AAS 196th Meeting, June 2000
Session 4. Young Stars and Their Environments
Display, Monday, June 5, 2000, 9:20am-6:30pm, Empire Hall South

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[4.06] Periodicities in the T Tauri Star SU Aurigae from Stroomgren Photometry

I. Nadalin, L.E. DeWarf, E.F. Guinan (Villanova University)

Intensive long-term photoelectric photometry of SU Aurigae (HD 282624; G2 IIIe; < V > = +9.23 mag; < B-V > = +0.83) was made using the 0.8m Four College Automatic Photoelectric Telescope (APT), in Arizona. This concentrated (nightly) photometry was made in the Stromgren uvby system. The observations reported here were began in October 1993 and continue to the present.

Classical T Tauri stars (CTTS) typically have spectral types from F to K, exhibit weak H and Ca II emissions, have broad absorption lines (implying rapid rotation), and are located well above the main-sequence. One of the brightest archetypical CTT stars, SU Aur is observed to undergo rapid and dramatic light variations. Large (\Delta V \approx \Delta y \approx 0.40 mag) "eclipse-like" dimming events have been observed frequently, but with no predictable regularity. These light variations appear not to be accompanied by spectral changes (i.e. veiling effects), which implies possible obscuration of the star by dust with scattering properties similar to ISM dust. Since CTT stars are pre-main sequence objects that have extensive accretion disks, these dimming events could be caused by concentrations of matter orbiting in the outer regions of the disk. It is also possible that dust clouds condense from ejected matter and obscure the star. During the 1998/9 observing season, four such events were observed nearly 48 days apart and lasting for about 8 days each. In a previous paper by the authors, the extinction to SU Aur was derived, and when combined with the Hipparcos distance, provided for the determination of the absolute brightness and color. These values place SU Aur about 1.8 mag above the main-sequence for its respective unreddened spectral type. Plotting SU Aur on PMS evolution tracks yielded an age of about 4 Myrs and a mass of 1.9 ± 0.1 M\odot.

We present the analysis of our search for possible short period modulations in brightness that could arise from the rotational effects of starspots. Several T Tau stars have their rotation periods established this way. From this analysis, and the projected rotational velocity (v sin i), the physical size of the star can be estimated. This research is supported by NSF/RUI Grant AST-93 15365, which we gratefully acknowledge.

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