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

¹ Korea Astronomy and Space Science Institute, 61-1, Hwaam-dong, Yuseong-gu, Daejeon 305-348, Republic of Korea e-mail: maheswar@kasi.re.kr; maheswar@aries.res.in
² Aryabhatta Research Institute of Observational Sciences, Manora Peak, Nainital 263 129, India
³ Indian Institute of Astrophysics, Koramangala, Bangalore 560 034, India
⁴ Service d'Astrophysique, DSM/Irfu, CEA/Saclay, 91191 Gif-sur-Yvette Cedex, France
⁵ Lebanese University, Faculty of Sciences, Department of Physics, El-Hadath, Beirut, Lebanon

Received: 29 May 2009
Accepted: 23 September 2009

Abstract

Aims. We aim to develop a method to determine distances to molecular clouds using JHK near-infrared photometry.

Methods. 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 () and () colours are dereddened simultaneously using trial values of A_V and a normal interstellar extinction law. The best fit of the dereddened colours to the intrinsic colours giving a minimum value of then yields the corresponding spectral type and A_V for the star. The main sequence stars, thus classified, are then utilized in an A_V versus distance plot to bracket the cloud distances.

Results. We applied the method to four clouds, L1517, Chamaeleon I, Lupus 3 and NGC 7023 and estimated their distances as , , and pc respectively, which are in good agreement with the previous distance estimations available in the literature.