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Session 60 - Stellar Astrophysics I.
Oral session, Tuesday, January 16
Salon del Rey North, Hilton
Knowledge about the individual components of O-type binaries is difficult to obtain because of the severe line blending present in their spectra. An important new method is Doppler tomography, an iterative scheme that uses a set of orbital phase distributed spectra and both radial velocity curves to reconstruct the individual component spectra (see Bagnuolo, Gies amp; Wiggs 1992, ApJ, 385, 708). These individual spectra can then be analyzed to determine various physical properties of the stars. The spectral types and luminosity classes obtained provide indicators of the temperatures and gravities. The individual projected rotational velocities can be used to test for rotational synchronization of the orbit or rapid spin-up due to mass transfer. An estimate of the magnitude difference together with the combined absolute magnitude results in individual luminosity estimates. Finally, it is possible to search for abundance differences due to mass transfer or loss.
Here I present the first results of a program of Doppler tomography of O-binaries observed with the IUE. The use of IUE high dispersion spectra is optimal for O-type binaries because of the presence of many photospheric lines in the UV (high excitation lines which are relatively free from contamination from circumstellar emission often found in their optical spectra). I describe cross-correlation methods that use narrow-lined spectral templates to obtain precise radial velocities and orbital velocity curves which are used in the tomography algorithm. I also show how these cross-correlation results can be used to estimate projected rotational velocities and UV magnitude differences. I have identified new spectral classification criteria based on UV photospheric lines that are directly applicable to these O-binaries. I present results for three systems: DH Cep, HD 165052, and HD 93403. All are double-lined spectroscopic binaries with periods ranging from 2.1 to 15.1 days. These systems are used as tests of current theories for massive close binary evolution.
