HAZMAT. VII. The Evolution of Ultraviolet Emission with Age and Rotation for Early M Dwarf Stars. (arXiv:2011.10158v2 [astro-ph.SR] UPDATED)

HAZMAT. VII. The Evolution of Ultraviolet Emission with Age and Rotation for Early M Dwarf Stars. (arXiv:2011.10158v2 [astro-ph.SR] UPDATED)
<a href="http://arxiv.org/find/astro-ph/1/au:+Loyd_R/0/1/0/all/0/1">R. O. Parke Loyd</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Shkolnik_E/0/1/0/all/0/1">Evgenya L. Shkolnik</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schneider_A/0/1/0/all/0/1">Adam C. Schneider</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Richey_Yowell_T/0/1/0/all/0/1">Tyler Richey-Yowell</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jackman_J/0/1/0/all/0/1">James A. G. Jackman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Peacock_S/0/1/0/all/0/1">Sarah Peacock</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Barman_T/0/1/0/all/0/1">Travis S. Barman</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pagano_I/0/1/0/all/0/1">Isabella Pagano</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Meadows_V/0/1/0/all/0/1">Victoria S. Meadows</a>

The ultraviolet (UV) emission from the most numerous stars in the universe, M
dwarfs, impacts the formation, chemistry, atmospheric stability, and surface
habitability of their planets. We have analyzed the spectral evolution of UV
emission from M0-M2.5 (0.3-0.6 Msun) stars as a function of age, rotation, and
Rossby number, using Hubble Space Telescope observations of Tucana Horologium
(40 Myr), Hyades (650 Myr), and field (2-9 Gyr) objects. The quiescent surface
flux of their C II, C III, C IV, He II, N V, Si III, and Si IV emission lines,
formed in the stellar transition region, remains elevated at a constant level
for 240 $pm$ 30 Myr before declining by 2 orders of magnitude to field ages.
Mg II and far-UV pseudocontinuum emission, formed in the stellar chromosphere,
exhibit more gradual evolution with age, declining by 1 and 1.5 orders of
magnitude, respectively. The youngest stars exhibit a scatter of 0.1 dex in
far-UV line and pseudocontinuum flux attributable only to rotational
modulation, long-term activity cycles, or an unknown source of variability.
Saturation-decay fits to these data can predict an M0-M2.5 star’s quiescent
emission in UV lines and the far-UV pseudocontinuum with an accuracy of 0.2-0.3
dex, the most accurate means presently available. Predictions of UV emission
will be useful for studying exoplanetary atmospheric evolution, the destruction
and abiotic production of biologically relevant molecules, and interpreting
infrared and optical planetary spectra measured with observatories like the
James Webb Space Telescope.

The ultraviolet (UV) emission from the most numerous stars in the universe, M
dwarfs, impacts the formation, chemistry, atmospheric stability, and surface
habitability of their planets. We have analyzed the spectral evolution of UV
emission from M0-M2.5 (0.3-0.6 Msun) stars as a function of age, rotation, and
Rossby number, using Hubble Space Telescope observations of Tucana Horologium
(40 Myr), Hyades (650 Myr), and field (2-9 Gyr) objects. The quiescent surface
flux of their C II, C III, C IV, He II, N V, Si III, and Si IV emission lines,
formed in the stellar transition region, remains elevated at a constant level
for 240 $pm$ 30 Myr before declining by 2 orders of magnitude to field ages.
Mg II and far-UV pseudocontinuum emission, formed in the stellar chromosphere,
exhibit more gradual evolution with age, declining by 1 and 1.5 orders of
magnitude, respectively. The youngest stars exhibit a scatter of 0.1 dex in
far-UV line and pseudocontinuum flux attributable only to rotational
modulation, long-term activity cycles, or an unknown source of variability.
Saturation-decay fits to these data can predict an M0-M2.5 star’s quiescent
emission in UV lines and the far-UV pseudocontinuum with an accuracy of 0.2-0.3
dex, the most accurate means presently available. Predictions of UV emission
will be useful for studying exoplanetary atmospheric evolution, the destruction
and abiotic production of biologically relevant molecules, and interpreting
infrared and optical planetary spectra measured with observatories like the
James Webb Space Telescope.

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