A method to determine distances to molecular clouds using near-IR photometry

Abstract

We aim to develop a method to determine distances to molecular clouds using JHK near-infrared photometry. The method is based on a technique that aids spectral classification of stars lying towards the fields containing the clouds into main sequence and giants. In this technique, the observed (J − H) and (H − Ks) colours are dereddened simultaneously using trial values of Av and a normal interstellar extinction law. The best fit of the dereddened colours to the intrinsic colours giving a minimum value of X² then yields the corresponding spectral type and Av for the star. The main sequence stars, thus classified, are then utilized in an Av versus distance plot to bracket the cloud distances. We applied the method to four clouds, L1517, Chamaeleon I, Lupus 3 and NGC 7023 and estimated their distances as 167 ± 30, 151 ± 28, 157 ± 29 and 408 ± 76 pc respectively, which are in good agreement with the previous distance estimations available in the literature.