1 Introduction

The dynamical evolution and the final fate of open star clusters in the Milky Way is nowadays a very active research field. Open star clusters are weakly bound objects with a typical lifetime of less than a Gyr (Dutra & Bica 2000; Bergond et al. 2001), which ultimately depends on the initial mass of the cluster, the birthplace and the fraction of primordial binaries (de la Fuente Marcos 1998, 2001).

Recently, Bica et al. (2001) drew attention to a sample of high Galactic latitude ( $b > 15^{\circ}$) star clusters presumably in an advanced stage of dynamic evolution, which they baptized Probable Open Cluster Remants (POCR). The prototype of this class of objects is NGC 6994 (M 73), recently studied by Bassino et al. (2001) and Carraro (2001), who performed the first multicolor photometric studies of this cluster, but arrived at opposite conclusions on the nature of this object. While Bassino et al. suggest that M 73 is the remnant of a star cluster, Carraro (2000) proposes that it is just a chance alignment of four bright stars.

Although it is a difficult task to unravel the nature of a star concentration based only on photometry, it however remains the first necessary step. Indeed sometimes the Color Magnitude Diagrams (CMDs) and Color-Color Diagrams (CCDs) are sufficient to disentangle a real bound system or a random enhancement of stars (Carraro & Patat 1995; Piatti & Clarià 2001). In many cases however, photometry cannot help to decide unambiguously about the nature of a star concentration: in this situation radial velocities and/or proper motion studies are necessary (Baumgardt 1998; Baumgardt et al. 2000; Odenkirchen & Soubiran 2002).

The census provided by Bica et al. (2001) lists 20 candidate dissolving open clusters, some of which are completely unstudied. This is the case for NGC 7036 and NGC 7772, two high latitude objects traditionally considered genuine open clusters, which are the subject of the present study. The basic idea of this paper is to present the first photometric study of these clusters and to provide a list of probable member stars to be further studied with high resolution spectroscopy.

We note the recent spectroscopic follow-up of NGC 6994 by Odenkirchen & Soubiran (2002), who confirmed the Carraro (2000) suggestions that this object is a chance alignment of four bright stars.

In Sect. 2 we briefly present the observations and data reduction. Sections 3 and 4 illustrate our results for NGC 7036 and NGC 7772, and, finally, Sect. 5 draws some conclusions and suggests further lines of research.

 

Table 1: Basic parameters of the observed objects. Coordinates are for J2000.0 equinox

Name	$\alpha$	$\delta$	l	b
	hh:mm:ss	$^{\circ}$:$^{\prime}$: $^{\prime\prime}$	$^{\circ}$	$^{\circ}$
NGC 7036	21:10:02	+15:31:06	64.55	-21.44
NGC 7772	23:51:46	+16:14:48	102.74	-44.27