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IAUC 6269: GRS 1915+105; Sats OF SATURN

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IAUC number

                                                  Circular No. 6269
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
IAUSUBS@CFA.HARVARD.EDU or FAX 617-495-7231 (subscriptions)
Phone 617-495-7244/7440/7444 (for emergency use only)

GRS 1915+105
     G. Pooley, Mullard Radio Astronomy Observatory, Cambridge,
writes: "Observations of GRS 1915+105 with the Ryle Telescope at 15
GHz show evidence for variations in flux density with a period
close to 38 min.  During these oscillations, the mean flux is in
the range 10-30 mJy and the amplitude varies typically by a factor
of 2.  Oscillations were observed on Sept. 8, Nov. 15, 16, 17, 29,
30, and Dec. 1, but none was apparent on any of 16 observation days
during October.  It is not yet possible to say whether the
oscillations are coherent in phase from one day to the next.  It is
important to search for variations at other wavelengths."

     B. Sicardy, Paris Observatory; J.-L. Beuzit, European Southern
Observatory (ESO), Garching; F. Poulet, Paris Observatory; and P.
Prado, ESO, La Silla, report:  "During a 6-night period spanning
the Aug. 10 ring-plane crossing, we obtained 60-s exposures of
Saturn's rings using the ESO 3.6-m telescope (+ Adonis adaptive
optics camera + short K filter; bandpass centered at 2.16 microns).
Besides Saturn X (Janus), Saturn XI (Epimetheus), and Saturn XVII
(Pandora), observed at their expected locations, an unresolved
object is detected on two occasions, at maximum eastern and western
elongations, respectively.  It then coincides with the location of
the F ring.  No conspicuous point-like object is visible there on
good-quality images taken at other times.  The object is visible on
Aug. 9.4388 and 9.4493 UT, located 21".6 and 21".7 eastward of
Saturn's center, respectively.  During Aug. 10.3462-10.3710, it
appears 21".9 westward of the planet's center on seven images.
Typical astrometric accuracy is estimated as 0".2; within this
accuracy, these positions agree with the ephemerides of the object
S/1995 S6, discovered with the Hubble Space Telescope (HST) a few
hours after our last observations (cf. IAUC 6243).  No other ESO
images are available at the times when S/1995 S6 should have been
visible.  The ESO detections may be prediscovery images of S/1995
S6.  However, comparison of the ESO object brightness with Saturn
III (Tethys) yields a consistent K magnitude of 14.7 +/- 0.2.  This
indicates a geometric albedo intrinsically five times higher in our
short K filter (2.16 microns) than in the HST methane band (0.89
micron), from which the value V = 17.8 is derived (ibid.).  This
large color effect is not yet explained."

1995 December 4                (6269)            Daniel W. E. Green

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