[Paper Review] 207 New Open Star Clusters within 1 kpc from Gaia Data Release 2

Gyuheon Sim, Sang Hyun Lee+2 more|arXiv (Cornell University)|Jul 16, 2019

Stellar, planetary, and galactic studies16 references58 citations

TL;DR

The study visually searches Gaia DR2 data to identify 655 cluster candidates within 1 kpc, validates them with isochrones, and presents 207 newly discovered open clusters after cross-matching with existing catalogs.

ABSTRACT

We conducted a survey of open clusters within 1 kpc from the Sun using the astrometric and photometric data of the Gaia Data Release 2. We found 655 cluster candidates by visual inspection of the stellar distributions in proper motion space and spatial distributions in l-b space. All of the 655 cluster candidates have a well defined main-sequence except for two candidates if we consider that the main sequence of very young clusters is somewhat broad due to differential extinction. Cross-matching of our 653 open clusters with known open clusters in various catalogs resulted in 207 new open clusters. We present the physical properties of the newly discovered open clusters. The majority of the newly discovered open clusters are of young to intermediate age and have less than ~50 member stars.

Motivation & Objective

• Identify previously unknown open clusters within 1 kpc using Gaia DR2 data.
• Develop a two-step approach combining visual inspection and quantitative validation to minimize field-star contamination.
• Derive cluster parameters (center, radius, distance, age, shape) and assess physical reality via CMDs.
• Provide a catalog of newly discovered clusters with their basic astrometric and structural properties.

Proposed method

• Split the sky into 3628 areas and perform visual searches in proper motion, parallax, and spatial distributions to identify cluster candidates.
• Apply mean-shift for cluster center in proper motion space and Gaussian mixture modeling to define the spatial distribution.
• Estimate cluster distance from the mode of parallax distribution and use Gaussian kernel CMD fitting to derive ages with Z=0.02 PARSEC isochrones.
• Iteratively refine centers, radii, and shapes in proper motion and l-b space until convergence of six parameters.
• Cross-match candidates with DALM, MWSC, and COCD catalogs to identify new clusters, assigning codes based on agreement criteria.

Experimental results

Research questions

• RQ1 Can Gaia DR2 data reveal new open clusters within 1 kpc that were not identified in previous catalogs?
• RQ2 How reliably can visual inspection combined with multi-dimensional Gaia data separate cluster members from field stars?
• RQ3 What are the structural and astrometric properties (center, radius, distance, age) of the newly found clusters?
• RQ4 What fraction of visually selected candidates represents physically real clusters after CMD validation?
• RQ5 How do the new clusters spatially and kinematically relate to known clusters and MW structure?

Key findings

• 655 visually selected cluster candidates were analyzed.
• 653 of the 655 candidates are confirmed as physical open clusters after CMD validation (99.7%).
• 207 new open clusters were identified after cross-matching with known catalogs (DALM, MWSC, COCD) and applying the three-condition agreement test.
• Distances, proper motions, and spatial extents were derived using GMM and mean-shift analyses, with CMDs fitted to PARSEC Z=0.02 isochrones to determine ages.
• The catalog provides Galactic coordinates, proper motions, parallaxes, GMM radii, core radii, member counts, and ages for the new clusters.