The Habitable-zone Planet Finder Reveals A High Mass and a Low Obliquity for the Young Neptune K2-25b. (arXiv:2007.12766v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Stefansson_G/0/1/0/all/0/1">Gudmundur Stefansson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Mahadevan_S/0/1/0/all/0/1">Suvrath Mahadevan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Maney_M/0/1/0/all/0/1">Marissa Maney</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ninan_J/0/1/0/all/0/1">Joe P. Ninan</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Robertson_P/0/1/0/all/0/1">Paul Robertson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Rajagopal_J/0/1/0/all/0/1">Jayadev Rajagopal</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Haase_F/0/1/0/all/0/1">Flynn Haase</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Allen_L/0/1/0/all/0/1">Lori Allen</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ford_E/0/1/0/all/0/1">Eric B. Ford</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Winn_J/0/1/0/all/0/1">Joshua Winn</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wolfgang_A/0/1/0/all/0/1">Angie Wolfgang</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Dawson_R/0/1/0/all/0/1">Rebekah I. Dawson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wisniewski_J/0/1/0/all/0/1">John Wisniewski</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Bender_C/0/1/0/all/0/1">Chad F. Bender</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Canas_C/0/1/0/all/0/1">Caleb Cañas</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Cochran_W/0/1/0/all/0/1">William Cochran</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Diddams_S/0/1/0/all/0/1">Scott A. Diddams</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Fredrick_C/0/1/0/all/0/1">Connor Fredrick</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Halverson_S/0/1/0/all/0/1">Samuel Halverson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hearty_F/0/1/0/all/0/1">Fred Hearty</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Hebb_L/0/1/0/all/0/1">Leslie Hebb</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Kanodia_S/0/1/0/all/0/1">Shubham Kanodia</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Levi_E/0/1/0/all/0/1">Eric Levi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Metcalf_A/0/1/0/all/0/1">Andrew J. Metcalf</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Monson_A/0/1/0/all/0/1">Andrew Monson</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Ramsey_L/0/1/0/all/0/1">Lawrence Ramsey</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Roy_A/0/1/0/all/0/1">Arpita Roy</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Schwab_C/0/1/0/all/0/1">Christian Schwab</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Terrien_R/0/1/0/all/0/1">Ryan Terrien</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wright_J/0/1/0/all/0/1">Jason T. Wright</a>
Using radial-velocity data from the Habitable-zone Planet Finder, we have
measured the mass of the Neptune-sized planet K2-25b, as well as the obliquity
of its M4.5-dwarf host star in the 600-800MYr Hyades cluster. This is one of
the youngest planetary systems for which both of these quantities have been
measured, and one of the very few M dwarfs with a measured obliquity. Based on
a joint analysis of the radial velocity data, time-series photometry from the
K2 mission, and new transit light curves obtained with diffuser-assisted
photometry, the planet’s radius and mass are $3.44pm 0.12 mathrm{R_oplus}$
and $24.5_{-5.2}^{+5.7} mathrm{M_oplus}$. These properties are compatible
with a rocky core enshrouded by a thin hydrogen-helium atmosphere (5% by mass).
We measure an orbital eccentricity of $e=0.43 pm 0.05$. The sky-projected
stellar obliquity is $lambda=3 pm 16^{circ}$, compatible with spin-orbit
alignment, in contrast to other “hot Neptunes” that have been studied around
older stars.
Using radial-velocity data from the Habitable-zone Planet Finder, we have
measured the mass of the Neptune-sized planet K2-25b, as well as the obliquity
of its M4.5-dwarf host star in the 600-800MYr Hyades cluster. This is one of
the youngest planetary systems for which both of these quantities have been
measured, and one of the very few M dwarfs with a measured obliquity. Based on
a joint analysis of the radial velocity data, time-series photometry from the
K2 mission, and new transit light curves obtained with diffuser-assisted
photometry, the planet’s radius and mass are $3.44pm 0.12 mathrm{R_oplus}$
and $24.5_{-5.2}^{+5.7} mathrm{M_oplus}$. These properties are compatible
with a rocky core enshrouded by a thin hydrogen-helium atmosphere (5% by mass).
We measure an orbital eccentricity of $e=0.43 pm 0.05$. The sky-projected
stellar obliquity is $lambda=3 pm 16^{circ}$, compatible with spin-orbit
alignment, in contrast to other “hot Neptunes” that have been studied around
older stars.
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