Le brocanteur des étoiles

Electronic Telegram No. 2632
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 [mailto:cbatiau@eps.harvard.edu] (alternate
cbat@iau.org [mailto:cbat@iau.org] )
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Prepared using the Tamkin Foundation Computer Network

(596) SCHEILA
     E. S. Howell, Arecibo Observatory, Cornell University; and A. J. Lovell,
Agnes Scott College, report that observations with the Arecibo Observatory
obtained on six nights between 2010 Dec. 14 and 2011 Jan. 4 show no clear
detection of the 1667-MHz line of OH in the coma of (596), currently in
outburst (cf. IAUC 9188). The 3-sigma upper limit of the line strength is 0.90
mJy km/s, which corresponds to production rates of log Q(OH) = 26.31
(Despois. et al. 1981, Astron. Astrophys. 99, 320-340) or logQ(OH) = 26.30
(Schleicher and A'Hearn 1988, Ap.J. 331, 1058-1077).
     E. Jehin, J. Manfroid, D. Hutsemekers, M. Gillon, and P. Magain, Fonds
National de la Recherche Scientifique, Liege University, report on broad- and
narrow-band imaging of the (596) Scheila outburst (CBET 2583) with the
TRAPPIST 0.60-m telescope at La Silla, and on optical spectroscopy with the
European Southern Observatory's Very Large Telescope (VLT) at Paranal. R-band
imaging from 2010 Dec. 12.3 to 21.3 UT revealed two arc-like coma features
expanding at a regular pace. The first such feature was 1' long on 2010 Dec.
12, oriented to the northeast and bending to p.a. 280 deg (the anti-solar
direction). The second feature was shorter, 30" on Dec. 12, oriented to the
south and bending to p.a. 230 deg. Both features were getting larger and
fainter with time (4' and 2' long, respectively, on Dec. 21.3). A narrow
45"-long tail, opposite the sun (p.a. 280 deg), was also observed in good
seeing. R-band images taken on 2011 Jan. 4.3 and 5.3 after the full moon
allowed Jehin et al. to again observe these features, seen as 7' and 4' long,
respectively -- and much fainter. This discards any sustained activity of
the minor planet. Narrow-band images obtained on 2010 Dec. 12.3 with
cometary filters do not show any contribution from gases. A 20-min optical
spectrum was obtained with FORS2 at the VLT on Dec. 13.3; it does not show
any extended cometary gaseous emissions, but only a spatially extended
continuum due to dust-scattered sunlight. Short B, V, R, and I exposures
performed nearly every two nights from 2010 Dec. 12.3 to 2011 Jan. 5.3 give
a magnitude for the nuclear condensation of V = 14.2 +/- 0.1 over the whole
period, in agreement with the "APmag" value reported in the Jet Propulsion
Laboratory ephemeris. No flux variation of the nuclear condensation was
observed. Those preliminary results are in favor of a collisional scenario
to explain the outburst of (596) Scheila, rather than a cometary driven
activity. This case might be similar to the outburst of comet P/2010 A2,
which may have resulted from an impact of a minor planet (Snodgrass 2010,
Nature 467, 814).

NOTE: These 'Central Bureau Electronic Telegrams' are sometimes
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                         (C) Copyright 2011 CBAT
2011 January 12                  (CBET 2632)              Daniel W. E. Green