Stellar models of evolved secondaries in CVs

Abstract

In this paper we study the impact of chemically evolved secondaries on CV evolution. We find that when evolved secondaries are included a spread in the secondary mass-orbital period plane comparable to that seen in the data is produced for either the saturated prescription for magnetic braking or the unsaturated model commonly used for CVs. We argue that in order to explain this spread a considerable fraction of all CVs should have evolved stars as the secondaries. The evolved stars become fully convective at lower orbital periods. Therefore, even if there was an abrupt decrease in magnetic braking for fully convective stars (contrary to open cluster data) it would not be expected to produce a sharp break in the period distribution for CVs. We also explore recent proposed revisions to the angular momentum loss rate for single stars, and find that only modest increases over the saturated prescription are consistent with the overall observed spindown pattern. We compare predictions of our models with diagnostics of the mass accretion rate in WDs and find results intermediate between the saturated and the older braking prescription. Taken together these suggest that the angular momentum loss rate may be higher in CV secondaries than in single stars of the same rotation period, but is still significantly lower than in the traditional model. Alternative explanations for the CV period gap are discussed.

arXiv comment24 pages, 9 figures. Submitted to ApJ

References in corpus (15)

• Absolute dimensions of the M-type eclipsing binary YY Geminorum (Castor C): a challenge to evolutionary models in the lower main-sequence
• Keck Spectra of Pleiades Brown Dwarf Candidates and a Precise Determination of the Lithium Depletion Edge in the Pleiades
• First radius measurements of very low mass stars with the VLTI
• Theoretical Modeling of the Thermal State of Accreting White Dwarfs Undergoing Classical Novae
• The 0.4-Mo Eclipsing Binary CU Cancri: Absolute Dimensions, Comparison with Evolutionary Models and Possible Evidence for a Circumstellar Dust Disk
• Cataclysmic Variables: An Empirical Angular Momentum Loss Prescription From Open Cluster Data
• Magnetic Braking Revisited
• Measuring White Dwarf Accretion Rates via their Effective Temperatures
• Why are the K dwarfs in the Pleiades so Blue?
• Rotation of Horizontal Branch Stars in Globular Clusters
• On the late spectral types of cataclysmic variable secondaries
• The Secondary Star in Cataclysmic Variables and Low Mass X-ray Binaries
• A New Pleiades Member at the Lithium Substellar Boundary
• Angular Momentum Evolution of Stars in the Orion Nebula Cluster
• On a mechanism for enhancing magnetic activity in tidally interacting binaries

Cited by in corpus (14)

• Older and Colder: The impact of starspots on pre-main sequence stellar evolution
• Population Synthesis of Cataclysmic Variables: I. Inclusion of Detailed Nuclear Evolution
• Rotation, inflation, and lithium in the Pleiades
• A Tale of Two Anomalies: Depletion, Dispersion, and the Connection Between the Stellar Lithium Spread and Inflated Radii on the Pre-Main Sequence
• Mergers of close primordial binaries
• Pulsational Instabilities in Accreting White Dwarfs
• A He3 driven instability near the fully convective boundary
• ULTRACAM observations of SDSS J170213.26+322954.1 - an eclipsing cataclysmic variable in the period gap
• Spectroscopy of Nine Cataclysmic Variable Stars
• Cyclical period changes in HT Cas: a clear difference between systems above and below the period gap
• Li I and K I Scatter in Cool Pleiades Dwarfs
• Infrared Spectroscopic Observations of the Secondary Stars of Short Period Sub-Gap Cataclysmic Variables
• An Illustration of Modeling Cataclysmic Variables: HST, FUSE, SDSS Spectra of SDSSJ080908.39+381406.2
• A deep HST view of the open cluster NGC2158: binaries, mass functions, and M-dwarf discontinuity