J/AJ/170/51 HD 93963 radial velocities from Keck/KPF (Teng+, 2025)
Stellar obliquity of the ultra-short-period planet system HD 93963.
Teng H.-Y., Dai F., Howard A.W., Halverson S., Isaacson H., Kokubo E.,
Rubenzahl R.A., Fulton B., Householder A., Lubin J., Giacalone S.,
Handley L., Van Zandt J., Petigura E.A., Ong J.M.J., Premnath P., Yu H.,
Gibson S.R., Rider K., Roy A., Baker A., Edelstein J., Smith C.,
Walawender J., Lee B.-C., Liu Y.-J., Winn J.N.
<Astron. J., 170, 51 (2025)>
=2025AJ....170...51T 2025AJ....170...51T
ADC_Keywords: Exoplanets; Radial velocities; Spectroscopy; Optical
Keywords: Exoplanets ; Mini Neptunes ; Super Earths ; Exoplanet dynamics
Abstract:
We report an observation of the Rossiter-McLaughlin (RM) effect of the
transiting planet HD 93963 Ac, a mini-Neptune planet orbiting a
G0-type star with an orbital period of Pc=3.65d, accompanied by an
inner super-Earth planet with Pb=1.04d. We observed a full transit
of planet c on 2024 May 3 UT with the Keck/Keck Planet Finder. The
observed RM effect has an amplitude of ∼1m/s and implies a
sky-projected obliquity of λ=14-19+17 degrees for HD 93963
Ac. Our dynamical analysis suggests that the two inner planets are
likely well aligned with the stellar spin, to within a few degrees,
thus allowing both to transit. Along with WASP-47, 55 Cnc, and HD
3167, HD 93963 is the fourth planetary system with an
ultrashort-period planet and obliquity measurement(s) of any planet(s)
in the system. HD 93963, WASP-47, and 55 Cnc favor largely coplanar
orbital architectures, whereas HD 3167 has been reported to have a
large mutual inclination (∼100°) between its transiting planets b
and c. In this configuration, the probability that both planets
transit is low. Moreover, one planet would quickly evolve to be
nontransiting due to nodal precession. Future missions such as
ESO/PLATO should detect the resulting transit duration variations. We
encourage additional obliquity measurements of the HD 3167 system to
better constrain its orbital architecture.
Description:
We observed the RM effect of HD 93963 Ac on 2024 May 3 (UTC) with the
Keck Planet Finder (KPF) on the 10m Keck I Telescope at Maunakea,
Hawaii, USA. The spectrograph offers a resolution of ∼98,000 and
covers a wavelength range of 4450-8700Å. KPF achieves a noise floor
of ∼0.3m/s.
The binary companion is located 5.9" away (Serrano+2022, J/A+A/667/A1),
far enough for its light to be excluded from our spectroscopic
observations. We scheduled the observations according to the ephemeris
provided by Serrano+2022 and captured the full transit event.
Observations began ∼1.2hr before ingress and ended ∼1.1hr after
egress. We used an exposure time of 360s, yielding a signal-to-noise
ratio (S/N) of ∼270 near 5500Å. In total, we obtained 43 usable
spectra, 25 of which were taken during the transit.
We observed HD 93963 A with Keck/HIRES in iodine-free mode on 2020
December 25 to refine the stellar parameters. The spectrum was
obtained with an S/N of 105 at the spectral center, under a spectral
resolution of ∼72,000 and wavelength range of 3360-8100Å. The
raw frames and the spectral information can be downloaded from the
Keck Observatory Archive website.
We measured the stellar rotational period of HD 93963 A using TESS
photometry. HD 93963 A was observed by TESS during Sectors 22
(2020 February 18 to 2020 March 18) and 48 (2022 January 28 to
2022 February 26) at a 2min cadence. We downloaded the light curves
from the Mikulski Archive for Space Telescopes (MAST). Two transiting
planets (b and c) orbiting HD 93963 A were confirmed from the TESS
light curve.
Objects:
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RA (2000) DE Designation(s)
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10 51 06.51 +25 38 28.1 HD 93963 = Gaia DR3 729899906357408768
10 51 06.51 +25 38 28.1 HD 93963c = HD 93963Ac
10 51 06.51 +25 38 28.1 HD 93963b = HD 93963Ab
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 24 43 Keck/KPF radial velocity data during transit
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See also:
I/350 : Gaia EDR3 (Gaia Collaboration, 2020)
I/355 : Gaia DR3 Part 1. Main source (Gaia Collaboration, 2022)
VI/120 : High-resolution synthetic stellar library (Coelho+, 2005)
J/ApJS/159/141 : Spectroscopic properties of cool stars. I. (Valenti+, 2005)
J/ApJ/757/18 : RVs for 16 hot Jupiter host stars (Albrecht+, 2012)
J/ApJ/790/146 : Planets in Kepler's multi-transiting systems (Fabrycky+, 2014)
J/ApJ/787/47 : 106 Kepler ultra-short-period planets (Sanchis-Ojeda+, 2014)
J/ApJ/821/47 : KOI transit proba. of multi-planet syst. (Brakensiek+, 2016)
J/AJ/154/109 : California-Kepler Surv. (CKS). III. Planet radii (Fulton+, 2017)
J/ApJ/844/102 : KIC star plxs from asteroseismology vs Gaia (Huber+, 2017)
J/AJ/154/107 : California-Kepler Survey (CKS). I. 1305 stars (Petigura+, 2017)
J/ApJ/836/77 : A library of high-S/N optical spectra of FGKM stars (Yee+, 2017)
J/AJ/156/264 : California-Kepler Survey. VII. Planet radius gap (Fulton+, 2018)
J/AJ/155/48 : California-Kepler Survey (CKS). V. Masses & radii (Weiss+, 2018)
J/A+A/667/A1 : HD93963 CHEOPS light curves (Serrano+, 2022)
J/AJ/166/33 : The TESS-Keck Survey. XV. 108 TESS Planets (MacDougall+, 2023)
J/AJ/168/109 : Resonant and ultra-short-period planet systems (Schmidt+, 2024)
J/AJ/169/235 : TESS-Keck Survey. XXIV. 47 distant giants RVs (Van Zandt+, 2025)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 11 F11.6 d BJD [3433.72/3433.93] Barycentric Julian Date -
2457000 (1)
13- 18 F6.3 m/s RVel [-2.69/3.23] Radial velocity
20- 24 F5.3 m/s e_RVel [0.33/0.55] Uncertainty in RV
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Note (1): The airmass ranged from 1.01 and 1.26 during the observation. More
information about the observing weather condition can be found at
http://mkwc.ifa.hawaii.edu.
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History:
From electronic version of the journal
(End) Prepared by [AAS], Robin Leichtnam [CDS] 29-Apr-2026