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IAUC 5673: AN UMa; 1992t

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                                                  Circular No. 5673
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
Telephone 617-495-7244/7440/7444 (for emergency use only)
TWX 710-320-6842 ASTROGRAM CAM     EASYLINK 62794505

     J. M. Bonnet-Bidaud, Centre d'Etudes Nucleaires de Saclay; M.
Mouchet, Observatoire de Meudon; and T. A. Somova and N. N. Somov,
Special Astronomical Observatory, communicate:  "Optical spectroscopic
data obtained at the Russian 6-m telescope during 1991 Mar.-
1992 Jan. show a significant phase shift (0.20 cycle) in the
velocity curves of AN UMa with respect to the ephemeris period of
Liebert et al. (1982, Ap.J. 254, 232), evidently due to an inaccuracy
in the orbital/rotation period.  From a reanalysis of all published
spectroscopic data for the narrow-line components, we have
determined a new ephemeris for the 'blue-to-red gamma crossing
time':  1977 Feb. 16.5255 (+/- 0.0024 day) UT + 0.079 752 82 (+/-
0.000 000 04) E.  With this new period, we find that all published
photometric light curves are also correctly phased over more than
15 yr.  The updated ephemeris eliminates, in particular, the phase
discrepancy reported in x-rays; the 1984-85 EXOSAT light curves now
show x-ray minimum near phase 0.0 (with the above ephemeris),
compatible with previous SAS-3 data.  This is evidence for the
geometrical stability of the system.  To the accuracy of the measurements,
we find no evidence of a higher term of period variation (P-
dot < 10E-10) nor of any asynchronism in the system.  Polarimetric
observations are strongly encouraged to improve the accuracy of the
revised period.  We predict a linear polarimetric maximum at a
present offset of 0.35 cycles with the previous (Liebert et al.)

     U. Fink and M. Hicks, University of Arizona, report:  "We
regret to be forced to issue a retraction to our report of the split
nuclei of P/Swift-Tuttle (cf. IAUC 5672).  Though the secondary
nuclei appeared quite strongly in our H2O+ filter images, they have
not shown up in any of our other filter images.  After carefully
checking our standard- and comparison-star exposures through our
H2O+ filter, we find similar faint 'satellite' images as on the
exposures of the comet.  It would seem that the secondary nuclei are
a reflection in the optics and therefore spurious."
     Total visual magnitude estimates:  Nov. 28.71, 4.8 (H. Luthen,
Dahlenburg, Germany, 20x60 binoculars); 30.28, 5.3 (A. Mizser,
Budapest, Hungary, 20x60 binoculars); Dec. 4.68, 5.3 (L. T. Heen,
Trondheim, Norway, 7x50 binoculars); 5.73, 4.9 (J.-C. Merlin, Le
Creusot, France, 8x30 binoculars); 9.93, 5.0 (D. W. E. Green,
Cambridge, MA, 12x50 binoculars).

1992 December 10               (5673)            Daniel W. E. Green

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