The complex stellar populations in the lines of sight to open clusters in the third Galactic quadrant

Abstract

Multi-color photometry of the stellar populations in five fields in the third Galactic quadrant centred on the clusters NGC 2215, NGC 2354, Haffner 22, Ruprecht 11, and ESO489SC01 is interpreted in terms of a warped and flared Galactic disk, without resort to an external entity such as the popular Monoceros or Canis Major overdensities. Except for NGC 2215, the clusters are poorly or unstudied previously. The data generate basic parameters for each cluster, including the distribution of stars along the line of sight. We use star counts and photometric analysis, without recourse to Galactic-model-based predictions or interpretations, and confirms earlier results for NGC 2215 and NGC 2354. ESO489SC01 is not a real cluster, while Haffner~22 is an overlooked cluster aged about 2.5 Gyr. Conclusions for Ruprecht~11 are preliminary, evidence for a cluster being marginal. Fields surrounding the clusters show signatures of young and intermediate-age stellar populations. The young population background to NGC~2354 and Ruprecht~11 lies 8-9 kpc from the Sun and $\sim$1 kpc below the formal Galactic plane, tracing a portion of the Norma-Cygnus arm, challenging Galactic models that adopt a sharp cut-off of the disk 12-14 kpc from the Galactic center. The old population is metal poor with an age of 2-3 Gyr, resembling star clusters like Tombaugh 2 or NGC 2158. It has a large color spread and is difficult to locate precisely. Young and old populations follow a pattern that depends critically on the vertical location of the thin and/or thick disk, and whether or not a particular line of sight intersects one, both, or none.

16 pages, 9 eps figures, in press in MNRAS

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Cited by in corpus (7)

• Mapping the Galactic Metallicity Gradient with Open Clusters: The State-of-the-Art and Future Challenges
• On the Motion of Stars in the Pleiades according to Gaia DR2 Data
• Galactic structure in the outer disk: the field in the line of sight to the intermediate-age open cluster Tombaugh 1
• A deep investigation of two poorly studied open clusters Haffner 22 and Melotte 71 in Gaia era
• On the assessment of the nature of open star clusters and the determination of their basic parameters with limited data
• Solving the distance discrepancy for the open cluster NGC 2453. The planetary nebula NGC 2452 is not a cluster member
• Outer Regions of the Milky Way