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.
<Astron. Astrophys. 624, A38 (2019)>
=2019A&A...624A..38D 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 (Rb=1.43±0.08R{earth}
and Rc=3.2±0.3R{earth}, close-in (ab=0.022AU and ac=0.054AU)
transiting planets discovered by the Kepler/K2 space observatory. They
are representatives of two distinct families of small planets
(Rp<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 mb=3.9±1.1M{earth} and
mc=7.8±2.3M{earth}. The derived planet bulk densities
ρb=7.2+2.5-2.1g/cm3 and ρc=1.3+0.7_-0.5g/cm3^
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:
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RA (2000) DE Designation(s)
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11 17 47.78 +03 51 59.0 K2-36 = EPIC 201713348
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File Summary:
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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
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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 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 Hα line
63- 69 F7.5 -- e_Halpha Error on the Hα activity index
73- 79 F7.5 -- Vasy ?=- CCF line asymmetry
83- 89 F7.5 -- e_Vasy ?=- Error on the CCF line asymmetry
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Byte-by-byte Description of file: tablea2.dat
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Bytes Format Units Label Explanations
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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)
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Acknowledgements:
Mario Damasso, mario.damasso(at)inaf.it
(End) Mario Damasso [INAF-OATo, Italia], Patricia Vannier [CDS] 11-Feb-2019