127 research outputs found
Discussion - Rapid rotation and mixing in active OB stars
The general discussion following Session 1: Rapid Rotation and Mixing in Active OB Stars is summarized. Topics that focus on observational and theoretical issues are include
Revealing the Nature of Algol Disks through Optical and UV Spectroscopy, Synthetic Spectra, and Tomography of TT Hydrae
We have developed a systematic procedure to study the disks in Algol-type
binaries using spectroscopic analysis, synthetic spectra, and tomography. We
analyzed 119 H-alpha spectra of TT Hya, an Algol-type eclipsing interacting
binary, collected from 1985-2001. The new radial velocities enabled us to
derive reliable orbital elements, including a small non-zero eccentricity, and
to improve the accuracy of the absolute dimensions of the system. High
resolution IUE spectra were also analyzed to study the formation of the
ultraviolet lines and continuum. Synthetic spectra of the iron curtain using
our new shellspec program enabled us to derive a characteristic disk
temperature of 7000K. We have demonstrated that the UV emission lines seen
during total primary eclipse cannot originate from the accretion disk, but most
likely arise from a hotter disk-stream interaction region.
The synthetic spectra of the stars, disk, and stream allowed us to derive a
lower limit to the mass transfer rate of 2e-10 solar masses per year. Doppler
tomography of the observed H-alpha profiles revealed a distinct accretion disk.
The difference spectra produced by subtracting the synthetic spectra of the
stars resulted in an image of the disk, which virtually disappeared once the
composite synthetic spectra of the stars and disk were used to calculate the
difference spectra. An intensity enhancement of the resulting tomogram revealed
images of the gas stream and an emission arc. We successfully modeled the gas
stream using shellspec and associated the emission arc with an asymmetry in the
accretion disk.Comment: 46 pages, 15 figures, 6 tables, accepted by Ap
Detection of a Hot Subdwarf Companion to the Be Star FY Canis Majoris
The rapid rotation of Be stars may be caused in some cases by past mass and
angular momentum accretion in an interacting binary in which the mass donor is
currently viewed as a small, hot subdwarf stripped of its outer envelope. Here
we report on the spectroscopic detection of such a subdwarf in the Be binary
system FY Canis Majoris from the analysis of data acquired by the IUE
spacecraft and KPNO Coude Feed Telescope over the course of 16 and 21 years,
respectively. We present a double-lined spectroscopic orbit for the binary
based upon radial velocities from the IUE spectra and use the orbital solutions
with a Doppler tomography algorithm to reconstruct the components' UV spectra.
The subdwarf is hot (T_eff = 45+/-5 kK) and has a mass of about 1.3 M_sun and a
radius of about 0.6 R_sun. It contributes about 4% as much flux as the Be star
does in the FUV. We also present observations of the H-alpha and He I 6678
emission features that are formed in the circumstellar disk of the Be star.
Orbital flux and velocity variations in the He I 6678 profile indicate that
much of the emission forms along the disk rim facing the hot subdwarf where the
disk is probably heated by the incident radiation from the subdwarf. A study of
the FUV infall shell lines discovered in the 1980s confirms their episodic
presence but reveals that they tend to be found around both quadrature phases,
unlike the pattern in Algol binaries. Phase-dependent variations in the UV N V
doublet suggest the presence of a N-enhanced wind from the subdwarf and a
possible shock-interaction region between the stars where the subdwarf's wind
collides with the disk of the Be star.Comment: 46 pages, 15 figures, ApJ in pres
- …