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ATEL # 1754; Josep M. Trigo-Rodriguez (Institute Space Sciences, CSIC-IEEC)
on 2 Oct 2008; 12:12 UT
Distributed as an Instant Email Notice (Request for Observations)
Password Certification: Josep M. Trigo-Rodriguez (firstname.lastname@example.org)
Subjects: Infra-Red, Optical, Request for Observations, Comets
COMET 29P/SCHWASSMANN-WACHMANN IN OUTBURST
J. M. Trigo-Rodriguez, Institute of Space Sciences, Consejo Superior de Investigaciones Cientificas and Institut Estudis Espacials de Catalunya, reports that the present outburst experienced by this Centaur (#IAUC 8978) is the brightest detected since September 2004 [for more details see Trigo-Rodriguez et al. (2008) A&A485, pp. 599-606]. In the previously reported work the outburst frequency was established in 7.3 outbursts/year, typically reaching a +13 maximum magnitude or less. The comet recovery, after several months unobserved due to solar conjunction, was achieved by A. Sanchez (MPC 442) on Sept. 06.178 when the comet was imaged through a SC 36.0 f/6 exhibiting 14.9 R magnitude (all magnitudes here are given for a 10 arcsec standardized aperture). By Sept. 09.77 the outburst was confirmed visually by S. Yoshida (Gunma, Japan) by using a 0.40-m reflector reporting 12.8V to the ICQ. An increase in the CCD magnitude was observed by A. Sanchez on Sept. 13.158 when the comet was in magn. 14.1R. D. Rodriguez (MPC 458) confirmed the outburst on Sept. 15.177 when the comet was in magn. 14.2R. Since then this comet has developed the coma due to the released micron-sized grains that are expanding outwards. The increase in magnitude has continued as is suggested from ulterior observations by A. Sanchez (Sept. 25.118, 11.9R; Sept. 29.155, 12.4R, 12.3I, 12.9V; Oct. 01.154, 13.4R, 13.5I, 13.8V). In the Sept. 29 observation an asymmetric distribution of a 55 arcsec-wide coma is visible that at the current comet distance corresponds to a coma diameter of 255000 km. A bright fan of material extending from the nucleus was present in p.a. 235 deg. Such fan is usually reported in bright outbursts of this comet, being produced by micron-sized particles that are contributing to solar light scattering. In any case, this outburst seems to be quite unusual due to the long extent of the activity that is suggesting a continuous re-supply of large grains from the nucleus. Gunnarson (2003), A&A 398, 353 performed grain lifetime sublimation calculations, finding that the lifetime of mm-sized clusters producing the micron-sized particles should be of 2 or 3 days. As the magnitude of the comet has been increasing progressively in the last two weeks, seems evident that some active area has been massively re-supplying material to the coma. A future follow-up of the magnitude decay of this object can be very useful in order to perform an accurate modeling of 29P activity.