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Published November 1, 2011 | Published
Journal Article Open

Young Brown Dwarfs at High Cadence: Warm Spitzer Time Series Monitoring of Very Low Mass σ Orionis Cluster Members


The continuous temporal coverage and high photometric precision afforded by space observatories have opened up new opportunities for the study of variability processes in young stellar cluster members. Of particular interest is the phenomenon of deuterium-burning pulsation in brown dwarfs (BDs) and very low mass stars, whose existence on 1-4 hr timescales has been proposed but not yet borne out by observations. To investigate short-timescale variability in young, low-mass objects, we carried out high-precision, high-cadence time series monitoring with the Warm Spitzer mission on 14 low mass stars and BDs in the ~3 Myr σ Orionis cluster. The flux in many of our raw light curves is strongly correlated with subpixel position and can vary systematically by as much as 10%. We present a new approach to disentangle true stellar variability from this "pixel-phase effect," which is more pronounced in Warm Spitzer observations as compared to the cryogenic mission. The light curves after correction reveal that most of the sample is devoid of variability down to the few-millimagnitude (mmag) level, on the minute to day timescales probed. However, one exceptional BD displays erratic brightness changes at the 10%-15% level, suggestive of variable obscuration by dusty material. The uninterrupted 24 hr datastream and sub-1% photometric precision enable limits on pulsation in the near-infrared. If this phenomenon is present in our light curves, then its amplitude must lie below 2-3 mmag. In addition, we present three field eclipsing binaries and one pulsator for which optical ground-based data are also available.

Additional Information

© 2011 American Astronomical Society. Received 2011 June 17; accepted 2011 July 28; published 2011 October 10. This work is based on observations made with the Spitzer Space Telescope, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with NASA. We acknowledge support from NASA under contract 1382589 administered through JPL/Caltech. We thank the referee, Kevin Luhman, for helpful comments. We also express appreciation to Sean Carey and Roberta Paladini for help in correcting pull-down and bias residuals, as well as María Morales-Calderón for extensive advice on Warm Spitzer reductions.

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Published - Cody2011p16386Astrophys_J.pdf


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