Electronic Telegram No. 4068 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 C/2015 C2 (SWAN) R. Matson, Newport Coast, CA, USA, found a moving object in public website images obtained with the Solar Wind Anisotropies (SWAN) camera on the Solar and Heliospheric Observer (SOHO) spacecraft, located at the earth- sun L_1 Lagrange point, taking daily full-sky hydrogen Lyman-alpha images. Matson circulated a preliminary parabolic orbit and ephemeris from observations spanning Feb. 15-22 that he circulated to some observers for attempts at ground-based confirmation (solar elongation only about 32 degrees and getting worse); he estimated visual magnitude based on the comet's moderately easy detectability in the last several images. Very approximate positions measured by Matson: 2015 UT R.A. (2000) Decl. Feb. 15.5 0 18.6 -35 14 16.5 0 20.4 -33 12 17.5 0 24.3 -31 34 18.5 0 28.3 -29 55 19.5 0 30.3 -28 11 20.5 0 32.6 -26 26 21.5 0 33.3 -24 34 22.5 0 36.8 -23 00 M. Mattiazzo, Swan Hill, Victoria, Australia, also independently found this comet candidate (at website URL http://swan.projet.latmos.ipsl.fr/), noting that is has shown rapid brightening over a week until Feb. 22. V. Bezugly, Dnepropetrovsk, Ukraine, also subsequently reported an apparently independent detection of the object in SWAN images, providing rough positions for Feb. 19-22. T. Lovejoy, Birkdale, Queensland, Australia, reports that CCD images obtained with a 36-cm f/1.9 Schmidt-Cassegrain telescope on Feb. 25.4 UT show a comet of diameter 2' with a short stubby tail, the magnitude given as 11 (astrometry provided below). 2015 UT R.A. (2000) Decl. Mag. Observer Feb. 25.39289 0 41 43.76 -19 10 34.2 13.9 Lovejoy 25.39975 0 41 44.67 -19 09 53.2 13.8 " 25.40668 0 41 45.54 -19 09 12.6 13.8 " Mattiazzo also obtained CCD images of the comet shortly after Lovejoy did, using a Canon 60Da Camera (+ Sigma 200-mm-f.l. f/2.8 lens), but was unable to see the comet visually using 25x100mm binoculars, at low altitude and with moonlight interfering (making it fainter than mag 10); his CCD astrometry yielded mag 11.9-12.1 on Feb. 25.43-25.45, adding that the coma appears moderately condensed but of a small diameter, measured at 1'.5 across, with a bluish-green color. Mattiazzo did manage to locate the comet visually on Feb. 26.43 at mag about 11.5, with a slightly condensed coma of diameter 1'.5, as seen at altitude 13 degrees in moonlight with a 20-cm reflector. After the comet was posted on the Minor Planet Center's PCCP webpage H. Sato, Tokyo, Japan, reported that images taken with an iTelescope 0.51-m f/6.8 astrograph (+ luminance filter) at Siding Spring on Feb. 26.4 show a strongly condensed coma 35" in diameter with a possible tail 5' long toward p.a. 120 degrees on two stacked 20-s exposures; the w-band magnitude was 12.0 as measured within a circular aperture of radius 17".5. The available astrometry, the following preliminary parabolic orbital elements by G. V. Williams, and an ephemeris appear on MPEC 2015-D110. T = 2015 Mar. 4.4438 TT Peri. = 333.8468 Node = 49.4465 2000.0 q = 0.711818 AU Incl. = 94.5959 NOTE: These 'Central Bureau Electronic Telegrams' are sometimes superseded by text appearing later in the printed IAU Circulars. (C) Copyright 2015 CBAT 2015 February 28 (CBET 4068) Daniel W. E. Green