J/A+A/641/A92 K2-38 ESPRESSO RVs (Toledo-Padron+, 2020)
Characterization of the K2-38 planetary system.
Unraveling one of the densest planets knows to date.
Toledo-Padron B.. Lovis C., Suarez Mascareno A., Barros S.C.C.,
Gonzalez Hernandez J.I., Sozzetti A., Bouchy F., Zapatero Osorio M.R.,
Rebolo R., Cristiani S., Pepe F.A., Santos N.C., Sousa S.G., Tabernero H.M.,
Lillo-Box J., Bossini D., Adibekyan V., Allart R., Damasso M.,
D'Odorico V., Figueira P., Lavie B., Lo Curto G., Mehner A., Micela G.,
Modigliani A., Nunes N.J., Palle E., Abreu M., Affolter M., Alibert Y.,
Aliverti M., Allende Prieto C., Alves D., Amate M., Avila G., Baldini V.,
Bandy T., Benatti S., Benz W., Bianco A., Broeg C., Cabral A., Calderone G.,
Cirami R., Coelho J., Conconi P., Coretti I., Cumani C., Cupani G.,
Deiries S., Dekker H., Delabre B., Demangeon O., Di Marcantonio P.,
Ehrenreich D., Fragoso A., Genolet L., Genoni M., Genova Santos R.,
Hughes I., Iwert O., Knudstrup J., Landoni M., Lizon J.L., Maire C.,
Manescau A., Martins C.J.A.P., Megevand D., Molaro P., Monteiro M.J.P.F.G.,
Monteiro M.A., Moschetti M., Mueller E., Oggioni L., Oliveira A., Oshagh M.,
Pariani G., Pasquini L., Poretti E., Rasilla J.L., Redaelli E., Riva M.,
Santana Tschudi S., Santin P., Santos P., Segovia A., Sosnowska D.,
Spano P., Tenegi F., Udry S., Zanutta A., Zerbi F.
<Astron. Astrophys. 641, A92 (2020)>
=2020A&A...641A..92T 2020A&A...641A..92T (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Radial velocities
Keywords: techniques: radial velocities - techniques: photometric -
instrumentation: spectrographs - stars: individual: K2-38 -
planets and satellites: detection -
planets and satellites: composition
Abstract:
An accurate characterization of the known exoplanet population is key
to understand the origin and evolution of planetary systems. The
determination of true planetary masses through the radial velocity
(RV) method is expected to experience a great improvement thanks to
the availability of ultra-stable echelle spectrographs.
We took advantage of the extreme precision of the new- generation
echelle spectrograph ESPRESSO to characterize the transiting planetary
system orbiting the G2V star K2-38 located at 194pc from the Sun with
V∼11.4. This system is particularly interesting because it could
contain the densest planet detected to date.
We carried out a photometric analysis of the available K2 photometric
light curve of this star to measure the radius of its two known
planets K2-38b and K2-38c with Pb=4.01593±0.00050d and
Pc=10.56103±0.00090d, respectively. Using 43 ESPRESSO high-precision
radial velocity measurements taken over 8 months along with the 14
previously published HIRES RV measurements, we modeled the orbits of
the two planets through a Markov Chain Monte Carlo (MCMC) analysis,
significantly improving their mass measurements.
Using ESPRESSO spectra we derived the stellar paremeters,
Teff=5731±66K, logg=4.38±0.11dex, and [Fe/H]=0.26±0.05dex, and
thus the mass and radius of K2-38, Ms=1.03+0.04-0.02M☉ and
Rs=1.06+0.09-0.06R[sun. We determined new values for the
planetary properties of both planets. We characterized K2-38b as a
super-Earth with Rp=1.54±0.14R{earth} and
Mp=7.3+1.1-1.0M{earth}, and K2-38c as a sub-Neptune with
Rp=2.29±0.26R{earth} and Mp=8.3±1.3M{earth}. Combining the
radius and mass measurements, we derive a mean density of
rhop=11.0+4.1-2.8g/cm3 for K2-38b and
rhop=3.8+1.8-1.1g/cm3 for K2-38c, confirming K2-38b as one of
the densest planets known to date.
The best description for the composition of K2-38b comes from an
iron-rich Mercury-like model, while K2-38c is better described by an
ice-rich model. The maximum collision stripping boundary shows how
giant impacts could be the cause for the high density of K2-38b. The
irradiation received by each planet places them on opposite sides of
the radius valley. We find evidence of a long-period signal in the
radial velocity time-series whose origin could be linked to a
0.25-3MJup planet or stellar activity.
Description:
We used the public version of the ESPRESSO pipeline
Data-Reduction-Software (DRS) to compute the RVs of K2-38. The
pipeline provides a crosscorrelation function (CCF) for each spectrum
using a G2 mask that covers the entire wavelength range of the
instrument (between 3800 and 7880Å). The CCFs were built using a RV
step of 0.5km/s within a range between -55 and -15km/s centered on the
systemic velocity of the star. This RV time-series presents a RV
precision of 1.0m/s with a RMS of 3.6m/s, an extremely good result for
a relatively faint G2 star (V=11.34) like K2-38.
Objects:
---------------------------------------------------
RA (2000) DE Designation(s)
---------------------------------------------------
16 00 08.06 -23 11 21.33 K2-38 = EPIC 204221263
---------------------------------------------------
File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table1.dat 47 43 ESPRESSO radial velocities
--------------------------------------------------------------------------------
Byte-by-byte Description of file: table1.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 17 F17.12 d BJD Barycentric Julian date (BJD-2450000)
19- 32 F14.7 m/s RV Radial velocity
34- 47 F14.12 m/s e_RV Radial velocity uncertainty
--------------------------------------------------------------------------------
Acknowledgements:
Borja Toledo Padron, btoledo(at)iac.es
(End) Borja Toledo Padron [IAC], Patricia Vannier [CDS] 01-Jul-2020