
560 appears to have been dominated by optically thick shell features
in late-1990/early-1991. By November 1991, the shell signatures have
weakened, and a variable high-velocity wind profile is evident at Hα
. This research was partially supported by grants from NASA.
Title: Fe II Fluorescence and Anomalous C IV Doublet Intensities in
Symbiotic Novae
Authors: Michalitsianos, A. G.; Kafatos, M.; Meier, S. R.
Bibcode: 1992ApJ...389..649M
Altcode:
The variation of absolute intensities of Bowen-excited Fe II emission
in the symbiotic stars RR Tel, RX Pup, and AG Peg is examined. The
C IV doublet intensity ratios in RR Tel were not anomalous between
1979 and 1989, and the ratio had typical values within the optically
thin range. The intensity of individual Fe II Bowen-excited lines is
correlated with the C IV 1548.2 A flux, suggesting the presence of a
foreground Fe II region in which fluorescent-excited material responds
to flux variations of C IV 1548.2 A. In RX Pup the combined fluxes of
Fe II Bowen-pumped lines can account for an appreciable fraction of the
flux deficit in the C IV 1548.2 A line when the C IV doublet ratio is
less than the optically thick limit of unity. The Fe II Bowen lines
in RX Pup exhibit a velocity range from 0 to 80 km/s, where several
strong Fe II emission lines correspond to deep absorption structure
in the C IV 1548.2 A line profile. In AG Peg and C IV 1548.2 A flux
deficit cannot be explained by Fe II fluorescent absorption alone when
the C IV doublet ratio anomaly is at an extreme.
Title: UV & High Speed FES Photometry of MWC 560
Authors: Michalitsianos, Andrew G.
Bibcode: 1992iue..prop.4364M
Altcode:
No abstract at ADS
Title: MWC 560
Authors: Michalitsianos, A. G.; Oliversen, R. J.; Sonneborn, G.;
Maran, S. P.; Shore, S. N.; Starrfield, S.
Bibcode: 1991IAUC.5355....1M
Altcode:
A. G. Michalitsianos, R. J. Oliversen, G. Sonneborn, and S. P. Maran,
Goddard Space Flight Center; S. N. Shore, Computer Sciences Corporation;
and S. Starrfield, Arizona State University, communicate: "We observe
a major change in the ultraviolet spectrum of the peculiar variable
star MWC 560, detected on Sept. 28 with the International Ultraviolet
Explorer. The spectrum seen during 1990 Sept. 26-1991 Apr. 27,
which resembles that of the opaque shell of a nova several days after
outburst, has been replaced by a highly blueshifted array of strong,
blended absorption lines, as had been observed in this star during
1990 Feb. 4-1990 Apr. 29. The velocity shift on 1991 Sept. 28 is about
-1000 km/s relative to the IUE spectrum of 1984 Mar. 10, which has
been adopted as a reference (Michalitsianos et al. 1991, Ap.J. 371,
761). The integrated flux in the range 120-320 nm, which had dropped
to 1 x 10E-10 erg cmE-2 sE-1 on 1991 Apr. 27 during the 'shell phase',
was 5.2 x 10E-10 erg cmE-2 sE-1 on 1991 Sept. 28. Rather than heralding
the impending appearance of a symbiotic star emission line spectrum,
the novalike spectrum has reverted to its peculiar Be-star spectrum in
the ultraviolet. This suggests that the 'shell phase' may be cyclic
on a timescale of the order of 18 months. Groundbased spectroscopic
and photometric measurements are urgently needed."
Title: Plans for a High-Earth Orbit for the Lyman/FUSE Mission
Authors: Sonneborn, G.; Friedman, S.; Holmes, C.; Mark, D.;
Michalitsianos, A.; Moos, W.
Bibcode: 1991BAAS...23.1318S
Altcode:
No abstract at ADS
Title: Fourteen Years of Astronomical Research with the International
Ultraviolet Explorer
Authors: Kondo, Y.; Michalitsianos, A. G.; West, D. K.
Bibcode: 1991BAAS...23.1454K
Altcode:
No abstract at ADS
Title: Alternating States of the Unusual Emission Object MWC 560
Authors: Michalitsianos, A. G.; Maran, S. P.; Oliversen, R. J.;
Sonneborn, G.; Shore, S. N.; Starrfield, S. G.
Bibcode: 1991BAAS...23.1377M
Altcode:
No abstract at ADS
Title: Ultraviolet and Optical Spectroscopy of the R Aquarii
Symmetrical Jet
Authors: Hollis, J. M.; Oliversen, R. J.; Kafatos, M.; Michalitsianos,
A. G.; Wagner, R. M.
Bibcode: 1991ApJ...377..227H
Altcode:
The first ultraviolet spectrum of the southwest (SW) component of the
symmetrical jet in the R Aquarii binary system has been obtained in
the range 1200-2000 A with the IUE. These results are compared to more
encompassing spectra of the central H II region taken at the same time
and also similar spectra of the northeast (NE) jet component obtained
six months earlier. Moreover, optical spectra of both the NE and SW jet
components in the range 3400-9800 A were obtained within about 6 months
and about 1 month, respectively, of the ultraviolet spectra. These
highly complementary observations argue that excitation of the
symmetrical jet may be due to shock excitation as the jet components
overtake and impact the previously ionized material associated with the
expanding inner nebulosity. The problems with this shock model as well
as problems with competing photoionization models are discussed. It is
suggested that the jet components were ejected less than 90 years ago.
Title: C IV Line Profile Correlations in NGC 4151
Authors: Fahey, R. P.; Michalitsianos, A. G.; Kazanas, D.
Bibcode: 1991ApJ...371..136F
Altcode:
The core of the strong UV resonance line C IV in the Seyfert 1 galaxy
NGC 4151 is characterized by a double-peaked profile whose narrow
emission features have relative intensities that vary as a function
of the total C IV line strength. We present herein a set of novel
correlations between the peak emission of each of these two components
and the total luminosity of the C IV line. These correlations are
distinctly different for the red and the blue peaks of the double-peaked
C IV profile, implying that the physical parameters involved in their
formation are quite different. The behavior of the red component
appears more in accordance with the behavior of lines observed in
other objects, with the peak intensity steadily increasing as the line
brightens and broadens (though no specific correlations between these
two quantities have, to our knowledge, been previously reported). The
blue peak, however, appears much more directly and strongly related
to C IV luminosity, and exhibits greater sensitivity to the C IV flux
changes, becoming almost extinct when the active nucleus is in its
low state. The very presence of these tight correlations, and the very
simple, model-independent and direct method employed in obtaining them,
imply the existence of specific (hitherto unknown) underlying physical
processes. The distinctly different correlations exhibited by the
blue and red peaks also suggests that distinct line-forming regions
(in velocity space) produce the characteristic double-peaked profile
of the C IV line in NGC 4151.
Title: Observations of the Peculiar Object MWC 560 in Outburst
Authors: Michalitsianos, A. G.; Maran, S. P.; Oliversen, R. J.; Bopp,
B.; Kontizas, E.; Dapergolas, A.; Kontizas, M.
Bibcode: 1991ApJ...371..761M
Altcode:
The results of ultraviolet spectroscopy, photoelectric photometry, and
supplemental high-resolution H(alpha) spectroscopy of a photometric
outburst of MWC 560 are discussed. Ultraviolet spectra are shown
to be consistent with the ejection of an optically thick shell that
produced strong absorption blends of Fe II and Cr II. The velocities
reported exceed by far those previously found in symbiotic stars or
recurrent novas. In addition to the variable high-velocity system of
broad absorption features, a relatively stable system of Mg II, Mg I,
Fe II, Cr II, and other ionic absorptions is observed. It is pointed
out that the spectroscopic phenomena in MWC 560 resemble those found
in XX Ophiuchi, but the velocities in the MWC 560 are an order of
magnitude higher than those found in XX Oph.
Title: Spectral transformation of the unusual variable star MWC560
to resemble a nova
Authors: Maran, Stephen P.; Michalitsianos, Andrew G.; Oliversen,
Ronald J.; Sonneborn, George
Bibcode: 1991Natur.350..404M
Altcode:
MWC560 is an emission-line star catalogued1in 1943 and
later described2 as an 'extraordinary symbiotic-like
variable'. It was recently found3 to be undergoing a
photometric and spectroscopic outburst. A dramatic change has occurred
in the ultraviolet spec-trum of MWC560, so that it now closely resembles
the spectrum of a nova shortly after outburst. This event, detected by
the International Ultraviolet Explorer satellite, may signal a major
mass-ejection episode such as presumably occurred in past centuries
in the symbiotic star R Aquarii to produce the well-known bipolar
nebula, and it may herald the emergence of a standard symbiotic-star
emission-line spectrum in MWC560, corresponding to a change in
evolutionary state.
Title: UIT Observations of the Interstellar Light Echoes from SN1987A
Authors: Crotts, A. P.; Hill, R. S.; Landsman, W. B.; Gull, T. R.;
Hintzen, P. M. N.; Maran, S. P.; Michalitsianos, A. G.; Stecher,
T. P.; O'Connell, R. W.
Bibcode: 1991BAAS...23Q.901C
Altcode: 1991BAAS...23..901C
No abstract at ADS
Title: UIT Imagery of Omega Centauri
Authors: Landsman, W. B.; Cornett, R. H.; Hill, J. K.; Parise, R. A.;
Hintzen, P. M. N.; Maran, S. P.; Michalitsianos, A. G.; Stecher,
T. P.; O'Connell, R. W.; Roberts, M. S.
Bibcode: 1991BAAS...23R.947L
Altcode:
No abstract at ADS
Title: ASTRO-UIT UV Images of the Magellanic Clouds: Search for
Ultraviolet Counterparts to Discrete X-Ray Sources
Authors: Michalitsianos, A. G.; Greason, M.; Hill, R. S.; Hintzen,
P. M. N.; Isensee, J.; O'Connell, R. W.; Smith, A. M.; Stecher, T. P.
Bibcode: 1991BAAS...23..946M
Altcode:
No abstract at ADS
Title: Ultraviolet Imaging Telescope (UIT) Observations of the
Globular Cluster NGC 1851
Authors: Parise, R. A.; Hintzen, P. M.; Maran, S. P.; Michalitsianos,
A. G.; Stecher, T. P.; Roberts, M. S.; Cornett, R. H.; Greason, M. R.;
Hill, J. K.; Landsman, W. B.; O'Connell, R.
Bibcode: 1991BAAS...23R.948P
Altcode:
No abstract at ADS
Title: UIT Images of the Globular Cluster M79
Authors: Hill, R. S.; Greason, M. R.; Hill, J. K.; Cornett, R. H.;
Landsman, W. B.; Parise, R. A.; Hintzen, P. M. N.; Maran, S. P.;
Michalitsianos, A. G.; Stecher, T. P.; Roberts, M. S.; O'Connell, R. W.
Bibcode: 1991BAAS...23..947H
Altcode:
No abstract at ADS
Title: IUE Observations of the R Aquarii Jet and Counterjet
Authors: Michalitsianos, Andrew G.
Bibcode: 1991iue..prop.4005M
Altcode:
R Aquarii is a symbiotic variable containing a 387-day period Mira
and a hot a hot accreting compact star. Although this system has been
studied quite extensively at X-ray, UV, optical and radio wavelengths,
many important questions concerning the origin of its nebular emission
remain obscure. The presence of a bright optical/radio jet suggests that
material is expelled in the form of a series of discrete emission knots,
that define a broad, one sided arc, that is nearly ~7" (~2.5xlO^15cm)
in NE extent. The presence of N V 1238,1240 and He II 1640 emission in
the knots indicate this region is substantially hotter compared with the
central HII region, where these lines are weak or absent. Application
of accretion disk models to this system, that purport mass expulsion
in the form of bipolar flow that is directed along the accretion
disk poles, has been frustrated by the apparent one sidedness of this
structure. However, recently obtained [O III] 5007 images, and deep
6-cm radio continuum maps obtained with the Very Large Array (VLA),
indicate the presence of counterjet structure, which extends ~4 10^16cm
(~1375 AU) SW from the central object. We propose to obtain IUE LORES
SWP and LWP spectra of the SW structure, in order to determine if this
newly found region exhibits similar excitation properties as the knots
NE of the central object. The detection of N V and He II emission formed
in a region of similar electron densities as that estimated for the
structure to the NE (ne >= 10^4cm^-3), would lend further support
for the bipolar nature of mass expulsion from this system. Moreover,
continued monitoring of the central HII region and jet structure is
needed because the NE knots appear to be increasing in UV line emission,
since the discovery of soft X-rays from this system in 1985 observed
with EXOSAT. We plan to coordinate IUE observations of R Aquarii with
ROSAT observations which will be obtained with the High Resolution
Imager (HRI). Our observing program, data analysis method follow.
Title: Coodinated IUE-Groundbased Observations of the Peculiar Object
MWC 560
Authors: Michalitsianos, Andrew G.
Bibcode: 1991iue..prop.3995M
Altcode:
We propose to investigate the evolution of the ultraviolet spectrum of
the peculiar emission-line object 14WC 560 in the postoutburst stage,
to see if it develops a classical symbiotic-star (nebular) spectrum,
as we have predicted, or if it behaves otherwise. We have recently
observed this object with IUE in two prior phases: (a) an "unstable
preoutburst phase", in which a complex broad-line or blended absorption
spectrum (system velocity, always blue-shifted, attains absolute values
as large as 6000 km/s) of Fe II and other cool species are seen to
shift by hundreds or thousands of km/s from one velocity to another
in a systematic way, while a narrow-line absorption system remains at
a constant velocity of about 50 km/s; (b) a novalike "outburst phase"
in which the spectrum just described under "(a)" was replaced by an
ultraviolet spectrum with no identifiable features, but which closely
resembles the ultraviolet spectra of several recent novae as observed
within a week or two after their photometric eruptions. We suspect that
MWC 560 may be undergoing a mass ejection event resembling those that
presumably produced one or more of the prominent circumstellar jets and
nebulae in the classical symbiotic star R Aquarii. The current outburst
in MWC 560 thus may offer a very rare opportunity to investigate such
a phenomenon. Specific astrophysical objectives of the study include:
determining the dynamical timescale of the envelope, measuring the
ultraviolet flux distribution of the hot component(s) in the system
(which is/are presently obscured by the dense ejected shell), and
determining the light curves of permitted and intersystem emission
lines that emerge as the optical depth of the shell decreases. These
observations will be coordinated with ground-based spectral observations
of MWC 560 to monitor the visual emission line spectrum during the
shell phase.
Title: C IV Line Profile Correlations in NGC 4151
Authors: Kazanas, D.; Fahey, R. P.; Michalitsianos, A. G.
Bibcode: 1991vagn.conf..375K
Altcode:
No abstract at ADS
Title: Early phases of LMC star clusters?
Authors: Kontizas, Evangelos; Michalitsianos, Andrew; Kontizas, Mary
Bibcode: 1991ASPC...13..404K
Altcode: 1991fesc.book..404K
On the basis of optical and IUE observations the authors have
investigated the possibility that some of the very young stellar systems
of the LMC, such as SL 360, may be regarded as globular clusters
at the very early phases of their dynamical evolution after the gas
cloud expulsion.
Title: The Symbiotic PHENOMENA:CONTINUATION of Early Acq pt 2
Authors: Michalitsianos, A.
Bibcode: 1990hst..prop.4162M
Altcode:
Symbiotic stars are interacting binaries. The relevant interaction
processes include mass expulsion from a common envelope between the two
stars, collimated flows, accretion disk formation around the compact
hot star, evolution of outbursts, as well as mass outflow leading to
jet-like features with particularly intriguing characteristics. However,
the nature of these systems and the physical processes that explain
their behavior remain unsettled. Spectroscopy with HRS will decisively
advance our knowledge of the kinematical and ionization structure of
the central HII region that surrounds the binary. It is hoped that
this will finally answer the controversial question concerning the
nature of the hot object in symbiotics. High spatial resolution radio
Title: The Symbiotic Phenomena
Authors: Michalitsianos, A.
Bibcode: 1990hst..prop.2342M
Altcode:
Symbiotic stars are interacting binaries. The relevant interaction
processes include mass expulsion from a common envelope between the two
stars, collimated flows, accretion disk formation around the compact
hot star, evolution of outbursts, as well as mass outflow leading to
jet-like features with particularly intriguing characteristics. However,
the nature of these systems and the physical processes that explain
their behavior remain unsettled. Spectroscopy with HRS will decisively
advance our knowledge of the kinematical and ionization structure of
the central HII region that surrounds the binary. It is hoped that
this will finally answer the controversial question concerning the
nature of the hot object in symbiotics. High spatial resolution radio
Title: MWC 560
Authors: Michalitsianos, A. G.; Oliversen, R. J.; Maran, S. P.;
Sonneborn, G.
Bibcode: 1990IAUC.5108....1M
Altcode:
A. G. Michalitsianos, R. J. Oliversen, S. P. Maran, and G. Sonneborn,
NASA/Goddard Space Flight Center, report: "Observations with the
International Ultraviolet Explorer on Sept. 26 show that the ultraviolet
spectrum of the unusual erupting star MWC 560 (cf. IAUC 4969, 4979,
4989), sometimes classified as symbiotic, has changed noticeably
since previously observed on Apr. 29. The total flux of MWC 560 in
the range 120-320 nm dropped by roughly a factor of 10 since Apr. 29,
although the visual brightness measured by the IUE Fine Error Sensor
decreased by < 10 percent. The ultraviolet spectrum now resembles
some classical novae early in outburst, particularly OS And on 1986
Dec. 11 and PW Vul on 1984 Sept. 1, 5 and 15 days after outburst,
respectively (see Stryker et al. 1988, ESA SP-281, 1, 149). The spectral
features in the range 120-200 nm of MWC 560 match those in OS And, but
with MWC 560 being blueshifted by 1240 km/s. This may mean that MWC
560 is a cataclysmic variable star of a new type, which has ejected
a cool, optically thick shell. Observers should monitor MWC 560 for
the possible emergence of a nebular-phase spectrum."
Title: Comparisons of SiO Maser and Long-Period Variable Positions
in the R Aquarii and Omicron Ceti Binary Systems
Authors: Hollis, J. M.; Wright, M. C. H.; Welch, W. J.; Jewell, P. R.;
Crull, H. E., Jr.; Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1990ApJ...361..663H
Altcode:
It has been determined that the absolute position of the centroid
of SiO maser-emitting spots toward both R Aqr and Omicron Cet are
coincident with the position of the long-period variables (LPVs)
in these binary systems to within the errors of measurement. The
SiO positions were determined with the Hat Creek interferometer,
while the LPV positions were determined with the 8-in transit circle
of the US Naval Observatory. These results contradict an earlier
report of a circumbinary SiO maser far removed from the LPV in the
R Aqr binary system; statistical reasons for the discrepancy are
suggested. High-resolution spectra of both sources are presented and
possible models are discussed.
Title: An Extremely Carbon-poor Planetary Nebula in the Small
Magellanic Cloud
Authors: Meatheringham, Stephen J.; Maran, Stephen P.; Stecher,
Theodore P.; Michalitsianos, Andrew G.; Gull, Theodore R.; Aller,
Lawrence H.; Keyes, Charles D.
Bibcode: 1990ApJ...361..101M
Altcode:
New optical and ultraviolet observations of the type I planetary
nebula SMP 28 in the Small Magellanic Cloud show that it is remarkably
deficient in carbon (abundance less than 1/450th solar) and that the
electron temperature is very high (25,200 K). The nebula may be so hot
due to the lack of efficient cooling by carbon. Optical and UV data are
well represented by a model in which the central star has temperature
T_*_ = 1.8 x 10^5^ K and radius R_*_ = 0.09 R_sun_. A nebular mass
of 0.71 M_sun_ and a central star mass in the range 0.65- 0.71 M_sun_
are inferred. Nitrogen is overabundant relative to oxygen by a factor
of 1.57 compared to the mean abundances in SMC planetary nebulae (other
type I objects excluded). It appears that SMC-SMP 28 has evolved from
a massive progenitor, with main-sequence mass M_init_ greater than
at least 5 M_sun_ and perhaps larger than 7 M_sun_, which underwent
both second and third nuclear dredge-up, as well as very efficient hot
bottom burning. These processes raised the surface abundances of He
and N while depleting O and drastically reducing C. It appears that
the study of type I nebulae can help constrain theoretical estimates
of the efficiency of convective burning in the lower envelopes of
intermediate-mass stars.
Title: Emergence of a Nova Spectrum in the Peculiar Star MWC 560
Authors: Maran, S. P.; Michalitsianos, A. G.; Oliversen, R. J.;
Sonneborn, G.
Bibcode: 1990BAAS...22.1342M
Altcode:
No abstract at ADS
Title: C IV line profile correlations in NGC 4151
Authors: Michalitsianos, A. G.; Fahey, R. P.; Kazanas, D. M.
Bibcode: 1990ESASP.310..527M
Altcode: 1990eaia.conf..527M
No abstract at ADS
Title: MWC 560
Authors: Maran, S. P.; Michalitsianos, A. G.
Bibcode: 1990IAUC.5004....1M
Altcode: 1990IAUC.5004....0M
S. P. Maran and A. G. Michalitsianos, Laboratory for Astronomy and
Solar Physics, Goddard Space Flight Center, write: "Observations made
on Apr. 29 with the International Ultraviolet Explorer show that
the strong, velocity-variable absorption spectrum seen in the 120-
to 200-nm range, previously observed to be blueshifted (IAUC 4979)
by amounts ranging up to 3500 km/s during Feb. 4-Mar. 29 with respect
to the spectrum observed with IUE on 1984 Mar. 14, has returned to a
nominal 'home state' velocity defined by the 1984 observation. In home
state, the Al III absorption at 185.4 nm has a velocity of -530 km/s
with respect to rest. The total flux in the 120- to 320-nm range on
Apr. 29, 1.1 x 10E-9 erg cmE-2 sE-1, was four times brighter than on
1984 Mar. 14. The occurrence of rapid ultraviolet spectral variations
is indicated by two 16-min exposures, made 172 min apart on Apr. 29,
that showed a substantial decrease in the equivalent widths of several
strong absorption features in the 120-200 nm range during that interval,
while the total flux in that range increased by about 10 percent."
Title: MWC 560
Authors: Michalitsianos, A. G.; Maran, S. P.; Oliversen, R.
Bibcode: 1990IAUC.4989....1M
Altcode: 1990IAUC.4989....0M
A. G. Michalitsianos, S. P. Maran, and R. Oliversen, Laboratory for
Astronomy and Solar Physics, Goddard Space Flight Center, communicate:
"High-resolution spectra taken with the International Ultraviolet
Explorer on Mar. 14 and 29 contain variable absorption, emission,
and continuum features in the 200- to 320-nm region. Mg I, Mg II,
Fe II, and Cr II absorptions are observed with velocities of about
+50 km/s, in contrast with the Fe II system at about -2500 km/s seen
in low-resolution ultraviolet spectra. A deep P Cyg-type absorption
trough with highly variable structure, associated with Mg II h and k,
extends to velocities of at least -10 000 km/s. Emission lines of Fe
II and Cr II attributed to the +50 km/s system appear within this
trough. Variations in the visible-light magnitudes determined with
the IUE Fine Error Sensor since Feb. 4 do not follow the changes in
the ultraviolet flux; V = 9.1 on Mar. 29. The +50 km/s and -2500 km/s
systems may correspond to the systemic velocity of an old circumstellar
shell and to the present outburst, respectively."
Title: MWC 560
Authors: Maran, S. P.; Michalitsianos, A. G.; Oliversen, R.; Bond, H.
Bibcode: 1990IAUC.4979....3M
Altcode: 1990IAUC.4979....0M
S. P. Maran, A. G. Michalitsianos, and R. Oliversen, Laboratory for
Astronomy and Solar Physics, Goddard Space Flight Center, report:
"An optically-thick shell appears to have been ejected at a novalike
velocity of approximately -3000 km/s, as shown by a comparison of
the strong absorption spectrum attributed to Fe II and other low
excitation lines in recent IUE spectra (Feb. 4.02 and Mar. 7.04 UT)
with that obtained by H. Bond on 1984 Mar. 13, when the same features
were observed at rest velocity."
Title: Ultraviolet and Visible Light Observations of the Peculiar
Star MWC 560 in Outburst
Authors: Maran, S. P.; Michalitsianos, A. G.; Oliversen, R.; Bopp,
B.; Kontizas, E.; Kontizas, M.; Dapergolas, A.
Bibcode: 1990BAAS...22..835M
Altcode:
No abstract at ADS
Title: MWC 560
Authors: Dapergolas, A.; Kontizas, E.; Kontizas, M.; Michalitsianos,
A. G.; Maran, S. P.; Schmeer, P.
Bibcode: 1990IAUC.4982....2D
Altcode: 1990IAUC.4982....0D
A. Dapergolas, E. Kontizas, and M. Kontizas, National Observatory
of Greece at Kryonerio; and A. G. Michalitsianos and S. P. Maran,
Laboratory for Astronomy and Solar Physics, Goddard Space Flight
Center, write: "We report the following new photometric observations
of MWC 560: Mar. 12.75 UT, V = 9.45, B = 9.77, U = 9.71; Mar. 14.75,
9.85, 10.20, 9.81; Mar. 16.75, 9.66, 10.01, 9.61. This object is
continuing to increase slowly in U. Short-term variations in U are
indicated on a timescale of approximately 15 to 20 min, as also
reported by Buckley et al. (IAUC 4980), with approximately 0.1-
to 0.2-mag fluctuations." Visual magnitude estimates by P. Schmeer,
Bischmisheim, W. Germany: Mar. 14.91 UT, 9.6; 15.93, 9.5; 16.90, 9.6;
17.89, 9.1; 18.85, 9.1.
Title: MWC 560
Authors: Kontizas, E.; Kontizas, M.; Dapergolas, A.; Michalitsianos,
A. G.; Maran, S. P.; Oliversen, R.; Bopp, B.
Bibcode: 1990IAUC.4978....2K
Altcode: 1990IAUC.4978....0K
E. Kontizas, M. Kontizas, A. Dapergolas, National Observatory of Greece
at Kryoneri; and A. G. Michalitsianos and S. P. Maran, Laboratory for
Astronomy and Solar Physics, Goddard Space Flight Center, write: "We
obtained the following UBV photometry of the peculiar emission star MWC
560: Feb. 25.75 UT, V = 9.7, B = 10.0, U = 9.7; Feb. 26.75, 9.89, 10.18,
9.85; Mar. 5.75, 9.7, 10.5, 9.76. UBV colors indicate that MWC 560 is
definitely not of M spectral type as presently catalogued. The range
in B-V between Feb. 25 and Mar. 5 indicates a variation in spectral
type from early F to late G (or early K). However, the U-B color
suggests a late B or early A type star. U is anomalously bright. Our
Feb. 25 B-V colors are consistent with the SAAO observations reported
on IAUC 4976." A. G. Michalitsianos, S. P. Maran, and R. Oliversen,
Laboratory for Astronomy and Solar Physics, Goddard Space Flight Center;
and B. Bopp, Department of Physics and Astronomy, University of Toledo,
communicate: "Additional observations of MWC 560 with the International
Ultraviolet Explorer (IUE) on Mar. 7 indicate that the visual brightness
obtained with the IUE Fine Error Sensor (FES) has increased from
magnitude 10.1 (countrate 350) on Feb. 4 to 9.8 (countrate 475) on
Mar. 7. A preliminary inspection of the Mar. 7 spectra indicates that
the ultraviolet continuum has increased by approximately 30 percent
when compared with our Feb. 4 data. The strong Fe II absorption
features present throughout the IUE sensitivity range (120-320 nm)
have strengthened and changed line-profile structure considerably since
Feb. 4. Echelle CCD spectra (spectral resolution 0.03 nm) of H-alpha
(656.3 nm), obtained Mar. 2 at the University of Toledo, show that
the base of the line has very broad wings of approximately 3.0 nm
full-base-width, and a narrow, central strong emission peak at +64
km/s. The H-alpha line profile is not characteristic of conventional
Be stars, but it is seen in certain symbiotic stars, such as Z And."
Title: MWC 560
Authors: Michalitsianos, A. G.; Maran, S. P.; Oliversen, R.; Bopp, B.
Bibcode: 1990IAUC.4969....2M
Altcode: 1990IAUC.4969....0M
A. G. Michalitsianos, S. P. Maran, and R. Oliversen, Laboratory for
Astronomy and Solar Physics, Goddard Space Flight Center, write:
"Observations of the peculiar M4e giant star MWC 560 (IAUC 4955) on
Feb. 4 with the International Ultraviolet Explorer show that since 1984
March, when the star was previously examined with IUE, the ultraviolet
flux (120-320 nm) has increased by about 50 percent and the visible
light (400-700 nm) countrate registered by the IUE Fine Error Sensor
has approximately doubled. The 120- to 320-nm continuum is marked by
prominent Fe II absorption lines (many of which have strengthened since
1984) and by absorption from other low-excitation metals, consistent
with the presence of an optically-thick shell around a mass-accreting
companion star. Strong emission in the Si II 126.5-nm multiplet (4), O I
130.1 nm, and C II 133.5 nm is found in the Feb. 4 spectra, suggesting
that the shell may be thinning optically. A visual estimate obtained
recently by B. Bopp indicates that MWC 560 is at magnitude 11.5."
Title: Book-Review - Supernova 1987A in the Large Magellanic Cloud
Authors: Kafatos, M.; Michalitsianos, A.; Dopita, M. A.
Bibcode: 1990SSRv...53..171K
Altcode:
No abstract at ADS
Title: Moderate Resolution Spectroscopy of the Lensed Quasar
2237+0305: A Search for CA II Absorption due to the Interstellar
Medium in the Foreground Lensing Galaxy
Authors: Hintzen, Paul; Maran, Stephen P.; Michalitsianos, Andrew G.;
Foltz, Craig B.; Chaffee, Frederic H., Jr.; Kafatos, Minas
Bibcode: 1990AJ.....99...45H
Altcode:
The gravitational lens system 2237+0305 consists of a low-redshift
barred spiral galaxy (z=0.0394) centered on a more distant quasar
(z=1.695). Because the lensing galaxy is nearly face on, spectroscopy
of the background quasar affords a unique opportunity to study
the interstellar medium in the galaxy's center and bulge. We report
moderate-resolution spectroscopy of QS0 2237+0305 yielding a 3σ upper
limit of 72 mA for the rest equivalent width of Ca II K absorption due
to gas in the intervening galaxy. Since gas in the Milky Way "thick
disk" typically produces 220 mA Ca II lines along lines of sight at
high galactic latitude, while our line of sight to QSO 2237+0305 is
effectively the weighted mean of four lines of sight, each of which
transects an entire halo diameter in the lensing galaxy rather than
just a radius, our Ca II upper limit argues against the presence of
such a thick disk near the center of the lensing galaxy. Also, published
studies indicate that at 8200 A, QSO 2237+0305 suffers roughly 0.5 mag
of extinction due to the lensing galaxy. Assuming a normal gas-to-dust
ratio and allowing for various sources of uncertainty, this absorption
estimate combined with our Ca II K upper limit implies that calcium is
depleted with respect to hydrogen by at least 2.7-3.7 dex, compared
to solar abundances. This depletion is similar to the more extreme
cases seen in our own galaxy, and higher-dispersion observations may
further decrease the upper limit on Ca II absorption.
Title: IUE Observations of Binary Star Clusters in the Large
Magellanic Cloud
Authors: Michalitsianos, Andrew G.
Bibcode: 1990iue..prop.3722M
Altcode:
Identification of approximately 70 binary star clusters in the Large
Magellanic Cloud provides compelling evidence that these objects
constitute a new category of astronomical phenomenon in which star
clusters can form and evolve from a common parent cloud. We propose IUE
observations of a select number of binary star clusters found in the
LMC. From UK Schmidt plate surveys of the LMC, these systems have an
average center-to-center separation of less than ~1.3 arcmin (>=15
pc). Our goal is to determine the UV spectral properties of a select
number of young clusters in binary associations, and compare their
energy flux distribution, and stellar absorption to determine to what
extent similarities exist in the UV. Results from these observations
could provide further evidence supporting the common origin of the
binary cluster, if the ages of each member of a pair are found to be
roughly similar. We also plan to compare their ages from their UV
properties to known young clusters, in order to investigate clues
concerning their origin, and specifically how these systems differ
from open clusters in the LMC. IUE is especially well suited for
this investigation because the age of young clusters observed in the
LMC is particularly sensitive to UV colors, which mainly reflects the
contribution of the main sequence population. Together with ground-based
objective pries surveys of the LMC, these IUE observations will be
crucial for establishing the existence of binary star clusters as a
distinct object class, through a detailed population synthesis study
of their UV spectra.
Title: Outburst From an Unusual Interacting Binary Star System
Authors: Michalitsianos, A. G.
Bibcode: 1990rete.conf...10M
Altcode:
No abstract at ADS
Title: C 560
Authors: Michalitsianos, Andrew G.
Bibcode: 1990iue..prop.3847M
Altcode:
No abstract at ADS
Title: Massive Stars in Large Magellanic Cloud and Small Magellanic
Cloud Clusters
Authors: Kontizas, E.; Kontizas, M.; Michalitsianos, A. G.
Bibcode: 1990mss..conf...22K
Altcode:
No abstract at ADS
Title: R Aquarii: Evidence for a Two-sided Radio Jet and a
Circumbinary SiO Maser
Authors: Kafatos, M.; Hollis, J. M.; Yusef-Zadeh, F.; Michalitsianos,
A. G.; Elitzur, M.
Bibcode: 1989ApJ...346..991K
Altcode:
We have detected collimated 4.86 GHz (∼6 cm) radio continuum emission
southwest (5W) of the symbiotic variable R Aquarii by combining data
corresponding to different configurations of the Very Large Array
(VLA). In the context of a previously reported northeast (NE) 6 cm
jet structure, the orientation of the newly found SW radio structure
suggests bipolar symmetry, extending to distances of ∼2500 AU on
either side of the central H ii region. The amorphous morphology of
the new collimated SW structure is distinct from the discrete radio
knots NE of the central object. Further, we have determined the radio
spectral index distribution between 2 and 6 cm for nearly all of the
radio features found in R Aquarii. Additionally, we have detected 14.94
GHz (∼2 cm) continuum emission at the SiO maser position which is
located ∼250 AU away from the binary system whose orbital semimajor
axis is ∼17 AU. This provides further evidence that the maser-emitting
region is far removed from the system's Mira envelope and may well
be due to local shock phenomena in the circumbinary nebulosity. The
implications concerning the newly detected bipolar 6 cm structure, the
spectral index gradient of the NE jet structure, and the 2 cm emission
component at the SiO maser location are described in context of a thick
accretion disk model that has been previously proposed to explain the
morphology and kinematics of the R Aquarii radio/optical jet.
Title: Sanduleak's Star (LMC Anonymous): Its Similarity in the
Far-Ultraviolet with the Luminous Object eta Carinae and SN 1987A
Authors: Michalitsianos, A. G.; Kafatos, M.; Shore, S. N.
Bibcode: 1989ApJ...341..367M
Altcode:
Spectra obtained in the far UV wavelength range 1200-2000 A with
the International Ultraviolet Explorer (IUE) of the peculiar emission
object LMC Anonymous, or Sanduleak's Star in the Large Magellanic Cloud,
indicate the presence of circumstellar-high-excitation gas, which is
rich in CNO processed material. Although LMC Anonymous is a field star
whose nebular line-forming region can not be resolved, and whose mass
may be considerably smaller than the massive-luminous galactic object
η Carinae, the far-UV spectrum of LMC Anonymous closely resembles
that of the S Condensation of η Carinae. The similarity between
LMC Anonymous and the S Condensation is apparent from the absolute
intensity of the N V, N IV], and N III] emission lines compared
with the reduced strength of C IV or C III] emission. The narrow-low
velocity emission lines observed in SN 1987A indicate strong evidence
for circumstellar emission that is rich in CNO-processed material,
which was formed when the progenitor was in the high mass-loss phase
as a red supergiant. IUE spectra of the S-Condensation and SN 1987A
may provide important clues concerning the nature of LMC Anonymous,
which indicates departures from normal cosmic abundances of nitrogen
relative to carbon that are extreme. This could suggest that carbon
envelope burning and dredge-up have occurred simultaneously during
the helium shell burning stage. These points are discussed in detail.
Title: An Extremely Carbon-Poor Planetary Nebula in the Small
Magellanic Cloud
Authors: Meatheringham, S. J.; Maran, S. P.; Gull, T. R.;
Michalitsianos, A. G.; Stecher, T. P.; Aller, L. H.
Bibcode: 1989BAAS...21..781M
Altcode:
No abstract at ADS
Title: Book-Review - Supernova 1987A in the Large Magellanic Cloud
Authors: Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1989S&T....77..273K
Altcode:
No abstract at ADS
Title: RX Puppis: Detection of Asymmetrical Radio Structure
Authors: Hollis, J. M.; Yusef-Zadeh, F.; Cornwell, T. J.; Oliversen,
R. J.; Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1989ApJ...337..514H
Altcode:
Subarcsecond observations of the RX Puppis symbiotic system with the VLA
have resolved 2 cm continuum emission which deviates from a previously
reported circularly symmetric radio distribution. The radio structure
is comprised of at least three nearly colinear components. Under
the assumption that the strongest feature is coincident with the hot
star, the other two features lie 230 and 590 AU distant. These radio
features are reminiscent of small-scale radio structure detected toward
R Aquarii, another symbiotic star system, and probably represents
material ejected from the RX Puppis system at an earlier epoch.
Title: Pnk 14
Authors: Michalitsianos, Andrew G.
Bibcode: 1989iue..prop.3557M
Altcode:
No abstract at ADS
Title: Book-Review - Supernova 1987A in the Large Magellanic Cloud
Authors: Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1988Sci...242.1714K
Altcode:
No abstract at ADS
Title: Book-Review - Supernova 1987A in the Large Magellanic Cloud
Authors: Kafatos, M.; Michalitsianos, A.
Bibcode: 1988JBAA...98R.316K
Altcode:
No abstract at ADS
Title: The C IV Doublet Ratio Intensity Effect in Symbiotic Stars
Authors: Michalitsianos, A. G.; Kafatos, M.; Fahey, R. P.; Viotti,
R.; Cassatella, A.; Altamore, A.
Bibcode: 1988ApJ...331..477M
Altcode:
High-resolution UV spectra in the 1200-2000 wavelength range of
the symbiotic variable R Aqr and its nebular jet were obtained in
July 1987 with the IUE. The line profile structure of the C IV 1548,
1550 doublet in the jet indicates multicomponent velocity structure
from an optically thin emitting gas. The C IV doublet profiles in the
compact H II region engulfing the Mira and hot companion binary also
suggest multicomponent structure with radial velocities up to about
-100 km/s. The value of the doublet intensity ratio in the R Aqr H
II region has been observed in other similar symbiotic stars, such
as RX Pup. It is suggested that the anomalous behavior of the C IV
doublet intensities may be useful for studying the spatial structure
and temporal nature of winds in symbiotic stars.
Title: The anomalous C IV intensity ratio in symbiotic stars
Authors: Michalitsianos, A. G.; Kafatos, M.; Fahey, R. P.
Bibcode: 1988ESASP.281a.385M
Altcode: 1988IUE88...1..385M; 1988uvai....1..385M
The C IV lambda lambda 1548.2,1550.8 resonance doublet in a symbiotic
stars was shown to exhibit anomalous line intensity ratios in which
I (lambda 1548.2)/I(lambda 1550.8) less than 1, or less than the
optically-thick limit of unity. The R Aquarii-central HII region
and RX Puppis exhibit this phenomena. The I(lambda 1548.2)/I(lambda
1550.8) ratio in RX Puppis is found to vary inversely with the total
C IV line intensity, and with the FES-visual light, as the object
declined over a 5 yr period following a brightening in UV and optical
emission which peaked in 1982. This doublet intensity behavior could
be explained by a wind which has a narrow velocity range of 600
approx. less thanv wind approx. less than 1000 km/sec,
or by the pumping of the Fe II (mul. 45.01) transition a4
F9/2 - y4 H(o)11/2 by C IV lambda
1548.2, which effectively scatters C IV photons into the Fe II spectrum
in these objects.
Title: R Aquarii: The Large-Scale Optical Nebula and the Mira
Variable Position
Authors: Michalitsianos, A. G.; Oliversen, R. J.; Hollis, J. M.;
Kafatos, M.; Crull, H. E.; Miller, R. J.
Bibcode: 1988AJ.....95.1478M
Altcode:
The R Aquarii symbiotic star system is surrounded by a large-scale
optical nebula. The authors present observations of the nebular [O III]
structure and discuss its morphological significance in context with
previously observed small-scale radio-continuum features, which may
be related. They suggest that a precessing accretion disk may explain
the global features of both the large-scale optical emission and the
small-scale radio emission. Moreover, the authors have determined an
accurate position of the system's Mira, which suggests that a recent
theoretical model, yielding an egg-shaped central H II region for
symbiotic systems with certain physical parameters, may apply to
R Aquarii. The optical position of the 387d period Mira
variable is consistent with the authors' previous findings in the radio,
that SiO maser emission is far removed from the Mira photosphere.
Title: Physical Parameters for 12 Planetary Nebulae and Their Central
Stars in the Magellanic Clouds: Erratum
Authors: Aller, Lawrence H.; Keyes, Charles D.; Maran, Stephen P.;
Gull, Theodore R.; Michalitsianos, Andrew G.; Stecher, Theodore P.
Bibcode: 1988ApJ...326.1040A
Altcode:
In the paper "Physical Parameters for 12 Planetary Nebulae and Their
Central Stars in the Magellanic Clouds" by Lawrence H. Aller, Charles
D. Keyes, Stephen P. Maran, Theodore R. Gull, Andrew C. Michalitsianos,
and Theodore P. Stecher (Ap. J., 320, 159[1987]), all stellar radii
in Table 5 should be decreased by a factor of π^1/2^.
Title: Sanduleak's Star: A Possible Supernova Progenitor in the LMC
Authors: Michalitsianos, Andrew G.
Bibcode: 1988iue..prop.3148M
Altcode:
The pronounced enhancement of nitrogen relative to carbon emission in
the SWP 1200-2000 wavelength range of Sanduleak's Star in the Large
Magellanic Cloud is strikingly similar to the emission line spectrum
which characterizes the SCondensation in -Carinae, and provides one of
the first clear examples of an object which exhibits evidence for CNO
processing in another galaxy. Far-UV spectra obtained previously with
IUE of Sanduleak's Star (LMC Anonymous) provides compelling evidence
that the surface composition of this star contains highly processed
nuclear-synthesized material. LORES-SWP spectra obtained nearly
three years apart indicate that C IV emission is variable, while the
emission lines of N V, N IV] and N III] appear to remain essentially
constant. The progenitor stars of Type II supernova are believed to
undergo a significant phase of mass loss via a high velocity wind,
in which core-envelope mixing results in a significant overabundance
of nitrogen relative to carbon at the stellar surface, prior to core
collapse. Thus, the supernova remnant is expected to contain enhanced
nitrogen. The 14N/12C ratio of LMC Anonymous has been found previously
to lie in the range 70 to 150, which brackets the value determined for
the remnant of the recent supernova in the LMC. The similarity of LMC
Anonymous with Eta-Carinae in the far-UV provides further indications
that Sanduleak's Star could become a Type II supernova. IUE observations
are proposed to further investigate the properties of this unusual
object for possible time-dependent effects in the abundance of carbon.
Title: As 296
Authors: Michalitsianos, Andrew G.
Bibcode: 1988iue..prop.3239M
Altcode:
No abstract at ADS
Title: A Review of the R Aquarli System
Authors: Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1988ASSL..145..235M
Altcode: 1988syph.book..235M; 1988IAUCo.103..235M
The spatially resolved nebula that characterizes the D-type symbiotic
R Aquarii has afforded investigators a unique opportunity to probe
the extended emisison line regions. Its extensive and complex radio
morphology, that includes SiO maser emission, has provided important
clues concerning the mass expulsion process in interacting binary
radio stars. Infrared, radio, optical, UV and X-ray observations of the
system are discussed in context with models which have been proposed
to explain the appearance of the brilliant jet.
Title: The Ultraviolet Spectrum of RX Puppis
Authors: Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1988ASSL..145..245K
Altcode: 1988syph.book..245K; 1988IAUCo.103..245K
The UV spectrum of the peculiar star RX Puppis has afforded symbiotic
star investigators a wealth of information for unraveling its
mysteries. RX Pup and R Aqr, both being of the D-type variety,
are now better understood as result of an extended coverage of
observations at different wavelengths including radio observations
using the VLA. These stars present challenges to the understanding of
the symbiotic phenomenon and clues to other astrophysical phenomena
like jets. Resolution of the question whether RX Pup has a jet system
and an associated system of rings/extended disk or, alternatively,
a colliding winds region will be resolved by high resolution radio
observations or future observations using the Hubble Space Telescope.
Title: Supernova 1987A in the Large Magellanic Cloud
Authors: Kafatos, Minas; Michalitsianos, Andrew G.
Bibcode: 1988slmc.proc.....K
Altcode:
Papers concerning SN 1987A are presented, covering topics such as images
and spectrograms of the SN 1987A progenitor, a linear polarimetric study
of SN 1987A, the energetics, nature, and uniqueness of the supernova,
comparison of the SN 1987A light curve with other type II supernovae,
P-Cygni features and photospheric velocities, the neutrino burst from SN
1987A, mass determination of neutrinos, neutrino transport, energetics,
and oscillations. Additional papers discuss supernovae light echoes,
the UV interstellar spectrum of SN 1987A, theoretical models of SN
1987A, circumstellar and interstellar interaction, the supernova as a
stripped asymptotic-branch giant in a binary system, pulsar formation
and the fall back mass fraction, the signals of particle acceleration
at SN 1987A, the effects of the mixing of the ejecta on the hard X-ray
emissions from the supernova, possible s-process gamma-ray lines in
supernovae, detectability of early thermal radiation from a neutron star
in SN 1987A, NASA studies of the supernova, and information exchange
for SN 1987A. Observational studies presented include optical, IR,
radio, and UV observations, IR speckle-interferometry, coded mask X-ray
observations, broad band X-ray imaging spectrophotometry, gamma-ray
and thermal X-ray observations, and reports from several observatories.
Title: The Large-Scale Radio Structure of R Aquarii
Authors: Hollis, J. M.; Kafatos, M.; Michalitsianos, A. G.; Oliversen,
R. J.; Yusef-Zadeh, F.
Bibcode: 1987ApJ...321L..55H
Altcode:
Radio continuum observations of the R Aqr symbiotic star system, using
the compact D configuration of the VLA at 6-cm wavelength, reveal a
large-scale about 2-arcmin structure engulfing the binary, which has
long been known to have a similar optical nebula. This optical/radio
nebula possesses about 4 x 10 to the 42nd ergs of kinetic energy which
is typical of a recurrent nova outburst. Moreover, a cluster of a dozen
additional 6-cm radio sources were observed in proximity to R Aqr, most
of these discrete sources lie about 3 arcmin south and/or west of R Aqr
and, coupled with previous 20-cm data, spectral indices limits suggest
a thermal nature for some of these sources. If the thermal members of
the cluster are associated with R Aqr, it may indicate a prehistoric
eruption of the system's suspected recurrent nova. The nonthermal
cluster members may be extragalactic background radio sources.
Title: Physical Parameters for 12 Planetary Nebulae and Their Central
Stars in the Magellanic Clouds
Authors: Aller, Lawrence H.; Keyes, Charles D.; Maran, Stephen P.;
Gull, Theodore R.; Michalitsianos, Andrew G.; Stecher, Theodore P.
Bibcode: 1987ApJ...320..159A
Altcode:
Nebular and central star parameters and elemental abundances of C,
N, O, Ne, S, and Ar are presented for the planetary nebulae N2, N5,
N43, N54, and N67 in the SMC and P2, P7, P9, P25, P33, and P40 in
the LMC. The nebular chemical compositions are affected by nuclear
processes in the precursor stars, which may not have been sufficiently
massive to synthesize Ne, S, or Ar, which appear to be deficient with
respect to their solar abundances by factors of roughly four and five
for the LMC and SMC, respectively. Even after excluding nebulae formed
by stars in which O apparently was destroyed by nuclear processes, O
depletion in the LMC and SMC nebulae is significantly greater than in
galactic planetaries. The estimated masses of the 12 remnant central
stars range from 0.58 to 0.71 solar mass.
Title: Status Report on the VAX-Based IUE Regional Data Analysis
Facility at GSFC
Authors: Grady, C. A.; Thompson, R. W.; Michalitsianos, A.
Bibcode: 1987BAAS...19..739G
Altcode:
No abstract at ADS
Title: Jets from symbiotic stars.
Authors: Kafatos, M.; Cassatella, A.; Michalitsianos, A. G.; Piro,
L.; Viotti, R.
Bibcode: 1987IAUS..122..491K
Altcode:
R Aquarii is the closest symbiotic variable that shows extended emission
with multiple jet components. A number of other symbiotics also show
jet activity and this phenomenon may be common, particularly among
D-type symbiotics.
Title: Hires IUE Observations of the Peculiar Stars RX Puppis and
R Aquarii
Authors: Michalitsianos, Andrew G.
Bibcode: 1987iue..prop.2814M
Altcode:
The symbiotic variables R Aquarii and RX Puppis exhibit a variety of
emission properties over a wide range of wavelengths that includes
centimeter, IR, X-ray, optical as well as intense emission in the near
and far-UV. They are regarded as prototypes for detailed investigation
of the symbiotic phenomena, because the morphology discerned with high
spatial radio continuum maps indicate jet, or collimated flow from
these systems. We have undertaken a detailed study of these objects
in order to determine the UV line and continuum emission properties of
these systems in context with the radio morphology. Recently obtained
IUE spectra of R Aqr (M7e+pec) indicate that the region of maximum UV
line emission appears displaced relative to the suspected location
of the Mira and hot subdwarf, which are surrounded in a compact HII
region. This is indicated from LORES-SWP spectra by a systematic
wavelength shift evident in most of the high excitation UV emission
lines in the direction of the jet; the 10x20" aperture of IUE is
centered at the radio position that corresponds to the HII region, and
the position angle of the aperture is oriented so that the dispersion
of the SWP-LORES camera is closely aligned with the axis by the radio
emitting features which comprise the jet. When the large IUE entrance
aperture is recentered at radio Feature-A (approximately 2.7 NE from
the HIT region), the high excitation emission lines of C IV, He II,
Si III] and C III] appear at their respective nominal wavelengths,
providing further evidence that the compact HII region, which is the
brightest component in 6-cm radio continuum maps, is not the primary
source of high excitation UV line emission, as previously assumed. We
propose collaborative NASA-ESA, HIRES-SWP observations of the central
HII region surrounding R Aqr, enabling us to examine for the first time
the line profile properties of strong high excitation resonance and
intercombination emission lines for velocity and spatially extended
structure with ~0.1A resolution. These observations may have direct
application to more distant and spatially unresolved symbiotics. For
example, the C IV emission doublet recently observed in HIRES-SWP
spectra of the nebular jet (feature B) region in R Aqr, reveals
multi-component structure, similar to that seen in RX Puppis. But
recently obtained sub-arcsecond VLA observations of RX Puppis indicates
it also possesses a jet, reminiscent of the R Aqr radio morphology, but
smaller in scale owing to its greater distance. Collaborative (NASA-ESA)
deep SWPHIRES exposures of RX Puppis are requested in order to properly
expose the broad wings of the C IV doublet and other high excitation
emission lines, for comparison with the line profile structure of the
central HII region of R Aqr. Similarity of line profile structure may
be generally indicative of collimated mass expulsion in a subset of
symbiotic stars which are strong emitters at centimeter wavelengths,
and which contain Mira-type variable.
Title: The R Aquarii jet.
Authors: Cassatella, A.; Kafatos, M.; Michalitsianos, A. G.; Piro,
L.; Viotti, R.
Bibcode: 1987IAUS..122..469C
Altcode:
The X-ray (EXOSAT) and ultraviolet (IUE) observations of R Aqr and
its jet are discussed in the light of a proposed model.
Title: Ultraviolet Variability and Mass Expulsion from R Aquarii
Authors: Kafatos, M.; Michalitsianos, A. G.; Hollis, J. M.
Bibcode: 1986ApJS...62..853K
Altcode:
Ultraviolet spectra in the 1200-3200 A range indicate that the extended
nebular features which resemble a jet in the peculiar variable R
Aquarii (M7e + pec) increased in excitation in 1985. The emission
properties of the compact H II region that surrounds the unresolved
binary, and those of the extended nebular jet, have been analyzed from
low-resolution IUE spectra of these regions. In particular, the UV
line intensities observed in the jet appear variable on a time scale
of about 1.5 yr. A new accretion disk model is proposed that explains
the kinematic and ionization properties of discrete components which
comprise the jet emission nebulosity, the appearance of the jet in
the 1980s, and morphology that uniquely characterizes the R Aquarii
system at radio, optical, UV, and X-ray wavelengths.
Title: Sub--Arc Second 2 Centimeter Continuum and SiO Spectral Line
Observations of R Aquarii
Authors: Hollis, J. M.; Michalitsianos, A. G.; Kafatos, M.; Wright,
M. C. H.; Welch, W. J.
Bibcode: 1986ApJ...309L..53H
Altcode:
Sub-arc second (≡0arcsec.15) VLA observations at 2 cm have resolved
the previously reported 6 cm H II region, which engulfs the R Aquarii
binary system, into two components. The stronger component is itself
partially resolved and distorted in shape, which may be a consequence
of the long-period variable (LPV) wind being subjected to the intense
ionizing radiation field of the hot companion's accretion disk. The
accretion disk, which may be precessing, can be formed by tidal mass
exchange between the LPV and its hot companion. The authors also report
SiO observations that suggest maser action occurs in the circumbinary
nebulosity far removed from the LPV photosphere.
Title: The R-Aquarii Jet at Ultraviolet and Radio Wavelengths
Authors: Michalitsianos, A. G.; Kafatos, M.; Hollis, J. M.
Bibcode: 1986ESASP.263..443M
Altcode: 1986niia.conf..443M; 1986NIA86......443M
The peculiar symbiotic variable R Aquarii embodies a number of
distinguishing properties, the most significant being a column of
nebular emission that extends NE from the central star, that was
discovered nearly a decade ago. High spatial resolution VLA observations
indicate the jet is composed of four discrete radio emitting knots,
which form a broad arc, about 6arcsec.5 in extent. The authors have
monitored the jet and central star with IUE LORES-SWP λλ1200 -
2000 spectra, in order to detect possible temporal variations. The
absolute line intensities of N V, C IV and He II, as well as numerous
other ionic species in the jet, were found to vary on a timescale
of ≡1.5 years. The authors present these new findings, in context
with high spatial resolution radio VLA maps and SiO maser millimeter
interferometer observations.
Title: IUE survey of planetary nebulae in the large and small
Magellanic Clouds
Authors: Gull, T. R.; Michalitsianos, A. G.; Maran, S. P.; Stecher,
T. P.; Aller, L. H.; Keyes, C. D.
Bibcode: 1986ESASP.263..295G
Altcode: 1986NIA86......295G; 1986niia.conf..295G
The ultraviolet survey of planetary nebulae in the Magellanic Clouds
now emcompasses 15 objects detected with IUE during 1981 - 86. Twelve
of these have now been analyzed and highlights of the results are
presented here. Specifically, chemical abundances and other nebular
parameters have been determined, along with masses for the central
stars. The latter are clustered in the range 0.58 to 0.71 solar masses,
contrary to our preliminary finding. This difference is attributed to
the adoption of new stellar atmosphere models that better represent
the emergent flux distributions below the Lyman limit.
Title: Jet activity in the symbiotic variable R Aquarii.
Authors: Michalitsianos, A. G.; Hollis, J. M.; Kafatos, M.
Bibcode: 1986CaJPh..64..523M
Altcode:
Low-resolution ultraviolet spectra of the R Aquarii jet have been
obtained with the International Ultraviolet Explorer (IUE). The
most recent IUE observations indicate the ionization state of the
jet is increasing. Subarcsecond, Very Large Array observations of
R Aquarii have resolved the radio-continuum structure into discrete
parcels of emission that are extended and nearly collinear. R Aquarii
provides evidence that indicates stellar jet activity is not unique to
objects associated with high-energy emission processes alone. Rather,
the nature of the aligned radio-optical features that comprise the R
Aquarii jet indicate that directional mass expulsion, in the form of
discrete-collimated ejecta, probably reflect a general, underlying,
physical process associated with a wide variety of peculiar stellar
objects. As such, the R Aquarii jet constitutes a prototype for jet
activity in composite or peculiar emission stars.
Title: Characteristics of Some High-Excitation Planetary Nebulae
and Central Stars in the Magellanic Clouds
Authors: Aller, L. H.; Keyes, C. D.; Maran, S. P.; Gull, T. R.;
Stecher, T. P.; Michalitsianos, A. G.
Bibcode: 1986BAAS...18..693A
Altcode:
No abstract at ADS
Title: Evidence for Extended Radio Emission Surrounding RX Puppis
Authors: Hollis, J. M.; Oliversen, R. J.; Kafatos, M.; Michalitsianos,
A. G.
Bibcode: 1986ApJ...301..877H
Altcode:
Evidence for an approximately 1-arcsec extended structure in 6
cm continuum emission emanating from the symbiotic star system RX
Puppis is reported. Hourly continuum flux changes were not detected
as suggested in previous radio experiments by others. The observations
indicate that the predominant nature of the radio emission is thermal
and consistent with an optically thick stellar wind emanating from
the symbiotic star system. The results presented here are discussed
with regard to other similar stellar binary systems.
Title: R Aquarii
Authors: Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1986IAUC.4157....2K
Altcode: 1986IAUC.4157....0K
M. Kafatos, George Mason University; and A. G. Michalitsianos, Goddard
Space Flight Center, report: "IUE observations of this symbiotic star
over the past four years indicate that line emission from the jet
components is variable with period 1.5 yr. Because of the distances
involved we interpret this variability as 'light echo', in the sense
that ionizing radiation from the inner region of an accreting disk
surrounding the hot star excites the jet components ~ 10**14 m. Our
most recent observations of 1985 Jan. and July show that N V, He II and
C IV emission has been increasing, indicating the system is returning
to a high-excitation state."
Title: Temporal UV-Line Profile Variations in the Peculiar Object
RX Puppis
Authors: Michalitsianos, Andrew G.
Bibcode: 1986iue..prop.2496M
Altcode:
The complex nature of the UV and optical emission lines observed in
the peculiar nova-like star RX Puppis makes this object especially
interesting for further IUE investigations. The C IV 1548 and He II
1640 emission lines are characterized by multiple structure in which
seven distinct emission components in the C IV doublet have been
identified. These components are predominantly redward of the rest
wavelength; the highest velocity components are typically V max >
+300 km s^-1. Multiple component structure is also evident in the
intercombination lines of N III], N IV], O III], Si III] and C III],
which suggests complex motion in the hot gaseous environment of the
system. The dramatic variations observed in the emission line profiles
of UV permitted and intercombination lines suggest that material
motion in this system occurs on a minimum timescale of at least -6
months, i.e. the shortest time interval sampled during our previous
IUE monitoring program. However, microwave observations obtained of
RX Puppis at 5.0, 6.0 and 8.7 GHz indicate that its radio flux can
vary by as much as 50-percent, on timescales less than 24 hours. It
is extremely important to determine if the multiple structure which
characterizes the C IV, He II and other lines vary on similar timescales
< 24hours. Short timescale variability in line profile structure
of UV resonance lines could provide important clues concerning the
nature of dynamical activity between the component stars; the system
is believed to consist of a hot subdwarf that tidally accretes mass
from a 580-day period Mira. We propose to combine our high resolution
IUE observations of RX Puppis with Very Large Array (VLA) radio data,
for which observing time is presently being scheduled. Our observing
program and description of general research goals follow.
Title: Mass Ejection in R-Aquarii
Authors: Michalitsianos, A.; Kafatos, M.; Hollis, J.
Bibcode: 1986ppm..conf..215M
Altcode:
The symbiotic star R Aquarii embodies a number of distinguishing
properties, the most significant being a collimated jet that
extends approximately out to 6-arcsec NE from the star. The authors
have obtained low resolution ultraviolet spectra of the R Aquarii
jet with the International Ultraviolet Explorer (IUE). Their most
recent IUE observations indicate the ionization state of the jet is
increasing. Sub-arcsecond VLA observations of the R Aquarii have
resolved the radio continuum structure into discrete parcels of
emission, which are extended and highly collinear. R Aquarii provides
evidence that indicates stellar jet activity is not unique to objects
associated with high energy emission processes alone.
Title: High-dispersion ultraviolet spectra of the peculiar star
RX Puppis.
Authors: Kafatos, M.; Michalitsianos, A. G.; Fahey, R. P.
Bibcode: 1985ApJS...59..785K
Altcode:
High spectral resolution observations of the peculiar star RX Puppis
obtained with the International Ultraviolet Explorer suggest the
presence of a complex gaseous ring system which surrounds an accreting
hot secondary. The anomalous line intensity ratio of the C IV 1548,
1550 A doublet during the observations exceeded the optically thick
limit, implying the presence of a high-velocity wind. Additionally, the
C IV doublet exhibits about four or five narrow emission components,
which are redshifted up to velocities of at least about + 300 km/s
(with respect to the rest wavelength).
Title: The 1984 eclipse of the symbiotic binary SY Muscae.
Authors: Kenyon, S. J.; Michalitsianos, A. G.; Lutz, J. H.; Kafatos, M.
Bibcode: 1985PASP...97..268K
Altcode:
The authors present ultraviolet and optical observations of the 1984
eclipse of the symbiotic binary star SY Mus. The optical light curve
shows a 627-day variation which is reflected in the intensity of the
far-UV continuum (λ < 2000 Å) and in the intensities of all strong,
permitted UV emission lines. This contrasts sharply with other eclipsing
systems, in which some high ionization permitted lines show little
evidence for large-scale variability. The behavior of the emission
lines and the UV continuum is most naturally understood if the hot
stellar source and a surrounding ionized nebula in the SY Mus binary
are eclipsed by a red-giant companion every 627 days. The depth of
the eclipse in the He II λ1640 emission line allows estimating the
radius of the partially eclipsed He+ region (75 R_sun;)
and that of the cool giant (60 R_sun;), for a distance of 1.3 kpc.
Title: The R Aquarii system at optical and radio wavelengths.
Authors: Hollis, J. M.; Kafatos, M.; Michalitsianos, A. G.; McAlister,
H. A.
Bibcode: 1985ApJ...289..765H
Altcode:
New continuum observations of all radio components of the R Aquarii
system at 2, 6, and 20 cm are reported which allow determination
of polarization properties, integrated flux levels, spectral
indices, and hence the emission mechanisms of the individual
components. Complementary wide-band optical observations are also
reported to help determine the nature and structure of the compact
double radio source (CDRS) and the R Aquarii radio jet. The results
of these observations are discussed in detail with regard to models
currently or previously proposed for the R Aquarii system. It is
concluded that the compact H II region spectral index is about +0.6,
indicative of a thermal and optically thick expanding wind from the
long-period variable. The radio jet emission is shown to be optically
thin, thermal, cospatial with optical emission, and stable over the last
few years. The CDRS is shown to be an extragalactic background object.
Title: The Origin of nonradiative heating/momentum in hot stars :
proceedings of a workshop sponsored by the National Aeronautics and
Space Administration, Washington, D.C., and the American Astronomical
Society, Washington, D.C., and held at NASA Goddard Space Flight
Center, Greenbelt, Maryland, June 5-7, 1984
Authors: Underhill, A. B.; Michalitsianos, A. G.
Bibcode: 1985NASCP2358.....U
Altcode: 1985QB843.E2O75....; 1985onhm.rept.....U
No abstract at ADS
Title: Characteristics of Infrared Variable Stars as Observed
from Orbit
Authors: Maran, S. P.; Heinsheimer, T. F.; Stocker, T. L.; Chapman,
R. D.; Hobbs, R. W.; Michalitsianos, A. G.
Bibcode: 1985SPIE..513..213M
Altcode:
No abstract at ADS
Title: UV Variability in Two Peculiar Emission Stars in the Magellanic
Clouds
Authors: Michalitsianos, Andrew G.
Bibcode: 1985iue..prop.2190M
Altcode:
The peculiar emission star SMC S-18 is characterized by a variety of
spectral properties in the UV and optical that suggest high mass loss
rates, turbulence from wide emission lines and indications of both
high and low density material in the stellar neighborhood. S 18 is by
far the most peculiar emission star studied in the Small Magellanic
Cloud with IUE, because it exhibits significant temporal variations
on timescales of months in high ionization emission lines of C IV
1548,1550 and He II 1640, and particularly N V 1245,1249. However,
the UV emission line spectrum of SMC S-18 is strikingly similar to
another recently observed peculiar star LMC " Anonymous" (Sanduleak's
Star in the Large Magellanic Cloud). Sanduleak's star in the LMC appears
deficient in carbon, while three stages nitrogen, together with doubly
ionized Helium, dominate the far-UV 1200-2000 wavelength range. Strong N
V 1239,1243 emission in contrast to the relatively weak C IV emission in
LMC 5 "Anonymous" indicates that a highly ionized gas at approximately
-10^5K gives rise to the chemically peculiar spectrum of the object,
and suggests the presence of CNO processed material that is expected
during advanced stages of evolution. We suspect that the emission line
spectrum of Sanduleak's Star (in the LMC) is variable, since it is
strikingly similar (based on the one IUE spectrum that exists of this
object) to the UV emission line spectrum of SMC S18. We request IUE
observing time in order to determine if the UV emission line spectrum
of LMC "Anonymous" shares similar temporal variability as found for its
counterpart in the SMC. If variability which is suggested from optical
observations is confirmed in high excitation UV emission lines, the
distinguishing characteristics of SMC S-18 and LMC "Anonymous" could
indicate the existence of a highly evolved group of peculiar emission
stars which are unique to the Magellanic Clouds, our observing program,
justification and method of data analysis are discussed.
Title: R Aqr Jet
Authors: Michalitsianos, Andrew G.
Bibcode: 1985iue..prop.2303M
Altcode:
No abstract at ADS
Title: Temporal Variability: UV Emission from the R Aquarii Jet
Authors: Michalitsianos, Andrew G.
Bibcode: 1985iue..prop.2188M
Altcode:
IUE observing time is requested to monitor variations in
emission line strength that have been observed in the recently
discovered optical/radio jet feature in the percular emission star
R Aquarii. Previous IUE observations suggest a possible association
between the intrinsic light output of the 387-day period Mira and the
UV emission line strengths in the jet. We propose to extend our IUE
cover-age in order to obtain short and long wavelength low dispersion
spectra of the jet at particular phases of the Mira light cycle. As
such, models that have been advanced to explain the origin of the
newly discovered emission feature in R Aquarii can be tested. These
IUE observations will be supplemented with high spatial resolution
6cm radio maps that will be obtained at the Very Large Array by the
proposers. It is the aim of this program to develop a model for the
ionization structure of both the jet feature as well as the central
unresolved region, by examining in detail the differences in the UV
emission line properties. Our observing program, goals and method of
data analysis follow.
Title: IUE observations of the "jet" emission feature in R Aquarii.
Authors: Michalitsianos, A. G.; Hollis, J. M.; Kafatos, M.
Bibcode: 1984NASCP2349..163M
Altcode: 1984fiue.rept..163M; 1984IUE84......163M
IUE low dispersion observations of the "jet" emission feature in
the symbiotic variable R Aquarii were obtained over the course of
two years. A comparison SWP λλ1200 - 2000 spectra obtained of
both this feature and the central UV star indicates significant
differences exist between these emission regions; Si III] λ1893
which is prominent in the central star is virtually absent in the
"jet". Based upon analyses of UV and optical emission line spectra,
the spectral properties of the feature suggest it is a highly excited
tenuous region ≡104cm-3 characterized by
prominent forbidden nebular line emission.
Title: Temporal UV emission from the peculiar star RX Puppis.
Authors: Kafatos, M.; Michalitsianos, A. G.; Brugioni, J.
Bibcode: 1984NASCP2349..326K
Altcode: 1984IUE84......326K; 1984fiue.rept..326K
The peculiar emission star RX Puppis was monitored with the
International Ultraviolet Explorer in low and high dispersion. The
ultraviolet spectrum of RX Ruppis is characterized by strong permitted
and intercombination emission lines similar to that observed in slow
novae and symbiotic stars. The absolute emission fluxes of most lines
appear to have increased since the first year of observations, during
which the reasonance doublet of C IV lambda lambda1548,1550 increased
by approximately 14 percent. During this period the intensity ratio of
the C II I(lambda1548)/I(lambda1550) typically had values less than
unity, and thus exceeded the optically thick limit. Over the several
years of observations following maximum UV emission, the doublet
ratio appears to be approaching values approximately 1. C IV doublet
ratios 1 could be explained by P-Cygni structure in the lambda1550.7
line, in which the broad absorption component deminishes emission at
lambda1548.2 during ejection. This would imply expansion velocities
500 Km/s. The high dispersion line profile structure in both permitted
and intercombination lines appear generally complex and time dependent.
Title: Symbiotic stars.
Authors: Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1984SciAm.251a..70K
Altcode: 1984SciAm.251...70K
Satellite observations have revealed that certain celestial objects
with a peculiar spectrum consist of a red-giant star surrounded by a
small dense nebula heated by a compact hot companion star.
Title: Symbiotic stars
Authors: Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1984SciAm.251a..84K
Altcode: 1984SciAm.251...84K
The physical characteristics of symbiotic star systems are discussed,
based on a review of recent observational data. A model of a symbiotic
star system is presented which illustrates how a cool red-giant star is
embedded in a nebula whose atoms are ionized by the energetic radiation
from its hot compact companion. UV outbursts from symbiotic systems
are explained by two principal models: an accretion-disk-outburst
model which describes how material expelled from the tenuous envelope
of the red giant forms an inwardly-spiralling disk around the hot
companion, and a thermonuclear-outburst model in which the companion
is specifically a white dwarf which superheats the material expelled
from the red giant to the point where thermonuclear reactions occur
and radiation is emitted. It is suspected that the evolutionary course
of binary systems is predetermined by the initial mass and angular
momentum of the gas cloud within which binary stars are born. Since
red giants and Mira variables are thought to be stars with a mass of
one or two solar mass, it is believed that the original cloud from
which a symbiotic system is formed can consist of no more than a few
solar masses of gas.
Title: Mass ejection from the peculiar emission star R Aquarii
Authors: Michalitsianos, A. G.
Bibcode: 1984ComAp..10...85M
Altcode:
It is pointed out that the composite emission object R Aquarii embodies
a number of characteristic properties which distinguish it from other
peculiar emission stars. The visual spectrum indicates the presence
of a cool Mira variable in close association with a hot unresolved
ionizing source of radiation which appears to be responsible for the
high excitation nebular emission observed. It has been suggested by
Hubble (1943) and Baade (1944) that the distinguishing meniscus-shaped
nebula was formed by a nova outburst which occurred about 600 years
ago. Wallerstein and Greenstein (1980) reported the appearance of a
new feature in R Aquarii which resembles a brilliant 'spike' or 'jet'
protruding a distance approximately 7 arcsec from the central compact
region. Attention is given to several models which have been considered
to explain the emission feature.
Title: Variable ultraviolet emission in SY Muscae.
Authors: Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1984MNRAS.207..575M
Altcode:
The results of continued IUE monitoring of the symbiotic variable SY
Muscae, following an earlier report of a radical enhancement in UV
emission from the star, are reported. Over the course of one year,
the prominent emission lines of N V, O V, C IV, and He II appear to be
gradually decreasing in absolute intensity. This appears to coincide
with a steady decline in electron density in the emission line forming
region. The data are consistent with a sudden ejection event in which
material expelled from the surface of a hot subdwarf has exposed the
underlying UV continuum of the star. A number of strong emission
lines that are photoexcited by the intense radiation field of the
secondary also exhibit broad pedestal emission that suggests turbulent
velocities of about 150-300 km/s in an expanding shell or possibly in
an accretion disk.
Title: Temporal UV Emission From the Peculiar Star RX Puppis
Authors: Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1984BAAS...16..515M
Altcode:
No abstract at ADS
Title: Symbiotic stars.
Authors: Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1984SciAm.251g..70K
Altcode:
No abstract at ADS
Title: Observations of two peculiar emission objects in the Large
MagellanicCloud.
Authors: Kafatos, M.; Michalitsianos, A. G.; Allen, D. A.; Stencel,
R. E.
Bibcode: 1983ApJ...275..584K
Altcode:
Ultraviolet and visual wavelength spectra were obtained of two
peculiar emission objects, Henize S63 and Sanduleak's star in the
Large Magellanic Cloud. Previously not observed in the near- or
far-ultraviolet, both objects exhibit strong permitted and semiforbidden
line emissions. Estimates based on the absolute continuum flux of the
hot companion star in Hen S63 indicate that it rivals the luminosity
of the carbon star primary. The emission-line profile structure in
both objects does not suggest Wolf-Rayet type emission. Carbon in
Sanduleak's star (LMC anonymous) is conspicuously absent, while
N V, semiforbidden N IV, and semiforbidden N III dominate the UV
emission-line spectrum. Nitrogen is overabundant with respect to carbon
and oxygen in both objects. The large overabundance of nitrogen in
Sanduleak's star suggests evidence for CNO processes material similar
to that seen in Nu Car.
Title: High spatial resolution VLA observations of the R Aquarii jet.
Authors: Kafatos, M.; Hollis, J. M.; Michalitsianos, A. G.
Bibcode: 1983ApJ...267L.103K
Altcode:
High spatial resolution observations (≡1arcsec) of the jet feature
associated with the symbiotic variable R Aquarii were obtained with the
VLA. If the line defined by the jet and star is extended ≡196arcsec,
it intercepts a previously reported and heretofore unresolved radio
source. In the high spatial resolution 6 cm map this feature is
resolved into a compact double radio source, whose peak intensity
lies on an axis defined by the jet and star. The possible association
of this feature with R Aquarii cannot be determined from these radio
morphology studies alone. If this feature is associated with R Aquarii,
it may represent ejecta from the system which occurred previously.
Title: Ultraviolet observations of the R Aquarii jet.
Authors: Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1983HiA.....6..639M
Altcode:
Observations of the recently discovered jet feature in the symbiotic
variable R Aquarii (M7e+pec) were obtained with the IUE. A comparison
of low disperison UV-spectra between the central ionized source and
the jet feature is given.
Title: Low Dispersion UV Observations of the R Aquarii Jet
Authors: Michalitsianos, Andrew G.
Bibcode: 1983iue..prop.1493M
Altcode:
The symbiotic variable R Aquarii exhibits complex emission structure
at a variety wavelengths. This symbiotic variable has been recently
found to contain a jet, which in addition to SS 433 constitutes
it as the only other known. stellar source associated with jet
activity. The newly discovered optical-radio jet feature which is
seen extending about 10 arcsec from the central object suggests R
Aquarii is expelling material in a directional manner. Preliminary
ultraviolet spectra obtained with IUE indicate the far UV spectrum
of the jet feature is characterized by strong continuum which rises
with decreasing wavelength over the 1200-2000A wavelength range,
and which is considerably different in appearance if compared to
the relatively flat continuum which arises from the central ionized
nebulosity which engulfs the star system. Prominent Si III] 1892A and
Si II 1808,1816A seen in the central object are virtually absent in
the jet feature. Because of the prevailing low electron densities,
the absence of Si III] emission in the jet possibly is explained by
depletion of this particular element in ejected material. The appearance
of S II 1250,1259A emission in the jet feature is consistent with the
carbon line ratios which indicate the overall thermal excitation of
the jet is comparatively lower than the central ionized nebula. Optical
intensity emission line ratios indicate that the surrounding nebulosity
is highly variable in time. We request IUE observing time in order to
further investigate the temporal and spatial UV emission properties
of the jet and associated optical-radio features which have recently
been detected. Owing to the spatial extent of the jet feature (about
10 arcsec), R Aquarii affords us a unique opportunity to directly
investigate the ionization structure and chemical composition of
ejected material. Together with high spatial resolution radio maps
recently obtained at 6-cm with the Very Large Array, we anticipate
being able to correlate radio and UV emission in various emission
features associated with R Aquarii. Our observing program, objectives
and method of analysis are described in the following proposal.
Title: International Ultraviolet Explorer observations of the R
AQR jet.
Authors: Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1982ApJ...262L..47M
Altcode:
Ultraviolet spectra were obtained with the International Ultraviolet
Explorer of the newly discovered optical-radio jet feature in the
symbiotic variable R Aquarii. The far-UV continuum of the jet is
characterized by strong continuum which rises with decreasing wavelength
in the 1200-2000 A wavelength range and is considerably different in
appearance from the relatively flat continuum exhibited by ionized
nebulosity in the central star. Prominent Si III semi-forbidden lines
and Si II emission lines seen in the central region are virtually
absent in the jet. This could reflect the depletion of silicon in
the feature, the result of grain formation in material that has been
ejected by the central star. Consistent with this interpretation is
the overall excitation of the jet that suggests it is cooler than the
nebulosity that engulfs the central UV object.
Title: High Spatial Resolution VLA Observations of the R Aquarii Jet
Authors: Kafatos, M.; Hollis, J. M.; Michalitsianos, A. G.
Bibcode: 1982BAAS...14..903K
Altcode:
No abstract at ADS
Title: The peculiar variable star R Aquarii and its jet
Authors: Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1982Natur.298..540K
Altcode:
Outward motion of the nebula associated with the symbiotic variable
R Aquarii was suspected by Hubble1 and confirmed by
Baade2, who estimated its ejection ~600 yr ago. A new
feature of the nebulosity near the star appeared between 1970 and
1977 as found by Herbig from direct plates obtained with the 3-metre
telescope at Lick Observatory. The `spike' or `jet' so-called by
Wallerstein and Greenstein3 appears as a protrusion from
the central star. The observational properties of the jet in both the
optical and radio are described by Sopka et al.4. The near
UV image obtained in 1980 by Herbig and the VLA radio map4
are shown combined in Fig. 1. Here we suggest that the jet is the
result of supercritical accretion of mass transferred from the cool
387-day period Mira to the hot companion in a highly elliptical
orbit. Ancient Japanese astronomical records suggest a nova outburst
in AD 930 may be associated with R Aquarii which formed the outer
extended nebulosity. The jet may help explain the outbursts of this
object as well as the excitation of the R Aquarii nebula.
Title: Radio optical observations of the R AQR jet.
Authors: Sopka, R. J.; Herbig, G.; Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1982ApJ...258L..35S
Altcode:
VLA observations at 6 cm and Lick Observatory optical plates of R
Aquarii indicate the existence of a jetlike feature extending 7 to
10 arcsec from the central star. A wide field map at 6 cm shows an
unresolved compact radio source which lies close to the axis defined
by the jet at a distance of about three arcmin from R Aqr. Episodic
mass transfer in this symbiotic variable could explain the erratic
outbursts that R Aqr is known to undergo. Formation of an accretion
disk and the accompanying radio-optical jet may characterize the
observed outbursts in this system.
Title: IUE observations of the peculiar star RX Pup.
Authors: Kafatos, M.; Michalitsianos, A. G.; Feibelman, W. A.
Bibcode: 1982ApJ...257..204K
Altcode:
The first set of high-dispersion UV observations of RX Pup are
presented. Anomalous line profile structure observed in a number of
high-excitation emission lines is discussed in context with a model that
includes streams and complex mass motions in the system. Anomalies in
high-excitation lines suggest dynamic activity in circumstellar material
that probably has the form of rings and/or gas streamers between the
cool giant and the hot companion. The continuum in low dispersion is
fairly flat around 1200-2000 and rises toward longer wavelengths,
and cannot be due to a star earlier than A0 II. Alternatively, it
may be from an accretion disk. Photoionizing radiation may be due to
the presence of an unseen, hot subdwarf with most probable effective
temperature 75,000-90,000 K. Alternatively, it may be due to an
accretion disk around a secondary with boundary layer temperature
about 100,000 K.
Title: A brightness of the symbiotic variable SY Mus.
Authors: Michalitsianos, A. G.; Kafatos, M.; Feibelman, W. A.;
Wallerstein, G.
Bibcode: 1982A&A...109..136M
Altcode:
The symbiotic variable SY Muscae has been observed with IUE in September
1980 and June 1981 and in the photographic region in May 1981. The
entire ultraviolet spectrum brightened between September and June by
about a factor of 5. The spectrum shows high excitation including
emission from N v and high electron density, about 10-billion per
cu cm as determined from various line ratios in the ultraviolet. The
optical spectrum is dominated by permitted lines; even forbidden O III
is very weak again indicating high density in the ionized region. The
increase in ultraviolet continuum and line emission may be due to
enhanced mass transfer from the cool star whose period is 623d and
whose maximum was predicted to occur very close to the time of the
June 1981 observations. Alternatively the hot star and much of the
emitting gas could have been in eclipse in September 1980.
Title: Ultraviolet observations of four symbiotic stars.
Authors: Michalitsianos, A. G.; Kafatos, M.; Feibelman, W. A.; Hobbs,
R. W.
Bibcode: 1982ApJ...253..735M
Altcode:
Observations were obtained with the International Ultraviolet Explorer
(IUE) of four symbiotic stars. The UV spectra of YY Her, SY Mus,
CL Sco, and BX Mon are characterized by varying degrees of thermal
excitation. These low resolution spectra have been analyzed in terms
of line-blanketed model atmospheres of early A, B, and F type stars in
order to identify the nature of the hot companion in these systems. The
expected emission from early main sequence stars does not fully explain
the observed distribution of UV continuum energy over the entire IUE
spectral range (1200-3200 A). More likely the observed continuum may be
originating from an accretion disk and/or hot subdwarf that photoionizes
circumstellar material, and gives rise to the high excitation lines
that have been detected. The Bowen fluorescent excited lines of O III
in SY Mus exhibit slightly broadened profiles that suggest possible
turbulent motions in an extended circumstellar cloud with characteristic
velocities of approximately 300 km/s.
Title: Ultraviolet observations of the 1980 eclipse of the symbiotic
star CICyg.
Authors: Stencel, R. E.; Boiarchuk, A. A.; Michalitsianos, A. G.;
Kafatos, M.
Bibcode: 1982ApJ...253L..77S
Altcode:
The paper presents secular and eclipse variations of ultraviolet
lines and continua in the course of nearly a complete orbit of
CI Cygni. High-excitation resonance lines show minimal effects of
eclipse, while intercombination lines have faded and show pronounced
but nontotal eclipse effects. The observations are examined in terms
of mass transfer from the extended cool envelope of the red giant to a
compact secondary. The formation of an accretion disk is a transitory
phenomenon in which viscosity eventually dissipates the disk over
orbital time scales. The intercombination line emission is explained by
a large-scale low-density nebula, and it is found that the resonance
line emission apparently arises in a large volume emitting region,
possibly formed through shock collision from interacting stellar winds
from the primary and secondary.
Title: Observations and analysis of the R Aquarii jet.
Authors: Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1982NASCP2238..452K
Altcode: 1982IUE82......452K; 1982NASCP2338..452K; 1982auva.nasa..452K
Ultraviolet, optical and radio observations of the symbiotic star R
Aquarii are discussed in the light of the discovery of a bright radio
and optical jet from this star. The star is probably a binary with
a period of 44 years. The VLA maps of the jet reveal a protruding
structure extending approximately 10 arc sec from the central radio
source with a position angle virtually identical to that of the optical
jet observed at Lick. The observations of R Aqr are interpreted
as indicating the existence of an accretion disk around an unseen
companion. The hot subdwarf has effective temperature approximately
65,000 K. It is suggested that the Mira primary and the hot secondary
are in orbit around each other with a high eccentricity. At periastron
the hot subdwarf accretes at super critical rates and a jet forms. It
is difficult to understand how an accretion disk would have eclipsed
the Mira in 1928-1935 and 1974-1980. The suppression of maximum light
in these two periods is interpreted as due to a distortion of the Mira
envelope at periastron by the tidal interaction with the secondary. The
jet may help to explain the excitation of the R Aqr nebula. It is
possible that R Aqr flared up as a nova approximately 1000 years ago
forming the nebula.
Title: The peculiar star RX Puppis.
Authors: Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1982ASSL...95..203K
Altcode: 1982nss..coll..203K; 1982IAUCo..70..203K
The first high dispersion observations of RX Puppis in the wavelength
region 1200-3200 A were obtained with the International Ultraviolet
Explorer. The anomalies observed in lines such as He II, semiforbidden
C III, C IV, semiforbidden N III, semiforbidden N IV, semiforbidden
O III, and semiforbidden Si III, which show split line profiles and
Doppler displaced components, suggest dynamic activity in circumstellar
material that probably has the form of rings and/or gas streamers
between the cool giant and the hot companion. The Mg II lines show
P-Cygni structure arising in the Mira primary. The continuum cannot
be due to a star earlier than AO II and it may arise in an accretion
disk around the hot secondary. Moreover, the line emission requires
photoionization either from a hot subdwarf or the inner accretion disk.
Title: UV time-dependent emission in SY Muscae.
Authors: Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1982ASSL...95..191M
Altcode: 1982IAUCo..70..191M; 1982nss..coll..191M
IUE ultraviolet spectra of SY Mus for September 20, 1980 and June
11, 1981 indicate a substantial enhancement of UV emission over a
nine-month period. The general UV flux level appears to have increased
by about one order of magnitude between the two observing epochs. The
strong UV continuum evident throughout the entire IUE spectral range
1200-3200 A on June 11, 1981 is closely approximated by a star with
an effective temperature of 40,000 K. On September 20, 1980, however,
the continuum distribution manifested a more complex structure, which
is possibly explained by a combination of thermal emission from an
early type main sequence star and nebular recombination emission.
Title: Sy Muscae
Authors: Michalitsianos, Andrew G.
Bibcode: 1982iue..prop.1241M
Altcode:
No abstract at ADS
Title: UV eclipse observations of CI Cyg.
Authors: Michalitsianos, A. G.; Kafatos, M.; Stencel, R. E.; Boiarchuk,
A. A.
Bibcode: 1982ASSL...95..141M
Altcode: 1982IAUCo..70..141M; 1982nss..coll..141M
Low spectral resolution observations were obtained with the IUE during
the eclipse phase. Additional data obtained by other IUE groups have
been included in the eclipse observations, making it possible to
examine the UV spectral properties of CI Cyg over nearly an entire
orbit which spans early 1979 through mid 1981. Data obtained over this
period suggest an overall decline in UV emission, consistent with
the decline of optical emission following the outburst of 1975. The
short-wavelength spectrum 1200-2000 A is characterized by numerous
intense high-excitation emission lines which become more prominent out
of eclipse. The LWR wavelength range 2000-3200 A exhibits a few more
additional lines of O III, Mg II, and He II which are superimposed
on continuum that rises gradually with increasing wavelength. The
observations are consistent with a binary star model which involves
mass transfer from the extended cool envelope of the primary to the
compact secondary.
Title: SY MUSCAE
Authors: Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1982IAUC.3657....2M
Altcode:
A. G. Michalitsianos, Laboratory for Solar Physics and Astrophysics,
Goddard Space Flight Center; and M. Kafatos, George Mason University,
communicate: "IUE observations on 1981 Nov. 29 and Dec. 10 show that the
symbiotic star SY Mus continues to undergo substantial enhancement in
ultraviolet emission. C IV 155 nm has increased in emission intensity
by a factor of 26 since 1981 June 11, N V 124 nm has increased by a
factor of 5 and He II 164 nm by a factor of 13. Intercombination lines
of O III, N III, Si III and C III have remained essentially at the same
flux level since 1981 June 11 or have perhaps decreased slightly. The
IUE FeS monitor recorded an apparent magnitude of 10.4 in both June and
December, suggesting that the star system is not following the 623-day
regular period indicated by the visual lightcurves of Greenstein
(1937, Bull. Harvard Coll. No. 906) and Uitterdijk (1934, B.A.N. 7,
177). Visual observations are important now since the object may
be entering an enhanced phase of ultraviolet and possibly optical
emission."
Title: UV emission from the M1 supergiant TV Gem.
Authors: Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1982NASCP2238..263M
Altcode: 1982NASCP2338..263M; 1982auva.nasa..263M; 1982IUE82......263M
Low and high dispersion ultraviolet spectra were obtained of the
M1 supergiant TV Gem with IUE. Previous IUE observations of this
late type supergiant revealed unexpected UV continuum emission,
perhaps arising from an early B companion. Low resolution spectra
obtained approximately one year apart suggest that the strong Si
III in combination perhaps with O I at wavelengths approximately
1300 A varies considerably with time. Large variation in the column
density is required to explain these changes. Sporadic mass expulsion
with mass loss rates dM/dt approximately 0.00001 solar mass yr minus
1st power from the M supergiant could lead to a dense circumstellar
wind near the hot early companion, and thus could account for these
observed variations in equivalent width. The high resolution spectrum
in the 2000 to 3200 A wavelength range is characterized by narrow
absorption lines primarily due to Fe II, Mn II and Mg II (h and k),
which are skewed in profile with an extended red wing. This profile
structure is tentatively attributed to interstellar absorption and an
intervening differentially moving cloud in the direction of Gem OB1,
of which TV Gem is a known association member.
Title: CI Cygni since the 1980 eclipse.
Authors: Stencel, R. E.; Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1982NASCP2238..509S
Altcode: 1982IUE82......509S; 1982auva.nasa..509S; 1982NASCP2338..509S
During the 1980 eclipse of the 855 day period symbiotic binary CI Cyg,
a data set showing high excitation resonance lines which were largely
uneclipsed but brightening on an orbital timescale, and intercombination
lines exhibiting pronounced but nontotal eclipses and which were
fading on an orbital timescale were obtained. A model invoking a low
density dissipating nebula surrounding the hot companion to explain the
intercombination lines, and a shock between stellar winds to interpret
the resonance lines, is described. Subsequent synoptic observations
revealed continuing changes in the UV emission line fluxes consistent
with those described above, except for the brightening of Mg II and the
emergence of strong, not previously seen Mg V emission. Post-outburst
and phase dependent changes must be included in any interpretation
of this system as the archetypal symbiotic binary. Observations to be
made during the 1982 October eclipse are summarized.
Title: OH emission in the direction of TV Gem and BI Cyg.
Authors: Brown, L. W.; Hobbs, R. W.; Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1981AJ.....86.1926B
Altcode:
The NRAO-Green Bank 43-m telescope and 18-cm receiver have detected
OH maser main-line emission at 1665 MHz, in the direction of the two
late-type supergiants TV Gem and BI Cyg. The detection of the two new
OH maser sources is noteworthy in view of the small number of late-type
supergiants known to be molecular radio sources, or associated in close
proximity with OH emission clouds. The IR, UV and radio properties of
the two stars are discussed.
Title: Observations of the 1980 April 30 limb flare by the ultraviolet
spectrometer and polarimeter on the Solar Maximum Mission
Authors: Woodgate, B. E.; Shine, R. A.; Brandt, J. C.; Chapman,
R. D.; Michalitsianos, A. G.; Kenny, P. J.; Bruner, E. C.; Rehse,
R. A.; Schoolman, S. A.; Cheng, C. C.
Bibcode: 1981ApJ...244L.133W
Altcode:
Observations of the M2 limb flare of 1980 April 30 by the ultraviolet
spectrometer and polarimeter in the C IV 1548 A line are described
and compared with observations from other SMM instruments and with
ground-based H-alpha data. Events observed during the 18 minutes leading
up to the flare impulsive phase include the filling of a small loop
with material moving at about 20 km/s, followed by a rapid brightening
in C IV, H-alpha, and hard X-rays, with a subsequent brightening of
a higher set of loops. The rapid brightening appears to be at the
junction of the small loop with the overlying magnetic structures,
which suggests the flare may be caused by their interaction.
Title: CH Cygni
Authors: Kafatos, M.; Michalitsianos, A. G.; Feibelman, W. A.; Hobbs,
R. W.; Stencel, R. E.
Bibcode: 1981IAUC.3570....1K
Altcode:
M. Kafatos, A. G. Michalitsianos, W. A. Feibelman and R. W. Hobbs,
Goddard Space Flight Center; and R. E. Stencel, Joint Institute for
Laboratory Astrophysics, report: "IUE observations of the symbiotic
star CH Cyg were made on 1980 Dec. 23.3 UT, and the fine-error-sensor
indicated V = 5.9. High-dispersion spectrograms showed He II 164.0 nm,
Si III 189.2 nm and C III 190.6 and 190.9 nm in emission; there was
also complex emission and absorption of Mg II 279.6 and 280.3 nm. The
continuum had a strong discontinuity at 172.0 nm in low dispersion,
consistent with a star having a temperature near 7000 K."
Title: Solar maximum mission experiment: Ultraviolet spectroscopy
and polarimetry on the solar maximum mission
Authors: Tandberg-Hanssen, E.; Cheng, C. C.; Woodgate, B. E.; Brandt,
J. C.; Chapman, R. D.; Kenney, P. J.; Michalitsianos, A. G.; Shine,
R. A.; Athay, R. G.; Beckers, J. M.; Bruner, E. C.; Rehse, R. A.;
Schoolman, S. A.; Gurman, J. B.; Hyder, C. L.; Henze, W.
Bibcode: 1981AdSpR...1m.275T
Altcode: 1981AdSpR...1..275T
We describe the Ultraviolet Spectrometer and Polarimeter (UVSP) on the
Solar Maximum Mission (SMM) spacecraft. The instrument, which operates
in the wavelength range 1150 - 3600 Å, has a spatial resolution of 2-3
arc sec and a spectral resolution of 0.02 Å FWHM in second order. A
Gregorian telescope, focal length 1.8 m, feeds a 1 m Ebert-Fastie
spectrometer. A polarimeter comprising rotating Mg F2
waveplates can be inserted behind the spectrometer entrance slit and
allows all four Stokes parameters to be determined. The observing
modes include rasters, spectral scans, velocity measurements, and
polarimetry. Finally, we present examples of initial observations made
since launch.
Title: VLA Observations of R-Aquarii
Authors: Sopka, R.; Dwek, E.; Zuckerman, B.; Michalitsianos, A.;
Hobbs, R.
Bibcode: 1981syst.work...17S
Altcode:
No abstract at ADS
Title: IUE Observations of Symbiotic Stars
Authors: Michalitsianos, A.
Bibcode: 1981syst.work....5M
Altcode:
No abstract at ADS
Title: IUE observations of circumstellar emission from the late type
variable R Aqr (M7+pec).
Authors: Hobbs, R. W.; Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1981NASCP2171..355H
Altcode: 1980IUE80......355H; 1981NASCP3171..355H; 1981uviu.nasa..355H
The IUE observations of R Aqr (M7 + pec) obtained in low dispersion are
discussed with particular reference to circumstellar emission. Strong
permitted, semiforbidden, and forbidden emission lines are seen,
superimposed on a bright ultraviolet continuum. It is deduced that the
strong emission line spectrum that involves C III, C IV, Si III, (0 II)
and (0 III) probably arises from a dense compact nebula the size of
which is comparable to the orbital radius of the binary system of which
R Aqr is the primary star. The low excitation emission lines of Fe II,
Mg II, 0 I, and Si II probably a white dwarf, comparable to or somewhat
brighter than the Sun, since such a star can produce enough ionizing
photons to excite the continuum and emission line spectrum and yet be
sufficiently faint as to escape detection by direct observation. The UV
continuum is attributed to Balmer recombination from the dense nebula
and not to blackbody emission from the hot companion.
Title: Ultraviolet Eclipse Observations of Ci-Cygni
Authors: Stencel, R.; Kafatos, M.; Michalitsianos, A. G.; Boyarchuk,
N. A.
Bibcode: 1981syst.work....5S
Altcode:
No abstract at ADS
Title: Ultraviolet observations of tau/4/ Serpentis /M5 IIb - IIIa/
Authors: Kafatos, M.; Michalitsianos, A. G.; Feibelman, W. A.; Hobbs,
R. W.
Bibcode: 1981ASSL...88..263K
Altcode: 1981pprg.work..263K
IUE data of this late giant reveal strong Mg II resonance doublet
emission that in high dispersion exhibits reversed symmetric h and
k line profile emission, suggesting that material ejected from the
surface forms a low excitation expanding circumstellar shell. The weak
continuum is identified as being a combination of possibly stellar
continuum and blended Fe II features of multiplets. The UV spectra
does not suggest the presence of a hot companion as believed to exist
in symbiotic stars, because a number of high excitation lines such as
C IV and He II are not observed in the short wavelength range. The
UV and Mg II line emission is most likely the result of the M giant
having undergone an eruptive event in which a moderate excitation
shell heated by hydromagnetic shocks dominates the UV emission. The
general properties of the circumstellar shell are obtained from the
Mg II line profiles.
Title: MGII Profiles of Symbiotic Stars
Authors: Stencel, R.; Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1981syst.work...30S
Altcode:
No abstract at ADS
Title: Solar Maximum Mission experiment: ultraviolet spectroscopy
and polarimetry on the Solar Maximum Mission.
Authors: Tandberg-Hanssen, E.; Woodgate, B. E.; Athay, R. G.; Beckers,
J. M.; Brandt, J. C.; Bruner, E. C.; Chapman, R. D.; Cheng, C. -C.;
Gurman, J. B.; Hyder, C. L.; Kenney, P. J.; Michalitsianos, A. G.;
Rehse, R. A.; Schoolman, S. A.; Shine, R. A.; Henze, W.
Bibcode: 1981hea..conf..275T
Altcode:
No abstract at ADS
Title: Ingress observations of the 1980 eclipse of the symbiotic
star CI Cygni.
Authors: Stencel, R. E.; Michalitsianos, A. G.; Kafatos, M.; Boyarchuk,
A. A.
Bibcode: 1981NASCP2171..459S
Altcode: 1981NASCP3171..459S; 1981uviu.nasa..459S; 1980IUE80......459S
One of the major results from the IUE may prove to be the
knowledge gained by studies of the ultraviolet spectra of symbiotic
stars. Symbiotics combine spectral features of a cool M giant like
photosphere with strong high excitation emission lines of nebular
origin, superposed. The UV spectra are dominated by intense permitted
and semiforbidden emission lines and weak continua indicative of hot
compact objects and accretion disks. Two symbiotics, AR Pav and CI
Cyg are thought to be eclipsing binaries and IUE observations during
the 1980 eclipse of CI Cygni are discussed.
Title: Ultraviolet Observations of M-Type Symbiotic Stars
Authors: Michalitsianos, Andrew G.
Bibcode: 1981iue..prop..803M
Altcode:
The significant differences revealed in high dispersion short
wavelength spectra of two M-type symbiotic stars RW Hya (gM2 + pec)
and RX Pup (M5 + pec) observed previously with IUE emphasizes the
need for high resolution observations of a wide range of similar
objects. The anomalies observed in high excitation lines in RX Pup
of He II, N III], N IV], O III], C III], C IV and Si III] that show
split line profiles, multiple component Doppler displaced components,
and broadened blue wing emission structure in N III] and N IV] suggest
motion in circumstellar material. In contrast, high dispersion UV
spectra of RW Hya reveal narrow high excitation emission lines that
give no suggestion of macroscopic motions in the circumstellar gas. We
wish to extend observations of a selected number of symbiotic stars
observed previously but in low resolution, to high dispersion in order
to determine if particular M-type symbiotic stars exhibit anomalies
in their line profile. As such, symbiotic stars exhibiting velocity
structure in emission lines may form a subset of objects that are
characterized by mass motions in their circumstellar envelops that
create high excitation emission. UV line and continuum emission from
other M-type symbiotics may arise from mainly photo-excitation processes
that results from the intense radiation field associated with the hot
secondary companion.
Title: RX Puppis
Authors: Kafatos, M.; Michalitsianos, A. G.; Feibelman, W. A.; Hobbs,
R. W.
Bibcode: 1981IAUC.3568....2K
Altcode:
M. Kafatos, A. G. Michalitsianos, W. A. Feibelman and
R. W. Hobbs, Goddard Space Flight Center, report: "We observed the
peculiar-line-emission star RX Pup in the high-resolution (0.01 nm)
mode of the IUE on 1980 Sept. 20.2 UT, and anomalous line-profile
structure was seen in high-excitation emission lines. Split-line
profiles characterized a number of high-excitation emission lines
that included He II 164.0 nm, [Si III] 189.2 nm and [O III] 166.0
and 166.6 nm. The C IV resonance doublet exhibited multiple-component
blue-shifted features, in which the intensity ratio, I(154.8 nm)/I(155.0
nm), was opposite to that usually seen in these lines. [N IV] 148.6
nm exhibited an extended blue-wing emission that gave the appearance
of an inverse P-Cyg profile."
Title: IUE observations and interpretation of the symbiotic star
RW Hya.
Authors: Kafatos, M.; Michalitsianos, A. G.; Hobbs, R. W.
Bibcode: 1981NASCP2171..349K
Altcode: 1981uviu.nasa..349K; 1981NASCP3171..349K; 1980IUE80......349K
The IUE observations of the high excitation symbiotic star RW Hya (gM2
+ pec) are discussed. Analysis of the intense UV continuum observed
between 1100 A to 2000 A suggests this star is a binary system in which
the secondary is identified as a hot subdwarf with Teff
being approximately 100,000 K. A distance to the system of 1000 pc is
deduced. The UV spectrum consists of mainly semiforbidden and allowed
transition lines of which the CIV (1548 A, 1550 A) emission lines
are particularly strong, and UV continuum at both shorter and longer
wavelengths. Strong forbidden lines seem to be absent suggesting the
presence of a nebula of high densities. Tidal interaction between the
red giant primary and the hot subdwarf is suggested as a likely means
to form the observed nebula. RW Hya is suggested as a possible source of
soft X-ray emission from material accreting onto the surface of the hot
subdwarf. Detection of such emission with HEAO-B would give information
if this accretion is taking place via Roche lobe overlow or via capture
from a stellar wind emitted by the primary. A general discussion of
elemental and ionic abundances in the nebula is also presented.
Title: IUE observations of two late type stars BX Mon (M4+pec)
and TV Gem (M1 Iab).
Authors: Michalitsianos, A. G.; Hobbs, R. W.; Kafatos, M.
Bibcode: 1981NASCP2171..367M
Altcode: 1981NASCP3171..367M; 1980IUE80......367M; 1981uviu.nasa..367M
The IUE observations of two late type stars BX Mon and TV Gem that
reveal the emission properties in the ultraviolet of subluminous
companions are discussed. Analysis of the continuum emission observed
from BX Mon suggests the companion, is a middle A III star. High
excitation emission lines observed between 1200 A and 2000 A that
generally do not typify emission observed in either late M type
variables or A type stars are also detected. It is suggested that these
strong high excitation lines arise in a large volume of gas heated by
nonradiation processes that could be the result of tidal interaction
and mass exchange in the binary system. In contrast to stars such as
BX Mon, the luminous M1 supergiant TV Gem shows unexpected intense
UV continuum throughout the sensitivity range of IUE. The UV spectrum
of TV Gem is characterized by intense continuum with broad absorption
features detected in the short wavelength range. The analysis shows that
the companion could be a B9 or A1 III-IV star. Alternate suggestions
are presented for explaining the UV continuum in terms of an accretion
disk in association with TV Gem.
Title: IUE observations of two late type stars : R AQL and W Hya.
Authors: Kafatos, M.; Michalitsianos, A. G.; Hobbs, R. W.
Bibcode: 1980A&A....92..320K
Altcode:
Ultraviolet spectra of two late type M stars R Aql and W Hya were
obtained with the International Ultraviolet Explorer (IUE). Spectra
were obtained of R Aql near maximum (φ=0.21) and minimum φ=0.65)
of the visible light curve. We find that the absolute flux intensity
of the Mg II resonance doublet (2796 Å, 2803 Å) is essentially the
same at these phases in the visible light curve. A nebular emission
feature at 3133 A is detected at minimum light in R Aql that is
possibly due to O III. Mg II emission is totally absent in W Hya,
which contradicts earlier predictions that this star has an 8000 K
permanent chromosphere. These results are discussed as they pertain
to the formation of silicate grains in cool M giant atmospheres.
Title: IUE observations of a luminous M supergiant that exhibits
emission continuum in the far ultraviolet.
Authors: Michalitsianos, A. G.; Kafatos, M.; Hobbs, R. W.
Bibcode: 1980ApJ...241..774M
Altcode: 1980STIN...8028273M
IUE observations of the late-type M supergiant star TV Gem which reveal
an intense continuum in the far ultraviolet are discussed. TV Gem
was observed in low dispersion in November 1979 and in high and low
dispersion in January 1980 by the short and long wavelength cameras
of the IUE spectrometer. An essentially featureless UV continuum was
obtained, with the exception of a number of broad absorption features in
the short wavelength region. A comparison with ground-based observations
indicates that at wavelengths greater than 3200 A the continuum emission
is essentially due to the M1 supergiant, while at shorter wavelengths
the continuum is dominated by a hot companion. The UV continuum can
be explained by a B9 or A1 III-IV early companion approximately 2
to 3 magnitudes fainter than the M1 supergiant, or by an accretion
disk formed by mass transfer from the extended envelope of the M1
primary onto the surface of a highly condensed secondary. Soft X-ray
observations from HEAO 2 are suggested as a means to investigate
these interpretations.
Title: Moderate Resolution McGraw-Hill Scanner Observations of
Symbiotic and Related Stars
Authors: Blair, W.; Stencel, R.; Feibelman, W.; Michalitsianos, A.
Bibcode: 1980BAAS...12..869B
Altcode:
No abstract at ADS
Title: IUE Observations of the Peculiar Star RX Pup
Authors: Kafatos, M.; Michalitsianos, A. G.; Feibelman, W. A.; Hobbs,
R. W.
Bibcode: 1980BAAS...12..848K
Altcode:
No abstract at ADS
Title: UV Observations of the 1980 Eclipse of the Symbiotic Star
CI Cygni
Authors: Boyarchuk, A.; Stencel, R.; Michalitsianos, A.; Kafatos, M.
Bibcode: 1980BAAS...12..868B
Altcode:
No abstract at ADS
Title: IUE observations of RW Hya (gM2+pec).
Authors: Kafatos, M.; Michalitsianos, A. G.; Hobbs, R. W.
Bibcode: 1980ApJ...240..114K
Altcode:
Analysis of the intense UV continuum observed between 1100 and
2000 A suggested that observations of the late type star RW Hya
is a binary system in which the secondary is the central star of a
planetary nebula. The UV spectrum is characterized by semiforbidden
and allowed transition lines, of which the C IV doublet is particularly
strong. Tidal interaction from the M giant is proposed as a method of
forming a nebula with the characteristic densities inferred from the UV
line analysis. RW Hya is suggested as a possible source of soft X-ray
emission if material is accreting onto the surface of the secondary.
Title: Satellite infrared observations of late-type variable stars.
Authors: Maran, S. P.; Michalitsianos, A. G.; Heinsheimer, T. F.;
Stocker, T. L.
Bibcode: 1980cpsp.book..629M
Altcode:
No abstract at ADS
Title: IUE observations of circumstellar emission from the late type
variable R AQR (M7+pec).
Authors: Michalitsianos, A. G.; Kafatos, M.; Hobbs, R. W.
Bibcode: 1980ApJ...237..506M
Altcode:
IUE observations of R Aquarii (M7 + pec) have been obtained in
low dispersion in order to study its circumstellar emission. Strong
permitted, semiforbidden, and forbidden emission lines are identified
that are superposed on a bright ultraviolet continuum. From the
analysis it is deduced that the strong emission-line spectrum that
involves semiforbidden C III, C IV, semiforbidden Si III, forbidden O
II, and forbidden O III probably arises from a dense compact nebula
the size of which is comparable to the binary system of which R
Aqr is the primary star. Low-excitation emission lines of Fe II,
Mg II, O I, and Si II suggest the presence of a warm chromosphere
(T less than about 10,000 K) in the primary M7 late type giant. The
secondary is identified as a white dwarf, comparable to or somewhat
brighter than the sun, since such a star can produce enough ionizing
photons to excite the continuum and emission-line spectrum and yet
be sufficiently faint to escape detection by direct observation. The
UV continuum observed is attributed to Balmer recombination and not
to blackbody emission from the hot companion. The general spectral
properties of R Aqr between 1200 A and 3200 A are discussed in the
context of the model for the circumstellar nebula, the companion,
and the mass-loss rate of the primary star.
Title: Sunspot Observations with the Ultraviolet Spectrometer and
Polarimeter Experiment on the Solar Maximum Mission
Authors: Gurman, J. B.; Woodgate, B. E.; Shine, R. A.; Brandt, J. C.;
Chapman, R. D.; Michalitsianos, A. G.; Kenny, P. J.; Bruner, E. C.;
Rehse, R.; Schoolman, S. A.; Cheng, C. C.; Tandberg-Hanssen, E. A.;
Athay, G. R.; Beckers, J. M.; Henze, W.; Brown, Teledyne; Hyder, C. L.
Bibcode: 1980BAAS...12..535G
Altcode:
No abstract at ADS
Title: Density Diagnostic of Solar Active Region and Flare Plasmas
from Si IV/O IV Line Ratio as Observed from SMM
Authors: Bruner, E. C.; Rehse, R.; Schoolman, S. A.; Brandt, J. C.;
Chapman, R. D.; Kenny, P. J.; Michalitsianos, A. G.; Shine, R. A.;
Woodgate, B. E.; Cheng, C. C.; Tandberg-Hanssen, E. A.; Athay, G. R.;
Beckers, J. M.; Gurman, J.; Henze, W.; Brown, Teledyne; Hyder, C. L.
Bibcode: 1980BAAS...12R.539B
Altcode:
No abstract at ADS
Title: Density diagnostic of solar active region and flare plasmas
from Si IV/O IV line ratio as observed from SMM (Solar Maximum
Mission).
Authors: Bruner, E. C.; Rehse, R.; Schoolman, S. A.; Brandt, J. C.;
Chapman, R. D.; Kenny, P. J.; Michalitsianos, A. G.; Shine, R. A.;
Woodgate, B. E.; Cheng, C. -C.; Tandberg-Hanssen, E. A.; Athay, G. R.;
Beckers, J. M.; Gurman, J. B.; Henze, W.; Hyder, C. L.
Bibcode: 1980BAAS...12..534B
Altcode:
No abstract at ADS
Title: Solar Flare and Surge Image Sequences as Seen by the
Ultraviolet Spectrometer and Polarimeter on SMM
Authors: Henze, W.; Brown, Teledyne; Brandt, J. C.; Chapman,
R. D.; Kenny, P. J.; Michalitsianos, A. G.; Shine, R. A.; Woodgate,
B. E.; Bruner, E. C.; Rehse, R.; Schoolman, S. A.; Cheng, C. C.;
Tandberg-Hanssen, E. A.; Athay, G. R.; Beckers, J. M.; Gurman, J.;
Hyder, C. L.
Bibcode: 1980BAAS...12..532H
Altcode:
No abstract at ADS
Title: IUE Observations of UV Continuum Emission From TV Gem (Ml Iab)
Authors: Michalitsianos, A. G.; Hobbs, R. W.; Kafatos, M.
Bibcode: 1980BAAS...12..539M
Altcode:
No abstract at ADS
Title: The Ultraviolet Spectrometer and Polarimeter (UVSP) on the
Solar Maximum Mission and Initial Results in Polarimetry
Authors: Tandberg-Hanssen, E.; Athay, R. G.; Bruner, E. C.; Beckers,
J. M.; Brandt, J. C.; Chapman, R. D.; Cheng, C. C.; Gurman, J.;
Henze, W.; Brown, Teledyne; Hyder, C. L.; Michalitsianos, A. G.;
Shine, R. A.; Schoolman, S. A.; Woodgate, B. E.
Bibcode: 1980BAAS...12..534T
Altcode:
No abstract at ADS
Title: The Dynamics of Solar Flares and Surges as Seen at the Solar
Limb in the Transition Zone
Authors: Woodgate, B. E.; Brandt, J. C.; Chapman, R. D.; Kenny,
P. J.; Michalitsianos, A. G.; Shine, R. A.; Bruner, E. C.; Rehse, R.;
Schoolman, S. A.; Cheng, C. C.; Tandbert-Hanssen, E. A.; Athay, G. R.;
Beckers, J. M.; Gurman, J.; Henze, W.; Brown, Teledyne; Hyder, C. L.
Bibcode: 1980BAAS...12Q.535W
Altcode:
No abstract at ADS
Title: Active Region Morphology and Evolution Images from the
Ultraviolet Spectrometer and Polarimeter
Authors: Shine, R. A.; Brandt, J. C.; Chapman, R. D.; Kenny, P. J.;
Michalitsianos, A. G.; Woodgate, B. E.; Bruner, E. C.; Rehse, R.;
Schoolman, S. A.; Cheng, C. C.; Tandberg-Hanssen, E. A.; Athay, G. R.;
Beckers, J. M.; Gurman, J.; Henze, W.; Brown, Teledyne; Hyder, C. L.
Bibcode: 1980BAAS...12R.531S
Altcode:
No abstract at ADS
Title: IUE observations of the hot components in two symbiotic stars
Authors: Michalitsianos, A. G.; Kafatos, M.; Hobbs, R. W.; Maran, S. P.
Bibcode: 1980Natur.284..148M
Altcode:
Recent IUE observations reveal striking differences in the UV spectra
of two symbiotic stars, R Aqr and RW Hya. RW Hya is found to be
an unexpectedly intense source of UV radiation. The measurements
reported here demonstrate the presence of a hot component in each
star, supporting the view that each is a binary system with a luminous
red primary and a hot, sub-luminous companion. In one case, the hot
companion manifests itself by exciting a compact nebulosity; in the
other case we believe that the continuous spectrum of the hot star is
directly detected, while the continuum of nebulosity excited by the
hot star is detected at longer wavelengths.
Title: The ultraviolet spectrometer and polarimeter on the Solar
Maximum Mission.
Authors: Woodgate, B. E.; Tandberg-Hanssen, E. A.; Bruner, E. C.;
Beckers, J. M.; Brandt, J. C.; Henze, W.; Hyder, C. L.; Kalet, M. W.;
Kenny, P. J.; Knox, E. D.; Michalitsianos, A. G.; Rehse, R.; Shine,
R. A.; Tinsley, H. D.
Bibcode: 1980SoPh...65...73W
Altcode:
The Ultraviolet Spectrometer and Polarimeter (UVSP) on the Solar Maximum
Mission spacecraft is described, including the experiment objectives,
system design, performance, and modes of operation. The instrument
operates in the wavelength range 1150-3600 Å with better than 2 arc
sec spatial resolution, raster range 256 × 256 arc sec2,
and 20 mÅ spectral resolution in second order. Observations can be
made with specific sets of 4 lines simultaneously, or with both sides
of 2 lines simultaneously for velocity and polarization. A rotatable
retarder can be inserted into the spectrometer beam for measurement
of Zeeman splitting and linear polarization in the transition region
and chromosphere.
Title: IUE Observations of Nebular Emission in Symbiotic Stars
Authors: Michalitsianos, A. G.
Bibcode: 1980iue..prop..490M
Altcode:
IUE observing time is requested to observe a selected number of
symbiotic variables in both low and high dispersion. Previous emission
line and continuum observations of R Aqr obtained in low dispersion
suggest the presence of a low excitation nebula whose source of
ionization is a luminous white dwarf. Ambiguity in line identification
from low dispersion spectra (~6 A resolution) of certain spectral
features raises some doubt concerning nebular parameters of electron
density and temperature that have been derived from [O II], [O III] and
[O IV] line intensities. High resolution observations of R Aqr (~0.l A
resolution) will resolve these questions. IUE observations of RW Hya
also suggest an ionized nebula but with far higher excitation than
that observed in R Aqr. The large differences in the UV continuum and
emission line spectrum between these two stars suggests that symbiotic
objects might be defined by a distinct class of emission that is
most likely determined to a large extent by the intrinsic luminosity
and physical nature of the hot companion. A selected target list of
proposed stars is given.
Title: Intense Ultraviolet Emission from RW Hydrae
Authors: Kafatos, M.; Michalitsianos, A. G.; Hobbs, R. W.; Maran, S. P.
Bibcode: 1979BAAS...11R.730K
Altcode:
No abstract at ADS
Title: IUE Observations of Circumstellar Emission from the Late Type
Variable R Aqr (M7 + pec)
Authors: Michalitsianos, A. G.; Kafatos, M.; Hobbs, R. W.
Bibcode: 1979BAAS...11..730M
Altcode:
No abstract at ADS
Title: Pre-Flight Calibration of the Solar Maximum Mission Ultraviolet
Spectrometer and Polarimeter I. Instrumentation &Spectrometer
Performance
Authors: Michalitsianos, A. G.; Kenney, P. J.; Shine, R. A.; Woodgate,
B. E.; Bruner, E. C., Jr.; Henze, W.; Tandbaer-Hanssen, E.
Bibcode: 1979BAAS...11..447M
Altcode:
No abstract at ADS
Title: Pre-Flight Calibrations of Solar Maximum Missions Ultraviolet
Spectrometer &Polarimeter II: Polarimeter Performance
Authors: Shine, R. A.; Kenny, P. J.; Michalitsianos, A. G.; Woodgate,
B. E.; Bruner, E. C.; Rehse, R. A.; Henze, W.; Tandberg-Hanssen, E.
Bibcode: 1979BAAS...11..447S
Altcode:
No abstract at ADS
Title: Sporadic mass ejection in red supergiants.
Authors: Kafatos, M.; Michalitsianos, A. G.
Bibcode: 1979ApJ...228L.115K
Altcode:
A general mechanism first proposed by Burke (1969) is applied to red
supergiants for determining the spin-down rate and angular-momentum
loss of rotating stars. This model relies principally on sporadic
mass ejection, which is assumed to be the result of turbulent
elements accelerating material in cool supergiant atmospheres. Mass is
preferentially expelled in the forward direction of rotation, resulting
in a rapid loss of angular momentum on time scales of 10,000 to 1
million years in the supergiant evolutionary phase. Such rotational
breaking will occur if the turbulent elements have characteristic
sizes a few percent of the stellar radius and rms velocities one-third
the escape speed of the star. This model predicts the formation of a
cool silicate disk or torus around the star because of the preferred
expulsion of material near equatorial regions of the supergiant.
Title: Observations of Circumstellar Shells Around Late Type Stars
Authors: Michalitsianos, Andrew G.
Bibcode: 1979iue..prop..225M
Altcode:
Observing time with IUE is requested to detect ultraviolet emission in
ionization fronts near Mira variables and M giants caused by material
ejected from the stars interacting with the interstellar medium. Fifty
hours of time would be needed to study eight stars.
Title: Solar maximum ultraviolet spectrometer and polarimeter
Authors: Tandberg-Hanssen, E.; Woodgate, B. E.; Brandt, J. C.;
Chapman, R. D.; Hyder, C. L.; Michalitsianos, A. G.; Shine, R. A.;
Athay, R. G.; Beckers, J. M.; Bruner, E. C.
Bibcode: 1979SPIE..184..264T
Altcode:
The objectives of the UVSP experiment are to study solar ultraviolet
radiations, particularly from flares and active regions, and to measure
constituents in the terrestrial atmosphere by the extinction of sunlight
at satellite dawn and dusk. The instrument is designed to observe the
Sun at a variety of spectral and spatial resolutions in the range from
1150 to 3600 A. A Gregorian telescope with effective focal length of
1.8 m is used to feed a 1 m Ebert-Fastie spectrometer. A polarimeter
containing rotatable magnesium fluoride waveplates is included behind
the spectrometer entrance slit and will allow all four Stokes parameters
to be determined. Velocities on the Sun can also be measured. The
instrument is controlled by a computer which can interact with the data
stream to modify the observing program. The observing modes, including
rasters, spectral scans, velocity measurements, and polarimetry, are
also described along with plans for mission operations, data handling,
and analysis of the observations.
Title: Mass loss and OH maser emission from Mira variables.
Authors: Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1978ApJ...226..430M
Altcode:
The mass, radius, and luminosity of 26 Mira variables that are known
OH sources of radio emission at 1612 MHz have been estimated. The
time-independent solution of Salpeter's (1974) stellar-wind equation
and a period-density relation are used to solve for basic stellar
parameters, with the aid of the terminal expansion velocity of the OH
maser cloud. Masses obtained from these calculations are consistent with
other estimated values for masses of Mira variables. Good agreement
is obtained when comparing the rate of mass loss as determined from
Reimers's (1977) semiempirical relation with estimates of the mass-loss
rate as deduced from theoretical models involving radiation pressure
on grains. These calculations suggest a strong correlation between
the mass-loss rate and the pulsation period. Arguments concerning the
general properties of silicate grains from radiation-pressure-driven
stellar-wind equations are discussed.
Title: Sporadic Mass Ejection in Red Supergiants
Authors: Michalitsianos, A. G.; Kafatos, M.
Bibcode: 1978BAAS...10..646M
Altcode:
No abstract at ADS
Title: Long-term infrared monitoring of stellar sources from Earth
orbit.
Authors: Maran, S. P.; Heinsheimer, T. F.; Stocker, T. L.; Anand,
S. P. S.; Chapman, R. D.; Hobbs, R. W.; Michalitsanos, A. G.; Wright,
F. H.; Kipp, S. L.
Bibcode: 1977InfPh..17..565M
Altcode:
These are the preliminary results of the first systematic program of
infrared astronomy measurements made from an artificial satellite in
Earth orbit.The program consists of intensive. broad-band photometric
monitoring of variable sources at wavelength 2.7 μm. The sources,
red giant and supergiant stars, are in some cases associated with
circumstellar molecules (OH, H 2O, SiO) that emit variable
radio maser radiation that may be pumped by the stellar infrared light.
Title: Mass loss, long-period variables, and the formation of
circumnebular shells.
Authors: Kafatos, M.; Michalitsanos, A. G.; Vardya, M. S.
Bibcode: 1977ApJ...216..526K
Altcode:
We have found that the rate of mass loss M increases with an increase
in the period of pulsation for Mira-type variables. This result
suggests that the rate of mass loss is accelerated with time until a
maximum value is reached before the ejection of the outer envelope. The
matter from the continuous mass loss during the evolution of the star
produces supersonic shock waves that sweep up the interstellar gas upon
encountering the interstellar medium, so that a shell is formed. This
phenomenon may account for the observations of extended regions of
emission that surround planetary nebulae.
Title: Long Period Variables and Mass Loss.
Authors: Kafatos, M.; Michalitsianos, A. G.; Vardya, M. S.
Bibcode: 1977BAAS....9..345K
Altcode:
No abstract at ADS
Title: Long-Term Infrared Monitoring of Stellar Sources from Earth
Orbit (Abstract)
Authors: Moran, S. P.; Heinsheimer, T. F.; Stocker, T. L.; Anand,
S. P. S.; Chapman, R. D.; Hobbs, R. W.; Michalitsanos, A. G.; Wright,
F. H.; Kipp, S. L.
Bibcode: 1977ASSL...63...35M
Altcode: 1977isa..symp...35M
No abstract at ADS
Title: Characteristics Of Ir Variable Stars As Observed From Orbit
Authors: Maran, Stephen P.; Heinsheimer, Thomas F.; Stocker, Thomas
L.; Chapman, Robert D.; Hobbs, Robert W.; Michalitsanos, Andrew G.
Bibcode: 2021ITPS...49.3126C
Altcode:
We have studied a selection of infrared variable stars at wavelength
2.7 μm during 1971-1975 with data from U.S. Air Force satellites. Stars
observed in this program are classified as long-period variable stars,
semiregular variables, and irregular variables and are among the
strongest stellar sources at this wavelength. In addition, a few new,
as yet unclassified variable stars were identified during the course of
the investigation. Time scales of reproducible variations range from
a few weeks to a few years, and amplitudes of variation are as large
as a factor of three for stars with periods of order one year. The
minimum infrared flux density of a long-period star repeats accurately
from one cycle to the next, whereas the maximum flux density was found
to be unstable. This behavior may be related to the propagation of
shocks in the stellar atmosphere near the time of maximum light or to
coupling between large-scale convection and pulsation. It suggests that
phenomena in these stars be timed with respect to minimum phase, rather
than maximum phase as done previously. Maximum infrared flux density
occurs after maximum visible light, whereas the visible and infrared
minima are essentially simultaneous. The correlation of 2.7 μm and
radio emission line data from one, well-studied long-period variable
is consistent with the hypothesis that the H2O and OH circumstellar
masers are saturated, if pumped by the stellar infrared flux near 2.7
μm, as suggested by Litvak. However, an alternate model, namely that
the radio maser clouds are pumped by long-wave infrared radiation,
cannot be excluded.
Title: Nonlinear Coupling between Pulsation and Convection in Late
Type Stars
Authors: Anand, S. P. S.; Michalitsanos, A. G.
Bibcode: 1976Ap&SS..45..175A
Altcode:
A simple idealized nonlinear model applicable to long period variable
stars has been formulated that assumes the convective envelope ofM
giants is composed of giant convection cells, which are comparable in
size to the stellar radius. The simplicity of this model essentially
constitutes a physical analog to the strong dynamic coupling that
occurs if the convective envelope of the star undergoes both modes of
motion. As shown implicitly in the time scales associated with these
motions, the coupling produces asymmetrical fluctuations of the entire
star, the mean velocity of which is comparable to the escape velocity
of the star at particular values of the ratio of the pulsation and
convection time scales. It is suggested that this can account for the
mass loss from late type stars, and the circumstellar dust shells that
are associated extensively with long period variables. For critical
values of the pulsation and convection time scales, the solutions
correspond to the rapid expansion of the entire convective envelope,
and is the basis of a new mechanism that simulates the manner in which
pulsating stars ballistically accelerate their convective shells to
form planetary nebulae.
Title: Long-term infrared monitoring of stellar sources from earth
orbit
Authors: Maran, S. P.; Heinsheimer, T. F.; Stocker, T. L.; Anand,
S. P. S.; Chapman, R. D.; Hobbs, R. W.; Michalitsianos, A. G.; Wright,
F. H.; Kipp, S. L.
Bibcode: 1976cosp.meetQ....M
Altcode:
A program is discussed which involved monitoring the photometric
activity of 18 bright variable IR stars at 2.7 microns with satellite-
and rocket-borne instrumentation in the period from 1971 to 1975. The
stellar sample includes 3 Lb variables, 8 semiregular variables,
5 Mira-type variables, and 2 previously unknown and unclassified
IR variables. Detailed light curves of many of these stars were
determined for intervals of 3 yr or more; spectra from 2.7 to 20 microns
were constructed for nine of them using data obtained entirely with
instruments above the atmosphere. Photometric IR light curves and other
data are presented for SW Virginis, R Aquilae, S Scuti, IRC 00265, RT
Hydrae, S Orionis, S Canis Minoris, Omicron Ceti, and R Leonis. Several
hypotheses concerning the interpretation of the IR data are examined.
Title: Solar Pulsations
Authors: Michalitsanos, A. G.
Bibcode: 1976BASI....4...13M
Altcode:
No abstract at ADS
Title: Characteristics of IR variable stars as observed from orbit
Authors: Maran, S. P.; Heinsheimer, T. F.; Stocker, T. L.; Chapman,
R. D.; Hobbs, R. W.; Michalitsianos, A. G.
Bibcode: 1976SPIE...95...23M
Altcode:
A selection of infrared variable stars was studied at wavelength 2.7
microns during 1971-1975 with data from U.S. Air Force satellites. Stars
observed in this program are classified as long-period variable stars,
semiregular variables, and irregular variables and are among the
strongest stellar sources at this wavelength. In addition, a few new,
as yet unclassified variable stars were identified during the course of
the investigation. Time scales of reproducible variations range from
a few weeks to a few years, and amplitudes of variation are as large
as a factor of three for stars with periods of order one year. The
minimum infrared flux density of a long-period star repeats accurately
from one cycle to the next, whereas the maximum flux density was found
to be unstable. The correlation of 2.7 micron and radio emission line
data from one, well-studied long-period variable is consistent with
the hypothesis that the H2O and OH circumstellar masers are saturated,
if pumped by the stellar infrared flux near 2.7 microns.
Title: Characteristics of IR variable stars as observed from orbit.
Authors: Maran, S. P.; Heinsheimer, T. F.; Stocker, T. L.; Chapman,
R. D.; Hobbs, R. W.; Michalitsianos, A. G.
Bibcode: 1976muit.conf...23M
Altcode:
No abstract at ADS
Title: Video-magnetograph observations of moving magnetic features
around sunspots.
Authors: Michalitsanos, A. G.; Bhatnagar, A.
Bibcode: 1975BASI....3...27M
Altcode:
No abstract at ADS
Title: Observations of Large-Scale Moving Magnetic Features Near
Sunspots
Authors: Michalitsanos, A. G.; Bhatnagar, A.
Bibcode: 1975ApL....16...43M
Altcode:
High time and spatial resolution magnetograms taken with a longitudinal
video magnetograph show the systematic motion of large crescents and
ridges of magnetic field at the outer penumbral boundary of a large
complex sunspot group. Both ridges and crescents are resolved into
knots of flux which are typically 2 arc sec to 3 arc sec in extent,
and which move in unison with velocities in the range of 0.2 to 0.3
km/sec. Over a four-hour period, these ridges of magnetic field,
which are predominantly of opposite polarity to the parent sunspot,
are observed to move over distances of from 4 arc sec to 6 arc sec,
and merge with existing outlying magnetic fields. It is suggested that
large-scale crescents or ridges of magnetic field emerge periodically at
penumbral boundaries. Preliminary models for the transport of magnetic
fields around sunspots are proposed.
Title: Spectrograph, Filtergraph and Magnetograph Observations of
the Two-Ribbon Flare of 29 July, 1973
Authors: Michalitsanos, A. G.; Kupferman, P.
Bibcode: 1974SoPh...36..403M
Altcode:
We present high resolution detailed observations of the class 3N
two-ribbon flare of 1973, July 29 (McMath 12461), which was associated
with the disappearance of a large filament (`disparition brusque'). This
flare occurred in a diffuse bipolar magnetic region completely devoid
of sunspots, and was further associated with a type IV radio burst
and a soft X-ray event. Extensive Hα filtergraph, spectrograph
and magnetograph records during the main phase of the flare suggest
that downfalling and streaming material is present on both ribbons
for several hours during the Hα emission enhancement, but only at a
small number of points located both on and off the ribbons. We find a
poor spatial correspondence between bright emission knots in the Hα
ribbons and the positions of the observed downward motion. We conclude
that the model of infall-impact of Hyder (1967a, b) is not consistent
with our filtergraph and spectrograph observations.
Title: Chromospheric activity associated with moving photospheric
magnetic fields
Authors: Roy, J. -René; Michalitsanos, A. G.
Bibcode: 1974SoPh...35...47R
Altcode:
With the aid of Hα and Ca II K filtergrams and magnetograms of region
McMath 12417 on 3, 4 and 5 July 1973, we have followed the evolution of
a moving rim of positive magnetic flux 50″ long in an area dominated
by negative flux. Chromospheric activity in the form of brightenings
and small surges was associated with this moving flux; a concentration
of activity is observed at the locations where magnetic fields of
opposite sign meet together. The weakening of the Ca II K emission
along the edges of colliding opposite fields supports evidence from
magnetograms that the photospheric magnetic field at that location
has decreased strikingly over a period of six hours.
Title: Spectrograph, Filtergraph and Magnetograph Observations of
the Two Ribbon Flare of 29 July 1973
Authors: Michalitsianos, A. G.; Kupferman, P.
Bibcode: 1974BAAS....6T.291M
Altcode:
No abstract at ADS
Title: Chromospheric Activity Associated With Moving Photospheric
Magnetic Field
Authors: Roy, J. R.; Michalitsianos, A. G.
Bibcode: 1974BAAS....6S.293R
Altcode:
No abstract at ADS
Title: The Five Minute Period Oscillation in Magnetically Active
Regions
Authors: Michalitsanos, A. G.
Bibcode: 1973SoPh...30...47M
Altcode:
The magnetohydrodynamic frequency-wavelength relation, derived by
McLellan and Winterberg (1968), has been evaluated for an isothermal
atmosphere. In particular, the effect which an inclined magnetic field
and a finite horizontal wavelength have on the critical sonic and
internal-gravity cut-off frequencies has been examined, in which it has
been assumed that the magnetic field vector, wave vector, and gravity
vector are coplanar. It is shown that the frequency band in which
vertical wave propagation is impossible in the non-magnetic photosphere,
becomes smaller when an inclined uniform magnetic field is introduced,
and that low frequency magnetically coupled internal-gravity waves do
not propagate vertically if the horizontal wavelengths associated with
this mode are greater than a critical wavelength which decreases with
field strength.
Title: Magnetohydrodynamic processes in the active solar atmosphere
Authors: Michalitsianos, Andrew Gerasimos Andy
Bibcode: 1973PhDT.......152M
Altcode:
No abstract at ADS
Title: Recent Theoretical Interpretations of the Solar Five Minute
Period Oscillation
Authors: Michalitsanos, A. G.
Bibcode: 1973EExSc...2..125M
Altcode:
No abstract at ADS
Title: Shock Wave Dissipation in Magnetically Active Regions
Authors: Durrant, C. J.; Michalitsanos, Andrew G.
Bibcode: 1971SoPh...18...60D
Altcode:
No abstract at ADS
Title: Observing the Eclipse from Peru
Authors: Michalitsanos, Andrew; Goldstone, Steven
Bibcode: 1965S&T....30...76M
Altcode:
No abstract at ADS