Unexpected Short-Period Variability in Dwarf Carbon Stars from the Zwicky Transient Facility

Abstract

Dwarf carbon (dC) stars, main sequence stars showing carbon molecular bands, are enriched by mass transfer from a previous asymptotic-giant-branch (AGB) companion, which has since evolved to a white dwarf. While previous studies have found radial-velocity variations for large samples of dCs, there are still relatively few dC orbital periods in the literature and no dC eclipsing binaries have yet been found. Here, we analyze photometric light curves from DR5 of the Zwicky Transient Facility for a sample of 944 dC stars. From these light curves, we identify 34 periodically variable dC stars. Remarkably, of the periodic dCs, 82\% have periods less than two days. We also provide spectroscopic follow-up for four of these periodic systems, measuring radial velocity variations in three of them. Short-period dCs are almost certainly post-common-envelope binary systems, since the periodicity is most likely related to the orbital period, with tidally locked rotation and photometric modulation on the dC either from spots or from ellipsoidal variations. We discuss evolutionary scenarios that these binaries may have taken to accrete sufficient C-rich material while avoiding truncation of the thermally pulsing AGB phase needed to provide such material in the first place. We compare these dCs to common-envelope models to show that dC stars probably cannot accrete enough C-rich material during the common-envelope phase, suggesting another mechanism like wind-Roche lobe overflow is necessary. The periodic dCs in this paper represent a prime sample for spectroscopic follow-up and for comparison to future models of wind-Roche lobe overflow mass transfer.

arXiv comment23 pages, 5 figures, 5 tables, accepted to ApJ

References in corpus (53)

• Scikit-learn: Machine Learning in Python
• SciPy 1.0--Fundamental Algorithms for Scientific Computing in Python
• Astropy: A Community Python Package for Astronomy
• The Zwicky Transient Facility: System Overview, Performance, and First Results
• Evolution of binary stars and the effect of tides on binary populations
• Sloan Digital Sky Survey IV: Mapping the Milky Way, Nearby Galaxies, and the Distant Universe
• Understanding the Lomb-Scargle Periodogram
• The Zwicky Transient Facility: Data Processing, Products, and Archive
• The Palomar Transient Factory: System Overview, Performance and First Results
• Common Envelope Evolution: Where we stand and how we can move forward
• A new generation of PARSEC-COLIBRI stellar isochrones including the TP-AGB phase
• The Zwicky Transient Facility: Science Objectives
• Exploring the Optical Transient Sky with the Palomar Transient Factory
• The RAVE Survey: Constraining the Local Galactic Escape Speed
• The Evolution of Cataclysmic Variables as Revealed by their Donor Stars
• Chemo-spectrophotometric evolution of spiral galaxies: I. The model and the Milky Way
• The Stellar Populations of Praesepe and Coma Berenices
• Supernova Type Ia progenitors from merging double white dwarfs: Using a new population synthesis model
• Population synthesis for double white dwarfs. II. Semi-detached systems: AM CVn stars
• Post-common-envelope binaries from SDSS. IX: Constraining the common-envelope efficiency
• Introduction to astroML: Machine Learning for Astrophysics
• Interrelated Main-Sequence Mass-Luminosity, Mass-Radius and Mass-Effective Temperature Relations
• On the Binding Energy Parameter $\lambda$ of Common Envelope Evolution
• The MagE Spectrograph
• Wind Roche-lobe overflow: Application to carbon-enhanced metal-poor stars
• The Interaction of Stellar Objects within a Common Envelope
• The effect of common-envelope evolution on the visible population of post-common-envelope binaries
• Magnetic Braking Revisited
• Analysis of the carbon-rich very metal-poor dwarf G77-61
• Mass transfer from a giant star to a main sequence companion and its contribution to long-orbital-period blue stragglers
• Discovery of $\sim$ 9,000 new RR Lyrae in the Southern Catalina Surveys
• Monte Carlo simulations of post-common-envelope white dwarf + main sequence binaries: comparison with the SDSS DR7 observed sample
• Binary properties of CH and Carbon-Enhanced Metal-Poor stars
• A Medium-Resolution Near-Infrared Spectral Library of Late Type Stars: I
• The Necklace: equatorial and polar outflows from the binary central star of the new planetary nebula IPHASXJ194359.5+170901
• Detection of white dwarf companions to blue stragglers in the open cluster NGC 188: direct evidence for recent mass transfer
• Barium & related stars and their white-dwarf companions II. Main-sequence and subgiant stars
• Innocent Bystanders: Carbon Stars from the Sloan Digital Sky Survey
• Carbon stars identified from LAMOST DR4 using Machine Learning
• A carbon dwarf wearing a Necklace: first proof of accretion in a post-common-envelope binary central star of a planetary nebula with jets
• Discovery of Extreme Carbon Stars in the Large Magellanic Cloud
• White Dwarf - Red Dwarf Systems Resolved with the Hubble Space Telescope. II. Full Snapshot Survey Results
• Slowly, slowly in the wind: 3D hydrodynamical simulations of wind mass transfer and angular-momentum loss in AGB binary systems
• Gone with the wind: the impact of wind mass transfer on the orbital evolution of AGB binary systems
• Wind-accelerated orbital evolution in binary systems with giant stars
• Inferred timescales for common envelope ejection using wide astrometric companions
• Constraints on the common-envelope evolution process from wide triple systems
• Search for carbon stars and DZ white dwarfs in SDSS spectra survey through machine learning
• Dwarf carbon stars are likely metal-poor binaries and unlikely hosts to carbon planets
• Evidence for Halo Kinematics among Cool Carbon-Rich Dwarfs
• Are extreme AGB stars post-common envelope binaries?
• Carbon-enhanced stars with short orbital and spin periods
• Evidence for bimodal orbital separations of white dwarf-red dwarf binary stars

Cited by in corpus (6)

• Jets in Common Envelopes: a low mass main sequence star in a red giant
• A ZTF Look at Optical Variability of Young Stellar Objects in the North America and Pelican Nebulae Complex
• Formation of long-period post-common-envelope binaries II. Explaining the self-lensing binary KOI 3278
• Blue Stragglers and Friends: Initial Evolutionary Pathways in Close Low-Mass Binaries: Literature Review
• New Clues to the Evolution of Dwarf Carbon Stars From Their Variability and X-ray Emission
• Appraising the Necklace: A post-common-envelope carbon dwarf inside an apparently carbon-poor planetary nebula