Population synthesis of DA white dwarfs: constraints on soft X-ray spectra evolution

TL;DR

This study extends population synthesis to young white dwarfs, using ROSAT data to constrain models of their X-ray spectra and evolution, resulting in consistent birth rates and temperature limits with previous research.

Contribution

It introduces a method to model X-ray spectra evolution of white dwarfs and validates it against observational data, providing new constraints on spectral temperature limits and birth rates.

Findings

X-ray spectrum temperature is given by T_{X-ray} = min(T_eff, T_max)

DA white dwarf birth rate is approximately 0.61×10^{-12} pc^{-3} yr^{-1}

Maximum X-ray temperature T_max is 41000 K

Abstract

Extending the population synthesis method to isolated young cooling white dwarfs we are able to confront our model assumptions with observations made in ROSAT All-Sky Survey (Fleming et al., 1996). This allows us to check model parameters such as evolution of spectra and separation of heavy elements in DA WD envelopes. It seems like X-ray spectrum temperature of these objects is given by the formula T_{X-ray} = min(T_eff, T_max). We have obtained DA WD's birth rate and upper limit of the X-ray spectrum temperature: DA birth rate $= 0.61\times 10^{-12}$ in cubic parsec per year and T_max = 41000 K. These values are in good correspondence with values obtained by other authors (Liebert et al., 2004; Wolff et al., 1996). From this fact we also conclude that our population synthesis method is applicable to the population of close-by isolated cooling white dwarfs as well as to the population of the isolated cooling neutron stars.