A Photometric Catalog of Herbig Ae/Be Stars and Discussion of the Nature and Cause of the Variations of UX Orionis Stars

摘要: UBVR photometric monitoring of Herbig Ae/Be stars and some related objects has been carried out at Maidanak Observatory in Uzbekistan since 1983. More than 71,000 observations about 230 have obtained are made available for anonymous ftp. Virtually all observed irregular variables (called "UXors" after UX Ori), but there is a wide range amplitudes from barely detectable to more 4 mag V. Our data confirm the results previous studies, which indicate that large-amplitude variability confined with spectral types later B8. The distribution ranges quite similar what seen classical T Tauri stars. A careful search failed reveal any evidence periodic variations up 30 days, can be interpreted as rotation periods. This clear distinction between light low-mass high-mass pre–main-sequence evidently do not possess either large, stable cool spots or persistent hot associated strong surface magnetic fields magnetically funneled accretion variety shapes, timescales, exists, most common behavior well illustrated by curve LkHα 234. There two principal components: (1) on timescales days around mean brightness level changes much longer timescale (typically years), sometimes quasi-cyclic fashion, (2) occasional episodes deep minima, occurring intervals frequently near low points cycles. suggest many K0 earlier type share same characteristics should regarded UXors. Two FU Orionis ("FUors"), Ori V1515 Cyg, also recent curves similar, respects, developed model account UXors involves variable obscuration circumstellar dust clumps orbiting star disk viewed nearly edge-on. However, problems extending this entire class, lead us propose an alternative mechanism, i.e., unsteady accretion. Evidence favoring over presented. It suggested thermal instability mechanism responsible outbursts interacting binary system disks, possibly FUors, may cause minima