Central Bureau for Astronomical Telegrams
IAUC 9023: S/2008 S 1; C/2007 N3
The following International Astronomical Union Circular may be linked-to from your own Web pages, but must not otherwise be redistributed (see these notes on the conditions under which circulars are made available on our WWW site).
Read IAUC 9024
.dvi,
.ps or
.PDF format.
Circular No. 9023
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)
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
Read IAUC 9024
.dvi,
.ps or
.PDF format.
Our Web policy. Index to the CBAT/MPC/ICQ pages.
