We identify 108 M subdwarfs（sd Ms） out of more than two hundred thousand M type spectra from the second data release（DR2） of the LAMOST regular survey. This sample, among which 58 members are identified for the fi...We identify 108 M subdwarfs（sd Ms） out of more than two hundred thousand M type spectra from the second data release（DR2） of the LAMOST regular survey. This sample, among which 58 members are identified for the first time, includes 33 extreme subdwarfs（esd Ms） and 11 ultra subdwarfs（usd Ms）.The selection is based on the usual ratio of absorption depth of Ca H2, Ca H3 and TiO 5 band systems.We also emphasize the use of the Ca H1 band. We provide estimates of spectral subtype（SPT）, L′epine metallicity index ζ, effective temperature and [Fe/H]. Both ζ–[Fe/H] and SPT–Teff figures show reasonable consistency; compared to PHOENIX model spectra, average rounded values of [Fe/H] for sd Ms, esd Ms and usd Ms are respectively –0.5, –1 and –1.5. The photometric distances are estimated, indicating that most sources are located within 500 pc of the Sun and 350 pc of the Galactic disk. Velocities and 3D Galactic motions are also briefly discussed. Among the 108 subdwarfs, seven stars appear to be active with a significant Hα emission line. The source LAMOST J104521.52＋482823.3 is a white dwarf- M subdwarf binary, while LAMOST J123045.52＋410943.8, also active, exhibits carbon features in red.展开更多
The development of large-scale time-domain surveys provides an opportunity to study the physical properties as well as the evolutionary scenario of B-type subdwarfs(sdBs)and M-type dwarfs(dMs).Here,we obtained 33 sdB+...The development of large-scale time-domain surveys provides an opportunity to study the physical properties as well as the evolutionary scenario of B-type subdwarfs(sdBs)and M-type dwarfs(dMs).Here,we obtained 33 sdB+dM eclipsing binaries based on the Zwicky Transient Facility(ZTF)light curves and Gaia Early Data Release3(EDR3)parallaxes.By using the PHOEBE code for light curve analysis,we obtain probability distributions for parameters of 29 sdB+dMs.R1,R2 and i are well determined,and the average uncertainty of mass ratio q is 0.08.Our parameters are in good agreement with previous works if a typical mass of sdB is assumed.Based on parameters of 29 sdB+dMs,we find that both the mass ratio q and the companion’s radius R2 decrease with the shortening of the orbital period.For the three sdB+dMs with orbital periods less than 0.075 days,their companions are all brown dwarfs.The masses and radii of the companions satisfy the mass–radius relation for low-mass stars and brown dwarfs.Companions with radii between 0.12 R_(⊙)and 0.15 R_(⊙)seem to be missing in the observations.As more short-period sdB+dM eclipsing binaries are discovered and classified in the future with ZTF and Gaia,we will have more information to constrain the evolutionary ending of sdB+dMs.展开更多
Although supernovae are well-known endpoints of accreting white dwarfs,alternative theoretical possibilities have been widely discussed,such as the accretion-induced collapse(AIC)event as the endpoint of oxygen-neon(O...Although supernovae are well-known endpoints of accreting white dwarfs,alternative theoretical possibilities have been widely discussed,such as the accretion-induced collapse(AIC)event as the endpoint of oxygen-neon(ONe)white dwarfs,either accreting up to or merging to exceed the Chandrasekhar limit(the maximum mass of a stable white dwarf).AIC is an important channel to form neutron stars,especially for those unusual systems that are unlikely produced by core-collapse supernovae.However,the observational evidence for this theoretically predicted event and its progenitor is very limited.In all of the known progenitor systems,white dwarfs increase in mass through accretion.Here,we report the discovery of an intriguing binary system Lan 11,composed of a stripped core-helium-burning hot subdwarf and an unseen compact object with a mass of 1.08M_(⊙)to 1.35M_(⊙).Our binary population synthesis calculations suggest that the latter is most likely to be an ONe white dwarf.Furthermore,the nondetection in deep radio observations by the Five-hundred-meter Aperture Spherical Radio Telescope(FAST)does not exclude this interpretation.The total mass of this binary ranges from 1.67M_(⊙)to 1.92M_(⊙),significantly exceeding the Chandrasekhar limit.The reproduction of its evolutionary history indicates that the unique system has undergone two phases of common envelope ejection,implying a born nature of this massive ONe white dwarf rather than an accretion growth from its companion.These results,together with short orbital period of this binary(3.65 h),suggest that this system will merge in 500-540 Myr,largely triggering an AIC event,although the possibility of type Ia supernova cannot be entirely ruled out.This finding greatly provides valuable constraints on our understanding of stellar endpoints,whatever leading to an AIC or a supernova.展开更多
基金partly supported by the National Key Basic Research Program of China(Grant No.2014CB845700)the National Natural Science Foundation of China(Grant No.11390371)+1 种基金a National Major Scientific Project built by the Chinese Academy of Sciencesprovided by the National Development and Reform Commission.LAMOST is operated and managed by National Astronomical Observatories,Chinese Academy of Sciences
文摘We identify 108 M subdwarfs（sd Ms） out of more than two hundred thousand M type spectra from the second data release（DR2） of the LAMOST regular survey. This sample, among which 58 members are identified for the first time, includes 33 extreme subdwarfs（esd Ms） and 11 ultra subdwarfs（usd Ms）.The selection is based on the usual ratio of absorption depth of Ca H2, Ca H3 and TiO 5 band systems.We also emphasize the use of the Ca H1 band. We provide estimates of spectral subtype（SPT）, L′epine metallicity index ζ, effective temperature and [Fe/H]. Both ζ–[Fe/H] and SPT–Teff figures show reasonable consistency; compared to PHOENIX model spectra, average rounded values of [Fe/H] for sd Ms, esd Ms and usd Ms are respectively –0.5, –1 and –1.5. The photometric distances are estimated, indicating that most sources are located within 500 pc of the Sun and 350 pc of the Galactic disk. Velocities and 3D Galactic motions are also briefly discussed. Among the 108 subdwarfs, seven stars appear to be active with a significant Hα emission line. The source LAMOST J104521.52＋482823.3 is a white dwarf- M subdwarf binary, while LAMOST J123045.52＋410943.8, also active, exhibits carbon features in red.
基金supported by Sichuan Science and Technology Program(grant No.2020YFSY0034)National Natural Science Foundation of China(NSFC)through the projects 12003022,12173047,11903045,12003046,and U1731111+2 种基金supported by the Major Science and Technology Project of Qinghai Province 2019-ZJ-A10funded in part by the National Science Foundation(NSF#1517474,#1909109)the National Aeronautics and Space Administration(NASA 17ADAP17-68)。
文摘The development of large-scale time-domain surveys provides an opportunity to study the physical properties as well as the evolutionary scenario of B-type subdwarfs(sdBs)and M-type dwarfs(dMs).Here,we obtained 33 sdB+dM eclipsing binaries based on the Zwicky Transient Facility(ZTF)light curves and Gaia Early Data Release3(EDR3)parallaxes.By using the PHOEBE code for light curve analysis,we obtain probability distributions for parameters of 29 sdB+dMs.R1,R2 and i are well determined,and the average uncertainty of mass ratio q is 0.08.Our parameters are in good agreement with previous works if a typical mass of sdB is assumed.Based on parameters of 29 sdB+dMs,we find that both the mass ratio q and the companion’s radius R2 decrease with the shortening of the orbital period.For the three sdB+dMs with orbital periods less than 0.075 days,their companions are all brown dwarfs.The masses and radii of the companions satisfy the mass–radius relation for low-mass stars and brown dwarfs.Companions with radii between 0.12 R_(⊙)and 0.15 R_(⊙)seem to be missing in the observations.As more short-period sdB+dM eclipsing binaries are discovered and classified in the future with ZTF and Gaia,we will have more information to constrain the evolutionary ending of sdB+dMs.
基金supported by the National Natural Science Foundation of China(Grant Nos.11988101,11933004,12288102,12125303,12090040,12225304,12373037,and 12422303)the National Key R&D Program of China(Grant Nos.2021YFA1600400,and 2021YFA1600401)+17 种基金the Science Research Grants from the China Manned Space Project.Zhenwei Li acknowledges support from the National Natural Science Foundation of China(Grant No.12473034)the Yunnan Fundamental Research Projects(YFRP)(Grant No.202401AT070139)supported by the YFRP(Grant No.202401CF070035)the Young Talent Project of Yunnan Revitalization Talent Support Program.Dongdong Liu is supported by the National Natural Science Foundation of China(Grant No.12273105)the Youth Innovation Promotion Association CAS(Grant No.2021058)the Yunnan Revitalization Talent Support Program-Young Talent Project,and the Yunnan Fundamental Research Projects(Grant Nos.202401AV070006,and 202201AW070011)support from the National Natural Science Foundation of China(Grant No.12173028)suport from the National Natural Science Foundation of China(Grant No.12203068)support from the National Natural Science Foundation of China(Grant Nos.11988101,and 12041303)the CAS Youth Interdisciplinary Team,the Youth Innovation Promotion Association CAS(Grant No.2021055)the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMSCAS.P´eter N´emeth acknowledges support from the Grant Agency of the Czech Republic(Grant No.GACR 22-34467S)supported by the Project(Grant No.RVO:67985815)support from the National Natural Science Foundation of China(Grant Nos.12288102,12125303,and 12090043)the International Centre of Supernovae,Yunnan Key Laboratory(Grant No.202302AN360001)the Yunnan Fundamental Research Projects(Grant Nos.202201BC070003,and 202001AW070007)the Yunnan Revitalization Talent Support Program-Science&Technology Champion Project(Grant No.202305AB350003)support from the National Natural Science Foundation of China(Grant Nos.11988101,and 11933004)the New Cornerstone Science Foundation through the New Cornerstone Investigator Program and the XPLORER PRIZE。
文摘Although supernovae are well-known endpoints of accreting white dwarfs,alternative theoretical possibilities have been widely discussed,such as the accretion-induced collapse(AIC)event as the endpoint of oxygen-neon(ONe)white dwarfs,either accreting up to or merging to exceed the Chandrasekhar limit(the maximum mass of a stable white dwarf).AIC is an important channel to form neutron stars,especially for those unusual systems that are unlikely produced by core-collapse supernovae.However,the observational evidence for this theoretically predicted event and its progenitor is very limited.In all of the known progenitor systems,white dwarfs increase in mass through accretion.Here,we report the discovery of an intriguing binary system Lan 11,composed of a stripped core-helium-burning hot subdwarf and an unseen compact object with a mass of 1.08M_(⊙)to 1.35M_(⊙).Our binary population synthesis calculations suggest that the latter is most likely to be an ONe white dwarf.Furthermore,the nondetection in deep radio observations by the Five-hundred-meter Aperture Spherical Radio Telescope(FAST)does not exclude this interpretation.The total mass of this binary ranges from 1.67M_(⊙)to 1.92M_(⊙),significantly exceeding the Chandrasekhar limit.The reproduction of its evolutionary history indicates that the unique system has undergone two phases of common envelope ejection,implying a born nature of this massive ONe white dwarf rather than an accretion growth from its companion.These results,together with short orbital period of this binary(3.65 h),suggest that this system will merge in 500-540 Myr,largely triggering an AIC event,although the possibility of type Ia supernova cannot be entirely ruled out.This finding greatly provides valuable constraints on our understanding of stellar endpoints,whatever leading to an AIC or a supernova.
