J/A+A/700/A216 Ross 176 phot., RVs, activity indices (Geraldia-Gonzalez+, 2025)
Discovery of a transiting hot water world candidate orbiting Ross 176 with
TESS and CARMENES.
Geraldia-Gonzalez S., Orell-Miquel J., Palle E., Murgas F., Lacedelli G.,
Bejar V.J.S., Caballero J.A., Duque-Arribas C., Lillo-Box J., Montes D.,
Morello G., Nagel E., Schweitzer A., Tabernero H.M., Calatayud-Borras Y.,
Cifuentes C., Fernandez-Rodriguez G., Fukui A., de Leon J., Lodieu N.,
Luque R., Mori M., Narita N., Parviainen H., Poultourtzidis E., Reiners A.,
Ribas I., Schlecker M., Seager S., Stassun K.G., Trifonov T.,
Vanaverbeke S., Winn J.N.
<Astron. Astrophys. 700, A216 (2025)>
=2025A&A...700A.216G 2025A&A...700A.216G (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Radial velocities ;
Photometry ; Optical ; Spectroscopy
Keywords: planets and satellites: composition -
planets and satellites: detection -
planets and satellites: individual: Ross 176
Abstract:
The Transiting Exoplanet Survey Satellite (TESS) discovers several new
planet candidates that need to be confirmed and characterized with
ground-based observations. This is the case for Ross 176, a late
K-type star that hosts a promising water world candidate planet. The
star has a radius of Rstar=0.569±0.020R☉ and a mass of
Mstar=0.577±0.024M☉. Here, we constrain the planetary mass
using spectroscopic data from CARMENES, an instrument that has already
played a major role in confirming the planetary nature of the transit
signal detected by TESS. We make use of Gaussian Processes (GP) to
improve the analysis because the host star has a relatively strong
activity that affects the radial-velocity dataset. In addition, we
applied a GP to the TESS light curves to reduce the correlated-noise
in the detrended dataset. The stellar activity indicators show a
strong signal related to the star rotation period of ∼32-days. This
stellar activity signal was also confirmed on the TESS light curves.
Ross 176b is an inner hot transiting planet with a low eccentricity
orbit of ecc=0.25±0.04, an orbital period of P∼5-days, and an
equilibrium temperature of Teq∼682K. With a radius of
Rp=1.84±0.08R⊕ (4% precision), a mass of
Mp=4.57+0.89-0.93M⊕ (20% precision), and a mean density
of rhop=4.03+0.49-0.81g/cm3, the composition of Ross 176b is
consistent with a water world scenario. Moreover, Ross 176b is a
promising target for atmospheric characterization, which could lead to
more information on the existence, formation and composition of water
worlds. This detection increases the sample of planets orbiting K-type
stars, which is valuable to investigate the presence of the small
planet radius valley around this type of star. This study also
showcases the efficiency of the dual detection between space- and
ground-based telescopes to confirm new planets.
Description:
Ground-based photometry take with MuSCAT2, radial velocity, and
activity indices of Ross 176 taken with CARMENES. Photometric data
reduced by the standard procedure via the MuSCAT2 pipeline described
by Parviainen et al. (2020A&A...633A..28P 2020A&A...633A..28P) and Parviainen
(2022ascl.soft07013P). Spectroscopic data reduced with SERVAL.
Objects:
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RA (2000) DE Designation(s)
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20 22 45.19 +47 18 27.8 Ross 176 = Karmn J20227+473
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
muscat2.dat 105 1147 MuSCAT2 photometry data
rv.dat 56 98 CARMENES (VIS) radial velocity measurements
actind.dat 353 99 SERVAL spectral line activity indices
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Byte-by-byte Description of file: muscat2.dat
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Bytes Format Units Label Explanations
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1- 18 F18.10 d BJD Barycentric Julian date
20- 29 F10.8 --- Fg Relative flux for the g band
31- 40 F10.8 --- e_Fg Relative flux error for the g band
42- 51 F10.8 --- Fr Relative flux for the r band
53- 62 F10.8 --- e_Fr Relative flux error for the r band
64- 73 F10.8 --- Fi Relative flux for the i band
75- 84 F10.8 --- e_Fi Relative flux error for the i band
86- 95 F10.8 --- Fzs Relative flux for the zs band
97-105 F9.7 --- e_Fzs Relative flux error for the zs band
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Byte-by-byte Description of file: rv.dat
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Bytes Format Units Label Explanations
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1- 17 F17.9 d BJD Barycentric Julian date
19- 37 F19.15 m/s RV Radial velocity (VIS channel)
39- 56 F18.15 m/s e_RV Radial velocity error (VIS channel)
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Byte-by-byte Description of file: actind.dat
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Bytes Format Units Label Explanations
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1- 18 F18.10 d BJD Barycentric Julian date
20- 37 F18.16 --- Halpha Hα index
39- 59 F21.19 --- e_Halpha Hα index uncertainty
61- 79 F19.17 --- NaD1 Na D1 index
81-101 F21.19 --- e_NaD1 Na D1 index uncertainty
103-121 F19.17 --- NaD2 Na D2 index
123-143 F21.19 --- e_NaD2 Na D2 index uncertainty
145-162 F18.16 --- CaIRT1 Ca IRT 1 index
164-184 F21.19 --- e_CaIRT1 Ca IRT 1 index uncertainty
186-204 F19.17 --- CaIRT2 Ca IRT 2 index
206-226 F21.19 --- e_CaIRT2 Ca IRT 2 index uncertainty
228-246 F19.17 --- CaIRT3 Ca IRT 3 index
248-268 F21.19 --- e_CaIRT3 Ca IRT 3 index uncertainty
270-291 F22.17 --- CRX Chromatic index (in m/s/Np)
293-311 F19.15 --- e_CRX Chromatic index uncertainty(in m/s/Np)
313-333 F21.17 m2/s2 dLW Differential line width
335-353 F19.16 m2/s2 e_dLW Differential line width uncertainty
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Acknowledgements:
Samuel Geraldia Gonzalez, sgeraldia(at)iac.es
(End) Samuel Geraldia Gonzalez [IAC, Spain], Patricia Vannier [CDS] 27-May-2025