New analyses of earlier ALMA observations of oxygen-rich AGB star EP Aquarii are presented,which complete a previously published analysis and offer a different interpretation of the morpho-kinematics of the circumstel...New analyses of earlier ALMA observations of oxygen-rich AGB star EP Aquarii are presented,which complete a previously published analysis and offer a different interpretation of the morpho-kinematics of the circumstellar envelope.The birth of the equatorial density enhancement(EDE)is shown to occur very close to the star where evidence for rotation has been obtained.Close to the star and where outflows have been observed:their interaction with the gas of the nascent EDE is seen to play an important role in the development of the wind and the evolution of its radial velocity from 8 to 10 km s^(-1) on the polar symmetry axis to~2 km s^(-1) at the equator.It implies complex morpho-kinematics:making reliable interpretations with reasonable confidence is difficult.In particular,it questions an earlier interpretation implying the presence of a white dwarf companion orbiting the star at an angular distance of -0″4 from its center.It proposes instead an interpretation in terms of a standard mass ejection associated with a shock wave leaving a void of emission in its wake.High Doppler velocity wings are seen to consist of two components,the upper velocity end of the global wind,reaching above±12 km s^(-1),and an effective line broadening,confined within 200 mas from the center of the star,reaching above±20 km s^(-1) and interpreted as caused by the pattern of shock waves resulting from the interaction between stellar pulsation and convective cell partition.展开更多
Atacama Large Millimetre/sub-millimetre Array(ALMA) observations of CO(1–0) and CO(2–1) emissions from the circumstellar envelope of the asymptotic giant branch(AGB) star EP Aqr have been made with four times better...Atacama Large Millimetre/sub-millimetre Array(ALMA) observations of CO(1–0) and CO(2–1) emissions from the circumstellar envelope of the asymptotic giant branch(AGB) star EP Aqr have been made with four times better spatial resolution than previously available. They are analysed with emphasis on the de-projection in space of the effective emissivity and flux of matter using as input a prescribed configuration of the velocity field, assumed to be radial. The data are found to display an intrinsic axisymmetry with respect to an axis making a small angle with respect to the line of sight. A broad range of wind configurations, from prolate(bipolar) to oblate(equatorial) has been studied and found to be accompanied by significant equatorial emission. Qualitatively, the effective emissivity is enhanced near the equator to produce the central narrow component observed in the Doppler velocity spectra and its dependence on star latitude generally follows that of the wind velocity with the exception of an omni-present depression near the poles. In particular, large equatorial expansion velocities produce a flared disc or a ring of effective emissivity and mass loss. The effect on the determination of the orientation of the star axis of radial velocity gradients, and possibly competing rotation and expansion in the equatorial disc, is discussed. In general,the flux of matter is found to reach a broad maximum at distances of the order of 500 AU from the star.Arguments are given that may be used to favour one wind velocity distribution over another. As a result of the improved quality of the data, a deeper understanding of the constraints imposed on morphology and kinematics has been obtained.展开更多
We present modeling work on three young stellar objects that are promising targets for future high-resolution observations to investigate circumstellar disk evolution. The currently available data comprise the spectra...We present modeling work on three young stellar objects that are promising targets for future high-resolution observations to investigate circumstellar disk evolution. The currently available data comprise the spectral energy distribution from optical to millimeter wavelengths which allow constraining the structure of the circumstellar disk using self-consistent radiative transfer models. The results suggest that the assumption of well-mixed dust and gas leads to overestimation of flux in the far-infrared. Observational and theoretical arguments suggest that an overall decrease in far-infrared excess can be explained by dust settling towards the midplane. A new disk model is hence employed to take the effect of dust sedimentation into account. The extended model satisfactorily reproduces all existing observations. The three targets studied here therefore deserve follow-up observations to reveal the evolutionary state of their protoplanetary disks.展开更多
The circumstellar envelope of evolved stars of low- and intermediate-mass is an important site for dust formation. In comparison with the interstellar medium, they have more types of organics and different types of in...The circumstellar envelope of evolved stars of low- and intermediate-mass is an important site for dust formation. In comparison with the interstellar medium, they have more types of organics and different types of inorganics. Various infrared features in the circumstellar envelope can reveal the composition and abundance of dust, as well as the chemical and physical conditions of the circumstellar shell. Infrared features and their carriers are different in the C-rich or O-rich environment, and the mixed-environment where the C-rich and O-rich circumstellar materials co-exist. The C-rich sources exhibit a series of spectral features which are attrib- uted to organic molecules. They also show two prominent features at 21 μm and 30 μm which emit a large portion of infrared radiation. The O-rich sources exhibit the strong 9.7 μm and 18 μm features attributed to the Si-O bending and O-Si-O stretching modes of amorphous silicate dust. With the ISO/SWS spectrometer, about 50 narrow bands are identified with the crystalline silicate grains, mainly forsterite and enstatite. In addition, a series of features, at 13 μm, 16.8 μm, 19.5 μm and 31.8 μm, appearing to be correlated with each other, are attributed to oxides. Some objects simultaneously show the C-rich and O-rich features, e.g. some C-rich sources have silicate features. There is no well-accepted interpretation for such mixed appearance, though a binary model is suggested.展开更多
Physical properties of the supernova remnant expanding in a dumpy circumstellar medium are studied. Taking into account the effect of cloud evaporation in the clumpy medium, it is found that the evolution and internal...Physical properties of the supernova remnant expanding in a dumpy circumstellar medium are studied. Taking into account the effect of cloud evaporation in the clumpy medium, it is found that the evolution and internal structure of supernova remnant in a clumpy medium of a power-law density distribution in the radius are generally serf-similar as long as the minus power-law index is in the range of about 0-3. In the case where the index equals -2, namely, the medium is composed of the inhomogeneous free stellar wind, based on the detailed hydrodynamic solution, the formulae, figures, and tables for describing the observable properties, such as the relative distribution of the remnant’s surface brightness, X-ray luminosity, the mass of X-ray-emitting gas, emission-measure-weighted mean temperature, infrared luminosity, and Ha luminosity, are provided. It is indicated that the evaporated matter may pile up near the center and the X-ray emission there is brighter than that near the limb when some展开更多
In this paper,we present a study on the impact of radiation pressure and circumstellar dust on the motion of a test particle in the framework of the restricted four-body problem under the Manev’s field.We show that t...In this paper,we present a study on the impact of radiation pressure and circumstellar dust on the motion of a test particle in the framework of the restricted four-body problem under the Manev’s field.We show that the distribution of equilibrium points on the plane of motion is slightly different from that of the classical Newtonian problem.With the aid of the Lyapunov characteristic exponents,we show that the system is sensitive to changes in initial conditions;hence,the orbit of the system is found to be chaotic in the phase space for the given initial conditions.Furthermore,a numerical application of this model to a stellar system(Gliese 667C)is considered,which validates the dependence of the equilibrium points on the mass parameter.We show that the non-collinear equilibrium points of this stellar system are distributed symmetrically about the x-axis,and five of them are linearly stable.The basins of attraction of the system show that the equilibrium points have irregular boundaries,and we use the energy integral and the Manev parameter to illustrate the zero-velocity curves showing the permissible region of motion of the test particle with respect to the Jacobi constant.展开更多
1 Introduction The circumstellar envelope has a complex structure. Therefore, much present work is on the envelope of Mira variable, and especially on its structure. Some distribution maps of character velocity region...1 Introduction The circumstellar envelope has a complex structure. Therefore, much present work is on the envelope of Mira variable, and especially on its structure. Some distribution maps of character velocity region of M-type supergiants can be obtained from observation of VLBI. We have proposed and adopted a new idea and method,展开更多
We use archival ALMA observations of the CO(2-1)and SiO(5-4)molecular line emissions of AGB star R Hya to illustrate the relative contributions of rotation,expansion and line broadening to the morphology and kinematic...We use archival ALMA observations of the CO(2-1)and SiO(5-4)molecular line emissions of AGB star R Hya to illustrate the relative contributions of rotation,expansion and line broadening to the morphology and kinematics of the circumstellar envelope(CSE)within some~70 au(~0."5)from the centre of the star.We give evidence for rotation and important line broadening to dominate the inner region,within~14 au(~100 mas)from the centre of the star.The former is about an axis that projects a few degrees west of north and has a projected rotation velocity of a few km s^(-1).The latter occurs within some 7-14 au(50-100 mas)from the centre of the star,with the line width reaching two to three times its value outside this region.We suggest that it is caused by shocks induced by stellar pulsations and convective cell granulation.We show the importance of properly accounting for the observed line broadening when discussing rotation and evaluating the radial dependence of the rotation velocity.展开更多
This paper reports on SiO 86GHz observations of 33 IRAS evolved stars with H 2O or OH maser, drawn from Priscilla’s “ A catalog of observations for stellar masers ”. SiO maser emission was detected in five sources ...This paper reports on SiO 86GHz observations of 33 IRAS evolved stars with H 2O or OH maser, drawn from Priscilla’s “ A catalog of observations for stellar masers ”. SiO maser emission was detected in five sources all without previously known SiO detections. A tentative SiO emission was detected from the source IRAS18585+0900. The oxygen/carbonrichness of the circumstellar of IRAS18585+0900 is discussed with reference to its IRAS low resolution spectral (LRS) class 41. The low detection rate is discussed.展开更多
基金funded by the Vietnam Academy of Science and Technology(VAST)under grant No.NVCC39.01/24-25。
文摘New analyses of earlier ALMA observations of oxygen-rich AGB star EP Aquarii are presented,which complete a previously published analysis and offer a different interpretation of the morpho-kinematics of the circumstellar envelope.The birth of the equatorial density enhancement(EDE)is shown to occur very close to the star where evidence for rotation has been obtained.Close to the star and where outflows have been observed:their interaction with the gas of the nascent EDE is seen to play an important role in the development of the wind and the evolution of its radial velocity from 8 to 10 km s^(-1) on the polar symmetry axis to~2 km s^(-1) at the equator.It implies complex morpho-kinematics:making reliable interpretations with reasonable confidence is difficult.In particular,it questions an earlier interpretation implying the presence of a white dwarf companion orbiting the star at an angular distance of -0″4 from its center.It proposes instead an interpretation in terms of a standard mass ejection associated with a shock wave leaving a void of emission in its wake.High Doppler velocity wings are seen to consist of two components,the upper velocity end of the global wind,reaching above±12 km s^(-1),and an effective line broadening,confined within 200 mas from the center of the star,reaching above±20 km s^(-1) and interpreted as caused by the pattern of shock waves resulting from the interaction between stellar pulsation and convective cell partition.
基金supported by the Programme National "Physique et Chimie du MilieuInterstellaire" (PCMI) of CNRS/INSU with INC/INP co-funded by CEA and CNESfinancial support from VNSC/VAST+4 种基金the NAFOSTED funding agency under grant number 103.99–2015.39the World Laboratorythe Odon Vallet Foundationthe Rencontres du Viet Namfunded by Graduate University of Science and Technology undergrant number GUST.STS.DT 2017-VL01
文摘Atacama Large Millimetre/sub-millimetre Array(ALMA) observations of CO(1–0) and CO(2–1) emissions from the circumstellar envelope of the asymptotic giant branch(AGB) star EP Aqr have been made with four times better spatial resolution than previously available. They are analysed with emphasis on the de-projection in space of the effective emissivity and flux of matter using as input a prescribed configuration of the velocity field, assumed to be radial. The data are found to display an intrinsic axisymmetry with respect to an axis making a small angle with respect to the line of sight. A broad range of wind configurations, from prolate(bipolar) to oblate(equatorial) has been studied and found to be accompanied by significant equatorial emission. Qualitatively, the effective emissivity is enhanced near the equator to produce the central narrow component observed in the Doppler velocity spectra and its dependence on star latitude generally follows that of the wind velocity with the exception of an omni-present depression near the poles. In particular, large equatorial expansion velocities produce a flared disc or a ring of effective emissivity and mass loss. The effect on the determination of the orientation of the star axis of radial velocity gradients, and possibly competing rotation and expansion in the equatorial disc, is discussed. In general,the flux of matter is found to reach a broad maximum at distances of the order of 500 AU from the star.Arguments are given that may be used to favour one wind velocity distribution over another. As a result of the improved quality of the data, a deeper understanding of the constraints imposed on morphology and kinematics has been obtained.
基金Supported by the National Natural Science Foundation of China(Grant Nos.10733030,10921063 and 11173060)
文摘We present modeling work on three young stellar objects that are promising targets for future high-resolution observations to investigate circumstellar disk evolution. The currently available data comprise the spectral energy distribution from optical to millimeter wavelengths which allow constraining the structure of the circumstellar disk using self-consistent radiative transfer models. The results suggest that the assumption of well-mixed dust and gas leads to overestimation of flux in the far-infrared. Observational and theoretical arguments suggest that an overall decrease in far-infrared excess can be explained by dust settling towards the midplane. A new disk model is hence employed to take the effect of dust sedimentation into account. The extended model satisfactorily reproduces all existing observations. The three targets studied here therefore deserve follow-up observations to reveal the evolutionary state of their protoplanetary disks.
基金the Program for New Century Excellent Talents in University of China (Grant No. NCET-05-0144)the Doctoral Fund of Ministry of Education of China (Grant No. 20060027013)the National Natural Science Foundation of China (Grant No. 10473003)
文摘The circumstellar envelope of evolved stars of low- and intermediate-mass is an important site for dust formation. In comparison with the interstellar medium, they have more types of organics and different types of inorganics. Various infrared features in the circumstellar envelope can reveal the composition and abundance of dust, as well as the chemical and physical conditions of the circumstellar shell. Infrared features and their carriers are different in the C-rich or O-rich environment, and the mixed-environment where the C-rich and O-rich circumstellar materials co-exist. The C-rich sources exhibit a series of spectral features which are attrib- uted to organic molecules. They also show two prominent features at 21 μm and 30 μm which emit a large portion of infrared radiation. The O-rich sources exhibit the strong 9.7 μm and 18 μm features attributed to the Si-O bending and O-Si-O stretching modes of amorphous silicate dust. With the ISO/SWS spectrometer, about 50 narrow bands are identified with the crystalline silicate grains, mainly forsterite and enstatite. In addition, a series of features, at 13 μm, 16.8 μm, 19.5 μm and 31.8 μm, appearing to be correlated with each other, are attributed to oxides. Some objects simultaneously show the C-rich and O-rich features, e.g. some C-rich sources have silicate features. There is no well-accepted interpretation for such mixed appearance, though a binary model is suggested.
文摘Physical properties of the supernova remnant expanding in a dumpy circumstellar medium are studied. Taking into account the effect of cloud evaporation in the clumpy medium, it is found that the evolution and internal structure of supernova remnant in a clumpy medium of a power-law density distribution in the radius are generally serf-similar as long as the minus power-law index is in the range of about 0-3. In the case where the index equals -2, namely, the medium is composed of the inhomogeneous free stellar wind, based on the detailed hydrodynamic solution, the formulae, figures, and tables for describing the observable properties, such as the relative distribution of the remnant’s surface brightness, X-ray luminosity, the mass of X-ray-emitting gas, emission-measure-weighted mean temperature, infrared luminosity, and Ha luminosity, are provided. It is indicated that the evaporated matter may pile up near the center and the X-ray emission there is brighter than that near the limb when some
文摘In this paper,we present a study on the impact of radiation pressure and circumstellar dust on the motion of a test particle in the framework of the restricted four-body problem under the Manev’s field.We show that the distribution of equilibrium points on the plane of motion is slightly different from that of the classical Newtonian problem.With the aid of the Lyapunov characteristic exponents,we show that the system is sensitive to changes in initial conditions;hence,the orbit of the system is found to be chaotic in the phase space for the given initial conditions.Furthermore,a numerical application of this model to a stellar system(Gliese 667C)is considered,which validates the dependence of the equilibrium points on the mass parameter.We show that the non-collinear equilibrium points of this stellar system are distributed symmetrically about the x-axis,and five of them are linearly stable.The basins of attraction of the system show that the equilibrium points have irregular boundaries,and we use the energy integral and the Manev parameter to illustrate the zero-velocity curves showing the permissible region of motion of the test particle with respect to the Jacobi constant.
文摘1 Introduction The circumstellar envelope has a complex structure. Therefore, much present work is on the envelope of Mira variable, and especially on its structure. Some distribution maps of character velocity region of M-type supergiants can be obtained from observation of VLBI. We have proposed and adopted a new idea and method,
基金funded by the Vietnam Academy of Science and Technology(VAST)under Grant No.NCVCC39.02/22-23。
文摘We use archival ALMA observations of the CO(2-1)and SiO(5-4)molecular line emissions of AGB star R Hya to illustrate the relative contributions of rotation,expansion and line broadening to the morphology and kinematics of the circumstellar envelope(CSE)within some~70 au(~0."5)from the centre of the star.We give evidence for rotation and important line broadening to dominate the inner region,within~14 au(~100 mas)from the centre of the star.The former is about an axis that projects a few degrees west of north and has a projected rotation velocity of a few km s^(-1).The latter occurs within some 7-14 au(50-100 mas)from the centre of the star,with the line width reaching two to three times its value outside this region.We suggest that it is caused by shocks induced by stellar pulsations and convective cell granulation.We show the importance of properly accounting for the observed line broadening when discussing rotation and evaluating the radial dependence of the rotation velocity.
文摘This paper reports on SiO 86GHz observations of 33 IRAS evolved stars with H 2O or OH maser, drawn from Priscilla’s “ A catalog of observations for stellar masers ”. SiO maser emission was detected in five sources all without previously known SiO detections. A tentative SiO emission was detected from the source IRAS18585+0900. The oxygen/carbonrichness of the circumstellar of IRAS18585+0900 is discussed with reference to its IRAS low resolution spectral (LRS) class 41. The low detection rate is discussed.
