Overlapping Open Clusters NGC 1750 and NGC 1758 behind the Taurus Dark Clouds. II. CCD Photometry in the Vilnius System

Abstract

Abstract. Seven-color photometry in the Vilnius system has been obtained for 420 stars down to V = 16 mag in the area containing the overlapping open clusters NGC 1750 and NGC 1758 in Taurus. Spectral and luminosity classes, color excesses, interstellar extinctions and distances are given for 287 stars. The classi cation of stars is based on their reddening-free Q-parameters. 18 stars observed photoelectrically were used as standards. The extinction vs. distance diagram exhibits the presence of one dust cloud at a distance of 175 pc which almost coincides with a distance of other dust clouds in the Taurus complex. The clusters NGC 1750 and NGC 1758 are found to be at the same distance of 760 pcand may penetrate each other. Their interstellar extinction A V is 1.06 mag which corresponds to E B;V = 0.34 mag. (1992, hereafter Paper I). Photoelectric photometry of 116 stars down to 13th magnitude has revealed that the clusters are at 510 and 680 pc distances, respectively. Interstellar reddeningE B;V of both clusters was found to beclose to 0.4 mag. The distance of the dust layer responsible for the reddening was found to be at 175 pc. The reality of the clusters was veri ed by their photometric distances and proper motions of the cluster members.Paper I has increased the interest in this pair of clusters. In a series of papers Galadi-Enriquez et al. (1998a,b,c) have con rmed the reality of the two clusters. Their investigation was based on stellar photometry in the UBVRI photometric system by CCD and photographic techniques down to 18{20 mag and on the proper motions of stars based on a plate collection covering a broad range of epochs (from 1891 to 1994). The lists of NGC 1750 and NGC 1758 members down to V = 15 mag were composed containing 79 and 57 stars respectively. For bothclusters the reddening E B;V = 0.34 mag, based on the member stars measured by Strai zys et al. (1992) in the Vilnius system and by the authors in the Str omgren system. The distances to the clusters were found to be630 pc and 760 pc. Another proper motion study in the area was published by Tian et al. (1998).Trying to obtain an independent criterion of membership to both clusters, based on photometric classi cation of stars in terms of MK spectral and luminosity classes, we have started a new investigation of the cluster area in the Vilnius system by CCD photometry, extending photometric classi cation down to a fainter limit in comparison to Paper I. Although the preliminary results of the present study were known already in 1995{1996, the publication was delayed due to problems of at-elding and CCD non-linearity.

On the metallicity of open clusters

“…For NGC 581 (Sanner et al 1999) and NGC 2244 (Bonatto & Bica 2009), we also find a published solar metallicity. The cluster NGC 1750 is very interesting in the sense that it overlaps with NGC 1758 (Straižys et al 2003). Therefore the choice of the members is essential to derive correct values.…”

Clusterix 2.0: a virtual observatory tool to estimate cluster membership probability

“…There are six stars with coherent Gaia radial velocity (v rad = 0.5±2.1 km s −1 ) that produce an average parallax of = 0.34±0.04 mas. (Straižys et al 2003;Galadi-Enriquez et al 1998c,b;Galadí-Enríquez et al 1998a;Tian et al 1998 Figure 14. The two known overlapping clusters: NGC 1750 in blue with 504 member stars, and NGC 1758 in light blue with 363 member stars.…”

“…There are six stars with coherent Gaia radial velocity (v rad = 0.5±2.1 km s −1 ) that produce an average parallax of = 0.34±0.04 mas. et al 2003;Galadi-Enriquez et al 1998c,b;Galadí-Enríquez et al 1998a;Tian et al 1998).…”