Magnetic Inflation and Stellar Mass. V. Intensification and saturation of M dwarf absorption lines with Rossby number

• Published in: arXiv.org
• Main Authors: Muirhead, Philip S, Veyette, Mark J, Newton, Elisabeth R, Theissen, Christopher A, Mann, Andrew W
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 02.12.2019
• Subjects: Absorption; Alpha rays; Cyclones; Equivalence; Field strength; Indicators; Magnetic saturation; Photosphere; Physics - Solar and Stellar Astrophysics; Radio emission; Red dwarf stars; Stellar coronas; Stellar mass
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1912.01004

In young sun-like stars and field M dwarf stars, chromospheric and coronal magnetic activity indicators such as H\(\alpha\), X-ray and radio emission are known to saturate with low Rossby number (\(Ro \lesssim 0.1\)), defined as the ratio of rotation period to convective turnover time. The mechanism for the saturation is unclear. In this paper, we use photospheric Ti I and Ca I absorption lines in \(Y\) band to investigate magnetic field strength in M dwarfs for Rossby numbers between 0.01 and 1.0. The equivalent widths of the lines are magnetically enhanced by photospheric spots, a global field or a combination of the two. The equivalent widths behave qualitatively similar to the chromospheric and coronal indicators: we see increasing equivalent widths (increasing absorption) with decreasing \(Ro\) and saturation of the equivalent widths for \(Ro \lesssim 0.1\). The majority of M dwarfs in this study are fully convective. The results add to mounting evidence that the magnetic saturation mechanism occurs at or beneath the stellar photosphere.