Near-infrared extinction measurements at the Indian observatory sites

Abstract

Regular near-infrared astronomical measurements have been made since 1978 at the Uttar Pradesh State Observatory, Nainital (79°.46 E; 29°.36 N) and the Indian Institute of Astrophysics Observatory, Kavalur (78°.83 E; 12°.58 N) using liquid nitrogen cooled InSb photometers developed at the Physical Research Laboratory (PRL), Ahmedabad. Using the observations of the standard stars from the list of Johnson et al (1966) the JHKL photometric system of PRL has been tied to the broad-band infrared photometric system defined by Johnson (1965, 1966). The average J, H and K band extinction coefficients are 0.15 mag, 0.07 mag and 0.09 mag respectively. These are in general agreement with the theoretical extinction coefficients calculated by Manduca ana Bell (1979) for 5 m m atmospheric water vapour and the Kitt Peak J H K filters. The details of the transformation from instrumental system to standard system are also discussed.