J/MNRAS/507/1847 A HARPS-N mass for the elusive Kepler-37d (Rajpaul+, 2021)
A HARPS-N mass for the elusive Kepler-37d:
a case study in disentangling stellar activity and planetary signals.
Rajpaul V.M., Buchhave L.A., Lacedelli G., Rice K., Mortier A.,
Malavolta L., Aigrain S., Borsato L., Mayo A.W., Charbonneau D.,
Damasso M., Dumusque X., Ghedina A., Latham D.W., Lopez-Morales M.,
Magazzu A., Micela G., Molinari E., Pepe F., Piotto G., Poretti E.,
Rowther S., Sozzetti A., Udry S., Watson C.A.
<Mon. Not. R. Astron. Soc. 507, 1847-1868 (2021)>
=2021MNRAS.507.1847R 2021MNRAS.507.1847R (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Stars, G-type ; Stars, K-type ;
Exoplanets ; Radial velocities ; Optical
Keywords: methods: data analysis - techniques: radial velocities -
techniques: spectroscopic - planetary systems - stars: activity -
stars: individual: Kepler-37
Abstract:
To date, only 18 exoplanets with radial velocity (RV) semi-amplitudes
<2m/s have had their masses directly constrained. The biggest obstacle
to RV detection of such exoplanets is variability intrinsic to stars
themselves, e.g. nuisance signals arising from surface magnetic
activity such as rotating spots and plages, which can drown out or
even mimic planetary RV signals. We use Kepler-37 - known to host
three transiting planets, one of which, Kepler-37d, should be on the
cusp of RV detectability with modern spectrographs - as a case study
in disentangling planetary and stellar activity signals. We show how
two different statistical techniques - one seeking to identify
activity signals in stellar spectra, and another to model activity
signals in extracted RVs and activity indicators - can enable
detection of the hitherto elusive Kepler-37d. Moreover, we show that
these two approaches can be complementary, and in combination,
facilitate a definitive detection and precise characterisation of
Kepler-37d. Its RV semi-amplitude of 1.22±0.31m/s (mass
5.4±1.4M⊕) is formally consistent with TOI-178b's
1.05+0.25-0.30m/s, the latter being the smallest detected RV
signal of any transiting planet to date, though dynamical simulations
suggest Kepler-37d's mass may be on the lower end of our 1σ
credible interval. Its consequent density is consistent with either a
water-world or that of a gaseous envelope (∼0.4% by mass) surrounding
a rocky core. Based on RV modelling and a re-analysis of Kepler-37
TTVs, we also argue that the putative (non-transiting) planet
Kepler-37e should probably be stripped of its 'confirmed' status.
Description:
k37_pwgp.dat contains the radial velocities and activity indicators
for Kepler-37 obtained with the HARPS-N spectrograph. RVs extracted
with both the HARPS-N DRS pipeline and the pairwise GP (PWGP) method
are presented; all activity indicators are from the DRS.
Objects:
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RA (2000) DE Designation(s)
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18 56 14.31 +44 31 05.4 Kepler-37 = KOI-245 = BD+44 3020 = KIC 8478994
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File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
k37-pwgp.dat 92 110 Kepler-37 RVs (DRS, PWGP) + activity indicators
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Byte-by-byte Description of file: k37-pwgp.dat
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Bytes Format Units Label Explanations
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1- 14 F14.6 d BJD Barycentric Julian date
16- 24 F9.2 m/s RV-DRS DRS radial velocity
26- 29 F4.2 m/s e_RV-DRS DRS radial velocity error
31- 35 F5.2 m/s RV-PWGP PWGP radial velocity
37- 40 F4.2 m/s e_RV-PWGP PWGP radial velocity error
42- 48 F7.2 km/s FWHM Full-width-at-half-maximum of the CCF
50- 54 F5.2 m/s BIS-span Bisector span
56- 61 F6.3 --- Contrast CCF contrast
63- 69 F7.4 --- log(R'HK) log R'HK index
71- 76 F6.4 --- e_log(R'HK) log R'HK error index
78- 84 F7.5 --- SMW Mount Wilson S index
86- 92 F7.5 --- e_SMW Mount Wilson S index error
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Acknowledgements:
Vinesh Maguire Rajpaul, vr325(at)cantab.ac.uk
(End) Patricia Vannier [CDS] 24-Sep-2021