To study the chemical evolution during the formation of molecular clouds,we model three types of clouds with different density structures:collapsing spherical,collapsing ellipsoidal,and static spherical profiles.The c...To study the chemical evolution during the formation of molecular clouds,we model three types of clouds with different density structures:collapsing spherical,collapsing ellipsoidal,and static spherical profiles.The collapsing models are better than the static models in matching the observational characteristics in typical molecular clouds.This is mainly because the gravity can speed up the formation of some important molecules(e.g.,H_(2),CO,OH)by increasing the number density during collapse.The different morphologies of prolate,oblate,and spherical clouds lead to differences in chemical evolution,which are mainly due to their different evolution of number density.We also study the effect of initial chemical compositions on chemical evolution,and find that H atoms can accelerate OH formation by two major reactions:O+H→OH in gas phase and on dust grain surfaces,leading to the models in which hydrogen is mainly atomic initially better match observations than the models in which hydrogen is mainly molecular initially.Namely,to match observations,initially hydrogen must be mostly atomic.The CO molecules are able to form even without the pre-existence of H_(2).We also study the influence of gas temperature,dust temperature,intensity of interstellar radiation field and cosmic-ray ionization rate on chemical evolution in static clouds.The static CO clouds with high dust temperature,strong radiation field,and intensive cosmic rays are transient due to rapid CO destruction.展开更多
Newly born stars are surrounded by gas and dust with a attened axisymmetric distribution termed protoplanetary disk,in which planets are formed.Observations of these objects are necessary for understanding the formati...Newly born stars are surrounded by gas and dust with a attened axisymmetric distribution termed protoplanetary disk,in which planets are formed.Observations of these objects are necessary for understanding the formation and early evolution of stars and planets,and for revealing the composition of the raw material from which planets are made.Numerical models can extract important parameters from the observational data,including the gas and dust mass of the disk.These parameters are used as input for further modeling,e.g.,to calculate the chemical composition of the disk.A consistent thermochemical model should be able to reproduce the abundances of di erent species in the disk.However,this good wish has been challenged for many disks:models over-predict the emission line intensity of some species;namely,they are depleted(with respect to expectations from canonical models).In this review we show how this disparity indicates that dust evolution has signi cant e ects on gas chemistry,and may indicate the earliest stages of planet formation.展开更多
Structures in molecular ISM are observed to follow a power-law relation between the velocity dispersion and spatial size,known as Larson’s first relation,which is often attributed to the turbulent nature of molecular...Structures in molecular ISM are observed to follow a power-law relation between the velocity dispersion and spatial size,known as Larson’s first relation,which is often attributed to the turbulent nature of molecular ISM and imprints the dynamics of molecular cloud structures.Using the^(13)CO(J=1-0)data from the Milky Way Imaging Scroll Painting survey,we built a sample with 360 structures having relatively accurate distances obtained from either the reddened background stars with Gaia parallaxes or associated maser parallaxes,spanning from 0.4 to~15 kpc.Using this sample and about 0.3 million pixels,we analyzed the correlations between velocity dispersion,surface/column density,and spatial scales.Our structure-wise results show power-law indices smaller than 0.5 in both theσ_(v)-R_(eff)andσ_(v)-R_(eff)·Σrelations.In the pixel-wise results,the v spix is statistically scaling with the beam physical size(R_(s)≡ΘD/2)in form ofσ_(v)^(pix)■R_(s)^(0.43±0.03).Meanwhile,σ_(v)_(pix)in the inner Galaxy is statistically larger than the outer side.We also analyzed correlations betweenσ_(v)_(pix)and the H_(2)column density N(H_(2)),finding thatσ_(v)_(pix)stops increasing with N(H_(2))after>10^(22)cm^(-2).The structures with and without high-column-density(>10^(22)cm^(-2))pixels show differentσ_(v)_(pix)■N(H_(2))^(ξ)relations,where the mean(std)ξvalues are 0.38(0.14)and 0.62(0.27),respectively.展开更多
Astrochemical modeling is needed for understanding the formation and evolution of interstellar molecules,and for extracting physical information from spectroscopic observations of interstellar clouds.The modeling usua...Astrochemical modeling is needed for understanding the formation and evolution of interstellar molecules,and for extracting physical information from spectroscopic observations of interstellar clouds.The modeling usually involves the handling of a chemical reaction network and solution of a set of coupled nonlinear ordinary differential equations,which is traditionally done using code written in compiled languages such as Fortran or C/C++.While being computationally efficient,there is room for improvement in the ease of use and interactivity for such an approach.In this work we present a new public code named CHEMPL,which emphasizes interactivity in a modern Python environment,while remaining computationally efficient.Common reaction mechanisms and a three-phase formulation of gasgrain chemistry are implemented by default.It is straightforward to run 0 D models with CHEMPL,and only a small amount of additional code is needed to construct 1 D or higher-dimensional chemical models.We demonstrate its usage with a few astrochemically relevant examples.展开更多
Molecules reside broadly in the interstellar space and can be detected via spectroscopic observations.To date,more than 271 molecular species have been identified in interstellar medium or circumstellar envelopes.Mole...Molecules reside broadly in the interstellar space and can be detected via spectroscopic observations.To date,more than 271 molecular species have been identified in interstellar medium or circumstellar envelopes.Molecular spectroscopic parameters measured in laboratory make the identification of new species and derivation of physical parameters possible.These spectroscopic parameters are systematically collected into databases,two of the most commonly used being the CDMS and JPL databases.While new spectroscopic parameters are continuously measured/calculated and added to those databases,at any point in time it is the existing spectroscopic data that ultimately limits what molecules can possibly be identified in astronomical data.In this work,we conduct a meta-analysis of the CDMS and JPL databases.We show the statistics of transition frequencies and their uncertainties in these two databases,and discuss the line confusion problem under certain physical environments.We then assess the prospects of detecting molecules in common ISM environments using a few facilities that are expected to be conducting spectroscopic observations in the future.Results show that CSST/HSTDM and SKA1-mid have the potential to detect some complex organic molecules,or even amino acids,with reasonable assumptions about ISM environments.展开更多
Dust grains in protoplanetary disks are the building blocks of planets.Investigating the dust composition and size,and their variation over time,is crucial for understanding the planet formation process.The PDS 70 dis...Dust grains in protoplanetary disks are the building blocks of planets.Investigating the dust composition and size,and their variation over time,is crucial for understanding the planet formation process.The PDS 70 disk is so far the only protoplanetary disk with concrete evidence for the presence of young planets.Mid-infrared spectra were obtained for PDS 70 by the Infrared Spectrograph(IRS)on the Spitzer Space Telescope(SST)and the Mid-Infrared Instrument(MIRI)on the James Webb Space Telescope(JWST)in 2007 and 2022,respectively.In this work,we investigate the dust mineralogy through a detailed decomposition of the observed mid-infrared spectra.The results show that both the dust size and crystallinity increased by a factor of about two during the two epochs of observation,indicating evident dust processing in the terrestrial planet-forming region of the PDS 70 disk.The dust size(~0.8μm)and crystallinity(~6%)in the PDS 70 disk are similar to those of other disks,which implies that the two nascent planets,PDS 70b and PDS 70c located at radial distances of~22 AU and~34 AU,do not have a significant impact on the dust processing in the inner disk.The flux densities atλ16μm measured by JWST/MIRI are only 60%of those obtained by Spitzer/IRS.Based on self-consistent radiative transfer modeling,we found that such a strong variability in mid-infrared fluxes can be produced by adjustments to the dust density distribution and structure of the inner disk probably induced by planet-disk interaction.展开更多
Submillimeter astronomy is poised to revolutionize our understanding of the Universe by revealing cosmic phenomena hidden from optical and near-infrared observations,particularly those associated with interstellar dus...Submillimeter astronomy is poised to revolutionize our understanding of the Universe by revealing cosmic phenomena hidden from optical and near-infrared observations,particularly those associated with interstellar dust,molecular gas,and star formation.The Xue-shan-mu-chang 15-meter SubMillimeter Telescope(XSMT-15m),to be constructed at a premier high-altitude site(4813 m)in Qinghai,China,marks a major milestone for Chinese astronomy,establishing the Chinese mainland first independently developed,world-class submillimeter facility.Equipped with state-of-the-art instruments,XSMT-15m will address a diverse range of frontier scientific questions spanning extragalactic astronomy,Galactic structure,time-domain astrophysics,and astrochemistry.In synergy with current and forthcoming observatories,XsMT-15m will illuminate the formation and evolution of galaxies,unravel the physical and chemical processes shaping the interstellar medium,and explore transient phenomena in the submillimeter regime.These capabilities will advance our understanding across extragalactic astronomy,Galactic ecology,astrochemistry,and time-domain astrophysics,inaugurating a new era for submillimeter research in China and the northern hemisphere.展开更多
基金financially supported by the National Natural Science Foundation of China through grants 12041305 and 11873094。
文摘To study the chemical evolution during the formation of molecular clouds,we model three types of clouds with different density structures:collapsing spherical,collapsing ellipsoidal,and static spherical profiles.The collapsing models are better than the static models in matching the observational characteristics in typical molecular clouds.This is mainly because the gravity can speed up the formation of some important molecules(e.g.,H_(2),CO,OH)by increasing the number density during collapse.The different morphologies of prolate,oblate,and spherical clouds lead to differences in chemical evolution,which are mainly due to their different evolution of number density.We also study the effect of initial chemical compositions on chemical evolution,and find that H atoms can accelerate OH formation by two major reactions:O+H→OH in gas phase and on dust grain surfaces,leading to the models in which hydrogen is mainly atomic initially better match observations than the models in which hydrogen is mainly molecular initially.Namely,to match observations,initially hydrogen must be mostly atomic.The CO molecules are able to form even without the pre-existence of H_(2).We also study the influence of gas temperature,dust temperature,intensity of interstellar radiation field and cosmic-ray ionization rate on chemical evolution in static clouds.The static CO clouds with high dust temperature,strong radiation field,and intensive cosmic rays are transient due to rapid CO destruction.
基金the"Hundred Talents Program"of Chinese Academy of Sciences,and the National Natural Science Foundation of China(No.11873094).
文摘Newly born stars are surrounded by gas and dust with a attened axisymmetric distribution termed protoplanetary disk,in which planets are formed.Observations of these objects are necessary for understanding the formation and early evolution of stars and planets,and for revealing the composition of the raw material from which planets are made.Numerical models can extract important parameters from the observational data,including the gas and dust mass of the disk.These parameters are used as input for further modeling,e.g.,to calculate the chemical composition of the disk.A consistent thermochemical model should be able to reproduce the abundances of di erent species in the disk.However,this good wish has been challenged for many disks:models over-predict the emission line intensity of some species;namely,they are depleted(with respect to expectations from canonical models).In this review we show how this disparity indicates that dust evolution has signi cant e ects on gas chemistry,and may indicate the earliest stages of planet formation.
基金supported by the National Key R&D Program of China(grant No.2023YFA1608000)the National Natural Science Foundation of China(NSFC,grant Nos.U2031202,12373030,and 11873093)+2 种基金sponsored by the National Key R&D Program of China with grant 2023YFA1608000the CAS Key Research Program of Frontier Sciences with grant QYZDJ-SSW-SLH047Z.C.acknowledges the Natural Science Foundation of Jiangsu Province(grant No.BK20231509)。
文摘Structures in molecular ISM are observed to follow a power-law relation between the velocity dispersion and spatial size,known as Larson’s first relation,which is often attributed to the turbulent nature of molecular ISM and imprints the dynamics of molecular cloud structures.Using the^(13)CO(J=1-0)data from the Milky Way Imaging Scroll Painting survey,we built a sample with 360 structures having relatively accurate distances obtained from either the reddened background stars with Gaia parallaxes or associated maser parallaxes,spanning from 0.4 to~15 kpc.Using this sample and about 0.3 million pixels,we analyzed the correlations between velocity dispersion,surface/column density,and spatial scales.Our structure-wise results show power-law indices smaller than 0.5 in both theσ_(v)-R_(eff)andσ_(v)-R_(eff)·Σrelations.In the pixel-wise results,the v spix is statistically scaling with the beam physical size(R_(s)≡ΘD/2)in form ofσ_(v)^(pix)■R_(s)^(0.43±0.03).Meanwhile,σ_(v)_(pix)in the inner Galaxy is statistically larger than the outer side.We also analyzed correlations betweenσ_(v)_(pix)and the H_(2)column density N(H_(2)),finding thatσ_(v)_(pix)stops increasing with N(H_(2))after>10^(22)cm^(-2).The structures with and without high-column-density(>10^(22)cm^(-2))pixels show differentσ_(v)_(pix)■N(H_(2))^(ξ)relations,where the mean(std)ξvalues are 0.38(0.14)and 0.62(0.27),respectively.
基金partially funded by the National Natural Science Foundation of China(Grant Nos.11873094 and 11873097)financially supported by the Hundred Talents Program of Chinese Academy of Sciences。
文摘Astrochemical modeling is needed for understanding the formation and evolution of interstellar molecules,and for extracting physical information from spectroscopic observations of interstellar clouds.The modeling usually involves the handling of a chemical reaction network and solution of a set of coupled nonlinear ordinary differential equations,which is traditionally done using code written in compiled languages such as Fortran or C/C++.While being computationally efficient,there is room for improvement in the ease of use and interactivity for such an approach.In this work we present a new public code named CHEMPL,which emphasizes interactivity in a modern Python environment,while remaining computationally efficient.Common reaction mechanisms and a three-phase formulation of gasgrain chemistry are implemented by default.It is straightforward to run 0 D models with CHEMPL,and only a small amount of additional code is needed to construct 1 D or higher-dimensional chemical models.We demonstrate its usage with a few astrochemically relevant examples.
基金financially supported by the National Natural Science Foundation of China through grants 12041305 and 11873094by the China Manned Space Project。
文摘Molecules reside broadly in the interstellar space and can be detected via spectroscopic observations.To date,more than 271 molecular species have been identified in interstellar medium or circumstellar envelopes.Molecular spectroscopic parameters measured in laboratory make the identification of new species and derivation of physical parameters possible.These spectroscopic parameters are systematically collected into databases,two of the most commonly used being the CDMS and JPL databases.While new spectroscopic parameters are continuously measured/calculated and added to those databases,at any point in time it is the existing spectroscopic data that ultimately limits what molecules can possibly be identified in astronomical data.In this work,we conduct a meta-analysis of the CDMS and JPL databases.We show the statistics of transition frequencies and their uncertainties in these two databases,and discuss the line confusion problem under certain physical environments.We then assess the prospects of detecting molecules in common ISM environments using a few facilities that are expected to be conducting spectroscopic observations in the future.Results show that CSST/HSTDM and SKA1-mid have the potential to detect some complex organic molecules,or even amino acids,with reasonable assumptions about ISM environments.
基金financial supports by the National Natural Science Foundation of China(Grant No.11973090)the International Partnership Program of Chinese Academy of Sciences(Grant No.019GJHZ2023016FN)+5 种基金the Natural Science Foundation of Sichuan Province of China(Grant No.2025ZNSFSC0060)the financial support by the National Natural Science Foundation of China(Grant No.11973091)financial supports by the National Natural Science Foundation of China(Grant No.12041305)the National Key R&D Program of China(Grant No.2023YFA1608000)support from the Carlsberg Foundation(Grant No.CF23-0481)the Max Planck Society。
文摘Dust grains in protoplanetary disks are the building blocks of planets.Investigating the dust composition and size,and their variation over time,is crucial for understanding the planet formation process.The PDS 70 disk is so far the only protoplanetary disk with concrete evidence for the presence of young planets.Mid-infrared spectra were obtained for PDS 70 by the Infrared Spectrograph(IRS)on the Spitzer Space Telescope(SST)and the Mid-Infrared Instrument(MIRI)on the James Webb Space Telescope(JWST)in 2007 and 2022,respectively.In this work,we investigate the dust mineralogy through a detailed decomposition of the observed mid-infrared spectra.The results show that both the dust size and crystallinity increased by a factor of about two during the two epochs of observation,indicating evident dust processing in the terrestrial planet-forming region of the PDS 70 disk.The dust size(~0.8μm)and crystallinity(~6%)in the PDS 70 disk are similar to those of other disks,which implies that the two nascent planets,PDS 70b and PDS 70c located at radial distances of~22 AU and~34 AU,do not have a significant impact on the dust processing in the inner disk.The flux densities atλ16μm measured by JWST/MIRI are only 60%of those obtained by Spitzer/IRS.Based on self-consistent radiative transfer modeling,we found that such a strong variability in mid-infrared fluxes can be produced by adjustments to the dust density distribution and structure of the inner disk probably induced by planet-disk interaction.
基金supported by the National Key R&D Program of China(Grant No.2023YFA1608200)the National Natural Science Foundation of China(Grant Nos.12427901 and 12333013)the Chinese Academy of Sciences(Grant No.PTYQ2024BJ0010).
文摘Submillimeter astronomy is poised to revolutionize our understanding of the Universe by revealing cosmic phenomena hidden from optical and near-infrared observations,particularly those associated with interstellar dust,molecular gas,and star formation.The Xue-shan-mu-chang 15-meter SubMillimeter Telescope(XSMT-15m),to be constructed at a premier high-altitude site(4813 m)in Qinghai,China,marks a major milestone for Chinese astronomy,establishing the Chinese mainland first independently developed,world-class submillimeter facility.Equipped with state-of-the-art instruments,XSMT-15m will address a diverse range of frontier scientific questions spanning extragalactic astronomy,Galactic structure,time-domain astrophysics,and astrochemistry.In synergy with current and forthcoming observatories,XsMT-15m will illuminate the formation and evolution of galaxies,unravel the physical and chemical processes shaping the interstellar medium,and explore transient phenomena in the submillimeter regime.These capabilities will advance our understanding across extragalactic astronomy,Galactic ecology,astrochemistry,and time-domain astrophysics,inaugurating a new era for submillimeter research in China and the northern hemisphere.
