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Published November 2015 | Published + Submitted
Journal Article Open

YSOVAR: Mid-infrared Variability Among YSOs in the Star Formation Region GGD 12-15


We present an IR-monitoring survey with the Spitzer Space Telescope of the star-forming region GGD 12-15. More than 1000 objects were monitored, including about 350 objects within the central 5', which is found to be especially dense in cluster members. The monitoring took place over 38 days and is part of the Young Stellar Object VARiability project. The region was also the subject of a contemporaneous 67 ks Chandra observation. The field includes 119 previously identified pre-main sequence star candidates. X-rays are detected from 164 objects, 90 of which are identified with cluster members. Overall, we find that about half the objects in the central 5' are young stellar objects (YSOs) based on a combination of their spectral energy distribution, IR variability, and X-ray emission. Most of the stars with IR excess relative to a photosphere show large amplitude (>0.1 mag) mid-infrared (mid-IR) variability. There are 39 periodic sources, and all but one is found to be a cluster member. Almost half of the periodic sources do not show IR excesses. Overall, more than 85% of the Class I, flat spectrum, and Class II sources are found to vary. The amplitude of the variability is larger in more embedded YSOs. Most of the Class I/II objects exhibit redder colors in a fainter state, which is compatible with time-variable extinction. A few become bluer when fainter, which can be explained with significant changes in the structure of the inner disk. A search for changes in the IR due to X-ray events is carried out, but the low number of flares prevented an analysis of the direct impact of X-ray flares on the IR light curves. However, we find that X-ray detected Class II sources have longer timescales for change in the MIR than a similar set of non-X-ray detected Class IIs.

Additional Information

© 2015. The American Astronomical Society. Received 2015 March 31; accepted 2015 July 7; published 2015 October 12. 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. Support for this work was provided by NASA through an award issued by JPL/Caltech. This research made use of Astropy, a community-developed core Python package for Astronomy (Astropy Collaboration et al. 2013). This research has made use of the SIMBAD database and the VizieR catalog access tool (Ochsenbein et al. 2000), both operated at CDS, Strasbourg, France, and of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation. H.M.G. acknowledges Spitzer grant 1490851. K.P. was funded through the Sagan Fellowship program executed by the NASA Exoplanet Science Institute. H.Y.A.M. and P.P. acknowledge support by the IPAC Visiting Graduate Fellowship program at Caltech/IPAC. P.P. also acknowledges the JPL Research and Technology Development and Exoplanet Exploration programs. R.A.G. gratefully acknowledges funding support from NASA ADAP grants NNX11AD14G and NNX13AF08G and Caltech/JPL awards 1373081, 1424329, and 1440160 in support of Spitzer Space Telescope observing programs. S.J.W. was supported by NASA contract NAS8-03060. We thank Fabio Favata and David James for critical readings of this paper. Facilities: Spitzer - Spitzer Space Telescope satellite, Chandra - .

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Published - Wolk_2015p145.pdf

Submitted - 1507.04368v2.pdf


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