Long-term 4.6 μm Variability in Brown Dwarfs and a New Technique for Identifying Brown Dwarf Binary Candidates

Creators: Brooks, Hunter; Kirkpatrick, J. Davy; Meisner, Aaron M.; Gelino, Christopher R.; Bardalez Gagliuffi, Daniella C.; Marocco, Federico; Schneider, Adam C.; Faherty, Jacqueline K.; Casewell, S. L.; Raghu, Yadukrishna; Kuchner, Marc J.

Abstract

Using a sample of 361 nearby brown dwarfs, we have searched for 4.6 μm variability, indicative of large-scale rotational modulations or large-scale, long-term changes on timescales of over 10 yr. Our findings show no statistically significant variability in Spitzer's Infrared Array Camera (IRAC) channel 2 (ch2) or Wide-field Infrared Survey Explorer W2 photometry. For Spitzer the ch2 1σ limits are ∼8 mmag for objects at 11.5 mag and ∼22 mmag for objects at 16 mag. This corresponds to no variability above 4.5% at 11.5 mag and 12.5% at 16 mag. We conclude that highly variable brown dwarfs, at least two previously published examples of which have been shown to have 4.6 μm variability above 80 mmag, are very rare. While analyzing the data, we also developed a new technique for identifying brown dwarf binary candidates in Spitzer data. We find that known binaries have IRAC ch2 point response function (PRF) flux measurements that are consistently dimmer than aperture flux measurements. We have identified 59 objects that exhibit such PRF versus aperture flux differences and are thus excellent binary brown dwarf candidates.

Additional Information

© 2023. The Author(s). Published by the American Astronomical Society. Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. This Backyard Worlds research was supported by NASA grant No. 2017-ADAP17-0067. We thank the Student Astrophysics Society 14 for providing the resources that enabled the pairing of high school and undergraduate students with practicing astronomers. This work makes use of data products from WISE/NEOWISE, which is a joint project of UCLA and JPL/Caltech, funded by NASA. Work in this paper is based on observations made with the Spitzer Space Telescope, which is operated by JPL/Caltech, under a contract with NASA. Support for the original parallax work was provided to J.D.K. by NASA through a Cycle 14 award issued by JPL/Caltech. Some data presented here were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among Caltech, the University of California, and NASA. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation. This research has made use of the Keck Observatory Archive (KOA), which is operated by the W. M. Keck Observatory and the NASA Exoplanet Science Institute (NExScI), under contract with the National Aeronautics and Space Administration. This research has made use of the NASA/IPAC Infrared Science Archive, which is funded by the National Aeronautics and Space Administration and operated by the California Institute of Technology. This research has made use of the SIMBAD database, operated at CDS, Strasbourg, France. The Digitized Sky Survey was produced at the Space Telescope Science Institute under U.S. Government grant NAG W-2166. The images of these surveys are based on photographic data obtained using the Oschin Schmidt Telescope on Palomar Mountain and the UK Schmidt Telescope. The plates were processed into the present compressed digital form with the permission of these institutions. Our finder charts also used observations obtained as part of the VISTA Hemisphere Survey, ESO Progam, 179.A-2010 (PI: McMahon). The UHS is a partnership between the UK STFC, The University of Hawaii, The University of Arizona, Lockheed Martin, and NASA. 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, The 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.

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