Electronic Telegram No. 3633
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 17P/HOLMES DUST TRAIL
     Esko Lyytinen (Helsinki, Finland), Harry J. Lehto (Tuorla Observatory,
University of Turku; Markku Nissinen, Kuvansi, Finland; Peter Jenniskens, SETI
Institute; and Jari Suomela, Helsinki, Finland, report that dust ejected by
comet 17P/Holmes during the 2007 Oct. 23-24 outburst has completed half an
orbit and is now converging in a more concentrated volume of space, making it
again visible in small telescopes.  With the orbital plane crossing predicted
for 2013 Aug. 19.8 UT, the converged dust was detected on Aug. 10.4071 in
twelve 300-s exposures and on Aug. 11.4016 in four 300-s exposures, when it
had a surface brightness of 27 mag/square arcsec, using the 51-cm T30 telescope
remotely at Siding Spring Observatory (operated at effective focal length 228
cm, with a 27'.8 x 41'.6 field-of-view, with images taken in white light with
a Luminance filter).  This observation follows an earlier detection on 2013
Feb. 17.7 and 19.7 with the same instrument (seven 300-s exposures) during the
previous orbital plane crossing (2013 Feb. 15), when the surface brightness was
measured to be 26.8 mag/square arcsec and the sky brightness was 21.0 magnitude
per square arcsec (Lyytinen et al. 2013, JIMO 41, 77-83).
     During the present orbital plane crossing, further sightings (with the
trail progressively broader and dimmer) should be possible during moonless
nights after Aug. 20 at the following geocentric apparent positions:

Date UT        R.A. (2000.0) Decl.      p.a. (deg)
Aug. 19.5     13h53m40s   -31d02'.0       62.4
Aug. 21.5     13 54 35    -30 58.4        62.6
Aug. 23.5     13 55 33    -30 55.4        62.8
Aug. 25.5     13 56 34    -30 52.5        63.0
Aug. 27.5     13 57 37    -30 50.1        63.2
Aug. 29.5     13 58 43    -30 48.0        63.4
Aug. 31.5     13 59 51    -30 46.3        63.6

The convergence of the dust is predicted to peak centered on 2014 Sept. 25,
when the comet itself is again at the eruption site.  Starting on 2013 Nov 12,
uncertain by about 10 days, it may be observed even when the earth is not in
the comet's orbital plane from northern-hemisphere locations at a surface
brightness of about 25.5 mag/square arcsec.  In early November, the apparent
trail direction coincides with the apparent direction of motion, permitting
longer exposure times.  Ephemerides for those times are given by Lyytinen et
al. (op. cit.) and plotted in a figure posted at the following website URL:
http://clayhole.com/holmescloud/holmes_meteoroid_converging_north.jpg (with
dashes showing the orientation of the trail).


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

                         (C) Copyright 2013 CBAT
2013 August 19                   (CBET 3633)              Daniel W. E. Green