Astrophys. J., 656, 1075-1091 (2007/February-3)
Revealing the nature of Algol disks through optical and UV spectroscopy, synthetic spectra, and tomography of TT Hydrae.
MILLER B., BUDAJ J., RICHARDS M., KOUBSKY P. and PETERS G.J.
Abstract (from CDS):
We have developed a systematic procedure to study the disks in Algol-type binaries using spectroscopic analysis, synthetic spectra, and tomography. We analyzed 119 Hα spectra of TT Hya, an Algol-type eclipsing interacting binary, collected from 1985 to 2001. The new radial velocities enabled us to derive reliable orbital elements, including a small nonzero 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 UV lines and continuum. Synthetic spectra of the iron curtain using our new SHELLSPEC program enabled us to derive a characteristic disk temperature of 7000 K. 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 mass transfer rate ≥2x10–10 M☉/yr. Doppler tomography of the observed Hα 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.
Accretion, Accretion Disks - Stars: Binaries: Eclipsing - Stars: Novae, Cataclysmic Variables - Radiative Transfer - Stars: Individual: Constellation Name: TT Hydrae
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