Astronomy & Astrophysics最新文献

{"title":"The first SRG/eROSITA All-Sky Survey","authors":"F. Balzer, E. Bulbul, M. Kluge, A. Liu, M. Salvato, M. Fabricius, R. Seppi, E. Artis, Y. E. Bahar, R. Bender, N. Clerc, J. Comparat, V. Ghirardini, S. Grandis, S. Krippendorf, G. Lamer, N. Malavasi, A. Merloni, K. Nandra, M. E. Ramos-Ceja, J. S. Sanders, S. Zelmer, X. Zhang","doi":"10.1051/0004-6361/202553942","DOIUrl":"https://doi.org/10.1051/0004-6361/202553942","url":null,"abstract":"The detection of the extended X-ray emission of the intracluster medium by the first SRG/eROSITA All-Sky Survey (eRASS1), combined with optical and near-infrared follow-up, resulted in the identification of more than 12 000 galaxy clusters, yielding precise constraints on cosmological parameters. However, some clusters of galaxies can be misclassified as point sources by eROSITA’s source detection algorithm due to the interplay between the point spread function, the shallow depth of the survey, compact (cool core) X-ray emission, and bright active galactic nuclei hosted in their centers or nearby. To identify such misclassified galaxy clusters and groups, we apply optical follow-up to the eRASS1 X-ray point sources analogously to the treatment of the extent-selected catalog. After rigorous filtering to ensure purity, we find a total of 8347 clusters of galaxies, of which 5819 are novel detections, in a redshift range 0.05 < <i>z<i/> ≲ 1.1. This corresponds to a 70% discovery rate, a fraction similar to that of the extent-selected sample. To facilitate finding new exceptional clusters such as the Phoenix cluster (which is recovered in our sample), we divide the clusters into five classes based on the optical properties of likely single-source counterparts to the X-ray emission. We further investigate potential biases in our selection process by analyzing the optical and X-ray data. With this work, we provide a catalog of galaxy clusters and groups in the eRASS1 point source catalog, including their optical and X-ray properties along with a meaningful classification.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"21 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145141351","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}

{"title":"Broadband spectroscopy of astrophysical ice analogues","authors":"A. A. Gavdush, A. V. Ivlev, K. I. Zaytsev, V. E. Ulitko, I. N. Dolganova, S. V. Garnov, B. M. Giuliano, P. Caselli","doi":"10.1051/0004-6361/202556110","DOIUrl":"https://doi.org/10.1051/0004-6361/202556110","url":null,"abstract":"<i>Context<i/>. The quantification of the terahertz (THz) and IR optical properties of astrophysical ice analogs, which have different molecular compositions, phases, and structural properties, is required to model both the continuum emission by the dust grains covered with thick icy mantles and the radiative transfer in the dense cold regions of the interstellar medium.<i>Aims<i/>. We developed a model to define a relationship between the THz-IR response and the ice porosity. It includes the reduced effective optical properties of porous ices and the additional wave extinction due to scattering on pores. The model is applied to analyze the measured THz-IR response of CO and CO<sub>2<sub/> laboratory ices and to estimate their scattering properties and porosity.<i>Methods<i/>. Our model combines the Bruggeman effective medium theory, the Lorentz-Mie and Rayleigh scattering theories, and the radiative transfer theory to analyze the measured THz-IR optical properties of laboratory ices.<i>Results<i/>. We apply this model to show that the electromagnetic-wave scattering in studied laboratory ices occurs mainly in the Rayleigh regime at frequencies below 32 THz. We conclude that pores of different shapes and dimensions can be approximated by spheres of effective radius. By comparing the measured broadband response of our laboratory ices with those of reportedly compact ices from earlier studies, we quantify the scattering properties of our CO and CO<sub>2<sub/> ice samples. Their porosity is shown to be as high as 15 and 22%, respectively. Underestimating the ice porosity in the data analysis leads to a proportional relative underestimate of the THz-IR optical constants.<i>Conclusions<i/>. The scattering properties and porosity of ices have to be quantified along with their THz-IR response in order to adequately interpret astrophysical observations. The developed model paves the way for solving this demanding problem of laboratory astrophysics.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"42 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145141382","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}

{"title":"Quantifying thermal water dissociation in the dayside photosphere of WASP-121 b using NIRPS","authors":"Luc Bazinet, Romain Allart, Björn Benneke, Stefan Pelletier, Joost P. Wardenier, Neil J. Cook, Thierry Forveille, Louise D. Nielsen, Khaled Al Moulla, Étienne Artigau, Frédérique Baron, Susana C. C. Barros, Xavier Bonfils, François Bouchy, Marta Bryan, Bruno L. Canto Martins, Ryan Cloutier, Nicolas B. Cowan, Daniel Brito de Freitas, Jose Renan De Medeiros, Xavier Delfosse, René Doyon, Xavier Dumusque, David Ehrenreich, Jonay I. González Hernández, David Lafrenière, Izan de Castro Leão, Christophe Lovis, Lison Malo, Claudio Melo, Lucile Mignon, Christoph Mordasini, Francesco Pepe, Rafael Rebolo, Jason Rowe, Nuno C. Santos, Damien Ségransan, Alejandro Suárez Mascareño, Stéphane Udry, Diana Valencia, Gregg Wade, Manuel Abreu, José L. A. Aguiar, Guillaume Allain, Tomy Arial, Hugues Auger, Nicolas Blind, David Bohlender, Anne Boucher, Vincent Bourrier, Sébastien Bovay, Christopher Broeg, Denis Brousseau, Alexandre Cabral, Charles Cadieux, Andres Carmona, Zalpha Challita, Bruno Chazelas, João Coelho, Marion Cointepas, Ana Rita Costa Silva, Louis-Philippe Coulombe, Eduardo Cristo, Antoine Darveau-Bernier, Laurie Dauplaise, Roseane de Lima Gomes, Dasaev O. Fontinele, Yolanda G. C. Frensch, Frédéric Genest, Ludovic Genolet, Félix Gracia Témich, Olivier Hernandez, H. Jens Hoeijmakers, Norbert Hubin, Ray Jayawardhana, Hans-Ulrich Käufl, Dan Kerley, Johann Kolb, Vigneshwaran Krishnamurthy, Benjamin Kung, Pierrot Lamontagne, Olivia Lim, Gaspare Lo Curto, José Luis Rasilla, Allan M. Martins, Jaymie Matthews, Jean-Sébastien Mayer, Yuri S. Messias, Stan Metchev, Dany Mounzer, Nicola Nari, Ares Osborn, Mathieu Ouellet, Léna Parc, Luca Pasquini, Céline Peroux, Caroline Piaulet-Ghorayeb, Emanuela Pompei, Anne-Sophie Poulin-Girard, Vladimir Reshetov, Jonathan Saint-Antoine, Mirsad Sarajlic, Robin Schnell, Alex Segovia, Julia Seidel, Armin Silber, Peter Sinclair, Michael Sordet, Danuta Sosnowska, Avidaan Srivastava, Atanas K. Stefanov, Márcio A. Teixeira, Simon Thibault, Philippe Vallée, Thomas Vandal, Valentina Vaulato, Bachar Wehbe, Drew Weisserman, Ivan Wevers, François Wildi, Vincent Yariv, Gérard Zins","doi":"10.1051/0004-6361/202553724","DOIUrl":"https://doi.org/10.1051/0004-6361/202553724","url":null,"abstract":"The intense stellar irradiation of ultra-hot Jupiters results in some of the most extreme atmospheric environments in the planetary regime. On their daysides, temperatures can be sufficiently high for key atmospheric constituents to thermally dissociate into simpler molecular species and atoms. This dissociation drastically changes the atmospheric opacities and, in turn, critically alters the temperature structure, atmospheric dynamics, and day-night heat transport. To date, however, simultaneous detections of the dissociating species and their thermally dissociation products in exoplanet atmospheres have remained rare. In this work we present the simultaneous detections of H<sub>2<sub/>O and its thermally dissociation product OH on the dayside of the ultra-hot Jupiter WASP-121 b based on high-resolution emission spectroscopy with the recently commissioned <i>Near InfraRed Planet Searcher<i/> (NIRPS). We retrieved a photospheric abundance ratio of log<sub>10<sub/>(OH/H<sub>2<sub/>O) = −0.15 ± 0.20, indicating that there is about as much OH as H<sub>2<sub/>O at photospheric pressures, which confirms predictions from chemical equilibrium models. We compared the dissociation on WASP-121 b with other ultra-hot Jupiters and show that a trend in agreement with equilibrium models arises. We also discuss an apparent velocity shift of 4.79<sub>−0.97<sub/><sup>+0.93<sup/> km s<sup>−1<sup/> in the H<sub>2<sub/>O signal, which is not reproduced by current global circulation models. Finally, in addition to H<sub>2<sub/>O and OH, the NIRPS data reveal evidence of Fe and Mg, from which we inferred a Fe/Mg ratio consistent with the solar and host star ratios. Our results demonstrate that NIRPS can be an excellent instrument to obtain simultaneous measurements of refractory and volatile molecular species, thus paving the way for many future studies on the atmospheric composition, chemistry, and the formation history of close-in exoplanets.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"42 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145141377","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}

{"title":"Closing the solar dynamo loop: Poloidal field generated at the surface by plasma flows","authors":"R. H. Cameron, H. Schunker, A. S. Brun, A. Strugarek, A. J. Finley, W. Roland-Batty, A. C. Birch, L. Gizon","doi":"10.1051/0004-6361/202553844","DOIUrl":"https://doi.org/10.1051/0004-6361/202553844","url":null,"abstract":"<i>Context.<i/> The large-scale magnetic field of the Sun is produced by dynamo action due to convection and rotation. The toroidal magnetic field is maintained by the Sun’s differential rotation that winds up the azimuthally averaged radial and latitudinal (poloidal) magnetic field. The generation of the poloidal flux has long been considered to be due to an alpha effect acting on the toroidal magnetic field.<i>Aims.<i/> We investigated the observed flows associated with the longitudinal and latitudinal separation of the two magnetic polarities of an active region during and immediately after it has emerged. The observed separations are known to statistically obey Joy’s law, and this paper aims to identify the flows and transport mechanisms involved in producing Joy’s law.<i>Methods.<i/> We analyzed 182 isolated active region emergences observed using the Helioseismic and Magnetic Imager (HMI) from the Solar Dynamics Observatory (SDO) satellite that were previously reported in the literature. We investigated the different terms contributing to the separation in both longitude and latitude. We performed a similar analysis on the emergences in a dynamo simulation performed using the Anelastic Spherical Harmonics (ASH) code.<i>Results.<i/> While we do not exclude the possibility of an alpha effect operating in the convection zone, our results show that the poloidal field corresponding to Joy’s law, which reverses the polar fields and which is required to close the dynamo loop, is generated at the surface not from an alpha effect, but instead from the delta effect (also called the Rädler effect). The difference between the two is that the alpha effect generates a poloidal magnetic field from the presence of toroidal field, while the delta effect does so via the turbulent transport of toroidal field.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"1 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145134333","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}

{"title":"20 years of disk winds in 4U 1630−47","authors":"M. Parra, S. Bianchi, P. -O. Petrucci, T. Bouchet, M. Shidatsu, F. Capitanio, M. Dovčiak, T. D. Russell, V. E. Gianolli, F. Carotenuto","doi":"10.1051/0004-6361/202554976","DOIUrl":"https://doi.org/10.1051/0004-6361/202554976","url":null,"abstract":"Highly ionized X-ray wind signatures have been found in the soft states of high-inclination black hole low mass X-ray binaries (BHLMXBs) for more than two decades. Yet signs of a systematic evolution of the outflow itself along the outburst remain elusive, due to the limited sampling of individual sources and the necessity to consider the broadband evolution of the spectral energy distribution (SED). We performed an holistic analysis of archival X-ray wind signatures in the most observed wind-emitting transient BHLMXB to date, 4U 1630−47. The combination of <i>Chandra<i/>, <i>NICER<i/>, <i>NuSTAR<i/>, <i>Suzaku<i/>, and XMM-<i>Newton<i/>, complemented in hard X-rays by <i>Swift<i/>/BAT and <i>INTEGRAL<i/>, spans more than 200 individual days over nine individual outbursts, and provides a near complete broadband coverage of the brighter portion of the outburst. Our results show that the hard X-ray contribution is strongly correlated with the equivalent width (EW) of the lines, and allows one to define “soft” states with ubiquitous wind detections. We then constrained the evolution of the outflow parameters in a set of representative observations, using thermal stability curves and photoionization modeling. The first confirms that the switch to unstable SEDs occurs well after the wind signatures disappear, to the point where the last canonical hard states are thermally stable. The second shows that intrinsic changes in the outflow are required to explain the main correlations of the line EWs, be it with luminosity or the hard X-rays. These behaviors are seen systematically over all outbursts and confirm the longstanding expectation of individual links between the wind properties, the thermal disk, and the corona.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"59 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145134331","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}

{"title":"Tight correlation of star formation with [CI] and CO lines across cosmic time","authors":"Theodoros Topkaras, Thomas G. Bisbas, Zhi-Yu Zhang, V. Ossenkopf-Okada","doi":"10.1051/0004-6361/202451269","DOIUrl":"https://doi.org/10.1051/0004-6361/202451269","url":null,"abstract":"<i>Context.<i/> Cold molecular gas tracers, such as C I and CO lines, have been widely used to infer specific characteristics of the interstellar medium (ISM) and to derive star formation relations among galaxies.<i>Aims.<i/> However, there is still a lack of systematic studies of the star formation scaling relation of CO and [C I] lines across cosmic time on multiple physical scales.<i>Methods.<i/> We used observations of the ground state transitions of [C I], CO, and [C II], for 885 sources collected from the literature, to infer possible correlations between line luminosities of , L′<sub>CO(1 − 0)<sub/>, and with star formation rates (SFRs). With linear regression, we fit the relations between SFR and molecular mass derived from CO, C I, and C II lines.<i>Results.<i/> The relation between [C I]- and CO-based total molecular masses is weakly superlinear. Nevertheless, they can be calibrated against each other. For <i>α<i/><sub>CO<sub/> = 0.8 and 4.0 M<sub>⊙<sub/>(K km s<sup>−1<sup/> pc<sup>2<sup/>)<sup>−1<sup/> we derived <i>α<i/><sub>[CI]<sub/> = 3.9 and ∼ 17 M<sub>⊙<sub/>(K km s<sup>−1<sup/> pc<sup>2<sup/>)<sup>−1<sup/>, respectively. Using the <i>lmfit<i/> package, we derived relation slopes of SFR–L′<sub>[CI](1 − 0)<sub/>, SFR–L′<sub>CO(1 − 0)<sub/>, and SFR–L′<sub>[CII](1 − 0)<sub/> to be <i>β<i/> = 1.06 ± 0.02, 1.24 ± 0.02, and 0.74 ± 0.02, respectively. With a Bayesian inference <i>linmix<i/> method, we find consistent results.<i>Conclusions.<i/> Our relations for [C I](1–0) and CO(1–0) indicate that they trace similar molecular gas contents, across different redshifts and different types of galaxies. This suggests that these correlations do not have strong evolution with cosmic time.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"37 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145134330","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}

{"title":"Extended multi-phase gas reservoirs in the z = 4.3 protocluster SPT2349-56: Non-stellar ionisation sources?","authors":"Kevin C. Harrington, Amit Vishwas, Allison W. S. Man, Carlos De Breuck, Padelis P. Papadopoulos, Paola Andreani, Thomas. G. Bisbas","doi":"10.1051/0004-6361/202555071","DOIUrl":"https://doi.org/10.1051/0004-6361/202555071","url":null,"abstract":"We aim to characterise the multi-phase gas in the SPT2349-56 protocluster at <i>z<i/> = 4.3, which is known to host one of the most starbursting and Active Galactic Nuclei (AGN)-rich high redshift environments. For this purpose, we conducted Atacama Pathfinder EXperiment (APEX) single-dish observations of the [C II] 158 μm (hereafter [C II]) line towards the core and north components, which were previously imaged with the Atacama Large Millimeter/submillimeter Array (ALMA). We also present the first [O III] 88 μm (hereafter [O III]) line observations in such a high-redshift protocluster system. We obtain a [C II] line luminosity approximately 1.7 times greater than that recovered by ALMA towards the core, while we recover four times more [C II] line emission than that found in deep ALMA images towards the north component. This suggests that the most massive gas reservoirs lie in the less extreme regions of this protocluster system. A minimum ionised gas mass of M<sub>min<sub/>(<i>H<i/><sup>+<sup/>)∼3.7 × 10<sup>10<sup/> M<sub>⊙<sub/> is deduced from the [O III] line, which amounts to 30% of the molecular gas mass in the same area, indicating that a full map of the cluster is necessary for determining the large-scale value. Finally, we obtain star formation rate (SFR) estimates using the [O III] line luminosity and the corresponding ionised gas mass. These yield values that can surpass the far-infrared (IR) continuum-derived SFR under the assumption of a standard stellar Initial Mass Function (IMF), which can be reconciled only if non-stellar ionising sources contribute to the [O III] line luminosity, or if a top-heavy stellar IMF produces a larger fraction of O stars per total stellar mass. This is a distinct possibility in high-energy-particle (HEP)-dominated, rather than UV-photon-dominated, environments in clusters. Future work using far-IR fine-structure and molecular or neutral-atomic lines is necessary to determine the thermal and ionisation states of the multi-phase medium in this protocluster, to understand their maintenance, and to resolve the apparent SFR discrepancy. These line ratios must be measured over a wide range of spatial scales, from individual galaxies up to circumgalactic medium (CGM) and intracluster medium (ICM) scales, which ultimately requires combining wide-field single-dish and high-resolution interferometric observations of such lines in protocluster environments where HEP- and UV-dominated ISM phases can co-exist.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"25 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145134282","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}

{"title":"Magnetohydrodynamic simulations preliminarily predict the habitability and radio emission of TRAPPIST-1e","authors":"BoRui Wang, ShengYi Ye, Jacobo Varela, XinYi Luo","doi":"10.1051/0004-6361/202555471","DOIUrl":"https://doi.org/10.1051/0004-6361/202555471","url":null,"abstract":"<i>Context<i/>. TRAPPIST-1e, an Earth-sized exoplanet in the habitable zone of the nearby M dwarf TRAPPIST-1, may experience magnetospheric responses that vary with stellar space weather, which could potentially influence both its habitability and radio emissions.<i>Aims<i/>. Our objective is to investigate how different Earth-like magnetospheric configurations of TRAPPIST-1e – specifically variations in dipolar magnetic field strength and axial tilt – respond to diverse stellar space weather conditions, including events analogous to coronal mass ejections (CMEs), and to assess their implications for potential habitability and expected radio emissions.<i>Methods<i/>. We conducted 3D magnetohydrodynamic simulations of the TRAPPIST-1e system using the PLUTO code in spherical coordinates. The planetary magnetic field was modelled as dipolar, with equatorial strengths from Earth-like to several times stronger. The dipole axis spans a representative range of axial tilts. We investigate four stellar wind environments, from sub-Alfvénic flow to CME-like disturbances. Planetary shielding was quantified based on the magnetopause standoff distance, and radio powers were estimated via empirical scaling laws.<i>Results<i/>. Our simulations show that both shielding and radio power depend strongly on the magnetic configuration. Stronger fields increase protection, while larger tilts reduce it. Radio power increases with both field strength and tilt across all wind regimes. An Earth-like magnetic field can provide effective shielding even under intense CMEs, whereas high tilts require stronger fields. Predicted radio powers reach ~10<sup>20<sup/> erg s<sup>−1<sup/> during CMEs, making bursts from close-in, magnetised planets more detectable. However, for TRAPPIST-1e, the maximum cyclotron frequency lies below the Earth’s ionospheric cutoff (~10 MHz), making ground-based detection currently infeasible.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"18 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145134332","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}

{"title":"X-ray reverberation modelling of the observed UV/optical power spectra of quasars","authors":"M. Papoutsis, I. E. Papadakis, C. Panagiotou, E. Kammoun, M. Dovčiak","doi":"10.1051/0004-6361/202554220","DOIUrl":"https://doi.org/10.1051/0004-6361/202554220","url":null,"abstract":"<i>Context.<i/> Over the past decade, a significant amount of effort has been put into investigating the ultraviolet (UV) and optical variability of active galactic nuclei (AGNs). Comprehensive studies of intensive multi-wavelength monitoring and surveys of local and high-redshift AGNs have shown that X-ray illumination of AGN accretion discs is a potential explanation for the observed variability.<i>Aims.<i/> Our main objective is to study the UV/optical power spectra of AGNs under the assumption of X-ray reverberation and to test whether this model can explain the observed power spectra of distant quasars.<i>Methods.<i/> We computed the disc transfer function in the case of X-ray reverberation using a recent physical model and studied its dependence on the parameters of the model. This model allows us to explore the variability of X-ray illuminated discs under the scenario in which the X-ray corona is powered by the accretion process or by an external source. We then calculated UV/optical power spectra using the disc transfer function and assuming a bending power law for the X-ray power spectrum. We fitted our models to the observed power spectra of quasars determined by a recent power spectrum analysis of the SDSS Stripe-82 light curves.<i>Results.<i/> We demonstrate that X-ray reverberation can fit the power spectra of quasars in our sample well at all wavelengths, from ∼1300 Å up to 4000 Å. Our best-fit models imply that the X-ray corona is powered by the accretion disc, and that the black hole spin is probably lower than 0.7, while the X-ray corona height is in the range of 20 − 60 <i>R<i/><sub>g<sub/>. This is in agreement with previous findings from the application of the X-ray reverberation model to the quasar micro-lensing disc size problem, as well as recent time-lag measurements.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"41 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145134281","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}

{"title":"Rotation of young solar-type stars as seen by Gaia and K2","authors":"S. N. Breton, E. Distefano, A. C. Lanzafame, D. B. Palakkatharappil","doi":"10.1051/0004-6361/202553912","DOIUrl":"https://doi.org/10.1051/0004-6361/202553912","url":null,"abstract":"<i>Context<i/>. Accurate surface rotation measurements are crucial to estimate stellar ages and improve our understanding of stellar rotational evolution. Comparisons of datasets obtained from different space missions on common targets represent in this sense a way to explore the respective biases and reliability of the considered instruments, as well as a possibility to perform a more in-depth investigation of the properties of the observed stars.<i>Aims<i/>. In this perspective, we used observations from the K2 mission to provide an external validation to <i>Gaia<i/> rotation measurements, and confront observables available from <i>Gaia<i/>, K2, and <i>Kepler<i/>.<i>Methods<i/>. We therefore cross-matched the <i>Gaia<i/> rotation catalogue and the K2 mission Ecliptic Plane Input Catalogue (EPIC) in order to find <i>Gaia<i/> stars with both measured rotation and periods and available K2 light curves. Using our cross-match, we analysed 1063 light curves from the K2 mission in order to characterise stellar rotational modulations and compare the recovered periods with <i>Gaia <i/>reference values. The K2/<i>Gaia<i/> cross-validated sample was used as a random-forest classifier training set to identify a subsample of <i>Gaia<i/> stars with similar properties.<i>Results<i/>. We validate the <i>Gaia<i/> rotation measurements for a large fraction of the sample and we discuss the possible origin of the discrepancies between some K2 and <i>Gaia<i/> measurements. We note that the K2 sample does not include members of the low-activity ultra-fast-rotating (UFR) population that was highlighted by <i>Gaia<i/> observations, a feature that we explain considering the instrumental capabilities of K2. Placing our sample in perspective with the full <i>Gaia<i/> rotation catalogues and <i>Kepler<i/> observations, we show that the population for which both <i>Gaia<i/> and K2 are able to measure rotation is composed of young late-type stars, a significant fraction of which are not yet converged on the slow-rotator gyrochronological sequence. In order to identify additional targets that have properties similar to the cross-validated K2 sample (considering in particular rotation and activity index), we computed the local outlier factor (LOF) of the stars in the <i>Gaia<i/> DR3 rotation catalogue, considering the K2 stars as reference, and we identified 40 423 stars with a high degree of similarity, which can be useful for future statistical studies.<i>Conclusions<i/>. For the purpose of characterising the properties of young solar-type fast rotators, future photometric space-borne missions such as PLATO will greatly benefit from the synergies with <i>Gaia<i/> observations that we illustrate in this work.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"194 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145134334","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}