KELT-21b: A Hot Jupiter Transiting the Rapidly-Rotating Metal-Poor Late-A Primary of a Likely Hierarchical Triple System

Abstract

We present the discovery of KELT-21b, a hot Jupiter transiting the $V=10.5$ A8V star HD 332124. The planet has an orbital period of $P=3.6127647\pm 0.0000033$ days and a radius of $1.586_{-0.040}^{+0.039}$ $R_J$. We set an upper limit on the planetary mass of $M_P<3.91$ $M_J$ at $3\sigma$ confidence. We confirmed the planetary nature of the transiting companion using this mass limit and Doppler tomographic observations to verify that the companion transits HD 332124. These data also demonstrate that the planetary orbit is well-aligned with the stellar spin, with a sky-projected spin-orbit misalignment of $\lambda =-5.6_{-1.9}^{+1.7\circ }$. The star has $T_{\mathrm{eff}}=7598_{-84}^{+81}$ K, $M_{\ast }=1.458_{-0.028}^{+0.029}$ $M_{\odot }$, $R_{\ast }=1.638\pm 0.034$ $R_{\odot }$, and $v\sin I_{\ast }=146$ km s${}^{-1}$, the highest projected rotation velocity of any star known to host a transiting hot Jupiter. The star also appears to be somewhat metal-poor and $\alpha$-enhanced, with [Fe/H]$=-0.405_{-0.033}^{+0.032}$ and [$\alpha$/Fe]$=0.145\pm 0.053$; these abundances are unusual, but not extraordinary, for a young star with thin-disk kinematics like KELT-21. High-resolution imaging observations revealed the presence of a pair of stellar companions to KELT-21, located at a separation of 1.2" and with a combined contrast of $\Delta K_S=6.39\pm 0.06$ with respect to the primary. Although these companions are most likely physically associated with KELT-21, we cannot confirm this with our current data. If associated, the candidate companions KELT-21 B and C would each have masses of $\sim 0.12$ $M_{\odot }$, a projected mutual separation of $\sim 20$ AU, and a projected separation of $\sim 500$ AU from KELT-21. KELT-21b may be one of only a handful of known transiting planets in hierarchical triple stellar systems.

arXiv commentAccepted for publication in AJ. Updated to match accepted version. 25 pages, 14 figures

References in corpus (93)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Measuring Reddening with SDSS Stellar Spectra and Recalibrating SFD
• The 2.5 m Telescope of the Sloan Digital Sky Survey
• Intrinsic Colors, Temperatures, and Bolometric Corrections of Pre-Main Sequence Stars
• Gaia Data Release 1. Summary of the astrometric, photometric, and survey properties
• A Survey of Stellar Families: Multiplicity of Solar-Type Stars
• The Apache Point Observatory Galactic Evolution Experiment (APOGEE)
• Direct Imaging of Multiple Planets Orbiting the Star HR 8799
• Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe
• galpy: A Python Library for Galactic Dynamics
• Accurate masses and radii of normal stars: modern results and applications
• Shrinking binary and planetary orbits by Kozai cycles with tidal friction
• Radial Mixing in Galactic Discs
• Images of a fourth planet orbiting HR 8799
• A giant planet imaged in the disk of the young star Beta Pictoris
• Achieving better than 1 minute accuracy in the Heliocentric and Barycentric Julian Dates
• EXOFAST: A fast exoplanetary fitting suite in IDL
• Hot Stars with Hot Jupiters Have High Obliquities
• AstroImageJ: Image Processing and Photometric Extraction for Ultra-Precise Astronomical Light Curves
• AstroImageJ: Image Processing and Photometric Extraction for Ultra-Precise Astronomical Light Curves (Expanded Edition)
• Modelling the Galactic Interstellar Extinction Distribution in Three Dimensions
• Star counts in the Galaxy. Simulating from very deep to very shallow photometric surveys with the TRILEGAL code
• A Three-Dimensional Map of Milky-Way Dust
• Gaia broad band photometry
• Spin-orbit angle measurements for six southern transiting planets; New insights into the dynamical origins of hot Jupiters
• Abundances, Stellar Parameters, and Spectra From the SDSS-III/APOGEE Survey
• The Kilodegree Extremely Little Telescope (KELT): A Small Robotic Telescope for Large-Area Synoptic Surveys
• Gaia Data Release 1: Catalogue validation
• HAT-P-16b: A 4 Mj Planet Transiting A Bright Star On An Eccentric Orbit
• The VAST Survey - III. The multiplicity of A-type stars within 75 pc
• The APOKASC Catalog: An Asteroseismic and Spectroscopic Joint Survey of Targets in the Kepler Fields
• Parameter Estimation from Time-Series Data with Correlated Errors: A Wavelet-Based Method and its Application to Transit Light Curves
• Line-profile tomography of exoplanet transits -- II. A gas-giant planet transiting a rapidly-rotating A5 star
• KELT-1b: A Strongly Irradiated, Highly Inflated, Short Period, 27 Jupiter-mass Companion Transiting a mid-F Star
• On the Formation of Hot Jupiters in Stellar Binaries
• Evidence of Possible Spin-Orbit Misalignment Along the Line of Sight in Transiting Exoplanet Systems
• A giant planet undergoing extreme ultraviolet irradiation by its hot massive-star host
• Precise Radial Velocities of Giant Stars VII. Occurrence Rate of Giant Extrasolar Planets as a Function of Mass and Metallicity
• Rotational velocities of A-type stars. III. Velocity distributions
• Giant planets orbiting metal-rich stars show signatures of planet-planet interactions
• The stellar population structure of the Galactic disk
• Young [$\alpha$/Fe]-enhanced stars discovered by CoRoT and APOGEE: What is their origin?
• PEPSI: The high-resolution echelle spectrograph and polarimeter for the Large Binocular Telescope
• The KELT-South Telescope
• Retired A Stars and Their Companions: Eighteen New Jovian Planets
• Friends of Hot Jupiters. IV. Stellar companions beyond 50 AU might facilitate giant planet formation, but most are unlikely to cause Kozai-Lidov migration
• The First APOKASC Catalog of Kepler Dwarf and Subgiant Stars
• Transiting hot Jupiters from WASP-South, Euler and TRAPPIST: WASP-95b to WASP-101b
• Local Stellar Kinematics from RAVE Data: I. Local Standard of Rest
• Asymmetric transit curves as indication of orbital obliquity: clues from the late-type dwarf companion in KOI-13
• Evidence for the Tidal Destruction of Hot Jupiters by Subgiant Stars
• Overabundance of alpha-elements in exoplanet host stars
• Detection Of KOI-13.01 Using The Photometric Orbit
• Evidence for a systematic offset of $-$0.25 mas in the Gaia DR1 parallaxes
• KELT-20b: A giant planet with a period of P~ 3.5 days transiting the V~ 7.6 early A star HD 185603
• Binary stars in the Galactic thick disc
• Cannibals in the thick disk: the young $\alpha -$rich stars as evolved blue stragglers
• A Misaligned Prograde Orbit for Kepler-13 Ab via Doppler Tomography
• "Retired" Planet Hosts: Not So Massive, Maybe Just Portly After Lunch
• HAT-P-57b: A Short-Period Giant Planet Transiting A Bright Rapidly Rotating A8V Star Confirmed Via Doppler Tomography
• Measurement of the Nodal Precession of WASP-33 b via Doppler Tomography
• WASP-12b and HAT-P-8b are Members of Triple Star Systems
• KELT-17b: A hot-Jupiter transiting an A-star in a misaligned orbit detected with Doppler tomography
• KELT-3b: A Hot Jupiter Transiting a V=9.8 Late-F Star
• Transiting exoplanets from the CoRoT space mission XIV. CoRoT-11b: a transiting massive "hot-Jupiter" in a prograde orbit around a rapidly rotating F-type star
• The TRENDS High-Contrast Imaging Survey. I. Three Benchmark M-dwarfs Orbiting Solar-type Stars
• KELT-8b: A highly inflated transiting hot Jupiter and a new technique for extracting high-precision radial velocities from noisy spectra
• GRACES observations of young [alpha/Fe]-rich stars
• POET: A Model for (P)lanetary (O)rbital (E)volution due to (T)ides on Evolving Stars
• WASP-167b/KELT-13b: Joint discovery of a hot Jupiter transiting a rapidly-rotating F1V star
• High-resolution Imaging of Transiting Extrasolar Planetary systems (HITEP). I. Lucky imaging observations of 101 systems in the southern hemisphere
• KELT-11b: A Highly Inflated Sub-Saturn Exoplanet Transiting the V=8 Subgiant HD 93396
• KELT-19Ab: A P~4.6 Day Hot Jupiter Transiting a Likely Am Star with a Distant Stellar Companion
• MASCARA-1 b: A hot Jupiter transiting a bright $m_V=8.3$ A-star in a misaligned orbit
• Discovery of XO-6b: a hot Jupiter transiting a fast rotating F5 star on an oblique orbit
• KELT-16b: A highly irradiated, ultra-short period hot Jupiter nearing tidal disruption
• HAT-P-25b: a Hot-Jupiter Transiting a Moderately Faint G Star
• Retired A Stars: The Effect of Stellar Evolution on the Mass Estimates of Subgiants
• KELT-6b: A P~7.9 d Hot Saturn Transiting a Metal-Poor Star with a Long-Period Companion
• Spin orbit alignment for KELT-7b and HAT-P-56b via Doppler tomography with TRES
• Doppler tomography of transiting exoplanets: A prograde, low-inclined orbit for the hot Jupiter CoRoT-11b
• KELT-4Ab: An inflated Hot Jupiter transiting the bright (V~10) component of a hierarchical triple
• SOPHIE velocimetry of Kepler transit candidates VI. An additional companion in the KOI-13 system
• Classical and relativistic node precessional effects in WASP-33b and perspectives for detecting them
• Luminosity and surface brightness distribution of K-band galaxies from the UKIDSS Large Area Survey
• Asteroseismic masses of retired planet-hosting A-stars using SONG
• Spin-Orbit Misalignments of Three Jovian Planets via Doppler Tomography
• Constructing Polynomial Spectral Models for Stars
• On the formation of hot and warm Jupiters via secular high-eccentricity migration in stellar triples
• Accelerated Fitting of Stellar Spectra
• KELT-12b: A $P\sim 5$ Day, Highly Inflated Hot Jupiter Transiting a Mildly Evolved Hot Star
• KELT-18b: Puffy Planet, Hot Host, Probably Perturbed
• Constraints on the Obliquities of Kepler Planet-Hosting Stars

Cited by in corpus (32)

• Stellar obliquities in exoplanetary systems
• TESS Transit Timing of Hundreds of Hot Jupiters
• ExoClock Project III: 450 new exoplanet ephemerides from ground and space observations
• The GAPS Programme with HARPS-N at TNG XIX. Atmospheric Rossiter-McLaughlin effect and improved parameters of KELT-9b
• A-type Stars, the Destroyers of Worlds: The lives and deaths of Jupiters in evolving stellar binaries
• High-resolution transmission spectroscopy study of ultra-hot Jupiters HAT-P-57b, KELT-17b, KELT-21b, KELT-7b, MASCARA-1b, and WASP-189b
• K2-260 b: a hot Jupiter transiting an F star, and K2-261 b: a warm Saturn around a bright G star
• HATS-60b - HATS-69b: Ten Transiting Planets From HATSouth
• Eating Planets for Lunch and Dinner: Signatures of Planet Consumption by Evolving Stars
• New transiting hot Jupiters discovered by WASP-South, Euler/CORALIE and TRAPPIST-South
• KELT-25b and KELT-26b: A Hot Jupiter and a Substellar Companion Transiting Young A-stars Observed by TESS
• An Aligned Orbit for the Young Planet V1298 Tau b
• Revised Exoplanet Radii and Habitability Using Gaia Data Release 2
• Radial Velocity Discovery of an Eccentric Jovian World Orbiting at 18 au
• KELT-24b: A 5M${}_{\mathrm{J}}$ Planet on a 5.6 day Well-Aligned Orbit around the Young V=8.3 F-star HD 93148
• The GAPS Programme with HARPS-N at TNG. XXXI. The WASP-33 system revisited with HARPS-N
• Sub-stellar Companions of Intermediate-mass Stars with CoRoT: CoRoT-34b, CoRoT-35b, and CoRoT-36b
• Doppler Tomographic Measurement of the Nodal Precession of WASP-33b
• HIP 33609 b: An Eccentric Brown Dwarf Transiting a V=7.3 Rapidly Rotating B-Star
• Discovery of WASP-174b: Doppler tomography of a near-grazing transit
• An Extreme-mass Ratio, Short-period Eclipsing Binary Consisting of a B Dwarf Primary and a Pre-main Sequence M Star Companion Discovered by KELT
• KELT-23Ab: A Hot Jupiter Transiting a Near-Solar Twin Close to the TESS and JWST Continuous Viewing Zones
• TESS Timings of 31 Hot Jupiters with Ephemeris Uncertainties
• The K2 & TESS Synergy II: Revisiting 26 systems in the TESS Primary Mission
• Lack of close-in, massive planets of main-sequence A-type stars from Kepler
• KELT: The Kilodegree Extremely Little Telescope, a Survey for Exoplanets Transiting Bright, Hot Stars
• Precise Transit Photometry Using TESS II: Revisiting 28 Additional Transiting Systems With Updated Physical Properties
• Rapidly rotating stars and their transiting planets: KELT-17b, KELT-19Ab, and KELT-21b in the CHEOPS and TESS era
• A Transmission Spectrum Of HD 189733b From Multiple Broadband Filter Observations
• The effects of stellar gravity darkening on high-resolution transmission spectra
• A Substellar Companion to a Hot Star in K2's Campaign 0 Field
• Evidence for the Late Arrival of Hot Jupiters in Systems with High Host-star Obliquities