A new study has accurately estimated the abundance of Helium in our Sun for the first time. This could be a major step in assessing the opacity of the Sun’s photosphere.
Astronomers have traditionally assumed the abundance of Helium in the photosphere of Sun-like stars to be one tenth of that of Hydrogen by extrapolating from hotter stars, or from the outer atmosphere of the Sun (solar corona, solar wind), or from seismology studies of the interior of the Sun. None of these methods are based on direct observations of the photosphere due to the absence of Helium spectral lines.
An accurate and reliable measurement of the abundance of the element Helium in the photosphere of our Sun remains a challenge for astronomers to this day. The abundance of various elements in our Sun, or in any other star, is estimated from their absorption spectral lines. Since Helium does not produce any observable spectral lines from the visible surface, or the photosphere, of the Sun, its abundance has usually been estimated through indirect means.
Indian Institute of Astrophysics (IIA), an autonomous institute of the Department of Science and Technology (DST), has used Magnesium and Carbon features in the observed high-resolution spectrum of the Sun to accurately calculate the abundance of Helium in our Sun, in a recent study. This study published as a paper in “Astrophysical Journal, has been carried out by Satyajeet Moharana, B.P. Hema, and Gajendra Pandey, all from the Indian Institute of Astrophysics, based on an earlier novel method developed by the latter two authors. Moharana is also a student at IISER Berhampur.
“Using a novel and consistent technique, whereby the spectral lines of neutral Magnesium and Carbon atoms in conjunction with the lines from the Hydrogenated molecules of these two elements are carefully modelled, we are able to constrain the relative abundance of Helium in the Sun’s photosphere now”, said Satyajeet Moharana, the first author of the published study and currently a PhD scholar at KASI, South Korea.