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IAUC 8857: C/2007 N3; S/2007 S 4

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IAUC number 

                                                  Circular No. 8857
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 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://www.cfa.harvard.edu/iau/cbat.html  ISSN 0081-0304
Phone 617-495-7440/7244/7444 (for emergency use only)


COMET C/2007 N3 (LULIN)
     An apparently asteroidal object discovered by Quanzhi Ye, a
student at Sun Yat-sen University (Guangzhou, China), on images
acquired by Chi Sheng Lin (Institute of Astronomy, National Central
University, Jung-Li, Taiwan) with the 0.41-m f/8.8 Ritchey-Chretien
reflector in the course of the Lulin Sky Survey (discovery
observation tabulated below), has been found to show marginal
cometary appearance by J. Young, who reports that CCD images taken
with the Table Mountain 0.61-m reflector on July 17.4 UT in 1"
seeing shows a small coma of diameter 2"-3" of total mag 18.8
surrounding a bright central core.

     2007 UT             R.A. (2000) Decl.       Mag.
     July 11.77867   22 33 35.14   - 8 46 38.8   18.9

The available astrometry, preliminary parabolic orbital elements (T
= 2009 Jan. 7.354 TT, q = 1.18775 AU, i = 178.380 deg, Peri. =
137.379 deg, Node = 338.515 deg, equinox 2000.0), and an ephemeris
appear on MPEC 2007-O05.


S/2007 S 4
     C. C. Porco, CICLOPS, Space Science Institute, Boulder; and
the Cassini Imaging Science Team report the discovery of S/2007 S 4,
a satellite orbiting in the region between Saturn XXXII (Methone)
and Saturn XXXIII (Pallene).  The satellite was first discovered in
a series of fifteen pairs of Cassini wide-angle camera images with
exposure times of 10 and 15 s, taken through the clear filter on
2007 May 30, spanning 6 hr.  Following a preliminary orbit fit, an
exhaustive search of other Cassini images generated a number of
additional detections.  The current observation arc, comprising 47
detections, spans 3.03 years between June 2004 and June 2007.
Numerical integration of the equations of motion shows that the
object is being influenced by a 10:11 mean-motion resonance with
Mimas.  A precessing-ellipse model fitted to the integrated orbit
for S/2007 S 4 over the month of May 2007 yields a = 197700 km, e =
0.001, i = 0.1 deg, and P = 1.03650 days.  S/2007 S 4 is located
approximately 3400 km beyond Saturn XXXII, but still interior to
the orbit of Saturn XXXIII, suggesting that the three may be part
of a larger group of satellites in this region.  Saturn XXXIII was
also observed in some of the S/2007 S 4 discovery frames.  If
S/2007 S 4 has the same disk-integrated reflectivity as Saturn
XXXIII, preliminary estimates suggest a physical radius for S/2007
S 4 of about 1 km.

                      (C) Copyright 2007 CBAT
2007 July 18                   (8857)            Daniel W. E. Green

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