Magnetic Inflation and Stellar Mass. V. Intensification and saturation of M dwarf absorption lines with Rossby number. (arXiv:1912.01004v1 [astro-ph.SR])

Magnetic Inflation and Stellar Mass. V. Intensification and saturation of M dwarf absorption lines with Rossby number. (arXiv:1912.01004v1 [astro-ph.SR])
<a href="http://arxiv.org/find/astro-ph/1/au:+Muirhead_P/0/1/0/all/0/1">Philip S. Muirhead</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Veyette_M/0/1/0/all/0/1">Mark J. Veyette</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Newton_E/0/1/0/all/0/1">Elisabeth R. Newton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Theissen_C/0/1/0/all/0/1">Christopher A. Theissen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mann_A/0/1/0/all/0/1">Andrew W. Mann</a>

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.

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.

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