Physical Parameters of the Multi-Planet Systems HD 106315 and GJ 9827

Abstract

HD 106315 and GJ 9827 are two bright, nearby stars that host multiple super-Earths and sub-Neptunes discovered by K2 that are well suited for atmospheric characterization. We refined the planets' ephemerides through Spitzer transits, enabling accurate transit prediction required for future atmospheric characterization through transmission spectroscopy. Through a multi-year high-cadence observing campaign with Keck/HIRES and Magellan/PFS, we improved the planets' mass measurements in anticipation of HST transmission spectroscopy. For GJ 9827, we modeled activity-induced radial velocity signals with a Gaussian process informed from the Calcium II H&K lines in order to more accurately model the effect of stellar noise on our data. We found planet masses of M${}_b$=$4.87\pm 0.37$ M${}_{\oplus }$, M${}_c$=$1.92\pm 0.49$ M${}_{\oplus }$, and M${}_d$=$3.42\pm 0.62$ M${}_{\oplus }$. For HD 106315, we found that such activity-radial velocity decorrelation was not effective due to the reduced presence of spots and speculate that this may extend to other hot stars as well (T${}_{\mathrm{eff}}>6200$ K). We found planet masses of M${}_b$=$10.5\pm 3.1$ M${}_{\oplus }$ and M${}_c$=$12.0\pm 3.8$ M${}_{\oplus }$. We investigated all of the planets' compositions through comparing their masses and radii to a range of interior models. GJ 9827 b and GJ 9827 c are both consistent with an Earth-like rocky composition, GJ 9827 d and HD 106315 b both require additional volatiles and are consistent with moderate amounts of water or hydrogen/helium, and HD 106315 c is consistent with 10% hydrogen/helium surrounding an Earth-like rock and iron core.

References in corpus (49)

• Astropy: A Community Python Package for Astronomy
• emcee: The MCMC Hammer
• The NumPy array: a structure for efficient numerical computation
• Gaia Data Release 2. Summary of the contents and survey properties
• The Gaia mission
• The Infrared Array Camera (IRAC) for the Spitzer Space Telescope
• The California-Kepler Survey. III. A Gap in the Radius Distribution of Small Planets
• batman: BAsic Transit Model cAlculatioN in Python
• Kepler planets: a tale of evaporation
• The evaporation valley in the Kepler planets
• Gaia Data Release 2: using Gaia parallaxes
• Understanding the Mass-Radius Relation for Sub-Neptunes: Radius as a Proxy for Composition
• A Framework for Prioritizing the TESS Planetary Candidates Most Amenable to Atmospheric Characterization
• RadVel: The Radial Velocity Modeling Toolkit
• Planets and Stellar Activity: Hide and Seek in the CoRoT-7 system
• Chromospheric Activity and Jitter Measurements for 2630 Stars on the California Planet Search
• Mass-Radius Relation for Rocky Planets based on PREM
• The California Planet Survey I. Four New Giant Exoplanets
• A Framework for Quantifying the Degeneracies of Exoplanet Interior Compositions
• The California-Kepler Survey. I. High Resolution Spectroscopy of 1305 Stars Hosting Kepler Transiting Planets
• Precision Stellar Characterization of FGKM Stars using an Empirical Spectral Library
• Spitzer Secondary Eclipses of the Dense, Modestly-irradiated, Giant Exoplanet HAT-P-20b Using Pixel-Level Decorrelation
• Asteroseismology and Gaia: Testing Scaling Relations Using 2200 Kepler Stars with TGAS Parallaxes
• A Detailed Model Grid for Solid Planets from 0.1 through 100 Earth Masses
• APF - The Lick Observatory Automated Planet Finder
• Low stellar obliquities in compact multiplanet systems
• H-alpha Activity of Old M Dwarfs: Stellar Cycles and Mean Activity Levels For 93 Low-Mass Stars in the Solar Neighborhood
• The Precision of Mass Measurements Required for Robust Atmospheric Characterization of Transiting Exoplanets
• Predicting the long-term stability of compact multiplanet systems
• Filtering solar-like oscillations for exoplanet detection in radial velocity observations
• Two Transiting Earth-size Planets Near Resonance Orbiting a Nearby Cool Star
• Testing exoplanet evaporation with multi-transiting systems
• Three Super-Earths Orbiting HD 7924
• Revised Masses and Densities of the Planets around Kepler-10
• Non-detection of Helium in the Upper Atmospheres of Three Sub-Neptune Exoplanets
• Three Small Super-Earths Transiting the nearby star GJ 9827
• Bulk composition of the transiting hot Neptune around GJ 436
• Masses and radii for the three super-Earths orbiting GJ 9827, and implications for the composition of small exoplanets
• Two Small Transiting Planets and a Possible Third Body Orbiting HD 106315
• Exoplanet Imitators: A test of stellar activity behavior in radial velocity signals
• A Multi-Planet System Transiting the $V$ = 9 Rapidly Rotating F-Star HD 106315
• The warm Neptunes around HD 106315 have low stellar obliquities
• A System of Three Super Earths Transiting the Late K-Dwarf GJ 9827 at Thirty Parsecs
• Precise masses for the transiting planetary system HD 106315 with HARPS
• Revisiting the HIP41378 system with K2 and Spitzer
• Photometry as a proxy for stellar activity in radial velocity analyses
• Mass determination of the 1:3:5 near-resonant planets transiting GJ 9827 (K2-135)
• Ground-based photometry of the 21-day Neptune HD106315c
• Magellan/PFS Radial Velocities of GJ 9827, a late K dwarf at 30 pc with Three Transiting Super-Earths

Cited by in corpus (11)

• JWST/NIRISS reveals the water-rich "steam world" atmosphere of GJ 9827 d
• Analysis of Early Science observations with the CHaracterising ExOPlanets Satellite (CHEOPS) using pycheops
• DREAM I. Orbital architecture orrery
• Evidence for the volatile-rich composition of a 1.5-$R_{\oplus }$ planet
• Water absorption in the transmission spectrum of the water-world candidate GJ9827d
• A multi-wavelength look at the GJ 9827 system -- No evidence of extended atmospheres in GJ 9827 b and d from HST and CARMENES data
• Connection between planetary He I $\lambda$10830 Å absorption and extreme-ultraviolet emission of planet-host stars
• Tentative Evidence for Water Vapor in the Atmosphere of the Neptune-Size Exoplanet HD 106315 c
• Absence of extended atmospheres in low-mass star radius-gap planets GJ 9827 b, GJ 9827 d and TOI-1235 b
• Another super-dense sub-Neptune in K2-182 b and refined mass measurements for K2-199 b and c
• Correlating Intrinsic Stellar Parameters with Mg II Self-Reversal Depths