Electronic Telegram No. 4249
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)
URL http://www.cbat.eps.harvard.edu/index.html
Prepared using the Tamkin Foundation Computer Network


COMET C/2015 ER61 (PANSTARRS)
  [Editor's note:  this text replaces that on CBET 4248 (missing text).]
     An apparently asteroidal object discovered with the 1.8-m Pan-STARRS1
telescope on Haleakala last March (discovery observations tabulated below;
with additional observations subsequently identified in the prior two
months), and then given the minor-planet designation 2015 ER61 (cf. MPS
592555), has been found to show cometary activity.

     2015 UT             R.A. (2000) Decl.       Mag.
     Jan. 21.56437   11 06 06.68   - 1 13 13.2   22.4
          21.57588   11 06 06.50   - 1 13 12.7   22.2
          21.58746   11 06 06.35   - 1 13 12.2   22.4
          23.48852   11 05 39.09   - 1 11 31.6   22.8
          23.49998   11 05 38.91   - 1 11 31.3   22.6
     Feb. 16.44711   10 58 07.80   - 0 35 53.4   21.9
          16.46003   10 58 07.53   - 0 35 51.8   21.8
          16.48585   10 58 06.93   - 0 35 48.7   21.9
     Mar. 14.36931   10 47 50.76   + 0 25 40.0   20.7
          14.38147   10 47 50.49   + 0 25 42.0   20.6
          14.39357   10 47 50.16   + 0 25 44.0   20.6
          14.40571   10 47 49.86   + 0 25 45.5   21.0
          15.38177   10 47 26.41   + 0 28 19.9   21.5
          15.39411   10 47 26.12   + 0 28 21.8   21.6
          15.40643   10 47 25.82   + 0 28 23.8   21.7
          15.41872   10 47 25.54   + 0 28 25.6   21.8

H. Sato, Tokyo, Japan, writes that ten stacked 60-s exposures taken with an
iTelescope 0.70-m f/6.6 astrograph (+ luminance filter) at Siding Spring on
2015 Dec. 27.7 UT shows a strongly condensed coma 10" in diameter with a hint
of tail 40" long toward p.a. 85 degrees; the w-band magnitude was 18.6 as
measured within a circular aperture of radius 5".4.  K. Sarneczky, Konkoly
Observatory, reports that nine stacked 150-s unfiltered CCD images taken the
0.60-m Schmidt telescope at Piszkesteto, Hungary, on 2016 Jan. 19.1 UT show
a clearly extended appearance (FWHM 3".8 in 2".9 seeing); the coma is
slightly elongated to the northwest, but with no obvious tail; he added
that the object is about two magnitudes brighter predicted by an asteroidal
brightening, the R magnitude measured as 18.1 within a circular aperture of
radius 5".  Following a query, K. Meech, University of Hawaii, writes that
four 200-s images obtained with the 8.2-m telescope on 2015 June 12.3 show
weak cometary activity in the form of a slightly extended point-spread
function (FWHM 1".0, compared with 0".8 seeing) and a weak tail-like
extension 2" long at p.a. about 120 degrees; Meech, M. Micheli, J. Kleyna,
R. Wainscoat, J. Keane, O. Hainaut, and B. Yang were involved with the
observations.
     The available astrometry (spanning 2015 Jan. 21-2016 Jan. 23), the
following nearly-parabolic orbital elements by G. V. Williams, and an
ephemeris appear on MPEC 2016-C01.

                    Epoch = 2017 May   7.0 TT
     T = 2017 May   9.95601 TT        Peri. =  68.19844
     e = 0.9972866                    Node  = 235.21721 2000.0
     q = 1.0421357 AU                 Incl. =   6.34908


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

                         (C) Copyright 2016 CBAT
2016 February 1                  (CBET 4249)              Daniel W. E. Green