Evolved cataclysmic variables as progenitors of AM CVn stars

Abstract

We model cataclysmic variables (CVs) with solar metallicity donors ($X=0.7,Z=0.02$) that evolve to form AM CVn stars through the Evolved CV formation channel using various angular momentum loss mechanisms by magnetic braking ($\mathrm{AM}{\mathrm{L}}_{\mathrm{MB}}$). We find that the time-scale for $\mathrm{AM}{\mathrm{L}}_{\mathrm{MB}}$ in our double-dynamo (DD) model is shorter than that of previously used empirical formulae. Owing to the shorter time-scales, a larger parameter space of initial conditions evolves to form AM CVn stars with the DD model than with other models. We perform an analysis of the expected number of AM CVn stars formed through the Evolved CV channel and find about $3$ times as many AM CVn stars as reported before. We evolve these systems in detail with the Cambridge stellar evolution code (STARS) and show that evolved CVs populate a region with orbital period $P_{\mathrm{orb}}\ge 5.5\mathrm{hr}$. We evolve our donors beyond their orbital period minimum and find that a significant number become extremely H-exhausted systems. This makes them indistinguishable from systems evolved from the He-star and the White Dwarf (WD) channels in terms of the absence of H in their spectra. We also compare the masses, mass-transfer rates of the donor, and the orbital period with observations. We find that the state of the donor and the absence of H in systems such as YZ LMi and V396 Hya match with our modelled trajectories, while systems such as CR Boo and HP Lib match with our modelled tracks if their actual donor mass lies on the lower-end of the observed mass range.

15 pages, 15 figures. Accepted for publication in MNRAS

References in corpus (15)

• Every interacting double white dwarf binary may merge
• Population Synthesis of Cataclysmic Variables: I. Inclusion of Detailed Nuclear Evolution
• Evolution of Low-Mass Helium Stars in Semidetached Binaries
• HST/FGS Parallaxes of AM CVn Stars and Astrophysical Consequences
• Adiabatic mass loss in binary stars. III. From the base of the red giant branch to the tip of asymptotic giant branch
• The Thermal Evolution of the Donors in AM CVn Binaries
• Evolution of Cataclysmic Variables and Related Binaries Containing a White-Dwarf
• A Catalogue of Potential Post Common Envelope Binaries
• Discovery and characterization of five new eclipsing AM CVn systems
• White dwarf masses in cataclysmic variables
• The white dwarf mass-radius relation and its dependence on the hydrogen envelope
• Evolution of AM CVn binaries with WD donors
• Phase-Resolved Spectroscopy of Gaia14aae: Line Emission From Near the White Dwarf Surface
• A unified model for the evolution of cataclysmic variables
• New insights into the helium star formation channel of AM CVn systems with explanations of Gaia14aae and ZTFJ1637+49

Cited by in corpus (9)

• Reversing the verdict: Cataclysmic variables could be the dominant progenitors of AM CVn binaries after all
• A Catalogue of Ultracompact Mass-Transferring White Dwarf Binaries
• Compact Objects in close orbits as Gravitational Wave Sources: Formation Scenarios and Properties
• Discovery and characterization of ZTF J0112+5827: An 80.9-minute polar with strong cyclotron features
• Towards a holistic magnetic braking model from the evolution of cataclysmic variables to stellar spin-down -- I: the spin-down of fully convective M-dwarfs
• TCP J07222683$+$6220548: a new AM CVn type system with infrequent outbursts
• Towards a holistic magnetic braking model -- II: explaining several long-term internal- and surface-spin properties of solar-like stars and the Sun
• The evolutionary history of ultra-compact accreting binaries. I. Chemical abundances and formation channel of the eclipsing AM CVn system ZTF J225237.05-051917.4 from HST spectroscopy
• Optical Spectroscopy of the Most Compact Accreting Binary Harboring a Magnetic White Dwarf and a Hydrogen-rich Donor