------------------------------------------------------------------- THE ASTRONOMER Electronic Circular No 2397 2007 Dec 05 10.33UT Ed:Guy M Hurst, 16,Westminster Close, Kempshott Rise, Basingstoke, Hants, RG22 4PP,England.Telephone/FAX(01256)471074Int:+441256471074 INTERNET: GUY@TAHQ.DEMON.CO.UK Backup: gmh@wdcc1.bnsc.rl.ac.uk WORLD WIDE WEB http://www.theastronomer.org ------------------------------------------------------------------- COMET 17P/HOLMES B. Gaillard, J. Lecacheux, and F. Colas, Paris Observatory, elaborate on CBET 1123 on observations of comet 17P obtained from Oct. 24 to Nov. 4 with the 1-m telescope at Pic du Midi Observatory. During this 10-day interval beginning just at the outburst, they have followed the evolution of dust streams and condensations inside the expanding "coma blob". The dust streams appear to come from cometary fragments that quickly recede from the nucleus, though such fragments remain below their detection threshold. Nevertheless, they have measured (with a 2000-km precision) the increasing distance from the nucleus of the well-defined head of these streams. Apparent velocities ranging from 50 to 100 m/s (projected on the sky) have been found for four of these stream heads, showing no trace of acceleration. The separation of the parent fragments from the nucleus is calculated to have occurred at different times between Oct. 23.7 and 24.8 UT, so the most probable scenario is that the comet outburst began a few hours before Oct. 24.0. Different discrete releases of dusty material took place over the two subsequent days, with a dominant event around Oct.24.40 being perhaps responsible for the final brightness rise of the comet, and undoubtedly for the obvious circular shell that continues expanding at 570 m/s. B. Yang and D. Jewitt, University of Hawaii, report on IAUC 8892 near- infrared (0.8- to 4.2-micron) spectra taken with the 3.0-m NASA Infrared Telescope Facility by S. J. Bus on Oct. 27 and 28 UT. Two broad absorption bands were found centred at 2.02 microns (the depth being 10 percent of the continuum) and 3.03 microns (30-percent deep), respectively, in the reflectance spectra of 17P. These features, which appeared on both nights, are consistent with abundant water ice grains in the central coma. The overall slope of the infrared reflectance spectrum of this comet is blue, with a normalized reflectance gradient near -2.3 percent per 100 nm. 2007 VA_85 An apparently asteroidal object of mag 18.5-19 discovered by the LINEAR survey on Nov. 4.1 UT has the shortest known period (P = 7.6 yr) for a sun-orbiting natural object with a retrograde orbit (i = 132.6 deg). Attempts to find cometary activity have been unsuccessful. (IAUC 8894) SUPERNOVA 2007on IN NGC 1404 Discovery by TAROT collaboration of a possible supernova (CBET 1121): SN 2007 UT R.A. (2000.0) Decl. Mag. Offset 2007on Nov 5.25 03 38 50.9 -35 34 30 14.9R 12"W 68"N The object was also found to be present on Nov 2.20 at R=17.1. SUPERNOVA 2007oo IN UGC 12558 Discovery by Mostardi and Li of a possible supernova (CBET 1122): SN 2007 UT R.A. (2000.0) Decl. Mag. Offset 2007oo Nov 6.21 23 22 19.50 +50 09 20.0 18.9 2.7"E 12.4"S SUPERNOVA 2007op Discovery by Quimby et. al., of a possible supernova (CBET 1124): SN 2007 UT R.A. (2000.0) Decl. Mag. Offset 2007op Oct 20.22 01 53 12.36 +33 44 34.0 18.7 2.4"E 2.6"S A spectrum of Nov 8 shows it to be a type-Ia and past maximum. Guy M Hurst