| 其他摘要 | Accreting white dwarfs (WDs) are important for the study of binary evolution andaccretion physics. Under di?erent conditions, they are the progenitors of componentsof double WDs, Type Ia supernovae (SNe Ia) and binary millisecond pulsars. Theemission of accreting WDs is an important component of the unresolved soft X-rayemission of elliptical galaxies. Their emission may signi?cantly in?uence the opticalline emission from warm interstellar medium. Additionally, some outcomes of theirevolution (such as SNe Ia, novae) are also of great importance for galactic chemicalevolution. However, the contribution of X-ray emission of accreting WDs to the totalX-ray emission of elliptical galaxy is still unclear. The in?uence of their emission on theline emission from warm interstellar medium is also unclear. In addition, the propertiesof 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 andmesa to study the population of accreting WDs. With this approach, we study thesoft X-ray and UV emission of accreting WDs and their in?uence on the line emissionof elliptical galaxies, particularly He II 4686?. In addition, we have produced modelpopulations 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 theoreticalvresults, we have compare these results with the available observational data. Our mainresults are summarized as follows. 1) We ?nd that the number of rapidly accreting WDs at 10 Gyr is 160 ? 180 foran elliptical-like galaxy of 10 11 M⊙ and 2250 ? 2500 for a spiral-like galaxy with thesame mass. Additionally, we ?nd that the number of SNBWD at 10 Gyr is 750 ? 1900in an elliptical-like galaxy and 4550 ? 6550 in a spiral-like galaxy with 10 11 M⊙. Inan elliptical-like galaxy of 10 11 M⊙, assuming NH = 3.0 × 10 20 cm? 2 , the number ofsupersoft X-ray source (SNBWDs with Lx > 10 36 erg s?1 , SSSs) at 10 Gyr is 10 ? 20. Inan spiral-like galaxy of 10 11 M⊙, assuming NH = 3.0 × 10 21 cm? 2 , the number of SSSsat 10 Gyr is 40 ? 130.2) In our standard model, using commonly (although not universally) adoptedassumptions, our predictions for the soft X-ray luminosity of old stellar populationsare consistent with Chandra observations of several nearby elliptical galaxies. Likewise,for stellar ages of ～ 10 Gyr, the He II 4686?/Hβ line ratio from warm ISM predictedby our model is consistent with that measured in the stacked SDSS spectra of retiredgalaxies. However, for stellar ages of ～4–8 Gyr our model signi?cantly overpredicts thesoft X-ray luminosity and the He II 4686?/Hβ line ratio. Replacement of Hjellming &Webbink (1987) criterion by ?xed critical mass ratios (qc = 1.7 or 1.9), brings the softX-ray luminosity and line ratio He II 4686?/Hβ in the new models to consistency withthe observations.3) The mass-speci?c nova rate for elliptical-like galaxies at 10 Gyr in our calcula-tion is ～ (1 ? 2) × 10? 10 M⊙? 1 yr? 1 . However, the mass-speci?c nova rate for spiral-likegalaxies at 10 Gyr is ～ (20 ? 40) × 10? 10 M⊙? 1 yr? 1 .4) The current nova population is dominated by novae with low mass WDsin elliptical-like galaxies and by novae with massive WDs in spiral-like galaxies. Inelliptical-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 ofthe current nova population have short mass loss times, are relatively bright, and haveshort recurrence periods.5) Given the uncertainties in both our calculation and observations, the predictedvinova rate and the distribution of nova mass loss times in our M31-like galaxy are ingood agreement with observational data for M31. The observed distribution may besubject to incompleteness at tml < 10 day and tml > 300 day.With this work, we have partially explained the origin of unresolved X-ray emissionin elliptical galaxies and quantitatively studied the in?uence of the emission of accretingWDs on the optical line emission of elliptical galaxies. In addition, we have explainedthe properties of nova population in galaxies of different Hubble types. |
修改评论