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Photometric variations of Orion population stars. II Ae-irregular variables and T Tauri stars

1983; Institute of Physics; Volume: 88; Linguagem: Inglês

10.1086/113455

1538-3881

W. Herbst, Jon A. Holtzman, R. Klasky,

Astronomy and Astrophysical Research

UBVRI and H-alpha photometry of five T Tauri stars and three Ae-irregular variables obtained during the 1982/83 observing season at VVO and KPNO is presented. RY Tau shows very little change in color with brightness, except in (V-R) where it actually becomes bluer as it fades. The 'turnaround' in (U-B) suggested in last year's data on CO Ori has been confirmed when faint, the star ceases becoming redder as it dims and begins to get bluer. The turnaround is also now clearly seen in B - V. Similar turnarounds are found in two of the Ae stars, BF Ori and UX Ori, the latter confirming Zajtseva's (1973) result. These 'blueing' trends make interpretations of the variability based on dust obscuration implausible. The Ae stars monitored were nearly indistinguishable in their photometric behavior from the G-type weak emission line T Tauri stars SU Aur and CO Ori, suggesting a common mechanism for their variability. A general scheme for integrating the diverse properties of these variables is proposed, which involves photospheric and chromospheric responses to strong surface magnetic fields.