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

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                                                  Circular No. 8857Central Bureau for Astronomical TelegramsINTERNATIONAL ASTRONOMICAL UNIONMailstop 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 0081-0304Phone 617-495-7440/7244/7444 (for emergency use only)COMET C/2007 N3 (LULIN)     An apparently asteroidal object discovered by Quanzhi Ye, astudent at Sun Yat-sen University (Guangzhou, China), on imagesacquired by Chi Sheng Lin (Institute of Astronomy, National CentralUniversity, Jung-Li, Taiwan) with the 0.41-m f/8.8 Ritchey-Chretienreflector in the course of the Lulin Sky Survey (discoveryobservation tabulated below), has been found to show marginalcometary appearance by J. Young, who reports that CCD images takenwith 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 18.8surrounding a bright central core.     2007 UT             R.A. (2000) Decl.       Mag.     July 11.77867   22 33 35.14   - 8 46 38.8   18.9The 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 ephemerisappear onMPEC 2007-O05.S/2007 S 4     C. C. Porco, CICLOPS, Space Science Institute, Boulder; andthe 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 ina series of fifteen pairs of Cassini wide-angle camera images withexposure times of 10 and 15 s, taken through the clear filter on2007 May 30, spanning 6 hr.  Following a preliminary orbit fit, anexhaustive search of other Cassini images generated a number ofadditional detections.  The current observation arc, comprising 47detections, spans 3.03 years between June 2004 and June 2007.Numerical integration of the equations of motion shows that theobject is being influenced by a 10:11 mean-motion resonance withMimas.  A precessing-ellipse model fitted to the integrated orbitfor 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 locatedapproximately 3400 km beyond Saturn XXXII, but still interior tothe orbit of Saturn XXXIII, suggesting that the three may be partof a larger group of satellites in this region.  Saturn XXXIII wasalso observed in some of the S/2007 S 4 discovery frames.  IfS/2007 S 4 has the same disk-integrated reflectivity as SaturnXXXIII, preliminary estimates suggest a physical radius for S/2007S 4 of about 1 km.                      (C) Copyright 2007 CBAT2007 July 18                   (8857)            Daniel W. E. Green

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