J/A+A/702/A69 TOI-1438 HARPS-N and HIRES radial velocities (Persson+, 2025)
TOI-1438: A rare system with two short-period sub-Neptunes and a tentative
long-period Jupiter-like planet orbiting a K0V star.
Persson C.M., Knudstrup E., Carleo I., Acuna-Aguirre L., Nowak G.,
Muresan A., Jankowski D., Gozdziewski K., Garcia R.A., Mathur S.,
Palakkatharappil D.B., Borg L., Mustill A.J., Barrena R., Fridlund M.,
Gandolfi D., Hatzes A.P., Korth J., Luque R., Martin E.L., Masseron T.,
Morello G., Murgas F., Orell-Miquel J., Palle E., Albrecht S.H., Bieryla A.,
Cochran W.D., Crossfield I.J.M., Deeg H.J., Furlan E., Guenther E.W.,
Howell S.B., Isaacson H., Lam K.W.F., Livingston J., Matson R.A.,
Matthews E.C., Redfield S., Schlieder Jo.E., Seager S., Smith Al.M.S.,
Stassun K.G., Twicken J.D., Van Eylen V., Watkins C.N., Weiss L.M.
<Astron. Astrophys. 702, A69 (2025)>
=2025A&A...702A..69P 2025A&A...702A..69P (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Radial velocities ;
Optical
Keywords: planets and satellites: composition -
planets and satellites: detection -
techniques: photometric - techniques: radial velocity -
planets and satellites: fundamental parameters -
planets and satellites: general - planets and satellites: interiors
Abstract:
We present the detection and characterisation of the TOI-1438
multi-planet system discovered by the Transiting Exoplanet Survey
Satellite (TESS). To confirm the planetary nature of the candidates
and determine their masses, we collected a series of follow-up
observations including high-spectral resolution observations with
HARPS-N and HIRES over a period of five years. Our combined modelling
shows that the K0V star hosts two transiting sub-Neptunes with
Rb=3.04±0.19R⊕, Rc=2.75±0.14R⊕,
Mb=9.4±1.8M⊕, and Mc=10.6±2.1M⊕. The orbital
periods of planets b and c are 5.1 and 9.4 days, respectively,
corresponding to instellations of 145±10F⊕ and
65±4F⊕. The bulk densities are 1.8±0.5 and
2.9±0.7g/cm3, respectively, suggesting a volatile-rich interior
composition. We computed a set of planet interior structure models.
Planet b presents a high-metallicity envelope that can accommodate up
to 2.5% in H/He in mass, while planet c cannot have more than 0.2% as
H/He in mass. For any composition of the core considered (Fe-rock or
ice-rock), both planets would require a volatile-rich envelope. In
addition to the two planets, the radial velocity (RV) data clearly
reveal a third signal, likely coming from a non-transiting planet,
with an orbital period of 7.6+1.6-2.4 years and a radial velocity
semi-amplitude of 35+3-5m/s. Our best fit model finds a minimum
mass of 2.1±0.3MJ and an eccentricity of 0.25+0.08-0.11.
However, several RV activity indicators also show strong signals at
similar periods, suggesting this signal might (partly) originate from
stellar activity. More data over a longer period of time are needed to
conclusively determine the nature of this signal. If it is confirmed
as a triple-planet system, TOI-1438 would be one of the few detected
systems to date characterised by an architecture with two small,
short-period planets and one massive, long-period planet, where the
inner and outer systems are separated by an orbital period ratio of
the order of a few hundred.
Description:
Within the KESPRINT consortium program, we observed TOI-1438 with the
high resolution spectrograph HARPS-N mounted on the 3.58-m Telescopio
Nazionale Galileo (TNG) of Roque de los Muchachos Observatory in La
Palma5 covering wavelengths between 378nm and 691nm at a spectral
resolution of R∼115000. We followed this target between 17 March 2020
and 15 March 2025 collecting 85 RVs with exposure times of 1500-3300s
and an average signal-to-noise ratio (S/N) of 51 at 550nm.
We collected 20 spectra with the High Resolution Echelle Spectrometer
(HIRES) at the Keck Observatory over two years. With a resolving power
of ∼60000 and wavelength range from 374-970nm, HIRES provided
precision RVs with a median uncertainty of 1.7m/s from spectra with an
S/N of 150 for TOI-1438.
We tabulate radial velocities (RVs) of TOI-1438 with HARPS-N and
HIRES.
Objects:
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RA (2000) DE Designation(s)
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18 43 41.79 +74 56 15.3 TOI-1438 = 2MASS J18434182+7456152
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 81 85 RVs with HARPS-N, DRS pipeline
tablea2.dat 107 85 RVs with HARPS-N, Serval pipeline
tablea3.dat 63 20 RVs with HIRES
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Byte-by-byte Description of file: tablea1.dat
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Bytes Format Units Label Explanations
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1- 10 F10.5 d Time Barycentric Julian date, TBD (BJD-2457000)
12- 21 F10.3 m/s RV Radial velocity
23- 27 F5.3 m/s e_RV RV error
29- 35 F7.3 m/s BIS Activity indicator, Bisector span of the CCF
37- 41 F5.3 m/s e_BIS BIS error
43- 47 F5.3 km/s FWHM Activity indicator, FWHM of the CCF
49- 54 F6.3 % Contrast Activity indicator, contrast of the CCF
56- 62 F7.4 --- logR'HK Activity indicator, Mount Wilson logRHK index
64- 69 F6.4 --- e_logR'HK log R'HK error
71- 74 F4.1 --- SNR Signal to noise at 550nm
76- 81 F6.1 s ExpTime Exposure time
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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1- 10 F10.5 d Time Barycentric Julian date, TBD (BJD-2457000)
12- 18 F7.3 m/s RV Radial velocity
20- 24 F5.3 m/s e_RV RV error
26- 32 F7.3 m/s CRX Activity indicator, chromatic index
(in m/s/Np unit)
34- 39 F6.3 m/s e_CRX CRX error (in m/s/Np unit)
41- 47 F7.3 m2/s2 dlW Activity indicator, differential linewidth
49- 53 F5.3 m2/s2 e_dlW dlW error
55- 60 F6.4 --- Halpha Activity indicator, Halpha line index
62- 67 F6.4 --- e_Halpha Halpha error
69- 74 F6.4 --- NaD1 Activity indicator, Na D1 index
76- 81 F6.4 --- e_NaD1 NaD1 error
83- 88 F6.4 --- NaD2 Activity indicator, Na D2 index
90- 95 F6.4 --- e_NaD2 NaD2 error
97-100 F4.1 --- SNR Signal to noise at 600nm
102-107 F6.1 s ExpTime Exposure time
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Byte-by-byte Description of file: tablea3.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d Time Barycentric Julian date, TBD (BJD-2457000)
16- 33 F18.14 m/s RV Radial velocity
35- 50 F16.14 m/s e_RV RV error
52- 57 F6.4 --- Sindex Activity indicator, S-index
59- 63 F5.3 --- e_Sindex Sindex error
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Acknowledgements:
Carina M. Persson, carina.persson(at)chalmers.se
(End) Patricia Vannier [CDS] 05-Sep-2025