Zodiacal Exoplanets in Time. XI. The Orbit and Radiation Environment of the Young M Dwarf-Hosted Planet K2-25b. (arXiv:2007.12701v1 [astro-ph.EP])

Zodiacal Exoplanets in Time. XI. The Orbit and Radiation Environment of the Young M Dwarf-Hosted Planet K2-25b. (arXiv:2007.12701v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Gaidos_E/0/1/0/all/0/1">E. Gaidos</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hirano_T/0/1/0/all/0/1">T. Hirano</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wilson_D/0/1/0/all/0/1">D. J. Wilson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+France_K/0/1/0/all/0/1">K. France</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rockcliffe_K/0/1/0/all/0/1">K. Rockcliffe</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Newton_E/0/1/0/all/0/1">E. Newton</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Feiden_G/0/1/0/all/0/1">G. Feiden</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Krishnamurthy_V/0/1/0/all/0/1">V. Krishnamurthy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Harakawa_H/0/1/0/all/0/1">H. Harakawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hodapp_K/0/1/0/all/0/1">K. W. Hodapp</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ishizuka_M/0/1/0/all/0/1">M. Ishizuka</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jacobson_S/0/1/0/all/0/1">S. Jacobson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Konishi_M/0/1/0/all/0/1">M. Konishi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kotani_T/0/1/0/all/0/1">T. Kotani</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kudo_T/0/1/0/all/0/1">T. Kudo</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kurokawa_T/0/1/0/all/0/1">T. Kurokawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kuzuhara_M/0/1/0/all/0/1">M. Kuzuhara</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Nishikawa_J/0/1/0/all/0/1">J. Nishikawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Omiya_M/0/1/0/all/0/1">M. Omiya</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Serizawa_T/0/1/0/all/0/1">T. Serizawa</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Tamura_M/0/1/0/all/0/1">M. Tamura</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ueda_A/0/1/0/all/0/1">A. Ueda</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vievard_S/0/1/0/all/0/1">S. Vievard</a>

M dwarf stars are high-priority targets for searches for Earth-size and
potentially Earth-like planets, but their planetary systems may form and evolve
in very different circumstellar environments than those of solar-type stars. To
explore the evolution of these systems, we obtained transit spectroscopy and
photometry of the Neptune-size planet orbiting the ~650 Myr-old Hyades M dwarf
K2-25. An analysis of the variation in spectral line shape induced by the
Doppler “shadow” of the planet indicate that the planet’s orbit is closely
aligned with the stellar equator (lambda = -1.7+5.8/-3.7 deg), and that an
eccentric orbit found by previous work could arise from perturbations by
another planet on a co-planar orbit. We detect no significant variation in the
depth of the He I line at 1083 nm during transit. A model of atmospheric escape
as a isothermal Parker wind with a solar composition show that this
non-detection is not constraining compared to escape rate predictions of ~0.1
Mearth/Gyr; at such rates, at least several Gyr are required for a Neptune-like
planet to evolve into a rocky super-Earth.

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