PI: Ann Marie Cody, California Institute of Technology, firstname.lastname@example.org
Address: Department of Astronomy, MS 249-17, 1201 E California Blvd., Pasadena, CA 91125, USA
CoI: Lynne Hillenbrand, California Institute of Technology
Title: A spectroscopic census of the Sigma Orionis cluster
Abstract: Comprehensive surveys of young star clusters are crucial for studies of the initial mass function, angular momentum distribution, and spatial aggregation that are thought to bear the imprint of the star formation process. We have recently carried out an extensive photometric monitoring campaign on low-mass (0.02-0.2 M_\odot) candidate members of the ~3 Myr \sigma Orionis cluster with the CTIO 1.0-meter telescope, to identify variability on 10-minute to two-week timescales. The resulting lightcurves have revealed signs of numerous physical phenomena, producing variability down to the millimagnitude level, including periodic modulation by rotating stellar spots, accretion- related brightness fluctuations, and eclipses by companions. However, the cluster membership status of many of these objects is uncertain. What is needed now is a dedicated spectroscopic follow-up of the photometric sample, to determine spectral types for mass estimates and to examine gravity-sensitive features for youth. The combined photometric and spectroscopic dataset will not only provide a more complete membership census of the \sigma Orionis cluster, but also enable new studies of the dependence of star and brown dwarf variability amplitude and rotation rate on mass.
National Optical Astronomy Observatory, 950 North Cherry Avenue, P.O. Box 26732, Tucson, Arizona 85726, Phone: (520) 318-8000, Fax: (520) 318-8360