The double helium-white dwarf channel for the formation of AM CVn binaries  

作　　者：Xian-Fei Zhang Jin-Zhong Liu C.Simon Jeffery Philip D.Hall Shao-Lan Bi 

机构地区：[1]Department of Astronomy,Beijing Normal University [2]Xinjiang Astronomical Observatory,Chinese Academy of Sciences [3]Armagh Observatory and Planetarium,College Hill [4]School of Physics,Trinity College Dublin

出　　处：《Research in Astronomy and Astrophysics》2018年第1期101-112,共12页天文和天体物理学研究（英文版）

基　　金：supported by the CAS ‘Light of West China’ program(2015-XBQNA-02);the National Natural Science Foundation of China(NSFC,Grant Nos.10933002,11703001 and 11273007);the Joint Research Fund in Astronomy(U1631236) under cooperative agreement between the NSFC and the Chinese Academy of Sciences(CAS);the Strategic Priority Research Program of the Chinese Academy of Sciences(No.XDB2304100);the China Postdoctoral Science Foundation;the Fundamental Research Funds for the Central Universities;The Armagh Observatory and Planetarium are supported by a grant from the Northern Ireland Department for Communities;support from the UK Science and Technology Facilities Council(STFC)(Grant No.ST/M000834/1)

摘　　要：Most close double helium white dwarfs will merge within a Hubble time due to orbital decay by gravitational wave radiation.However,a significant fraction with low mass ratios will survive for a long time as a consequence of stable mass transfer.Such stable mass transfer between two helium white dwarfs（He WDs） provides one channel for the production of AM CVn binary stars.In previous calculations of double He WD progenitors,the accreting He WD was treated as a point mass.We have computed the evolution of 16 double He WD models in order to investigate the consequences of treating the evolution of both components in detail.We find that the boundary between binaries having stable and unstable mass transfer is slightly modified by this approach.By comparing with observed periods and mass ratios,we redetermine masses of eight known AM CVn stars by our double He WDs channel,i.e.HM Cnc,AM CVn,V406 Hya,J0926,J1240,GP Com,Gaia14 aae and V396 Hya.We propose that central spikes in the triple-peaked emission spectra of J1240,GP Com and V396 Hya and the surface abundance ratios of N/C/O in GP Com can be explained by the stable double He WD channel.The mass estimates derived from our calculations are used to discuss the predicted gravitational wave signal in the context of the Laser Interferometer Space Antenna（LISA） project.Most close double helium white dwarfs will merge within a Hubble time due to orbital decay by gravitational wave radiation.However,a significant fraction with low mass ratios will survive for a long time as a consequence of stable mass transfer.Such stable mass transfer between two helium white dwarfs（He WDs） provides one channel for the production of AM CVn binary stars.In previous calculations of double He WD progenitors,the accreting He WD was treated as a point mass.We have computed the evolution of 16 double He WD models in order to investigate the consequences of treating the evolution of both components in detail.We find that the boundary between binaries having stable and unstable mass transfer is slightly modified by this approach.By comparing with observed periods and mass ratios,we redetermine masses of eight known AM CVn stars by our double He WDs channel,i.e.HM Cnc,AM CVn,V406 Hya,J0926,J1240,GP Com,Gaia14 aae and V396 Hya.We propose that central spikes in the triple-peaked emission spectra of J1240,GP Com and V396 Hya and the surface abundance ratios of N/C/O in GP Com can be explained by the stable double He WD channel.The mass estimates derived from our calculations are used to discuss the predicted gravitational wave signal in the context of the Laser Interferometer Space Antenna（LISA） project.

关 键 词：stars：peculiar（helium） stars：white dwarfs binaries：close gravitational waves 

分 类 号：P145.5[天文地球—天体物理] P153[天文地球—天文学]