(6478) Gault: Physical characterization of an active main-belt asteroid

Abstract

In December 2018, the main-belt asteroid (6478)~Gault was reported to display activity. Gault is an asteroid belonging to the Phocaea dynamical family and was not previously known to be active, nor was any other member of the Phocaea family. In this work we present the results of photometric and spectroscopic observations that commenced soon after the discovery of activity. We obtained observations over two apparitions to monitor its activity, rotation period, composition, and possible non-gravitational orbital evolution. We find that Gault has a rotation period of $P=2.4929\pm 0.0003$ hours with a lightcurve amplitude of $0.06$ magnitude. This short rotation period close to the spin barrier limit is consistent with Gault having a density no smaller than $\rho =1.85$~g/cm${}^3$ and its activity being triggered by the YORP spin-up mechanism. Analysis of the Gault phase curve over phase angles ranging from $0.4^{\circ }$ to $23.6^{\circ }$ provides an absolute magnitude of $H=14.81\pm 0.04$, $G1=0.25\pm 0.07$, and $G2=0.38\pm 0.04$. Model fits to the phase curve find the surface regolith grain size constrained between 100-500 $\mu$m. Using relations between the phase curve and albedo we determine that the geometrical albedo of Gault is $p_{\mathrm{v}}=0.26\pm 0.05$ corresponding to an equivalent diameter of $D=2.8_{-0.2}^{+0.4}$ km. Our spectroscopic observations are all consistent with an ordinary chondrite-like composition (S, or Q-type in the Bus-DeMeo taxonomic classification). A search through archival photographic plate surveys found previously unidentified detections of Gault dating back to 1957 and 1958. Only the latter had been digitized, which we measured to nearly double the observation arc of Gault. Finally, we did not find any signal of activity during the 2020 apparition or non-gravitational effects on its orbit.

arXiv comment15 pages, 11 figures; Accepted in MNRAS

References in corpus (33)

• Astropy: A Community Python Package for Astronomy
• Gaia Data Release 2. Summary of the contents and survey properties
• The VizieR database of Astronomical Catalogues
• The Ninth Data Release of the Sloan Digital Sky Survey: First Spectroscopic Data from the SDSS-III Baryon Oscillation Spectroscopic Survey
• ATLAS: A High-Cadence All-Sky Survey System
• Astrometry.net: Blind astrometric calibration of arbitrary astronomical images
• Density of asteroids
• On the use of Gaia magnitudes and new tables of bolometric corrections
• Dynamics of rotationally fissioned asteroids: Source of observed small asteroid systems
• Activity in Geminid Parent (3200) Phaethon
• Near Earth Asteroids with measurable Yarkovsky effect
• Setting UBVRI Photometric Zero-Points Using Sloan Digital Sky Survey ugriz Magnitudes
• PHOTOMETRYPIPELINE: An Automated Pipeline for Calibrated Photometry
• Yarkovsky Drift Detections for 247 Near-Earth Asteroids
• Pluto's Haze as a Surface Material
• A 2 km-size asteroid challenging the rubble-pile spin barrier - a case for cohesion
• Is the Missing Ultra-Red Material Colorless Ice?
• Visible spectroscopy from the Mission Accessible Near-Earth Object Survey (MANOS): Taxonomic dependence on asteroid size
• The Sporadic Activity of (6478) Gault: A YORP-driven event?
• Episodically Active Asteroid 6478 Gault
• Properties of Near-Sun Asteroids
• Asteroid Photometry
• A dark asteroid family in the Phocaea region
• Multiple Outbursts of Asteroid (6478) Gault
• A common origin for dynamically associated near-Earth asteroid pairs
• Dust Properties of Double-Tailed Active Asteroid (6478) Gault
• Time-series and Phasecurve Photometry of Episodically-Active Asteroid (6478) Gault in a Quiescent State Using APO, GROWTH, P200 and ZTF
• Physical Characterization of Active Asteroid (6478) Gault
• Active asteroid (6478) Gault: a blue Q-type surface below the dust?
• New Active Asteroid (6478) Gault
• Rotational Mass Shedding from Asteroid (6478) Gault
• Secular and Rotational Light Curves of 6478 Gault
• Spinning and color properties of the active asteroid (6478) Gault

Cited by in corpus (8)

• SPECULOOS Northern Observatory: searching for red worlds in the northern skies
• The Active Asteroids Citizen Science Program: Overview and First Results
• Long-lasting activity of asteroid (248370) 2005 QN 173
• Photometric and dynamic characterisation of active asteroid (248370) 2005 QN173
• The Discovery and Evolution of a Possible New Epoch of Cometary Activity by the Centaur (2060) Chiron
• Physical characterization of the active asteroid (6478) Gault
• Constraining the Interiors of Asteroids Through Close Encounters
• Rapid-response characterization of near-Earth asteroid 2024 YR4 during a Torino Scale 3 alert