[IAUC] CBET 4270: 20160408 : COMET P/2015 HG_16 (PANSTARRS)

[quai en eps.harvard.edu]

                                                  Electronic Telegram No. 4270
Central Bureau for Astronomical Telegrams
Mailing address:  Hoffman Lab 209; Harvard University;
 20 Oxford St.; Cambridge, MA  02138; U.S.A.
e-mail:  cbatiau en eps.harvard.edu (alternate cbat en iau.org)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


COMET P/2015 HG_16 (PANSTARRS)
     R. Weryk and R. J. Wainscoat reported the discovery of a comet on four
w-band CCD exposures taken on 2016 Apr. 4 UT with the 1.8-m Pan-STARRS1
telescope at Haleakala (those observations are tabulated below, together with
additional Pan-STARRS1 observations from the previous night); the comet's
images appeared slightly larger than those of nearby stars (FWHM approximately
1".5, vs. 1".2 for stars), and there is evidence of a tail extending for
approximately 10" towards position angle approximately 310 degrees.  Weryk
subsequently identified an object seen in faint detections from three w-band
Pan-STARRS1 exposures taken on 2016 Feb. 11 (also tabulated below), from which
a stacked image showed evidence of a tail extending for approximately 6"
toward p.a. 300 degrees (with the comet's head again being slightly larger
than nearby stars, 1".4 vs. 1".0); Weryk adds that there are also Pan-STARRS1
detections on 2016 Mar. 17 and 31, but they are too faint for measurements.
Follow-up CCD observations by Wainscoat and C. Wipper taken on 2016 Apr. 6.44
with the 3.6-m Canada-France-Hawaii Telescope (measured by M. Micheli and
Wainscoat) show the object to be clearly cometary with a 20" tail in p.a.
305 deg (and the coma have red mag 21.4-21.5 and size FWHM 1".15 in 0".75
seeing).

     2016 UT             R.A. (2000) Decl.       Mag.
     Feb. 11.58765   14 35 40.96   - 2 33 36.1   22.3
          11.60001   14 35 41.04   - 2 33 36.2   22.2
          11.61243   14 35 41.18   - 2 33 35.8   22.3
     Apr.  3.49148   14 23 55.38   - 1 26 55.5   21.6
           3.50351   14 23 55.01   - 1 26 54.5   21.6
           3.51551   14 23 54.59   - 1 26 53.3   21.9
           3.52752   14 23 54.20   - 1 26 52.2   21.7
           4.47614   14 23 22.27   - 1 25 12.6   21.7
           4.48805   14 23 21.85   - 1 25 11.4   21.9
           4.49994   14 23 21.43   - 1 25 10.0   21.6
           4.51189   14 23 21.02   - 1 25 08.6   21.9

G. V. Williams, Minor Planet Center, noted that the 2016 April 3 observations
appeared to belong to a supposedly asteroidal object found a year ago by
Pan-STARRS1 on 2015 Apr. 20, 21, and 24 (and then given the minor-planet
designation 2015 HG_16 on MPS 603395 and 603396).  Weryk had already
identified earlier Pan-STARRS1 observations from 2015 Mar. 24 and Apr. 9
(which are also tabulated below) when Williams made his link between the
2015 and 2016 observations.

     2015 UT             R.A. (2000) Decl.       Mag.
     Mar. 24.32890   10 50 40.70   +34 10 21.6   21.0
          24.33947   10 50 40.32   +34 10 20.1   20.9
          24.35011   10 50 39.93   +34 10 18.7   21.0
          24.36079   10 50 39.57   +34 10 17.2   20.9
     Apr.  9.36430   10 43 38.42   +33 09 22.5   20.5
           9.37531   10 43 38.21   +33 09 19.4   20.6
           9.38648   10 43 37.97   +33 09 15.9   20.8
          20.33256   10 41 38.34   +32 04 40.5   20.7
          20.34540   10 41 38.27   +32 04 35.4   20.8
          20.35827   10 41 38.18   +32 04 30.2   20.8
          20.37126   10 41 38.12   +32 04 25.2   20.9
          21.35606   10 41 34.44   +31 57 52.2   20.6
          21.36813   10 41 34.34   +31 57 47.3   20.7
          21.38025   10 41 34.30   +31 57 42.4   20.5
          21.39369   10 41 34.24   +31 57 36.4   20.5
          24.35765   10 41 30.14   +31 37 15.7   20.6
          24.36817   10 41 30.13   +31 37 11.1   20.5
          24.37870   10 41 30.13   +31 37 06.8   20.7
          24.38998   10 41 30.11   +31 37 02.0   20.6

The following elliptical orbital elements by Williams and an ephemeris appear
on MPEC 2016-G114:

                    Epoch = 2014 July  2.0 TT
     T = 2014 June 28.97674 TT        Peri. =  48.15343
     e = 0.3462278                    Node  =  59.52587 2000.0
     q = 3.1317834 AU                 Incl. =  18.86851
       a =  4.7903284 AU   n = 0.09400612   P =  10.48 years


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

                         (C) Copyright 2016 CBAT
2016 April 8                     (CBET 4270)              Daniel W. E. Green