Alone but not lonely: Observational evidence that binary interaction is always required to form hot subdwarf stars

Abstract

Hot subdwarfs are core-helium burning stars that show lower masses and higher temperatures than canonical horizontal branch stars. They are believed to be formed when a red giant suffers an extreme mass-loss episode. Binary interaction is suggested to be the main formation channel, but the high fraction of apparently single hot subdwarfs (up to 30%) has prompted single star formation scenarios to be proposed. If such formation scenarios without interaction were possible, that would also imply the existence of hot subdwarfs in wide binaries that have undergone no interaction. We probe the existence of these systems by analysing light curves from the Transiting Exoplanet Survey Satellite (TESS) for all known hot subdwarfs with a main sequence wide binary companion, and by searching for common proper motion pairs to spectroscopically confirmed hot subdwarfs. We find that (i) the companions in composite hot subdwarfs show short rotation periods when compared to field main sequence stars. They display a triangular-shaped distribution with a peak around 2.5 days, similar to what is observed for young open clusters. This observed distribution of rotation rates for the companions in known wide hot subdwarf binaries provides evidence of previous interaction causing spin-up. We also report (ii) a shortage of hot subdwarfs with candidate common proper motion companions, considering the frequency of such systems among progenitors. We identify only 16 candidates after probing 2938 hot subdwarfs with good astrometry. Out of those, at least six seem to be hierarchical triple systems, in which the hot subdwarf is part of an inner binary. These results suggest that binary interaction is always required for the formation of hot subdwarfs.

arXiv comment17 pages, 11 figures, 5 tables. Accepted for publication in A&A

References in corpus (79)

• Astropy: A Community Python Package for Astronomy
• Gaia Data Release 2. Summary of the contents and survey properties
• The Transiting Exoplanet Survey Satellite
• Binary companions of evolved stars in APOGEE DR14: Search method and catalog of ~5,000 companions
• Gaia Data Release 2: The astrometric solution
• A Survey of Stellar Families: Multiplicity of Solar-Type Stars
• The K2 Mission: Characterization and Early results
• Stellar Multiplicity
• Mind your Ps and Qs: the Interrelation between Period (P) and Mass-ratio (Q) Distributions of Binary Stars
• The Origin of Subdwarf B Star (I): the Formation Channels
• Gaia Data Release 2: Photometric content and validation
• The origin of sdB stars (II)
• Binarity in Brown Dwarfs: T Dwarf Binaries Discovered with the Hubble Space Telescope WPFC2
• Hot subluminous stars
• Gaia-2MASS 3D maps of Galactic interstellar dust within 3 kpc
• The VAST Survey - III. The multiplicity of A-type stars within 75 pc
• The binary fraction of extreme horizontal branch stars
• Supernova Type Ia progenitors from merging double white dwarfs: Using a new population synthesis model
• The Origin of Extreme Horizontal Branch Stars
• Far-Ultraviolet Radiation from Elliptical Galaxies
• The Close Binary Fraction of Solar-type Stars is Strongly Anti-correlated with Metallicity
• Rotation in the Pleiades with K2: I. Data and First Results
• KPD1930+2752 - a candidate Type Ia supernova progenitor
• LISA verification binaries with updated distances from Gaia Data Release 2
• Can Planets Influence the Horizontal Branch Morphology?
• Rotation, differential rotation, and gyrochronology of active Kepler stars
• Rotation of Low-Mass Stars in Upper Scorpius and Rho Ophiuchus with K2
• A selection of hot subluminous stars in the GALEX survey II. Subdwarf atmospheric parameters
• Gaia Data Release 2: processing of the photometric data
• Where are the most ancient stars in the Milky Way?
• Orbital periods of twenty two subdwarf B stars
• First Kepler results on compact pulsators I. Survey target selection and the first pulsators
• The fastest unbound star in our Galaxy ejected by a thermonuclear supernova
• The population of hot subdwarf stars studied with Gaia II. The Gaia DR2 catalogue of hot subluminous stars
• Detection of additional Be+sdO systems from IUE spectroscopy
• The ELM Survey. VIII. 98 Double White Dwarf Binaries
• On type Ia supernovae and the formation of single low-mass white dwarfs
• Wide Binaries in Tycho-{\it Gaia}: Search Method and the Distribution of Orbital Separations
• Radial velocity measurements of Subdwarf B stars
• Close Binary White Dwarf Systems: Numerous New Detections and Their Interpretation
• The MUCHFUSS project - Searching for hot subdwarf binaries with massive unseen companions: Survey, target selection and atmospheric parameters
• Stellar rotation periods from K2 Campaigns 0-18 -- Evidence for rotation period bimodality and simultaneous variability decrease
• The Evolution of Flare Activity with Stellar Age
• Population of hot subdwarf stars studied with Gaia III. Catalogue of known hot subdwarf stars: Data Release 2
• The wide binary fraction of solar-type stars: emergence of metallicity dependence at a < 200 AU
• The orbital periods of subdwarf B binaries produced by the first stable Roche overflow channel
• The orbits of subdwarf-B + main-sequence binaries. II. Three eccentric systems; BD+29 3070, BD +34 1543 and Feige 87
• A pulsation zoo in the hot subdwarf B star KIC 10139564 observed by Kepler
• Resolving subdwarf B stars in binaries by HST imaging
• Gaia Data Release 2 Catalogue of Extremely-low Mass White Dwarf Candidates
• Single and Composite Hot Subdwarf Stars in the Light of 2MASS Photometry
• The orbits of subdwarf-B + main-sequence binaries: III. The period - eccentricity distribution
• The orbits of subdwarf B + main-sequence binaries. I: The sdB+G0 system PG 1104+243
• Critically-rotating accretors and non-conservative evolution in Algols
• Seismic evidence for non-synchronization in two close sdB+dM binaries from Kepler photometry
• Composite hot-subdwarf binaries -- I. The spectroscopically confirmed sdB sample
• Hot subdwarf stars in close-up view - II. Rotational properties of single and wide binary subdwarf B stars
• The Classificiation of Kepler B star Variables
• PG1018-047: the longest period subdwarf B binary
• Double-Dipping: A New Relation between Stellar Rotation and Starspot Activity
• Observed binary populations reflect the Galactic history. Explaining the orbital period-mass ratio relation in wide hot subdwarf binaries
• Population synthesis of Galactic subdwarf B stars
• How to Make a Singleton sdB Star via Accelerated Stellar Evolution
• The Hyper-MUCHFUSS project: probing the Galactic halo with sdB stars
• A fast and reliable method to measure stellar differential rotation from photometric data
• A CCD Imaging Search for Wide Metal-Poor Binaries
• Precise Ages of Field Stars from White Dwarf Companions
• The pulsating hot subdwarf Balloon 090100001: results of the 2005 multisite campaign
• The ELM Survey South. I. An Effective Search for Extremely Low Mass White Dwarfs
• Inferred timescales for common envelope ejection using wide astrometric companions
• A Radial Velocity Study of Composite-Spectra Hot Subdwarf Stars with the Hobby-Eberly Telescope
• The origin of single low-mass WDs: another problem that consequential angular momentum loss in CVs might solve
• Observations of Spin-Down in Post-Mast-Transfer Stars and the Possibility for Blue Straggler Gyrochronology
• SHOTGLAS I: The ultimate spectroscopic census of extreme horizontal branch stars in $\omega$ Centauri
• HE 0430-2457: a post merger extremely low-mass pre-white dwarf in a wide binary posing as an extreme horizontal branch star
• The subdwarf B star SB 290 - A fast rotator on the extreme horizontal branch
• Two New Long-Period Hot Subdwarf Binaries with Dwarf Companions
• The fast rotating, low gravity subdwarf B star EC 22081-1916 - Remnant of a common envelope merger event
• The masses of hot subdwarfs

Cited by in corpus (41)

• The population of hot subdwarf stars studied with Gaia -- IV. Catalogues of hot subluminous stars based on Gaia EDR3
• Hot subdwarfs in close binaries observed from space I: orbital, atmospheric, and absolute parameters and the nature of their companions
• Hot subdwarf Atmospheric parameters, Kinematics, and Origins -- Based on 1587 hot subdwarf stars observed in Gaia DR2 and LAMOST DR7
• Phases of Mass Transfer from Hot Subdwarfs to White Dwarf Companions and Their Photometric Properties
• Radial velocity variability and evolution of hot subdwarf stars
• A transit survey to search for planets around hot subdwarfs: I. methods and performance tests on light curves from Kepler, K2, TESS, and CHEOPS
• Hot subdwarf stars identified in LAMOST DR8 with single-lined and composite spectra
• Birth of a Be star: an APOGEE search for Be stars forming through binary mass transfer
• Hot subdwarfs in close binaries observed from space II: Analysis of the light curves
• Discovery of a highly magnetic He-sdO star from a double-degenerate binary merger
• Forming Hot Subluminous Stars from Hierarchical Triples -- I. The Role of an Outer Tertiary on Formation Channels
• Mass distribution for single-lined hot subdwarf stars in LAMOST
• Looking into the cradle of the grave: J22564-5910, a young post-merger hot subdwarf?
• Orbital and atmospheric parameters of two wide O-type subdwarf binaries: BD$-$11${}^{\mathrm{o}}$162 and Feige 80
• Discovery of new TESS pulsating hot subdwarfs
• SHOTGLAS II. MUSE spectroscopy of blue horizontal branch stars in the core of $\omega$ Centauri and NGC 6752
• A spectroscopic and kinematic survey of fast hot subdwarfs
• EPIC 216747137: a new HW Vir eclipsing binary with a massive sdOB primary and a low-mass M-dwarf companion
• Simulating a stellar contact binary merger -- I. Stellar models
• Physical Properties of 29 sdB+dM Eclipsing Binaries in Zwicky Transient Facility
• The first massive compact companion in a wide orbit around a hot subdwarf star
• Identification of new hot subdwarf binary systems by means of Virtual Observatory tools
• Advanced Classification of Hot Subdwarf Binaries Using Artificial Intelligence Techniques and Gaia DR3 data
• A super-Chandrasekhar mass type Ia supernova progenitor at 49 pc set to detonate in 23 Gyr
• A 500 pc volume-limited sample of hot subluminous stars II. Atmospheric parameters, mass distribution, and kinematics
• Pulse Timing Discovery of a Three-Day Companion to the Hot Subdwarf BPM 36430
• Population synthesis of hot subdwarf B stars with COMPAS: on the observed Galactic population
• A Grid of Synthetic Spectra for Subdwarfs: Non-LTE line-blanketed atmosphere models
• Evolution of binaries containing a hot subdwarf and a white dwarf to double white dwarfs, and double detonation supernovae with hypervelocity runaway stars
• Where are the binaries? -- Searching for blue horizontal-branch stars in binary systems in the inner Galactic Halo
• Limiting the accretion disk light in two mass transferring hot subdwarf binaries
• The $i$-processes nucleosynthesis during the formation of He-rich hot-subdwarf stars
• Discovery of periodic variables in the hot subdwarf catalogue through a systematic search in Zwicky Transient Facility data
• Detection of hot subdwarf binaries and sdB stars using machine learning methods and a large sample of Gaia XP spectra
• Hot Subdwarfs in Close Binaries Observed from Space III: Reflection Effect Asymmetry Induced by Relativistic Beaming
• Hidden Figures of Globular Clusters: Integrated Stellar Populations Impacted by Hot Subdwarfs
• Wide sdB binaries. I. Orbital and atmospheric parameters
• Onset of common envelope evolution during a core helium flash by rapid envelope expansion
• Stars on the ascending helium giant branch I. From white dwarf merger to helium giant: the evolutionary state of the rapidly rotating hot subdwarf HE 1518-0948
• Discovery of the first outbursting hot subdwarf binary: ZTF J0007+4804
• Discovery and analysis of three magnetic hot subdwarf stars: evidence for merger-induced magnetic fields