Observational evidence and theoretical arguments are summarized which indicate that regions of partially ionized hydrogen extending several stellar radii are an important feature of red giant and supergiant stars. The implications of the existence of extended chromospheres are examined in terms of the nature of the other atmospheres of, and mass loss from cool stars.
Topics: NASA Technical Reports Server (NTRS), ASTRONOMICAL SPECTROSCOPY, ASTROPHYSICS, CHROMOSPHERE, RED...
Circumstellar gas and dust surrounding M giants and supergiants show luminous M stars to split into two distinct classes. Stars with a high gas to dust ratio all show chromospheric Ca II, H, and K emission. Stars with a high dust to gas ratio do not show chromospheric Ca II emission but are the only ones to show Balmer emission indicative of atmospheric shocks and are also the only ones to show maser emission. In order to determine whether all chromospheric indicators disappear in high dust to...
Topics: NASA Technical Reports Server (NTRS), DUST, GAS ANALYSIS, INFRARED ASTRONOMY SATELLITE, IUE, M...
Observations were made in the IUE LWP camera, low dispersion mode, with alpha Ori being offset various distances from the center of the Long Wavelength Large Aperture along its major axis. Signal was acquired at all offset positions and is comprised of unequal components of background/dark counts, telescope-scattered light, and scattered light emanating from the extended circumstellar shell. The star is known from optical and infrared observations to possess an extended, arc-minute sized, shell...
Topics: NASA Technical Reports Server (NTRS), IUE, SPACEBORNE ASTRONOMY, STELLAR ENVELOPES, SUPERGIANT...
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...
Topics: NASA Technical Reports Server (NTRS), ECLIPSING BINARY STARS, SPACEBORNE ASTRONOMY, STELLAR...
As a result of this work it was found that light scattered from the longer wavelengths constitutes a small but non-negligible, wavelength and time dependent fraction of the measured flux in the far UV. The reality of the UV excess has not been unambigiously ruled out. However, it is noted that there are still uncertainties in the assumed scattering profile. New measurements of the scattering properties of the cross disperser grating are planned in order to verify the results of Mount and Fastie...
Topics: NASA Technical Reports Server (NTRS), AURIGA CONSTELLATION, ECLIPSING BINARY STARS, IUE, LIGHT...
Interstellar dust grains are presumed in part to have their origins in the outer atmospheres of red giant and supergiant stars because, despite the efficiency of shock destruction of grains in the interstellar medium (ISM), meteoritic samples possess isotopic signatures that are consistent with nucleosynthetic origin in the interior of evolved stars. There is ample evidence to suggest that once dust grains form near red giants and supergiants, radiation pressure is sufficient to drive them to...
Topics: NASA Technical Reports Server (NTRS), CHROMOSPHERE, COSMIC DUST, INTERSTELLAR MATTER, RED GIANT...
The central results of a survey of the Mg II resonance line emission in a sample of over 50 evolved late type stars, including spectral-luminosity type F8 to M5 and La to IV are presented. Observed and surface fluxes are derived and correlations noted. The major findings include: (1) Mg II k emission core asymmetry transition near K1 III, analogous to that known for Ca II K; (2) a small gravity and temperature dependence of the Mg II chromospheric radiative loss rate.
Topics: NASA Technical Reports Server (NTRS), LATE STARS, LINE SPECTRA, RESONANCE LINES, STELLAR SPECTRA,...
A survey of F supergiant stars to evaluate the extension of chromospheric and circumstellar characteristics commonly observed in the slightly cooler G, K, and M supergiant is discussed. An ultraviolet survey was elected since UV features of Mg II and Fe II might persist in revealing outer atmosphere phenomena even among F supergiants. The encompassed spectral types F0 to G0, and luminosity classes Ib, Ia, and Ia-0. In addition, the usefulness of the emission line width-to-luminosity correlation...
Topics: NASA Technical Reports Server (NTRS), CHROMOSPHERE, F STARS, STELLAR ENVELOPES, STELLAR SPECTRA,...
Accomplishments under this grant effort include: successful scientific utilization of the IRAS Low Resolution Spectrometer (LRS) database of over 150,000 scans of 7-23 micron spectra for over 50,000 celestial sources; publication in refereed journal of an additional 486 critically evaluated spectra of sources brighter than 20 Jy, completing the LRS ATLAS (Olnon and Raimond 1986 A&A) uniformly to that level, and production of an additional 1,830 critically evaluated spectra of sources...
Topics: NASA Technical Reports Server (NTRS), ASTRONOMICAL CATALOGS, DATA BASES, INFRARED ASTRONOMY,...
Coronal heating by resonant absorption of Alfvenic surface waves (quiescent), and magnetic tearing instabilities (impulsive), is discussed with emphasis on three principles which may have application to late-type evolved stars. (1) If sq B/8 pi greater than sq. rho V is observed 2 in a stellar atmosphere, then the observed magnetic field must originate in an interior dynamo. (2) Low mass loss rates could imply the presence of closed magnetic flux loops within the outer atmosphere which...
Topics: NASA Technical Reports Server (NTRS), GIANT STARS, M STARS, MAGNETIC FLUX, STELLAR MAGNETIC FIELDS,...
A workshop proceedings concerned with the new data collected during the 1982-1984 eclipse period of the 27-year system Epsilon Aurigae is presented. This binary star has been a classic problem in astrophysics because the opaque eclipsing object is nonstellar, and probably disk shaped. Invited papers concerning the history of the system, optical, infrared and ultraviolet photometry, optical polarimetry and ultraviolet spectroscopy are included. An invited paper concerning comprehensive...
Topics: NASA Technical Reports Server (NTRS), ASTRONOMICAL PHOTOMETRY, ASTRONOMICAL SPECTROSCOPY, AURIGA...
A multistep scenario which describes a plausible mass loss mechanism associated with red giant and related stars is outlined. The process involves triggering a condensation instability in an extended chromosphere, leading to the formation of cool, dense clouds which are conducive to the formation of molecules and dust grains. Once formed, the dust can be driven away from the star by radiation pressure. Consistency with various observed phenomena is discussed.
Topics: NASA Technical Reports Server (NTRS), CHROMOSPHERE, INTERSTELLAR MATTER, RED GIANT STARS, STELLAR...
The density sensitivity of the emission lines within the UV 0.01 multiplet of C II near 2325 A was examined in additional late type giants and supergiants with deep LWR high dispersion exposures. The new data support the original contention based on these lines that noncoronal red giants possess geometrically extended chromospheres.
Topics: NASA Technical Reports Server (NTRS), ATMOSPHERIC DENSITY, CHROMOSPHERE, EMISSION SPECTRA, GIANT...
Both IUE short and long wavelength exposures of the 56 Peg system are discussed. This mild barium star has an X-ray luminosity of 3 x 10 to the 31st power ergs/1, comparable to the rapidly rotating RS CVn binary systems, yet lies in a region of the HR diagram where stellar X-rays are generally not observed. This cool, bright giant is not a rapid rotator and the key to understanding its emission lies in the recent discovery of its white dwarf companion. Accretion onto the white dwarf of...
Topics: NASA Technical Reports Server (NTRS), ASTRONOMICAL SPECTROSCOPY, BINARY STARS, GIANT STARS, STELLAR...
Proceedings of a workshop held from February 27 to March 1, l985. The workshop was attended by 50 astronomers, astrophysicists, planetary scientists and meteoriticists; and emphasized the interdisciplinary nature of studies of cosmic dust.
Topics: NASA Technical Reports Server (NTRS), ASTROPHYSICS, COSMIC DUST, INTERPLANETARY DUST, INTERSTELLAR...