Main-belt comet 238P/read revisited

Abstract

We present a series of observations of the return of activity in main-belt comet (MBC) 238P/Read. Using data obtained in 2010 July and August when 238P appeared to be largely inactive, we find best-fit IAU phase function parameters of H = 19.05 0.05mag, corresponding to a nucleus radius of rn 0.4km (assuming an albedo of pR = 0.05), and G = -0.03 0.05. Observations from 2010 September onward show a clear rise in activity, causing both a notable change in visible morphology and increasing photometric excesses beyond what would be expected based on bare nucleus observations. By the end of the observing period reported on here, the dust mass in the coma shows indications of reaching a level comparable to that observed in 2005, but further observations are highly encouraged once 238P again becomes observable from Earth in mid-2011 to confirm whether this level of activity is achieved, or if the comet shows a noticeable drop in activity strength compared with 2005. Comet 238P is now the second MBC (after 133P/Elst-Pizarro) observed to exhibit recurrent activity, providing strong corroboration for the conclusion that it is a true comet whose active episodes are driven by sublimation of volatile ice. © 2011. The American Astronomical Society. All rights reserved.