Electronic Telegram No. 4095
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 H1 (BRESSI)
     T. H. Bressi reports the discovery of a comet with a diffuse extended
center on CCD mosaic images taken with the Spacewatch 0.9-m f/3 reflector
at Kitt Peak (discovery observations tabulated below).

     2015 UT             R.A. (2000) Decl.       Mag.   Observer
     Apr. 20.46356   21 35 25.72   + 4 54 51.2   18.2   Bressi
          20.47534   21 35 25.08   + 4 55 07.1   18.1     "
          20.48713   21 35 24.43   + 4 55 23.3   18.0     "

After the object was posted on the Minor Planet Center's PCCP webpage, other
CCD astrometrists obtained images showing the cometary appearance.  A. R.
Gibbs notes that images taken in fair seeing and transparency on Apr. 21.5 UT
with the Steward Observatory 1.0-m reflector at Mount Lemmon show a round
coma 6" in diameter and a short fan tail 6" long in p.a. 260-310 deg on four
30-s exposures.  H. Sato (Tokyo, Japan; ten stacked 60-s exposures taken with
a 0.61-m f/6.5 astrograph + luminance filter at the Sierra Remote Observatory
near Auberry, CA, USA, on Apr. 21.50 UT) finds the comet to be strongly
condensed with a round coma 10" in diameter, w-band magnitude 17.7 as measured
within a circular aperture of radius 5".0, and a hint of tail 10" long toward
p.a. 315 degrees.  A. Novichonok writes that seven 60-s exposures taken by S.
Nazarov with the Crimean Astrophysical Observatory 0.70-m f/4 AZT-8 reflector
near Nauchny, Crimea, on Apr. 22.06 shows a diffuse, round coma 15" in
diameter with no visible tail and total red mag around 16.6-17.2.
     The available astrometry, the following preliminary parabolic orbital
elements by G. V. Williams, and an ephemeris appear on MPEC 2015-H100.

     T = 2015 Apr.  8.3782 TT         Peri. =  27.6910
                                      Node  = 326.4655  2000.0
     q = 1.941464 AU                  Incl. = 141.2590


NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2015 CBAT
2015 April 23                    (CBET 4095)              Daniel W. E. Green