Electronic Telegram No. 4223
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)
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Prepared using the Tamkin Foundation Computer Network


COMET C/2015 X7 (ATLAS)
     Larry Denneau, on behalf of the "Asteroid Terrestrial-impact Last Alert
System" (ATLAS) Team, reports the discovery of a slightly diffuse comet with
the new ATLAS 0.5-m f/2.0 Schmidt telescope at Haleakala from nine wide-band
"orange" (r + i bands) CCD exposures taken on Dec. 12 and 13 (discovery
observations tabulated below).  The ATLAS Team obtained confirming images
on Dec. 17 with the 3.6-m Canada-France-Hawaii Telescope at Mauna Kea by
(queue observer D. Woodworth) that show the comet to have a small coma with
a short tail at p.a. 30 deg and a longer, fainter tail extending for about
1' in p.a. approximately 110 deg.

     2015 UT             R.A. (2000) Decl.       Mag.
     Dec. 12.46909    7 10 04.33   -29 38 58.6   17.6
          12.47361    7 10 04.24   -29 38 57.0   17.2
          12.50213    7 10 03.38   -29 38 55.6   17.4
          12.52072    7 10 02.78   -29 38 53.6   17.6
          12.52884    7 10 02.54   -29 38 52.5   17.5
          13.48565    7 09 34.45   -29 37 24.5   17.4
          13.49790    7 09 34.12   -29 37 22.0   17.5
          13.50899    7 09 33.64   -29 37 21.0   17.3
          13.53470    7 09 32.79   -29 37 18.6   17.2

After the object was posted on the Minor Planet Center's NEOCP and PCCP
webpages, L. Buzzi (Varese, Italy) writes that his stacked CCD exposures
taken on Dec. 17.04-17.05 UT with a 0.60-m f/4.6 reflector at low
altitude (15 deg above his southern horizon) shows a condensed coma 10"
in size with no clear tail visible in the crowded star field; he measured
red magnitude 18.0.
     The available astrometry (spanning Dec. 12-17), the following
preliminary parabolic orbital elements by G. V. Williams, and an ephemeris
appear on MPEC 2015-Y18.

     T = 2016 July 30.2202 TT         Peri. = 348.3329
                                      Node  = 139.8842  2000.0
     q = 3.694139 AU                  Incl. =  57.6047


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2015 CBAT
2015 December 18                 (CBET 4223)              Daniel W. E. Green