Open clusters in the Third Galactic Quadrant III. Alleged binary clusters

Abstract

Aims. We aim to determine accurate distances and ages of eight open clusters in order to: (1) assess their possible binarity (2) provide probes to trace the structure of the Third Galactic Quadrant. Methods. Cluster reddenings, distances, ages and metallicities are derived from ZAMS and isochrone fits in UBVRI photometric diagrams. Field contamination is reduced by restricting analysis to stars within the cluster limits derived from star counts. Further membership control is done by requiring that stars have consistent positions in several diagrams and by using published spectral types. Results. The derived distances, ages and metallicities have shown that none of the analysed clusters compose binary/double systems. Of the four candidate pairs, only NGC 2383/NGC 2384 are close to each other, but have different metallicities and ages. Ruprecht 72 and Ruprecht 158 are not clusters but fluctuations of the field stellar density. Haffner 18 is found to be the superposition of two stellar groups at different distances: Haffner 18(1) at 4.5 kpc and Haffner 18(2) between 9.5 and 11.4 kpc from the Sun. The derived distances and ages have been used to situate the clusters in the Galactic context. In particular, young stellar groups trace spiral structure at large Galactocentric radii. At least two clusters formed during the last few 10 8 yr in an interstellar medium with less than solar abundances. Conclusions. In contrast with the LMC, double clusters are apparently rare, or even non existent, in the undisturbed environment of the Third Galactic Quadrant. This leaves open the question of whether binary clusters form more easily toward denser and more violent regions of the Milky Way such as the inner Galaxy.

ASteCA: Automated Stellar Cluster Analysis

“…[10], Vázquez et al 2010;[11], Moreno-Corral et al 2002 and [12], Munari & Carraro 1996;respectively). The age and reddening parameters obtained by the code show very similar values to those present in the three DP sources as seen in Table 7, the only difference arises in the assignment of the metal content.…”

A guided map to the spiral arms in the galactic disk of the Milky Way

“…They are seen as pseudo 'chains of O-B starts elongated along the line of sight' [48], visible in their Figure 4 at galactic longitudes 78°,174°, 189°, and 290°, and in their Figure 6 at longitudes 134°, 189°, 290°, 342°. These are seen as a pseudo line of open star clusters, near l = 242° and near l = 258° [49,50]. Other spiral galaxies have been observed, and spiral galaxies have never shown such 'fingers' pointing at a specific star in a specific location inside a galaxy.…”

Fitting isochrones to open cluster photometric data

“…Generally, visual isochrone fits can provide estimates of the metallicity, but typically do not provide estimates of the error (in some works the error estimates are given as in Vázquez et al 2010, although obtained by visual fit). Our method provides a robust [Fe/H] with consistent error estimates.…”