IC4665 is a young (~30 Myr), nearby (350 pc) open cluster. This properties make them a good candidate to study the outcome of the star formation process. First, its proximity allows us to observe the faintest and least massive objects which are most sensible to gravitational interactions. Second, at 30 Myr the formation process is finished but we can still find most of the stars in a similar configuration in which they where born.
Combining ground-based images from a time span of 20 years, we computed proper motions and multi-band photometry for more than 2 million sources, covering a magnitude range of 15 mag (7 < J < 22). We complemented this sample with the Gaia mission (GDR2) which includes parallaxes, more precise proper motions, and three photometric bands for the brightest sources (more than a million in this region).
We used a probabilistic model of the distribution of the observable quantities (i.e. parallaxes, proper motions and multi-band photometry) to search for members in this cluster. We find 819 members of IC4665, 50% of which are new members. We used them to study different properties of the cluster which are a diagnostic of the cluster formation and initial evolution. We obtained the present-day system mass function in the range of 0.02–6 Msun, which reveals a number of details not seen in previous studies. The observed projected (2D) spatial distribution of the cluster favors a spherically symmetric model with no mass segregation.
Our membership analysis represents a significant increase in the quantity and quality (low contamination) with respect to previous studies. We are currently profiting it to carry on other investigations such as the detection of debris discs or exoplanets which can shed light on the planetary formation process. Additionally, we are analyzing GTC spectra of the most ultra-cool dwarfs to increase the small, known sample of these objects, crucial to test evolutionary models at young ages and low masses.
Figure: color image of the faintest members discovered by our study. Its mass is estimated to lie between 12 ans 15 Jupiter masses, according to the latest evolutionary models.
© Last Update: 03-11-2020 by H. Bouy