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Published November 2014 | Submitted + Published
Journal Article Open

Young Stellar Object Variability (YSOVAR): Long Timescale Variations in the Mid-Infrared


The YSOVAR (Young Stellar Object VARiability) Spitzer Space Telescope observing program obtained the first extensive mid-infrared (3.6 and 4.5 μm) time series photometry of the Orion Nebula Cluster plus smaller footprints in 11 other star-forming cores (AFGL 490, NGC 1333, Mon R2, GGD 12-15, NGC 2264, L1688, Serpens Main, Serpens South, IRAS 20050+2720, IC 1396A, and Ceph C). There are ~29,000 unique objects with light curves in either or both IRAC channels in the YSOVAR data set. We present the data collection and reduction for the Spitzer and ancillary data, and define the "standard sample" on which we calculate statistics, consisting of fast cadence data, with epochs roughly twice per day for ~40 days. We also define a "standard sample of members" consisting of all the IR-selected members and X-ray-selected members. We characterize the standard sample in terms of other properties, such as spectral energy distribution shape. We use three mechanisms to identify variables in the fast cadence data—the Stetson index, a χ^2 fit to a flat light curve, and significant periodicity. We also identified variables on the longest timescales possible of six to seven years by comparing measurements taken early in the Spitzer mission with the mean from our YSOVAR campaign. The fraction of members in each cluster that are variable on these longest timescales is a function of the ratio of Class I/total members in each cluster, such that clusters with a higher fraction of Class I objects also have a higher fraction of long-term variables. For objects with a YSOVAR-determined period and a [3.6]-[8] color, we find that a star with a longer period is more likely than those with shorter periods to have an IR excess. We do not find any evidence for variability that causes [3.6]-[4.5] excesses to appear or vanish within our data set; out of members and field objects combined, at most 0.02% may have transient IR excesses.

Additional Information

© 2014 American Astronomical Society. Received 2014 June 3; accepted 2014 August 27; published 2014 October 14. We are grateful to the SSC scheduling staff for accommodating this complex cadence over the two years of the survey program. We thank L. Hartmann and M. Skrutskie for early help with the program and for helpful suggestions on the manuscript; we also thank N. Calvet, D. Ciardi, J. Holtzmann, J. Muzerolle, G. Rieke, K. Stapelfeldt, H. Sung, M. Werner, B. Whitney, E. Winston, and K. Wood for early help with the program. We thank T. Mazeh, L. Tal-Or, and the Wise Observatory for help in preliminary observations of Orion YSOs. R.G. gratefully acknowledges funding support from NASA ADAP grants NNX11AD14G and NNX13AF08G and Caltech/ JPL awards 1373081, 1424329, and 1440160 in support of the Spitzer Space Telescope observing programs. H. Bouy is funded by the Ramόn y Cajal fellowship program number RYC-2009-04497. This research has been funded by Spanish grants AYA2012-38897-C02-01, AYA2010-21161-C02-02, CDS2006-00070 and PRICIT-S2009/ESP-1496. This work is based in part 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. Support for this work was provided by NASA through an award issued by JPL/Caltech. The research described in this paperwas partially carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. The scientific results reported in this article are based in part on data obtained from the Chandra Data Archive including observations made by the Chandra X-ray Observatory and published previously in cited articles. This research has made use of NASA's Astrophysics Data System (ADS) Abstract Service, and of the SIMBAD database, operated at CDS, Strasbourg, France. This research has made use of data products from the Two Micron All-Sky Survey (2MASS), which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center, funded by the National Aeronautics and Space Administration and the National Science Foundation. The 2MASS data are served by the NASA/IPAC Infrared Science Archive, which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. This research has made use of the NASA Exoplanet Archive, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program.

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Published - 1538-3881_148_5_92.pdf

Submitted - 1408.6756v1.pdf


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