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HD 76920 b pinned down : A detailed analysis of the most eccentric planetary system around an evolved star

Bergmann, C. ; Jones, M. I. ; Zhao, J. ; Mustill, A. J. LU orcid ; Brahm, R. ; Torres, P. ; Wittenmyer, R. A. ; Gunn, F. ; Pollard, K. R. and Zapata, A. , et al. (2021) In Publications of the Astronomical Society of Australia 38.
Abstract

We present 63 new multi-site radial velocity (RV) measurements of the K1III giant HD 76920, which was recently reported to host the most eccentric planet known to orbit an evolved star. We focused our observational efforts on the time around the predicted periastron passage and achieved near-continuous phase coverage of the corresponding RV peak. By combining our RV 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 <![CDATA[ $e=0.8782 \pm 0.0025$ ]]>, an orbital period of <![CDATA[ $415.891^{+0.043}_{-0.039}\,\textrm{d}$ ]]>, and a minimum mass of <![CDATA[ $3.13^{+0.41}_{-0.43}\,\textrm{M}_{\textrm{J}}$... (More)

We present 63 new multi-site radial velocity (RV) measurements of the K1III giant HD 76920, which was recently reported to host the most eccentric planet known to orbit an evolved star. We focused our observational efforts on the time around the predicted periastron passage and achieved near-continuous phase coverage of the corresponding RV peak. By combining our RV 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 <![CDATA[ $e=0.8782 \pm 0.0025$ ]]>, an orbital period of <![CDATA[ $415.891^{+0.043}_{-0.039}\,\textrm{d}$ ]]>, and a minimum mass of <![CDATA[ $3.13^{+0.41}_{-0.43}\,\textrm{M}_{\textrm{J}}$ ]]> 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 (<![CDATA[ $M_∗, R_∗, L_∗$ ]]>), 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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organization
publishing date
type
Contribution to journal
publication status
published
subject
keywords
76920, Keywords:, planetary systems, stars: individual: HD, techniques: radial velocities
in
Publications of the Astronomical Society of Australia
volume
38
article number
e019
publisher
CSIRO Publishing
external identifiers
  • scopus:85104929656
ISSN
1323-3580
DOI
10.1017/pasa.2021.8
project
A unified picture of white dwarf planetary systems
What will the PLATO observatory tell us about star-planet tidal interactions?
IMPACT: Comets, asteroids and the habitability of planets
language
English
LU publication?
yes
id
88a282b5-7ad8-4ded-aaf8-b1135f2f8b35
alternative location
https://arxiv.org/abs/2102.08902
date added to LUP
2021-05-17 11:38:36
date last changed
2024-04-20 06:20:21
@article{88a282b5-7ad8-4ded-aaf8-b1135f2f8b35,
  abstract     = {{<p>We present 63 new multi-site radial velocity (RV) measurements of the K1III giant HD 76920, which was recently reported to host the most eccentric planet known to orbit an evolved star. We focused our observational efforts on the time around the predicted periastron passage and achieved near-continuous phase coverage of the corresponding RV peak. By combining our RV 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 &lt;![CDATA[ $e=0.8782 \pm 0.0025$ ]]&gt;, an orbital period of &lt;![CDATA[ $415.891^{+0.043}_{-0.039}\,\textrm{d}$ ]]&gt;, and a minimum mass of &lt;![CDATA[ $3.13^{+0.41}_{-0.43}\,\textrm{M}_{\textrm{J}}$ ]]&gt; 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 (&lt;![CDATA[ $M_∗, R_∗, L_∗$ ]]&gt;), 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. </p>}},
  author       = {{Bergmann, C. and Jones, M. I. and Zhao, J. and Mustill, A. J. and Brahm, R. and Torres, P. and Wittenmyer, R. A. and Gunn, F. and Pollard, K. R. and Zapata, A. and Vanzi, L. and Wang, Songhu}},
  issn         = {{1323-3580}},
  keywords     = {{76920; Keywords:; planetary systems; stars: individual: HD; techniques: radial velocities}},
  language     = {{eng}},
  month        = {{04}},
  publisher    = {{CSIRO Publishing}},
  series       = {{Publications of the Astronomical Society of Australia}},
  title        = {{HD 76920 b pinned down : A detailed analysis of the most eccentric planetary system around an evolved star}},
  url          = {{http://dx.doi.org/10.1017/pasa.2021.8}},
  doi          = {{10.1017/pasa.2021.8}},
  volume       = {{38}},
  year         = {{2021}},
}