IC 4665 DANCe I. Members, empirical isochrones, magnitude distributions, present-day system mass function, and spatial distribution

Miret Roig, N., Bouy, H., Olivares, J., Sarro, L. M., Tamura, M., Allen, L., Bertin, E., Serre, S., Berihuete, A., Beletsky, Y., Barrado, D., Huelamo, N., Cuillandre, J. C., Moraux, E., Bouvier, J. 2019. IC 4665 DANCe I. Members, empirical isochrones, magnitude distributions, present-day system mass function, and spatial distribution. Astronomy and Astrophysics 631 DOI: 10.1051/0004-6361/201935518

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 o ffers 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-circle dot, 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 o ffers an excellent opportunity to revisit other fundamental parameters such as age.

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