Pub Date : 2024-11-13DOI: 10.1051/0004-6361/202451339
Zesen Lin, Renbin Yan
Dust attenuations observed by stars and ionized gas are not necessarily the same. The lack of observational constraints on the nebular dust attenuation curve leaves a large uncertainty when correcting nebular dust attenuation with stellar continuum-based attenuation curves. Making use of the DAP catalogs of the MaNGA survey, we investigate the nebular dust attenuation of H II regions traced by the Balmer and Paschen lines. Based on a simple simulation, we find that star-forming regions on kpc scales favor the classic foreground screen dust model rather than the uniform mixture model. We propose a novel approach to fit the dust attenuation curve using the emission-line fluxes directly. For strong hydrogen recombination lines (e.g., Hγ, Hδ, and Hϵ), the slopes of the nebular attenuation curve can be well determined and are found to be in good agreement with the Fitzpatrick Milky Way extinction curve with an accuracy of ≲4% in terms of the correction factor. However, severe contaminations and/or systematic uncertainties prevent us from obtaining reasonable values of the slopes for weak recombination lines (e.g., the high-order Balmer lines or the Paschen lines). We discuss how the choice of emission line measurement methods affects the results. Our results demonstrate the difficulty of deriving an average nebular dust attenuation curve given the current ground-based emission-line measurements.
{"title":"Nebular dust attenuation with the Balmer and Paschen lines based on the MaNGA survey","authors":"Zesen Lin, Renbin Yan","doi":"10.1051/0004-6361/202451339","DOIUrl":"https://doi.org/10.1051/0004-6361/202451339","url":null,"abstract":"Dust attenuations observed by stars and ionized gas are not necessarily the same. The lack of observational constraints on the nebular dust attenuation curve leaves a large uncertainty when correcting nebular dust attenuation with stellar continuum-based attenuation curves. Making use of the DAP catalogs of the MaNGA survey, we investigate the nebular dust attenuation of H II regions traced by the Balmer and Paschen lines. Based on a simple simulation, we find that star-forming regions on kpc scales favor the classic foreground screen dust model rather than the uniform mixture model. We propose a novel approach to fit the dust attenuation curve using the emission-line fluxes directly. For strong hydrogen recombination lines (e.g., H<i>γ<i/>, H<i>δ<i/>, and H<i>ϵ<i/>), the slopes of the nebular attenuation curve can be well determined and are found to be in good agreement with the Fitzpatrick Milky Way extinction curve with an accuracy of ≲4% in terms of the correction factor. However, severe contaminations and/or systematic uncertainties prevent us from obtaining reasonable values of the slopes for weak recombination lines (e.g., the high-order Balmer lines or the Paschen lines). We discuss how the choice of emission line measurement methods affects the results. Our results demonstrate the difficulty of deriving an average nebular dust attenuation curve given the current ground-based emission-line measurements.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"13 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142610352","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 : 2024-11-11DOI: 10.1051/0004-6361/202451588
Lucas Einig, Pierre Palud, Antoine Roueff, Jérôme Pety, Emeric Bron, Franck Le Petit, Maryvonne Gerin, Jocelyn Chanussot, Pierre Chainais, Pierre-Antoine Thouvenin, David Languignon, Ivana Bešlić, Simon Coudé, Helena Mazurek, Jan H. Orkisz, Miriam G. Santa-Maria, Léontine Ségal, Antoine Zakardjian, Sébastien Bardeau, Karine Demyk, Victor de Souza Magalhães, Javier R. Goicoechea, Pierre Gratier, Viviana V. Guzmán, Annie Hughes, François Levrier, Jacques Le Bourlot, Dariusz C. Lis, Harvey S. Liszt, Nicolas Peretto, Evelyne Roueff, Albrecht Sievers
Observations of ionic, atomic, or molecular lines are performed to improve our understanding of the interstellar medium (ISM). However, the potential of a line to constrain the physical conditions of the ISM is difficult to assess quantitatively, because of the complexity of the ISM physics. The situation is even more complex when trying to assess which combinations of lines are the most useful. Therefore, observation campaigns usually try to observe as many lines as possible for as much time as possible. We have searched for a quantitative statistical criterion to evaluate the full constraining power of a (combination of) tracer(s) with respect to physical conditions. Our goal with such a criterion is twofold. First, we want to improve our understanding of the statistical relationships between ISM tracers and physical conditions. Secondly, by exploiting this criterion, we aim to propose a method that helps observers to make their observation proposals; for example, by choosing to observe the lines with the highest constraining power given limited resources and time. We propose an approach based on information theory, in particular the concepts of conditional differential entropy and mutual information. The best (combination of) tracer(s) is obtained by comparing the mutual information between a physical parameter and different sets of lines. The presented analysis is independent of the choice of the estimation algorithm ( neural network or $ minimization). We applied this method to simulations of radio molecular lines emitted by a photodissociation region similar to the Horsehead Nebula. In this simulated data, we considered the noise properties of a state-of-the-art single dish telescope such as the IRAM 30m telescope. We searched for the best lines to constrain the visual extinction or the ultraviolet illumination field . We ran this search for different gas regimes, namely translucent gas, filamentary gas, and dense cores. The most informative lines change with the physical regime ( cloud extinction). However, the determination of the optimal (combination of) line(s) to constrain a physical parameter such as the visual extinction depends not only on the radiative transfer of the lines and chemistry of the associated species, but also on the achieved mean signal-to-noise ratio. The short integration time of the CO isotopologue $J=1-0$ lines already yields much information on the total column density for a large range of ( ) space. The best set of lines to constrain the visual extinction does not necessarily combine the most informative individual lines. Precise constraints on the radiation field are more difficult to achieve with molecular lines. They require spectral lines emitted at the cloud surface ( and lines). This approach allows one to better explore the knowledge provided by ISM codes, and to guide future observation campaigns.
对离子、原子或分子线进行观测是为了增进我们对星际介质（ISM）的了解。然而，由于星际介质物理学的复杂性，很难定量评估某条线在约束星际介质物理条件方面的潜力。如果要评估哪种光谱线组合最有用，情况就更加复杂了。因此，观测活动通常会尝试在尽可能多的时间内观测尽可能多的线条。我们一直在寻找一种定量统计标准，以评估示踪线（组合）在物理条件方面的全部约束能力。我们的目标有两个。首先，我们希望加深对 ISM 示踪剂与物理条件之间统计关系的理解。其次，通过利用这一标准，我们希望提出一种方法，帮助观测者提出观测建议；例如，在资源和时间有限的情况下，选择观测约束能力最强的谱线。我们提出的方法基于信息论，特别是条件差分熵和互信息的概念。通过比较物理参数与不同线路组之间的互信息，可以获得最佳（组合）示踪线。所提出的分析方法与估算算法（神经网络或美元最小化）的选择无关。我们将这种方法应用于模拟类似马头星云的光解离区域发射的射电分子线。在模拟数据中，我们考虑了最先进的单碟望远镜（如 IRAM 30 米望远镜）的噪声特性。我们寻找最佳的线条来约束视觉消光或紫外线照明场。我们对不同的气体状态进行了搜索，即半透明气体、丝状气体和致密核心。信息量最大的线条会随着物理机制（云消光）的变化而变化。然而，确定用于约束视觉消光等物理参数的最佳（组合）谱线不仅取决于谱线的辐射传递和相关物种的化学性质，还取决于所达到的平均信噪比。CO 同素异形体$J=1-0$线的积分时间很短，在很大的（ ）空间范围内已经可以获得很多关于总柱密度的信息。用于约束视觉消光的最佳线组不一定是信息量最大的单条线的组合。分子线更难实现对辐射场的精确约束。它们需要云表面发射的光谱线（ 和 线）。这种方法可以更好地探索 ISM 代码提供的知识，并为未来的观测活动提供指导。
{"title":"Quantifying the informativity of emission lines to infer physical conditions in giant molecular clouds","authors":"Lucas Einig, Pierre Palud, Antoine Roueff, Jérôme Pety, Emeric Bron, Franck Le Petit, Maryvonne Gerin, Jocelyn Chanussot, Pierre Chainais, Pierre-Antoine Thouvenin, David Languignon, Ivana Bešlić, Simon Coudé, Helena Mazurek, Jan H. Orkisz, Miriam G. Santa-Maria, Léontine Ségal, Antoine Zakardjian, Sébastien Bardeau, Karine Demyk, Victor de Souza Magalhães, Javier R. Goicoechea, Pierre Gratier, Viviana V. Guzmán, Annie Hughes, François Levrier, Jacques Le Bourlot, Dariusz C. Lis, Harvey S. Liszt, Nicolas Peretto, Evelyne Roueff, Albrecht Sievers","doi":"10.1051/0004-6361/202451588","DOIUrl":"https://doi.org/10.1051/0004-6361/202451588","url":null,"abstract":"Observations of ionic, atomic, or molecular lines are performed to improve our understanding of the interstellar medium (ISM). However, the potential of a line to constrain the physical conditions of the ISM is difficult to assess quantitatively, because of the complexity of the ISM physics. The situation is even more complex when trying to assess which combinations of lines are the most useful. Therefore, observation campaigns usually try to observe as many lines as possible for as much time as possible. We have searched for a quantitative statistical criterion to evaluate the full constraining power of a (combination of) tracer(s) with respect to physical conditions. Our goal with such a criterion is twofold. First, we want to improve our understanding of the statistical relationships between ISM tracers and physical conditions. Secondly, by exploiting this criterion, we aim to propose a method that helps observers to make their observation proposals; for example, by choosing to observe the lines with the highest constraining power given limited resources and time. We propose an approach based on information theory, in particular the concepts of conditional differential entropy and mutual information. The best (combination of) tracer(s) is obtained by comparing the mutual information between a physical parameter and different sets of lines. The presented analysis is independent of the choice of the estimation algorithm ( neural network or $ minimization). We applied this method to simulations of radio molecular lines emitted by a photodissociation region similar to the Horsehead Nebula. In this simulated data, we considered the noise properties of a state-of-the-art single dish telescope such as the IRAM 30m telescope. We searched for the best lines to constrain the visual extinction or the ultraviolet illumination field . We ran this search for different gas regimes, namely translucent gas, filamentary gas, and dense cores. The most informative lines change with the physical regime ( cloud extinction). However, the determination of the optimal (combination of) line(s) to constrain a physical parameter such as the visual extinction depends not only on the radiative transfer of the lines and chemistry of the associated species, but also on the achieved mean signal-to-noise ratio. The short integration time of the CO isotopologue $J=1-0$ lines already yields much information on the total column density for a large range of ( ) space. The best set of lines to constrain the visual extinction does not necessarily combine the most informative individual lines. Precise constraints on the radiation field are more difficult to achieve with molecular lines. They require spectral lines emitted at the cloud surface ( and lines). This approach allows one to better explore the knowledge provided by ISM codes, and to guide future observation campaigns.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"71 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598499","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 : 2024-11-11DOI: 10.1051/0004-6361/202451114
Piia Maria Tomberg, Anders Johansen
In this work, we present results of numerical simulations of the formation and early evolution of rocky planets through pebble accretion, with an emphasis on hydrogen envelope longevity and the composition of the outgassed atmosphere. We modelled planets with a range in mass from 0.1 to 5 Earth masses that orbit between 0.7 and 1.7 AU. The composition of the outgassed atmosphere was calculated with the partial pressure of free oxygen fit to geophysical models of magma ocean self-oxidation. The combined X-ray and UV (XUV) radiation-powered photoevaporation is considered as the main driver of atmospheric escape. We modelled planets that remain below the pebble isolation mass and hence accrete tenuous envelopes only. We considered slow, medium, or fast initial stellar rotation for the temporal evolution of the XUV flux. The loss of the envelope is a key event that allows the magma ocean to crystallise and outgas its bulk volatiles. The atmospheric composition of the majority of our simulated planets is dominated by CO$_2$. Our planets accrete a total of 11.6 Earth oceans of water, the majority of which enters the core. The hydrospheres of planets lighter than the Earth reach several times the mass of the Earth's modern oceans, while the hydrospheres of planets ranging from 1 to 3.5 Earth masses are comparable to those of our planet. However, planets of 4-5 Earth masses have smaller hydrospheres due to the trapping of volatiles in their massive mantles. Overall, our simulations demonstrate that hydrogen envelopes are easily lost from rocky planets and that this envelope loss triggers the most primordial partitioning of volatiles between the solid mantle and the atmosphere.
{"title":"Evolution of gas envelopes and outgassed atmospheres of rocky planets that formed via pebble accretion","authors":"Piia Maria Tomberg, Anders Johansen","doi":"10.1051/0004-6361/202451114","DOIUrl":"https://doi.org/10.1051/0004-6361/202451114","url":null,"abstract":"In this work, we present results of numerical simulations of the formation and early evolution of rocky planets through pebble accretion, with an emphasis on hydrogen envelope longevity and the composition of the outgassed atmosphere. We modelled planets with a range in mass from 0.1 to 5 Earth masses that orbit between 0.7 and 1.7 AU. The composition of the outgassed atmosphere was calculated with the partial pressure of free oxygen fit to geophysical models of magma ocean self-oxidation. The combined X-ray and UV (XUV) radiation-powered photoevaporation is considered as the main driver of atmospheric escape. We modelled planets that remain below the pebble isolation mass and hence accrete tenuous envelopes only. We considered slow, medium, or fast initial stellar rotation for the temporal evolution of the XUV flux. The loss of the envelope is a key event that allows the magma ocean to crystallise and outgas its bulk volatiles. The atmospheric composition of the majority of our simulated planets is dominated by CO$_2$. Our planets accrete a total of 11.6 Earth oceans of water, the majority of which enters the core. The hydrospheres of planets lighter than the Earth reach several times the mass of the Earth's modern oceans, while the hydrospheres of planets ranging from 1 to 3.5 Earth masses are comparable to those of our planet. However, planets of 4-5 Earth masses have smaller hydrospheres due to the trapping of volatiles in their massive mantles. Overall, our simulations demonstrate that hydrogen envelopes are easily lost from rocky planets and that this envelope loss triggers the most primordial partitioning of volatiles between the solid mantle and the atmosphere.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"10 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598503","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 : 2024-11-11DOI: 10.1051/0004-6361/202450535
P.J. Pessi, R. Durgesh, L. Nakazono, E. Hayes, R.A.P. Oliveira, E.O. Ishida, A. Moitinho, A. Krone-Martins, B. Moews, R.S. de Souza, R. Beck, M.A. Kuhn, K. Nowak, S. Vaughan
Transient astronomical events that exhibit no discernible association with a host galaxy are commonly referred to as hostless. These rare phenomena can offer unique insights into the properties and evolution of stars and galaxies. However, the sheer number of transients captured by contemporary high-cadence astronomical surveys renders the manual identification of all potential hostless transients impractical. Therefore, creating a systematic identification tool is crucial for studying these elusive events. We present the ExtragaLactic alErt Pipeline for Hostless AstroNomical Transients ( a framework for filtering hostless transients in astronomical data streams. It was designed to process alerts from the Zwicky Transient Facility (ZTF) presented in the Fink broker; however, its underlying concept can be applied to other data sources. We used Fink to access all the ZTF alerts produced between January 2022 and December 2023, selecting alerts associated with extragalactic transients reported in SIMBAD or TNS, as well as those classified as supernovae (SNe) or kilonovae (KNe) by the machine learning (ML) classifiers within the broker. We then processed the associated stamps using a sequence of image analysis techniques to retrieve hostless candidates. We find that lesssim 2 of all analyzed transients are potentially hostless. Among them, only sim 10 have a spectroscopic class reported on TNS, with type Ia SNe being the most common class, followed by superluminous SNe. In particular, among the hostless candidates retrieved by our pipeline, there is SN 2018ibb, which has been proposed to be a pair instability SN candidate, and SN 2022ann, one of only five known SNe Icn. When no class is reported on TNS, the dominant classes are quasi-stellar object (QSO) and SN candidates, with the former obtained from SIMBAD and the latter inferred using the Fink ML classifier. represents an effective strategy to filter extragalactic events within large and complex astronomical alert streams. There are many applications for which this pipeline will be useful, ranging from transient selection for follow-up to studies of transient environments. The results presented here demonstrate the feasibility of developing specially crafted pipelines that enable a variety of scientific studies based on large-scale surveys.
{"title":"ELEPHANT: ExtragaLactic alErt Pipeline for Hostless AstroNomical Transients","authors":"P.J. Pessi, R. Durgesh, L. Nakazono, E. Hayes, R.A.P. Oliveira, E.O. Ishida, A. Moitinho, A. Krone-Martins, B. Moews, R.S. de Souza, R. Beck, M.A. Kuhn, K. Nowak, S. Vaughan","doi":"10.1051/0004-6361/202450535","DOIUrl":"https://doi.org/10.1051/0004-6361/202450535","url":null,"abstract":"Transient astronomical events that exhibit no discernible association with a host galaxy are commonly referred to as hostless. These rare phenomena can offer unique insights into the properties and evolution of stars and galaxies. However, the sheer number of transients captured by contemporary high-cadence astronomical surveys renders the manual identification of all potential hostless transients impractical. Therefore, creating a systematic identification tool is crucial for studying these elusive events. We present the ExtragaLactic alErt Pipeline for Hostless AstroNomical Transients ( a framework for filtering hostless transients in astronomical data streams. It was designed to process alerts from the Zwicky Transient Facility (ZTF) presented in the Fink broker; however, its underlying concept can be applied to other data sources. We used Fink to access all the ZTF alerts produced between January 2022 and December 2023, selecting alerts associated with extragalactic transients reported in SIMBAD or TNS, as well as those classified as supernovae (SNe) or kilonovae (KNe) by the machine learning (ML) classifiers within the broker. We then processed the associated stamps using a sequence of image analysis techniques to retrieve hostless candidates. We find that lesssim 2<!PCT!> of all analyzed transients are potentially hostless. Among them, only sim 10<!PCT!> have a spectroscopic class reported on TNS, with type Ia SNe being the most common class, followed by superluminous SNe. In particular, among the hostless candidates retrieved by our pipeline, there is SN 2018ibb, which has been proposed to be a pair instability SN candidate, and SN 2022ann, one of only five known SNe Icn. When no class is reported on TNS, the dominant classes are quasi-stellar object (QSO) and SN candidates, with the former obtained from SIMBAD and the latter inferred using the Fink ML classifier. represents an effective strategy to filter extragalactic events within large and complex astronomical alert streams. There are many applications for which this pipeline will be useful, ranging from transient selection for follow-up to studies of transient environments. The results presented here demonstrate the feasibility of developing specially crafted pipelines that enable a variety of scientific studies based on large-scale surveys.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"196 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598505","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 : 2024-11-08DOI: 10.1051/0004-6361/202452168
C. Katsavrias, G. Nicolaou, G. Livadiotis
Context. A polytropic process describes the transition of a fluid from one state to another through a specific relationship between the fluid density and temperature, while the value of the polytropic index that governs this relationship determines the heat transfer and the effective degrees of freedom of that specific process.Aims. In this paper we investigate in depth the relationship between the proton effective polytropic index γ in the solar wind, the proton anisotropy α, and plasma β, while – for the first time to our knowledge to such an extent – we further investigate the dependence of the partial (with respect to the magnetic field) polytropic index to both the above-mentioned plasma parameters.Methods. To this end we use the entire Wind dataset spanning the 1995 to 2023 time period to derive the distributions of the polytropic index in the near-Earth space (L1).Results. Our results indicate that the proton γ increases with increasing proton anisotropy and decreases with increasing plasma β. Finally, we show that even though the average (over long time periods) total and partial proton polytropic index values are very close, these values correspond to isotropic plasma alone, with a further balance between the thermal and magnetic pressure.On the contrary, for shorter time periods and/or specific solar wind structures, where the proton anisotropy and plasma β exhibit deviations from these average values, the partial proton polytropic index exhibits significant variation that is dependent on the anisotropy and on plasma β.
{"title":"Dependence of the polytropic behaviour of solar wind protons on temperature anisotropy and plasma β near L1","authors":"C. Katsavrias, G. Nicolaou, G. Livadiotis","doi":"10.1051/0004-6361/202452168","DOIUrl":"https://doi.org/10.1051/0004-6361/202452168","url":null,"abstract":"<i>Context.<i/> A polytropic process describes the transition of a fluid from one state to another through a specific relationship between the fluid density and temperature, while the value of the polytropic index that governs this relationship determines the heat transfer and the effective degrees of freedom of that specific process.<i>Aims.<i/> In this paper we investigate in depth the relationship between the proton effective polytropic index <i>γ<i/> in the solar wind, the proton anisotropy <i>α<i/>, and plasma <i>β<i/>, while – for the first time to our knowledge to such an extent – we further investigate the dependence of the partial (with respect to the magnetic field) polytropic index to both the above-mentioned plasma parameters.<i>Methods.<i/> To this end we use the entire Wind dataset spanning the 1995 to 2023 time period to derive the distributions of the polytropic index in the near-Earth space (L1).<i>Results.<i/> Our results indicate that the proton <i>γ<i/> increases with increasing proton anisotropy and decreases with increasing plasma <i>β<i/>. Finally, we show that even though the average (over long time periods) total and partial proton polytropic index values are very close, these values correspond to isotropic plasma alone, with a further balance between the thermal and magnetic pressure.On the contrary, for shorter time periods and/or specific solar wind structures, where the proton anisotropy and plasma <i>β<i/> exhibit deviations from these average values, the partial proton polytropic index exhibits significant variation that is dependent on the anisotropy and on plasma <i>β<i/>.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"95 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598500","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 : 2024-11-08DOI: 10.1051/0004-6361/202451306
M. Dorsch, C. S. Jeffery, A. Philip Monai, C. A. Tout, E. J. Snowdon, I. Monageng, L. J. A. Scott, B. Miszalski, V. M. Woolf
Magnetic fields with strengths ranging from 300 to 500 kG have recently been discovered in a group of four extremely similar helium-rich hot subdwarf (He-sdO) stars. In addition to their strong magnetic fields, these He-sdO stars are characterised by common atmospheric parameters, clustering around Teff = 46 500 K, a log ɡ/cm s−1 close to 6, and intermediate helium abundances. Here we present the discovery of three additional magnetic hot subdwarfs, J123359.44–674929.11, J125611.42-575333.45, and J144405.79–674400.93. These stars are again almost identical in terms of atmospheric parameters, but, at B ≈ 200 kG, their magnetic fields are somewhat weaker than those previously known. The close similarity of all known He-sdOs implies a finely tuned formation channel. We propose the merging of a He white dwarf with a H+He white dwarf. A differential rotation at the merger interface may initiate a toroidal magnetic field that evolves via a magnetic dynamo to produce a poloidal field. This field is either directly visible at the surface or might diffuse towards the surface if initially buried. We further discuss a broad absorption line centred at about 4630 Å that is common to all magnetic He-sdOs. This feature may not be related to the magnetic field but instead to the intermediate helium abundances in these He-sdO stars, allowing the strong He II 4686 Å line to be perturbed by collisions with hydrogen atoms.
最近在一组由四颗极其相似的富氦热亚矮星（He-sdO）组成的恒星中发现了强度在300到500 kG之间的磁场。除了强磁场之外，这些He-sdO恒星还具有共同的大气参数：聚集在Teff = 46 500 K附近，log ɡ/cm s-1接近6，以及中等的氦丰度。在这里，我们又发现了三颗磁热亚矮星：J123359.44-674929.11、J125611.42-575333.45 和 J144405.79-674400.93。这些恒星的大气参数也几乎相同，但是在B ≈ 200 kG时，它们的磁场比以前已知的要弱一些。所有已知的氦-∑Os 都非常相似，这意味着它们的形成渠道经过了微调。我们提出了 He 白矮星与 H+He 白矮星合并的设想。合并界面上的差分旋转可能会引发环形磁场，通过磁动力演变产生极性磁场。这个磁场或者在表面直接可见，或者在最初被掩埋时向表面扩散。我们进一步讨论了以大约 4630 Å 为中心的宽吸收线，这是所有磁性 He-sdO 的共同特征。这一特征可能与磁场无关，而是与这些 He-sdO 恒星中的中等氦丰度有关，使得强 He II 4686 Å 线受到与氢原子碰撞的扰动。
{"title":"Discovery of three magnetic helium-rich hot subdwarfs with SALT","authors":"M. Dorsch, C. S. Jeffery, A. Philip Monai, C. A. Tout, E. J. Snowdon, I. Monageng, L. J. A. Scott, B. Miszalski, V. M. Woolf","doi":"10.1051/0004-6361/202451306","DOIUrl":"https://doi.org/10.1051/0004-6361/202451306","url":null,"abstract":"Magnetic fields with strengths ranging from 300 to 500 kG have recently been discovered in a group of four extremely similar helium-rich hot subdwarf (He-sdO) stars. In addition to their strong magnetic fields, these He-sdO stars are characterised by common atmospheric parameters, clustering around <i>T<i/><sub>eff<sub/> = 46 500 K, a log <i>ɡ<i/>/cm s<sup>−1<sup/> close to 6, and intermediate helium abundances. Here we present the discovery of three additional magnetic hot subdwarfs, J123359.44–674929.11, J125611.42-575333.45, and J144405.79–674400.93. These stars are again almost identical in terms of atmospheric parameters, but, at <i>B<i/> ≈ 200 kG, their magnetic fields are somewhat weaker than those previously known. The close similarity of all known He-sdOs implies a finely tuned formation channel. We propose the merging of a He white dwarf with a H+He white dwarf. A differential rotation at the merger interface may initiate a toroidal magnetic field that evolves via a magnetic dynamo to produce a poloidal field. This field is either directly visible at the surface or might diffuse towards the surface if initially buried. We further discuss a broad absorption line centred at about 4630 Å that is common to all magnetic He-sdOs. This feature may not be related to the magnetic field but instead to the intermediate helium abundances in these He-sdO stars, allowing the strong He II 4686 Å line to be perturbed by collisions with hydrogen atoms.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"54 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598286","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 : 2024-11-08DOI: 10.1051/0004-6361/202452071
Fabian Menezes, Alexandre Araújo, Adriana Valio
Context. Starspots, regions of strong magnetic fields, serve as indicators of stellar activity and the dynamo mechanism at play in the interior of stars. The magnetic fields of main-sequence stars play a crucial role in driving stellar activity. An effective approach to better understanding stellar magnetic fields and activity lies in the detailed characterisation of starspot properties.Aims. We propose a new method for estimating the magnetic fields of starspots that employs modelling techniques of planetary transit mapping, which provides estimates of the size, intensity, and location of spots on the stellar photosphere.Methods. A starspot’s maximum magnetic field was calculated using the linear relationship with the spot flux deficit, ΔFspot (the spot’s brightness times its area) and the well-characterised relation for sunspots determined in this work, Bspot = 1170 + 844log ΔFspot (G).Results. Applying this relationship to previously mapped spots on the photospheres of 14 FGK and M stars yields spot maximum magnetic fields ranging from 2700 G to 4600 G, with an overall average of 3900 ± 400 G. We looked for correlations between starspot magnetic fields and stellar properties. We did not find any correlation between a spot’s mean extreme magnetic field and effective temperature, nor the differential shear. However, a weak anti-correlation is seen between the spots’ magnetic field and stellar age as well as between the magnetic field and the rotation period.Conclusions. When compared with previous results of small-scale magnetic field measurements, the B values obtained here are basically constant and near the saturation limit found for rapid rotators. This implies that it is not the intensity of the magnetic field of starspots that decreases with age but rather the filling factor. This result offers a unique window into the magnetic dynamo of stars.
背景。星斑是强磁场区域，是恒星活动和恒星内部动力机制的指示器。主序恒星的磁场在驱动恒星活动方面起着至关重要的作用。更好地理解恒星磁场和活动的有效方法在于详细描述星斑的特性。我们提出了一种估算星斑磁场的新方法，利用行星凌日绘图的建模技术，对恒星光球上星斑的大小、强度和位置进行估算。星斑的最大磁场是利用星斑磁通量赤字ΔFspot（星斑亮度乘以其面积）的线性关系和这项工作中确定的太阳黑子的特征关系（Bspot = 1170 + 844log ΔFspot (G)）计算出来的。将这一关系应用于之前绘制的 14 颗 FGK 和 M 恒星光球上的斑点，得到的斑点最大磁场从 2700 G 到 4600 G 不等，总平均值为 3900 ± 400 G。我们没有发现星斑的平均极端磁场与有效温度或差分剪切力之间有任何相关性。然而，我们发现星斑磁场与恒星年龄以及磁场与自转周期之间存在微弱的反相关性。与之前的小尺度磁场测量结果相比，这里获得的 B 值基本恒定，接近快速旋转体的饱和极限。这意味着随着年龄的增长，星点的磁场强度并不会降低，而是填充因子会降低。这一结果为了解恒星的磁动力提供了一个独特的窗口。
{"title":"Probing the magnetic fields of starspots with transit mapping","authors":"Fabian Menezes, Alexandre Araújo, Adriana Valio","doi":"10.1051/0004-6361/202452071","DOIUrl":"https://doi.org/10.1051/0004-6361/202452071","url":null,"abstract":"<i>Context.<i/> Starspots, regions of strong magnetic fields, serve as indicators of stellar activity and the dynamo mechanism at play in the interior of stars. The magnetic fields of main-sequence stars play a crucial role in driving stellar activity. An effective approach to better understanding stellar magnetic fields and activity lies in the detailed characterisation of starspot properties.<i>Aims.<i/> We propose a new method for estimating the magnetic fields of starspots that employs modelling techniques of planetary transit mapping, which provides estimates of the size, intensity, and location of spots on the stellar photosphere.<i>Methods.<i/> A starspot’s maximum magnetic field was calculated using the linear relationship with the spot flux deficit, Δ<i>F<i/><sub>spot<sub/> (the spot’s brightness times its area) and the well-characterised relation for sunspots determined in this work, <i>B<i/><sub>spot<sub/> = 1170 + 844log Δ<i>F<i/><sub>spot<sub/> (G).<i>Results.<i/> Applying this relationship to previously mapped spots on the photospheres of 14 FGK and M stars yields spot maximum magnetic fields ranging from 2700 G to 4600 G, with an overall average of 3900 ± 400 G. We looked for correlations between starspot magnetic fields and stellar properties. We did not find any correlation between a spot’s mean extreme magnetic field and effective temperature, nor the differential shear. However, a weak anti-correlation is seen between the spots’ magnetic field and stellar age as well as between the magnetic field and the rotation period.<i>Conclusions.<i/> When compared with previous results of small-scale magnetic field measurements, the B values obtained here are basically constant and near the saturation limit found for rapid rotators. This implies that it is not the intensity of the magnetic field of starspots that decreases with age but rather the filling factor. This result offers a unique window into the magnetic dynamo of stars.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"34 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598501","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 : 2024-11-08DOI: 10.1051/0004-6361/202451511
Shuo Huang, Nienke van der Marel, Simon Portegies Zwart
Context. Protoplanetary disks surrounding young stars are the birth places of planets. Among them, transition disks with inner dust cavities of tens of au are sometimes suggested to host massive companions. Yet, such companions are often not detected.Aims. Some transition disks exhibit a large amount of gas inside the dust cavity and relatively high stellar accretion rates, which contradicts typical models of gas-giant-hosting systems. Therefore, we investigate whether a sequence of low-mass planets can create the appearance of cavities in the dust disk.Methods. We evolve the disks with low-mass growing embryos in combination with 1D dust transport and 3D pebble accretion, to investigate the reduction of the pebble flux at the embryos’ orbits. We vary the planet and disk properties to understand the resulting dust profile.Results. We find that multiple pebble-accreting planets can efficiently decrease the dust surface density, resulting in dust cavities consistent with transition disks. The number of low-mass planets necessary to sweep up all pebbles decreases with decreasing turbulent strength and is preferred when the dust Stokes number is 10−2 − 10−4. Compared to dust rings caused by pressure bumps, those by efficient pebble accretion exhibit more extended outer edges. We also highlight the observational reflections: the transition disks with rings featuring extended outer edges tend to have a large gas content in the dust cavities and rather high stellar accretion rates.Conclusions. We propose that planet-hosting transition disks consist of two groups. In Group A disks, planets have evolved into gas giants, opening deep gaps in the gas disk. Pebbles concentrate in pressure maxima, forming dust rings. In Group B, multiple Neptunes (unable to open deep gas gaps) accrete incoming pebbles, causing the appearance of inner dust cavities and distinct ring-like structures near planet orbits. The morphological discrepancy of these rings may aid in distinguishing between the two groups using high-resolution ALMA observations.
背景。年轻恒星周围的原行星盘是行星的诞生地。在这些星盘中，有的过渡星盘内部有数十u的尘埃空腔，有时被认为可以容纳大质量的伴星。然而，这类伴星往往没有被探测到。一些过渡盘的尘腔内有大量气体，恒星吸积率相对较高，这与典型的气体-大质量伴星系统模型相矛盾。因此，我们研究了一系列低质量行星是否会在尘埃盘中形成空腔。我们结合一维尘埃传输和三维卵石吸积来演化具有低质量成长胚胎的尘埃盘，以研究胚胎轨道上卵石通量的减少。我们改变了行星和星盘的属性，以了解由此产生的尘埃剖面。我们发现多颗卵石吸积行星可以有效地降低尘埃表面密度，从而产生与过渡盘一致的尘埃空洞。扫除所有卵石所需的低质量行星数量随着湍流强度的降低而减少，当尘埃斯托克斯数为10-2 - 10-4时，低质量行星是首选。与由压力凸起引起的尘埃环相比，由高效卵石吸积引起的尘埃环显示出更长的外缘。我们还强调了观测结果的反映：具有延伸外缘环的过渡盘往往尘腔中气体含量大，恒星吸积率相当高。我们提出行星寄居过渡盘由两组组成。在A组星盘中，行星已经演化成气体巨行星，在气体盘中打开了很深的空隙。鹅卵石集中在压力最大处，形成尘环。在 B 组中，多个海王星（无法打开深层气体间隙）吸积了进入的卵石，导致行星轨道附近出现内部尘穴和明显的环状结构。这些环的形态差异可能有助于利用高分辨率 ALMA 观测来区分这两组。
{"title":"Origin of transition disk cavities","authors":"Shuo Huang, Nienke van der Marel, Simon Portegies Zwart","doi":"10.1051/0004-6361/202451511","DOIUrl":"https://doi.org/10.1051/0004-6361/202451511","url":null,"abstract":"<i>Context<i/>. Protoplanetary disks surrounding young stars are the birth places of planets. Among them, transition disks with inner dust cavities of tens of au are sometimes suggested to host massive companions. Yet, such companions are often not detected.<i>Aims<i/>. Some transition disks exhibit a large amount of gas inside the dust cavity and relatively high stellar accretion rates, which contradicts typical models of gas-giant-hosting systems. Therefore, we investigate whether a sequence of low-mass planets can create the appearance of cavities in the dust disk.<i>Methods<i/>. We evolve the disks with low-mass growing embryos in combination with 1D dust transport and 3D pebble accretion, to investigate the reduction of the pebble flux at the embryos’ orbits. We vary the planet and disk properties to understand the resulting dust profile.<i>Results<i/>. We find that multiple pebble-accreting planets can efficiently decrease the dust surface density, resulting in dust cavities consistent with transition disks. The number of low-mass planets necessary to sweep up all pebbles decreases with decreasing turbulent strength and is preferred when the dust Stokes number is 10<sup>−2<sup/> − 10<sup>−4<sup/>. Compared to dust rings caused by pressure bumps, those by efficient pebble accretion exhibit more extended outer edges. We also highlight the observational reflections: the transition disks with rings featuring extended outer edges tend to have a large gas content in the dust cavities and rather high stellar accretion rates.<i>Conclusions<i/>. We propose that planet-hosting transition disks consist of two groups. In Group A disks, planets have evolved into gas giants, opening deep gaps in the gas disk. Pebbles concentrate in pressure maxima, forming dust rings. In Group B, multiple Neptunes (unable to open deep gas gaps) accrete incoming pebbles, causing the appearance of inner dust cavities and distinct ring-like structures near planet orbits. The morphological discrepancy of these rings may aid in distinguishing between the two groups using high-resolution ALMA observations.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"5 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598504","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 : 2024-11-08DOI: 10.1051/0004-6361/202451604
I. Martín-Navarro, A. Vazdekis
Over the last few decades, evolutionary population synthesis models have powered an unmatched leap forward in our understanding of galaxies. From dating the age of the first galaxies in the Universe to providing detailed measurements of the chemical composition of nearby galaxies, the success of this approach built upon simple stellar population (SSP) spectro-photometric models is unquestionable. However, the internal constraints inherent to the construction of SSP models can hinder our ability to analyze the integrated spectra of galaxies in situations where the SSP assumption does not sufficiently hold. Thus, here we revisit the possibilities of fitting galaxy spectra as a linear combination of stellar templates without assuming any a priori knowledge on stellar evolution. We showcase the sensitivity of this alternative approach to changes in the stellar population properties, in particular the direct connection to variations in the stellar initial mass function, as well as its advantages when dealing with noncanonical integrated populations and semi-resolved observations. Furthermore, our analysis demonstrates that the absorption spectra of galaxies can be used to independently constrain stellar evolution theory beyond the limited conditions of the solar neighborhood.
{"title":"Counting stars from the integrated spectra of galaxies","authors":"I. Martín-Navarro, A. Vazdekis","doi":"10.1051/0004-6361/202451604","DOIUrl":"https://doi.org/10.1051/0004-6361/202451604","url":null,"abstract":"Over the last few decades, evolutionary population synthesis models have powered an unmatched leap forward in our understanding of galaxies. From dating the age of the first galaxies in the Universe to providing detailed measurements of the chemical composition of nearby galaxies, the success of this approach built upon simple stellar population (SSP) spectro-photometric models is unquestionable. However, the internal constraints inherent to the construction of SSP models can hinder our ability to analyze the integrated spectra of galaxies in situations where the SSP assumption does not sufficiently hold. Thus, here we revisit the possibilities of fitting galaxy spectra as a linear combination of stellar templates without assuming any a priori knowledge on stellar evolution. We showcase the sensitivity of this alternative approach to changes in the stellar population properties, in particular the direct connection to variations in the stellar initial mass function, as well as its advantages when dealing with noncanonical integrated populations and semi-resolved observations. Furthermore, our analysis demonstrates that the absorption spectra of galaxies can be used to independently constrain stellar evolution theory beyond the limited conditions of the solar neighborhood.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"80 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598502","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 : 2024-11-08DOI: 10.1051/0004-6361/202450329
I. Martí-Vidal, C.-I. Björnsson, M. A. Pérez-Torres, P. Lundqvist, J. M. Marcaide
Context. Observations of radio emission from young core-collapse supernovae (CCSNe) allow one to study the history of the pre-supernova stellar wind, trace the density structure of the ejected material, and probe the magnetohydrodynamics that describe the interaction between the two, as the forward shock expands into the circumstellar medium. The radio shell of supernova SN 1993J has been observed with very long baseline interferometry (VLBI) for ∼20 years, giving one of the most complete pictures of the evolution of a CCSN shock. However, different results about the expansion curve and properties of the radio-emitting structure have been reported by different authors, likely due to systematics in the data calibration and/or model assumptions made by each team.Aims. We aim to perform an analysis of the complete set of VLBI observations of SN 1993J that accounts for different instrumental and source-intrinsic effects, in order to retrieve robust conclusions about the shock expansion and physics in SN 1993J.Methods. We have explored the posterior probability distribution of a complete data model, using a technique based on Markov chains. Our model accounts for antenna calibration effects, as well as different kinds of radio-emission structures for the supernova.Results. The posterior parameter distributions strongly favor a spherical shell-like radio structure with a nonuniform radial intensity profile, with a broad brightness distribution that peaks close to or just above the region where the contact discontinuity is expected to be located. Regarding the shell expansion, the full dataset can be well described using one single deceleration parameter, β ∼ 0.80, being the shell outer radius R ∝ tβ. There is clear evidence of a relative widening of the shell width beyond day 2600−3300 after the explosion, which is due to an increased deceleration of the inner shell boundary. This is similar to findings previously reported by other authors.Conclusions. The radial intensity profile and the late evolution of the shell suggest a scenario in which the magnetic field is amplified mainly by the Rayleigh-Taylor instability, which emanates from the contact discontinuity. Furthermore, the increased deceleration of the inner boundary indicates that the reverse shock enters a region of the ejecta at around 3000 days, where the density distribution is substantially flatter. Such a weakening of the reverse shock can also explain the achromatic break in the radio light curves, which occurs at the same time. The deduced radial intensity distribution for SN 1993J is quite similar to that observed in the spatially well-resolved supernova remnant Cassiopeia A.
背景通过对年轻的核坍缩超新星（CCSNe）射电辐射的观测，我们可以研究超新星前恒星风的历史，追踪抛射物质的密度结构，并探测描述前向冲击向周星际介质膨胀时两者相互作用的磁流体动力学。超新星 SN 1993J 的射电壳体已经被超长基线干涉测量法（VLBI）观测了 20 年之久，这是最完整的 CCSN 冲击演化图之一。然而，不同的作者对射电发射结构的膨胀曲线和特性有不同的报道，这可能是由于每个团队在数据校准和/或模型假设方面的系统性造成的。我们的目的是对 SN 1993J 的整套 VLBI 观测数据进行分析，以考虑不同的仪器效应和源内在效应，从而获得有关 SN 1993J 的冲击膨胀和物理特性的可靠结论。我们利用基于马尔可夫链的技术，探索了完整数据模型的后验概率分布。我们的模型考虑了天线校准效应以及超新星的不同射电发射结构。后验参数分布强烈倾向于一个具有非均匀径向强度剖面的球壳状射电结构，其亮度分布宽广，峰值接近或刚好高于预计的接触不连续性所在区域。关于壳的扩展，整个数据集可以用一个单一的减速参数β∼0.80（即壳的外半径R∝tβ）来很好地描述。有明显的证据表明，爆炸后第 2600-3300 天以后，壳体宽度相对增宽，这是由于壳体内边界的减速效应增强所致。这与其他作者之前报告的结果类似。壳体的径向强度分布和后期演变表明，磁场主要是由接触不连续性产生的瑞利-泰勒不稳定性放大的。此外，内部边界的减速增加表明，反向冲击在 3000 天左右进入了喷出物的一个区域，在这个区域，密度分布要平坦得多。反向冲击的减弱也可以解释同时出现的射电光曲线消色差断裂。推导出的SN 1993J的径向强度分布与在空间分辨率较高的超新星残余仙后座A中观测到的非常相似。
{"title":"The radial distribution of radio emission from SN 1993J: Magnetic field amplification due to the Rayleigh-Taylor instability","authors":"I. Martí-Vidal, C.-I. Björnsson, M. A. Pérez-Torres, P. Lundqvist, J. M. Marcaide","doi":"10.1051/0004-6361/202450329","DOIUrl":"https://doi.org/10.1051/0004-6361/202450329","url":null,"abstract":"<i>Context.<i/> Observations of radio emission from young core-collapse supernovae (CCSNe) allow one to study the history of the pre-supernova stellar wind, trace the density structure of the ejected material, and probe the magnetohydrodynamics that describe the interaction between the two, as the forward shock expands into the circumstellar medium. The radio shell of supernova SN 1993J has been observed with very long baseline interferometry (VLBI) for ∼20 years, giving one of the most complete pictures of the evolution of a CCSN shock. However, different results about the expansion curve and properties of the radio-emitting structure have been reported by different authors, likely due to systematics in the data calibration and/or model assumptions made by each team.<i>Aims.<i/> We aim to perform an analysis of the complete set of VLBI observations of SN 1993J that accounts for different instrumental and source-intrinsic effects, in order to retrieve robust conclusions about the shock expansion and physics in SN 1993J.<i>Methods.<i/> We have explored the posterior probability distribution of a complete data model, using a technique based on Markov chains. Our model accounts for antenna calibration effects, as well as different kinds of radio-emission structures for the supernova.<i>Results.<i/> The posterior parameter distributions strongly favor a spherical shell-like radio structure with a nonuniform radial intensity profile, with a broad brightness distribution that peaks close to or just above the region where the contact discontinuity is expected to be located. Regarding the shell expansion, the full dataset can be well described using one single deceleration parameter, <i>β<i/> ∼ 0.80, being the shell outer radius <i>R<i/> ∝ <i>t<i/><sup><i>β<i/><sup/>. There is clear evidence of a relative widening of the shell width beyond day 2600−3300 after the explosion, which is due to an increased deceleration of the inner shell boundary. This is similar to findings previously reported by other authors.<i>Conclusions.<i/> The radial intensity profile and the late evolution of the shell suggest a scenario in which the magnetic field is amplified mainly by the Rayleigh-Taylor instability, which emanates from the contact discontinuity. Furthermore, the increased deceleration of the inner boundary indicates that the reverse shock enters a region of the ejecta at around 3000 days, where the density distribution is substantially flatter. Such a weakening of the reverse shock can also explain the achromatic break in the radio light curves, which occurs at the same time. The deduced radial intensity distribution for SN 1993J is quite similar to that observed in the spatially well-resolved supernova remnant Cassiopeia A.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"28 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2024-11-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142598506","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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