HD 76920b pinned down: a detailed analysis of the most eccentric planetary system around an evolved star. (arXiv:2102.08902v1 [astro-ph.EP])
<a href="http://arxiv.org/find/astro-ph/1/au:+Bergmann_C/0/1/0/all/0/1">C. Bergmann</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Jones_M/0/1/0/all/0/1">M. I. Jones</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zhao_J/0/1/0/all/0/1">J. Zhao</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Brahm_R/0/1/0/all/0/1">R. Brahm</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Torres_P/0/1/0/all/0/1">P. Torres</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wittenmyer_R/0/1/0/all/0/1">R. A. Wittenmyer</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Gunn_F/0/1/0/all/0/1">F. Gunn</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Pollard_K/0/1/0/all/0/1">K. R. Pollard</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Zapata_A/0/1/0/all/0/1">A. Zapata</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Vanzi_L/0/1/0/all/0/1">L. Vanzi</a>, <a href="http://arxiv.org/find/astro-ph/1/au:+Wang_S/0/1/0/all/0/1">S. Wang</a>

We present 63 new multi-site radial velocity measurements of the K1III giant
HD 76920, which was recently reported to host the most eccentric planet known
to orbit an evolved star. We focussed our observational efforts on the time
around the predicted periastron passage and achieved near-continuous phase
coverage of the corresponding radial velocity peak. By combining our radial
velocity measurements from four different instruments with previously published
ones, we confirm the highly eccentric nature of the system, and find an even
higher eccentricity of $e=0.8782 pm 0.0025$, an orbital period of
$415.891^{+0.043}_{-0.039},mathrm{d}$, and a minimum mass of
$3.13^{+0.41}_{-0.43},mathrm{M_J}$ for the planet. The uncertainties in the
orbital elements are greatly reduced, especially for the period and
eccentricity. We also performed a detailed spectroscopic analysis to derive
atmospheric stellar parameters, and thus the fundamental stellar parameters
($M_*, R_*, L_*$), taking into account the parallax from Gaia DR2, and
independently determined the stellar mass and radius using asteroseismology.
Intriguingly, at periastron the planet comes to within 2.4 stellar radii of its
host star’s surface. However, we find that the planet is not currently
experiencing any significant orbital decay and will not be engulfed by the
stellar envelope for at least another $50-80$ Myr. Finally, while we calculate
a relatively high transit probability of $16%$, we did not detect a transit in
the TESS photometry.

We present 63 new multi-site radial velocity measurements of the K1III giant
HD 76920, which was recently reported to host the most eccentric planet known
to orbit an evolved star. We focussed our observational efforts on the time
around the predicted periastron passage and achieved near-continuous phase
coverage of the corresponding radial velocity peak. By combining our radial
velocity measurements from four different instruments with previously published
ones, we confirm the highly eccentric nature of the system, and find an even
higher eccentricity of $e=0.8782 pm 0.0025$, an orbital period of
$415.891^{+0.043}_{-0.039},mathrm{d}$, and a minimum mass of
$3.13^{+0.41}_{-0.43},mathrm{M_J}$ for the planet. The uncertainties in the
orbital elements are greatly reduced, especially for the period and
eccentricity. We also performed a detailed spectroscopic analysis to derive
atmospheric stellar parameters, and thus the fundamental stellar parameters
($M_*, R_*, L_*$), taking into account the parallax from Gaia DR2, and
independently determined the stellar mass and radius using asteroseismology.
Intriguingly, at periastron the planet comes to within 2.4 stellar radii of its
host star’s surface. However, we find that the planet is not currently
experiencing any significant orbital decay and will not be engulfed by the
stellar envelope for at least another $50-80$ Myr. Finally, while we calculate
a relatively high transit probability of $16%$, we did not detect a transit in
the TESS photometry.

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