Time-series Photometric Lightcurves of Episodically Active Asteroid (6478) Gault in an Inactive State

We present photometry of the episodically active asteroid (6478) Gault during a recent period of inactivity. Detections in deep-stack R-band images were obtained with the Mount Laguna Observatory 1.0-meter telescope on 2020 June 24 UTC several months after Gault was leaving Solar conjunction with a heliocentric distance of 2.07 AU. The asteroid was measured to have an angular FWHM of ~2" similar to nearby background stars and a 3-sigma lower limit surface brightness magnitude of R~25.8 mag/sq.arcsec within a 3.5”-5” annulus (Purdum et al. ATel #13885). In comparison, detections of (6478) Gault in measurements made by the Astrophysical Research Consortium 3.5-meter telescope taken on 2019 February 9 UTC, soon after its apparent outburst starting in late 2018/2019 (Ye et al. 2019 APJ 874 L16), show the comet had a double-tailed morphology and a 3.5"-5" annulus surface brightness of R~24 ± 0.1 mag/sq.arcsec. This outburst observation occurred when Gault had a farther heliocentric distance of 2.41 AU, indicating that water ice sublimation is not a clear driver for activity as the frost line for the Sun is located near 2.7 AU (Martin et al. 2012 MNRAS 425 L6). We also analyzed lightcurve variation data of Gault from the Canada France Hawaii Telescope that showed Gault as having an inactive, stellar morphology over 4 days starting on 2005 April 3 UTC. We present the results of time-series measurements of (6478) Gault from our recent and archival observations when the asteroid is in both an active and inactive state.