J/A+A/641/A170 Ultracool dwarf K2 light curves (Sestovic+, 2020)
Occurrence rate of exoplanets orbiting ultracool dwarfs as probed by K2.
Sestovic M., Demory B.-O.
<Astron. Astrophys. 641, A170 (2020)>
=2020A&A...641A.170S 2020A&A...641A.170S (SIMBAD/NED BibCode)
ADC_Keywords: Photometry ; Stars, M-type ; Stars, late-type ; Exoplanets
Keywords: planets and satellites: detection - methods: statistical
Abstract:
With the discovery of a planetary system around the ultracool dwarf
TRAPPIST-1, there has been a surge of interest in such stars as
potential planet hosts. Planetary systems around ultracool dwarfs
represent our best chance of characterising temperate rocky-planet
atmospheres with the James Webb Space Telescope. However, TRAPPIST-1
remains the only known system of its kind and the occurrence rate of
planets around ultracool dwarfs is still poorly constrained.
We seek to perform a complete transit search on the ultracool dwarfs
observed by NASA's K2 mission, and use the results to constrain the
occurrence rate of planets around these stars.
We filter and characterise the sample of ultracool dwarfs observed by
K2 by fitting their spectral energy distributions and using parallaxes
from Gaia. We build an automatic pipeline to perform photometry,
detrend the light curves, and search for transit signals. Using
extensive injection-recovery tests of our pipeline, we compute the
detection sensitivity of our search, and thus the completeness of our
sample. We infer the planetary occurrence rates within a hierarchical
Bayesian model (HBM) to treat uncertain planetary parameters.With the
occurrence rate parametrised by a step-wise function, we present a
convenient way to directly marginalise over the second level of our
HBM (the planetary parameters). Our method is applicable generally and
can greatly speed up inference with larger catalogues of detected
planets.
We detect one planet in our sample of 702 ultracool dwarfs: a
previously validated mini-Neptune. We thus infer a mini-Neptune
(2-4R⊕) occurrence rate of η=0.20+0.160.11 within
orbital periods of 1-20 days. For super-Earths (1-2R⊕) and ice
or gas giants (4-6R⊕) within 1-20 days, we place 95% credible
intervals of η<1.14 and η<0.29, respectively. If
TRAPPIST-1-like systems were ubiquitous, we would have a 96% chance of
finding at least one.
Description:
This dataset contains the detrended lightcurves and stellar parameters
of the ultracool dwarf targets observed by K2 and analysed in the
paper.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
target.dat 745 888 All K2 target stars used
lc/* . 888 Individual light curves
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See also:
IV/34 : K2 Ecliptic Plane Input Catalog (EPIC) (Huber+, 2017)
Byte-by-byte Description of file: target.dat
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Bytes Format Units Label Explanations
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1- 18 A18 --- FileName Name of the light curve file in
subdirectory lc
20- 28 I9 --- Epic K2's EPIC identifier
30- 31 I2 --- Campaign K2's observation campaign
33- 53 F21.14 --- dtcdpp Detrended CDPP of light curve
55- 56 A2 --- dtkernel [c pq] Gaussian Process kernel used in
detrending, qp is "quasiperiodic",
c is "classic". See paper.
58- 77 F20.17 --- dtpv ? Detrended PV of light curve
79- 83 F5.3 Msun Mstarfit Stellar mass from fitted spectral type (1)
85- 89 F5.3 Rsun Rstarfit Stellar radius from fitted spectral type (1)
91- 96 F6.1 K Tefffit ? Effective temperature from
fitted spectral type (1)
98-102 A5 --- SpTypefit Spectral type from fitted spectral type (1)
104-108 F5.3 Msun Mstar Stellar mass
110-114 F5.3 Rsun Rstar Stellar radius
116-134 F19.15 deg RAdeg ? Gaia DR2 right ascension (ICRS)
at Ep=2015.5
136-156 F21.17 deg DEdeg ? Gaia DR2 declination (ICRS) at Ep=2015.5
158-162 A5 --- GaiaFound [False/True ] Found in Gaia DR2 ?
164-181 F18.15 mag Gmag ? Gaia DR2 G magnitude
183-203 F21.19 mas Plx ? Gaia DR2 parallax
205-227 E23.19 mas/yr pmRA* ? Gaia DR2 proper motion along RA,
pmRA*cosDE
229-251 E23.19 mas/yr pmDE ? Gaia DR2 proper motion along DE
253-271 I19 --- GaiaDR2 ? Gaia DR2 source ID
273-288 A16 --- 2MASS 2MASS identifier
290-294 A5 --- ggFound [False/True ] Found in gg (2)
296-305 A10 --- ggName gg name (JHHMM-DDMM) (2)
307-323 A17 --- ggSpType gg spectral type (2)
325 A1 --- ggClass gg luminosity class (2)
327-331 F5.2 --- ggStelIndex ? gg stellar index (2)
333-336 F4.2 --- ggStelNum ? gg stellar number (2)
338-358 F21.17 deg DEpred ? Predicted declination during the K2
observation, calculated with Gaia
proper motions
360-378 F19.15 deg RApred ? Predicted right ascension during the K2
observation, calculated with Gaia
proper motions
380-521 A142 --- ProgramID Program ID(s)
523-540 F18.15 mag Jmag ? 2MASS J magnitude
542-545 A4 --- irm [True] IRM valid
547-550 A4 --- ultracool [True] Ultracool valid
552-570 F19.15 kpc vosaD ? Distance obtained from the VOSA SED fit
572-586 F15.10 kpc e_vosaD ? Distance error obtained from the
VOSA SED fit
588-609 E22.16 --- e_vosaFtot ? Total flux error obtained from the
VOSA SED fit
611-632 E22.16 --- vosaFtot ? Total flux obtained from the VOSA SED fit
634-655 E22.16 --- vosaLbol ? Bolometric luminosity obtained from the
VOSA SED fit
657-678 E22.16 --- e_vosaLbol ? Bolometric luminosity error obtained from
the VOSA SED fit
680-699 F20.18 Rsun vosaRstar ? Stellar radius parameters obtained from
the VOSA SED fit
701-722 E22.16 Rsun e_vosaRstar ? Stellar radius error parameters obtained
from the VOSA SED fit
724-729 F6.1 K vosaTeff ? Effective temperature obtained from the
VOSA SED fit
731-734 F4.1 K e_vosaTeff ? Effective temperature error obtained
from the VOSA SED fit
736-739 A4 --- dtFlag [False/True ] dt flag
741-745 A5 --- irmFlag [False/True ] IRM flag
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Note (1): stellar parameters obtained from the fitted spectral type
(from either VOSA SED fit or J. Gagne's table value), taken from the table
compiled by E. Mamajek,
see: pas.rochester.edu/∼emamajek/EEMdwarfUBVIJHKcolorsTeff.txt
Note (2): parameters from the table compiled by J. Gagne,
see: https://jgagneastro.com/list-of-ultracool-dwarfs/
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Byte-by-byte Description of file: lc/*
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Bytes Format Units Label Explanations
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1- 18 F18.13 d TimeK Time (BKJD)
20- 37 F18.13 d Time Time (BJD)
39- 44 I6 ---- Cad K2 cadence number
46- 51 I6 --- Qual K2 quality flag
53- 75 E23.20 pix Xtrack pixel position obtained by centroid/PSF fit
77-101 E25.20 pix Ytrack pixel position obtained by centroid/PSF fit
103-127 E25.20 pix Xpos pixel position (1)
129-151 E23.20 pix Ypos pixel position (1)
153-179 F27.19 ct Fabs Absolute value for the counts from the star
181-205 E25.20 --- Fraw Un-detrended normalised flux
207-229 E23.19 --- Fspatial Component of the flux that is correlated with
the position of the target on the TPF
231-255 F25.20 --- Ftemp Component of flux that is correlated with time
(stellar variability and long-term trends)
257-281 E25.20 --- Fdetrend Detrended/flattened flux
283-287 A5 --- Flag [False/True ] Flag, if True, the flux
measurement is an outlier and was not used in
the GP fit (though it is used during the
transit search and afterwards)
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Note (1): pixel positions obtained by locating the target on the TPF in
100 frames, and calculating the median offset from the TPF's own POS_CORR1
and POS_CORR1 position estimates (more stable)
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Acknowledgements:
Marko Sestovic, marko.sestovic(at)csh.unibe.ch
(End) Patricia Vannier [CDS] 19-Aug-2020