This page contains an overview of some of the global population properties in the MOCA database.
Currently, MOCAdb contains [...] adopted stellar associations and [...] astrophysical bodies (stars, brown dwarfs, planemos, exoplanets, white dwarfs, etc.), [119758] of which are assigned as candidate members to at least one coeval association and therefore benefit from an age constraint.
A large fraction of the database objects consist in relatively young (10-100 Myr) M dwarfs as seen in the figure below; this is not unexpected given the shape of the initial mass function and the ages of the nearest known young associations and open clusters.
We are attempting to include all stellar associations at distances up to 500 pc from the Sun in MOCAdb, but we have also included some open clusters that are further away:
Most of the masses in MOCAdb are estimated from the spectral type of the star and empirical sequences (shown below) derived from the [Mamajek] table for stars earlier than [M6], extended to young ages using members of young associations with dynamical masses (red diamonds), and extended to later spectral types using the BT-Settl models [URL]. While this is not the most precise method to estimate masses, it suffers from less biases from unresolved binaries and is not subject to systematic errors that are still present in evolutionary models (in the case of stars earlier than M6). The semi-empirical sequences shown below are stored as a 3D grid in the table data_astro_sequences with the unique sequence identifier moca_seqid='sptn_msun_age'.
The stellar and substellar radii in MOCAdb are estimated in a similar manner, except that the radii of young G to M dwarfs are a much stronger function of age because this is a period where stars are still contracting onto the main sequence. For this reason, the Mamajek et al[URL] empirical sequences for stars earlier than M6 were modified using a wider set of age-calibrated stars that benefit from semi-direct constraints on their radii with the use of spectral energy distributions (see e.g., Pecaut et al[X]). The semi-empirical sequences shown below are stored as a 3D grid in the table data_astro_sequences with the unique sequence identifier moca_seqid='sptn_rsun_age'.