Other
Scientific paper
Jul 1984
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1984iue..prop.1759a&link_type=abstract
IUE Proposal ID #VVGTA
Other
Scientific paper
Epsilon Aur (F0 Ia + ?) is a single-line spectroscopic binary which undergoes eclipse once every 27.1 years, the eclipse lasting nearly 2 years. The nature of the secondary is unknown, but the most viable model is that of a large disk or ring of material in which may be imbedded a hot central star. The 1982-84 eclipse has been followed by us with high and low resolution IUE observations as well as with extensive optical and infrared photometry, spectrophotometry and spectroscopy at the Mauna Kea Observatory of the University of Hawaii and McDonald Observatory of the University of Texas. As of September 1983, we have found that a broad, high-velocity absorption component has developed in Mg II and other low level absorption lines. This feature is of higher velocity than the shell features normally seen optically after mid-totality and may be evidence of a gas stream from the primary. The shape of the UV eclipse light curve is still indeterminant due to inadequate pre-eclipse observations. Particularly misleading was a brightening that occurred just before first contact, resulting in various interpretations of the detailed wavelength dependence of the eclipse depth. The UV light curve is dominated down to 1500 A by Cepheid-like pulsations of the primary, but below 1400 A the eclipse is much shallower than at other wavelengths and shows erratic behavior. Two possible models are that a hot star is being seen through openings in the disk around the secondary, or that the poles of the primary are warmer than the occulted part of its surface and the erratic behavior is seen due to variations of the primary behind the disk. During the seventh IUE episode, fourth contact is scheduled to occur. We are proposing further observations to address several issues. The timing and amplitude of the Cepheid variations, which are best observed outside of eclipse, needs to be defined to determine the shape of the UV eclipse light curve, which will yield information on the size and opacity of the occulting material. The UV brightening that occurred just prior to first contact will be searched for at fourth contact, as will a possible extension of UV eclipse beyond the geometrical end of eclipse. High quality SWP exposures are needed to compare with totality spectra to determine if the observed line blends below 1400 arise from a hot secondary or warmer gas of the primary's poles. Finally we wish to chart the presence of gas streams that are now apparent as high velocity absorption components in low level lines.
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