J/AJ/153/142 Radial velocities of systems hosting sub-Saturns (Petigura+, 2017)
Four sub-Saturns with dissimilar densities: windows into planetary cores and
envelopes.
Petigura E.A., Sinukoff E., Lopez E.D., Crossfield I.J.M., Howard A.W.,
Brewer J.M., Fulton B.J., Isaacson H.T., Ciardi D.R., Howell S.B.,
Everett M.E., Horch E.P., Hirsch L.A., Weiss L.M., Schlieder J.E.
<Astron. J., 153, 142-142 (2017)>
=2017AJ....153..142P 2017AJ....153..142P (SIMBAD/NED BibCode)
ADC_Keywords: Planets ; Stars, double and multiple ; Radial velocities
Keywords: planets and satellites: composition -
planets and satellites: detection -
planets and satellites: dynamical evolution and stability -
planets and satellites: formation -
planets and satellites: gaseous planets -
planets and satellites: interiors
Abstract:
We present results from a Keck/HIRES radial velocity campaign to study
four sub-Saturn-sized planets, K2-27b, K2-32b, K2-39b, and K2-108b,
with the goal of understanding their masses, orbits, and heavy-element
enrichment. The planets have similar sizes (RP=4.5-5.5R⊕),
but have dissimilar masses (MP=16-60M⊕), implying a
diversity in their core and envelope masses. K2-32b is the least
massive (MP=16.5±2.7M⊕) and orbits in close proximity to
two sub-Neptunes near a 3:2:1 period commensurability. K2-27b and
K2-39b are significantly more massive at MP=30.9±4.6M⊕ and
MP=39.8±4.4M⊕, respectively, and show no signs of
additional planets. K2-108b is the most massive at
MP=59.4±4.4M⊕, implying a large reservoir of heavy
elements of about ≃50M. Sub-Saturns as a population have a
large diversity in planet mass at a given size. They exhibit
remarkably little correlation between mass and size; sub-Saturns range
from ≃6-60M⊕, regardless of size. We find a strong
correlation between planet mass and host star metallicity, suggesting
that metal-rich disks form more massive planet cores. The most massive
sub-Saturns tend to lack detected companions and have moderately
eccentric orbits, perhaps as a result of a previous epoch of dynamical
instability. Finally, we observe only a weak correlation between the
planet envelope fraction and present-day equilibrium temperature,
suggesting that photo-evaporation does not play a dominant role in
determining the amount of gas sub-Saturns accrete from their
protoplanetary disks.
Description:
We observed K2-27, K2-32, K2-39, and K2-108 using the High Resolution
Echelle Spectrometer (HIRES) on the 10 m Keck Telescope I.
K2-27 hosts a single transiting sub-Saturn, K2-27b, with P=6.77 days
that was first confirmed in Van Eylen et al. (2016ApJ...820...56V 2016ApJ...820...56V)
using RVs. We obtained 15 spectra of K2-27 with HIRES between 2015
February 5 and 2016 July 17. Van Eylen et al. (2016ApJ...820...56V 2016ApJ...820...56V)
observed this star with HARPS, HARPS-N, and FIES. We included 6 and 19
measurements from HARPS and HARPS-N, respectively in our radial
velocity analysis.
K2-32 hosts three planets, K2-32b, K2-32c, and K2-32d, having orbital
periods of P=8.99 days, 20.66 days, and 31.7 days, respectively, which
are near the 3:2:1 period commensurability. The planets were first
confirmed in Sinukoff et al. (2016ApJ...827...78S 2016ApJ...827...78S) using multiplicity
arguments (Lissauer et al. 2012ApJ...750..112L 2012ApJ...750..112L). We obtained 31
spectra of K2-32 with HIRES between 2015 June 06 and 2016 August 20.
Dai et al. (2016ApJ...823..115D 2016ApJ...823..115D) obtained 43 spectra with HARPS and 6
with PFS, which we included in our radial velocity analysis.
K2-39 hosts a single transiting planet, K2-39b, with P=4.60 days,
which was first confirmed by Van Eylen et al. (2016AJ....152..143V 2016AJ....152..143V).
We obtained 42 spectra of K2-39 with HIRES between 2015 August 10 and
2016 August 21. Van Eylen et al. (2016AJ....152..143V 2016AJ....152..143V) obtained 7
spectra with HARPS, 6 with PFS, and 17 with FIES.
K2-108, listed as EPIC-211736671 in the Ecliptic Planet Input Catalog
(Huber et al. 2016, Cat. J/ApJS/224/2), is a V=12.3mag star observed
during K2 Campaign 5. We identified K2-108 as a likely planet
according to our team's standard methodology, described in detail in
Crossfield et al. 2016 (Cat. J/ApJS/226/7). In brief, we identified a
set of transits having P=4.73 days and elevated K2-108 to the status
of "planet candidate". We obtained 20 spectra of K2-108 with HIRES
between 2015 December 23 and 2016 November 25.
File Summary:
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FileName Lrecl Records Explanations
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ReadMe 80 . This file
stars.dat 53 3 Stars observed
table1.dat 44 198 *Radial velocities
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Note on table1.dat: The HIRES observations from this work along with other data
from the literature.
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See also:
J/ApJS/226/7 : Planet candidates using K2's 1st yr (Crossfield+, 2016)
J/ApJS/224/2 : K2 EPIC stellar properties for 138600 targets (Huber+, 2016)
Byte-by-byte Description of file: stars.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Name Stellar identifier
7- 14 F8.6 d Per Orbital period (1)
16- 23 F8.6 d e_Per Error in Per
25- 31 F7.4 d PerC ? Orbital period of planet c for K2-32
33- 38 F6.4 d e_PerC ? Error in PerC
40- 46 F7.4 d PerD ? Orbital period of planet d for K2-32
48- 53 F6.4 d e_PerD ? Error in PerD
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Note (1): For K2-32 the column "Per" gives the orbital period of the planet b.
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Byte-by-byte Description of file: table1.dat
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Bytes Format Units Label Explanations
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1- 5 A5 --- Name Stellar identifier (K2-27, K2-32, or K2-39)
7- 13 A7 --- Inst Instrument identifier (either FIES, HARPS,
HARPS-N, HIRES, or PFS) (1)
15- 28 F14.6 d BJD Barycentric Julian Date (BJDTBD) (2)
30- 38 F9.2 m/s RV [-38039/24595.5] Radial velocity
40- 44 F5.2 m/s e_RV [1.3/35.7] The 1σ uncertainty in RV
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Note (1): The instrument codes are defined as follows:
HARPS-N = High Accuracy Radial velocity Planet Searcher for the Northern
hemisphere;
HIRES = High Resolution Echelle Spectrometer (HIRES) on the 10m Keck
Telescope I;
HARPS = High-Accuracy Radial velocity Planetary Searcher;
FIES = FIber-fed Echelle Spectrograph (FIES) at the Nordic Optical
Telescope (NOT);
PFS = Planet Finder Spectrograph (PFS) on the 6.5 meter Magellan Clay
telescope at Las Campanas Observatory (LCO) in Chile.
Note (2): Barycentric Dynamical Time.
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History:
From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 31-Jul-2017