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\IBVShead{4102}{14 October 1994}      % Use it with dummy or empty arguments

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\centerline{\ft A PHOTOMETRIC  CAMPAIGN ON OW GEMINORUM}
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        The eclipsing nature of the 8th magnitude variable star OW Gem (BD+17\degr 1281, 
HDE\,258878) was 
discovered by Kaiser (Kaiser et al., 1988), who also determined the period of 1258.6 days from a study of 
Harvard patrol plates (Kaiser, 1988). The remarkable primary eclipse is more than 1.5 magnitudes deep and 
two weeks in duration.  Williams (1989) found the secondary eclipse, 0\fm 1 deep, at phase 0.23, indicating 
that the orbit is highly eccentric.

        Griffin and Duquennoy (1993) published a first general investigation of the system, based on 
radial velocity measures over a full orbital cycle and matches of model light curves to the available eclipse 
photometry.  They found that the system contains two luminous giants, the primary spectral type being  
F2\,Ib-II and the secondary about G8\,IIb.  Component masses are close to 6M$_{\odot}$
and 4M$_{\odot}$.

        The orbital eccentricity is 0.52, in such an orientation ($\omega$ = 140\degr) that the stars have twice the 
separation at secondary eclipse as at primary eclipse.  As a result, the primary eclipse lasts 16 days, the 
secondary 30 days.

        Eclipses and a double-lined spectrum make OW Gem a favorable subject for comprehensive 
investigation.  Radial velocity observations are continuing, so better understanding of the system is now 
constrained by the available photometry--mostly visual and photographic estimates for the primary 
eclipse and sparse photoelectric observations in only one color for the secondary eclipse.

        Since the 1988 primary and 1989 secondary minima, the eclipses have occurred near solar 
conjunction.  During 1995, however, both eclipses will be favorably placed for observation, the primary 
eclipse occurring from February 4-20 and the secondary eclipse from November 17 - December 17.

        Observations from widely spaced longitudes will help to fill in the eclipse light curves and avoid 
weather gaps during the northern hemisphere's winter months.  We therefore invite suitably equipped 
observers to participate in an international photometric campaign on OW Gem during 1995, with the lead 
author serving as coordinator.

        Participating observers should be able to achieve 0\fm 01 precision down to 9.9 in V and 10.6 in B 
during the primary eclipse.  The secondary minimum, 8.3 V, 9.0 B, is brighter, but the demand for 
precision remains high in order to define the shallow eclipse.  Multiple passband observations are very 
desirable and infrared observations would show a deeper secondary eclipse than visible ones.  Because 
observations from a variety of instruments and detectors must be combined, observers are asked to take 
particular care in determining color transformation coefficients and standardizing the observed differential 
magnitudes.

        All observers should use the same comparison and check stars.  The designated comparison star is 
SAO\,95777 (BD +17\degr 1280, HD\,258848), 9.0 V, marked as star \#2 on the chart in IBVS No. 3196 (Kaiser 
et al. 1988).  The check star is GSC 1332:0578, 9.9 V, star marked \#3 on the chart.  These stars are similar 
in color to the variable and are \ \ located
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\centerline{Figure 1. Finding chart for OW Geminorum}
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\noindent within 3.5 arcminutes, which will assist observers using CCD 
detectors with limited fields. Figure 1 shows a finding chart for the system.

        All interested observers are urged to register with the lead author.  We intend to distribute a 
circular with final information prior to the first 1995 event and again following each of the two eclipses.
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% Call for macros \authors - \authorsrightcol - \endauthors
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Dirk TERRELL
Department of Physics and Astronomy
University of Calgary
Calgary, Alberta T2N 1N4
E-Mail: terrell@algol.iras.ucalgary.ca
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Daniel H. KAISER
Crescent Moon Observatory, 
2631 Washington St., Columbus, 
IN 47201, USA
E-Mail: d.kaiser2@genie.geis.com
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David B. WILLIAMS
9270-A Racquetball Way, 
Indianapolis, IN 46260, USA
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\references

Griffin, R. F., and Duquennoy, A.: 1993, {\it The Observatory}, {\bf 113}, 53

Kaiser, D. H.: 1988, {\it Inf. Bull. Var. Stars}, No.\,3233

Kaiser, D. H., Williams, D. B., and Baldwin, M. E.: 1988, {\it Inf. Bull. Var.
        Stars}, No.\,3196

Williams, D. B.:  1989, {\it Journ. AAVSO}, {\bf 18}, 7

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