Searching for Main-Belt Comets Using the Canada-France-Hawaii Telescope Legacy Survey

TL;DR

This study used the Canada-France-Hawaii Telescope Legacy Survey to search for main-belt comets, finding only one candidate and setting upper limits on their population, consistent with asteroid collision rates.

Contribution

First comprehensive search for main-belt comets using the CFHT Legacy Survey data, employing a novel three-level detection technique and visual inspection.

Findings

No cometary activity detected in 952 objects using automated methods.

One candidate comet identified in a larger visual survey.

Upper limits on active main-belt comets are consistent with collision models.

Abstract

The Canada-France-Hawaii Telescope Legacy Survey, specifically the Very Wide segment of data, is used to search for possible main-belt comets. In the first data set, 952 separate objects with asteroidal orbits within the main-belt are examined using a three-level technique. First, the full-width-half-maximum of each object is compared to stars of similar magnitude, to look for evidence of a coma. Second, the brightness profiles of each object are compared with three stars of the same magnitude, which are nearby on the image to ensure any extended profile is not due to imaging variations. Finally, the star profiles are subtracted from the asteroid profile and the residuals are compared with the background using an unpaired T-test. No objects in this survey show evidence of cometary activity. The second survey includes 11438 objects in the main-belt, which are examined visually. One object, an unknown comet, is found to show cometary activity. Its motion is consistent with being a main-belt asteroid, but the observed arc is too short for a definitive orbit calculation. No other body in this survey shows evidence of cometary activity. Upper limits of the number of weakly and strongly active main-belt comets are derived to be 630+/-77 and 87+/-28, respectively. These limits are consistent with those expected from asteroid collisions. In addition, data extracted from the Canada-France-Hawaii Telescope image archive of main-belt comet 176P/LINEAR is presented.