Electronic Telegram No. 2920
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 P/2006 VW_139 = (300163) 2006 VW_139
     The numbered minor planet (300163) 2006 VW_139 was discovered as an
apparently asteroidal object by the Spacewatch survey on 2006 Nov. 15
(discovery observations tabulated below; published originally on MPS
188993 as 2006 VW_139); prediscovery observations from the Sloan Digital
Sky Survey (2000 Sept. 3 and 5), LONEOS (2000 Sept. 23) and Spacewatch
(2000 Sept. 23 and 2005 July 11) were published on MPS 190721.

     2006 UT             R.A. (2000) Decl.       Mag.   Observer
     Nov. 15.39947    5 04 38.31   +21 33 15.4   20.7   Spacewatch
          15.43924    5 04 36.41   +21 33 14.9   21.1     "

The following orbital elements are from MPO 211610:

                    Epoch = 2011 Aug. 27.0 TT
     T = 2011 July 18.5417 TT         Peri. = 281.8862
     e = 0.201125                     Node  =  83.2065  2000.0
     q = 2.437865 AU                  Incl. =   3.2392
       a =  3.051625 AU    n = 0.1848874    P =   5.33 years

     Henry Hsieh, Larry Denneau, and Richard Wainscoat, Institute for Astronomy
(IfA), University of Hawaii, report the discovery that the presumed asteroidal
object (300163) is a comet from images taken with the Pan-STARRS 1 (PS1) 1.8-m
Ritchey-Chretien telescope at Haleakala on 2011 Aug. 30 and Nov. 5 UT, noting
that the point-spread function (PSF) of the object's image showed excesses
compared to expected stellar PSFs.  On both nights, a FWHM of 1".3 was
measured for the object, while nearby stars had FWHMs of 1".0.  Follow-up
observations using the Faulkes Telescope North 2.0-m f/10 Ritchey-Chretien
reflector at Haleakala by Alan Fitzsimmons (Queens University, Belfast) and
J. D. Armstrong (IfA) on Nov. 13, 14, and 16, and the 2.24-m University of
Hawaii reflector on Mauna Kea by Bin Yang (IfA) on Nov. 14, consistently show
the object having a larger PSF than that of nearby stars, confirming the
measurements made of the PS1 data, and additionally show the presence of a
dust trail extending at least 30" from the object at a position angle of
approximately 250 degrees, aligned with the object's orbit plane.  The object
has an R-band magnitude of 18.6 in these data, approximately 1 magnitude
brighter than predicted; it was computed from a circular photometry aperture
(3".0 in radius) centered on the nucleus.
     The object has an orbit consistent with that of a main-belt asteroid, and
thus may be another main-belt comet, similar to 133P/Elst-Pizarro.
Alternatively, the object could have recently experienced a collision, thus
presumed similar to the outbursts of P/2010 A2 (LINEAR) or (596) Scheila,
which produced an ejecta cloud that is now dispersing from the nucleus.
However, it is noted that (300163) has a low-inclination, low-eccentricity
orbit in the outer main asteroid belt (a = 3.05 AU, e = 0.20, i = 3.24 deg),
is exhibiting comet-like activity shortly after perihelion (over a true
anomaly range of 12-34 deg), and is a km-scale object (H = 16.6 mag), similar
to several other main-belt comets.  Furthermore, this object's current
morphology is similar to that of 133P (a thin dust trail peaking in brightness
near the nucleus), and dissimilar to the unusual morphologies exhibited by
P/2010 A2 (a dust trail detached from the nucleus) and (596) Scheila (multiple
dust plumes).  As such, it is believed that (300163) is most likely to be a
main-belt comet whose dust emission is driven by sublimating ice.  Additional
imaging and spectroscopic observations are highly encouraged to help determine
whether this preliminary conclusion is correct.

     Observations by C. W. Hergenrother with the Kuiper 1.54-m reflector at
Kitt Peak on Nov. 23.34 UT confirm (300163) to be cometary.  A 1200-s co-added
R-band image shows a condensed 9" coma and two tails:  a broad tail 9" long in
p.a. 60 and a thin narrow tail 35" in p.a. 250.  Photometry of the coma with
an aperture radius of 4.5" gives a R magnitude of 18.6.


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

                         (C) Copyright 2011 CBAT
2011 November 28                 (CBET 2920)              Daniel W. E. Green