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\IBVShead{4919}{13 July 2000}

\IBVStitletl{The Population II Cepheid in the Galactic}{ globular cluster Palomar~3 }

\IBVSauth{Borissova, J.$^{1}$; Ivanov, V.D.$^{2}$; Catelan, M.$^3$}

\IBVSinst{Institute of Astronomy, Bulgarian Academy of Sciences, 72 Tsarigradsko chaussee, BG 1784, Sofia, Bulgaria,\\ \indent  
jura@haemimont.bg} %email


\IBVSinst{Steward Observatory, The University of Arizona, Tucson, AZ 85721, USA, 
vdivanov@as.arizona.edu} %email


\IBVSinst{``Hubble Fellow'', University of Virginia, Department of Astronomy,  P.O. Box 3818, Charlottesville,\\ \indent VA 22903-0818, USA, 
catelan@virginia.edu} %email


\IBVSobj{V4 in Palomar 3}

\begintext

We report a period and the first light curve for a Population II Cepheid 
in the outer-halo Galactic globular cluster Palomar~3. As well known, 
Pop. II Cepheids are usually found in clusters with well-developed 
blue-horizontal branch (HB) tails only (e.g., Wallerstein 1970; 
Smith \& Wehlau 1985). Pal~3 has a completely red HB and is a scarcely  
populated globular cluster, so that the presence of a Pop.~II Cepheid 
in this cluster would appear extremely unlikely. Yet, the star we 
studied was suspected to be a variable by Gratton \& Ortolani (1984). 
It is listed in the latest revision of the Catalogue of Variable 
Stars in Globular Clusters (Clement 1997) as V4. Gratton \& Ortolani  
obtained tentative values for the period $\approx 3$~days and 
mean $V$ magnitude $\langle V\rangle = 19.32$. No light curve has ever 
been published for V4. To the best of our knowledge, no follow-up 
observations were carried out for V4 since its discovery; in the 
recent HST study of the cluster by Stetson et al.\ (1999), V4 lies 
outside their observed field. Our analysis was based on approx.\ 20 CCD 
frames obtained on 6 nights: three in 18-20 January, 1997 at the 1.54-m 
telescope operated by the Steward Observatory, University of Arizona, 
one night in February 1997 at the 2-m telescope of NAO ``Rozhen'', 
(Bulgaria),  one in April 1999 at the Steward Observatory and one in 
April, 2000 at NAO ``Rozhen''. The photometric reductions were carried 
out using the {\sc daophot/allstar} package available in {\sc IRAF}. 

The $V$ light curve is displayed in Fig.~1. In Table~1 are summarized
the $V$ magnitudes for V4. The first four magnitudes in the Table~1 
are from Gratton \& Ortolani (1984), the five one is from Ortolani \& Gratton (1989)

The period we estimate from our new CCD data is slightly longer than 
the tentative value given in Gratton \& Ortolani (1984): $P=3\fday402$.
The derived mean $V$ magnitude obtained by directly averaging
over the pulsation cycle in intensity is $\langle V\rangle = 19.28$. 
The estimated amplitude in $V$ is 0\fmm 43. The indication of a 
bump on the descending branch of the light curve suggests that the 
star may be a Pop.~II Cepheid of the BL~Her type (Diethelm 1983).
However, a better sampled light curve is necessary 
to confirm this.

\newpage

\begin{table*}
\begin{center}
\caption{Photometry in $V$ band of V4.}
\begin {tabular}{ccc}
\hline
JD 24\dots & $V$&$\sigma$ \\ 
\hline
45350.76100&	19.230 &$-$\\
45351.82000&	19.540 &$-$\\
45352.80800&	19.170 &$-$\\
45353.80800&	19.160 &$-$\\
46449.71400&	19.260 &$-$\\
50466.96150&	19.150 &0.022\\
50467.89980&	19.287 &0.017\\
50468.95380&	19.311 &0.021\\
50491.47750 &    19.260 &0.015\\
51288.78170&	19.359 &0.017\\
51672.37109&	19.347 &0.014\\
\hline
\end{tabular}
\end{center}
\end{table*}

\IBVSfig{8cm}{4919-f1.eps}{Light curve of the Pop.~II Cepheid V4 in $V$ band.}

\references

Clement, C., 1997, {\it AAS Newsl.}, {\bf 84}, 15

Diethelm, R., 1983, {\it A\&A}, {\bf 124}, 108

Gratton, R., \& Ortolani, S., 1984, {\it A\&AS}, {\bf 57}, 177

Ortolani, S., \& Gratton, R., 1989, {\it A\&AS}, {\bf 79}, 155

Smith, H. A., \& Wehlau, A., 1985, {\it ApJ}, {\bf 298}, 572

Stetson et al., 1999, {\it AJ}, {\bf 117}, 247

Wallerstein, G., 1970, {\it ApJ}, {\bf 160}, 345

\endreferences 

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