J/AJ/170/34 TESS & KPF: TOI-2364 light & radial velocity curves (Tamburo+, 2025)
The true stellar obliquity of a sub-Saturn planet from the Tierras Observatory
and the Keck Planet Finder.
Tamburo P., Yee S.W., Garcia-mejia J., Stefansson G., Charbonneau D.,
Bieryla A., Howard A.W., Isaacson H., Fulton B.J., Householder A.
<Astron. J. 170, 34 (2025)>
=2025AJ....170...34T 2025AJ....170...34T (SIMBAD/NED BibCode)
ADC_Keywords: Exoplanets; Photometry, infrared; Spectroscopy; Radial velocities
Keywords: Exoplanet astronomy; Exoplanet systems; Planet hosting stars
Planetary alignment; Infrared photometry; Transits; Stellar rotation
Starspots
Abstract:
We measure the true obliquity of TOI-2364, a K dwarf with a
sub-Saturn-mass (Mp=0.18MJ) transiting planet on the upper edge of
the hot-Neptune desert. We used new Rossiter-McLaughlin observations
gathered with the Keck Planet Finder to measure the sky-projected
obliquity λ=7°+10°-11°. Combined with a stellar
rotation period of 23.47±0.29days measured with photometry from the
Tierras Observatory, this yields a stellar inclination of
90°±13° and a true obliquity ψ=15:6+7:7-7:3, indicating
that the planet's orbit is well aligned with the rotation axis of its
host star. The determination of ψ is important for investigating a
potential bimodality in the orbits of short-period sub-Saturns around
cool stars, which tend to be either aligned with or perpendicular to
their host stars' spin axes.
Description:
We observed a spectroscopic transit of TOI-2364b on UT 2023 October
22, using the newly commissioned optical spectrometer Keck Planet
Finder (KPF) on the Keck I telescope in Hawaii, USA. We obtained 31
exposures of 480s each in standard readout mode, over a total
observation time of 4.5hr, covering the full transit of the planet and
roughly 2hr of posttransit baseline.
We also obtained photometric observations of TOI-2364 from the
KeplerCam CCD on the 1.2m telescope at the Fred Lawrence Whipple
Observatory in Arizona, USA, catching the transit ingress
contemporaneous with the KPF observations on UT 2023 October 22. We
made observations in the Sloan i' filter with an exposure time of 18s.
We observed TOI-2364 with Tierras, a 1.3m telescope located at Fred
Lawrence Whipple Observatory in Arizona, USA, from UT 2024 October 4
to 2025 March 20. We took observations at a 30s exposure time and
typically performed 2-4 visits to the field over the course of each
observing night, each with a duration of about 5min. We obtained a
total of 1856 exposures of TOI-2364 with Tierras, and a total of 1249
photometric data points after quality selection.
TOI-2364 was observed by TESS (Transiting Exoplanet Survey Satellite)
in Sectors 6 (2018 December 11 to 2019 January 07), 33 (2020 December 17
to 2021 January 13), and 87 (2024 December 18 to 2025 January 14),
with cadences of 30 minutes, 10 minutes, and 2 minutes, respectively.
Objects:
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RA (2000) DE Designation(s)
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05 56 31.19 -05 00 43.0 TOI-2364 = Gaia DR3 3022644120017418496
05 56 31.19 -05 00 43.0 TOI-2364b = TOI-2364b
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
fig3a.dat 36 1338 TESS light curves of TOI-2364
fig3b.dat 42 398 KeplerCam light curve of TOI-2364
fig3c.dat 31 31 Kepler Planet Finder radial velocity curve of
TOI-2364
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See also:
J/PASP/134/H2001 : Stellar obliquities in exoplanetary syst. (Albrecht+, 2022)
J/MNRAS/474/2094 : Inferring probabilistic stellar rot. periods (Angus+, 2018)
J/AJ/168/185 : HATS-38b & WASP-139b: LCs & RVs (Espinoza-Retamal+, 2024)
J/A+A/690/A379 : Obliquities of exoplanet host stars (Knudstrup+, 2024)
J/MNRAS/510/5623 : Study of Kepler's FGKM stars (Masuda+, 2022)
J/ApJS/211/24 : Rotation periods of Kepler MS stars (McQuillan+, 2014)
J/A+A/557/L10 : Rotation periods of 12000 Kepler stars (Nielsen+, 2013)
J/A+A/635/A43 : Stellar rot. periods from K2 Campaigns 0-18 (Reinhold+, 2020)
J/ApJ/931/L15 : Obs. of two transits of GJ 3470b with NEID (Stefansson+, 2022)
J/AJ/163/253 : The Perkins INfrared Exosatellite Survey. I. (Tamburo+, 2022)
J/ApJS/159/141 : Spectroscopic properties of cool stars. I. (Valenti+, 2005)
J/ApJ/700/302 : Relative photometry of XO-3 (Winn+, 2009)
J/ApJS/265/1 : TESS Grand Unified Hot Jupiter Surveys. II. (Yee+, 2023)
Byte-by-byte Description of file: fig3a.dat
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Bytes Format Units Label Explanations
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1- 3 A3 --- Sector TESS sector identifier (1)
5- 18 F14.6 d BJD [2458471/2460687] Barycentric Julian Date; TDB
20- 27 F8.6 --- NFlux [0.98/1.01] Normalized flux
29- 36 F8.6 --- e_NFlux [6e-4/3e-3] Uncertainty in NFlux
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Note (1): TESS Sectors as follows:
S6 = Sector 6, 2018 December 11 to 2019 January 07 (82 occurrences)
S33 = Sector 33, 2020 December 17 to 2021 January 13 (290 occurrences)
S87 = Sector 87, 2024 December 18 to 2025 January 14 (966 occurrences)
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Byte-by-byte Description of file: fig3b.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD [2460239/2460241] Barycentric Julian Date; TDB
16- 23 F8.6 --- NFlux [0.98/1.02] Normalized flux
25- 32 F8.6 --- e_NFlux [1.1e-3/1.2e-3] Uncertainty in NFlux
34- 42 F9.6 --- Air [-0.3/1] Airmass
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Byte-by-byte Description of file: fig3c.dat
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Bytes Format Units Label Explanations
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1- 16 F16.8 d BJD [2460239/2460241] Barycentric Julian Date; TDB
18- 24 F7.4 m/s RVel [54.7/54.8] Radial velocity
26- 31 F6.4 m/s e_RVel [1.8e-3/2.2e-3] Uncertainty in RVel
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 15-Apr-2026