J/A+A/624/A38 Radial velocities of K2-36 (Damasso+, 2019) ================================================================================ So close, so different: characterization of the K2-36 planetary system with HARPS-N. Damasso M., Zeng L., Malavolta L., Mayo A., Sozzetti A., Mortier A., Buchhave L.A., Vanderburg A., Lopez-Morales M., Bonomo A.S., Cameron A.C., Coffinet A., Figueira P., Latham D.W., Mayor M., Molinari E., Pepe F., Phillips D.F., Poretti E., Rice K., Udry S., Watson C.A. =2019A&A...624A..38D (SIMBAD/NED BibCode) ================================================================================ ADC_Keywords: Stars, double and multiple ; Exoplanets ; Radial velocities Keywords: stars: individual: K2-36 planets and satellites: detection - planets and satellites: composition - techniques: radial velocities Abstract: K2-36 is a K dwarf orbited by two small (R_b_=1.43+/-0.08R_{earth}_ and R_c_=3.2+/-0.3R_{earth}_, close-in (a_b_=0.022AU and a_c_=0.054AU) transiting planets discovered by the Kepler/K2 space observatory. They are representatives of two distinct families of small planets (R_p_<4R_{earth}_) recently emerged from the analysis of Kepler data, with likely a different structure, composition and evolutionary pathways. We revise the fundamental stellar parameters and the sizes of the planets, and provide the first measurement of their masses and bulk densities, which we use to infer their structure and composition. We observed K2-36 with the HARPS-N spectrograph over ~3.5-years, collecting 81 useful radial velocity measurements. The star is active, with evidence for increasing levels of magnetic activity during the observing time span. The radial velocity scatter is ~17m/s due to the stellar activity contribution, which is much larger that the semi-amplitudes of the planetary signals. We tested different methods for mitigating the stellar activity contribution to the radial velocity time variations and measuring the planet masses with good precision. We find that K2-36 is likely a ~1Gyr old system, and by treating the stellar activity through a Gaussian process regression, we measured the planet masses m_b_=3.9+/-1.1M_{earth}_ and m_c_=7.8+/-2.3M_{earth}_. The derived planet bulk densities {rho}_b_=7.2^+2.5^_-2.1_g/cm^3^ and {rho}_c_=1.3^+0.7^_-0.5^g/cm^3^ point out that K2-36b has a rocky, Earth-like composition, and K2-36c is a low-density sub-Neptune. Composed of two planets with similar orbital separations but different densities, K2-36 represents an optimal laboratory for testing the role of the atmospheric escape in driving the evolution of close-in, low-mass planets after ~1Gyr from their formation. Due to their similarities, we performed a preliminary comparative analysis between the systems K2-36 and Kepler-36, which we deem worthy of a more detailed investigation. Description: We present data extracted from 81 HARPS-N spectra of the star K2-36: 1) Spectroscopic activity/Cross correlation function asymmetry indicators; 2) Radial velocities extracted with two different pipelines (DRS & TERRA). Objects: ---------------------------------------------------- RA (2000) DE Designation(s) ---------------------------------------------------- 11 17 47.78 +03 51 59.0 K2-36 = EPIC 201713348 ---------------------------------------------------- File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- ReadMe 80 . This file tablea1.dat 89 81 Spectroscopic activity/CCF asymmetry indicators for K2-36 with data extracted from the 81 spectra used in this work tablea2.dat 46 81 Radial velocities of K2-36 extracted from the 81 HARPS-N spectra analysed in this work -------------------------------------------------------------------------------- Byte-by-byte Description of file: tablea1.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 F12.6 d BJD Time of observation, TDB (BJD-2400000) 16- 22 F7.2 m/s FWHM FWHM of the CCF 26- 30 F5.2 m/s BIS CCF Bisector Inverse Slope (BIS) 34- 40 F7.4 [-] logR'HK Mount Wilson logR_HK index 44- 49 F6.4 [-] e_logR'HK Error on Mount Wilson logR_HK index 53- 59 F7.5 -- Halpha Activity index based on the H{alpha} line 63- 69 F7.5 -- e_Halpha Error on the H{alpha} activity index 73- 79 F7.5 -- Vasy ?=- CCF line asymmetry 83- 89 F7.5 -- e_Vasy ?=- Error on the CCF line asymmetry ----------------------------------------------------------------------------- Byte-by-byte Description of file: tablea2.dat -------------------------------------------------------------------------------- Bytes Format Units Label Explanations -------------------------------------------------------------------------------- 1- 12 F12.6 d BJD Time of observation, TDB (BJD-2400000) 16- 23 F8.2 m/s RVdrs Radial velocity (DRS pipeline) 27- 30 F4.2 m/s e_RVdrs Error radial velocity (DRS pipeline) 34- 39 F6.2 m/s RVterra Relative radial velocity (TERRA pipeline) 43- 46 F4.2 m/s e_RVterra Error Radial velocity (TERRA pipeline) ------------------------------------------------------------------------------ Acknowledgements: Mario Damasso, mario.damasso(at)inaf.it ================================================================================ (End) Mario Damasso [INAF-OATo, Italia], Patricia Vannier [CDS] 11-Feb-2019