Electronic Telegram No. 3586
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


NEW SATELLITE OF NEPTUNE:  S/2004 N 1
     M. R. Showalter, SETI Institute; I. de Pater, University of California,
Berkeley; J. J. Lissauer, NASA Ames Research Center; and R. S. French, SETI
Institute, report the discovery of a new satellite of Neptune.  The object,
provisionally designated S/2004 N 1, was detected in ten separate sets of
images taken by the Hubble Space Telescope (HST) spanning 2004-2009.  Each set
of images comprises multiple long exposures obtained within a single 50-min
observing window defined by one orbit of HST.  Images within each orbit were
co-added, while allowing for the small but predictable pixel shifts associated
with circular, equatorial motion around Neptune.  Observation times, measured
offsets from Neptune, and S/N ratios are as follows:

Date UT                   Offset           S/N
2004 Nov.  6.435    -4".73 E, -0".55 N     4.9
2004 Dec.  8.305    +4".60 E, +1".10 N     7.7
2004 Dec.  9.305    +4".19 E, +1".75 N     5.8
2004 Dec.  9.362    +3".12 E, +2".26 N     5.1
2005 Apr.  1.845    -4".09 E, -1".91 N     4.1
2005 May   6.961    -4".60 E, -1".53 N     5.1
2005 May  12.224    +4".23 E, +2".02 N     5.9
2005 May  17.021    +3".45 E, +2".42 N     3.6
2009 Aug. 19.609    -3".56 E, +0".26 N     4.4
2009 Aug. 19.673    -4".56 E, -0".79 N     8.2

The instruments used were ACS/HRC, except for WFC3/UVIS in 2009.  The initial
astrometry is consistent with a body traveling on a near-circular, uninclined
orbit.  The inferred mean motion (n) is 378.907 +/- 0.001 degrees/day (P =
0.95 days).  The projected radial distance from the planet's center is 105300
+/- 500 km, placing the satellite between the orbits of Neptune VII (Larissa)
and VIII (Proteus).  The orbital radius is consistent with a semimajor axis of
105283 km, as derived from n.  The satellite's V magnitude is 26.5 +/- 0.3.
If the satellite has an albedo of 0.1, comparable to that of the other nearby
satellites, then it has a radius of 8-10 km; this makes it much smaller than
any of Neptune's previously known satellites, and below the detection
threshold of the Voyager cameras.


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      superseded by text appearing later in the printed IAU Circulars.

                         (C) Copyright 2013 CBAT
2013 July 15                     (CBET 3586)              Michael Rudenko