From quai en eps.harvard.edu Thu Apr 7 20:40:28 2016 From: quai en eps.harvard.edu (quai en eps.harvard.edu) Date: Thu, 7 Apr 2016 23:40:28 +0000 (UTC) Subject: [IAUC] CBET 4270: 20160408 : COMET P/2015 HG_16 (PANSTARRS) Message-ID: <16040723402835_60542@epsps7.eps.harvard.edu> Electronic Telegram No. 4270 Central Bureau for Astronomical Telegrams Mailing address: Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau en eps.harvard.edu (alternate cbat en iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network COMET P/2015 HG_16 (PANSTARRS) R. Weryk and R. J. Wainscoat reported the discovery of a comet on four w-band CCD exposures taken on 2016 Apr. 4 UT with the 1.8-m Pan-STARRS1 telescope at Haleakala (those observations are tabulated below, together with additional Pan-STARRS1 observations from the previous night); the comet's images appeared slightly larger than those of nearby stars (FWHM approximately 1".5, vs. 1".2 for stars), and there is evidence of a tail extending for approximately 10" towards position angle approximately 310 degrees. Weryk subsequently identified an object seen in faint detections from three w-band Pan-STARRS1 exposures taken on 2016 Feb. 11 (also tabulated below), from which a stacked image showed evidence of a tail extending for approximately 6" toward p.a. 300 degrees (with the comet's head again being slightly larger than nearby stars, 1".4 vs. 1".0); Weryk adds that there are also Pan-STARRS1 detections on 2016 Mar. 17 and 31, but they are too faint for measurements. Follow-up CCD observations by Wainscoat and C. Wipper taken on 2016 Apr. 6.44 with the 3.6-m Canada-France-Hawaii Telescope (measured by M. Micheli and Wainscoat) show the object to be clearly cometary with a 20" tail in p.a. 305 deg (and the coma have red mag 21.4-21.5 and size FWHM 1".15 in 0".75 seeing). 2016 UT R.A. (2000) Decl. Mag. Feb. 11.58765 14 35 40.96 - 2 33 36.1 22.3 11.60001 14 35 41.04 - 2 33 36.2 22.2 11.61243 14 35 41.18 - 2 33 35.8 22.3 Apr. 3.49148 14 23 55.38 - 1 26 55.5 21.6 3.50351 14 23 55.01 - 1 26 54.5 21.6 3.51551 14 23 54.59 - 1 26 53.3 21.9 3.52752 14 23 54.20 - 1 26 52.2 21.7 4.47614 14 23 22.27 - 1 25 12.6 21.7 4.48805 14 23 21.85 - 1 25 11.4 21.9 4.49994 14 23 21.43 - 1 25 10.0 21.6 4.51189 14 23 21.02 - 1 25 08.6 21.9 G. V. Williams, Minor Planet Center, noted that the 2016 April 3 observations appeared to belong to a supposedly asteroidal object found a year ago by Pan-STARRS1 on 2015 Apr. 20, 21, and 24 (and then given the minor-planet designation 2015 HG_16 on MPS 603395 and 603396). Weryk had already identified earlier Pan-STARRS1 observations from 2015 Mar. 24 and Apr. 9 (which are also tabulated below) when Williams made his link between the 2015 and 2016 observations. 2015 UT R.A. (2000) Decl. Mag. Mar. 24.32890 10 50 40.70 +34 10 21.6 21.0 24.33947 10 50 40.32 +34 10 20.1 20.9 24.35011 10 50 39.93 +34 10 18.7 21.0 24.36079 10 50 39.57 +34 10 17.2 20.9 Apr. 9.36430 10 43 38.42 +33 09 22.5 20.5 9.37531 10 43 38.21 +33 09 19.4 20.6 9.38648 10 43 37.97 +33 09 15.9 20.8 20.33256 10 41 38.34 +32 04 40.5 20.7 20.34540 10 41 38.27 +32 04 35.4 20.8 20.35827 10 41 38.18 +32 04 30.2 20.8 20.37126 10 41 38.12 +32 04 25.2 20.9 21.35606 10 41 34.44 +31 57 52.2 20.6 21.36813 10 41 34.34 +31 57 47.3 20.7 21.38025 10 41 34.30 +31 57 42.4 20.5 21.39369 10 41 34.24 +31 57 36.4 20.5 24.35765 10 41 30.14 +31 37 15.7 20.6 24.36817 10 41 30.13 +31 37 11.1 20.5 24.37870 10 41 30.13 +31 37 06.8 20.7 24.38998 10 41 30.11 +31 37 02.0 20.6 The following elliptical orbital elements by Williams and an ephemeris appear on MPEC 2016-G114: Epoch = 2014 July 2.0 TT T = 2014 June 28.97674 TT Peri. = 48.15343 e = 0.3462278 Node = 59.52587 2000.0 q = 3.1317834 AU Incl. = 18.86851 a = 4.7903284 AU n = 0.09400612 P = 10.48 years NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2016 CBAT 2016 April 8 (CBET 4270) Daniel W. E. Green