NOAO >   Observing Info >   Approved Programs >   2009B-0521

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Proposal Information for 2009B-0521


PI: Ann Marie Cody, California Institute of Technology, amc@astro.caltech.edu
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.


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