Filters for NIR astronomical photometry: comparison of commercial IRWG filters and designs using OpenFilters

Abstract

The photometric accuracy in the near-infrared (NIR) wavelength range (0.9 -2.6 microns) is strongly affected by the variability of atmospheric transmission. The Infrared Working Group (IRWG) has recommended filters that help alleviate this issue and provide a common standard of NIR filtersets across different observatories. However, accurate implementation of these filters are yet to be available to astronomers. In the meantime, InGaAs based detectors have emerged as a viable option for small and medium telescopes. The present work explores the combination of IRWG filtersets with InGaAs detectors. A few commercially available filtersets that approximate the IRWG profile are compared. Design of more accurate IRWG filtersets suitable for the InGaAs sensitivity range is undertaken using an open-source filter design software - OpeFilters. Along with the photometric filters iZ, iJ and iH, design of a few useful narrow band filters is also presented. These filters present opportunities for small and medium telescopes for dedicated long-term observation of interesting infrared sources.