NGC 2401: A template of the young population of the Norma-Cygnus arm in the Third Galactic Quadrant

Abstract

Based on a deep optical CCD [<i>UBV(RI)</i><SUB>C</SUB>] photometric survey and on the Two-Micron All Sky Survey (2MASS) data, we derived the main parameters of the open cluster NGC 2401. We found that this cluster is placed at 6.3 ± 0.5 kpc (V<SUB>o</SUB> - M<SUB>v</SUB> = 14.0 ± 0.2) from the Sun and is 25 Myr old, which allows us to identify NGC 2401 as a member of the young population belonging to the innermost side of the extension of the Norma-Cygnus spiral arm in the Third Galactic Quadrant. A spectroscopic study of the emission star LSS 440 that lies in the cluster area revealed that it is a B0Ve star; however, we could not confirm that it is a cluster member. We also constructed the cluster luminosity function (LF) down to V ∼ 22 and the cluster initial mass function (IMF) for all stars with masses above M ∼ 1-2 M ⊙. It was found that the slope of the cluster IMF is x ≈ 1.8 ± 0.2. The presence of a probable pre-main-sequence (PMS) star population associated with the cluster is weakly revealed.