Title: X-shooter search for outgassing from Main Belt Comet P/2012 T1 (Pan-STARRS) Author: Colin Snodgrass, Bin Yang, Alan Fitzsimmons
Main Belt Comets are a recently identified population of minor bodies with stable asteroid-like orbits but cometary appearances. Sublimation of water ice is the most likely mechanism for their recurrent activity (i.e. dust tails and dust comae), although there has been no direct detection of gas. These peculiar objects could hold the key to the origin of water on Earth. In this paper we present a search for the gas responsible for lifting dust from P/2012 T1 (Pan-STARRS), and review previous attempts at such measurements. To date such searches have mainly been indirect, looking for the common cometary gas CN rather than gasses related to water itself. We use the VLT and X-shooter to search for emission from OH in the UV, a direct dissociation product of water. We do not detect any emission lines, and place an upper limit on water production rate from P/2012 T1 of 8-9 x 10^25 molecules s^-1. This is similar to limits derived from observations using the Herschel space telescope. We conclude that the best current facilities are incapable of detecting water emission at the exceptionally low levels required to produce the observed activity in Main Belt Comets.
WHT and GTC Follow Up Main Belt Comet P/2012 T1 (PANSTARRS)
Since the dynamical association of the Apollo-type asteroid (3200) Phaethon with the Geminid meteor shower was made two decades ago, another 10 active asteroids have been discovered. Some originate in the main asteroid belt and thus are known as main belt comets (MBCs), one of the last discovered being P/2012 T1 (PANSTARRS). Thanks to the possibility of target-of-opportunity observations at the WHT and GTC, a team of Spanish astronomers followed up its evolution and revealed the origin of its cometary activity. Read more
Title: Main-Belt Comet P/2012 T1 (PANSTARRS) Authors: Henry H. Hsieh, Heather M. Kaluna, Bojan Novakovic, Bin Yang, Nader Haghighipour, Marco Micheli, Larry Denneau, Alan Fitzsimmons, Robert Jedicke, Jan Kleyna, Peter Veres, Richard J. Wainscoat, Megan Ansdell, Garrett T. Elliott, Jacqueline V. Keane, Karen J. Meech, Nicholas A. Moskovitz, Timm E. Riesen, Scott S. Sheppard, Sarah Sonnett, David J. Tholen, Laurie Urban, Nick Kaiser, K. C. Chambers, William S. Burgett, Eugene A. Magnier, Jeffrey S. Morgan, Paul A. Price
We present initial results from observations and numerical analyses aimed at characterising main-belt comet P/2012 T1 (PANSTARRS). Optical monitoring observations were made between October 2012 and February 2013 using the University of Hawaii 2.2 m telescope, the Keck I telescope, the Baade and Clay Magellan telescopes, Faulkes Telescope South, the Perkins Telescope at Lowell Observatory, and the Southern Astrophysical Research (SOAR) telescope. The object's intrinsic brightness approximately doubles from the time of its discovery in early October until mid-November and then decreases by ~60% between late December and early February, similar to photometric behaviour exhibited by several other main-belt comets and unlike that exhibited by disrupted asteroid (596) Scheila. We also used Keck to conduct spectroscopic searches for CN emission as well as absorption at 0.7 microns that could indicate the presence of hydrated minerals, finding an upper limit CN production rate of QCN<1.5x10^23 mol/s, from which we infer a water production rate of QH2O<5x10^25 mol/s, and no evidence of the presence of hydrated minerals. Numerical simulations indicate that P/2012 T1 is largely dynamically stable for >100 Myr and is unlikely to be a recently implanted interloper from the outer solar system, while a search for potential asteroid family associations reveal that it is dynamically linked to the ~155 Myr-old Lixiaohua asteroid family.
Title: The dust environment of Main-Belt Comet P/2012 T1 (PANSTARRS) Authors: Fernando Moreno, Antonio Cabrera-Lavers, Ovidiu Vaduvescu, Javier Licandro, Francisco Pozuelos
Main-Belt Comet P/2012 T1 (PANSTARRS) has been imaged using the 10.4m Gran Telescopio Canarias (GTC) and the 4.2m William Herschel Telescope (WHT) at six epochs in the period from November 2012 to February 2013, with the aim of monitoring its dust environment. The dust tails brightness and morphology are best interpreted in terms of a model of sustained dust emission spanning 4 to 6 months. The total dust mass ejected is estimated at ~6--25 x 10^6 kg. We assume a time-independent power-law size distribution function, with particles in the micrometer to centimetre size range. Based on the quality of the fits to the isophote fields, an anisotropic emission pattern is favoured against an isotropic one, in which the particle ejection is concentrated toward high latitudes (±45° to ±90°) in a high obliquity object (I=80°). This seasonally-driven ejection behaviour, along with the modelled particle ejection velocities, are in remarkable agreement to those we found for P/2010 R2 (La Sagra) {Moreno11a}.