J/A+A/627/A43 Two super-Earths orbiting TOI-402 (Dumusque+, 2019)
Hot, rocky and warm, puffy super-Earths orbiting TOI-402 (HD15337).
Dumusque X., Turner O., Dorn C., Eastman J.D., Allart R., Adibekyan V.,
Sousa S., Santos N.C., Mordasini C., Bourrier V., Bouchy F., Coffinet A.,
Davies M.D., Diaz R.F., Fausnaugh M.M., Glidden A., Guerrero N., Henze C.E.,
Jenkins J.M., Latham D.W., Lovis C., Mayor M., Pepe F., Quintana E.V.,
Ricker G.R., Rowden P., Segransan D., Suarez Mascareno A., Seager S.,
Twicken J.D., Udry S., Vanderspek R.K., Winn J.N.
<Astron. Astrophys. 627, A43 (2019)>
=2019A&A...627A..43D 2019A&A...627A..43D (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Radial velocities
Keywords: techniques: radial velocities - techniques: spectroscopy -
stars: activity - stars: individual: HD 15337 -
stars: individual: TOI-402 - stars: individual: TIC 120896927
Abstract:
The Transiting Exoplanet Survey Satellite (TESS) is revolutionising
the search for planets orbiting bright and nearby stars. In sectors 3
and 4, TESS observed TOI-402 (TIC-120896927), a bright V=9.1 K1 dwarf
also known as HD15337, and found two transiting signals with periods
of 4.76 and 17.18 days and radii of 1.90 and 2.21R⊕,
respectively. This star was observed prior to the TESS detection as
part of the radial-velocity (RV) search for planets using the HARPS
spectrometer, and 85 precise RV measurements were obtained before the
launch of TESS over a period of 14 years.
In this paper, we analyse the HARPS RV measurements in hand to confirm
the planetary nature of these two signals.
HD15337 happens to present a stellar activity level similar to the
Sun, with a magnetic cycle of similar amplitude and RV measurements
that are affected by stellar activity. By modelling this stellar
activity in the HARPS radial velocities using a linear dependence with
the calcium activity index log(R'HK), we are able, with a
periodogram approach, to confirm the periods and the planetary nature
of TOI-402.01 and TOI-402.02. We then derive robust estimates from the
HARPS RVs for the orbital parameters of these two planets by modelling
stellar activity with a Gaussian process and using the marginalised
posterior probability density functions obtained from our analysis of
TESS photometry for the orbital period and time of transit.
By modelling TESS photometry and the stellar host characteristics, we
find that TOI-402.01 and TOI-402.02 have periods of 4.75642±0.00021
and 17.1784±0.0016 days and radii of 1.70±0.06 and 2.52±0.11
(precision 3.6 and 4.2%), respectively. By analysing the HARPS RV
measurements, we find that those planets are both super-Earths with
masses of 7.20±0.81 and 8.79±1.68 (precision 11.3 and 19.1%), and
small eccentricities compatible with zero at 2σ.
Although having rather similar masses, the radii of these two planets
are very different, putting them on different sides of the radius gap.
By studying the temporal evolution under X-ray and UV (XUV) driven
atmospheric escape of the TOI-402 planetary system, we confirm, under
the given assumptions, that photo-evaporation is a plausible
explanation for this radius difference. Those two planets, being in
the same system and therefore being in the same irradiation
environment are therefore extremely useful for comparative
exoplanetology across the evaporation valley and thus bring
constraints on the mechanisms responsible for the radius gap.
Description:
HARPS radial velocities and log(R'HK) measurements for TOI-402 (HD15337).
Objects:
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RA (2000) DE Designation(s)
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02 27 28.38 -27 38 06.7 TOI 402 = HD 15337
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea1.dat 50 85 Data
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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- 12 F12.6 d BJD Barycentric Julian Date (BJD-2400000)
14- 21 F8.5 km/s RV Radial velocity
23- 29 F7.5 km/s e_RV Uncertainty on radial velocity
31- 37 F7.4 --- logRHK Calcium index log(R'HK)
39- 44 F6.4 --- e_logRHK Uncertainty on log(R'HK)
46- 50 F5.1 e- SNR50 SNR in order 50
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Acknowledgements:
Xavier Dumusque, xavier.dumusque(at)unige.ch,
Astronomy Department Geneva University, Switzerland
(End) Xavier Dumusque [Geneva Univ.], Patricia Vannier [CDS] 18-Jun-2019