Electronic Telegram No. 4341 Central Bureau for Astronomical Telegrams Mailing address: 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/2017 A2 = P/2011 A5 (PANSTARRS) Richard Wainscoat, Eva Lilly, Rob Weryk, and Marco Micheli report the discovery of another apparent comet in w-band exposures obtained with the 1.8-m Ritchey-Chretien Pan-STARRS1 telescope at Haleakala on Jan. 2 (discovery observations tabulated below). While the faint comet has significant interference from background objects in the discovery images, it shows a point-like nuclear condensation and a tail towards p.a. approximately 300 degrees for approximately 15". 2017 UT R.A. (2000) Decl. Mag. Jan. 2.57733 11 10 09.21 - 0 44 19.0 21.3 2.58910 11 10 09.24 - 0 44 25.7 21.3 2.60083 11 10 09.27 - 0 44 32.0 21.1 2.61262 11 10 09.29 - 0 44 38.5 21.3 Three 60-s follow-up exposures (with g-, r-, and i-band filters) were obtained by R. J. Wainscoat, M. Micheli, and P. Forshay with the 3.6-m Canada-France- Hawaii Telescope on Mauna Kea on Jan. 3.6 UT, showing the new object to be clearly cometary with an obvious narrow tail 35" long toward p.a. 300 deg; the g-band magnitude was measured to be 20.8. After the comet was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists have also commented on the object's cometary appearance. Unfiltered exposures taken by A. Maury, J.-B. de Vanssay, and J.-F. Soulier on Jan. 4.27-4.36 UT with a 0.4-m f/5.4 Ritchey-Chretien reflector at San Pedro de Atacama, Chile, show a coma of size about 10" and a tail about 51" long in p.a. about 290 degrees, the red magnitude being 19.7- 19.9 in an aperture of radius 6".2. Soulier also obtained unfiltered stacked images on Jan. 5.09-5.16 with a 0.30-m f/3.8 Newtonian reflector at Maisoncelles, France, that show a coma of size about 15" and a tail about 58" long in p.a. about 310 deg; the red magnitude was measured as 19.7-20.0 in an aperture of radius 6".5. H. Sato, Tokyo, Japan, reports that six stacked 60-s exposures taken on Jan. 5.7 with a 0.40-m f/3.5 astrograph (+ luminance filter) at Siding Spring show the comet to be strongly condensed with a stellar nuclear condensation and a diffuse outer coma 12" in diameter but no tail; the w-band magnitude was 19.3 as measured within a circular aperture of radius 6".4. Pre-discovery observations obtained at Mount Lemmon were identified in incidental astrometry supplied to the Minor Planet Center last month (where the object was not reported to show cometary appearance): on 2016 Dec. 4.5 UT (the magnitude given then as 18.8-19.1), and on Dec. 24.45-24.47 (mag 19.2-19.4). Subsequently, G. V. Williams identified apparently asteroidal January 2011 observations made at Mt. Lemmon (observer R. A. Kowalski) and at Haleakala, for which the designation P/2011 A5 has been assigned. 2011 UT R.A. (2000) Decl. Mag. Observer Jan. 13.37928 7 46 52.42 +32 51 48.1 20.5 Kowalski 13.38691 7 46 51.85 +32 51 44.6 20.8 " 13.39459 7 46 51.27 +32 51 41.4 20.9 " 13.40218 7 46 50.73 +32 51 38.1 20.8 " 30.28430 7 28 18.98 +30 26 05.7 20.8 Pan-STARRS1 30.29870 7 28 18.16 +30 25 57.5 20.7 " 30.31395 7 28 17.27 +30 25 48.8 20.7 " 30.32826 7 28 16.45 +30 25 40.7 20.6 " The available astrometry, the following linked orbital elements by Williams (from 29 observations spanning 2011 Jan. 13-2017 Jan. 5; mean residual 0".7), and an ephemeris appear on MPEC 2017-A32. Epoch = 2010 Nov. 20.0 TT T = 2010 Nov. 1.75373 TT Peri. = 133.44468 e = 0.3010416 Node = 313.80783 2000.0 q = 2.2113937 AU Incl. = 17.58403 a = 3.1638416 AU n = 0.17513864 P = 5.63 years Epoch = 2016 June 21.0 TT T = 2016 June 22.14286 TT Peri. = 133.75508 e = 0.3009812 Node = 313.74714 2000.0 q = 2.2121519 AU Incl. = 17.58452 a = 3.1646529 AU n = 0.17507130 P = 5.63 years NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2017 CBAT 2017 January 7 (CBET 4341) Daniel W. E. Green