|CBAT 4091Electronic Telegram No. 4091
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: firstname.lastname@example.org (alternate email@example.com)
Prepared using the Tamkin Foundation Computer Network
COMET C/2015 F5 (SWAN-XINGMING)
Several people noticed a moving object on low-resolution public website
hydrogen Lyman-alpha images obtained during Mar. 29-Apr. 1 with the Solar Wind
Anisotropies (SWAN) camera on the Solar and Heliospheric Observer (SOHO)
spacecraft (see CBET 4068 and website URL http://swan.projet.latmos.ipsl.fr/)£¬
and the Central Bureau received two such reports during mid-day (UT) on Apr. 4
from Szymon Liwo (Swidnica，Poland) and from Worachate Boonplod (Samut
Songkhram，Thailand)，both of whom provided approximate positions. M.
Mattiazzo，Swan Hill，Victoria，Australia，reports the following approximate
positions for the object (uncertainty up to a degree，with an uncertain
assumption of 12h UT for each image).
2015 UT R.A. (2000) Decl.
Mar. 29.5 23 04.1 -00 53
30.5 23 06.4 +00 52
31.5 23 09.3 +02 56
Apr. 1.5 23 13.2 +04 58
For comparison，R. Matson (Newport Coast，CA， USA) provides his measurements
from the same images:
2015 UT R.A. (2000) Decl.
Mar. 29.5 23 06.1 -01 30
30.5 23 07.4 +01 05
31.5 23 09.6 +03 20
Apr. 1.5 23 13.5 +04 55
Early on Apr. 5 UT (apparently before any public posting of a possible new
comet on SWAN images was made)，a report was received from Xing Gao (XinJiang£¬
China) of the independent discovery of an unknown comet with a 30″ coma by
Guoyou Sun on images taken in twilight on Apr. 4.9 UT (discovery observations
tabulated below) by Gao with a 0.11-m f/5 refractor in the course of the
Xingming sky survey; they imaged about 32 square degrees of neighboring area
around the comet that morning. Sun then checked online SWAN images and
noticed the above-mentioned four images moving with a motion and location
consistent with the Xingming images.
2015 UT R.A. (2000) Decl. Mag. Observer
Apr. 4.93769 23 27 58.07 +11 48 08.5 12.7 Gao
4.94028 23 27 58.29 +11 48 32.3 12.2 ”
4.94288 23 27 59.40 +11 48 46.9 11.2 “
Additional images obtained by Gao with the 0.11-m refractor (and measured by
M.-T. Hui and G. Sun) show a coma diameter around 50″ on Apr. 5.9 and around
1′.0 on Apr. 6.9 (with magnitude V = 11.4-11.7); follow-up images on Apr. 7.9
show a 1′.2 coma of red mag 11.4-12.5 with a 4′.5 tail in p.a. 300 deg. After
the object was posted on the Minor Planet Center’s PCCP webpage，other
observations have also shown cometary appearance. Hui also reports that CCD
images taken by Z.-Q. Guo with another 0.11-m refractor in China on Apr. 5.8
show a cyan color to the coma，whose diameter was around 50″ with magnitude
11.3 and no tail in twilight. L. Buzzi (Varese， Italy，0.60-m f/4.64
reflector) writes that stacked images taken in twilight and at low altitude
(11 deg) on Apr. 8.15-8.16 show a 2′ coma of red mag 14.0 without a strong
central condensation and a thin，straight tail at least 6′.5 long in p.a.
307 deg; thirty stacked 10-s images taken in slightly better conditions at
10 deg altitude by Buzzi on Apr. 9.15 reveal a round coma 3′ wide and a tail
at least 6′ long in p.a. 300 deg (after the first 4’，the tail widens).
Visual total-magnitude and coma-diameter estimates: Apr. 8.19 UT，8.2£¬
1′.7 (J. J. Gonzalez，Leon，Spain; 20.3-cm reflector at Villaverde de
Arcayos; altitude 8 degrees in twilight; condensed coma); 10.10，7.9，5′ (M.
Reszelski，Szamotuly-Galowo，Poland，15×70 binoculars); 10.48，9.6:，2′ (A.
Hale，Cloudcroft，NM，0.41-m reflector; low altitude; bright moonlight£¬
The available ground-based astrometry，the following very preliminary
parabolic orbital elements by G. V. Williams (from the poor-quality ground-
based astrometry alone，spanning Apr. 4-10)，and an ephemeris appear on
T = 2015 Mar. 28.4308 TT Peri. = 15.3704
Node = 288.5830 2000.0
q = 0.347798 AU Incl. = 148.8845
NOTE: These ‘Central Bureau Electronic Telegrams’ are sometimes
superseded by text appearing later in the printed IAU Circulars.
(C) Copyright 2015 CBAT
2015 April 10 (CBET 4091) Daniel W. E. Green