Wendy Hagen Bauer

Additional late-type stars with technetium

The results of a survey of 279 late-type giants and supergiants for the spectral lines of the radioactive element technetium (Tc I) at 4297, 4262, and 4238 A are presented. The following conclusions are reached: (1) the presence of Tc correlates very strongly with the existence of light variability; (2) evolutionary MS stars show Tc and spectroscopic MS stars do not show Tc; (3) single S stars show Tc; (4) SC stars show Tc; (5) about 75 percent of the C stars show Tc; and (6) Ba II stars do not show Tc. The findings are compatible with predictions from stellar evolution theory. 78 references.

Infrared circumstellar shells - origins, and clues to the evolution of massive stars

The infrared fluxes, spatial and spectral characteristics for a sample of 111 supergiant stars of spectral types F0 through M5 are tabulated, and correlations examined with respect to the nature of their circumstellar envelopes. One-fourth of these objects were spatialy resolved by IRAS at 60 microns and possess extended circumstellar shell material, with implied expansion ages of about 10 to the 5th yr. Inferences about the production of dust, mass loss, and the relation of these characteristics of the evolution of massive stars, are discussed. 44 refs.

Extended 60 micrometers emission from nearby Mira variables

The Infrared Astronomy Satellite (IRAS) has detected extended emission around a number of evolved stars. Individual IRAS scans of nearby Mira variables which showed emission from circumstellar dust and for which distance estimates were available were examined. Extended emission at 60 micrometers was detected for R Cas, o Cet, R Leo, U Ori, and possibly for R Hor. The Leung code for the calculation of radiative transfer in a circumstellar dust shell was used to calculate the emission from model dust shells composed of silicate grains. The output was convolved with the IRAS beam profile to determine whether steady mass loss could explain the observed extension. The observed extensions for o Cet, R Hor and U Ori could be due to steady mass loss, while the model calculations do not produce enough extension to explain the observations of R Cas and R Leo.

Rapid mass-loss transients in VV Cephei

Biweekly ultraviolet observations of the red supergiant-hot dwarf binary, VV Cephei during 1991, obtained near third quadrature, have revealed the existence of short-term continuum variations. We infer these are superposed on an underlying emission-line spectrum. The viewing geometry of this long period system suggests we are seeing a process associated with non-uniform mass transfer to an accretion disk. This rapid variability can be related to global instabilities in the stellar wind and mass loss from the red supergiant.

Line identifications in the ultraviolet spectrum of 31 Cygni

Line identifications are presented for the Zeta Aur-type eclipsing binary system 31 Cyg (K4 Ib + B4 V). The rich absorption spectrum observed during chromospheric eclipse has been nearly completely identified. This list will be useful in analyzing spectra of related binaries, such as 32 Cyg and VV Cep. The large number of line transitions contributing to many of the observed features indicates that spectrum synthesis methods for determining chromospheric properties will be more useful than curve-of-growth analyses of individual lines. The emission spectrum seen during primary eclipse has also been described and identified.

An Atlas of Far-ultraviolet Spectra of the Zeta Aurigae Binary 31 Cygni with Line Identifications

The ζ Aurigae system 31 Cygni (K4 Ib + B4 V) was observed by the FUSE satellite during total eclipse and at three phases during chromospheric eclipse. We present the coadded, calibrated spectra and atlases with line identifications. During total eclipse, emission from high ionization states (e.g., Fe III and Cr III) shows asymmetric profiles redshifted from the systemic velocity, while emission from lower ionization states (e.g., Fe II and O I) appears more symmetric and is centered closer to the systemic velocity. Absorption from neutral and singly ionized elements is detected during chromospheric eclipse. Late in chromospheric eclipse, absorption from the K star wind is detected at a terminal velocity of ∼80 km s{sup –1}. These atlases will be useful for interpreting the far-UV spectra of other ζ Aur systems, as the observed FUSE spectra of 32 Cyg, KQ Pup, and VV Cep during chromospheric eclipse resemble that of 31 Cyg.

Spatial Extension in the Ultraviolet Spectrum of VV Cephei

Two-dimensional processing of Hubble Space Telescope/Space Telescope Imaging Spectrograph (HST/STIS) echelle spectra of the eclipsing M2 Iab + B binary system, VV Cep, has revealed extended emission in all 21 epochs observed, ranging from midtotality through the first quadrature. In the ultraviolet accessible to STIS (1150- 3150 ?), essentially all observed photons originate from the hot component. In total eclipse, a pure emission spectrum is seen, with strong lines from lower levels up to ~2 eV cut by blue-shifted absorption in the M supergiant wind. Out of eclipse, a continuum is observed upon which a rich absorption spectrum of mostly neutral and singly-ionized iron group elements is superimposed. Out of eclipse, the strongest absorption features sit atop the emission profiles seen during eclipse. Far from eclipse, the neutral lines disappear, and the strongest of the remaining absorption lines develop complex inverse P-Cygni profiles. The continuum and spectrally extended blue wings of the inverse P-Cygni spectral lines show a spatial extension characteristic of the HST/STIS response to an unresolved source. However, the emission components of spectral lines lying longward of the blue-shifted wind absorption typically show flux extending beyond the unresolved hot component, implying formation over an extended region much larger than the size of the binary orbit. This extended line emission is believed to be formed by scattering of photons from the hot components continuum by ions in ground and low-lying metastable levels in the extended wind of the M supergiant. Extension is observed out of eclipse for lines with lower levels up to approximately 4 eV, but the greatest degree of extension is observed for lines with lower levels less than 2 eV. Radial velocity differences across the spatially extended emission correlate with the aperture position angle, consistent with model predictions for wind flow in a binary system in which the wind outflow is comparable to the orbital velocity, and indicate an orbital plane oriented from +11? E of N (receding) through ?169? (approaching).

An Ultraviolet Spectral Atlas of VV Cephei during Total Eclipse

The first observations of the ultraviolet spectrum of the binary system VV Cep (M2 Iab + B?) during total eclipse have been made with the HST. A rich emission-line spectrum is seen, with over two thousand emission features present. Shortward of 1600 A, a weak continuum presumably due to Rayleigh scattering of the hot component is present, strengthening markedly shortward of 1500 A. The continuum of the M supergiant becomes apparent longward of 2650 A. Numerous circumstellar and interstellar absorption features are also seen. We present an atlas of the spectrum from 1300-3160 A as observed near midtotality and at two epochs closer to egress, when gas surrounding the hot component has begun to emerge from eclipse and the flux on the short-wavelength edges of many emission lines has increased. This atlas has been annotated with line identifications. The majority of the emission lines arise from singly ionized elements in the iron group with upper levels up to 14 eV, and generally correspond to absorption features seen out of eclipse. Circumstellar and interstellar absorption features seen out of eclipse remain in absorption during totality and are also annotated on the atlas. Well over 90% of the emission features have plausible identifications, but there are many blends. Only a few hundred features appear to be free enough from blending for useful measurement of the peak flux in the line. We present a list of these unblended features.

Far-infrared circumstellar 'debris' shell of red supergiant stars

Examination of IRAS data on late type evolved stars suggests that there is yet another transition line, between chromospheres and dust, which lies above and to the right of corona-wind transitions in the HR Diagram. The IRAS 60 µm data also appears to indicate the existence of very cool material extending tens of thousands of stellar radii around red supergiant stars. These circumstellar debris shells may prove useful in the analysis of the history of mass loss in given objects and larger scale galactic trends, such as metallicity.

The Special Case of VV Cephei

VV Cephei (M2 Iab + B0–2 V) is the only known ζ Aur binary that has an M-type supergiant. Studies of its atmospheric eclipses provide a valuable extension to what can be learned by eclipse mapping, but are fraught with many challenges. The space-UV absorption spectrum is extremely rich, and line blending is severe. Wind interaction and accretion effects are prominent, and the spectrum of the B star companion is heavily veiled by overlying Balmer continuum emission, which usually exceeds that of the B-star’s continuum flux in the UV. An accretion region immediately around the B star gives rise to a rich spectrum of lines, some of which sometimes show prominent inverse P Cygni profiles. The chromospheric absorption spectrum shows structure in the line profiles that persists throughout chromospheric eclipse, and implies the existence of large-scale supersonic, complex velocity flows across the whole extended chromosphere of the M supergiant. Spectrum formation in the atmosphere of VV Cep is more complex than in the other ζ Aur binaries owing to the much higher rate of mass loss from the primary. This chapter summarizes the fundamental stellar and orbit parameters of VV Cep, and presents key results found from three decades of UV astronomy. It also presents a simple model of the chromosphere and wind.