AN ULTRAVIOLET AND OPTICAL STUDY OF ACCRETING PRE-MAIN-SEQUENCE STARS - UXORS

UX Ori stars (UXors) are pre-main-sequence stars of both the Herbig Ae/Be and T Tauri type which show aperiodic eclipse-like minima. Their variations have been attributed to occultations by circumstellar material. We use archival IUE spectra and a catalog of UBVRI photometry to study the variations of five such objects, namely, RY Lup, RY Tau, CO Ori, BF Ori, and UX Ori. Relationships between UV spectral line fluxes and equivalent widths and V magnitude are found and displayed. Some shell features in UX Ori and BF Ori switch from absorption to emission during the minima. The equivalent widths of the emission features increase as the star fades. Spectral energy distributions (SEDs) covering the interval of 1200-8900 Angstrom were constructed for several stars at different V magnitude light levels. A strong depression in the SED around 2400 Angstrom, caused primarily by iron absorption Lines (the ''iron curtain'') is quite noticeable in UX Ori and BF Ori when the stars are bright, but is diminished or absent when faint. The data are discussed in the context of the variable circumstellar obscuration hypothesis and provide same additional support for it. (C) 1995 American Astronomical Society.