Spinning and color properties of the active asteroid (6478) Gault

Abstract

We report on accurate $BV{R}_c$ observations of (6478) Gault, a 5-6 km diameter inner main-belt asteroid in the Phocaea family, notable for its sporadic, comet-like ejection of dust. This curious behavior has been mainly interpreted as reconfigurations after YORP spin-up, although merging of a contact binary system cannot be fully excluded. We collected optical observations along the 2019 March-April period, at orbital phase angles between $12^{\circ }-21^{\circ }$, to search for direct evidence of asteroid quick spinning rotation. A prevailing period value of $3.34\pm 0.02$ hours is supported by our and other photometric observations. In the YORP spin-up hypothesis, this period points to a bulk density $\rho \approx 1$ $\text{g}/{\text{cm}}^3$. The mean colors are $B-V=+0.82_{\pm 0.3}$, $V-R_c=+0.28_{\pm 0.06}$ and $B-R_c=+1.11_{\pm 0.4}$, but we have observed a strong bluer color during the April session, with about $\Delta (B-V)\sim 0.35\pm 0.09$~mag. This color change can be due to asteroid rotation and support the hypothesis that there is a bluer surface under the Gault's dust, as indicated by spectroscopic observations made on 2019 March 31 and April 8 by Marsset et al. (2019).

8 pages, 12 figures, submitted to Mon. Not. R. Astron. Soc

References in corpus (6)

• The Sporadic Activity of (6478) Gault: A YORP-driven event?
• Episodically Active Asteroid 6478 Gault
• Multiple Outbursts of Asteroid (6478) Gault
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• New Active Asteroid (6478) Gault
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Cited by in corpus (6)

• (6478) Gault: Physical characterization of an active main-belt asteroid
• Time-series and Phasecurve Photometry of Episodically-Active Asteroid (6478) Gault in a Quiescent State Using APO, GROWTH, P200 and ZTF
• Rotational Mass Shedding from Asteroid (6478) Gault
• Long-lasting activity of asteroid (248370) 2005 QN 173
• Activity of (6478) Gault during January 13 - March 28, 2019
• Physical characterization of the active asteroid (6478) Gault