Conveners
Observed WD Populations 1: Observed populations
- JJ Hermes (Boston University)
Observed WD Populations 1: Formation
- Alina Istrate (Radboud University)
I will report on a programme of double white dwarf discovery from targets selected from Gaia DR2 from their location in the H-R diagram. Targets are chosen from their location above the main white dwarf cooling sequence in terms of luminosity. This favours double white dwarfs with equal contributions from the two stars and a number of new systems have been discovered. These are of particular...
The characterization of the local double white dwarf (DWD) population is crucial to our understanding of multiple questions, from stellar evolution, through the progenitors of Type-Ia supernovae (SNe Ia), to gravitational wave sources. From a spectroscopic sample of 439 WDs from the SPY survey, we measure the maximal changes in radial-velocity (DRVmax) between epochs, and model the observed...
We present the completed ELM Survey, a targeted survey of extremely low mass white dwarfs. The final sample contains 106 He+CO white dwarf binaries; their median orbital period is 6 hr. Combining our spectroscopy with Gaia astrometry reveals that half of the binaries orbit in the disk, half in the halo. We compare the disk and halo samples, and discuss the merger rate of He+CO white dwarf...
Common envelope evolution (CEE) is presently a poorly understood, yet critical, process in binary stellar evolution. I present results from a suite of high resolution global 3D hydrodynamical adaptive mesh refinement simulations of CEE involving a red giant branch or asymptotic giant branch primary and a white dwarf or main sequence secondary. The simulations are analyzed to understand how...
Gaia-DR2 has provided an unprecedented wealth of information about the white dwarf population of our Galaxy. In particular, our estimates show that the sample up to 100 pc from the Sun can be considered as practically complete. This fact permits to obtain accurate statistics about the percentages of the different subpopulations, such as the number of resolved/unresolved double degenerate...
Extremely low-mass white dwarfs (ELM WDs) are helium WDs with a mass less than $\sim 0.30\;M_\odot$. Most ELM WDs are found in double degenerates (DDs) in the ELM Survey led by Brown and Kilic. These systems are supposed to be significant gravitational-wave (GW) sources in the mHz frequency. In this talk, I first systematically investigated the formation of ELM WDs in DDs by a combination of...
