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IAUC 3315: 1978 (18) 1; WZ Sge

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                                                  Circular No. 3315
Central Bureau for Astronomical Telegrams
Postal Address: Central Bureau for Astronomical Telegrams
Smithsonian Astrophysical Observatory, Cambridge, MA 02138, U.S.A.
TWX 710-320-6842 ASTROGRAM CAM     Telephone 617-864-5758

1978 (18) 1
     R. M. Williamon, Fernbank Science Center, Atlanta, reports an
observation of a probable secondary event associated with the occultation
of SAO 114159 by (18) Melpomene on Dec. 11.  Photoelectric
tracings obtained using a 91-cm reflector showed that an occultation
began at 9h10m50s.9 +/- 0s.1 UT and lasted for 5s.77 +/- 0s.01.  Further,
there was a somewhat deeper occultation from 1s.14 (+/- 0s.01)
after immersion until 1s.14 before emersion, suggesting that the
star is a binary whose components are very roughly equal in brightness
and separated by 0".011.  If the occulting object were a satellite
of (18) Melpomene, the lower bound on its diameter is 37 km.
The photoelectric record was otherwise steady for several minutes
around the event.  D. W. Dunham, Silver Spring, Maryland, has informed
us that the observations of the primary occultation (IAUC
3314) photoelectrically by groups at the U.S. Naval. Observatory,
Goddard Space Flight Center and University of Maryland (during
roughly 9h11m.0-9h11m.5UT) are also consistent with the star's duplicity
and components separated by 0".01-0".02.  A very preliminary
result for the diameter of (18) Melpomene is 135 km.  The apparent
matching of the photoelectric tracings in Washington-Baltimore and
in Atlanta lends support to the presumption that the Atlanta occultation
was due to a satellite and that the less conclusive secondary
events reported during other occultations by minor planets,
e.g., that of SAO 120774 by (532) Herculina on June 7 (cf. IAUC
3241), are also due to satellites.

     M. Walker and M. Bell, Lick Observatory, communicate: "Spectroscopic
observations of WZ Sge on Dec. 10 UT show a velocity variation
of the Balmer absorption lines above H-beta of 2K = 400 km/s in
the orbital period of 82 min, maximum positive velocity occurring
at phase 0.75 in the photometric period.  Continued velocity measurements
during the outburst are essential."

     The following photoelectric V magnitudes were obtained by D.
Targan, Physics Department, Brown University, with a 36-cm Schmidt-Cassegrain
telescope.  The comparison star was HD 191083 (assumed V = 8.76).
The uncertainty is +/- 0.03 magnitude.  Dec. 10.965 UT,
9.50; 10.968, 9.60; 10.975, 9.54; 10.978, 9.61; 10.985, 9.45;
10.988, 9.38; 11.010, 9.51; 11.013, 9.51; 11.015, 9.35:; 11.018,
9.34:; 11.966, 9.67; 11.968, 9.55; 11.971, 9.60.

1978 December 14               (3315)              Brian G. Marsden

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