J/A+A/699/A344 K2-157 light curves and RVs curves (Castro-Gonzalez+, 2025)
Two neighbours to the ultra-short-period Earth-sized planet K2-157 b in the warm
Neptunian savanna.
Castro-Gonzalez A., Bouchy F., Correia A.C.M., Sozzetti A., Lillo-Box J.,
Figueira P., Lavie B., Lovis C., Hobson M.J., Sousa S.G., Adibekyan V.,
Standing M.R., Hara N.C., Barrado D., Silva A.M., Bourrier V., Korth J.,
Santos N.C., Damasso M., Zapatero Osorio M.R., Rodrigues J., Alibert Y.,
Barros S.C.C., Cristiani S., Di Marcantonio P., Gonzalez Hernandez J.I.,
Lo Curto G., Martins C.J.A.P., Nunes N.J., Palle E., Pepe F.,
Suarez Mascareno A., Tabernero H.M.
<Astron. Astrophys. 699, A344 (2025)>
=2025A&A...699A.344C 2025A&A...699A.344C (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Photometry ; Optical ;
Radial velocities ; Spectroscopy
Keywords: techniques: photometric - techniques: radial velocities -
planets and satellites: detection -
planets and satellites: dynamical evolution and stability -
planets and satellites: individual: K2-157 b -
stars: individual: K2-157 (EPIC 201130233)
Abstract:
The formation and evolution of ultra-short-period (USP) rocky planets
is poorly understood. However, it is widely thought that these planets
could not have formed at their present-day close-in orbits, but
instead migrated inwards through interactions with outer neighbours.
We aim to confirm and characterise the USP Earth-sized validated
planet K2-157 b (Porb=8.8h) and constrain the presence of additional
companions in the system through radial velocity (RV) measurements. We
measured 49 RVs with the ESPRESSO spectrograph and tested different
planetary and non-planetary configurations to infer the model that
best represents our data set. We derived the orbital and physical
properties of the system through a global RV and transit model. We
detected two additional super-Neptune-mass planets located within the
warm Neptunian savanna, K2-157 c (Porb,c=25.942+0.045-0.044d,
Mp,csini=30.8±1.9M⊕) and K2-157 d
(Porb,d=66.50+0.71-0.59d, Mp,dsini=23.3±2.5M⊕). The
joint analysis constrains the mass of K2-157 b at the 2.8σ
level, Mp,b=1.14+0.41-0.42M⊕ (<2.4M⊕ at
3σ), which, together with the inferred radius,
Rp=0.935±0.090R⊕, make the planet compatible with a rocky
composition with a likely (68% confidence) higher iron-to-silicate
mass fraction than Earth. K2 data discard non-grazing transit
configurations for K2-157 c (ic<88.4° at 3σ), and ESPRESSO
data constrain the eccentricities of K2-157 c and K2-157 d to ec<0.2
and ed<0.5 at 3σ. Our dynamical analysis indicates that the
system is stable for eccentricities up to ec, ed∼0.3 and mutual
inclinations up to ∼60°. At a population level, we find that the
trend that the closest USP planets tend to orbit late-type stars does
not hold when scaling the orbital separation to the Roche limit, which
suggests that the orbital distribution of the closest planets across
spectral types is primarily determined by tidal disruption. The
orbital architecture of K2-157 is unusual in the known exoplanet
plethora, with only one similar case reported to date: 55 Cnc. The USP
planets of these systems, being accompanied by massive, long-period,
relatively spaced, and possibly misaligned neighbours, could have
migrated inwards through eccentricity-based mechanisms triggered by
secular interactions.
Description:
Photometry and radial velocities used to measure the mass of K2-157 b
and to confirm the planetary nature and measure the minimum masses of
K2-157 c and K2-157 d.
Objects:
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RA (2000) DE Designation(s)
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12 15 00.32 -05 46 55.1 K2-157 = EPIC 201130233
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tableb1.dat 41 2444 K2 everest photometry of K2-157 (Campaign 10)
tableb2.dat 43 18152 TESS PDCSAP photometry of K2-157 (Sector 46)
tableb3.dat 190 49 ESPRESSO radial velocities of K2-157 obtained
under the programs 1102.C-0744, 1102.C-0958,
1104.C-0350, and 106.21M2.004
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Byte-by-byte Description of file: tableb1.dat
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Bytes Format Units Label Explanations
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1- 18 F18.10 d Time Baricentric Julian date (BJD)
20- 37 F18.16 --- Flux K2 everest normalised flux
39- 41 A3 --- Campaign [C10] K2 Campaign
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Byte-by-byte Description of file: tableb2.dat
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Bytes Format Units Label Explanations
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1- 18 F18.10 d Time Baricentric Julian date (BJD)
20- 28 F9.4 e-/s Flux ? TESS PDCSAP flux
30- 39 F10.7 e-/s e_Flux ? TESS PDCSAP flux error
41- 43 A3 --- Sector [S46] TESS Sector
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Byte-by-byte Description of file: tableb3.dat
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Bytes Format Units Label Explanations
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1- 16 F16.8 d BJD Baricentric Julian date
18- 29 F12.6 m/s RVDRS Radial velocity from the DRS
31- 38 F8.6 m/s e_RVDRS Radial velocity error from the DRS
40- 57 F18.12 m/s RVsbart Radial velocity from sbart
59- 76 F18.16 m/s e_RVsbart Radial velocity error from sbart
78- 88 F11.6 m/s FWHM Full width at half maximum (FWHM) of the
cross-correlation function (CCF)
90- 97 F8.6 m/s e_FWHM Error of the full width at half maximum (FWHM)
of the cross-correlation function (CCF)
99-108 F10.6 m/s BIS Bisector span
110-117 F8.6 m/s e_BIS Bisector span error
119-127 F9.6 % Contrast Contrast of the cross-correlation function
(CCF)
129-136 F8.6 % e_Contrast Error of the contrast of the cross-correlation
function (CCF)
138-145 F8.6 --- Halpha Hα line depth
147-154 F8.6 --- e_Halpha Hα line depth error
156-163 F8.6 --- Na Sodium line depth
165-172 F8.6 --- e_Na Sodium line depth error
174-181 F8.6 --- Ca Calcium line depth
183-190 F8.6 --- e_Ca Calcium line depth error
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Acknowledgements:
Amadeo Castro-Gonzalez, acastro(at)cab.inta-csic.es
amadeocastrogonzalez(at)gmail.com
(End) Amadeo Castro-Gonzalez [CAB, Spain], Patricia Vannier [CDS] 25-Jun-2025