Limits on the number distribution of Main Belt Comets

Details Limits on the number distribution of Main Belt Comets Limits on the number distribution of Main Belt Comets

Oct 2011

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011epsc.conf..391s&link_type=abstract

EPSC-DPS Joint Meeting 2011, held 2-7 October 2011 in Nantes, France. http://meetings.copernicus.org/epsc-dps2011, p.391

Computer Science

Scientific paper

We searched the Thousand Asteroid Light Curve Survey (TALCS, [1]) data for new Main Belt Comet (MBC) candidates in the most sensitive MBC survey effort to date, extending the search to objects as small as absolute magnitude H 21 (corresponding to diameters of about 150 m). We identified zero MBC candidates but found evidence that about 5% of all asteroids show low level activity in the form of a directionalized excess flux in the point spread function (PSF). To measure the fractional contribution of the coma to the total surface brightness we fit each of the 924 TALCS objects to a PSF model that incorporated both coma and nuclear components. We determined the significance of the coma detection using the same algorithm on a sample of null detections of comparable magnitude and rate of motion. We did not identify any MBC candidates with this technique to a sensitivity limit on the order of typical cometary mass loss rates of about 0.1 kg/s. Our tail detection algorithm relied on identifying statistically significant flux in a segmented annulus around the candidate object (see Figure 1). We show that the technique can detect tail activity throughout the asteroid belt to the level of the currently known MBCs. Although we did not identify any MBC candidates with this technique we found a statistically significant detection of faint activity in the entire ensemble of TALCS asteroids. This suggests that about 5% of main belt asteroids are active at very low levels. Our null detection of MBCs allows us to set 90% upper confidence limits on the number distribution of MBCs as a function of absolute magnitude, semimajor axis, eccentricity, and inclination. There are <400,000 MBCs in the main belt brighter than HV = 21 ( 150 m in diameter) and the MBC:MBA ratio is <1:400. We further comment on the ability of observations to meaningfully constrain the snow line's location. Under some reasonable and simple assumptions we claim 85% confidence that the contemporary snow line lies beyond 2.5 AU. Acknowledgements The TALCS work was made possible by NASA PAST grant NNG06GI46G. Henry Hsieh was very helpful in contributing ideas and test data.

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