Astronomers have long estimated the amount of Helium in Sun-like stars based on indirect methods, like studying hotter stars or the Sun’s outer layers. This is because Helium does not appear in the spectrum of cooler stars, making direct measurement difficult.
The challenge lies in determining the helium-to-hydrogen ratio in these stars. While this ratio is well-known for hot stars, it’s uncertain for cooler ones due to the lack of visible helium lines.
Astrophysicists focused on the Sun as a model cool star to bridge this gap. For the first time, they successfully determined its helium abundance directly, improving our understanding of stellar composition.
Researchers at the Indian Institute of Astrophysics (IIA) have accurately determined the amount of Helium in the Sun’s photosphere using a new technique. Since Helium doesn’t produce visible spectral lines in cooler stars like the Sun, previous estimates relied on indirect methods.
NASA sounding rocket discovered helium structures in the solar corona
Satyajeet Moharana, B.P. Hema, and Gajendra Pandey conducted this breakthrough study, which was published in the Astrophysical Journal. They used a refined approach, analyzing the spectral features of Magnesium and Carbon, including their hydrogenated molecular forms (MgH, CH, and C₂). They successfully constrained the Sun’s helium abundance by carefully modeling these lines and performing detailed calculations.
Scientists determine the Sun’s helium abundance by analyzing Magnesium and Carbon spectral lines. The amount of Magnesium and Carbon measured from their atomic lines must match the values obtained from their molecular lines. Since Hydrogen plays a role in forming these molecules, its abundance affects the results. Because helium is the second most abundant element in the Sun, its presence is tied to Hydrogen levels.
If Helium were slightly more abundant, it would reduce Hydrogen’s availability for molecular formation, altering absorption properties in the Sun’s photosphere. This would require adjusting the Magnesium and Carbon estimates to maintain consistency with observed spectral lines.
By testing different Helium-to-Hydrogen ratios in their calculations, researchers found that a ratio of 0.1 best fits both atomic and molecular features. Their results align with helioseismology studies, confirming that the commonly assumed He/H ratio of 0.1 is accurate. This validates their novel technique for measuring solar helium abundance.
The Sun is spinning round again
Journal Reference:
- Satyajeet Moharana, B. P. Hema, and Gajendra Pandey. Helium Abundance of the Sun: A Spectroscopic Analysis. Astrophysical Journal. DOI 10.3847/1538-4357/ad6ccf
