Dynamical masses of the primary Be star and the secondary sdB star in the single-lined binary kappa Dra (B6 IIIe)

Abstract

Because many classical Be stars may owe their nature to mass and angular-momentum transfer in a close binary, the present masses, temperatures, and radii of their components are of high interest for comparison to stellar evolution models. Kappa Dra is a 61.5-day single-lined binary with a B6 IIIe primary. With the CHARA Array instruments MIRC/MIRC-X and MYSTIC, we detected the secondary at (approximately photospheric) flux ratios of 1.49 +- 0.10% and 1.63 +- 0.09% in the H and K band, respectively. From a large and diverse optical spectroscopic database only the radial velocity curve of the Be star could be extracted. However, employing the parallaxes from Hipparcos and Gaia, which agree within their nominal 1-sigma errors, we could derive the total mass and found component masses of 3.65 +- 0.48 Msun and 0.426 +- 0.043 Msun for the Be star and the companion, respectively. Previous cross-correlation of the observed far-UV spectrum with sdO spectral model templates had not detected a companion belonging to the hot O-type subdwarf (sdO) population known from ~20 earlier-type Be stars. Guided by our full 3D orbital solution, we found a strong cross-correlation signal for a stripped subdwarf B-type companion (far-UV flux ratio of 2.3 +- 0.5%), enabling the first firm characterization of such a star, and making kappa Dra the first mid- to late-type Be star with a directly-observed subdwarf companion.

Accepted to ApJ. Figure sets available on request

References in corpus (25)

• The Gaia mission
• Gaia Early Data Release 3: The astrometric solution
• Imaging the Surface of Altair
• Effects of gravitational darkening on the determination of fundamental parameters in fast rotating B-type stars
• Stellar and substellar companions from Gaia EDR3 -- Proper motion anomaly and resolved common proper motion pairs
• On the formation of Be stars through binary interaction
• The Detection and Characterization of Be+sdO Binaries from HST/STIS FUV Spectroscopy
• Investigating the lack of main-sequence companions to massive Be stars
• Spectral and spatial imaging of the Be+sdO binary phi Persei
• Validation of the accuracy and precision of Gaia EDR3 parallaxes with globular clusters
• Detection of the Ultraviolet Spectrum of the Hot Subdwarf Companion of 60 Cygni (B1 Ve) from a Survey of IUE Spectra of Be Stars
• The Single Star Path to Be Stars
• Population Synthesis of Galactic Be-star Binaries with A Helium-star Companion
• Swift J011511.0-725611: Discovery of a rare Be Star / White Dwarf binary system in the SMC
• Interferometric detections of sdO companions orbiting three classical Be stars
• Observations of Binary Stars with the Differential Speckle Survey Instrument. IX. Observations of Known and Suspected Binaries, and a Partial Survey of Be Stars
• Swift J004427.3-734801- a probable Be/white dwarf system in the Small Magellanic Cloud
• Identification of new classical Be stars from the LAMOST MRS survey
• Properties and nature of Be stars XXIII. Long-term variations and physical properties of kappa Dra
• Surveying the Bright Stars by Optical Interferometry III: A Magnitude-Limited Multiplicity Survey of Classical Be-Stars
• $\nu$ Gem: a hierarchical triple system with an outer Be star
• Spectroscopic Detection of the Pre-White Dwarf Companion of Regulus
• The optical counterpart to the Be/X-ray binary SAX J2239.3+6116
• The Transformative Journey of HD 93521
• A Study of the Time Variability and Line Profile Variations of kappa Dra

Cited by in corpus (11)

• The orbital and physical properties of five southern Be+sdO binary systems
• Gamma Cas Stars as Be + White Dwarf Binary Systems
• The B-type Binaries Characterisation Programme II. VFTS 291: A stripped star from a recent mass transfer phase
• High-spatial-resolution simulations of Be star disks in binary systems: I. Structure and kinematics of coplanar disks
• Newborn Be star systems observed shortly after mass transfer
• A Be Star + He Star Binary as an Indicator of a Binary Mass Transfer Phase
• HIP 15429: A newborn Be star on an eccentric binary orbit
• AstroSat/UVIT Study of NGC 663: First detection of Be+sdOB systems in a young star cluster
• Ultraviolet spectroscopy reveals a hot and luminous companion to the Be star+black hole candidate MWC 656
• The Be star omicron Cas is indeed the primary of a triple system
• Formation of Extremely Low-mass White Dwarf Binaries Undergoing Enhanced Angular Momentum Loss