An in-depth analysis of the differentially expanding star cluster Stock 18 (Villafranca O-036) using Gaia DR3 and ground-based data

Abstract

(ABRIDGED) CONTEXT: The Villafranca project is combining Gaia data with ground-based surveys to analyze Galactic stellar groups with OB stars. AIMS: We want to analyze Stock 18 within the Villafranca project, a very young stellar cluster with a symmetrical and compact H II region around it. METHODS: We analyze the core, massive-star population, extinction, distance, membership, internal dynamics, density profile, age, IMF, total mass, stellar variability, and Galactic location of Stock 18 with Gaia data and ground-based spectroscopy. RESULTS: Stock 18 is a very young (~1.0 Ma) cluster located at a distance of 2.91+-0.10 kpc dominated by the GLS 13 370 system, whose primary is an O9 V star. We propose that Stock 18 was in a very compact state (~0.1 pc) about 1.0 Ma ago and that most massive stars were ejected at that time without significantly affecting the less massive stars as a result of multi-body dynamical interactions. Given its age close to 1.0 Ma, the dynamical interactions took place very soon after massive star formation. Well defined expanding stellar clusters have been observed before but none as young as this one. The IMF is top heavy but if we discard the ejected ones it becomes nearly canonical. Therefore, this is another example in addition to the one we previously found (the Bermuda cluster) of (a) a very young cluster with an already evolved PDMF (b) that has significantly contributed to the future population of free-floating compact objects. If confirmed in more clusters, the number of such compact objects may be higher in the Milky Way than previously thought. Stock 18 has a variable extinction with an average value of R_5495 higher than the canonical one of 3.1. The cluster is above our Galactic mid-plane and has a distinct motion with respect to its surrounding old population, which is possibly an influence of the Perseus spiral arm.

Accepted for publication in A&A

References in corpus (27)

• Gaia Data Release 3: Summary of the content and survey properties
• New evolutionary models for pre-main sequence and main sequence low-mass stars down to the hydrogen-burning limit
• Gaia Early Data Release 3: The astrometric solution
• Gaia Early Data Release 3: Photometric content and validation
• Painting a portrait of the Galactic disc with its stellar clusters
• Gaia Early Data Release 3 -- Catalogue validation
• Clusters and mirages: cataloguing stellar aggregates in the Milky Way
• The VLT-FLAMES Tarantula Survey XVI. The optical+NIR extinction laws in 30 Doradus and the photometric determination of the effective temperatures of OB stars
• Dependency of dynamical ejections of O stars on the masses of very young star clusters
• A Multi-Membership Catalogue for 1876 Open Clusters using UCAC4 data
• Validation of the accuracy and precision of Gaia EDR3 parallaxes with globular clusters
• Characterizing and correcting the proper motion bias of the bright Gaia EDR3 sources
• The Alma catalog of OB stars. II. A cross-match with Gaia DR2 and an updated map of the solar neighbourhood
• MONOS: Multiplicity Of Northern O-type Spectroscopic systems. I. Project description and spectral classifications and visual multiplicity of previously known objects
• Orbital and physical properties of the $\sigma$ Ori Aa,Ab,B triple system
• An estimation of the Gaia EDR3 parallax bias from stellar clusters and Magellanic Clouds data
• The Villafranca catalog of Galactic OB groups. II. From Gaia DR2 to EDR3 and ten new systems with O stars
• The Villafranca catalog of Galactic OB groups: I. Systems with O2-O3.5 stars
• High-Resolution Infrared Imaging of Herschel 36 SE: A Showcase for the Influence of Massive Stars in Cluster Environments
• Stellar variability in Gaia DR3. I. Three-band photometric dispersions for 145 million sources
• Westerlund 1 under the light of Gaia EDR3: Distance, isolation, extent, and a hidden population
• Galactic extinction laws: II. Hidden in plain sight, a new interstellar absorption band at 7700 Å broader than any known DIB
• Lucky spectroscopy, an equivalent technique to Lucky Imaging: II. Spatially-resolved intermediate-resolution blue-violet spectroscopy of 19 close massive binaries using the William Herschel Telescope
• Analysing spectral lines in Gaia low-resolution spectra
• Escape from the Bermuda cluster: orphanization by multiple stellar ejections
• Variable stars in the Sh 2-170 HII region
• The GALANTE photometric survey of the northern Galactic plane: Project description and pipeline

Cited by in corpus (1)

• The Alma catalogue of OB stars. III. A cross-match with Gaia DR3 and an extension based on new spectral classifications