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TESS and CHEOPS discover two warm sub-Neptunes transiting the bright K-dwarf HD 15906

Tuson, A. ; Davies, M.B. LU and Wohler, B. (2023) In Monthly Notices of the Royal Astronomical Society 523(2). p.3090-3118
Abstract
We report the discovery of two warm sub-Neptunes transiting the bright (G = 9.5 mag) K-dwarf HD 15906 (TOI 461, TIC 4646810). This star was observed by the Transiting Exoplanet Survey Satellite (TESS) in sectors 4 and 31, revealing two small transiting planets. The inner planet, HD 15906 b, was detected with an unambiguous period but the outer planet, HD 15906 c, showed only two transits separated by ∼ 734 d, leading to 36 possible values of its period. We performed follow-up observations with the CHaracterising ExOPlanet Satellite (CHEOPS) to confirm the true period of HD 15906 c and improve the radius precision of the two planets. From TESS, CHEOPS, and additional ground-based photometry, we find that HD 15906 b has a radius of 2.24 ±... (More)
We report the discovery of two warm sub-Neptunes transiting the bright (G = 9.5 mag) K-dwarf HD 15906 (TOI 461, TIC 4646810). This star was observed by the Transiting Exoplanet Survey Satellite (TESS) in sectors 4 and 31, revealing two small transiting planets. The inner planet, HD 15906 b, was detected with an unambiguous period but the outer planet, HD 15906 c, showed only two transits separated by ∼ 734 d, leading to 36 possible values of its period. We performed follow-up observations with the CHaracterising ExOPlanet Satellite (CHEOPS) to confirm the true period of HD 15906 c and improve the radius precision of the two planets. From TESS, CHEOPS, and additional ground-based photometry, we find that HD 15906 b has a radius of 2.24 ± 0.08 R and a period of 10.924709 ± 0.000032 d, whilst HD 15906 c has a radius of 2.93+−000607 R and a period of 21.583298+−00000055000052 d. Assuming zero bond albedo and full day-night heat redistribution, the inner and outer planet have equilibrium temperatures of 668 ± 13 K and 532 ± 10 K, respectively. The HD 15906 system has become one of only six multiplanet systems with two warm (700 K) sub-Neptune sized planets transiting a bright star (G ≤ 10 mag). It is an excellent target for detailed characterization studies to constrain the composition of sub-Neptune planets and test theories of planet formation and evolution. © 2023 The Author(s). (Less)
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keywords
planets and satellites: detection, planets and satellites: fundamental parameters, stars: fundamental parameters, stars: individual: HD 15906 (TOI 461, TIC 4646810), techniques: photometric, Extrasolar planets, Photometry, Stars, Exo-planets, Neptune, Outer planets, Planets and satellites: detections, Planets and satellites: fundamental parameters, Star: individual: HD 15906 (TOI 461, TIC 4646810), Stars: Be, Stars: individual: proxima Centauri, Stars:fundamental parameters, Techniques: photometric, Satellites
in
Monthly Notices of the Royal Astronomical Society
volume
523
issue
2
pages
29 pages
publisher
Oxford University Press
external identifiers
  • scopus:85162781287
ISSN
0035-8711
DOI
10.1093/mnras/stad1369
language
English
LU publication?
yes
id
451327bc-8b15-4bd7-9753-95f4c7fbbe51
date added to LUP
2023-11-15 11:26:43
date last changed
2023-11-15 11:28:11
@article{451327bc-8b15-4bd7-9753-95f4c7fbbe51,
  abstract     = {{We report the discovery of two warm sub-Neptunes transiting the bright (G = 9.5 mag) K-dwarf HD 15906 (TOI 461, TIC 4646810). This star was observed by the Transiting Exoplanet Survey Satellite (TESS) in sectors 4 and 31, revealing two small transiting planets. The inner planet, HD 15906 b, was detected with an unambiguous period but the outer planet, HD 15906 c, showed only two transits separated by ∼ 734 d, leading to 36 possible values of its period. We performed follow-up observations with the CHaracterising ExOPlanet Satellite (CHEOPS) to confirm the true period of HD 15906 c and improve the radius precision of the two planets. From TESS, CHEOPS, and additional ground-based photometry, we find that HD 15906 b has a radius of 2.24 ± 0.08 R and a period of 10.924709 ± 0.000032 d, whilst HD 15906 c has a radius of 2.93+−000607 R and a period of 21.583298+−00000055000052 d. Assuming zero bond albedo and full day-night heat redistribution, the inner and outer planet have equilibrium temperatures of 668 ± 13 K and 532 ± 10 K, respectively. The HD 15906 system has become one of only six multiplanet systems with two warm (700 K) sub-Neptune sized planets transiting a bright star (G ≤ 10 mag). It is an excellent target for detailed characterization studies to constrain the composition of sub-Neptune planets and test theories of planet formation and evolution. © 2023 The Author(s).}},
  author       = {{Tuson, A. and Davies, M.B. and Wohler, B.}},
  issn         = {{0035-8711}},
  keywords     = {{planets and satellites: detection; planets and satellites: fundamental parameters; stars: fundamental parameters; stars: individual: HD 15906 (TOI 461, TIC 4646810); techniques: photometric; Extrasolar planets; Photometry; Stars; Exo-planets; Neptune; Outer planets; Planets and satellites: detections; Planets and satellites: fundamental parameters; Star: individual: HD 15906 (TOI 461, TIC 4646810); Stars: Be; Stars: individual: proxima Centauri; Stars:fundamental parameters; Techniques: photometric; Satellites}},
  language     = {{eng}},
  number       = {{2}},
  pages        = {{3090--3118}},
  publisher    = {{Oxford University Press}},
  series       = {{Monthly Notices of the Royal Astronomical Society}},
  title        = {{TESS and CHEOPS discover two warm sub-Neptunes transiting the bright K-dwarf HD 15906}},
  url          = {{http://dx.doi.org/10.1093/mnras/stad1369}},
  doi          = {{10.1093/mnras/stad1369}},
  volume       = {{523}},
  year         = {{2023}},
}