Pub Date : 2025-12-10DOI: 10.1051/0004-6361/202555680
Charlotte Gehan
It has been observed that the fraction of low-mass (LM) stars (M ≤ 1.5 M⊙) showing photospheric activity in their light curve is larger on the horizontal branch (HB) than during the prior, red giant branch (RGB) phase, while the opposite trend has been observed for intermediate-mass (IM) stars (M > 1.5 M⊙). One hypothesis is that LM red giants (RGs) engulf more planets than IM RGs, which results in a faster surface rotation and a higher magnetic activity. This hypothesis is based on the fact that LM stars reach a maximum radius at the RGB tip that is much larger than that achieved for IM stars, making them more likely to engulf planets. However, we need to study the evolution of the active star fraction along the RGB to firmly check this hypothesis. I used independent indicators tracing the activity level in the chromosphere based on the Ca II H&K, Hα, Mg I, and infrared Ca II spectral lines from LAMOST data for ∼3000 RGs whose evolutionary stage has been determined by asteroseismology with the Kepler mission. I found that the fraction of active stars shows different trends for LM and IM stars along the RGB, decreasing for IM stars, but unexpectedly increasing for LM stars. Such an increase cannot be explained by models of single-star evolution and it is consistent with the fact that LM stars are more likely than IM stars to engulf planets. Indeed, the data show that IM main sequence stars exhibit a dearth of planets, which is consistent with predictions from planet formation theory. In addition, I observe that the fraction of active stars tends to increase for both LM and IM stars on the HB, which stands in partial contrast with previous findings. Finally, I discovered that the IM RGB star KIC 9780154 might have engulfed one or more planet(s) as its surface rotation from photometry is twice faster than its envelope rotation from asteroseismology. Characterizing planet engulfment by RGs provides insights into the evolution and fate of most planetary systems, since ∼97% of stars pass through the RG evolution stage.
{"title":"Evolution of stellar magnetic activity: Probing planet engulfment by red giants","authors":"Charlotte Gehan","doi":"10.1051/0004-6361/202555680","DOIUrl":"https://doi.org/10.1051/0004-6361/202555680","url":null,"abstract":"It has been observed that the fraction of low-mass (LM) stars (<i>M<i/> ≤ 1.5 <i>M<i/><sub>⊙<sub/>) showing photospheric activity in their light curve is larger on the horizontal branch (HB) than during the prior, red giant branch (RGB) phase, while the opposite trend has been observed for intermediate-mass (IM) stars (<i>M<i/> > 1.5 <i>M<i/><sub>⊙<sub/>). One hypothesis is that LM red giants (RGs) engulf more planets than IM RGs, which results in a faster surface rotation and a higher magnetic activity. This hypothesis is based on the fact that LM stars reach a maximum radius at the RGB tip that is much larger than that achieved for IM stars, making them more likely to engulf planets. However, we need to study the evolution of the active star fraction along the RGB to firmly check this hypothesis. I used independent indicators tracing the activity level in the chromosphere based on the Ca II H&K, H<i>α<i/>, Mg I, and infrared Ca II spectral lines from LAMOST data for ∼3000 RGs whose evolutionary stage has been determined by asteroseismology with the <i>Kepler<i/> mission. I found that the fraction of active stars shows different trends for LM and IM stars along the RGB, decreasing for IM stars, but unexpectedly increasing for LM stars. Such an increase cannot be explained by models of single-star evolution and it is consistent with the fact that LM stars are more likely than IM stars to engulf planets. Indeed, the data show that IM main sequence stars exhibit a dearth of planets, which is consistent with predictions from planet formation theory. In addition, I observe that the fraction of active stars tends to increase for both LM and IM stars on the HB, which stands in partial contrast with previous findings. Finally, I discovered that the IM RGB star KIC 9780154 might have engulfed one or more planet(s) as its surface rotation from photometry is twice faster than its envelope rotation from asteroseismology. Characterizing planet engulfment by RGs provides insights into the evolution and fate of most planetary systems, since ∼97% of stars pass through the RG evolution stage.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"72 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145711527","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 : 2025-12-10DOI: 10.1051/0004-6361/202557141
Daniele Manzoni, Andrea Ferrara
Order-unity star formation efficiencies (SFE) in early galaxies may explain the overabundance of bright galaxies observed by JWST at high redshift. Here we show that Lyman-α (Lyα) radiation pressure limits the gas mass converted into stars, particularly in primordial environments. We have developed a shell model including Lyα feedback, and we validate it with one-dimensional hydrodynamical simulations. To account for Lyα resonant scattering, we adopted the most recent force multiplier fits, including the effect of Lyα photon destruction by dust grains. We find that independent of their gas surface density, Σg, clouds are disrupted on a timescale shorter than the free-fall time and even before supernova explosions if . At log(Z/Z⊙) = − 2, which is relevant for high-redshift galaxies, the SFE is for . The SFE is even lower for decreasing metallicity. Bursts of star formation with near-unity SFEs are possible only for extreme surface densities, , and near-solar metallicities. We conclude that Lyα radiation pressure severely limits a possible extremely efficient, feedback-free phase of star formation in dense metal-poor clouds.
{"title":"Lyman-α radiation pressure regulates star formation efficiency","authors":"Daniele Manzoni, Andrea Ferrara","doi":"10.1051/0004-6361/202557141","DOIUrl":"https://doi.org/10.1051/0004-6361/202557141","url":null,"abstract":"Order-unity star formation efficiencies (SFE) in early galaxies may explain the overabundance of bright galaxies observed by JWST at high redshift. Here we show that Lyman-<i>α<i/> (Ly<i>α<i/>) radiation pressure limits the gas mass converted into stars, particularly in primordial environments. We have developed a shell model including Ly<i>α<i/> feedback, and we validate it with one-dimensional hydrodynamical simulations. To account for Ly<i>α<i/> resonant scattering, we adopted the most recent force multiplier fits, including the effect of Ly<i>α<i/> photon destruction by dust grains. We find that independent of their gas surface density, Σ<sub><i>g<i/><sub/>, clouds are disrupted on a timescale shorter than the free-fall time and even before supernova explosions if . At log(<i>Z<i/>/<i>Z<i/><sub>⊙<sub/>) = − 2, which is relevant for high-redshift galaxies, the SFE is for . The SFE is even lower for decreasing metallicity. Bursts of star formation with near-unity SFEs are possible only for extreme surface densities, , and near-solar metallicities. We conclude that Ly<i>α<i/> radiation pressure severely limits a possible extremely efficient, feedback-free phase of star formation in dense metal-poor clouds.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"7 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145711529","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 : 2025-12-10DOI: 10.1051/0004-6361/202555267
Yongmin Yoon, Yongjung Kim, Dohyeong Kim, Kyungwon Chun, Woowon Byun
We examine the connection between galaxy mergers and the triggering of active galactic nuclei (AGNs) using a sample of 614 type 1 AGNs at z < 0.07, along with a control sample of inactive galaxies matched to the AGNs for comparison. We used tidal features, detected in deep images from the DESI Legacy Imaging Survey, as direct evidence of recent mergers. We find that the fraction of type 1 AGN hosts with tidal features (fT) is higher for AGNs with higher luminosities and (to a lesser extent) more massive black holes. Specifically, fT rapidly increases from 0.05 ± 0.03 to 0.75 ± 0.13 as the luminosity of the [O III] λ5007 emission line (L[O III]), an indicator for bolometric AGN luminosity, increases in the range 1039.5 ≲ L[O III]/(erg s−1) ≲ 1042.5. In addition, fT increases from 0.13 ± 0.03 to 0.43 ± 0.09 as black hole mass (MBH) increases in the range 106.0 ≲ MBH/M⊙ ≲ 108.5. The fraction fT also increases with the Eddington ratio, although the trend is less significant compared to that with L[O III] and MBH. The excess of fT, defined as the ratio of fT for AGNs to that of their matched inactive counterparts, exhibits similar trends, primarily increasing with L[O III] and weakly with MBH. Our results indicate that, in the local Universe, galaxy mergers are the predominant triggering mechanism for high-luminosity AGNs, whereas they play a lesser role in triggering lower-luminosity AGNs. Additionally, strong events, such as galaxy mergers, may be more necessary to activate massive black holes in more massive galaxies due to their lower gas fractions.
{"title":"Direct observational evidence that higher-luminosity type 1 active galactic nuclei are most commonly triggered by galaxy mergers","authors":"Yongmin Yoon, Yongjung Kim, Dohyeong Kim, Kyungwon Chun, Woowon Byun","doi":"10.1051/0004-6361/202555267","DOIUrl":"https://doi.org/10.1051/0004-6361/202555267","url":null,"abstract":"We examine the connection between galaxy mergers and the triggering of active galactic nuclei (AGNs) using a sample of 614 type 1 AGNs at <i>z<i/> < 0.07, along with a control sample of inactive galaxies matched to the AGNs for comparison. We used tidal features, detected in deep images from the DESI Legacy Imaging Survey, as direct evidence of recent mergers. We find that the fraction of type 1 AGN hosts with tidal features (<i>f<i/><sub>T<sub/>) is higher for AGNs with higher luminosities and (to a lesser extent) more massive black holes. Specifically, <i>f<i/><sub>T<sub/> rapidly increases from 0.05 ± 0.03 to 0.75 ± 0.13 as the luminosity of the [O III] <i>λ<i/>5007 emission line (<i>L<i/><sub>[O III]<sub/>), an indicator for bolometric AGN luminosity, increases in the range 10<sup>39.5<sup/> ≲ <i>L<i/><sub>[O III]<sub/>/(erg s<sup>−1<sup/>) ≲ 10<sup>42.5<sup/>. In addition, <i>f<i/><sub>T<sub/> increases from 0.13 ± 0.03 to 0.43 ± 0.09 as black hole mass (<i>M<i/><sub>BH<sub/>) increases in the range 10<sup>6.0<sup/> ≲ <i>M<i/><sub>BH<sub/>/<i>M<i/><sub>⊙<sub/> ≲ 10<sup>8.5<sup/>. The fraction <i>f<i/><sub>T<sub/> also increases with the Eddington ratio, although the trend is less significant compared to that with <i>L<i/><sub>[O III]<sub/> and <i>M<i/><sub>BH<sub/>. The excess of <i>f<i/><sub>T<sub/>, defined as the ratio of <i>f<i/><sub>T<sub/> for AGNs to that of their matched inactive counterparts, exhibits similar trends, primarily increasing with <i>L<i/><sub>[O III]<sub/> and weakly with <i>M<i/><sub>BH<sub/>. Our results indicate that, in the local Universe, galaxy mergers are the predominant triggering mechanism for high-luminosity AGNs, whereas they play a lesser role in triggering lower-luminosity AGNs. Additionally, strong events, such as galaxy mergers, may be more necessary to activate massive black holes in more massive galaxies due to their lower gas fractions.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"7 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145711537","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 : 2025-12-09DOI: 10.1051/0004-6361/202555130
Jonathan Petersson, Michaela Hirschmann, Robin G. Tress, Marion Farcy, Simon C. O. Glover, Ralf S. Klessen, Thorsten Naab, Christian Partmann, David J. Whitworth
Aims. We study the individual and cumulative impact of stellar feedback on massive black hole (MBH) growth in a simulated low-mass dwarf galaxy. Furthermore, we explore the influence of the MBH’s initial mass (103−6 M⊙) on the gas accretion, and whether or not artificially induced gas inflows can ‘boost’ further gas accretion onto the MBH.Methods. A suite of high-resolution radiation-hydrodynamic simulations called NOCTUA were performed, using the AREPONOCTUA numerical framework. The chemical evolution of the interstellar medium (ISM) was modelled in a time-dependent non-equilibrium way. Two types of stellar feedback were considered: individually traced type II supernova (SNII) explosions, and radiatively transferred (on-the-fly) ionising stellar radiation (ISR) from OB stars. As part of AREPONOCTUA, we develop and apply a novel physically motivated model for MBH gas accretion, taking into account the angular momentum of the gas in the radiatively efficient regime, to estimate the gas accretion rate onto the MBH from its sub-grid accretion disc.Results. Without any stellar feedback, an initial 104 M⊙ MBH is able to steadily grow over time, roughly doubling its mass after 800 Myr. Surprisingly, the growth of the MBH more than doubles when only ISR feedback is considered, compared to the no stellar feedback run. This is due to the star formation rate (SFR) being highly suppressed (to a similar level or slightly above that when SNII feedback is considered), enabling a higher cumulative net gas inflow onto the MBH from not only the cold neutral and molecular medium phases, but also the unstable and warm neutral medium phases of the ISM. With SNII feedback included, the gas accretion onto the MBH is episodic over time, and is already suppressed by more than an order of magnitude during the first 150 Myr. When combining SNII with ISR feedback, the growth of the MBH remains suppressed due to SNII explosions, but to a lesser extent compared to the SNII-only feedback run, due to a slightly lower SFR, and thus a reduced number of SNII events.Conclusions. We conclude that SNII feedback is a strong regulator and suppressor of MBH growth, and that only an initial 105 M⊙ MBH is able to consistently accrete gas in the radiatively efficient regime (in the presence of SNII feedback). Combined with the fact that artificially induced gas inflows are unable to boost further gas accretion onto the MBH (even for an initial 106 M⊙ MBH), this suggests that it is primarily the nearby gravitational potential around the MBH that determines how much the MBH can grow via gas accretion over time (at least in an isolated non-cosmological environment).
{"title":"NOCTUA suite of simulations","authors":"Jonathan Petersson, Michaela Hirschmann, Robin G. Tress, Marion Farcy, Simon C. O. Glover, Ralf S. Klessen, Thorsten Naab, Christian Partmann, David J. Whitworth","doi":"10.1051/0004-6361/202555130","DOIUrl":"https://doi.org/10.1051/0004-6361/202555130","url":null,"abstract":"<i>Aims.<i/> We study the individual and cumulative impact of stellar feedback on massive black hole (MBH) growth in a simulated low-mass dwarf galaxy. Furthermore, we explore the influence of the MBH’s initial mass (10<sup>3−6<sup/> M<sub>⊙<sub/>) on the gas accretion, and whether or not artificially induced gas inflows can ‘boost’ further gas accretion onto the MBH.<i>Methods.<i/> A suite of high-resolution radiation-hydrodynamic simulations called NOCTUA were performed, using the AREPONOCTUA numerical framework. The chemical evolution of the interstellar medium (ISM) was modelled in a time-dependent non-equilibrium way. Two types of stellar feedback were considered: individually traced type II supernova (SNII) explosions, and radiatively transferred (on-the-fly) ionising stellar radiation (ISR) from OB stars. As part of AREPONOCTUA, we develop and apply a novel physically motivated model for MBH gas accretion, taking into account the angular momentum of the gas in the radiatively efficient regime, to estimate the gas accretion rate onto the MBH from its sub-grid accretion disc.<i>Results.<i/> Without any stellar feedback, an initial 10<sup>4<sup/> M<sub>⊙<sub/> MBH is able to steadily grow over time, roughly doubling its mass after 800 Myr. Surprisingly, the growth of the MBH more than doubles when only ISR feedback is considered, compared to the no stellar feedback run. This is due to the star formation rate (SFR) being highly suppressed (to a similar level or slightly above that when SNII feedback is considered), enabling a higher cumulative net gas inflow onto the MBH from not only the cold neutral and molecular medium phases, but also the unstable and warm neutral medium phases of the ISM. With SNII feedback included, the gas accretion onto the MBH is episodic over time, and is already suppressed by more than an order of magnitude during the first 150 Myr. When combining SNII with ISR feedback, the growth of the MBH remains suppressed due to SNII explosions, but to a lesser extent compared to the SNII-only feedback run, due to a slightly lower SFR, and thus a reduced number of SNII events.<i>Conclusions.<i/> We conclude that SNII feedback is a strong regulator and suppressor of MBH growth, and that only an initial 10<sup>5<sup/> M<sub>⊙<sub/> MBH is able to consistently accrete gas in the radiatively efficient regime (in the presence of SNII feedback). Combined with the fact that artificially induced gas inflows are unable to boost further gas accretion onto the MBH (even for an initial 10<sup>6<sup/> M<sub>⊙<sub/> MBH), this suggests that it is primarily the nearby gravitational potential around the MBH that determines how much the MBH can grow via gas accretion over time (at least in an isolated non-cosmological environment).","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"39 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145711526","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 : 2025-12-09DOI: 10.1051/0004-6361/202553882
Baoyi Zeng, Marc-Antoine Martinod, Denis Defrère
Context. Accurate null depth retrieval is critical in nulling interferometry. However, achieving accurate null depth calibration is challenging due to various noise sources, instrumental imperfections, and the complexity of real observational environments. These challenges necessitate advanced calibration techniques that can efficiently handle such uncertainties while maintaining a high accuracy.Aims. This paper aims to incorporate machine-learning techniques with a Bayesian inference to improve the accuracy and efficiency of null depth retrieval in nulling interferometry. Specifically, it explores the use of neural posterior estimation (NPE) to develop models that overcome the computational limitations of conventional methods, such as numerical self-calibration (NSC), providing a more robust solution for accurate null depth calibration.Methods. An NPE-based model was developed, with a simulator that incorporates real data to better represent specific conditions. The model was tested on both synthetic and observational data from the LBTI nuller for evaluation.Results. The NPE model successfully demonstrated improved efficiency, achieving results comparable to current methods in use. It achieved a null depth retrieval accuracy down to a few 10−4 on real observational data, matching the performance of conventional approaches while offering significant computational advantages, reducing the data retrieval time to one-quarter of the time required by self-calibration methods.Conclusions. The NPE model presents a practical and scalable solution for null depth calibration in nulling interferometry, offering substantial improvements in efficiency over existing methods with a better precision and application to other interferometric techniques.
{"title":"A scalable and accurate framework for self-calibrating null depth retrieval using neural posterior estimation","authors":"Baoyi Zeng, Marc-Antoine Martinod, Denis Defrère","doi":"10.1051/0004-6361/202553882","DOIUrl":"https://doi.org/10.1051/0004-6361/202553882","url":null,"abstract":"<i>Context<i/>. Accurate null depth retrieval is critical in nulling interferometry. However, achieving accurate null depth calibration is challenging due to various noise sources, instrumental imperfections, and the complexity of real observational environments. These challenges necessitate advanced calibration techniques that can efficiently handle such uncertainties while maintaining a high accuracy.<i>Aims<i/>. This paper aims to incorporate machine-learning techniques with a Bayesian inference to improve the accuracy and efficiency of null depth retrieval in nulling interferometry. Specifically, it explores the use of neural posterior estimation (NPE) to develop models that overcome the computational limitations of conventional methods, such as numerical self-calibration (NSC), providing a more robust solution for accurate null depth calibration.<i>Methods<i/>. An NPE-based model was developed, with a simulator that incorporates real data to better represent specific conditions. The model was tested on both synthetic and observational data from the LBTI nuller for evaluation.<i>Results<i/>. The NPE model successfully demonstrated improved efficiency, achieving results comparable to current methods in use. It achieved a null depth retrieval accuracy down to a few 10<sup>−4<sup/> on real observational data, matching the performance of conventional approaches while offering significant computational advantages, reducing the data retrieval time to one-quarter of the time required by self-calibration methods.<i>Conclusions<i/>. The NPE model presents a practical and scalable solution for null depth calibration in nulling interferometry, offering substantial improvements in efficiency over existing methods with a better precision and application to other interferometric techniques.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"144 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145711530","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 : 2025-12-09DOI: 10.1051/0004-6361/202555043
Herbert Gunell, Gabriella Stenberg Wieser, Anja Moeslinger, Charlotte Goetz, Romain Canu-Blot, Pierre Henri
In the plasma environment of a comet, waves are generated on vastly different temporal and spatial scales. Wave observations were carried out during the cometary flybys in the 1980s and 1990s as well as by the Rosetta spacecraft which accompanied comet 67P/Churyumov-Gerasimenko between 2014 and 2016. Waves are thought to contribute to the transfer of energy in the ionised coma. One of the fundamental plasma waves observed in space is the Langmuir wave, which appears at or above the electron plasma frequency. The Mutual Impedance Probe of the Rosetta Plasma Consortium (RPC-MIP) recorded frequency spectra of electric field fluctuations in the cometary plasma, and we used these spectra in order to detect and identify Langmuir waves. Langmuir waves were found during the part of the Rosetta mission when the comet was less than 2.65-2.8 AU from the Sun. The Langmuir waves appear near, but always outside, the diamagnetic cavity boundary, in a region where, at much lower frequencies, steepened magnetosonic waves also are present.
{"title":"Langmuir waves observed at comet 67P/Churyumov-Gerasimenko","authors":"Herbert Gunell, Gabriella Stenberg Wieser, Anja Moeslinger, Charlotte Goetz, Romain Canu-Blot, Pierre Henri","doi":"10.1051/0004-6361/202555043","DOIUrl":"https://doi.org/10.1051/0004-6361/202555043","url":null,"abstract":"In the plasma environment of a comet, waves are generated on vastly different temporal and spatial scales. Wave observations were carried out during the cometary flybys in the 1980s and 1990s as well as by the Rosetta spacecraft which accompanied comet 67P/Churyumov-Gerasimenko between 2014 and 2016. Waves are thought to contribute to the transfer of energy in the ionised coma. One of the fundamental plasma waves observed in space is the Langmuir wave, which appears at or above the electron plasma frequency. The Mutual Impedance Probe of the Rosetta Plasma Consortium (RPC-MIP) recorded frequency spectra of electric field fluctuations in the cometary plasma, and we used these spectra in order to detect and identify Langmuir waves. Langmuir waves were found during the part of the Rosetta mission when the comet was less than 2.65-2.8 AU from the Sun. The Langmuir waves appear near, but always outside, the diamagnetic cavity boundary, in a region where, at much lower frequencies, steepened magnetosonic waves also are present.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"7 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145711531","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 : 2025-12-09DOI: 10.1051/0004-6361/202554393
Anthony Noll, Sarbani Basu, Saskia Hekker
Context. Red clump (RC) stars still pose open questions regarding several physical processes, such as the mixing around the core or the nuclear reactions, which are ill-constrained by theory and experiments. The oscillations of RC stars, which are of a mixed gravito-acoustic nature, allow us to directly investigate the interior of these stars and thereby better understand their physics. In particular, the measurement of their period spacing is a good probe of the structure around the core.Aims. We aim to explain the distribution of period spacings in RC stars observed by Kepler by testing different prescriptions of core-boundary mixing and the nuclear reaction rate.Methods. Using the MESA stellar evolution code, we computed several grids of core-helium-burning tracks, with varying masses and metallicities. Each of these grids has been computed assuming a certain core boundary mixing scheme, or 12C(α, γ)16O reaction rate. We then sampled these grids, in a Monte-Carlo fashion, using observational spectroscopic metallicity and seismic mass priors, in order to retrieve a period spacing distribution, which we compared to the observations.Results. We find that the best-fitting distribution is obtained when using a “maximal overshoot” core-boundary scheme, which has similar seismic properties as a model whose modes are trapped outside a semi-convective region, and which does not exhibit core-breathing pulses at the end of the core-helium-burning phase. If no mode trapping is assumed, then no core boundary mixing scheme is compatible with the observations. Moreover, we find that extending the core with overshoot worsens the fit. Additionally, reducing the 12C(α, γ)16O reaction rate (by around 15%) improves the fit to the observed distribution. Finally, we note that an overpopulation of early RC stars with period spacing values around 250 s is predicted by the models but not found in the observations.Conclusions. Assuming a semi-convective region and mode trapping, along with a slightly lower than nominal 12C(α, γ)16O rate, allowed us to reproduce most of the features of the observed period spacing distribution, except for those of early RC stars.
{"title":"Ensemble seismic study of the properties of the core of red clump stars","authors":"Anthony Noll, Sarbani Basu, Saskia Hekker","doi":"10.1051/0004-6361/202554393","DOIUrl":"https://doi.org/10.1051/0004-6361/202554393","url":null,"abstract":"<i>Context.<i/> Red clump (RC) stars still pose open questions regarding several physical processes, such as the mixing around the core or the nuclear reactions, which are ill-constrained by theory and experiments. The oscillations of RC stars, which are of a mixed gravito-acoustic nature, allow us to directly investigate the interior of these stars and thereby better understand their physics. In particular, the measurement of their period spacing is a good probe of the structure around the core.<i>Aims.<i/> We aim to explain the distribution of period spacings in RC stars observed by <i>Kepler<i/> by testing different prescriptions of core-boundary mixing and the nuclear reaction rate.<i>Methods.<i/> Using the MESA stellar evolution code, we computed several grids of core-helium-burning tracks, with varying masses and metallicities. Each of these grids has been computed assuming a certain core boundary mixing scheme, or <sup>12<sup/>C(<i>α<i/>, <i>γ<i/>)<sup>16<sup/>O reaction rate. We then sampled these grids, in a Monte-Carlo fashion, using observational spectroscopic metallicity and seismic mass priors, in order to retrieve a period spacing distribution, which we compared to the observations.<i>Results.<i/> We find that the best-fitting distribution is obtained when using a “maximal overshoot” core-boundary scheme, which has similar seismic properties as a model whose modes are trapped outside a semi-convective region, and which does not exhibit core-breathing pulses at the end of the core-helium-burning phase. If no mode trapping is assumed, then no core boundary mixing scheme is compatible with the observations. Moreover, we find that extending the core with overshoot worsens the fit. Additionally, reducing the <sup>12<sup/>C(<i>α<i/>, <i>γ<i/>)<sup>16<sup/>O reaction rate (by around 15%) improves the fit to the observed distribution. Finally, we note that an overpopulation of early RC stars with period spacing values around 250 s is predicted by the models but not found in the observations.<i>Conclusions.<i/> Assuming a semi-convective region and mode trapping, along with a slightly lower than nominal <sup>12<sup/>C(<i>α<i/>, <i>γ<i/>)<sup>16<sup/>O rate, allowed us to reproduce most of the features of the observed period spacing distribution, except for those of early RC stars.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"169 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145711524","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}
1ES 1927+654 has exhibited a spectroscopic changing-look transition following dramatic ultraviolet/optical (UV/optical) and X-ray variability in recent years. X-ray observations have revealed a rapid flux decline, when the hard X-ray power-law component disappeared, the soft thermal emission reached a minimum ∼150 days after the UV/optical peak, and both components reemerged with the source re-brightening. This extreme variability suggests the destruction and subsequent reformation of the inner disk and corona. Here, we report the discovery of quasiperiodic X-ray variability with a period of ∼12 days (significance > 3.2σ), which persisted for about 220 days, based on high-cadence monitoring during the inner disk-corona rebuilding phase. The signal is coherent with a very high quality factor of ∼58. We interpret this periodicity as a signature of radiation-pressure instability in the accretion disk, which occurs when the accretion rate and magnetic field strength reach appropriate values. This mechanism has been proposed as an explanation for quasiperiodic eruptions, a recently discovered intriguing phenomenon associated with galactic nuclei. Our findings provide a representative example of disk instability at moderate accretion rates. This phenomenon was long predicted by accretion theory, but rarely observed in active galactic nuclei (AGNs). Our research suggests that extreme events in AGNs, such as tidal disruption events, could serve as novel probes for testing and refining accretion theory.
{"title":"Microhertz oscillations during the reformation of the inner disk-corona in the changing-look active galactic nucleus 1ES 1927+654","authors":"Wenjie Zhang, Xin Pan, Mingjun Liu, Tao Wu, Xinwen Shu, Luming Sun, Lei Yang, Bifang Liu, Chichuan Jin, Yuan Liu, Weimin Yuan","doi":"10.1051/0004-6361/202556066","DOIUrl":"https://doi.org/10.1051/0004-6361/202556066","url":null,"abstract":"1ES 1927+654 has exhibited a spectroscopic changing-look transition following dramatic ultraviolet/optical (UV/optical) and X-ray variability in recent years. X-ray observations have revealed a rapid flux decline, when the hard X-ray power-law component disappeared, the soft thermal emission reached a minimum ∼150 days after the UV/optical peak, and both components reemerged with the source re-brightening. This extreme variability suggests the destruction and subsequent reformation of the inner disk and corona. Here, we report the discovery of quasiperiodic X-ray variability with a period of ∼12 days (significance > 3.2<i>σ<i/>), which persisted for about 220 days, based on high-cadence monitoring during the inner disk-corona rebuilding phase. The signal is coherent with a very high quality factor of ∼58. We interpret this periodicity as a signature of radiation-pressure instability in the accretion disk, which occurs when the accretion rate and magnetic field strength reach appropriate values. This mechanism has been proposed as an explanation for quasiperiodic eruptions, a recently discovered intriguing phenomenon associated with galactic nuclei. Our findings provide a representative example of disk instability at moderate accretion rates. This phenomenon was long predicted by accretion theory, but rarely observed in active galactic nuclei (AGNs). Our research suggests that extreme events in AGNs, such as tidal disruption events, could serve as novel probes for testing and refining accretion theory.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"6 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145711523","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 : 2025-12-09DOI: 10.1051/0004-6361/202556215
C.-Z. Jiang, J.-X. Wang, H. Sou, W.-K. Ren
Context. The single-epoch virial method is a fundamental tool for estimating supermassive black hole (SMBH) masses in large samples of active galactic nuclei (AGNs) and has been extensively employed in studies of SMBH–galaxy coevolution across cosmic time. However, since this method is calibrated using reverberation-mapped AGNs, its validity across the entire AGN population remains uncertain.Aims. We aim to examine the breathing effect–the variability of emission line widths with continuum luminosity–beyond reverberation-mapped AGNs, to assess the validity and estimate potential systematic uncertainties of single-epoch virial black hole mass estimates.Methods. We constructed an unprecedentedly large multi-epoch spectroscopic dataset of quasars from Sloan Digital Sky Survey data release 16 (SDSS DR16), focusing on four key broad emission lines (Hα, Hβ, Mg II, and C IV). We assessed how breathing behavior evolves with the rest-frame time interval between observations.Results. We detect no significant breathing signal in Hα, Hβ, or Mg II at any observed timescale. In contrast, C IV exhibits a statistically significant anti-breathing trend, most prominent at intermediate timescales. Notably, for Hβ, which has shown breathing in previous reverberation-mapped samples, we recover the effect only in the small subset of quasars with clearly detected broad-line region (BLR) lags and only during the epochs when such lags are measurable–suggesting that both the lag and breathing signals are intermittent, possibly due to a weak correlation between optical and ionizing continua. These results highlight the complex, variable, and timescale-dependent nature of line profile variability and underscore its implications for single-epoch black hole mass estimates.
{"title":"A timescale-resolved analysis of the breathing effect in quasar broad-line regions","authors":"C.-Z. Jiang, J.-X. Wang, H. Sou, W.-K. Ren","doi":"10.1051/0004-6361/202556215","DOIUrl":"https://doi.org/10.1051/0004-6361/202556215","url":null,"abstract":"<i>Context.<i/> The single-epoch virial method is a fundamental tool for estimating supermassive black hole (SMBH) masses in large samples of active galactic nuclei (AGNs) and has been extensively employed in studies of SMBH–galaxy coevolution across cosmic time. However, since this method is calibrated using reverberation-mapped AGNs, its validity across the entire AGN population remains uncertain.<i>Aims.<i/> We aim to examine the breathing effect–the variability of emission line widths with continuum luminosity–beyond reverberation-mapped AGNs, to assess the validity and estimate potential systematic uncertainties of single-epoch virial black hole mass estimates.<i>Methods.<i/> We constructed an unprecedentedly large multi-epoch spectroscopic dataset of quasars from Sloan Digital Sky Survey data release 16 (SDSS DR16), focusing on four key broad emission lines (H<i>α<i/>, H<i>β<i/>, Mg II, and C IV). We assessed how breathing behavior evolves with the rest-frame time interval between observations.<i>Results.<i/> We detect no significant breathing signal in H<i>α<i/>, H<i>β<i/>, or Mg II at any observed timescale. In contrast, C IV exhibits a statistically significant anti-breathing trend, most prominent at intermediate timescales. Notably, for H<i>β<i/>, which has shown breathing in previous reverberation-mapped samples, we recover the effect only in the small subset of quasars with clearly detected broad-line region (BLR) lags and only during the epochs when such lags are measurable–suggesting that both the lag and breathing signals are intermittent, possibly due to a weak correlation between optical and ionizing continua. These results highlight the complex, variable, and timescale-dependent nature of line profile variability and underscore its implications for single-epoch black hole mass estimates.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"29 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145711525","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 : 2025-12-09DOI: 10.1051/0004-6361/202555203
A. P. Jones, N. Ysard
Context. Hydrogenated amorphous carbon materials, a-C(:H), are heterogeneous structures consisting of carbon atoms in different hybridisation states and bonding configurations and are thought to constitute a significant and observationally important fraction of the interstellar dust material. The stability of interstellar a-C(:H) nanoparticles against photo-thermo-dissociation and Coulomb fragmentation needs to take their intrinsic heterogeneity into account.Aims. This work aims to characterise semi-conducting a-C(:H) nanoparticle structures and, in particular, their property-characterising aromatic domain size distribution and so predict how they will behave in intense UV radiation fields that can fragment them through dissociative and charge effects as a result of carbon-carbon bond-breaking.Methods. Using a statistical approach, we determined the typical sizes of the aromatic domains, their size distribution, how they are network-bonded, and where they are to be found within the structure. We consider the effects of thermal excitation, photo-dissociation and charging of a-C(:H) nanoparticles, and the products of their fragmentation.Results. The derived UV photon-induced fragmentation lifetimes for nanometre-sized a-C(:H) nanoparticles, with radii ∼0.4-0.5 nm radius and containing ∼40-60 carbon atoms, are of the order of 106-107 yr in the diffuse interstellar medium and likely 102-104 times shorter in photodissociation regions, depending on the local radiation field intensity. Grains larger than this are stable against photodissociation. In HII regions only a-C(:H) nanoparticles with radii greater than 0.7 nm (≳150 carbon atoms) are likely to survive.Conclusions. The photon-driven fragmentation of sub-nanometre a-C(:H) particles was determined to be important in the diffuse interstellar medium and also in high excitation regions, such as photodissociation and H II regions. However, in these same regions Coulomb fragmentation is unlikely to be an important dust destruction process.
上下文。氢化非晶碳材料，a- c (:H)，是由不同杂化状态和成键构型的碳原子组成的非均相结构，被认为构成了星际尘埃物质中重要的观测部分。星际a-C（:H）纳米粒子对光热解离和库仑破碎的稳定性需要考虑其固有的非均质性。这项工作的目的是表征半导体a- c （:H）纳米颗粒结构，特别是表征其芳域尺寸分布的性质，从而预测它们在强烈的紫外线辐射场中的行为，这种辐射场可以通过碳-碳键断裂引起的解离和电荷效应将它们碎片化。使用统计方法，我们确定了芳香结构域的典型尺寸，它们的尺寸分布，它们是如何网络键合的，以及它们在结构中的位置。研究了a-C（:H）纳米颗粒及其破碎产物的热激发、光解离和充电的影响。导出的半径为~ 0.4-0.5 nm、含有~ 40-60个碳原子的纳米尺寸的a-C（:H）纳米粒子的紫外光子诱导碎片寿命在弥漫性星际介质中为106-107年，在光解区域可能短102-104倍，这取决于局部辐射场强度。比这大的颗粒抗光解作用是稳定的。在HII区，只有半径大于0.7 nm的a-C（:H）纳米粒子（约150个碳原子）才有可能存活。亚纳米a-C（:H）粒子的光子驱动破碎在弥漫性星际介质和高激发区（如光解离和H II区）中很重要。然而，在这些相同的区域，库仑破碎不太可能是一个重要的尘埃破坏过程。
{"title":"The essential elements of dust evolution: a-C(:H) nanoparticle sub-structures and photo-fragmentation","authors":"A. P. Jones, N. Ysard","doi":"10.1051/0004-6361/202555203","DOIUrl":"https://doi.org/10.1051/0004-6361/202555203","url":null,"abstract":"<i>Context.<i/> Hydrogenated amorphous carbon materials, a-C(:H), are heterogeneous structures consisting of carbon atoms in different hybridisation states and bonding configurations and are thought to constitute a significant and observationally important fraction of the interstellar dust material. The stability of interstellar a-C(:H) nanoparticles against photo-thermo-dissociation and Coulomb fragmentation needs to take their intrinsic heterogeneity into account.<i>Aims.<i/> This work aims to characterise semi-conducting a-C(:H) nanoparticle structures and, in particular, their property-characterising aromatic domain size distribution and so predict how they will behave in intense UV radiation fields that can fragment them through dissociative and charge effects as a result of carbon-carbon bond-breaking.<i>Methods.<i/> Using a statistical approach, we determined the typical sizes of the aromatic domains, their size distribution, how they are network-bonded, and where they are to be found within the structure. We consider the effects of thermal excitation, photo-dissociation and charging of a-C(:H) nanoparticles, and the products of their fragmentation.<i>Results.<i/> The derived UV photon-induced fragmentation lifetimes for nanometre-sized a-C(:H) nanoparticles, with radii ∼0.4-0.5 nm radius and containing ∼40-60 carbon atoms, are of the order of 10<sup>6<sup/>-10<sup>7<sup/> yr in the diffuse interstellar medium and likely 10<sup>2<sup/>-10<sup>4<sup/> times shorter in photodissociation regions, depending on the local radiation field intensity. Grains larger than this are stable against photodissociation. In HII regions only a-C(:H) nanoparticles with radii greater than 0.7 nm (≳150 carbon atoms) are likely to survive.<i>Conclusions.<i/> The photon-driven fragmentation of sub-nanometre a-C(:H) particles was determined to be important in the diffuse interstellar medium and also in high excitation regions, such as photodissociation and H II regions. However, in these same regions Coulomb fragmentation is unlikely to be an important dust destruction process.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"65 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-12-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145711528","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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