Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202450745
T. Callingham, Amina Helmi
In the solar neighbourhood, only $ of stars in the survey have a line-of-sight velocity ( contained within the RVS catalogue. These limitations restrict conventional dynamical analysis, such as finding and studying substructures in the stellar halo. We aim to present and test a method to infer a probability density function (PDF) for the missing of a star with 5D information within $2.5 kpc $. This technique also allows us to infer the probability that a 5D star is associated with the Milky Way's stellar Disc or the stellar Halo, which can be further decomposed into known stellar substructures. We use stars from the DR3 RVS catalogue to describe the local orbital structure in action space. The method is tested on a 6D DR3 RVS sample and a 6D sample crossmatched to ground-based spectroscopic surveys, stripped of their true The stars predicted membership probabilities, and inferred structure properties are then compared to the true 6D equivalents, allowing the method's accuracy and limitations to be studied in detail. Our predicted PDFs are statistically consistent with the true with accurate uncertainties. We find that the of Disc stars can be well-constrained, with a median uncertainty of $26 Halo stars are typically less well-constrained with a median uncertainty of $72 but those found likely to belong to Halo substructures can be better constrained. The dynamical properties of the total sample and subgroups, such as distributions of integrals of motion and velocities, are also accurately recovered. The group membership probabilities are statistically consistent with our initial labelling, allowing high-quality sets to be selected from 5D samples by choosing a trade-off between higher expected purity and decreasing expected completeness. We have developed a method to estimate 5D stars' and substructure membership. We have demonstrated that it is possible to find likely substructure members and statistically infer the group's dynamical properties.
{"title":"Filling in the blanks. A method to infer the substructure membership and dynamics of 5D stars","authors":"T. Callingham, Amina Helmi","doi":"10.1051/0004-6361/202450745","DOIUrl":"https://doi.org/10.1051/0004-6361/202450745","url":null,"abstract":"In the solar neighbourhood, only $ of stars in the survey have a line-of-sight velocity ( contained within the RVS catalogue. These limitations restrict conventional dynamical analysis, such as finding and studying substructures in the stellar halo. We aim to present and test a method to infer a probability density function (PDF) for the missing of a star with 5D information within $2.5 kpc $.\u0000 This technique also allows us to infer the probability that a 5D star is associated with the Milky Way's\u0000 stellar Disc or the stellar Halo, which can be further decomposed into known stellar substructures. We use stars from the DR3 RVS catalogue to describe the local orbital structure in action space.\u0000 The method is tested on a 6D DR3 RVS sample and a 6D sample crossmatched to ground-based spectroscopic surveys,\u0000 stripped of their true The stars predicted membership probabilities, and inferred structure properties are then compared to the true 6D equivalents, allowing the method's accuracy and limitations to be studied in detail. Our predicted PDFs are statistically consistent with the true with accurate uncertainties.\u0000 We find that the of Disc stars can be well-constrained, with a median uncertainty of $26 Halo stars are typically less well-constrained with a median uncertainty of $72 but those found likely to belong to Halo substructures can be better constrained. The dynamical properties of the total sample and subgroups, such as distributions of integrals of motion and velocities, are also accurately recovered. The group membership probabilities are statistically consistent with our initial labelling, allowing high-quality sets to be selected from 5D samples by choosing a trade-off between higher expected purity and decreasing expected completeness. We have developed a method to estimate 5D stars' and substructure membership.\u0000 We have demonstrated that it is possible to find likely substructure members\u0000 and statistically infer the group's dynamical properties.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"40 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141807632","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202449708
D. Porquet, J. Reeves, S. Hagen, A. Lobban, V. Braito, N. Grosso, F. Marin
ESO 141-G55 is a nearby X-ray bright broad-line Seyfert,1 (BLS1) that has been classified as a bare active galactic nucleus (AGN) due to a lack of warm absorption along its line of sight, providing an unhampered view into its disc-corona system. We aim to probe its disc-corona system thanks to the first simultaneous XMM-Newton and NuSTAR observation obtained October 1--2, 2022. We carried out an X-ray broadband spectral analysis to determine the dominant process(es) at work as well as a spectral energy distribution (SED) analysis to determine the disc-corona properties. The simultaneous broadband X-ray spectrum of ESO,141-G55 is characterised by the presence of a prominent smooth soft X-ray excess, a broad Fe,Kalpha emission line, and a significant Compton hump. The high-resolution reflection grating spectrometer spectra confirmed the lack of intrinsic warm-absorbing gas along our line of sight in the AGN rest frame, verifying that it is still in a bare state. However, soft X-ray emission lines were observed, indicating substantial warm gas out of our line of sight. The intermediate inclination of the disc-corona system (sim circ $) may offer us a favourable configuration to observe ultra-fast outflows from the disc, but none were found in this 2022 observation, contrary to a previous 2007 XMM-Newton one. We ruled out relativistic reflection alone on a standard disc based on the X-ray broadband analysis, while a combination of soft and hard Comptonisation by a warm and hot corona ( relagn ) plus relativistic reflection ( reflkerrd ) reproduces the ESO,141-G55 SED quite well. The hot corona temperature is very hot, sim 140,keV, and much higher than about 80 of AGNs, whereas the warm corona temperature, sim 0.3,keV, is similar to the values found in other sub-Eddington AGNs. ESO,141-G55 is accreting at a moderate Eddington accretion rate (sim 10--20). Our analysis points to a significant contribution of an optically thick warm corona to both the soft X-ray and UV emission in ESO,141-G55, adding to the growing evidence that the accretion of AGNs (even at a moderate accretion rate) appears to deviate from standard disc theory.
{"title":"Revealing the burning and soft heart of the bright bare active galactic nucleus ESO 141-G55: X-ray broadband and SED analysis","authors":"D. Porquet, J. Reeves, S. Hagen, A. Lobban, V. Braito, N. Grosso, F. Marin","doi":"10.1051/0004-6361/202449708","DOIUrl":"https://doi.org/10.1051/0004-6361/202449708","url":null,"abstract":"ESO 141-G55 is a nearby X-ray bright broad-line Seyfert,1 (BLS1) that has been classified as a bare active galactic nucleus (AGN) due to a lack of warm absorption along its line of sight, providing an unhampered view into its disc-corona system. We aim to probe its disc-corona system thanks to the first simultaneous XMM-Newton and NuSTAR observation obtained October 1--2, 2022. We carried out an X-ray broadband spectral analysis to determine the dominant process(es) at work as well as a spectral energy distribution (SED) analysis to determine the disc-corona properties. The simultaneous broadband X-ray spectrum of ESO,141-G55 is characterised by the presence of a prominent smooth soft X-ray excess, a broad Fe,Kalpha emission line, and a significant Compton hump. The high-resolution reflection grating spectrometer spectra confirmed the lack of intrinsic warm-absorbing gas along our line of sight in the AGN rest frame, verifying that it is still in a bare state. However, soft X-ray emission lines were observed, indicating substantial warm gas out of our line of sight. The intermediate inclination of the disc-corona system (sim circ $) may offer us a favourable configuration to observe ultra-fast outflows from the disc, but none were found in this 2022 observation, contrary to a previous 2007 XMM-Newton one. We ruled out relativistic reflection alone on a standard disc based on the X-ray broadband analysis, while a combination of soft and hard Comptonisation by a warm and hot corona ( relagn ) plus relativistic reflection ( reflkerrd ) reproduces the ESO,141-G55 SED quite well. The hot corona temperature is very hot, sim 140,keV, and much higher than about 80 of AGNs, whereas the warm corona temperature, sim 0.3,keV, is similar to the values found in other sub-Eddington AGNs. ESO,141-G55 is accreting at a moderate Eddington accretion rate (sim 10--20). Our analysis points to a significant contribution of an optically thick warm corona to both the soft X-ray and UV emission in ESO,141-G55, adding to the growing evidence that the accretion of AGNs (even at a moderate accretion rate) appears to deviate from standard disc theory.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"35 23","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141810085","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202449701
I. Chataigner, F. Pauzat, O. Tasseau, Y. Ellinger, J. Guillemin
Most of the molecules identified in the interstellar medium (ISM) are organic compounds and more than 50 have one isomer or more. Statistically, the most stable isomer of a given chemical formula is the most abundant. This occurrence is verified up to sim 90 of the detected species leading to the so-called minimum energy principle (MEP). Our main objective is to increase the list of the 14 bis-nitrogen species already detected. We focus on ten C$_ x $H$_ y $N$_ z $ isomer families with x=(1,2,3), y=(0,2,4,6,8), z=2. To this end, we look for a reliable and economic way to provide energy scales. We employed standard quantum chemistry methods to determine the relative position of each isomer on the energy scales of each family. We systematically applied density functional theory (DFT) treatments using basis sets of increasing size and quality (6-311++G** and cc-pVQZ). When reasonably feasible, we then performed high-level coupled cluster calculations (CCSD) using the same basis sets to refine relative energies. All 14 bis-nitrogen species already identified in the ISM indeed satisfy the MEP. We determine the relative thermodynamic stability of the isomers with a C$_ x $H$_ y $N$_ $ formula of each of the ten sets (94 compounds altogether), and hightlight those that are potentially detectable. By increasing the number of carbon atoms, we find 15 compounds that are by far the most stable candidates. We confirm that, within the limits of thermodynamics, MEP is an efficient and easily applicable tool for identifying the isomers in a given series that have a greater probability of being detected. Computationally, the combination “B3LYP/cc-pVQZ” provides a suitable compromise for determining energy differences and dipole moments. Clearly, the isomers containing the NCN sequence should be prioritized over those with CNN in future observation campaigns.
在星际介质（ISM）中发现的大多数分子都是有机化合物，其中 50 多种分子有一种或多种同分异构体。据统计，特定化学式中最稳定的异构体含量最高。根据所谓的 "最小能量原则"（MEP），这种情况在模拟 90 种被探测到的物质中得到了验证。我们的主要目标是增加已探测到的 14 种双氮物质。我们的重点是十个 C$_ x $H$_ y $N$_ z $ 异构体家族，x=(1,2,3)，y=(0,2,4,6,8)，z=2。为此，我们寻找一种可靠而经济的方法来提供能量标度。我们采用标准的量子化学方法来确定每个异构体在每个族的能级上的相对位置。我们系统地应用了密度泛函理论（DFT）处理方法，并使用了规模和质量不断增加的基集（6-311++G** 和 cc-pVQZ）。在合理可行的情况下，我们使用相同的基集进行了高水平耦合簇计算（CCSD），以完善相对能量。在 ISM 中已经确定的所有 14 种双氮物质都确实满足 MEP 的要求。我们确定了十组化合物（共 94 个化合物）中每一组的 C$_ x $H$_ y $N$_ $ 式的异构体的相对热力学稳定性，并突出了那些有可能被探测到的化合物。通过增加碳原子数，我们发现 15 种化合物是迄今为止最稳定的候选化合物。我们证实，在热力学的限制范围内，MEP 是一种高效且易于应用的工具，可用于识别特定系列中被检测到概率较大的异构体。在计算上，"B3LYP/cc-pVQZ "组合为确定能量差和偶极矩提供了一个合适的折衷方案。显然，在未来的观测活动中，含有 NCN 序列的同分异构体应优先于含有 CNN 序列的同分异构体。
{"title":"Thermodynamical stability of [CNN and NCN] sequences as indication of most abundant structures in the ISM","authors":"I. Chataigner, F. Pauzat, O. Tasseau, Y. Ellinger, J. Guillemin","doi":"10.1051/0004-6361/202449701","DOIUrl":"https://doi.org/10.1051/0004-6361/202449701","url":null,"abstract":"Most of the molecules identified in the interstellar medium (ISM) are organic compounds and more than 50 have one isomer or more. Statistically, the most stable isomer of a given chemical formula is the most abundant. This occurrence is verified up to sim 90 of the detected species leading to the so-called minimum energy principle (MEP). Our main objective is to increase the list of the 14 bis-nitrogen species already detected. We focus on ten C$_ x $H$_ y $N$_ z $ isomer families with x=(1,2,3), y=(0,2,4,6,8), z=2. To this end, we look for a reliable and economic way to provide energy scales. We employed standard quantum chemistry methods to determine the relative position of each isomer on the energy scales of each family. We systematically applied density functional theory (DFT) treatments using basis sets of increasing size and quality (6-311++G** and cc-pVQZ). When reasonably feasible, we then performed high-level coupled cluster calculations (CCSD) using the same basis sets to refine relative energies. All 14 bis-nitrogen species already identified in the ISM indeed satisfy the MEP. We determine the relative thermodynamic stability of the isomers with a C$_ x $H$_ y $N$_ $ formula of each of the ten sets (94 compounds altogether), and hightlight those that are potentially detectable. By increasing the number of carbon atoms, we find 15 compounds that are by far the most stable candidates. We confirm that, within the limits of thermodynamics, MEP is an efficient and easily applicable tool for identifying the isomers in a given series that have a greater probability of being detected. Computationally, the combination “B3LYP/cc-pVQZ” provides a suitable compromise for determining energy differences and dipole moments. Clearly, the isomers containing the NCN sequence should be prioritized over those with CNN in future observation campaigns.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"13 2","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141808982","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202450229
K. Belczynski, Christine Done, S. Hagen, J. Lasota, K. Sen
Black-hole (BH) high-mass X-ray binary (HMXB) systems are likely to be the progenitors of BH-BH mergers detected in gravitational waves by LIGO/Virgo/KAGRA (LVK). Yet merging BHs reach higher masses ($ than BHs in HMXBs ($ and typically exhibit lower spins BH 0.25$ with a larger values tail) than what is often claimed for BHs in HMXBs BH 0.9$). This could suggest that these two classes of systems belong to different populations, but here we show that this may not necessarily be the case. The difference in masses is easily explained as the known HMXB-BHs are in galaxies with relatively high metallicity, so their progenitor stars are subject to strong mass loss from winds, leading to relatively low-mass BH at core collapse. Conversely, LVK is also able to detect BHs from low-metallicity galaxies that are known to naturally produce more massive stellar-origin BHs. However, the difference in spin is more difficult to explain. Models with efficient angular momentum transport in stellar interiors produce slowly spinning progenitors for both LVK and HMXB BHs. Known HMXBs have orbital periods that are too long for efficient tidal spin-up and are also unlikely to have undergone significant accretion spin-up. Instead, we show that the derived value of the BH spin depends strongly on how the HMXB accretion disc emission is modelled. We argue that since Cyg X-1 is never observed to be in a soft spectral state, the appropriate spectral models must take into account the Comptonisation of the disc photosphere. We show that such models are consistent with low spin values, namely: $a_ BH This was recently confirmed by other teams for both Cyg X-1 and LMC X-1 and here we show this is also the case for M33 X-7. We conclude that all known HMXB BHs can exhibit a low spin in accordance with the results of stellar evolution models. Hence, the observations presented in this work are consistent with the scenario where LVK BHs and HMXB BHs belong to the same population.
{"title":"Common origin for black holes in both high mass X-ray binaries and gravitational-wave sources","authors":"K. Belczynski, Christine Done, S. Hagen, J. Lasota, K. Sen","doi":"10.1051/0004-6361/202450229","DOIUrl":"https://doi.org/10.1051/0004-6361/202450229","url":null,"abstract":"Black-hole (BH) high-mass X-ray binary (HMXB) systems are likely to be the progenitors of BH-BH mergers detected in gravitational waves by LIGO/Virgo/KAGRA (LVK). Yet merging BHs reach higher masses ($ than BHs in HMXBs ($ and typically exhibit lower spins BH 0.25$ with a larger values tail) than what is often claimed for BHs in HMXBs BH 0.9$). This could suggest that these two classes of systems belong to different populations, but here we show that this may not necessarily be the case. The difference in masses is easily explained as the known HMXB-BHs are in galaxies with relatively high metallicity, so their progenitor stars are subject to strong mass loss from winds, leading to relatively low-mass BH at core collapse. Conversely, LVK is also able to detect BHs from low-metallicity galaxies that are known to naturally produce more massive stellar-origin BHs. However, the difference in spin is more difficult to explain. Models with efficient angular momentum transport in stellar interiors produce slowly spinning progenitors for both LVK and HMXB BHs. Known HMXBs have orbital periods that are too long for efficient tidal spin-up and are also unlikely to have undergone significant accretion spin-up. Instead, we show that the derived value of the BH spin depends strongly on how the HMXB accretion disc emission is modelled. We argue that since Cyg X-1 is never observed to be in a soft spectral state, the appropriate spectral models must take into account the Comptonisation of the disc photosphere. We show that such models are consistent with low spin values, namely: $a_ BH This was recently confirmed by other teams for both Cyg X-1 and LMC X-1 and here we show this is also the case for M33 X-7. We conclude that all known HMXB BHs can exhibit a low spin in accordance with the results of stellar evolution models. Hence, the observations presented in this work are consistent with the scenario where LVK BHs and HMXB BHs belong to the same population.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"5 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141809281","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202450738
Bikramaditya Mandal, M. Żółtowski, Martin Cordiner, Francois Lique, D. Babikov
The goal is to develop a database of rate coefficients for rotational state-to-state transitions in H$_ $O + H$_ $O collisions that is suitable for the modeling of energy transfer in nonequilibrium conditions, in which the distribution of rotational states of H$_ $O deviates from local thermodynamic equilibrium. A two-temperature model was employed that assumed that although there is no equilibrium between all possible degrees of freedom in the system, the translational and rotational degrees of freedom can be expected to achieve their own equilibria independently, and that they can be approximately characterized by Boltzmann distributions at two different temperatures, $T_ kin $ and $T_ rot Upon introducing our new parameterization of the collisional rates, taking into account their dependence on both $T_ kin $ and $T_ rot $, we find a change of up to 20 in the H$_ $O rotational level populations for both ortho and para-H$_ $O for the part of the cometary coma where the nonequilibrium regime occurs.
{"title":"Rotational state-to-state transition rate coefficients for H2O + H2O collisions at nonequilibrium conditions","authors":"Bikramaditya Mandal, M. Żółtowski, Martin Cordiner, Francois Lique, D. Babikov","doi":"10.1051/0004-6361/202450738","DOIUrl":"https://doi.org/10.1051/0004-6361/202450738","url":null,"abstract":"The goal is to develop a database of rate coefficients for rotational state-to-state transitions in H$_ $O + H$_ $O collisions that is suitable for the modeling of energy transfer in nonequilibrium conditions, in which the distribution of rotational states of H$_ $O deviates from local thermodynamic equilibrium. A two-temperature model was employed that assumed that although there is no equilibrium between all possible degrees of freedom in the system, the translational and rotational degrees of freedom can be expected to achieve their own equilibria independently, and that they can be approximately characterized by Boltzmann distributions at two different temperatures, $T_ kin $ and $T_ rot Upon introducing our new parameterization of the collisional rates, taking into account their dependence on both $T_ kin $ and $T_ rot $, we find a change of up to 20 in the H$_ $O rotational level populations for both ortho and para-H$_ $O for the part of the cometary coma where the nonequilibrium regime occurs.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"49 7","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141809901","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202450552
Longkang Dai, Wencheng Shao, Zheng Sheng
Atmospheric chemistry plays a crucial role in the evolution of climate habitability on Venus. It has been widely explored by chemistry-transport models, but some characteristics are still poorly interpreted. This study is devoted to developing an open-access chemistry-transport model spanning both the middle and lower atmospheres of Venus. It provides a scheme for the structure of the chemistry, especially for the sulfur and oxygen, and investigates the influence of the cloud diffusivity and the SO$_ $ dissolution that are adopted in the clouds. The developed model is based on the VULCAN framework and was updated with the state-of-the-art Venusian atmospheric chemistry. It includes vertical eddy diffusion retrieved recently with the Venus Express observations, and it resolves radiative transfer containing gas absorption and scattering, Mie scattering of the cloud droplets, and absorption of the unknown UV absorber. The obtained abundance profiles of SO, SO$_ $, CO, COS, O, O$_ $, O$_ $, HCl, and NO are in overall agreement with the observations. The results show that the increase in cloud diffusivity has slight effects on the chemical structure. The SO$_ $ mainly dissolves in 50-90 km and evaporates below the clouds. The rapid dissolution-release cycle is responsible for the large upward flux of SO$_ $ at 58 km. At around 70 km, SO has a significant peak that is larger than that of previous studies by an order of magnitude, and S and SO$_ $ also show slight increases. They are attributed to the buffering effects of liquid SO$_ $ in the clouds. O$_ $ is significantly eliminated by SO in this layer. We emphasize the superior regulation of the sulfur cycle on O$_ $ at 70 km and its potential contributions to the long-standing problem of the overestimated O$_ $ abundance.
{"title":"An investigation into Venusian atmospheric chemistry based on an open-access photochemistry-transport model at 0-112 km","authors":"Longkang Dai, Wencheng Shao, Zheng Sheng","doi":"10.1051/0004-6361/202450552","DOIUrl":"https://doi.org/10.1051/0004-6361/202450552","url":null,"abstract":"Atmospheric chemistry plays a crucial role in the evolution of climate habitability on Venus. It has been widely explored by chemistry-transport models, but some characteristics are still poorly interpreted. This study is devoted to developing an open-access chemistry-transport model spanning both the middle and lower atmospheres of Venus. It provides a scheme for the structure of the chemistry, especially for the sulfur and oxygen, and investigates the influence of the cloud diffusivity and the SO$_ $ dissolution that are adopted in the clouds. The developed model is based on the VULCAN framework and was updated with the state-of-the-art Venusian atmospheric chemistry. It includes vertical eddy diffusion retrieved recently with the Venus Express observations, and it resolves radiative transfer containing gas absorption and scattering, Mie scattering of the cloud droplets, and absorption of the unknown UV absorber. The obtained abundance profiles of SO, SO$_ $, CO, COS, O, O$_ $, O$_ $, HCl, and NO are in overall agreement with the observations. The results show that the increase in cloud diffusivity has slight effects on the chemical structure. The SO$_ $ mainly dissolves in 50-90 km and evaporates below the clouds. The rapid dissolution-release cycle is responsible for the large upward flux of SO$_ $ at 58 km. At around 70 km, SO has a significant peak that is larger than that of previous studies by an order of magnitude, and S and SO$_ $ also show slight increases. They are attributed to the buffering effects of liquid SO$_ $ in the clouds. O$_ $ is significantly eliminated by SO in this layer. We emphasize the superior regulation of the sulfur cycle on O$_ $ at 70 km and its potential contributions to the long-standing problem of the overestimated O$_ $ abundance.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"22 6","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141808783","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202449167
C. Stadler, C. Laffon, Ph. Parent
Measuring the sticking coefficient of molecules pertinent to astrochemistry - such as CO - on substrates that mimic interstellar dust grains is crucial for the comprehensive understanding of gas-grain chemical processes. Although astrochemical models assume a sticking coefficient of 1, recent laboratory experiments on H2O and CO2 have revealed significantly lower values when measured on small grain analogs. As the effect of grain size on molecular adsorption has been largely ignored to date, further experiments are needed to determine the accretion rates of species known to freeze out on dust grains. Our aim is to determine the sticking coefficients of CO and N2 on sub-micrometric silicate and carbon grains. By quantifying realistic sticking coefficients on these dust grain analogs, we can improve the accuracy of astrochemists' predictions of molecular abundances as affected by gas-grain interactions. The molecules of interest were added to various substrates at 10 K in an ultra-high vacuum. The amount of adsorbate that stuck to the substrate was quantified using X-ray photoelectron spectroscopy. These quantities were compared to a reference with a sticking coefficient of 1, allowing the deduction of the sticking coefficient for each substrate. The average sticking coefficients of CO and N2 on grain analogs are 0.17 for CO and 0.14 for N2 on olivine powder, and 0.05 for CO and 0.07 on N2 on soot, instead of the presumed 1. This is in line with the low values previously reported for H2O and CO2 These laboratory results indicate that CO and N2 in addition to H2O and CO2 also exhibit a low sticking coefficient on dust grain analogs. It is thus necessary to reconsider the interactions between gaseous species and dust particles as a low-efficiency process. This reduction in accretion and reaction rates has important implications for how we understand astrochemistry.
测量与天体化学有关的分子（如一氧化碳）在模拟星际尘粒的基质上的粘滞系数，对于全面了解气粒化学过程至关重要。尽管天体化学模型假定粘滞系数为 1，但最近对 H2O 和 CO2 进行的实验室实验表明，在小颗粒模拟物上测量的粘滞系数要低得多。由于迄今为止人们在很大程度上忽视了颗粒大小对分子吸附的影响，因此需要进一步的实验来确定已知会冻结在尘埃颗粒上的物种的吸附率。我们的目标是确定 CO 和 N2 在亚微米硅酸盐和碳颗粒上的粘附系数。通过量化这些尘粒类似物上的实际粘滞系数，我们可以提高天体化学专家预测受气体-尘粒相互作用影响的分子丰度的准确性。在 10 K 的超高真空条件下，将相关分子添加到各种基底上。使用 X 射线光电子能谱对粘附在基底上的吸附物数量进行量化。将这些数量与吸附系数为 1 的参照物进行比较，从而推导出每种基底的吸附系数。这些实验室结果表明，除了 H2O 和 CO2 外，CO 和 N2 在尘粒类似物上的粘附系数也很低。因此，有必要将气体物种与尘粒之间的相互作用重新视为一种低效率过程。这种吸积和反应速率的降低对我们如何理解天体化学具有重要影响。
{"title":"Experimental sticking coefficients of CO and N_2 on sub-micrometric cosmic grain analogs","authors":"C. Stadler, C. Laffon, Ph. Parent","doi":"10.1051/0004-6361/202449167","DOIUrl":"https://doi.org/10.1051/0004-6361/202449167","url":null,"abstract":"Measuring the sticking coefficient of molecules pertinent to astrochemistry - such as CO - on substrates that mimic interstellar dust grains is crucial for the comprehensive understanding of gas-grain chemical processes. Although astrochemical models assume a sticking coefficient of 1, recent laboratory experiments on H2O and CO2 have revealed significantly lower values when measured on small grain analogs. As the effect of grain size on molecular adsorption has been largely ignored to date, further experiments are needed to determine the accretion rates of species known to freeze out on dust grains. Our aim is to determine the sticking coefficients of CO and N2 on sub-micrometric silicate and carbon grains. By quantifying realistic sticking coefficients on these dust grain analogs, we can improve the accuracy of astrochemists' predictions of molecular abundances as affected by gas-grain interactions. The molecules of interest were added to various substrates at 10 K in an ultra-high vacuum. The amount of adsorbate that stuck to the substrate was quantified using X-ray photoelectron spectroscopy. These quantities were compared to a reference with a sticking coefficient of 1, allowing the deduction of the sticking coefficient for each substrate. The average sticking coefficients of CO and N2 on grain analogs are 0.17 for CO and 0.14 for N2 on olivine powder, and 0.05 for CO and 0.07 on N2 on soot, instead of the presumed 1. This is in line with the low values previously reported for H2O and CO2 These laboratory results indicate that CO and N2 in addition to H2O and CO2 also exhibit a low sticking coefficient on dust grain analogs. It is thus necessary to reconsider the interactions between gaseous species and dust particles as a low-efficiency process. This reduction in accretion and reaction rates has important implications for how we understand astrochemistry.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"68 9","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141806730","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202449755
G. Valle, M. Dell'Omodarme, P. P. Prada Moroni, S. Degl'innocenti
We conducted an investigation on the chemical abundances of 4,316 stars in the red giant branch (RGB) phase from the recently released APO-K2 catalogue. Our aim was to characterize the abundance trends of the single elements with afe , mainly focusing on C, N, and O, which are the most relevant for the estimation of stellar ages. The chemical analysis of the RGB sample involved cross-matching data from the APO-K2 catalogue with individual element abundances from APOGEE DR17. The analysis detected a statistically significant difference in the (C+N+O)/Fe -- afe trend with respect to the simple alpha -enhancement scenario. This difference remained robust across different choices for the reference solar mixture and potential zero-point calibrations of C and N abundances. The primary discrepancy was a steeper increase in O/Fe with afe , reaching a 0.1 dex difference at $ = 0.3$. Notably, the impact on the evolutionary timescale of such oxygen over-abundance with respect to the commonly adopted uniform alpha -enhancement is rather limited. We verified that stellar models computed using an ad hoc O-rich mixture sped up the evolution by only 1 at $ = 0.3$, due to the counterbalancing effects of O enrichment on both the evolutionary timescale and the Fe/H relationship.
{"title":"Element abundances of galactic RGB stars in the APO-K2 catalogue. Dissimilarity in the scaling with [alpha/Fe]","authors":"G. Valle, M. Dell'Omodarme, P. P. Prada Moroni, S. Degl'innocenti","doi":"10.1051/0004-6361/202449755","DOIUrl":"https://doi.org/10.1051/0004-6361/202449755","url":null,"abstract":"We conducted an investigation on the chemical abundances of 4,316 stars in the red giant branch (RGB) phase from the recently released APO-K2 catalogue. Our aim was to characterize the abundance trends of the single elements with afe , mainly focusing on C, N, and O, which are the most relevant for the estimation of stellar ages. The chemical analysis of the RGB sample involved cross-matching data from the APO-K2 catalogue with individual element abundances from APOGEE DR17. The analysis detected a statistically significant difference in the (C+N+O)/Fe -- afe trend with respect to the simple alpha -enhancement scenario. This difference remained robust across different choices for the reference solar mixture and potential zero-point calibrations of C and N abundances. The primary discrepancy was a steeper increase in O/Fe with afe , reaching a 0.1 dex difference at $ = 0.3$. Notably, the impact on the evolutionary timescale of such oxygen over-abundance with respect to the commonly adopted uniform alpha -enhancement is rather limited. We verified that stellar models computed using an ad hoc O-rich mixture sped up the evolution by only 1 at $ = 0.3$, due to the counterbalancing effects of O enrichment on both the evolutionary timescale and the Fe/H relationship.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"9 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141809104","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202450288
T.H. Pramono, M. Kenworthy, R. van Boekel
The early-type star ASASSN-21js started to fade in 2021, as was detected by the All Sky Automated Survey for Supernovae, undergoing a multi-year eclipse that is still underway. We interpret this event as being due to a structured disc of material transiting in front of the star. The disc is in orbit around a substellar object with the mass and luminosity of a brown dwarf or smaller. We want to determine the expected duration and ending date of the eclipse. We modelled a tilted and inclined azimuthally symmetric ring system around an unseen companion and calculated the resulting time-varying light curve as the object transited in front of the star. We made an initial estimate of the ring parameters and used these as inputs to an MCMC algorithm to determine the geometric properties of the rings with associated uncertainties. The model most consistent with the light curve to date is a two-ring system at high inclination with respect to the line of sight that has a semi-major axis of 71.6 stellar radii. With an estimate of the stellar radius, the transverse velocity is around 0.7 which if bound to the star is an orbit with a semi-major axis of around 13000 au, placing it in the Oort cloud of the parent star. The transit is ongoing and will finish around MJD 61526 (May 1 2027). We encourage the community to continue observing this object in order to understand its properties.
{"title":"ASASSN-21js: A multi-year transit of a ringed disc","authors":"T.H. Pramono, M. Kenworthy, R. van Boekel","doi":"10.1051/0004-6361/202450288","DOIUrl":"https://doi.org/10.1051/0004-6361/202450288","url":null,"abstract":"The early-type star ASASSN-21js started to fade in 2021, as was detected by the All Sky Automated Survey for Supernovae, undergoing a multi-year eclipse that is still underway.\u0000 \u0000 We interpret this event as being due to a structured disc of material transiting in front of the star.\u0000 \u0000 The disc is in orbit around a substellar object with the mass and luminosity of a brown dwarf or smaller.\u0000 \u0000 We want to determine the expected duration and ending date of the eclipse. We modelled a tilted and inclined azimuthally symmetric ring system around an unseen companion and calculated the resulting time-varying light curve as the object transited in front of the star.\u0000 \u0000 We made an initial estimate of the ring parameters and used these as inputs to an MCMC algorithm to determine the geometric properties of the rings with associated uncertainties. The model most consistent with the light curve to date is a two-ring system at high inclination with respect to the line of sight that has a semi-major axis of 71.6 stellar radii.\u0000 \u0000 With an estimate of the stellar radius, the transverse velocity is around 0.7 which if bound to the star is an orbit with a semi-major axis of around 13000 au, placing it in the Oort cloud of the parent star.\u0000 \u0000 The transit is ongoing and will finish around MJD 61526 (May 1 2027).\u0000 \u0000 We encourage the community to continue observing this object in order to understand its properties.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"15 3","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141808016","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-07-24DOI: 10.1051/0004-6361/202348352
P.J. Wang, Y.P. Chen, L. Ji, S. Zhang, S. Zhang, L.D. Kong, Z. Chang, L. Zhang, L. Tao, J. L. Qu, M. Ge, J. Li, J. Peng, Q. Shui, Z.S. Li
We report the results of our analysis of 83 type-I bursts during the 2022 outburst of the newly discovered accreting millisecond pulsar MAXI J1816--195 based on Insight-HXMT and NICER observations. We focus on the burst-recurrence time and its correlation with persistent flux and outburst evolution. The extensive observations of Insight-HXMT and NICER confirm the presence of quasi-periodic thermonuclear bursts during this outburst, with a recurrence time in the range of 1.15 to 2 hours, which varies with the source persistent flux. The burst recurrence times are, in general, longer at comparable flux levels in the outburst rising phase than those in the fading phase, forming an apparent hysteresis phenomenon. These burst properties make MAXI J1816--195 a unique target for investigating the underlying burst-accretion mechanisms. We discuss the plausible explanations for the hysteresis phenomenon, which appears to be related to changes in the ignition condition or accretion geometry during the outburst.
{"title":"Burst-recurrence properties revealed with Insight-HXMT and NICER for the newly discovered accreting millisecond pulsar MAXI J1816--195","authors":"P.J. Wang, Y.P. Chen, L. Ji, S. Zhang, S. Zhang, L.D. Kong, Z. Chang, L. Zhang, L. Tao, J. L. Qu, M. Ge, J. Li, J. Peng, Q. Shui, Z.S. Li","doi":"10.1051/0004-6361/202348352","DOIUrl":"https://doi.org/10.1051/0004-6361/202348352","url":null,"abstract":"We report the results of our analysis of 83 type-I bursts during the 2022 outburst of the newly discovered accreting millisecond pulsar MAXI J1816--195 based on Insight-HXMT and NICER observations. We focus on the burst-recurrence time and its correlation with persistent flux and outburst evolution. The extensive observations of Insight-HXMT and NICER confirm the presence of quasi-periodic thermonuclear bursts during this outburst, with a recurrence time in the range of 1.15 to 2 hours, which varies with the source persistent flux.\u0000 The burst recurrence times are, in general, longer at comparable flux levels in the outburst rising phase than those in the fading phase, forming an apparent hysteresis phenomenon.\u0000 These burst properties make MAXI J1816--195 a unique target for investigating the underlying burst-accretion mechanisms.\u0000 We discuss the plausible explanations for the hysteresis phenomenon, which appears to be related to changes in the ignition condition or\u0000 accretion geometry during the outburst.","PeriodicalId":8585,"journal":{"name":"Astronomy & Astrophysics","volume":"40 16","pages":""},"PeriodicalIF":0.0,"publicationDate":"2024-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"141809806","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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