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J. Coffey, R. Jayawardhana, A. Scholz, A. Brandeker, M. H. van Kerkwijk (University of Toronto)
We present a study of disk accretion, activity, and rotation of young stars near the sun. We have obtained over 600 high-resolution spectra of approximately 100 young stars belonging to four nearby stellar associations: \eta Chamaeleontis, TW Hydrae, \beta Pictoris, and Tucanae-Horologium. These associations range in age from ~6 Myr to ~30 Myr, corresponding to the timescale on which it is believed that disk accretion ceases. We have analyzed these spectra, taken over a period of twelve nights from 2004 December to 2005 July, for signs of accretion from surrounding disks. As the H\alpha emission line in stars of late spectral types is broadened in the presence of high-velocity infalling matter, this analysis primarily consisted of measurements of equivalent width and width at ten percent of the peak flux of H\alpha. Variability of emission lines is common in young stars, making the use of multi-epoch spectra necessary for deriving robust conclusions. Signs of accretion are present in 3 of the 11 \eta Cha members (27%) and 4 of the 31 TW Hydrae members (13%), but we found no accretors in either BPMG or Tuc-Hor. This resulted in 95% confidence upper limits on accretion fractions of 13% and 8% for BPMG and Tuc-Hor, respectively. This suggests that while disk accretion may last up to 10 Myr, it is unlikely to be detected beyond this time. Furthermore, we have measured the projected rotational velocity for each of the stars. This allowed us to investigate whether accretion and activity are related to stellar rotation. The v\sin i values indicate that the accreting stars tend to be slow rotators, suggesting that rotational breaking due to magnetic coupling between the star and the disk may last for timescales of up to 8 Myr.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.