Central Bureau for Astronomical Telegrams
IAUC 5661: eta Car; N LMC 1992
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Circular No. 5661
Central Bureau for Astronomical Telegrams
INTERNATIONAL ASTRONOMICAL UNION
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
MARSDEN@CFA or GREEN@CFA (.SPAN, .BITNET or .HARVARD.EDU)
eta CARINAE
A. M. van Genderen, Leiden Observatory; M. de Groot, Armagh
Observatory; and P. S. The, Astronomical Institute, Amsterdam,
write: "A careful inspection of photometry obtained during 1974-
1992 in the framework of the Long-Term Photometry of Variables project
(Sterken 1983, ESO Messenger No. 33, 10) has revealed the presence
of a number of peculiar minima that are at most 0.1 mag deep
in the ultraviolet and much less at longer wavelengths. The precise
duration of these minima is unknown due to the many time gaps
between observations, but it is perhaps on the order of only a few
days. A least-squares solution for the 11 observed minima results
in an ephemeris with epoch 1989 Apr. 12.59 (+/- 2.75 m.e.) UT and
period 52.32 (+/- 0.11) days. We tentatively assume that there are
no secondary minima, but this is by no means certain. Although
this periodicity (if confirmed) suggests an eclipse phenomenon, we
urge caution, partly because of the relatively large standard
deviation in the O-C values of +/- 8.4 days. Bad weather around the
predicted minimum on Nov. 10 precluded verification with the 0.50-m
Danish telescope at La Silla. Photometry in the uvby system,
obtained by D. Beele (Astronomical Institute, University of Munster)
before and after this interval, are inconclusive. If the above
ephemeris is correct, the dates of the next four minima are 1993
Jan. 1, Feb. 21, Apr. 15, and June 6. The assistance of all
observers is requested, especially around these dates. Please contact
Arnout van Genderen (Leiden Observatory, Postbus 9513, 2300 RA
Leiden, The Netherlands; internet: vangenderen@rulhl1.leidenuniv.nl)
as soon as any indication about the validity of the ephemeris has
been found. The analysis of the color variations over periods of
1-2 yr shows that these are caused by S Dor-type eruptions similar
to those shown by S Dor, AG Car, HR Car and R71 (also observed in
the VBLUW system). Therefore, the main object in the core of eta
Car is almost certainly a hot S Dor-type star or a luminous blue
variable (see, e.g., Van Genderen and The 1985, Space Sci. Rev. 39,
317). If the present campaign results in further evidence, the
core of eta Car could contain an LBV binary."
NOVA IN THE LARGE MAGELLANIC CLOUD 1992
Further photometry by A. C. Gilmore at Mt. John (cf. IAUC
5659): Nov. 23.50 UT, V = 12.70 +/- 0.03, U-B = -0.75 +/- 0.03,
B-V = -0.03 +/- 0.04, V-R = +0.82 +/- 0.04 (reference star CPD
-65 433).
1992 November 25 (5661) Daniel W. E. Green
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