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IAUC 5609: V645 Cen; DRISSEN V211b; FG Sge

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IAUC number

                                                  Circular No. 5609
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

     G. F. Benedict, McDonald Observatory, reports for the Hubble
Space Telescope Astrometry Science Team:  "We announce the discovery
of a nearly-periodic variation in the brightness of V645 (Proxima)
Cen.  Science Verification and GTO astrometry observations secured
with HST Fine Guidance Sensor #3 over the past 154 days indicate
a period of 42 +/- 1 days with a half-amplitude of 0.012 +/-
0.001 magnitude.   The FGS bandpass used to obtain these data has
FWHM = 234 nm, centered at 583 nm.  Data acquisition will continue
with HST and a ten-day sampling rate through 1993 Apr., with a gap
from roughly 1992 Nov. 1 to Dec. 20, due to HST sun-pointing
constraints. There is evidence that we have undersampled the light
curve.  We encourage broadband photometric monitoring of Proxima
Cen with higher temporal resolution than presently scheduled with

     L. Drissen and M. Shara, Space Telescope Science Institute;
and M. Dopita and D. Wickramasinghe, Australian National University
(ANU), report:  "We have discovered a new AM Her-type variable,
based on a survey of the overlap regions of U.K. Schmidt plates for
large-amplitude variables.  The object, Drissen V211b, of apparent
magnitude V about 18, is located at R.A. = 20h04m17s.86, Decl. =
-65 36'08".0 (equinox 1950.0).  A spectrogram obtained at the Anglo-
Australian Telescope shows the strong emission lines of He II and H
I typical of the class.  A period of 2h40m was measured by M.
Dopita and J. Bell (ANU) using CCD photometry on the ANU 2.3-m
telescope at Siding Spring.  Both the period and the AM Her nature of
the object was confirmed by photometric, polarimetric, and spectroscopic
measurements by J. Bailey (Anglo-Australian Observatory), D.
Wickramasinghe (ANU), and J. Hough (University of Hertfordshire)
using the Hatfield polarimeter and the AAO spectropolarimeter on the
AAT.  The continuum polarization ranges from -20 to +5 percent.
The full amplitude of the velocity variation about the orbit is 650
km/s.  This variable is of unique interest, being of AM Her type in
the period gap of cataclysmic variables."

     Representative visual magnitude estimates (cf. IAUC 5604),
from E. Waagen, AAVSO:  Sept. 5.16 UT, 10.5 (R. Royer, Lakewood,
CA); 9.07, 10.8 (P. Sventek, Houston, TX); 10.17, 10.7 (Royer).

1992 September 11              (5609)            Daniel W. E. Green

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