J/A+A/631/A90 K2-138 HARPS radial velocities (Lopez+, 2019)
Exoplanet characterisation in the longest known resonant chain:
the K2-138 system seen by HARPS.
Lopez T.A., Barros S.C.C., Santerne A., Deleuil M., Adibekyan V.,
Almenara J.-M., J. Armstrong D., Brugger B., Barrado D., Bayliss D.,
Boisse I., Bonomo A.S., Bouchy F., Brown D.J.A., Carli E., Demangeon O.,
Dumusque X., Diaz R.F., Faria J.P., Figueira P., Foxell E., Giles H.,
Hebrard G., Hojjatpanah S., Kirk J., Lillo-Box J., Lovis C., Mousis O.,
da Nobrega H.J., Nielsen L.D., Neal J.J., Osborn H.P., Pepe F.,
Pollacco D., Santos N.C., Sousa S.G., Udry S., Vigan A., Wheatley P.J.
<Astron. Astrophys. 631, A90 (2019)>
=2019A&A...631A..90L 2019A&A...631A..90L (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Radial velocities
Keywords: planets and satellites: detection -
planets and satellites: fundamental parameters -
stars: individual: K2-138 - techniques: radial velocities -
techniques: photometric
Abstract:
The detection of low-mass transiting exoplanets in multiple systems
brings new constraints to planetary formation and evolution processes
and challenges the current planet formation theories. Nevertheless,
only a mere fraction of the small planets detected by Kepler and K2
have precise mass measurements, which are mandatory to constrain their
composition. We aim to characterise the planets that orbit the
relatively bright star K2-138. This system is dynamically particular
as it presents the longest chain known to date of planets close to the
3:2 resonance. We obtained 215 HARPS spectra from which we derived the
radial-velocity variations of K2-138. Via a joint Bayesian analysis of
both the K2 photometry and HARPS radial-velocities (RVs), we
constrained the parameters of the six planets in orbit. The masses of
the four inner planets, from b to e, are 3.1, 6.3, 7.9, and
13.0M⊕ with a precision of 34%, 20%, 18%, and 15%,
respectively. The bulk densities are 4.9, 2.8, 3.2, and 1.8g/cm3,
ranging from Earth to Neptune-like values. For planets f and g, we
report upper limits. Finally, we predict transit timing variations of
the order two to six minutes from the masses derived. Given its
peculiar dynamics, K2-138 is an ideal target for transit timing
variation (TTV) measurements from space with the upcoming
CHaracterizing ExOPlanet Satellite (CHEOPS) to study this
highly-packed system and compare TTV and RV masses.
Description:
File tablea3.dat contains the HARPS radial velocity and spectroscopic
data of K2-138 obtained as part of the ESO-K2 large programme ID
198.C-0169.
Objects:
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RA (2000) DE Designation(s)
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23 15 47.77 -10 50 58.9 K2-138 = EPIC 245950175
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
tablea3.dat 72 194 HARPS radial velocity and spectroscopic data
of K2-138
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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- 11 A11 --- Time Time (BJD_UTC) (BJD-2400000)
13- 19 F7.5 km/s RV Radial velocity (km/s)
21- 25 F5.2 m/s e_RV Radial velocity uncertainty (m/s)
27- 32 F6.4 km/s FWHM FWHM (km/s)
34- 37 F4.1 m/s e_FWHM FWHM uncertainty (m/s)
39- 43 F5.1 m/s BIS Bisector inverse slope (m/s)
45- 48 F4.1 m/s e_BIS Bisector inverse slope uncertainty (m/s)
50- 55 F6.4 --- SMW S index Mount Wilson calibrated
57- 62 F6.4 --- e_SMW Uncertainty on S index Mount Wilson calibrated
64- 67 I4 s Texp Exposure time (s)
69- 72 F4.1 --- S/N Signal-to-noise ratio per CCD pixel at 550nm
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Acknowledgements:
Theo Lopez, theo.lopez(at)lam.fr
(End) Patricia Vannier [CDS] 30-Sep-2019