Colder and Hotter: Interferometric imaging of β Cassiopeiae and α Leonis

Abstract

Near-infrared interferometers have recently imaged a number of rapidly rotating A-type stars, finding levels of gravity darkening inconsistent with theoretical expectations. Here, we present new imaging of both a cooler star β Cas (F2IV) and a hotter one α Leo (B7V) using the CHARA array and the MIRC instrument at the H band. Adopting a solid-body rotation model with a simple gravity darkening prescription, we modeled the stellar geometric properties and surface temperature distributions, confirming both stars are rapidly rotating and show gravity darkening anomalies. We estimate the masses and ages of these rapid rotators on L-Rpol and HR diagrams constructed for non-rotating stars by tracking their non-rotating equivalents. The unexpected fast rotation of the evolved subgiant β Cas offers a unique test of the stellar core-envelope coupling, revealing quite efficient coupling over the past ~ 0.5 Gyr. Lastly we summarize all our interferometric determinations of the gravity darkening coefficient for rapid rotators, finding none match the expectations from the widely used von Zeipel gravity darkening laws. Since the conditions of the von Zeipel law are known to be violated for rapidly rotating stars, we recommend using the empirically-derived β = 0.19 for such stars with radiation-dominated envelopes. Furthermore, we note that no paradigm exists for self-consistently modeling heavily gravity-darkened stars that show hot radiative poles with cool convective equators.

34 pages, 11 figures

References in corpus (7)

• The Geneva-Copenhagen Survey of the Solar neighbourhood II. New uvby calibrations and rediscussion of stellar ages, the G dwarf problem, age-metallicity diagram, and heating mechanisms of the disk
• Imaging the Surface of Altair
• Vega is a rapidly rotating star
• First Results from the CHARA Array VII: Long-Baseline Interferometric Measurements of Vega Consistent with a Pole-On, Rapidly Rotating Star
• Imaging and Modeling Rapidly Rotating Stars: Alpha Cephei and Alpha Ophiuchi
• The angular sizes of dwarf stars and subgiants - Non-linear surface brightness relations in BVRcIc from interferometry
• Surface temperature and synthetic spectral energy distributions for rotationally deformed stars

Cited by in corpus (69)

• Interferometric Observations of Rapidly Rotating Stars
• Gravity darkening in rotating stars
• Fundamental Parameters of 87 Stars from the Navy Precision Optical Interferometer
• Stellar Diameters and Temperatures III. Main Sequence A, F, G, & K Stars: Additional high-precision measurements and empirical relations
• Asymmetric transit curves as indication of orbital obliquity: clues from the late-type dwarf companion in KOI-13
• KOI 1224, a Fourth Bloated Hot White Dwarf Companion Found With Kepler
• A near-infrared interferometric survey of debris disc stars. III. First statistics based on 42 stars observed with CHARA/FLUOR
• Resolving Vega and the inclination controversy with CHARA/MIRC
• Self-consistent 2D models of fast rotating early-type star
• Gas Distribution, Kinematics, and Excitation Structure in the Disks around the Classical Be Stars Beta Canis Minoris and Zeta Tauri
• Searching for faint companions with VLTI/PIONIER. I. Method and first results
• The Ages of A-Stars I: Interferometric Observations and Age Estimates for Stars in the Ursa Major Moving Group
• Fluctuations and Flares in the Ultraviolet Line Emission of Cool Stars: Implications for Exoplanet Transit Observations
• ASTRI Mini-Array Core Science at the Observatorio del Teide
• Characterization of the gaseous companion κ Andromedae b: New Keck and LBTI high-contrast observations
• Optical Interferometry of early-type stars with PAVO@CHARA. I. Fundamental stellar properties
• Polarization due to rotational distortion in the bright star Regulus
• Contemporaneous Imaging Comparisons of the Spotted Giant $\sigma$ Geminorum Using Interferometric, Spectroscopic, and Photometric Data
• Critical angular velocity and anisotropic mass loss of rotating stars with radiation-driven winds
• Gravity-Darkening Analysis of Misaligned Hot Jupiter MASCARA-4 b
• The Effect of Density on the Thermal Structure of Gravitationally-Darkened Be Star Disks
• VISION: A Six-Telescope Fiber-Fed Visible Light Beam Combiner for the Navy Precision Optical Interferometer
• Analysis of Spin-Orbit Misalignment in Eclipsing Binary DI Herculis
• A Multi-observing-technique Study of the Dynamical Evolution of the Viscous Disk around the Be Star $\omega$ CMa
• Performance and first measurements of the MAGIC Stellar Intensity Interferometer
• Measured Diameters of 2 F-stars in the Beta Pic Moving Group
• beta Cas: the first delta Scuti star with a dynamo magnetic field
• Ultraviolet Spectropolarimetry: on the origin of rapidly rotating B stars
• Capabilities of future intensity interferometers for observing fast-rotating stars: imaging with two- and three-telescope correlations
• Hot Grain Dynamics by Electric Charging and Magnetic Trapping in Debris Disks
• Towards the true number of flaring giant stars in the Kepler field. Are there flaring specialities associated with the giant nature?
• The H-band Emitting Region of the Luminous Blue Variable P Cygni: Spectrophotometry and Interferometry of the Wind
• Gravity darkening in stars with surface differential rotation
• Detecting the Companions and Ellipsoidal Variations of RS CVn Primaries: II. omicron Draconis, a Candidate for Recent Low-Mass Companion Ingestion
• A versatile numerical method for obtaining structures of rapidly rotating baroclinic stars: self-consistent and systematic solutions with shellular-type rotation
• The rotation of alpha Oph investigated using polarimetry
• Dynamical Surface Imaging of lambda Andromedae
• The dependence of convective core overshooting on stellar mass
• On the Role of the $\Omega \Gamma$ Limit in the Formation of Population III Massive Stars
• Spectroscopic Detection of the Pre-White Dwarf Companion of Regulus
• Interferometry of chemically peculiar stars: theoretical predictions vs. modern observing facilities
• Angular Sizes and Effective Temperatures of O-type Stars from Optical Interferometry with the CHARA Array
• Critical study of the distribution of rotational velocities of Be stars; II: Differential rotation and some hidden effects interfering with the interpretation of the Vsin i parameter
• Assessing the quality of restored images in optical long-baseline interferometry
• Gravity darkening in late-type stars. The Coriolis effect
• The evolved fast rotator Sargas. Stellar parameters and evolutionary status from VLTI/PIONIER and VLT/UVES
• A model of anisotropic winds from rotating stars for evolutionary calculations
• Comparing Different Approaches for Stellar Intensity Interferometry
• The Habitable Zones of Rapidly Rotating Main Sequence A/F Stars
• Synthetic Spectra of Rotating Stars
• Differential interferometry of the rapid rotator Regulus
• Convective Differential Rotation in Stars and Planets II: Observational and Numerical Tests
• Science cases for a visible interferometer
• The Small Separation A-Star Companion Population: First Results with CHARA/MIRC-X
• Understanding the dynamical structure of pulsating stars: The Baade-Wesselink projection factor of the delta Scuti stars AI Vel and beta Cas
• RUBIS: a simple tool for calculating the centrifugal deformation of stars and planets
• Infrared interferometry to spatially and spectrally resolve jets in X-ray binaries
• Physics of rotation: problems and challenges
• Internal rapid rotation and its implications for stellar structure and pulsations
• Scaling of Observable Properties in Rapidly Rotating Stars
• Modeling the H$\alpha$ Emission Surrounding Spica using the Lyman Continuum from a Gravity-darkened Central Star
• Modeling rotating stars in two dimensions
• SDSS J100711.74+193056.2: A Candidate Common Motion Substellar Companion to the Nearest B-Type Star Regulus
• Extended Main Sequences in Star Clusters
• Measurement of the photosphere oblateness of $\gamma$ Cassiopeiae via Stellar Intensity Interferometry with the VERITAS Observatory
• A Lagrangian construction of rotating stars
• Scaling of oscillation frequencies in rotating stars
• Spectroscopic Line Modeling of the Fastest Rotating O-type Stars
• Application limit of the photocentre displacement to fundamental stellar parameters of fast rotators -- Illustration on the edge-on fast rotator Regulus