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 v ariations have been attributed to occultations by circumstellar materi al. We use archival IUE spectra and a catalog of UBVRI photometry to s tudy the variations of five such objects, namely, RY Lup, RY Tau, CO O ri, BF Ori, and UX Ori. Relationships between UV spectral line fluxes and equivalent widths and V magnitude are found and displayed. Some sh ell features in UX Ori and BF Ori switch from absorption to emission d uring the minima. The equivalent widths of the emission features incre ase as the star fades. Spectral energy distributions (SEDs) covering t he interval of 1200-8900 Angstrom were constructed for several stars a t different V magnitude light levels. A strong depression in the SED a round 2400 Angstrom, caused primarily by iron absorption Lines (the '' iron curtain'') is quite noticeable in UX Ori and BF Ori when the star s are bright, but is diminished or absent when faint. The data are dis cussed in the context of the variable circumstellar obscuration hypoth esis and provide same additional support for it. (C) 1995 American Ast ronomical Society.