[IAUC] IAUC 9023: S/2008 S 1; C/2007 N3 [25139-2009/08-R1]

[IAUC mailing list]

                                                  Circular No. 9023
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
Mailstop 18, Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS en CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
CBAT en 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)


S/2008 S 1
     C. C. Porco, on behalf of the Cassini Imaging Science Team,
reports the discovery of S/2008 S 1, an object orbiting within
Saturn's G ring in the region between Saturn X/XI (Janus/Epimetheus)
and Saturn I (Mimas), in two images of the G ring obtained with
Cassini's narrow-angle camera taken on 2008 Aug. 15 and separated
by approximately 30 min.  Subsequent observations, and a search of
earlier images based on a preliminary orbit fit, have provided
additional detections of this object, yielding 21 total detections
during 2007 June 15-2009 Feb. 20.  A high-precision orbit fit based
on a numerical integration of the equations of motion shows that
the object is being influenced by a 7:6 mean-motion resonance with
Mimas; averaged orbital elements for S/2008 S 1:  a = 167500 km; e
= 0.0002, i = 0.001 deg, revolution period = 0.80812 day.  The
integrated orbit shows that the resonance with Mimas causes a long-
period (about 4 yr) oscillation of about 4 km in the semi-major
axis of S/2008 S 1, with a corresponding oscillation of a few
degrees in its mean longitude.  S/2008 S 1 is located within a
bright arc in the G ring, so this body likely represents a
significant source of the small particles found in this ring.  If
S/2008 S 1 has the same disk-integrated reflectivity as Saturn
XXXIII (Pallene), preliminary estimates of the object's total
brightness suggest a physical radius for S/2008 S 1 of about 250 m.


COMET C/2007 N3 (LULIN)
     D. E. Harker, University of California, San Diego; and C. E.
Woodward, University of Minnesota, report on spectrophotometric
observations of comet C/2007 N3 using the NASA Infrared Telescope
Facilty (IRTF) telescope (+ MIRSI) on Feb. 22.6 UT.  The coma was
spatially extended at mid-infrared wavelengths, with a circularly
symmetric extent of approximately 6" in diameter (3-sigma surface
brightness).  Photometry in a 3".18-diameter circular aperture,
centered on the peak in the coma surface brightness coincident with
the nucleus position, yields fluxes of within the narrow-band IRTF
comet-silicate filters of [8.7 microns] = 3.58 +/- 0.06 Jy, [9.8
microns] = 4.98 +/- 0.09 Jy, [10.6 microns] = 5.99 +/- 0.03 Jy,
[11.6 microns] = 6.82 +/- 0.04 Jy, and [12.3 microns] = 7.54 +/-
0.06 Jy.  A Planck-function fit to the photometry yields a color
temperature of 267 +/- 10 K, which is 14 percent higher than that
of a blackbody at an equivalent heliocentric distance (1.38 AU).
Both the photometric spectral energy distribution and a low-
resolution 10-microns spectrum indicate that C/2007 N3 has no
silicate emission feature, implying a deficiency of small,
submicron-sized silicate grains in the coma.

                      (C) Copyright 2009 CBAT
2009 March 3                   (9023)            Daniel W. E. Green