Three Super-Earths Orbiting HD 7924

Abstract

We report the discovery of two super-Earth mass planets orbiting the nearby K0.5 dwarf HD 7924 which was previously known to host one small planet. The new companions have masses of 7.9 and 6.4 M${}_{\oplus }$, and orbital periods of 15.3 and 24.5 days. We perform a joint analysis of high-precision radial velocity data from Keck/HIRES and the new Automated Planet Finder Telescope (APF) to robustly detect three total planets in the system. We refine the ephemeris of the previously known planet using five years of new Keck data and high-cadence observations over the last 1.3 years with the APF. With this new ephemeris, we show that a previous transit search for the inner-most planet would have covered 70% of the predicted ingress or egress times. Photometric data collected over the last eight years using the Automated Photometric Telescope shows no evidence for transits of any of the planets, which would be detectable if the planets transit and their compositions are hydrogen-dominated. We detect a long-period signal that we interpret as the stellar magnetic activity cycle since it is strongly correlated with the Ca II H and K activity index. We also detect two additional short-period signals that we attribute to rotationally-modulated starspots and a one month alias. The high-cadence APF data help to distinguish between the true orbital periods and aliases caused by the window function of the Keck data. The planets orbiting HD 7924 are a local example of the compact, multi-planet systems that the Kepler Mission found in great abundance.

Accepted to ApJ on 4/7/2015

References in corpus (66)

• Validation of the new Hipparcos reduction
• Analytic Lightcurves for Planetary Transit Searches
• The James Webb Space Telescope
• Habitable Zones Around Main-Sequence Stars: New Estimates
• Accurate masses and radii of normal stars: modern results and applications
• Planet Occurrence within 0.25 AU of Solar-type Stars from Kepler
• The false positive rate of Kepler and the occurrence of planets
• Planetary Candidates Observed by Kepler, III: Analysis of the First 16 Months of Data
• Characteristics of planetary candidates observed by Kepler, II: Analysis of the first four months of data
• Towards a Deterministic Model of Planetary Formation I: a Desert in the Mass and Semi Major Axis Distributions of Extra Solar Planets
• Achieving better than 1 minute accuracy in the Heliocentric and Barycentric Julian Dates
• Prevalence of Earth-size planets orbiting Sun-like stars
• Most 1.6 Earth-Radius Planets are not Rocky
• Architecture and Dynamics of Kepler's Candidate Multiple Transiting Planet Systems
• No planet for HD 166435
• EXOFAST: A fast exoplanetary fitting suite in IDL
• Architecture of Kepler's Multi-transiting Systems: II. New investigations with twice as many candidates
• The Occurrence and Mass Distribution of Close-in Super-Earths, Neptunes, and Jupiters
• Stellar Diameters and Temperatures II. Main Sequence K & M Stars
• The Mass-Radius Relation for 65 Exoplanets Smaller than 4 Earth Radii
• Extrasolar planet population synthesis I: Method, formation tracks and mass-distance distribution
• Validation of Kepler's Multiple Planet Candidates. III: Light Curve Analysis & Announcement of Hundreds of New Multi-planet Systems
• First Results from the CHARA Array. II. A Description of the Instrument
• Chromospheric Activity and Jitter Measurements for 2630 Stars on the California Planet Search
• Improving the Efficiency of Markov Chain Monte Carlo for Analyzing the Orbits of Extrasolar Planets
• Masses, Radii, and Orbits of Small Kepler Planets: The Transition from Gaseous to Rocky Planets
• The Minimum-Mass Extrasolar Nebula: In-Situ Formation of Close-In Super-Earths
• The HARPS search for southern extra-solar planets XVIII. An Earth-mass planet in the GJ 581 planetary system
• The Exoplanet Orbit Database
• An extrasolar planetary system with three Neptune-mass planets
• Structure and Evolution of Nearby Stars with Planets II. Physical Properties of ~1000 Cool Stars from the SPOCS Catalog
• Friends of Hot Jupiters I: A Radial Velocity Search for Massive, Long-Period Companions to Close-In Gas Giant Planets
• Radial velocity planets de-aliased. A new, short period for Super-Earth 55 Cnc e
• SWEET-Cat: A catalogue of parameters for Stars With ExoplanETs I. New atmospheric parameters and masses for 48 stars with planets
• A simple method to estimate radial velocity variations due to stellar activity using photometry
• Migration then assembly: Formation of Neptune mass planets inside 1 AU
• The NASA-UC-UH Eta-Earth Program: IV. A Low-mass Planet Orbiting an M Dwarf 3.6 PC from Earth
• The HARPS search for Earth-like planets in the habitable zone: I -- Very low-mass planets around HD20794, HD85512 and HD192310
• Make Super-Earths, Not Jupiters: Accreting Nebular Gas onto Solid Cores at 0.1 AU and Beyond
• A Study of the Shortest-Period Planets Found With Kepler
• The Exoplanet Orbit Database II: Updates to exoplanets.org
• Architecture of Planetary Systems Based on Kepler Data: Number of Planets and Coplanarity
• Toward a Deterministic Model of Planetary Formation VI: Dynamical Interaction and Coagulation of Multiple Rocky Embryos and Super-Earth Systems around Solar Type Stars
• The Transit Light Curve (TLC) Project. I. Four Consecutive Transits of the Exoplanet XO-1b
• An Earth-sized planet with an Earth-like density
• Efficient fitting of multiplanet Keplerian models to radial velocity and astrometry data
• Theoretical models of planetary system formation: mass vs semi-major axis
• APF - The Lick Observatory Automated Planet Finder
• A Rocky Composition for an Earth-sized Exoplanet
• Retired A Stars and Their Companions: Eighteen New Jovian Planets
• Stellar Diameters and Temperatures V. Eleven Newly Characterized Exoplanet Host Stars
• Formation of close in Super-Earths \& Mini-Neptunes: Required Disk Masses \& Their Implications
• The NASA-UC Eta-Earth Program: I. A Super-Earth Orbiting HD 7924
• A Super-Earth and two Neptunes Orbiting the Nearby Sun-like star 61 Virginis
• The NASA-UC Eta-Earth Program: III. A Super-Earth orbiting HD 97658 and a Neptune-mass planet orbiting Gl 785
• Long-Term Transit Timing Monitoring and Refined Light Curve Parameters of HAT-P-13b
• The Hunt for Exomoons with Kepler (HEK): IV. A Search for Moons around Eight M-Dwarfs
• The NASA-UC Eta-Earth Program: II. A Planet Orbiting HD 156668 with a Minimum Mass of Four Earth Masses
• The Frequency of Low-mass Exoplanets
• Know the Star, Know the Planet. II. Speckle Interferometry of Exoplanet Host Stars
• The Albedos of Kepler's Close-in super-Earths
• Host Star Properties and Transit Exclusion for the HD 38529 Planetary System
• On the chromospheric activity of stars with planets
• The Stellar Obliquity and the Long-period planet in the HAT-P-17 Exoplanetary System
• The Lick-Carnegie Exoplanet Survey: Gliese 687b: A Neptune-Mass Planet Orbiting a Nearby Red Dwarf
• A Spitzer Search for Transits of Radial Velocity Detected Super-Earths

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• State of the Field: Extreme Precision Radial Velocities
• An Excess of Jupiter Analogs in Super-Earth Systems
• The Super Earth-Cold Jupiter Relations
• Statistics of Long Period Gas Giant Planets in Known Planetary Systems
• Precise Dynamical Masses of Directly Imaged Companions from Relative Astrometry, Radial Velocities, and Hipparcos-Gaia DR2 Accelerations
• The HARPS search for southern extra-solar planets. XXXVIII. Bayesian re-analysis of three systems. New super-Earths, unconfirmed signals, and magnetic cycles
• A non-interacting Galactic black hole candidate in a binary system with a main-sequence star
• Three's Company: An additional non-transiting super-Earth in the bright HD 3167 system, and masses for all three planets
• HAT-P-11: Discovery of a Second Planet and a Clue to Understanding Exoplanet Obliquities
• Understanding the Impacts of Stellar Companions on Planet Formation and Evolution: A Survey of Stellar and Planetary Companions within 25 pc
• K2-97b: A (Re-?)Inflated Planet Orbiting a Red Giant Star
• A Six-Planet System Orbiting HD 219134
• Orbit and Dynamical Mass of the Late-T Dwarf Gl 758 B
• KELT-11b: A Highly Inflated Sub-Saturn Exoplanet Transiting the V=8 Subgiant HD 93396
• The TESS-Keck Survey I: A Warm Sub-Saturn-mass Planet and a Caution about Stray Light in TESS Cameras
• The TESS-Keck Survey. VIII. Confirmation of a Transiting Giant Planet on an Eccentric 261 day Orbit with the Automated Planet Finder Telescope
• An upper boundary in the mass-metallicity plane of exo-Neptunes
• Simulating the M-R Relation from APF follow up of TESS targets: Survey design and strategies for overcoming mass biases
• Three Temperate Neptunes Orbiting Nearby Stars
• Radial Velocity Discovery of an Eccentric Jovian World Orbiting at 18 au
• The Pan-Pacific Planet Search III: Five companions orbiting giant stars
• TOI-1416: A system with a super-Earth planet with a 1.07d period
• Physical Parameters of the Multi-Planet Systems HD 106315 and GJ 9827
• Chemical Composition Of Bright Stars In The Northern Hemisphere: Star-Planet Connection
• Two warm, low-density sub-Jovian planets orbiting bright stars in K2 campaigns 13 and 14
• HD207897 b: A dense sub-Neptune transiting a nearby and bright K-type star
• KELT-12b: A $P\sim 5$ Day, Highly Inflated Hot Jupiter Transiting a Mildly Evolved Hot Star
• The HD 181433 Planetary System: Dynamics and a New Orbital Solution
• Giant Outer Transiting Exoplanet Mass (GOT 'EM) Survey: III. Recovery and Confirmation of a Temperate, Mildly Eccentric, Single-Transit Jupiter Orbiting TOI-2010
• Confirmation of the Long-Period Planet Orbiting Gliese 411 and the Detection of a New Planet Candidate
• Resolving Close Encounters: Stability in the HD 5319 and HD 7924 Planetary Systems
• The California-Kepler Survey. XI. A Survey of Chromospheric Activity Through the Lens of Precise Stellar Properties
• A High-Resolution Spectroscopic Survey of Directly Imaged Companion Hosts: I. Determination of diagnostic stellar abundances for planet formation and composition
• Revisiting the Full Sets of Orbital Parameters for the XO-3 System: No evidence for Temporal Variation of the Spin-Orbit Angle
• Null transit detections of 68 radial velocity exoplanets observed by TESS
• Automated Scheduling of Doppler Exoplanet Observations at Keck Observatory
• The California Legacy Survey I. A Catalog of 178 Planets from Precision Radial Velocity Monitoring of 719 Nearby Stars over Three Decades
• The California Legacy Survey III. On The Shoulders of (Some) Giants: The Relationship between Inner Small Planets and Outer Massive Planets