Stars with masses between 1 and 8 solar masses(M⊙)lose large amounts of material in the form of gas and dust in the late stages of stellar evolution,during their Asymptotic Giant Branch(AGB)phase.Such stars supply up...Stars with masses between 1 and 8 solar masses(M⊙)lose large amounts of material in the form of gas and dust in the late stages of stellar evolution,during their Asymptotic Giant Branch(AGB)phase.Such stars supply up to 35%of the dust in the interstellar medium and thus contribute to the material out of which our solar system formed.In addition,the circumstellar envelopes of these stars are sites of complex organic chemistry with over 80 molecules detected in them.We show that internal ultraviolet photons,either emitted by the star itself or from a close-in,orbiting companion,can significantly alter the chemistry that occurs in the envelopes particularly if the envelope is clumpy in nature.At least for the cases explored here,we find that in the presence of a stellar companion,such as a white dwarf star,the high flux of UV photons destroys H2O in the inner regions of carbon-rich AGB stars to levels below those observed and produces species such as C^+deep in the envelope in contrast to the expectations of traditional descriptions of circumstellar chemistry.展开更多
In this paper,a two-level search method for searching transfer opportunities between interplanetary halo orbits,exploiting the invariant manifolds of the restricted three-body problem,is proposed.In the method,the fir...In this paper,a two-level search method for searching transfer opportunities between interplanetary halo orbits,exploiting the invariant manifolds of the restricted three-body problem,is proposed.In the method,the first-level search procedure is performed under the conditions of the initial time of escape manifold trajectory of the Sun-Earth halo orbit and the terminal time of capture manifold of the target planet fixed,by solving the optimal two-impulsive heliocentric trajectory to connect the two manifold trajectories.The contour map,helpful to the understanding of the global characteristics of the transfer opportunities,taking the initial time of escape manifold and the terminal time of capture manifold as variables,the optimal velocity increment of the first-level search as objective function,is used for the second-level search.Finally,taking the Earth-Mars and Earth-Venus halo to halo transfers for example,the transfer opportunities in 2015-2017 are searched.The results show the effectiveness of the proposed method and reveal the property of quasi-period of transfer opportunities between interplanetary halo orbits.展开更多
Many dark energy models fail to pass the cosmic age test because of the old quasar APM 08279+5255 at redshift z=3.91,the ΛCDMmodel and holographic dark energy models being no exception.Inthis paper,we focus onthe top...Many dark energy models fail to pass the cosmic age test because of the old quasar APM 08279+5255 at redshift z=3.91,the ΛCDMmodel and holographic dark energy models being no exception.Inthis paper,we focus onthe topic of the age problem inthe new agegraphic dark energy(NADE)model.We determine the age of the universe in the NADE model by fitting the observational data,including type Ia supernovae(SNIa),baryon acoustic oscillations(BAO)and the cosmic microwave background(CMB).We find that the NADE model also faces the challenge of the age problem caused by the old quasar APM 08279+5255.In order to overcome such a difficulty,we consider the possible interaction between dark energy and dark matter.We show that this quasar can be successfully accommodated in the interacting new agegraphic dark energy(INADE)model at the 2σlevel under the current observational constraints.展开更多
文摘Stars with masses between 1 and 8 solar masses(M⊙)lose large amounts of material in the form of gas and dust in the late stages of stellar evolution,during their Asymptotic Giant Branch(AGB)phase.Such stars supply up to 35%of the dust in the interstellar medium and thus contribute to the material out of which our solar system formed.In addition,the circumstellar envelopes of these stars are sites of complex organic chemistry with over 80 molecules detected in them.We show that internal ultraviolet photons,either emitted by the star itself or from a close-in,orbiting companion,can significantly alter the chemistry that occurs in the envelopes particularly if the envelope is clumpy in nature.At least for the cases explored here,we find that in the presence of a stellar companion,such as a white dwarf star,the high flux of UV photons destroys H2O in the inner regions of carbon-rich AGB stars to levels below those observed and produces species such as C^+deep in the envelope in contrast to the expectations of traditional descriptions of circumstellar chemistry.
基金supported by the National Basic Research Program of China ("973" Program) (Grant No. 2012CB720000)the National Natural Science Foundation of China (Grant Nos. 10832004 and 11102020)
文摘In this paper,a two-level search method for searching transfer opportunities between interplanetary halo orbits,exploiting the invariant manifolds of the restricted three-body problem,is proposed.In the method,the first-level search procedure is performed under the conditions of the initial time of escape manifold trajectory of the Sun-Earth halo orbit and the terminal time of capture manifold of the target planet fixed,by solving the optimal two-impulsive heliocentric trajectory to connect the two manifold trajectories.The contour map,helpful to the understanding of the global characteristics of the transfer opportunities,taking the initial time of escape manifold and the terminal time of capture manifold as variables,the optimal velocity increment of the first-level search as objective function,is used for the second-level search.Finally,taking the Earth-Mars and Earth-Venus halo to halo transfers for example,the transfer opportunities in 2015-2017 are searched.The results show the effectiveness of the proposed method and reveal the property of quasi-period of transfer opportunities between interplanetary halo orbits.
基金supported by the National Natural Science Foundation of China(Grant Nos.10705041 and 10975032)the National Ministry of Education of China under the innovation program for undergraduate students
文摘Many dark energy models fail to pass the cosmic age test because of the old quasar APM 08279+5255 at redshift z=3.91,the ΛCDMmodel and holographic dark energy models being no exception.Inthis paper,we focus onthe topic of the age problem inthe new agegraphic dark energy(NADE)model.We determine the age of the universe in the NADE model by fitting the observational data,including type Ia supernovae(SNIa),baryon acoustic oscillations(BAO)and the cosmic microwave background(CMB).We find that the NADE model also faces the challenge of the age problem caused by the old quasar APM 08279+5255.In order to overcome such a difficulty,we consider the possible interaction between dark energy and dark matter.We show that this quasar can be successfully accommodated in the interacting new agegraphic dark energy(INADE)model at the 2σlevel under the current observational constraints.
