A Census of Rotation and Variability in L1495: A Uniform Analysis of Trans-atlantic Exoplanet Survey Light Curves for Pre-main-sequence Stars in Taurus
We analyze light curves obtained by the Trans-atlantic Exoplanet Survey (TrES) for a field centered on the L1495 dark cloud in Taurus. The Spitzer Taurus Legacy Survey catalog identifies 179 bona fide Taurus members within the TrES field; 48 of the known Taurus members are detected by TrES, as well as 26 candidate members identified by the Spitzer Legacy team. We quantify the variability of each star in our sample using the ratio of the standard deviation of the original light curve (σ_(orig.)) to the standard deviation of a light curve that has been smoothed by 9 or 1001 epochs (σ_9 and σ_(1001), respectively). Known Taurus members typically demonstrate (σ_(orig.)/σ_9) < 2.0, and (σ_(orig.)/σ_(1001)) < 5, while field stars reveal (σ_(orig.)/σ_9) ~ 3.0 and (σ_(orig.)/σ_(1001)) ~ 10, as expected for light curves dominated by unstructured white noise. Of the 74 Taurus members/candidates with TrES light curves, we detect significant variability in 49 sources. Adapting a quantitative metric originally developed to assess the reliability of transit detections, we measure the amount of red and white noise in each light curve and identify 18 known or candidate Taurus members with highly significant period measurements. These appear to be the first periods measured for four of these sources (HD 282276, CX Tau, FP Tau, TrES J042423+265008), and in two other cases, the first non-aliased periods (LkCa 21 and DK Tau AB). For the remainder, the TrES measurements typically agree very well (δP < 1%) with previously reported values. Including periods measured at lower confidence for 15 additional sources, we report periods for 11 objects where no previous periods were found, including 8 confirmed Taurus members. We also identify 10 of the 26 candidate Taurus members that demonstrate variability levels consistent with being bona fide T Tauri stars. A Kolomgorov-Smirnov (K-S) test confirms that these new periods confirm the distinction between the rotation period distributions of stars with and without circumstellar disks, with only a 10% probability of the two populations sharing the same parent period distribution. K-S tests do suggest, however, that the updated Taurus period distribution now more closely resembles those measured in other young star-forming clusters (i.e., NGC 2264, NGC 6530, and the ONC). This improved agreement may reflect the exclusion of long rotation periods which are detected in Taurus at lower significance, and which may be beyond the limits of detectability in more distant star-forming regions.
Additional Information© 2012 American Astronomical Society. Received 2012 January 6; accepted 2012 July 10; published 2012 August 28. The authors thank Lynne Hillenbrand for helping motivate the TrES team to monitor L1495; Michael Meyer and Eric Mamajek for useful discussions that inspired this analysis of the data; Eric Feigelson, Adam Miller, and Joseph Richards for informative discussions of period detection techniques that would be robust against the presence of red noise; and Jerome Bouvier for noting that v sin i measurements may support LkCa 21's sub-day period. We also thank the anonymous referee for thoughtful comments which spurred several improvements to the analysis and interpretation presented here. K.R.C. acknowledges support for this work from the Hubble Fellowship Program, provided by NASA through Hubble Fellowship grant HST-HF-51253.01-A awarded by the STScI, which is operated by the AURA, Inc., for NASA, under contract NAS 5-26555. This material is based on work that was supported by NASA under grants NNG05GJ29G issued through the Origins of Solar Systems Program. This research has made use of NASA's Astrophysics Data System Bibliographic Services, the SIMBAD database, operated at CDS, Strasbourg, France, the NASA/IPAC Extragalactic Database, operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration, and the VizieR database of astronomical catalogs (Ochsenbein et al. 2000). IRAF (Image Reduction and Analysis Facility) is distributed by the National Optical Astronomy Observatories, which are operated by the Association of Universities for Research in Astronomy, Inc., under cooperative agreement with the National Science Foundation. The Two Micron All Sky Survey was a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center (California Institute of Technology). The University of Massachusetts was responsible for the overall management of the project, the observing facilities, and the data acquisition. The Infrared Processing and Analysis Center was responsible for data processing, data distribution, and data archiving.
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