The nearby Galaxy structure toward the Vela Gum nebula

Abstract

We report on $UBVI$ photometry and spectroscopy for MK classification purposes carried out in the fields of five open clusters projected against the Vela Gum in the Third Galactic Quadrant of the Galaxy. They are Ruprecht 20, Ruprecht 47, Ruprecht 60, NGC 2660 and NGC 2910. We could improve/confirm the parameters of these objects derived before. The spectroscopic parallax method has been applied to several stars located in the fields of four out of the five clusters to get their distances and reddenings. With this method we found two blue stars in the field of NGC 2910 at distances that make them likely members of Vela OB1 too. Also, projected against the fields of Ruprecht 20 and Ruprecht 47 we have detected other young stars favoring not only the existence of Puppis OB1 and OB2 but conforming a young stellar group at $\sim1$ kpc from the Sun and extending for more than 6 kpc outward the Galaxy. If this is the case, there is a thickening of the thin Galactic disk of more than 300 pc at just 2-3 kpc from the Sun. Ruprecht 60 and NGC 2660 are too old objects that have no physical relation with the associations under discussion. An astonishing result has been the detection in the background of Ruprecht 47 of a young star at the impressive distance of 9.5 kpc from the Sun that could be a member of the innermost part of the Outer Arm. Another far young star in the field of NGC 2660, at near 6.0 kpc, may become a probable member of the Perseus Arm or of the inner part of the Local Arm. The distribution of young clusters and stars onto the Third Galactic Quadrant agrees with recent findings concerning the extension of the Local Arm as revealed by parallaxes of regions of star formation. We show evidences too that added to previous ones found by our group explain the thickening of the thin disk as a combination of flare and warp.Comment: Accepted for publication in New Astronom

On the assessment of the nature of open star clusters and the determination of their basic parameters with limited data

“…17 indicates a group of early type stars, that must belong to NGC 2910. They are reddened by E(B − V ) = 0.20, in perfect agreement with the recent study of NGC 2910 by Giorgi et al (2015). These authors as well stress the large differences between their cluster parameters and those determined by Kharchenko et al (2013).…”

“…This would place it well beyond the Vela Molecular Ridge Giorgi et al 2015) at the extreme periphery of the Galactic disk. We found that this cluster is very reddened, as Lynga 6, but lies much closer, at about 3 kpc from the Sun.…”

“…On maps this cluster appears as a shallow over density a few arcmin from the more conspicuous open cluster NGC 2910 (Giorgi et al 2015), from which it is separated by a clear dust lane (see the bottom-left panels of Figs. 1 and 4, or any DSS image).…”

Meta-analysis from different tracers of the small Local Arm around the Sun—extent, shape, pitch, origin

“…In GQ III, we show the 'stellar bridge' to the Perseus arm, near l=258 o from Fig. 15 in Giorgi et al (2015). In GQ IV, we copy the 'fork' to the Carina arm as sketched in Fig.…”

A comprehensive photometric study of dynamically evolved small van den Bergh–Hagen open clusters

“…In this paper, we present a comprehensive photometric study of vdBH 1, 10, 31, 72, 87, 92 and 118; the last four clusters were discovered by van den Bergh & Hagen (1975). As far as we are aware, previous photometric studies were performed for vdBH 1 (=Haffner 7), 10 (= Ruprecht 35) and 31 (= Ruprecht 60) (Moitinho et al 2006;Vázquez et al 2008;Bonatto & Bica 2010;Carraro et al 2013;Giorgi et al 2015). In Section 2 we describe the collection and reduction of the available photometric data and their thorough treatment in order to build extensive and reliable data sets.…”