Rotational studies of very low mass stars and brown dwarfs in the Orion Nebula Cluster

Details Rotational studies of very low mass stars and brown dwarfs in the Orion Nebula Cluster Rotational studies of very low mass stars and brown dwarfs in the Orion Nebula Cluster

Feb 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009aipc.1094..118r&link_type=abstract

COOL STARS, STELLAR SYSTEMS AND THE SUN: Proceedings of the 15th Cambridge Workshop on Cool Stars, Stellar Systems and the Sun.

Computer Science

Low Luminosity Stars, Subdwarfs, And Brown Dwarfs, Stellar Characteristics And Properties, Stellar Clusters And Associations

Scientific paper

Rotational studies at different ages and masses are important for constraining the angular momentum evolution of young stellar objects (YSO). Of particular interest are the rotational studies of very low mass (VLM) stars and brown dwarfs (BDs), because few rotational periods are known in that mass range. We aim to extend these studies well down into the substellar regime, providing for the first time information on rotational periods for a large sample of VLM stars and BDs. This extensive rotational period study of YSOs in the 1 Myr old Orion Nebula Cluster (ONC) is based on a deep photometric monitoring campaign using the Wide Field Imager (WFI) camera on the ESO/MPG 2.2 m telescope on La Silla, Chile. Time series data with about 95 data points were taken over 19 nights. Accurate I-band photometry of 2908 stars was obtained within a magnitude range between 13 and 21 mag, i.e. three magnitudes deeper than the previous studies in the ONC ([11]). Two different power spectral analysis techniques were used to search for periodic variability. In addition, the χ2 variability test was used for the detection of irregular variables. We measured rotational periods of 487 objects with estimated masses between 0.5 Msolar and 0.015 Msolar, 124 of which are BD candidates. This is by far the most extensive and complete rotational period data set for young VLM stars and BDs. Besides the periodic variables, 808 objects show strong non-periodic (i.e. irregular) brightness variations. We studied the dependence of the period distribution on the magnitude (mass) and variability level and compared the found period distribution with that of higher-mass objects in the ONC ([11]) and with the rotational data set existing for the twice as old cluster NGC 2264 ([18]). We found that substellar objects rotate on average faster than the VLM stars, a trend which was already observed for higher mass stars. In addition, we found a clear dependence of the rotational periods on position within the field. Objects located inside the so-called Rcluster rotate on average slower, which can be explained by an age spread in the ONC, with a somewhat younger central region. The results of a comparison between the period distributions of the ONC and NGC 2264 strongly favours this hypothesis. Interesting correlations between rotational period and variability level were also found in both clusters, probably explained by different magnetic field topologies.

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