Electronic Telegram No. 4117 Central Bureau for Astronomical Telegrams INTERNATIONAL ASTRONOMICAL UNION CBAT Director: Daniel W. E. Green; Hoffman Lab 209; Harvard University; 20 Oxford St.; Cambridge, MA 02138; U.S.A. e-mail: cbatiau@eps.harvard.edu (alternate cbat@iau.org) URL http://www.cbat.eps.harvard.edu/index.html Prepared using the Tamkin Foundation Computer Network COMET P/2015 M2 (PANSTARRS) R. Weryk and E. Lilly report the discovery of a comet in four i-band exposures taken with the 1.8-m Pan-STARRS1 telescope at Haleakala on June 30.6 UT (discovery observations tabulated below), noting it to be slightly larger than nearby stars of similar brightness and also evidence of a short tail extending for approximately 3" towards p.a. approximately 250 degrees. Weryk and Lilly add that they then looked back at three earlier w-band Pan-STARRS1 images from June 28.6 and found clear evidence of a tail, extending for at least 10" towards p.a. approximately 250 deg. Weryk further writes that three Pan-STARRS1 w-band exposures taken on July 14.5 show a short tail extending for approximately 8" towards p.a. approximately 250 deg. 2015 UT R.A. (2000) Decl. Mag. June 28.57115 21 03 03.71 -19 56 36.9 20.0 28.58217 21 03 03.50 -19 56 38.1 20.4 28.59316 21 03 03.34 -19 56 39.0 20.0 29.53286 21 02 48.17 -19 58 18.2 20.0 29.54387 21 02 47.99 -19 58 19.4 20.2 30.53905 21 02 31.36 -20 00 06.0 20.0 30.55041 21 02 31.13 -20 00 07.3 20.4 30.56182 21 02 30.96 -20 00 08.3 20.1 30.57320 21 02 30.75 -20 00 09.9 20.3 After the object was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists also have commented on the cometary appearance. H. Sato, Tokyo, Japan, reports that ten stacked 60-s exposures taken with an iTelescope 0.70-m f/6.6 astrograph (+ luminance filter) at Siding Spring on July 7.6 UT show the comet to be moderately condensed with an elongated coma 6" x 4" in size, with w-band magnitude 18.9 as measured within a circular aperture of radius 3".3, and a 20" tail toward p.a. 255 degrees. T. H. Bressi found a 5" tail in p.a. about 225 deg (and red mag 18.8-18.9) on images taken on July 8.4 with the Spacewatch 1.8-m f/2.7 reflector (+ Finger Lakes ProLine PL3041-LC camera + Schott OG-515 filter) at Kitt Peak. A. Maury and T. Noel compiled stacked exposures taken on July 10.3 with a 0.4-m f/8 Ritchey- Chretien reflector at San Pedro de Atacama, Chile, to find a coma of size 5" x 8" and red magnitude 18.9-19.1 in an aperture of size 5".5. J. V. Scotti writes that stacked images with the same Spacewatch 1.8-m telescope on July 11.4 reveal a well-condensed coma of diameter 7" and magnitude 17.6, with an obvious tail extending 0'.30 in p.a. 250 degrees. Scotti adds that additional exposures taken the following night (July 12.4) show coma diameter 7" with an 0'.59 tail in p.a. 250 degrees. Twelve 60-s exposures taken by A. C. Gilmore and P. M. Kilmartin with the Mt. John 1.0-m f/7.7 reflector at Lake Tekapo on July 11.65-11.66 show an oval coma of size 8" x 12" and a faint, narrow tail about 1' long in p.a. 260 degrees. The available astrometry, the following elliptical orbital elements by G. V. Williams, and an ephemeris appear on MPEC 2015-N46. T = 2015 Oct. 22.0203 TT Peri. = 228.4372 e = 0.174867 Node = 86.8012 2000.0 q = 5.918572 AU Incl. = 3.9898 a = 7.172873 AU n = 0.0513056 P = 19.2 years NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2015 CBAT 2015 July 15 (CBET 4117) Daniel W. E. Green