In star formation regions,the complex organic molecules(COMs)that contain peptide bonds(-NH-C(=O)-)play a major role in the metabolic process because-NH-C(=O)-is connected to amino acids(R-CHNH_2-COOH).Over the past f...In star formation regions,the complex organic molecules(COMs)that contain peptide bonds(-NH-C(=O)-)play a major role in the metabolic process because-NH-C(=O)-is connected to amino acids(R-CHNH_2-COOH).Over the past few decades,many COMs containing peptide-like bonds have been detected in hot molecular cores(HMCs),hot corinos,and cold molecular clouds,however,their prebiotic chemistry is poorly understood.We present the first detection of the rotational emission lines of formamide(NH_2CHO)and isocyanic acid(HNCO),which contain peptide-like bonds toward the chemically rich HMC G358.93-0.03 MM1,using high-resolution and high-sensitivity Atacama Large Millimeter/submillimeter Array bands 6 and 7.We estimate that the column densities of NH_2CHO and HNCO toward G358.93-0.03 MM1 are(2.80±0.29)×10~(15)cm~(-2)and(1.80±0.42)×10~(16)cm~(-2)with excitation temperatures of 165±21 K and 170±32 K,respectively.The fractional abundances of NH_2CHO and HNCO toward G358.93-0.03 MM1 are(9.03±1.44)×10~(-10)and(5.80±2.09)×10^(-9).We compare the estimated abundances of NH_2CHO and HNCO with the existing threephase warm-up chemical model abundance values and notice that the observed and modeled abundances are very close.We conclude that NH_2CHO is produced by the reaction of NH_2and H_2CO in the gas phase toward G358.93-0.03 MM1.Likewise,HNCO is produced on the surface of grains by the reaction of NH and CO toward G358.93-0.03 MM1.We also find that NH_2CHO and HNCO are chemically linked toward G358.93-0.03 MM1.展开更多
At low temperatures(10 K),hydrogen atoms can diffuse quickly on grain ice mantles and frequently encounter hydrogen molecules,which cover a notable fraction of grain surface.The desorption energy of H atoms on H2 subs...At low temperatures(10 K),hydrogen atoms can diffuse quickly on grain ice mantles and frequently encounter hydrogen molecules,which cover a notable fraction of grain surface.The desorption energy of H atoms on H2 substrates is much less than that on water ice.The H atom encounter desorption mechanism is adopted to study the enhanced desorption of H atoms on H_(2 )substrates.Using a small reaction network,we show that the steady-state surface H abundances predicted by the rate equation model that includes H atom encounter desorption agree reasonably well with the results from the more rigorous microscopic Monte Carlo method.For a full gas-grain model,H atom encounter desorption can reduce surface H abundances.Therefore,if a model adopts the encounter desorption of H atoms,it becomes more difficult for hydrogenation products such as methanol to form,but it is easier for C,O and N atoms to bond with each other on grain surfaces.展开更多
Phenol,which belongs to the C_(6)H_(6)O isomeric group,is the simplest molecule in the family of alcohol of the aromatic series.Although phenol has yet to be detected in the interstellar medium,a tentative identificat...Phenol,which belongs to the C_(6)H_(6)O isomeric group,is the simplest molecule in the family of alcohol of the aromatic series.Although phenol has yet to be detected in the interstellar medium,a tentative identification was reported toward the Orion KL hot core using the IRAM-30 m line survey.To explore some more species of this isomeric group,we consider ten species to study the fate of their astronomical detection.It is noticed that phenol is the most energetically favorable isomer of this group.In contrast,propargyl ether is the least favorable(having relative energy~103kcal mol^(-1)compared to phenol)species of this group.So far,the studies associated with the formation of phenol are heavily concentrated on combustion chemistry.Here,we suggest a few key reactions(C_(6)H_(6)+OH→C_(6)H_(5)+H_(2)O,C_(6)H_(6)+O→C_(6)H_(5)OH,C_(6)H_(6)+H→C_(6)H_(5)+H_(2),and C_(6)H_(5)+OH→C_(6)H_(5)OH+hν)for the formation of phenol.All these pathways are included in a large gas-grain chemical network to study its formation in high mass star-forming regions and dark cloud environments.It is noticed that the phenyl(-C_(6)H_(5))formation by the ice-phase hydrogen abstraction reaction of benzene(i.e.,C_(6)H_(6)+OH→C_(6)H_(5)+H_(2)O if allowed at~10 K)could serve as the starting point for the formation of phenol in the gas phase by radiative association reaction C_(6)H_(5)+OH→C_(6)H_(5)OH+hν.The gasphase reaction C_(6)H_(6)+O→C_(6)H_(5)OH significantly contributes to the formation of phenol,when the ice-phase reaction C_(6)H_(6)+OH→C_(6)H_(5)+H_(2)O is not considered at low temperature.Band 4 ALMA archival data of a hot molecular core,G10.47+0.03,are analyzed.It yields an upper limit on phenol abundance of 5.19×10^(-9).Our astrochemical model delivers an upper limit on phenol abundance of~2.20×10^(-9)in the hot molecular core,whereas its production in the dark cloud is not satisfactory.展开更多
High-resolution optical spectra of the zero age star HD77407 are analysed and its Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Co, Ni and Ba contents are determined using spectral synthesis method. The temperature of t...High-resolution optical spectra of the zero age star HD77407 are analysed and its Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Co, Ni and Ba contents are determined using spectral synthesis method. The temperature of the star is determined by fitting the Hα line wings. The parameters derived for this star are Teff=5900 K, log g=4.47 and [Fe/H] = ＋0.07. It is found that the derived iron content is slightly higher than what is given in the published literature. This star shows a relative overabundances of Ca and Ba, and underabundances of Na, V and Ni with respect to the solar mix. Activity of the star is indicated by the filled in Hα and Ca Ⅱ triplet line cores. It has been confirmed that our spectroscopic approach yields fairly reliable and consistent results for active stars.展开更多
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
For the first time, the OMC-2/3 region was mapped in C2H （1–0）, HC3N （10–9） and HNC （1–0） lines. In general, the emissions from all the three molecular species reveal an extended filamentary structure. The di...For the first time, the OMC-2/3 region was mapped in C2H （1–0）, HC3N （10–9） and HNC （1–0） lines. In general, the emissions from all the three molecular species reveal an extended filamentary structure. The distribution of C2H cores almost follows that of the 1300μm condensations, which might suggest that C2H is a good tracer to study the core structure of molecular clouds. The core masses traced by HNC are rather ？at, ranging from 18.8 to 49.5 M , while also presenting a large span for those from C2H, ranging from 6.4 to 36.0 M . The line widths of both HNC and C2H look very similar, and both are wider than that of HC3N. The line widths of the three lines are all wider than those from dark clouds, implying that the former is more active than the latter, and has larger turbulence caused by winds and UV radiation from the surrounding massive stars.展开更多
Using data from Millimetre Astronomy Legacy Team Survey at 90 GHz （MALT90）, we present a molecular line study of a sample of APEX Telescope Large Area Survey of the Galaxy （ATLASGAL） clumps. Twelve emission lines ...Using data from Millimetre Astronomy Legacy Team Survey at 90 GHz （MALT90）, we present a molecular line study of a sample of APEX Telescope Large Area Survey of the Galaxy （ATLASGAL） clumps. Twelve emission lines have been detected in all. We found that in most sources, emissions of HC3N, HN13C, CH3CN, HNCO and SiO show more compact distributions than those of HCO＋, HNC, HCN and N2H＋. By comparing with other molecular lines, we found that the abun- dance of HNCO （x（HNCO）） correlates well with other species such as HC3N, HNC, C2H, H13CO＋ and N2H＋. Previous studies indicate the HNCO abundance could be enhanced by shocks. However, in this study, we find the abundance of HNCO does not correlate well with that of SiO, which is also a good tracer of shocks. We suggest this may be because HNCO and SiO trace different parts of shocks. Our analysis indicates that the velocity of a shock traced by HNCO tends to be lower than that traced by SiO. In the low-velocity shocks traced by HNCO, the HNCO abundance increases faster than that of SiO. While in the relatively high-velocity shocks traced by SiO, the SiO abundance increases faster than that of HNCO. We suggest that in the infrared dark cloud MSXDC G331.71＋00.59, high-velocity shocks are destroying the molecule HNCO.展开更多
文摘In star formation regions,the complex organic molecules(COMs)that contain peptide bonds(-NH-C(=O)-)play a major role in the metabolic process because-NH-C(=O)-is connected to amino acids(R-CHNH_2-COOH).Over the past few decades,many COMs containing peptide-like bonds have been detected in hot molecular cores(HMCs),hot corinos,and cold molecular clouds,however,their prebiotic chemistry is poorly understood.We present the first detection of the rotational emission lines of formamide(NH_2CHO)and isocyanic acid(HNCO),which contain peptide-like bonds toward the chemically rich HMC G358.93-0.03 MM1,using high-resolution and high-sensitivity Atacama Large Millimeter/submillimeter Array bands 6 and 7.We estimate that the column densities of NH_2CHO and HNCO toward G358.93-0.03 MM1 are(2.80±0.29)×10~(15)cm~(-2)and(1.80±0.42)×10~(16)cm~(-2)with excitation temperatures of 165±21 K and 170±32 K,respectively.The fractional abundances of NH_2CHO and HNCO toward G358.93-0.03 MM1 are(9.03±1.44)×10~(-10)and(5.80±2.09)×10^(-9).We compare the estimated abundances of NH_2CHO and HNCO with the existing threephase warm-up chemical model abundance values and notice that the observed and modeled abundances are very close.We conclude that NH_2CHO is produced by the reaction of NH_2and H_2CO in the gas phase toward G358.93-0.03 MM1.Likewise,HNCO is produced on the surface of grains by the reaction of NH and CO toward G358.93-0.03 MM1.We also find that NH_2CHO and HNCO are chemically linked toward G358.93-0.03 MM1.
基金funded by the National Natural Science Foundation of China(Grant Nos.11673054,11973075 and 11973099)。
文摘At low temperatures(10 K),hydrogen atoms can diffuse quickly on grain ice mantles and frequently encounter hydrogen molecules,which cover a notable fraction of grain surface.The desorption energy of H atoms on H2 substrates is much less than that on water ice.The H atom encounter desorption mechanism is adopted to study the enhanced desorption of H atoms on H_(2 )substrates.Using a small reaction network,we show that the steady-state surface H abundances predicted by the rate equation model that includes H atom encounter desorption agree reasonably well with the results from the more rigorous microscopic Monte Carlo method.For a full gas-grain model,H atom encounter desorption can reduce surface H abundances.Therefore,if a model adopts the encounter desorption of H atoms,it becomes more difficult for hydrogenation products such as methanol to form,but it is easier for C,O and N atoms to bond with each other on grain surfaces.
基金the SVMCM scholarship,Government of West Bengalthe DST-INSPIRE Fellowship scheme for financial assistancethe CSIR fellowship。
文摘Phenol,which belongs to the C_(6)H_(6)O isomeric group,is the simplest molecule in the family of alcohol of the aromatic series.Although phenol has yet to be detected in the interstellar medium,a tentative identification was reported toward the Orion KL hot core using the IRAM-30 m line survey.To explore some more species of this isomeric group,we consider ten species to study the fate of their astronomical detection.It is noticed that phenol is the most energetically favorable isomer of this group.In contrast,propargyl ether is the least favorable(having relative energy~103kcal mol^(-1)compared to phenol)species of this group.So far,the studies associated with the formation of phenol are heavily concentrated on combustion chemistry.Here,we suggest a few key reactions(C_(6)H_(6)+OH→C_(6)H_(5)+H_(2)O,C_(6)H_(6)+O→C_(6)H_(5)OH,C_(6)H_(6)+H→C_(6)H_(5)+H_(2),and C_(6)H_(5)+OH→C_(6)H_(5)OH+hν)for the formation of phenol.All these pathways are included in a large gas-grain chemical network to study its formation in high mass star-forming regions and dark cloud environments.It is noticed that the phenyl(-C_(6)H_(5))formation by the ice-phase hydrogen abstraction reaction of benzene(i.e.,C_(6)H_(6)+OH→C_(6)H_(5)+H_(2)O if allowed at~10 K)could serve as the starting point for the formation of phenol in the gas phase by radiative association reaction C_(6)H_(5)+OH→C_(6)H_(5)OH+hν.The gasphase reaction C_(6)H_(6)+O→C_(6)H_(5)OH significantly contributes to the formation of phenol,when the ice-phase reaction C_(6)H_(6)+OH→C_(6)H_(5)+H_(2)O is not considered at low temperature.Band 4 ALMA archival data of a hot molecular core,G10.47+0.03,are analyzed.It yields an upper limit on phenol abundance of 5.19×10^(-9).Our astrochemical model delivers an upper limit on phenol abundance of~2.20×10^(-9)in the hot molecular core,whereas its production in the dark cloud is not satisfactory.
基金the National Natural Science Foundation of China
文摘High-resolution optical spectra of the zero age star HD77407 are analysed and its Li, C, O, Na, Mg, Al, Si, K, Ca, Sc, Ti, V, Co, Ni and Ba contents are determined using spectral synthesis method. The temperature of the star is determined by fitting the Hα line wings. The parameters derived for this star are Teff=5900 K, log g=4.47 and [Fe/H] = ＋0.07. It is found that the derived iron content is slightly higher than what is given in the published literature. This star shows a relative overabundances of Ca and Ba, and underabundances of Na, V and Ni with respect to the solar mix. Activity of the star is indicated by the filled in Hα and Ca Ⅱ triplet line cores. It has been confirmed that our spectroscopic approach yields fairly reliable and consistent results for active stars.
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supported by the National Natural Science Foundation of China (Grant Nos. 11003046, 11073054, 10733030 and 10621303)the National Basic Research Program of China (973 Program, Grant 2007CB815403)
文摘For the first time, the OMC-2/3 region was mapped in C2H （1–0）, HC3N （10–9） and HNC （1–0） lines. In general, the emissions from all the three molecular species reveal an extended filamentary structure. The distribution of C2H cores almost follows that of the 1300μm condensations, which might suggest that C2H is a good tracer to study the core structure of molecular clouds. The core masses traced by HNC are rather ？at, ranging from 18.8 to 49.5 M , while also presenting a large span for those from C2H, ranging from 6.4 to 36.0 M . The line widths of both HNC and C2H look very similar, and both are wider than that of HC3N. The line widths of the three lines are all wider than those from dark clouds, implying that the former is more active than the latter, and has larger turbulence caused by winds and UV radiation from the surrounding massive stars.
基金supported by the National Natural Science Foundation of China(Grant No.11503037)
文摘Using data from Millimetre Astronomy Legacy Team Survey at 90 GHz （MALT90）, we present a molecular line study of a sample of APEX Telescope Large Area Survey of the Galaxy （ATLASGAL） clumps. Twelve emission lines have been detected in all. We found that in most sources, emissions of HC3N, HN13C, CH3CN, HNCO and SiO show more compact distributions than those of HCO＋, HNC, HCN and N2H＋. By comparing with other molecular lines, we found that the abun- dance of HNCO （x（HNCO）） correlates well with other species such as HC3N, HNC, C2H, H13CO＋ and N2H＋. Previous studies indicate the HNCO abundance could be enhanced by shocks. However, in this study, we find the abundance of HNCO does not correlate well with that of SiO, which is also a good tracer of shocks. We suggest this may be because HNCO and SiO trace different parts of shocks. Our analysis indicates that the velocity of a shock traced by HNCO tends to be lower than that traced by SiO. In the low-velocity shocks traced by HNCO, the HNCO abundance increases faster than that of SiO. While in the relatively high-velocity shocks traced by SiO, the SiO abundance increases faster than that of HNCO. We suggest that in the infrared dark cloud MSXDC G331.71＋00.59, high-velocity shocks are destroying the molecule HNCO.
