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 (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) 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) 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) using multiplicity arguments (Lissauer et al. 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) 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). We obtained 42 spectra of K2-39 with HIRES between 2015 August 10 and 2016 August 21. Van Eylen et al. (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:
FileName Lrecl Records Explanations
ReadMe 80 . This file stars.dat 53 3 Stars observed table1.dat 44 198 *Radial velocities
Note on table1.dat: The HIRES observations from this work along with other data from the literature.
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
Bytes Format Units Label Explanations
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
Note (1): For K2-32 the column "Per" gives the orbital period of the planet b.
Byte-by-byte Description of file: table1.dat
Bytes Format Units Label Explanations
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
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.
History: From electronic version of the journal
(End) Prepared by [AAS]; Sylvain Guehenneux [CDS] 31-Jul-2017
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