The Search for Rotational Modulation of T Tauri Stars in the Ophiuchus Dark Clouds

We report some results of a long-term photometric program called ROTOR being carried out at Maidanak Observatory in the Republic of Uzbekistan. The goal of the program is to search for periodic components in the light of T Tauri stars (TTSs), Herbig Ae/Be stars (HAEBEs), FU Orionis stars, and related objects. In this paper we analyze results obtained for TTSs in the vicinity of the o Oph dark clouds obtained between 1986 and 1993. Our sample includes 6 weak-emission TTSs (WTTSs) and 11 classical TTSs (CTTSs). All of the WTTSs investigated have signicant photometric periods that are attributed to spottedness of the stellar photospheres. Two of them, SR 9 and SR 12, maintained stable periods and phases during the entire span of observation. The periods are between 1 and 4 days, except for SR 9, which has a period of 6.53 days ; its relatively large Ha equivalent width (for a WTTS) also suggests it may be a transition object between the WTTSs and CTTSs. Among the CTTSs in our sample, we found only three stars with denite periods, two of which were longer than 8 days. Generally speaking, therefore, our observations are in accordance with the canonical view of WTTSs and CTTSs, in which stars with more active accretion disks spin slower due to disk locking and show greater irregular variations due to accretion hot spots. The exception is V895 Sco (Haro 1-1), which seems to be a typical CTTS with a rotation period of less than 4 days. The stability of the periods and epochs of minima of some or most WTTSs is noted and discussed.

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