Electronic Telegram No. 4367
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/2017 D3 (ATLAS)
     Henry Weiland, University of Hawaii, on behalf of the "Asteroid
Terrestrial-impact Last Alert System" (ATLAS) Team, reports the discovery of
a comet on four c-band exposures taken with the ATLAS 0.5-m f/2.0 Schmidt
telescope at Haleakala (discovery observations tabulated below).  Four
stacked exposures show that the comet has a size of 7".7 (well larger than
the sizes of nearby stars).

     2017 UT             R.A. (2000) Decl.       Mag.
     Feb. 23.60692   13 25 53.87   -35 31 25.1   18.0
          23.62203   13 25 53.12   -35 31 17.9   18.1
          23.63716   13 25 52.33   -35 31 12.5   17.9
          23.65233   13 25 51.48   -35 31 07.3   18.0

     After the comet was posted on the Minor Planet Center's PCCP webpage,
other CCD astrometrists reported on the cometary appearance.  Three stacked
60-s exposures taken by C. Jacques, E. Pimentel, and J. Barros on Feb. 24.2
UT with a 0.45-m f/2.9 reflector at the SONEAR Observatory at Oliveira,
Brazil, show a diffuse coma of diameter 13" with a central condensation and
red mag 18.1-18.3.  Four stacked images obtained by S. Foglia, L. Buzzi, P.
Concari, C. Cremaschini, G. Galli, and M. Tombelli with an iTelescope 0.15-m
f/7 refractor at Siding Spring on Feb. 24.5 show a coma 10" in diameter and
red mag 17.7-17.8; three additional stacked images obtained in the same
manner on Feb. 27.6 also show a 10" coma but a brighter red magnitude of
17.1-17.2.  H. Sato, Tokyo, Japan, writes that eight stacked 60-s exposures
taken on Feb. 24.6 with an iTelescope 0.51-m f/6.8 astrograph (+ luminance
filter) show a strongly condensed coma 15" in diameter and a 20" tail toward
p.a. 200 degrees; the w-band magnitude was 16.6 as measured within a
circular aperture of radius 8".2.
     R. Weryk found two pre-discovery images of this comet at mag 18.6 on
exposures taken with the 1.8-m Pan-STARRS1 telescope at Haleakala on Feb.
10.65 UT; the object appeared more diffuse than neighboring stars (FWHM about
1".9, vs. 1".2 for stars) and appeared asymmetric, possibly due to a broad
tail towards the south.
     The available astrometry (spanning Feb. 10-28), the following preliminary
parabolic orbital elements by G. V. Williams, and an ephemeris appear on MPEC
2017-E06.

     T = 2017 Apr. 29.5264 TT         Peri. = 341.1099
                                      Node  = 186.5945  2000.0
     q = 4.967364 AU                  Incl. = 125.6559


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

                         (C) Copyright 2017 CBAT
2017 March 1                     (CBET 4367)              Daniel W. E. Green