Near infrared observations of the solar atmosphere

Abstract

Due to the availability of the advanced two dimensional array detectors for detecting the near infrared (IR) wavelength, it has become possible to study new aspects of solar atmosphere during the recent times. The main aspects of solar physics in near IR are: (1) The Zeeman sensitivity, which is the ratio of Zeeman splitting and Doppler width, is directly proportional to the wavelength. Therefore, compared to the visible window infrared is favourable for making accurate measurements of magnetic field. (2)The opacity for solar radiation reaches a minimum value at 1.6 micron. The study of the continuum radiation at this wavelength makes it possible to probe the solar atmosphere deeper than the visible photosphere. Also, the magnetic field at this layer can be measured by selecting the Zeeman sensitive lines near 1.6 micron. (3) Since the continuum and many other spectral lines are formed essentially in local thermodynamic equilibrium, the infrared spectrum provides a complementary view of the inhomogenities in solar atmosphere to that observed in short wavelengths. I shall review these aspects with special emphasis for future observations during the next solar maximum.