Pub Date : 2024-12-16DOI: 10.1051/0004-6361/202451975
Carolin Joy, Dulat Bostan, Bikramaditya Mandal, Dmitri Babikov
Aims. A new dataset of collisional rate coefficients for transitions between the rotational states of H2O collided with H2 background gas is developed. The goal is to expand over the other existing datasets in terms of the rotational states of water (200 states are included here) and the rotational states of hydrogen (10 states). All four symmetries of ortho- and para-water combined with ortho- and para-hydrogen are considered.Methods. The mixed quantum–classical theory of inelastic scattering implemented in the code MQCT was employed. A detailed comparison with previous datasets was conducted to ensure that this approximate method was sufficiently accurate. Integration over collision energies, summation over the final states of H2, and averaging over the initial states of H2 was carried out to provide state-to-state, effective, and thermal rate coefficients in a broad range of temperatures.Results. The rate coefficients for collisions with highly excited H2 molecules are presented for the first time. It is found that rate coefficients for rotational transitions in H2O molecules grow with the rotational excitation of H2 projectiles and exceed those of the ground state H2, roughly by a factor of two. These data enable a more accurate description of water molecules in high-temperature environments, where the hydrogen molecules of background gas are rotationally excited, and the H2O + H2 collision energy is high. The rate coefficients presented here are expected to be accurate up to the temperature of ~2000 K.
{"title":"Rate coefficients for rotational state-to-state transitions in H2O + H2 collisions as predicted by mixed quantum–classical theory","authors":"Carolin Joy, Dulat Bostan, Bikramaditya Mandal, Dmitri Babikov","doi":"10.1051/0004-6361/202451975","DOIUrl":"https://doi.org/10.1051/0004-6361/202451975","url":null,"abstract":"<i>Aims<i/>. A new dataset of collisional rate coefficients for transitions between the rotational states of H<sub>2<sub/>O collided with H<sub>2<sub/> background gas is developed. The goal is to expand over the other existing datasets in terms of the rotational states of water (200 states are included here) and the rotational states of hydrogen (10 states). All four symmetries of ortho- and para-water combined with ortho- and para-hydrogen are considered.<i>Methods<i/>. The mixed quantum–classical theory of inelastic scattering implemented in the code MQCT was employed. A detailed comparison with previous datasets was conducted to ensure that this approximate method was sufficiently accurate. Integration over collision energies, summation over the final states of H<sub>2<sub/>, and averaging over the initial states of H<sub>2<sub/> was carried out to provide state-to-state, effective, and thermal rate coefficients in a broad range of temperatures.<i>Results<i/>. The rate coefficients for collisions with highly excited H<sub>2<sub/> molecules are presented for the first time. It is found that rate coefficients for rotational transitions in H<sub>2<sub/>O molecules grow with the rotational excitation of H<sub>2<sub/> projectiles and exceed those of the ground state H<sub>2<sub/>, roughly by a factor of two. These data enable a more accurate description of water molecules in high-temperature environments, where the hydrogen molecules of background gas are rotationally excited, and the H<sub>2<sub/>O + H<sub>2<sub/> collision energy is high. The rate coefficients presented here are expected to be accurate up to the temperature of ~2000 K.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"11 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142825444","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-16DOI: 10.1051/0004-6361/202452049
XueGuang Zhang
We propose an oversimplified model to explain the different variability trends in the observed broad Hα emission line luminosity, LHα(t), and the tidal disruption event (TDE) model-determined bolometric luminosity, Lbol(t), of the TDE ASASSN-14li. Assuming that broad emission line regions (BLRs) in the central accretion disk are related to materials accreted onto the central black hole of a TDE, the mass evolution of central BLRs, MBLRs(t), can be determined as the maximum mass, MBLRs, 0, of central BLRs minus the corresponding accreted mass in a TDE. Meanwhile, through the simple linear dependence of broad Balmer emission line luminosity on the mass of BLRs, the mass evolution of central BLRs, MBLRs(t), can be applied to describe the observed LHα(t). Although our proposed model is oversimplified – with only one free model parameter, MBLRs, 0 – with MBLRs, 0 ∼ 0.02 M⊙, it describes the observed LHα(t) in the TDE ASASSN-14li well. Meanwhile, the oversimplified model also roughly describes the observed LHα(t) in the TDE ASASSN-14ae. The reasonable descriptions of the observed LHα(t) in ASASSN-14li and ASASSN-14ae indicate that our oversimplified model is probably efficient enough to describe mass evolutions of MBLRs related to central accreted debris in TDEs.
{"title":"Mass evolution of broad-line regions to explain the luminosity variability of broad Hα in the tidal disruption event ASASSN-14li","authors":"XueGuang Zhang","doi":"10.1051/0004-6361/202452049","DOIUrl":"https://doi.org/10.1051/0004-6361/202452049","url":null,"abstract":"We propose an oversimplified model to explain the different variability trends in the observed broad H<i>α<i/> emission line luminosity, <i>L<i/><sub>H<i>α<i/><sub/>(<i>t<i/>), and the tidal disruption event (TDE) model-determined bolometric luminosity, <i>L<i/><sub>bol<sub/>(<i>t<i/>), of the TDE ASASSN-14li. Assuming that broad emission line regions (BLRs) in the central accretion disk are related to materials accreted onto the central black hole of a TDE, the mass evolution of central BLRs, <i>M<i/><sub>BLRs<sub/>(<i>t<i/>), can be determined as the maximum mass, <i>M<i/><sub>BLRs, 0<sub/>, of central BLRs minus the corresponding accreted mass in a TDE. Meanwhile, through the simple linear dependence of broad Balmer emission line luminosity on the mass of BLRs, the mass evolution of central BLRs, <i>M<i/><sub>BLRs<sub/>(<i>t<i/>), can be applied to describe the observed <i>L<i/><sub>H<i>α<i/><sub/>(<i>t<i/>). Although our proposed model is oversimplified – with only one free model parameter, <i>M<i/><sub>BLRs, 0<sub/> – with <i>M<i/><sub>BLRs, 0<sub/> ∼ 0.02 M<sub>⊙<sub/>, it describes the observed <i>L<i/><sub>H<i>α<i/><sub/>(<i>t<i/>) in the TDE ASASSN-14li well. Meanwhile, the oversimplified model also roughly describes the observed <i>L<i/><sub>H<i>α<i/><sub/>(<i>t<i/>) in the TDE ASASSN-14ae. The reasonable descriptions of the observed <i>L<i/><sub>H<i>α<i/><sub/>(<i>t<i/>) in ASASSN-14li and ASASSN-14ae indicate that our oversimplified model is probably efficient enough to describe mass evolutions of <i>M<i/><sub>BLRs<sub/> related to central accreted debris in TDEs.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"7 Suppl 8 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142825507","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-16DOI: 10.1051/0004-6361/202452741
Emanuele Contini, Marilena Spavone, Rossella Ragusa, Enrichetta Iodice, Sukyoung K. Yi
Aims. We present theoretical predictions and extrapolations from observed data of the stellar halos surrounding central group and cluster galaxies, and the transition radius between them and the intracluster or diffuse light.Methods. Leveraging the state-of-the-art semi-analytic model of galaxy formation, FEGA (Formation and Evolution of GAlaxies), applied to two dark matter-only cosmological simulations, we derived both the stellar halo mass and its radius. Using theoretical assumptions about the diffuse light distribution and halo concentration, we extrapolated the same information for observed data from the VEGAS survey.Results. Our model, supported by observational data and independent simulation results, predicts an increasing transition radius with halo mass, a constant stellar halo-to-intracluster light ratio, and a stable stellar halo mass fraction with increasing halo mass. Specifically, we find that the transition radius between the stellar halo and the diffuse light ranges from 20 to 250 kpc, from Milky Way-like halos to large clusters, while the stellar halo mass comprises only a small fraction, between 7% and 18%, of the total stellar mass within the virial radius.Conclusions. These results support the idea that the stellar halo can be viewed as a transition region between the stars bound to a galaxy and those belonging to the intracluster light and are consistent with recent observations and theoretical predictions.
{"title":"Stellar halos of bright central galaxies","authors":"Emanuele Contini, Marilena Spavone, Rossella Ragusa, Enrichetta Iodice, Sukyoung K. Yi","doi":"10.1051/0004-6361/202452741","DOIUrl":"https://doi.org/10.1051/0004-6361/202452741","url":null,"abstract":"<i>Aims.<i/> We present theoretical predictions and extrapolations from observed data of the stellar halos surrounding central group and cluster galaxies, and the transition radius between them and the intracluster or diffuse light.<i>Methods.<i/> Leveraging the state-of-the-art semi-analytic model of galaxy formation, FEGA (Formation and Evolution of GAlaxies), applied to two dark matter-only cosmological simulations, we derived both the stellar halo mass and its radius. Using theoretical assumptions about the diffuse light distribution and halo concentration, we extrapolated the same information for observed data from the VEGAS survey.<i>Results.<i/> Our model, supported by observational data and independent simulation results, predicts an increasing transition radius with halo mass, a constant stellar halo-to-intracluster light ratio, and a stable stellar halo mass fraction with increasing halo mass. Specifically, we find that the transition radius between the stellar halo and the diffuse light ranges from 20 to 250 kpc, from Milky Way-like halos to large clusters, while the stellar halo mass comprises only a small fraction, between 7% and 18%, of the total stellar mass within the virial radius.<i>Conclusions.<i/> These results support the idea that the stellar halo can be viewed as a transition region between the stars bound to a galaxy and those belonging to the intracluster light and are consistent with recent observations and theoretical predictions.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"16 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142825513","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-16DOI: 10.1051/0004-6361/202450557
G. Cusumano, V. La Parola, M. Capalbi, M. Perri, E. Ambrosi, A. P. Beardmore, A. D’Aì, D. N. Burrows, S. Campana, P. A. Evans, J. A. Kennea, J. P. Osborne, B. Sbarufatti, G. Tagliaferri
Context. The Neil Gehrels Swift Observatory has been operational since November 2004. Its X-ray Telescope (XRT), operating in the 0.3–10.0 keV range, is designed to provide detailed position, timing, and spectroscopic information.Aims. The calibration procedure for assessing the absolute timing accuracy of XRT was described in a previous paper. Here we update the past analysis using the complete data set of the Crab pulsar observations up to October 2022 and using a new version of the data-processing software package that includes corrections to several issues that could have affected the previous results.Methods. We evaluate the accuracy of the Crab pulse period determination using the folding technique and the pulse-phase analysis and compare our results with the values derived from radio observations. We also check the absolute time reconstruction, measuring the phase position of the main peak in the Crab profile and comparing it with the value reported in the literature, which is based on Rossi X-Ray Timing Explorer (RXTE) observations.Results. We find that the accuracy in period determination for the Crab pulsar is of the order of a few picoseconds for the observations with the largest data time span. The absolute time reconstruction, measured using the position of the main pulse peak, shows that the main peak precedes the phase of the position reported in the literature for RXTE by ~263 µs on average. This corresponds to 0.982 in phase, with an observed dispersion of ±0.02 in phase values. We also find that observations very close in time (down to ~1 day separation) show a significant variation in absolute phase.
背景尼尔-盖尔斯-斯威夫特天文台（Neil Gehrels Swift Observatory）自 2004 年 11 月起开始运行。它的 X 射线望远镜（XRT）在 0.3-10.0 千伏范围内工作，旨在提供详细的位置、定时和光谱信息。上一篇论文介绍了评估 XRT 绝对定时精度的校准程序。在此，我们使用截至 2022 年 10 月的蟹脉冲星观测的完整数据集，并使用新版本的数据处理软件包更新了过去的分析。我们评估了利用折叠技术和脉冲相位分析确定蟹状体脉冲周期的准确性，并将我们的结果与射电观测得出的数值进行了比较。我们还检查了绝对时间重建，测量了蟹状体剖面中主峰的相位位置，并将其与文献中报道的基于罗西 X 射线定时探测器（RXTE）观测的值进行了比较。我们发现，在数据时间跨度最大的观测中，蟹状脉冲星的周期测定精度为几皮秒。利用主脉冲峰位置测量的绝对时间重建结果表明，主脉冲峰平均比 RXTE 文献中报道的位置相位早约 263 微秒。这相当于 0.982 的相位差，观测到的相位差为 ±0.02。我们还发现，时间上非常接近的观测（相距约 1 天）显示出绝对相位的显著变化。
{"title":"Tracking the long-term timing accuracy of the X-Ray Telescope on board the Neil Gehrels Swift Observatory","authors":"G. Cusumano, V. La Parola, M. Capalbi, M. Perri, E. Ambrosi, A. P. Beardmore, A. D’Aì, D. N. Burrows, S. Campana, P. A. Evans, J. A. Kennea, J. P. Osborne, B. Sbarufatti, G. Tagliaferri","doi":"10.1051/0004-6361/202450557","DOIUrl":"https://doi.org/10.1051/0004-6361/202450557","url":null,"abstract":"<i>Context<i/>. The <i>Neil Gehrels Swift<i/> Observatory has been operational since November 2004. Its X-ray Telescope (XRT), operating in the 0.3–10.0 keV range, is designed to provide detailed position, timing, and spectroscopic information.<i>Aims<i/>. The calibration procedure for assessing the absolute timing accuracy of XRT was described in a previous paper. Here we update the past analysis using the complete data set of the Crab pulsar observations up to October 2022 and using a new version of the data-processing software package that includes corrections to several issues that could have affected the previous results.<i>Methods<i/>. We evaluate the accuracy of the Crab pulse period determination using the folding technique and the pulse-phase analysis and compare our results with the values derived from radio observations. We also check the absolute time reconstruction, measuring the phase position of the main peak in the Crab profile and comparing it with the value reported in the literature, which is based on Rossi X-Ray Timing Explorer (RXTE) observations.<i>Results<i/>. We find that the accuracy in period determination for the Crab pulsar is of the order of a few picoseconds for the observations with the largest data time span. The absolute time reconstruction, measured using the position of the main pulse peak, shows that the main peak precedes the phase of the position reported in the literature for RXTE by ~263 µs on average. This corresponds to 0.982 in phase, with an observed dispersion of ±0.02 in phase values. We also find that observations very close in time (down to ~1 day separation) show a significant variation in absolute phase.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"22 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142825509","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-16DOI: 10.1051/0004-6361/202450829
Bernd Freytag, Susanne Höfner, Bernhard Aringer, Andrea Chiavassa
Context. The dramatic dimming episode of the red supergiant Betelgeuse in 2019 and 2020, caused by a partial darkening of the stellar disk, has highlighted gaps in the understanding of the evolution of massive stars.Aims. We analyzed numerical models to investigate the processes behind the formation of dark surface patches and the associated reduction in the disk-integrated stellar light.Methods. With the CO5BOLD code, we performed global 3D radiation-hydrodynamical simulations of evolved stars, including convection in the stellar interior, self-excited pulsations, and the resulting atmospheric dynamics with strong radiative shocks.Results. We attribute dimming phenomena to obscuring clouds of cool gas in the lower atmosphere, forming according to three different scenarios. One process transports material outward in a strong shock, similar to what occurs in 1D simulations of radially pulsating asymptotic giant branch (AGB) stars. However, in 3D models, deviations from spherical symmetry of the shock front can lead to further local density enhancements. Another mechanism is triggered by a large convective upflow structure, in combination with exceptionally strong radial pulsations. This induces Rayleigh-Taylor instabilities, causing plumes of material to be sent outward into the atmosphere. The third and rarest scenario involves large-amplitude convective fluctuations, leading to enhanced flows in deep downdrafts, which rebound and send material outward. In all cases, the dense gas above the stellar surface cools and darkens rapidly in visible light. AGB stars show localized dark patches regularly during intermediate phases of their large-amplitude pulsations, while more massive stars will only intermittently form such patches during luminosity minima.Conclusions. The episodic levitation of dense gas clumps above the stellar surface, followed by the formation of complex molecules in the cooling gas and possibly dust grains at a later stage, can account for the dark patches and strong dimming events of supergiant stars such as Betelgeuse.
{"title":"Dimming events of evolved stars due to clouds of molecular gas","authors":"Bernd Freytag, Susanne Höfner, Bernhard Aringer, Andrea Chiavassa","doi":"10.1051/0004-6361/202450829","DOIUrl":"https://doi.org/10.1051/0004-6361/202450829","url":null,"abstract":"<i>Context.<i/> The dramatic dimming episode of the red supergiant Betelgeuse in 2019 and 2020, caused by a partial darkening of the stellar disk, has highlighted gaps in the understanding of the evolution of massive stars.<i>Aims.<i/> We analyzed numerical models to investigate the processes behind the formation of dark surface patches and the associated reduction in the disk-integrated stellar light.<i>Methods.<i/> With the CO5BOLD code, we performed global 3D radiation-hydrodynamical simulations of evolved stars, including convection in the stellar interior, self-excited pulsations, and the resulting atmospheric dynamics with strong radiative shocks.<i>Results.<i/> We attribute dimming phenomena to obscuring clouds of cool gas in the lower atmosphere, forming according to three different scenarios. One process transports material outward in a strong shock, similar to what occurs in 1D simulations of radially pulsating asymptotic giant branch (AGB) stars. However, in 3D models, deviations from spherical symmetry of the shock front can lead to further local density enhancements. Another mechanism is triggered by a large convective upflow structure, in combination with exceptionally strong radial pulsations. This induces Rayleigh-Taylor instabilities, causing plumes of material to be sent outward into the atmosphere. The third and rarest scenario involves large-amplitude convective fluctuations, leading to enhanced flows in deep downdrafts, which rebound and send material outward. In all cases, the dense gas above the stellar surface cools and darkens rapidly in visible light. AGB stars show localized dark patches regularly during intermediate phases of their large-amplitude pulsations, while more massive stars will only intermittently form such patches during luminosity minima.<i>Conclusions.<i/> The episodic levitation of dense gas clumps above the stellar surface, followed by the formation of complex molecules in the cooling gas and possibly dust grains at a later stage, can account for the dark patches and strong dimming events of supergiant stars such as Betelgeuse.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"143 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142825676","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-16DOI: 10.1051/0004-6361/202451102
José María Arroyo-Polonio, Giuseppina Battaglia, Guillaume F. Thomas, Raffaele Pascale, Eline Tolstoy, Carlo Nipoti
Aims. Recently, both the presence of multiple stellar chemo-kinematic components and rotation in the Sculptor dwarf spheroidal galaxy have been put into question. Therefore, we re-examine the chemo-kinematic properties of this galaxy, making use of the best spectroscopic dataset available containing both the line-of-sight velocities and metallicities of individual stars.Methods. We carried out a detailed, quantitative analysis on a recent spectroscopic dataset from the literature that contains high precision velocities and metallicities for 1339 members of Sculptor. In particular, we assessed whether Sculptor is best represented by a single stellar population with a negative metallicity gradient or by the super-position of two or more components with a different mean metallicity, spatial distribution, and kinematic properties. For this analysis, we also include the incompleteness of the spectroscopic dataset.Results. We find that Sculptor is better described by a two-population model than by a single-population model with a metallicity gradient. Moreover, given the assumptions of the current modeling, we find evidence of a third population, composed of few stars, that is more extended and metal-poor than the two other populations. This very metal-poor group of stars shows a shift of ~15 km s−1 in its average line-of-sight velocity (vlos) with respect to the rest of the galaxy. We discuss several possible origins for this new population, finding a minor merger as the most likely one. We also find a vlos gradient of 4.0−1.5+1.5 km s−1 deg−1 but its statistical evidence is inconclusive and, moreover, its detection is partially driven by the group of stars with off-set velocities.
{"title":"Chemo-dynamics of the stellar component of the Sculptor dwarf galaxy","authors":"José María Arroyo-Polonio, Giuseppina Battaglia, Guillaume F. Thomas, Raffaele Pascale, Eline Tolstoy, Carlo Nipoti","doi":"10.1051/0004-6361/202451102","DOIUrl":"https://doi.org/10.1051/0004-6361/202451102","url":null,"abstract":"<i>Aims.<i/> Recently, both the presence of multiple stellar chemo-kinematic components and rotation in the Sculptor dwarf spheroidal galaxy have been put into question. Therefore, we re-examine the chemo-kinematic properties of this galaxy, making use of the best spectroscopic dataset available containing both the line-of-sight velocities and metallicities of individual stars.<i>Methods.<i/> We carried out a detailed, quantitative analysis on a recent spectroscopic dataset from the literature that contains high precision velocities and metallicities for 1339 members of Sculptor. In particular, we assessed whether Sculptor is best represented by a single stellar population with a negative metallicity gradient or by the super-position of two or more components with a different mean metallicity, spatial distribution, and kinematic properties. For this analysis, we also include the incompleteness of the spectroscopic dataset.<i>Results.<i/> We find that Sculptor is better described by a two-population model than by a single-population model with a metallicity gradient. Moreover, given the assumptions of the current modeling, we find evidence of a third population, composed of few stars, that is more extended and metal-poor than the two other populations. This very metal-poor group of stars shows a shift of ~15 km s<sup>−1<sup/> in its average line-of-sight velocity (<i>v<sub>los<sub/><i/>) with respect to the rest of the galaxy. We discuss several possible origins for this new population, finding a minor merger as the most likely one. We also find a <i>v<sub>los<sub/><i/> gradient of 4.0<sub>−1.5<sub/><sup>+1.5<sup/> km s<sup>−1<sup/> deg<sup>−1<sup/> but its statistical evidence is inconclusive and, moreover, its detection is partially driven by the group of stars with off-set velocities.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"41 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142825697","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-16DOI: 10.1051/0004-6361/202452300
T. Foglizzo
Context. During the core collapse of a massive star, and immediately before its supernova explosion, there is amplification of asymmetric motions by the standing accretion shock instability (SASI). This imprints a frequency signature on the neutrino flux and the gravitational waves that carries direct information about the explosion process.Aims. The physical interpretation of this multi-messenger signature requires a detailed understanding of the instability mechanism.Methods. We carried out a perturbative analysis to characterise the properties of SASI and assess the effect of the region of neutronization above the surface of the proto-neutron star. We compared the eigenfrequencies of the most unstable modes to those obtained in an adiabatic approximation where neutrino interactions are neglected above the neutrinosphere. We solved the differential system analytically using a Wronskian method and approximated it asymptotically for a large shock radius.Results. The oscillation period of SASI is well fitted with a simple analytic function of the shock radius, the radius of maximum deceleration, and the mass of the proto-neutron star. The oscillation period is weakly dependent on the parameterised cooling function, but this latter does affects the SASI growth rate. We describe the general properties of SASI eigenmodes using an adiabatic model. In this approximation, the eigenvalue problem is formulated as a self-forced oscillator. The forcing agent is the radial advection of baroclinic vorticity perturbations and entropy perturbations produced by the shock oscillation. We reduced the differential system defining the eigenfrequencies to a single integral equation. Its analytical approximation sheds light on the radially extended character of the region of advective-acoustic coupling. The simplicity of this adiabatic formalism opens new perspectives for the investigation of the effect of stellar rotation and non-adiabatic processes on SASI.
{"title":"Analytic insight into the physics of the standing accretion shock instability","authors":"T. Foglizzo","doi":"10.1051/0004-6361/202452300","DOIUrl":"https://doi.org/10.1051/0004-6361/202452300","url":null,"abstract":"<i>Context.<i/> During the core collapse of a massive star, and immediately before its supernova explosion, there is amplification of asymmetric motions by the standing accretion shock instability (SASI). This imprints a frequency signature on the neutrino flux and the gravitational waves that carries direct information about the explosion process.<i>Aims.<i/> The physical interpretation of this multi-messenger signature requires a detailed understanding of the instability mechanism.<i>Methods.<i/> We carried out a perturbative analysis to characterise the properties of SASI and assess the effect of the region of neutronization above the surface of the proto-neutron star. We compared the eigenfrequencies of the most unstable modes to those obtained in an adiabatic approximation where neutrino interactions are neglected above the neutrinosphere. We solved the differential system analytically using a Wronskian method and approximated it asymptotically for a large shock radius.<i>Results.<i/> The oscillation period of SASI is well fitted with a simple analytic function of the shock radius, the radius of maximum deceleration, and the mass of the proto-neutron star. The oscillation period is weakly dependent on the parameterised cooling function, but this latter does affects the SASI growth rate. We describe the general properties of SASI eigenmodes using an adiabatic model. In this approximation, the eigenvalue problem is formulated as a self-forced oscillator. The forcing agent is the radial advection of baroclinic vorticity perturbations and entropy perturbations produced by the shock oscillation. We reduced the differential system defining the eigenfrequencies to a single integral equation. Its analytical approximation sheds light on the radially extended character of the region of advective-acoustic coupling. The simplicity of this adiabatic formalism opens new perspectives for the investigation of the effect of stellar rotation and non-adiabatic processes on SASI.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"253 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142825707","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-16DOI: 10.1051/0004-6361/202452424
Priyanka Jalan, Maciej Bilicki, Wojciech A. Hellwing, Angus H. Wright, Andrej Dvornik, Christos Georgiou, Catherine Heymans, Hendrik Hildebrandt, Shahab Joudaki, Konrad Kuijken, Constance Mahony, Szymon Jan Nakoneczny, Mario Radovich, Jan Luca van den Busch, Ziang Yan, Mijin Yoon
Aims. We present a method for refining photometric redshift galaxy catalogs based on a comparison of their color-space matching with overlapping spectroscopic calibration data. We focus on cases where photometric redshifts (photo-z) are estimated empirically. Identifying galaxies that are poorly represented in spectroscopic data is crucial, as their photo-z may be unreliable due to extrapolation beyond the training sample.Methods. Our approach uses a self-organizing map (SOM) to project a multidimensional parameter space of magnitudes and colors onto a 2D manifold, allowing us to analyze the resulting patterns as a function of various galaxy properties. Using SOM, we compared the Kilo-Degree Survey’s bright galaxy sample (KiDS-Bright), limited to r < 20 mag, with various spectroscopic samples, including the Galaxy And Mass Assembly (GAMA).Results. Our analysis reveals that GAMA tends to underrepresent KiDS-Bright at its faintest (r ≳ 19.5) and highest-redshift (z ≳ 0.4) ranges; however, no strong trends are seen in terms of color or stellar mass. By incorporating additional spectroscopic data from the SDSS, 2dF, and early DESI, we identified SOM cells where the photo-z values are estimated suboptimally. We derived a set of SOM-based criteria to refine the photometric sample and improve photo-z statistics. For the KiDS-Bright sample, this improvement is modest, namely, it excludes the least represented 20% of the sample reduces photo-z scatter by less than 10%.Conclusions. We conclude that GAMA, used for KiDS-Bright photo-z training, is sufficiently representative for reliable redshift estimation across most of the color space. Future spectroscopic data from surveys such as DESI should be better suited for exploiting the full improvement potential of our method.
{"title":"Enhancing photometric redshift catalogs through color-space analysis: Application to KiDS-bright galaxies","authors":"Priyanka Jalan, Maciej Bilicki, Wojciech A. Hellwing, Angus H. Wright, Andrej Dvornik, Christos Georgiou, Catherine Heymans, Hendrik Hildebrandt, Shahab Joudaki, Konrad Kuijken, Constance Mahony, Szymon Jan Nakoneczny, Mario Radovich, Jan Luca van den Busch, Ziang Yan, Mijin Yoon","doi":"10.1051/0004-6361/202452424","DOIUrl":"https://doi.org/10.1051/0004-6361/202452424","url":null,"abstract":"<i>Aims.<i/> We present a method for refining photometric redshift galaxy catalogs based on a comparison of their color-space matching with overlapping spectroscopic calibration data. We focus on cases where photometric redshifts (photo-<i>z<i/>) are estimated empirically. Identifying galaxies that are poorly represented in spectroscopic data is crucial, as their photo-<i>z<i/> may be unreliable due to extrapolation beyond the training sample.<i>Methods.<i/> Our approach uses a self-organizing map (SOM) to project a multidimensional parameter space of magnitudes and colors onto a 2D manifold, allowing us to analyze the resulting patterns as a function of various galaxy properties. Using SOM, we compared the Kilo-Degree Survey’s bright galaxy sample (KiDS-Bright), limited to <i>r<i/> < 20 mag, with various spectroscopic samples, including the Galaxy And Mass Assembly (GAMA).<i>Results.<i/> Our analysis reveals that GAMA tends to underrepresent KiDS-Bright at its faintest (<i>r<i/> ≳ 19.5) and highest-redshift (<i>z<i/> ≳ 0.4) ranges; however, no strong trends are seen in terms of color or stellar mass. By incorporating additional spectroscopic data from the SDSS, 2dF, and early DESI, we identified SOM cells where the photo-<i>z<i/> values are estimated suboptimally. We derived a set of SOM-based criteria to refine the photometric sample and improve photo-<i>z<i/> statistics. For the KiDS-Bright sample, this improvement is modest, namely, it excludes the least represented 20% of the sample reduces photo-<i>z<i/> scatter by less than 10%.<i>Conclusions.<i/> We conclude that GAMA, used for KiDS-Bright photo-<i>z<i/> training, is sufficiently representative for reliable redshift estimation across most of the color space. Future spectroscopic data from surveys such as DESI should be better suited for exploiting the full improvement potential of our method.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"50 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-12-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142825672","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-13DOI: 10.1051/0004-6361/202451694
Stefano Rinaldi, María Claudia Ramírez-Tannus
Aims. Binarity plays a crucial role in star formation and evolution. Consequently, identifying binary stars is essential to deepening our understanding of these processes. We propose a method to investigate the observed radial velocity distribution of massive stars in young clusters with the goal of identifying binary systems.Methods. We reconstruct the radial velocity distribution using a three-layer hierarchical Bayesian non-parametric approach; nonparametric methods are data-driven models able to infer arbitrary probability densities under minimal mathematical assumptions. When applying our statistical framework, it is possible to identify variable stars and binary systems because these deviate significantly from the expected intrinsic Gaussian distribution for radial velocities.Results. We tested our method with the massive star-forming region within the giant HII region M17. We are able to confidently identify binaries and variable stars with as little as single-epoch observations. The distinction between variable and binary stars improves significantly when introducing additional epochs.
目的。双星在恒星形成和演化过程中起着至关重要的作用。因此，识别双星对于加深我们对这些过程的理解至关重要。我们提出了一种方法来研究观测到的年轻星团中大质量恒星的径向速度分布，目的是识别双星系统。我们使用一种三层分级贝叶斯非参数方法来重建径向速度分布；非参数方法是一种数据驱动模型，能够在最小的数学假设条件下推断出任意的概率密度。当应用我们的统计框架时，有可能识别出变星和双星系统，因为它们明显偏离了径向速度的预期本征高斯分布。我们用巨型 HII 区域 M17 中的大质量恒星形成区测试了我们的方法。我们只需进行一次单波段观测，就能有把握地识别出双星和变星。当引入更多的历元时，变星和双星之间的区别就会明显改善。
{"title":"Non-parametric identification of single-lined binary candidates in young clusters using single-epoch spectroscopy","authors":"Stefano Rinaldi, María Claudia Ramírez-Tannus","doi":"10.1051/0004-6361/202451694","DOIUrl":"https://doi.org/10.1051/0004-6361/202451694","url":null,"abstract":"<i>Aims<i/>. Binarity plays a crucial role in star formation and evolution. Consequently, identifying binary stars is essential to deepening our understanding of these processes. We propose a method to investigate the observed radial velocity distribution of massive stars in young clusters with the goal of identifying binary systems.<i>Methods<i/>. We reconstruct the radial velocity distribution using a three-layer hierarchical Bayesian non-parametric approach; nonparametric methods are data-driven models able to infer arbitrary probability densities under minimal mathematical assumptions. When applying our statistical framework, it is possible to identify variable stars and binary systems because these deviate significantly from the expected intrinsic Gaussian distribution for radial velocities.<i>Results<i/>. We tested our method with the massive star-forming region within the giant H<sub>II<sub/> region M17. We are able to confidently identify binaries and variable stars with as little as single-epoch observations. The distinction between variable and binary stars improves significantly when introducing additional epochs.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"18 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142825701","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2024-12-13DOI: 10.1051/0004-6361/202451078
Akash Gupta, Valentin D. Ivanov, Thomas Preibisch, Dante Minniti
Context. Milky Way star clusters provide important clues about the history of star formation in our Galaxy. However, the dust in the disk and in the innermost regions hides them from the observers.Aims. Our goal is twofold. First, to detect new clusters – we have applied the newest methods of detecting clusters with the best available wide-field sky surveys in the mid-infrared because they are the least affected by extinction. Second, we address the question of cluster detection’s completeness, for now limiting it to the most massive star clusters.Methods. This search is based on the mid-infrared Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), to minimize the effect of dust extinction. The search Ordering Points To Identify the Clustering Structure (OPTICS) clustering algorithm was applied to identify clusters, after excluding the bluest, presumably foreground sources, to improve the cluster-to-field contrast. The success rate for cluster identification was estimated with a semi-empirical simulation that adds clusters, based on the real objects, to the point source catalog, to be recovered later with the same search algorithm that was used in the search for new cluster candidates. As a first step, this was limited to the most massive star clusters with a total mass of ~104 M⊙.Results. Our automated search, combined with inspection of the color-magnitude diagrams and images, yielded 659 cluster candidates; 106 of these appear to have been previously identified, suggesting that a large hidden population of star clusters still exists in the inner Milky Way. However, the search for the simulated supermassive clusters achieves a recovery rate of 70–95%, depending on the distance and extinction toward them.Conclusions. The new candidates – if confirmed – indicate that the Milky Way still harbors a sizeable population of unknown clusters. However, they must be objects of modest richness, because our simulation indicates that there is no substantial hidden population of supermassive clusters in the central region of our Galaxy.
{"title":"Obscured star clusters in the inner Milky Way","authors":"Akash Gupta, Valentin D. Ivanov, Thomas Preibisch, Dante Minniti","doi":"10.1051/0004-6361/202451078","DOIUrl":"https://doi.org/10.1051/0004-6361/202451078","url":null,"abstract":"<i>Context.<i/> Milky Way star clusters provide important clues about the history of star formation in our Galaxy. However, the dust in the disk and in the innermost regions hides them from the observers.<i>Aims.<i/> Our goal is twofold. First, to detect new clusters – we have applied the newest methods of detecting clusters with the best available wide-field sky surveys in the mid-infrared because they are the least affected by extinction. Second, we address the question of cluster detection’s completeness, for now limiting it to the most massive star clusters.<i>Methods.<i/> This search is based on the mid-infrared Galactic Legacy Infrared Mid-Plane Survey Extraordinaire (GLIMPSE), to minimize the effect of dust extinction. The search Ordering Points To Identify the Clustering Structure (OPTICS) clustering algorithm was applied to identify clusters, after excluding the bluest, presumably foreground sources, to improve the cluster-to-field contrast. The success rate for cluster identification was estimated with a semi-empirical simulation that adds clusters, based on the real objects, to the point source catalog, to be recovered later with the same search algorithm that was used in the search for new cluster candidates. As a first step, this was limited to the most massive star clusters with a total mass of ~10<sup>4<sup/> M<sub>⊙<sub/>.<i>Results.<i/> Our automated search, combined with inspection of the color-magnitude diagrams and images, yielded 659 cluster candidates; 106 of these appear to have been previously identified, suggesting that a large hidden population of star clusters still exists in the inner Milky Way. However, the search for the simulated supermassive clusters achieves a recovery rate of 70–95%, depending on the distance and extinction toward them.<i>Conclusions.<i/> The new candidates – if confirmed – indicate that the Milky Way still harbors a sizeable population of unknown clusters. However, they must be objects of modest richness, because our simulation indicates that there is no substantial hidden population of supermassive clusters in the central region of our Galaxy.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"3 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-12-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142825529","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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