Discovery of Main-Belt Comet P/2006 Vw139 By Pan-Starrs1

The main-belt asteroid (300163) 2006 VW139 (later designated P/2006 VW139) was discovered to exhibit comet-like activity by the Pan-STARRS1 (PS1) survey telescope using automated point-spread-function analyses performed by PS1\u27s Moving Object Processing System. Deep follow-up observations show both a short (similar to 10 \u27\u27) antisolar dust tail and a longer (similar to 60 \u27\u27) dust trail aligned with the object\u27s orbit plane, similar to the morphology observed for another main-belt comet (MBC), P/2010 R2 (La Sagra), and other well-established comets, implying the action of a long-lived, sublimation-driven emission event. Photometry showing the brightness of the near-nucleus coma remaining constant over similar to 30 days provides further evidence for this object\u27s cometary nature, suggesting it is in fact an MBC, and not a disrupted asteroid. A spectroscopic search for CN emission was unsuccessful, though we find an upper limit CN production rate of Q(CN) \u3c 1.3 x 10(24) mol s(-1), from which we infer a water production rate of Q(H2O) \u3c 10(26) mol s(-1). We also find an approximately linear optical spectral slope of 7.2%/1000 angstrom, similar to other cometary dust comae. Numerical simulations indicate that P/2006 VW139 is dynamically stable for \u3e 100 Myr, while a search for a potential asteroid family around the object reveals a cluster of 24 asteroids within a cutoff distance of 68 m s(-1). At 70 m s(-1), this cluster merges with the Themis family, suggesting that it could be similar to the Beagle family to which another MBC, 133P/Elst-Pizarro, belongs