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\IBVShead{4567}{13 March 1998}

\IBVStitle{DZ Canis Majoris, a new double-mode Cepheid}
\vskip -2mm
\IBVSauth{L. N. Berdnikov$^1$, D. G. Turner$^2$}
\IBVSinsto{$^1$Sternberg Astronomical Institute, 13 Universitetskij prosp.,
 Moscow 119899, Russia}
\IBVSinsto{e-mail: berdnik@sai.msu.su}
\IBVSinsto{$^2$Saint Mary's University, Halifax, Nova Scotia,
 B3H 3C3, Canada}

\SIMBADobj{DZ CMa}
\IBVStyp{ CEPD(B) }

\begintext

DZ CMa is listed in the GCVS-IV as a classical Cepheid with a period
of 1.75434 days. It is of special interest owing to the fact that it
is projected on the open cluster NGC 2360. Just a small subset of
Cepheids are spatially coincident with open clusters. The only
previous photoelectric observations for DZ CMa are 10 measurements
by Diethelm (1986). Its light curve is therefore not well defined,
which is why we included the star on our program of photoelectric
observations for Cepheids.

New observations were made of DZ CMa using a one-channel photometer
attached to the 0.5-m telescope of the South African Astronomical
Observatory. A total of 28 measurements were obtained (Table 1),
mainly in $VI_c$, from December 25, 1997, to January 3, 1998. The
accuracy of the individual data is near $\pm$ 0\fmm 01 in all filters.
\vskip 5mm

\centerline{Table 1}
\vskip 1mm
\begin{center}
\begin{tabular}{cccccccc}
\hline
$JD_{hel}$&$V$&$B-V$&$(V-I)_c$&$JD_{hel}$&$V$&$B-V$&$(V-I)_c$\\
2450800+ & & & &2450800+ & & & \\
\hline
\\
08.4882&11.766&   -   &1.282&   14.5085&12.350&   -   &1.467\\
09.3916&12.346&   -   &1.447&   14.5534&12.367&   -   &1.476\\
09.4816&12.227&   -   &1.454&   15.3437&11.889&   -   &1.319\\
10.3889&12.052&   -   &1.365&   15.4396&11.956&   -   &1.348\\
10.5014&12.037&   -   &1.354&   15.4804&11.940&   -   &1.328\\
11.4083&11.904&   -   &1.324&   15.5103&11.955&   -   &1.349\\
11.5355&11.967&   -   &1.349&   15.5641&11.968&   -   &1.351\\
12.3677&12.313&   -   &1.456&   16.3042&12.060&   -   &1.381\\
12.4025&12.300&   -   &1.436&   16.3986&12.076&   -   &1.406\\
12.4394&12.313&   -   &1.460&   16.4773&12.102&   -   &1.404\\
12.4752&12.345&   -   &1.474&   17.3058&12.206& 1.193 &1.420\\
12.5077&12.342&   -   &1.461&   17.3518&12.206& 1.238 &1.412\\
12.5401&12.350&   -   &1.459&   17.3930&12.193&   -   &1.418\\
14.4925&12.371&   -   &1.460&   17.4335&12.158&   -   &1.407\\
\hline
\end{tabular}
\end{center}
\eject
\IBVSfig{14cm}{4567-f1.ps}{}

A frequency analysis of our data in combination with Diethelm's (1986)
observations shows that DZ CMa is most likely a double-mode Cepheid
with the elements:

   fundamental:    Max JD$_{hel}$ = 2450808.48 + 2\fday 362896 $\times$ E,

   first overtone: Max JD$_{hel}$ = 2450808.23 + 1\fday 700131 $\times$ E.

The elements are used in Figure 1 for plotting our observations (dots)
with those of Diethelm (circles). The observed period ratio for the
two pulsation modes is $f_1/f_0 = 0.7195$, which agrees closely with
the results for other double-mode pulsators and is further
confirmation that DZ CMa is a beat Cepheid.

The research described here was supported in part by the Russian
Foundation of Basic Research and the State Science and Technology
Program ``Astronomy" to LNB and through NSERC Canada to DGT. We are
grateful to the administration of SAAO for the allocation of observing
time which made possible the observations presented here.

\vskip 6mm
%Reference:
\reference

Diethelm, R., 1986, {\it Astron. Astrophys. Suppl. Ser.},
{\bf 64}, 261


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