------------------------------------------------------------------- THE ASTRONOMER Electronic Circular No 3097 2015 Aug 11 12.43UT 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 C/2015 P3 (SWAN) M. Mattiazzo, Swan Hill, Victoria, Australia, reports that he noticed a moving object on low-resolution public website hydrogen Lyman-alpha images obtained during Aug. 3 and 4 with the Solar Wind Anisotropies (SWAN) camera on the Solar and Heliospheric Observer (SOHO) spacecraft, and he confirmed the object as a comet on images obtained on Aug. 9.383 UT with a Canon 60Da camera (+ Sigma 200-mm-f.l. f/2.8 lens) from an observing location at Castlemaine, Qld.; the comet's appearance on his images was slightly condensed with a coma diameter of 2' and "photometric magnitude" 11.8. He subsequently found a possible earlier detection on July 28; he assumed 12h UT on each date (the SOHO website does not specify times within a day) and provides the following approximate positions from the poor-scale SWAN images: 2015 UT R.A. (2000) Decl. July 28.5 11 31 +31 30 Aug. 3.5 11 56 +22 15 4.5 12 05 +20 00 Mattiazzo's astrometry from his confirming camera images: 2015 UT R.A. (2000) Decl. Aug. 9.38326 12 24 21.72 +12 05 09.1 9.40301 12 24 28.07 +12 02 59.3 He adds that the comet is situated near the Virgo supercluster of galaxies. After the comet was posted on the Minor Planet Center's PCCP webpage, other CCD astrometrists have commented on the object's cometary appearance. A. Maury and J.-F. Soulier write that their unfiltered images taken on Aug. 9.97-9.99 UT with a 0.4-m f/8 Ritchey-Chretien reflector at San Pedro de Atacama, Chile, show a circular coma of diameter 1'.15 and no visible tail. H. Sato, Tokyo, Japan, notes that his images taken with an iTelescope 0.51-m f/6.8 astrograph (+ luminance filter) near Mayhill, NM, USA, on Aug. 10.1 show the comet to be strongly condensed with an outer coma 2'.0 in diameter with w-band magnitude 11.9 as measured within a circular aperture of radius 63"; no tail was visible in 24 stacked 10-s exposures. E. Guido et. al. report that thirteen stacked 15-s images taken remotely on Aug. 10.37 with an iTelescope 0.50-m f/6.8 astrograph at Siding Spring show a bright coma about 1' in diameter. Images taken by C. Jacques, E. Pimentel, and J. Barros with a 0.45-m f/2.9 reflector at the SONEAR Observatory, Oliveira, Brazil, on Aug. 10.9 reveal a sharp central condensation surrounded by a coma 90" in diameter in six stacked 60-s images. A. Hale, Cloudcroft, NM, USA, reports total visual magnitude 12.2 and coma diameter 2'.3 with a 0.41-m reflector on Aug. 10.14 UT. The available astrometry, the following very preliminary parabolic orbital elements by G. V. Williams, and an ephemeris appear on MPEC 2015-P25. T = 2015 July 27.2617 TT Peri. = 131.8065 Node = 86.9127 2000.0 q = 0.714631 AU Incl. = 59.3232 Ephemeris: Date TT R. A. (2000) Decl. Delta r Elong. m1 2015 08 10 12 27 09.8 +10 57 22 0.9228 0.7667 46.4 12.7 2015 08 11 12 31 37.2 +09 06 53 0.9202 0.7742 46.9 12.7 2015 08 12 12 35 59.2 +07 15 53 0.9185 0.7820 47.4 12.7 2015 08 18 13 00 33.7 -03 45 21 0.9278 0.8371 50.9 13.1 2015 08 26 13 30 08.8 -17 13 04 0.9863 0.9267 55.3 13.6 2015 09 10 14 21 40.1 -36 11 14 1.1916 1.1235 60.8 14.9 Guy M Hurst