J/AJ/158/133 Transit timing and light curves for K2-146 (Hamann+, 2019)
K2-146: discovery of planet c, precise masses from transit timing, and observed
precession.
Hamann A., Montet B.T., Fabrycky D.C., Agol E., Kruse E.
<Astron. J., 158, 133 (2019)>
=2019AJ....158..133H 2019AJ....158..133H
ADC_Keywords: Stars, dwarfs ; Stars, M-type ; Photometry ; Exoplanets
Keywords: planets and satellites: detection -
planets and satellites: dynamical evolution and stability -
planets and satellites: individual (EPIC 211924657, K2-146)
Abstract:
K2-146 is a mid-M dwarf (M*=0.331±0.009 M☉;
R*=0.330±0.010 R☉), observed in Campaigns 5, 16, and 18 of
the K2 mission. In Campaign 5 data, a single planet was discovered with
an orbital period of 2.6 days and large transit timing variations due
to an unknown perturber. Here, we analyze data from Campaigns 16 and 18,
detecting the transits of a second planet, c, with an orbital period
of 4.0 days, librating in a 3:2 resonance with planet b. Large,
anticorrelated timing variations of both planets exist due to their
resonant perturbations. The planets have a mutual inclination of
2.40°±0.25°, which torqued planet c more closely into our line
of sight. Planet c was grazing in Campaign 5 and thus missed in previous
searches; it is fully transiting in Campaigns 16 and 18, and its transit
depth is three times larger. We improve the stellar properties using data
from Gaia DR2 (Cat. I/345), and use dynamical fits to find that both
planets are sub-Neptunes: their masses are 5.77±0.18 and
7.50±0.23 M⊕, and their radii are 2.04±0.06 and
2.19±0.07 R⊕, respectively. These mass constraints set the
precision record for small exoplanets (a few gas giants have comparable
relative precision). These planets lie in the photoevaporation valley
when viewed in Radius-Period space, but due to the low-luminosity M-dwarf
host star, they lie among the atmosphere-bearing planets when viewed
in Radius-Irradiation space. This, along with their densities being 60-80%
that of Earth, suggests that they may both have retained a substantial
gaseous envelope.
Description:
Campaign 5 was observed as a part of the K2 mission from 2015 April 27
to 2015 July 10. Campaign 16 revisited a fraction of this field from
2017 December 7 to 2018 February 25, while Campaign 18 again revisited
this field from 2018 May 12 to 2018 July 2. These observations combine
to provide 205 days of observations over the "K2 Legacy Field" spread
over 3.2 yr. When first examining the system, our goal is to determine
the number of significant transit signals and obtain initial estimates
of transit times. We obtain C5 data from the EVEREST database of
detrended light curves at the Mikulski Archive for Space Telescopes
(MAST; Luger et al. 2018AJ....156...99L 2018AJ....156...99L). The C16 and C18 light curves
we download from MAST are unprocessed, as those campaigns have not yet
been fully processed within the EVEREST pipeline. We use the
standalone.py module within the EVEREST Python package to detrend
these light curves locally, selecting apertures that encompass the
star throughout their respective campaigns and minimize the Combined
Differential Photometric Precision (CDPP; a measure of the light
curve's noisiness described in Christiansen et al. (2012,
J/PASP/124/1279)).
Objects:
-----------------------------------------------------
RA (ICRS) DE Designation(s)
-----------------------------------------------------
08 40 06.42 +19 05 34.4 K2-146 = EPIC 211924657
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File Summary:
--------------------------------------------------------------------------------
FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table4.dat 231 39200 Differential Evolution Markov Chain Monte Carlo
(DEMCMC) dynamical samples
table5.dat 22 611 Predicted transit times for planet b
table6.dat 22 406 Predicted transit times for planet c
fig1a.dat 42 3664 Long cadence light curve for K2-146 during C16
fig1b.dat 42 113550 Short cadence light curve for K2-146 during C16
fig1c.dat 42 2348 Long cadence light curve for K2-146 during C18
fig1d.dat 42 72520 Short cadence light curve for K2-146 during C18
fig1e.dat 42 3491 Long cadence light curve for K2-146 during C5
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See also:
I/345 : Gaia DR2 (Gaia Collaboration, 2018)
J/PASP/124/1279 : Q3 Kepler's combined photometry (Christiansen+, 2012)
J/ApJS/224/2 : K2 EPIC stellar properties for 138600 targets (Huber+, 2016)
J/AJ/154/207 : K2 planetary systems orbiting low-mass stars
(Dressing+, 2017)
J/AJ/155/21 : Planet candidates from K2 campaigns 5-8 (Petigura+, 2018)
J/AJ/156/22 : Planetary candidates from K2 Campaign 16 (Yu+, 2018)
J/AJ/156/277 : Sixty validated planets from K2 campaigns 5-8
(Livingston+, 2018)
Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 17 F17.14 Sun rho* [6.44887750696/12.4918984765] Stellar density,
relative to the Sun, ρ*
19- 31 F13.11 d Pb [2.64439278952/2.64481606882] Period for planet b
33- 48 F16.11 d T0b [3371.58808107/3371.59223826] Time of a sample
transit for planet b (BKJD)
50- 62 F13.11 --- secwb [0.01181286323/0.33187384921] sqrt(e)cosω
for planet b
64- 77 F14.11 --- seswb [-0.39092356579/-0.23995868521] sqrt(e)sinω
for planet b
79- 92 F14.11 deg ib [88.5693239327/89.4510052858] Inclination for
planet b
94 I1 deg Omegab [0] Longitude of periastron Ω for planet b
96-108 F13.11 Mjup Mb [0.01729664139/0.01873442648] Mass of planet b
110-118 F9.7 --- Rb [0.0554467/0.0592313] Radius of planet b, relative
to star
120-132 F13.11 d Pc [4.00457876322/4.0053746211] Period for planet c
134-149 F16.11 d T0c [3371.12891058/3371.13425933] Time of a sample
transit for planet c (BKJD)
151-164 F14.11 --- secwc [-0.29730700286/-0.00691265158] sqrt(e)cosω
for planet c
166-178 F13.11 --- seswc [0.0494574229/0.2858422551] sqrt(e)sinω for
planet c
180-193 F14.11 deg ic [87.4198453867/87.65620229] Inclination for
planet c
195-207 F13.11 deg Omegac [0.8118583802/2.95924502312] Longitude of
periastron Ω for planet c
209-221 F13.11 Mjup Mc [0.02243419248/0.02433098732] Mass of planet c
223-231 F9.7 --- Rc [0.0573228/0.0648858] Radius of planet c, relative
to star
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Byte-by-byte Description of file: table5.dat table6.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 3 I3 --- N [0/610] Transit number
5- 14 F10.5 d t [3371.13159/4992.44805] Transit time (BKJD)
16- 22 F7.4 min e_t [0.36/20.0592] Uncertainty in t
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Byte-by-byte Description of file: fig1[abcde].dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 20 E20.14 d Time [2306.61/4985.3] Observation date (BKJD)
(Time (BKJD))
22- 42 E21.15 --- Flux [-0.597158/1.02738] Relative flux (Relative Flux)
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 24-Oct-2019