J/AJ/159/2 K2-19b and c transit times and radial velocities (Petigura+, 2020)
K2-19b and c are in a 3:2 commensurability but out of resonance: a challenge
to planet assembly by convergent migration.
Petigura E.A., Livingston J., Batygin K., Mills S.M., Werner M.,
Isaacson H., Fulton B.J., Howard A.W., Weiss L.M., Espinoza N.,
Jontof-Hutter D., Shporer A., Bayliss D., Barros S.C.C.
<Astron. J., 159, 2 (2020)>
=2020AJ....159....2P 2020AJ....159....2P (SIMBAD/NED BibCode)
ADC_Keywords: Exoplanets ; Radial velocities ; Stars, double and multiple
Keywords: Exoplanet astronomy - Exoplanet dynamics - Exoplanet formation -
Exoplanet evolution - Extrasolar gas giants - Exoplanet structure -
Radial velocity
Abstract:
K2-19b and c were among the first planets discovered by NASA's K2 mission
and together stand in stark contrast with the physical and orbital
properties of the solar system planets. The planets are between the size
of Uranus and Saturn at 7.0±0.2 R⊕ and 4.1±0.2 R⊕,
respectively, and reside a mere 0.1% outside the nominal 3:2 mean-motion
resonance. They represent a different outcome of the planet formation
process than the solar system, as well as the vast majority of known
exoplanets. We measured the physical and orbital properties of these
planets using photometry from K2, Spitzer, and ground-based telescopes,
along with radial velocities from Keck/HIRES. Through a joint
photodynamical model, we found that the planets have moderate
eccentricities of e∼0.20 and well-aligned apsides Δω∼0°.
The planets occupy a strictly nonresonant configuration: the resonant
angles circulate rather than librate. This defies the predictions of
standard formation pathways that invoke convergent or divergent migration,
both of which predict Δω∼180° and eccentricities of a few
percent or less. We measured masses of Mp,b=32.4±1.7 M⊕ and
Mp,c=10.8±0.6 M⊕. Our measurements, with 5% fractional
uncertainties, are among the most precise of any sub-Jovian exoplanet.
Mass and size reflect a planet's core/envelope structure. Despite having
a relatively massive core of Mcore∼15 M⊕, K2-19b is
envelope-rich, with an envelope mass fraction of roughly 50%. This planet
poses a challenge to standard models of core-nucleated accretion, which
predict that cores ≳10 M⊕ will quickly accrete gas and trigger
runaway accretion when the envelope mass exceeds that of the core.
Description:
The Kepler Space Telescope observed K2-19 from 2014 May 30 to 2014
August 21 during campaign 1 of its K2 mission. We used the Spitzer Space
Telescope to observe two additional transits of K2-19b and K2-19 c
to better sample this signal. Planet b observations were conducted on
2017 April 23 and 2017 September 5; planet c observations were conducted
on 2016 October 4 and 2017 April 8.
A total of 51 spectra of K2-19 was obtained using the High Resolution
Echelle Spectrometer (HIRES; Vogt et al. 1994SPIE.2198..362V 1994SPIE.2198..362V) on the
10 m Keck I telescope between 2015 February 5 and 2017 December 26.
RVs were determined using standard procedures of the California Planet
Search (Howard et al. 2010ApJ...721.1467H 2010ApJ...721.1467H) including forward modeling
of the stellar and iodine spectra convolved with the instrumental
response (Marcy & Butler 1992PASP..104..270M 1992PASP..104..270M; Valenti et al.
1995PASP..107..966V 1995PASP..107..966V).
Objects:
----------------------------------------------------
RA (ICRS) DE Designation(s)
----------------------------------------------------
11 39 50.48 +00 36 12.9 K2-19 = EPIC 201505350
----------------------------------------------------
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
table1.dat 38 8 Transit times
table2.dat 29 51 Radial velocities
table4.dat 33 1197 Predicted transit times
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See also:
J/A+A/579/A19 : K2 Variable Catalogue (Armstrong+, 2015)
J/A+A/601/A128 : K2-19b and K2-19c radial velocity curves (Nespral+, 2017)
Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 6 A6 --- Planet Planet (K2-19b or K2-19c)
8- 10 I3 --- Transit [30/150] Kepler transit number
12- 19 A8 --- Inst Instrument
21- 29 F9.4 d Tc [2218/3197.87] Transit time, BJDTBD-2454833
31- 36 F6.4 d e_Tc [0.0009/0.0074] Uncertainty in Tc
38 A1 --- r_Tc [AB] Reference for Tc (1)
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Note (1): Source of transit times as follows:
A = This work;
B = Narita et al. (2015ApJ...815...47N 2015ApJ...815...47N).
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Byte-by-byte Description of file: table2.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1- 11 F11.6 d BJD [2225/3281.12] Barycentric Dynamical Time,
BJDTBD-2454833
13- 18 F6.2 m/s RV [-27.89/15.11] Relative radial velocity with
respect to solar system barycenter
20- 23 F4.2 m/s e_RV [1.89/3.79] Uncertainty in RV
25- 29 F5.3 --- SHK [0.181/0.401] Mount Wilson SHK activity index
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Byte-by-byte Description of file: table4.dat
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Bytes Format Units Label Explanations
--------------------------------------------------------------------------------
1 A1 --- Planet [bc] K2-19 planet
3- 5 I3 --- i [0/718] Transit index
7- 16 A10 "date" Date Predicted transit date, UTC
18- 26 F9.4 d Tc [1980.38/7667.37] Predicted transit time,
BJDTBD-2454833
28- 33 F6.4 d e_Tc [0.0001/0.3689] Uncertainty in Tc
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History:
From electronic version of the journal
(End) Prepared by [AAS], Tiphaine Pouvreau [CDS] 07-Feb-2020