Abstract
Context. The study of star formation is extremely challenging, due to the lack of complete and clean samples of young nearby clusters and star-forming regions. The recent Gaia DR2 catalogue complemented with the deep ground-based COSMIC DANCe catalogue offers a new database of unprecedented accuracy to revisit the membership of clusters and star-forming regions. The 30 Myr open cluster IC 4665 is one of the few well-known clusters of this age and it is an excellent target where evolutionary models can be tested and planetary formation studied. Aims. We provide a comprehensive membership analysis of IC 4665 and study the following properties: empirical isochrones, distance, magnitude distribution, present-day system mass function, and spatial distribution. Methods. We used the Gaia DR2 catalogue together with the DANCe catalogue to look for members via a probabilistic model of the distribution of the observable quantities in both the cluster and background populations. Results. We obtained a final list of 819 candidate members that cover a 12.4 magnitude range (7 < J < 19.4). We find that 50% are new candidates, and we estimate a conservative contamination rate of 20%. This unique sample of members allows us to obtain a present-day system mass function in the range of 0.02–6 M⊙, which reveals a number of details not seen in previous studies. In addition, we find that a spherically symmetric spatial distribution is favoured by our final list of members for this young open cluster. Conclusions. Our membership analysis represents a significant increase in the quantity and quality (low contamination) with respect to previous studies. It offers an excellent opportunity to revisit other fundamental parameters such as age.
Highlights
The initial mass function (IMF), the frequency distribution of stellar masses at birth, is a fundamental parameter in the study of stellar formation and evolution
We present the cluster properties and in particular the empirical isochrones, distance, magnitude distribution, present-day system mass function (PDSMF), and spatial distribution
We searched the European Southern Observatory (ESO) archive, the National Optical Astronomy Observatory (NOAO) archive, 1 https://www.cosmos.esa.int/web/gaia/ dr2-known-issues 2 We refer to the IC 4665 catalogue based on Gaia DR2 data as GDR2
Summary
The initial mass function (IMF), the frequency distribution of stellar masses at birth, is a fundamental parameter in the study of stellar formation and evolution. Soon after, Cantat-Gaudin et al (2018) presented another study of open clusters using Gaia DR2 data They derived another membership list (with the same magnitude limit) made of 175 high-probability members, 146 of which are in common with Gaia Collaboration (2018b). Over the past few years, Bouy et al (2013) started a survey program, the DANCe project (standing for Dynamical Analysis of Nearby ClustErs), with the aim of deriving a comprehensive and homogeneous census of stellar and substellar sources in the nearby (
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