Population Synthesis Of Accreting White Dwarfs

Accreting white dwarfs (WDs) are important for the study of binary evolution and accretion physics. Under different conditions, they are the progenitors of components of double WDs, Type la supernovae (SNe Ia) and binary millisecond pulsars. The emission of accreting WDs is an important component of the unresolved soft X-ray emission of elliptical galaxies. Their emission may significantly influence the optical line emission from warm interstellar medium. Additionally, some outcomes of their evolution (such as SNe la, novae) are also of great importance for galactic chemical evolution. However, the contribution of X-ray emission of accreting WDs to the total X-ray emission of elliptical galaxy is still unclear. The influence of their emission on the line emission from warm interstellar medium is also unclear. In addition, the properties of nova population in galaxies of different Hubble types are far from clear.In this thesis, we use a hybrid binary population synthesis approach with BSE and MESA to study the population of accreting WDs. With this approach, we study the soft X-ray and UV emission of accreting WDs and their influence on the line emission of elliptical galaxies, particularly He Ⅱ 4686A. In addition, we have produced model populations of novae for galaxies with different star formation histories. In particular, we have modelled the nova population in M31 galaxies. In order to check our theoretical results, we have compare these results with the available observational data. Our main results are summarized as follows.1) We find that the number of rapidly accreting WDs at 10 Gyr is 160-180 for an elliptical-like galaxy of 1011 M☉ and 2250-2500 for a spiral-like galaxy with the same mass. Additionally, we find that the number of SNBWD at 10 Gyr is 750-1900 in an elliptical-like galaxy and 4550-6550 in a spiral-like galaxy with 1011 M☉. In an elliptical-like galaxy of 1011 M☉, assuming NH=3.0×1020 cm-2, the number of supersoft X-ray source (SNBWDs with Lx> 1036erg s-1, SSSs) at 10 Gyr is 10-20. In an spiral-like galaxy of 1011 M☉, assuming NH=3.0× 1021 cm-2, the number of SSSs at 10 Gyr is 40-130.2) In our standard model, using commonly (although not universally) adopted assumptions, our predictions for the soft X-ray luminosity of old stellar populations are consistent with Chandra observations of several nearby elliptical galaxies. Likewise, for stellar ages of ～10 Gyr, the He Ⅱ 4686A/Hβ line ratio from warm ISM predicted by our model is consistent with that measured in the stacked SDSS spectra of retired galaxies. However, for stellar ages of ～4-8 Gyr our model significantly overpredicts the soft X-ray luminosity and the He Ⅱ 4686A/Hβ line ratio. Replacement of Hjellming & Webbink (1987) criterion by fixed critical mass ratios (qc= 1.7 or 1.9), brings the soft X-ray luminosity and line ratio He Ⅱ 4686A/Hβ in the new models to consistency with the observations.3) The mass-specific nova rate for elliptical-like galaxies at 10 Gyr in our calcula-tion is ～(1-2)× 10-10 M☉-1 yr-1. Howev er, the mass-specific nova rate for spiral-like galaxies at 10 Gyr is ～(20-40)× 10-10M☉-1 yr-1.4) The current nova population is dominated by novae with low mass WDs in elliptical-like galaxies and by novae with massive WDs in spiral-like galaxies. In elliptical-like galaxies, the majority of current novae have long mass loss times, are rel-atively faint, and have long recurrence periods. In spiral-like galaxies, the majority of the current nova population have short mass loss times, are relatively bright, and have short recurrence periods.5) Given the uncertainties in both our calculation and observations, the predicted nova rate and the distribution of nova mass loss times in our M31-like galaxy are in good agreement with observational data for M31. The observed distribution may be subject to incompleteness at tml< 10 day and tml> 300 day.With this work, we have partially explained the origin of unresolved X-ray emission in elliptical galaxies and quantitatively studied the influence of the emission of accreting WDs on the optical line emission of elliptical galaxies. In addition, we have explained the properties of nova population in galaxies of different Hubble types.