Luminosity and Mass Function of the Galactic open cluster NGC 2422

Abstract

We present UBVRI photometry of the open cluster NGC 2422 (age $\sim 10^8$ yr) down to a limiting magnitude $V\simeq19$. These data are used to derive the Luminosity and Mass Functions and to study the cluster spatial distribution. By considering the color-magnitude diagram data and adopting a representative cluster main sequence, we obtained a list of candidate cluster members based on a photometric criterion. Using a reference field region and an iterative procedure, a correction for contaminating field stars has been derived in order to obtain the Luminosity and the Mass Functions in the $M=0.4-3.5 M_\odot$ range. By fitting the spatial distribution, we infer that a non-negligible number of cluster stars lies outside our investigated region. We have estimated a correction to the Mass Function of the cluster in order to take into account the "missing" cluster stars. The Present Day Mass Function of \ngc2422 can be represented by a power-law of index $\alpha = 3.07 \pm0.08 $ (rms) -- the Salpeter Mass Function in this notation has index $\alpha = 2.35$ -- in the mass range $ 0.9 \leq M/M_\odot\leq 2.5 $. The index $\alpha$ and the total mass of the cluster are very similar to those of the Pleiades.