Electronic Telegram No. 610
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
M.S. 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT@CFA.HARVARD.EDU (science)
URL http://cfa-www.harvard.edu/iau/cbat.html


PLUTO III (HYDRA)
     B. Sicardy, Observatoire de Paris; N. Ageorges and O. Marco,
European Southern Observatory (ESO); F. Roques, Observatoire de Paris;
O. Mousis and P. Rousselot, Observatoire de Besancon; O. Hainaut, ESO;
and A. Bellucci, F. Colas, E. Gendron, E. Lellouch, S. Renner, and T.
Widemann, Observatoire de Paris, report on their observation of Pluto
III (Hydra), the newly discovered satellite of Pluto (cf. IAUC 8625,
8676, 8686, 8723).  Observations were made using the NACO adaptive
optics camera of the ESO 8.2-m Yepun telescope at Paranal.  A
co-addition of J-band images, totaling 60 min of integration and
centered on Apr. 10.34725 UTC, shows Hydra with offset Delta(R.A.) =
+1".800, Delta(Decl.) = -2".180 with respect to Pluto's photocenter
(the uncertainty being about 0".02).  Pluto I (Charon) was observed at
an offset of Delta(R.A.) = +0".598, Delta(Decl.) = -0".053.  Hydra is
6900 times fainter than the Pluto/Charon system, with a typical error
of 20 percent.  A standard star and a nearby 2MASS star both yield a
consistent magnitude of J = 22.5 +/- 0.2 for Hydra.  Due to its
expected closeness to Pluto (1".4) at the moment of observation, Pluto
II (Nix) could not be detected in Pluto's glare.


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2006 CBAT
2006 August 31                   (CBET 610)               Daniel W. E. Green