Binary white dwarfs in the halo of the Milky Way

Abstract

Aims: We study single and binary white dwarfs in the inner halo of the Milky Way in order to learn more about the conditions under which the population of halo stars was born, such as the initial mass function (IMF), the star formation history, or the binary fraction. Methods: We simulate the evolution of low-metallicity halo stars at distances up to ~ 3 kpc using the binary population synthesis code SeBa. We use two different white dwarf cooling models to predict the present-day luminosities of halo white dwarfs. We determine the white dwarf luminosity functions (WDLFs) for eight different halo models and compare these with the observed halo WDLF of white dwarfs in the SuperCOSMOS Sky Survey. Furthermore, we predict the properties of binary white dwarfs in the halo and determine the number of halo white dwarfs that is expected to be observed with the Gaia satellite. Results: By comparing the WDLFs, we find that a standard IMF matches the observations more accurately than a top-heavy one, but the difference with a bottom-heavy IMF is small. A burst of star formation 13 Gyr ago fits slightly better than a star formation burst 10 Gyr ago and also slightly better than continuous star formation $10-13$ Gyrs ago. Gaia will be the first instrument to constrain the bright end of the field halo WDLF, where contributions from binary WDs are considerable. Many of these will have He cores, of which a handful have atypical surface gravities ($\log g<6$) and reach luminosities $\log (L/L_{\odot })>0$ in our standard model for WD cooling. These so called pre-WDs, if observed, can help us to constrain white dwarf cooling models and might teach us something about the fraction of halo stars that reside in binaries.

arXiv comment16 pages, 9 figures. Accepted for publication in Astronomy & Astrophysics

References in corpus (40)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Modules for Experiments in Stellar Astrophysics (MESA)
• The Dartmouth Stellar Evolution Database
• The Milky Way Tomography with SDSS: I. Stellar Number Density Distribution
• Kinematics of Metal-Poor Stars in the Galaxy. III. Formation of the Stellar Halo and Thick Disk as Revealed from a Large Sample of Non-Kinematically Selected Stars
• Gaia broad band photometry
• An Improved Spectroscopic Analysis of DA White Dwarfs from the Sloan Digital Sky Survey Data Release 4
• Evolutionary and pulsational properties of white dwarf stars
• A Comprehensive Spectroscopic Analysis of DB White Dwarfs
• Supernova Type Ia progenitors from merging double white dwarfs: Using a new population synthesis model
• Found: The missing blue opacity in atmosphere models of cool hydrogen white dwarfs
• New evolutionary sequences for extremely low mass white dwarfs: Homogeneous mass and age determinations, and asteroseismic prospects
• New cooling sequences for old white dwarfs
• The stellar halo of the Galaxy
• Multi-physics simulations using a hierarchical interchangeable software interface
• The Astrophysical Multipurpose Software Environment
• A multiphysics and multiscale software environment for modeling astrophysical systems
• The Merging History of the Milky Way
• The White Dwarf Cooling Sequence of NGC6397
• The effect of common-envelope evolution on the visible population of post-common-envelope binaries
• The Spheroid Luminosity and Mass Functions From HST Star Counts
• The Origin of Carbon-Enhancement and Initial Mass Function of Extremely Metal-Poor Stars in the Galactic Halo
• The Stellar Metallicity Distribution Function of the Galactic Halo from SDSS Photometry
• Kinematical and chemical vertical structure of the Galactic thick disk II. A lack of dark matter in the solar neighborhood
• The End of the White Dwarf Cooling Sequence in M4: an efficient approach
• The age and colors of massive white dwarf stars
• PopCORN: Hunting down the differences between binary population synthesis codes
• The Age of the Milky Way Inner Halo
• Implications of White Dwarf Galactic Halos
• The halo white dwarf population
• Gaia photometry for white dwarfs
• Evolution and colors of helium-core white dwarf stars with high-metallicity progenitors
• The Subdwarf Luminosity Function
• Transition of the Stellar Initial Mass Function Explored with Binary Population Synthesis
• Simulating Gaia performances on white dwarfs
• Neural Network identification of halo white dwarfs
• An Empirical Measure of the Rate of White Dwarf Cooling in 47 Tucanae
• Binary Frequencies in a Sample of Globular Clusters. I. Methodology and Initial Results
• White dwarf cooling sequences and cosmochronology
• The contribution of Oxygen-Neon white dwarfs to the MACHO content of the Galactic Halo

Cited by in corpus (11)

• The Dark Energy Survey: more than dark energy - an overview
• The binarity of the local white dwarf population
• A White Dwarf catalogue from Gaia-DR2 and the Virtual Observatory
• The ultracool helium-atmosphere white dwarf companion of PSR J0740+6620?
• The effects of ${}^{22}$Ne sedimentation and metallicity on the local 40 pc white dwarf luminosity function
• Revisiting the luminosity function of single halo white dwarfs
• Searching for optical companions to four binary millisecond pulsars with the Gran Telescopio Canarias
• Astrophysics with the Laser Interferometer Space Antenna
• The population of single and binary white dwarfs of the Galactic bulge
• Using Binary Population Synthesis to Calculate the Yields of Low- and Intermediate-Mass Binary Populations at Low Metallicity
• White dwarfs in the building blocks of the Galactic spheroid