J/AJ/156/89 RVs & predicted transit-times for the K2-24 system (Petigura+, 2018)
Dynamics and formation of the near-resonant K2-24 system: insights from
transit-timing variations and radial velocities.
Petigura E.A., Benneke B., Batygin K., Fulton B.J., Werner M., Krick J.E.,
Gorjian V., Sinukoff E., Deck K.M., Mills S.M., Deming D.
<Astron. J., 156, 89 (2018)>
=2018AJ....156...89P 2018AJ....156...89P (SIMBAD/NED BibCode)
ADC_Keywords: Stars, double and multiple ; Exoplanets ; Radial velocities ;
Models, evolutionary
Keywords: planets and satellites: dynamical evolution and stability -
planets and satellites: formation -
planets and satellites: individual (K2-24b, K2-24c) -
techniques: radial velocities
Abstract:
While planets between the size of Uranus and Saturn are absent within
the solar system, the star K2-24 hosts two such planets, K2-24b and c,
with radii equal to 5.4 R⊕ and 7.5 R⊕, respectively.
The two planets have orbital periods of 20.9 days and 42.4 days,
residing only 1% outside the nominal 2:1 mean-motion resonance. In
this work, we present results from a coordinated observing campaign to
measure planet masses and eccentricities that combines radial velocity
measurements from Keck/HIRES and transit-timing measurements from K2
and Spitzer. K2-24b and c have low, but nonzero, eccentricities of
e1∼e2∼0.08. The low observed eccentricities provide clues to the
formation and dynamical evolution of K2-24b and K2-24c, suggesting
that they could be the result of stochastic gravitational interactions
with a turbulent protoplanetary disk, among other mechanisms. K2-24b
and c are 19.0-2.1+2.2 M⊕ and 15.4-1.8+1.9 M⊕,
respectively; K2-24c is 20% less massive than K2-24b, despite being
40% larger. Their large sizes and low masses imply large envelope
fractions, which we estimate at 26-3+3 % and 52-3+5 %. In
particular, K2-24c's large envelope presents an intriguing challenge
to the standard model of core-nucleated accretion that predicts the
onset of runaway accretion when fenv∼50%.
Description:
K2-24 was observed during campaign 2 of the K2 mission from 2014
August 23 to 2014 October 13. To extract transit times, we used the
photometry published in Petigura et al. 2016ApJ...818...36P 2016ApJ...818...36P (P16) and
fit individual transits.
We used Spitzer to observe two additional transits of K2-24b on 2015
October 27 and 2016 June 13 and two additional transits of K2-24c on
2015 November 12 and 2016 June 10.
We obtained 63 spectra of K2-24 using HIRES (Vogt et al.
1994SPIE.2198..362V 1994SPIE.2198..362V) on the 10 m Keck I telescope between 2015 June 24
and 2017 October 03. We collected spectra through an iodine cell mounted
directly in front of the spectrometer slit. The iodine cell imprints a
dense forest of absorption lines which serve as a wavelength reference.
We used an exposure meter to achieve a consistent signal-to-noise
level of 110 per reduced pixel on blaze near 550 nm. We also obtained
a "template" spectrum without iodine. The first 32 of these
spectroscopic observations are described in P16.
Objects:
-------------------------------------------------------------
RA (ICRS) DE Designation(s)
-------------------------------------------------------------
16 10 17.70 -24 59 25.3 K2-24 = 2MASS J16101770-2459251
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File Summary:
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FileName Lrecl Records Explanations
--------------------------------------------------------------------------------
ReadMe 80 . This file
table2.dat 29 64 Radial velocities
table4.dat 33 296 Predicted transit times for K2-24 planet b or c
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See also:
J/ApJ/750/114 : Kepler TTVs. IV. 4 multiple-planet systems (Fabrycky+, 2012)
J/ApJ/787/80 : 139 Kepler planets transit time variations (Hadden+, 2014)
J/ApJS/210/20 : Small Kepler planets radial velocities (Marcy+, 2014)
J/AJ/153/142 : Radial velocities of systems hosting sub-Saturns
(Petigura+, 2017)
J/AJ/154/5 : Transit timing variations of 145 Kepler planets (Hadden+, 2017)
Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 F11.6 d BJD Barycentric Julian Date in Barycentric Dynamical
Time (BJD-2454833; TDB)
13- 18 F6.2 m/s RV [-14.14/14.2] Barycentric radial velocity
20- 23 F4.2 m/s e_RV [1.52/2.09] Uncertainty in RV
25- 29 F5.3 --- SHK [0.094/0.143] Mount Wilson SHK activity index (1)
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Note (1): SHK measured to 1% precision (Vaughan et al. 1978PASP...90..267V 1978PASP...90..267V).
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Byte-by-byte Description of file: table4.dat
--------------------------------------------------------------------------------
Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 1 A1 --- Planet [bc] K2-24 planet b or c
3- 5 I3 --- i [0/197] Individual transit index
7- 16 A10 "date" Date UTC date
18- 26 F9.4 d BJD Predicted transit time in Barycentric Dynamical
Time (BJD-2454833; TDB)
28- 33 F6.4 d e_BJD Uncertainty in BJD
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 15-Feb-2019