Time-series and Phase-curve Photometry of the Episodically Active Asteroid (6478) Gault in a Quiescent State Using APO, GROWTH, P200, and ZTF

Creators: Purdum, Josiah N.; Lin, Zhong-Yi; Bolin, Bryce T.; Sharma, Kritti; Choi, Philip I.; Bhalerao, Varun; Hanuš, Josef; Kumar, Harsh; Quimby, Robert; van Roestel, Joannes C.; Zhai, Chengxing; Fernandez, Yanga R.; Lisse, Carey M.; Bodewits, Dennis; Fremling, Christoffer; Ryan Golovich, Nathan; Hsu, Chen-Yen; Ip, Wing-Huen; Ngeow, Chow-Choong; Saini, Navtej S.; Shao, Michael; Yao, Yuhan; Ahumada, Tomás; Anand, Shreya; Andreoni, Igor; Burdge, Kevin B.; Burruss, Rick; Chang, Chan-Kao; Copperwheat, Chris M.; Coughlin, Michael; De, Kishalay; Dekany, Richard; Delacroix, Alexandre; Drake, Andrew; Duev, Dmitry; Graham, Matthew; Hale, David; Kool, Erik C.; Kasliwal, Mansi M.; Kostadinova, Iva S.; Kulkarni, Shrinivas R.; Laher, Russ R.; Mahabal, Ashish; Masci, Frank J.; Mróz, Przemyslaw J.; Neill, James D.; Riddle, Reed; Rodriguez, Hector; Smith, Roger M.; Walters, Richard; Yan, Lin; Zolkower, Jeffry

Abstract

We observed the episodically active asteroid (6478) Gault in 2020 with multiple telescopes in Asia and North America and found that it is no longer active after its recent outbursts at the end of 2018 and the start of 2019. The inactivity during this apparition allowed us to measure the absolute magnitude of Gault of H_r = 14.63 ± 0.02, G_r = 0.21 ± 0.02 from our secular phase-curve observations. In addition, we were able to constrain Gault's rotation period using time-series photometric lightcurves taken over 17 hr on multiple days in 2020 August, September, and October. The photometric lightcurves have a repeating ≾0.05 mag feature suggesting that (6478) Gault has a rotation period of ~2.5 hr and may have a semispherical or top-like shape, much like the near-Earth asteroids Ryugu and Bennu. The rotation period of ~2.5 hr is near the expected critical rotation period for an asteroid with the physical properties of (6478) Gault, suggesting that its activity observed over multiple epochs is due to surface mass shedding from its fast rotation spin-up by the Yarkovsky–O'Keefe–Radzievskii–Paddack effect.

Additional Information

© 2021. The American Astronomical Society. Received 2021 February 20; revised 2021 March 17; accepted 2021 March 26; published 2021 April 26. Based on observations obtained with the Samuel Oschin Telescope 48 inch and the 60 inch Telescope at the Palomar Observatory as part of the Zwicky Transient Facility project. ZTF is supported by the National Science Foundation under grant No. AST-2034437 and a collaboration including Caltech, IPAC, the Weizmann Institute for Science, the Oskar Klein Center at Stockholm University, the University of Maryland, Deutsches Elektronen-Synchrotron and Humboldt University, the TANGO Consortium of Taiwan, the University of Wisconsin at Milwaukee, Trinity College Dublin, Lawrence Livermore National Laboratories, and IN2P3, France. Operations are conducted by COO, IPAC, and UW. This work was supported by the GROWTH project funded by the National Science Foundation under PIRE grant No. 1545949. Part of this work was performed under the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. B.T.B. and F.J.M. acknowledge support from NASA with grant No. 80NSSC19K0780. C.F. gratefully acknowledges the support of his research by the Heising-Simons Foundation (# 2018-0907). M.C. acknowledges support from the National Science Foundation with grant No. PHY-2010970. This publication has made use of data collected at Lulin Observatory, partly supported by MoST grant 108-2112-M-008-001. C.C.N. thanks the funding from MOST grant 104-2923-M-008-004-MY5. C.Z. acknowledges support from JPL's internal research funds of the R&TD, JROC, and ESD HBCU/MSI programs. J.N.P. and R.Q. acknowledge support from JPL's ESD HBCU/MSI program under subcontract 1659249. The work of J.H. has been supported by the Czech Science Foundation through grant 20-08218S and by the Charles University Research program No. UNCE/SCI/023. V.B., K.S., and H.K. thank Kunal Deshmukh for help with data processing. The GROWTH-India telescope is a 70 cm telescope with a 0.7 degree field of view, set up by the Indian Institute of Astrophysics and the Indian Institute of Technology Bombay with support from the Indo-US Science and Technology Forum (IUSSTF) and the Science and Engineering Research Board (SERB) of the Department of Science and Technology (DST), Government of India (https://sites.google.com/view/growthindia/). It is located at the Indian Astronomical Observatory (Hanle), operated by the Indian Institute of Astrophysics (IIA). The GROWTH-India project is supported by SERB and administered by IUSSTF. H.K. thanks the LSSTC Data Science Fellowship Program, which is funded by LSSTC, NSF Cybertraining grant #1829740, the Brinson Foundation, and the Moore Foundation; his participation in the program has benefited this work. Facilities: Apache Point Astrophysical Research Consortium 3.5 m telescope - , GROWTH-India Telescope - , Lulin Optical Telescope - , Mount Laguna Observatory 40 inch Telescope - , P48 Oschin Schmidt telescope/Zwicky Transient Facility - , Table Mountain Observatory. - Software: Astropy (Astropy Collaboration et al. 2013, 2018), ZChecker (Kelley et al. 2019), Aperture Photometry Tool (Laher et al. 2012).

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