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1 Introduction

This paper continues a series dedicated to the presentation of near-infrared photometry (in J and K pass-bands) for northern galactic open clusters. We already reported on the very young open clusters NGC 1893 and Berkeley 86 (Vallenari et al. 1999a), the old clusters Berkeley 17 and Berkeley 18 (Carraro et al. 1999a), and the intermediate age clusters IC 166 and NGC 7789 (Vallenari et al. 1999b). Here we present J and K photometry for King 5, a poorly studied open cluster for which no detailed study has been reported so far.

King 5 is located near the galactic plane at $l~=~143\hbox{$.\!\!^\circ$ }75$ and $b~=-4\hbox{$.\!\!^\circ$ }27~$, and it is designated also as OCL 384 and C0311+525 by IAU. Its diameter is estimated to be about $5^{\prime}-8^{\prime}$.

A preliminary investigation was conducted by Phelps et al. (1994) who obtained VI photometry for 1343 stars in a region of $11^{\prime} \times 11^{\prime}$. This study revealed that King 5 is a cluster of the Hyades generation, with an age around one billion years, derived from a morphological age estimator.

These authors do not report estimates for cluster distance and reddening.

Moderate resolution spectra for 24 stars in the field of King 5 have been obtained by Scott et al. (1995). From this analysis it emerges that King 5 belongs to the old thin disk population, and its rotational velocity around the galactic center (-52 km s-1) is consistent with Hron (1987) rotation curve at the cluster location.

On the base of the radial velocities 19 members have been singled out.

More recently Durgapal et al. (1998) published UBVRI photometry of King 5, inferring by comparison with solar metallicity isochrones an age slightly lower than 1 Gyr, a distance of 2 kpc and a reddening E(V-I)=0.94.

Finally it is worth recalling that the metal abundance of King 5 has been determined by Friel et al. (1995) using medium resolution spectroscopy of twelve giant stars. From this study [Fe/H] turns out to be ( $-0.38\pm0.20$), half the solar value.

In this paper we combine together IR and optical photometry to obtain an estimate of the cluster fundamental parameters. We find that the cluster is 1.0 Gyr old.

The plan of the paper is as follows: Sect. 2 is devoted to the presentation of data acquisition and reduction; in Sect. 3 we discuss the morphology of the Color Magnitude Diagrams (CMDs) for different pass-bands; Sect. 4 is dedicated to the derivation of the color excess, while age and distance are inferred in Sect. 5. Finally our conclusions are summarized in Sect. 6.


 

 
Table 1: Observation log book
Cluster $\alpha$ $\delta$ Date Exposure Times (sec)
  (2000) (2000)   J K
King 5 3 14 47 52 42 39 Oct. 25, 1997 540 880
King 5 F1 3 14 23 52 48 39 Oct. 27, 1997 480 620
King 5 F2 3 15 42 52 33 17 Oct. 27, 1997 480 620
K5A 3 14 40 52 42 51 Oct. 25, 1997    
K5B 3 14 27 52 42 02 Oct. 25, 1997    



  \begin{figure}{\psfig{file=ds9007f1.eps,width=8.8cm} }
\end{figure} Figure 1: The field covered in the region of King 5 by the optical photometry of Phelps et al. (1994). The inner region shows the mosaic of the four fields observed by us in the IR. North is up, East on the left


  \begin{figure}{\psfig{file=ds9007f2.eps,width=8.8cm} }
\end{figure} Figure 2: The CMD of King 5. The optical photometry (V-(V-I), upper left panel) is taken from Phelps et al. (1994). The IR photometry (lower panel) is that presented in this paper, whereas the upper right panel presents the derived CMD in V-(V-K). Filled circles represent cluster members on the basis of the radial velocity


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