Near-Infrared Variability of Low Mass Stars in IC 1396A and TR 37

Creators: Meng, Huan Y. A.; Rieke, G. H.; Kim, Jinyoung Serena; Sicilia-Aguilar, Aurora; Cross, N. J. G.; Esplin, Taran; Rebull, L. M.; Hodapp, Klaus W.

Abstract

We have monitored nearly a square degree in IC 1396A/Tr 37 over 21 epochs extending over 2014–2016 for sources variable in the JHK bands. In our data, 65% ± 8% of previously identified cluster members show variations, compared with ≾0.3% of field stars. We identify 119 members of Tr 37 on the basis of variability, forming an unbiased sample down to the brown dwarf regime. The K-band luminosity function in Tr 37 is similar to that of IC 348 but shifted to somewhat brighter values, implying that the K- and M-type members of Tr 37 are younger than those in IC 348. We introduce methods to classify the causes of variability, based on behavior in the color–color and color–magnitude diagrams. Accretion hot spots cause larger variations at J than at K with substantial scatter in the diagrams; there are at least a dozen, with the most active resembling EXors. Eleven sources are probably dominated by intervention of dust clumps in their circumstellar disks, with color behavior indicating the presence of grains larger than for interstellar dust, presumably due to grain growth in their disks. Thirteen sources have larger variations at K than at J or H. For 11 of them, the temperature fitted to the variable component is very close to 2000 K, suggesting that the changes in output are caused by turbulence at the inner rim of the circumstellar disk exposing previously protected populations of grains.

Additional Information

© 2019 The American Astronomical Society. Received 2018 June 15; revised 2019 March 27; accepted 2019 April 13; published 2019 June 6. We thank Watson Varricatt at UKIRT for helping us with the WFCAM observations. We thank Michael A. Read (WSA, IfA, Edinburgh) for careful data reduction, image processing, and providing us with the WFCAM data catalogs. We also thank referee Scott Wolk for a critical reading of the paper. We used the UKIRT Wide Field Camera (WFCAM; Casali et al. 2007) and a photometric system described in Hewett et al. (2006). The pipeline processing and science archive are described in Irwin et al. (2007) and Hambly et al. (2008). We thank Roc Cutri for investigating the issues of deblending in the WISE data and alerting us to the likelihood of bad photometry for sources that are nominally reasonably well resolved but still close to each other on the sky. This publication makes use 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. This publication makes use of data products from the Wide-field Infrared Survey Explorer, which is a joint project of the University of California, Los Angeles, and the Jet Propulsion Laboratory/California Institute of Technology, funded by the National Aeronautics and Space Administration. When (some of) the data reported here were acquired, UKIRT was supported by NASA and operated under an agreement among the University of Hawaii, the University of Arizona, and Lockheed Martin Advanced Technology Center; operations were enabled through the cooperation of the East Asian Observatory. The Pan-STARRS1 Surveys (PS1) and the PS1 public science archive have been made possible through contributions by the Institute for Astronomy, the University of Hawaii, the Pan-STARRS Project Office, the Max-Planck Society and its participating institutes, the Max Planck Institute for Astronomy, Heidelberg, and the Max Planck Institute for Extraterrestrial Physics, Garching, Johns Hopkins University, Durham University, the University of Edinburgh, the Queen's University Belfast, the Harvard-Smithsonian Center for Astrophysics, the Las Cumbres Observatory Global Telescope Network Incorporated, the National Central University of Taiwan, the Space Telescope Science Institute, the National Aeronautics and Space Administration under grant No. NNX08AR22G issued through the Planetary Science Division of the NASA Science Mission Directorate, the National Science Foundation grant No. AST-1238877, the University of Maryland, Eotvos Lorand University (ELTE), the Los Alamos National Laboratory, and the Gordon and Betty Moore Foundation. Facility: UKIRT (WFCAM). -

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