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T.L. Farnham (U. Texas), D.G. Schleicher, L.M. Woodney (Lowell Obs.), C.A. Eberhardy (U. Washington), P.V. Birch (Perth Obs.), L. Levy (NAU)
We present an analysis of photometry and CCD imaging of Comet LINEAR (1999~S4) obtained both before and after break-up in late July.
Photometry was obtained at Lowell Observatory on 10 nights between 1999~Dec~5 and 2000~Jul~13 (r = 3.57-0.80 AU) with post-break-up measurements obtained on Jul~29 and Aug~1. From December to March, dust production, as measured by Af\rho, was essentially unchanged at about 200~cm, while the CN production rate increased from 2\times1024 to 1\times1025 mol~s-1. The flat dust production is consistent with the scenario that LINEAR, a dynamically new comet, experienced an outburst with very low outflow velocities at large r, and this older material overwhelmed subsequent dust emission during this period. Measured gas and dust production peaked during an apparent outburst centered on June~11, with Af\rho reaching 800~cm and Q(CN) reaching 5\times1025 mol~s-1. The corresponding values on July~13, 2 weeks before perihelion, were about 400~cm and 3\times1025 mol~s-1, and Q(OH; Haser) was 1.7\times1028 mol~s-1, yielding Q(water; vectorial) of 2.6\times1028 mol~s-1. On July 29, about 4 days after break-up, dust and gas production had fallen by a factor of 10.
Images of comet LINEAR were obtained on 31 pre-perihelion nights between 1999~Nov~2 and 2000~Jul~9 at McDonald and Lowell Observatories, and on eight post-break-up nights from Lowell and Perth Observatories. Analysis of these images will include: 1) Processing to enhance coma features and to look for fragments that broke off before the complete disruption; 2) Investigation of features that might constrain the nucleus rotation; and 3) Modeling of the dust tail to determine the particle size distribution and place a limit on the mass ejected during break-up. Preliminary results, focusing on the time around break-up, will be presented.
This research was supported by NASA.
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