Astronomy & Astrophysics最新文献

{"title":"The Northern Cross Fast Radio Burst project","authors":"A. Geminardi, P. Esposito, G. Bernardi, M. Pilia, D. Pelliciari, G. Naldi, D. Dallacasa, R. Turolla, L. Stella, F. Perini, F. Verrecchia, C. Casentini, M. Trudu, R. Lulli, A. Maccaferri, A. Magro, A. Mattana, G. Bianchi, G. Pupillo, C. Bortolotti, M. Tavani, M. Roma, M. Schiaffino, G. Setti","doi":"10.1051/0004-6361/202554386","DOIUrl":"https://doi.org/10.1051/0004-6361/202554386","url":null,"abstract":"<i>Context.<i/> The radio emission from magnetars is poorly understood and poorly characterized observationally, particularly for what concerns single pulses and sporadic events. Interest in this type of radio emission has been boosted by the detection of an extremely bright millisecond radio signal from the Galactic magnetar designated as SGR J1935+2154 in 2020, which occurred almost simultaneously with a typical magnetar short burst of X-rays. As of now, this event remains the Galactic radio pulse that is the most reminiscent of fast radio bursts, and it is the only one that has a sound association with a known progenitor.<i>Aims.<i/> We aim to constrain the rate of impulsive radio events from magnetars by means of intensive monitoring using a high-sensitivity radio telescope.<i>Methods.<i/> We performed a long-term campaign on seven Galactic magnetars (plus one candidate) using the Northern Cross transit radio telescope (in Medicina, Italy), searching for short timescales and dispersed radio pulses.<i>Results.<i/> We obtained no detections in ∼560 hours of observation, setting an upper limit at a 95% confidence level of < 52 yr<sup>−1<sup/> on the rate of events with energy ≳10<sup>28<sup/> erg, which is consistent with limits in the literature. Furthermore, under some assumptions regarding the properties and energetic behavior of magnetars, we find that our upper limits point toward the fact that the entire population of observed fast radio bursts cannot be explained by radio bursts emitted by magnetars.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"1 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144715432","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":"Phase reddening of Phobos and Deimos from TGO/CaSSIS observations","authors":"G. Munaretto, M. Pajola, J. Beccarelli, G. Cremonese, A. Lucchetti, C. Re, A. Tullo, M. Almeida, M. Read, K. Mason-Piercy, N. Thomas, M. R. Patel, A. Valantinas","doi":"10.1051/0004-6361/202555720","DOIUrl":"https://doi.org/10.1051/0004-6361/202555720","url":null,"abstract":"<i>Aims.<i/> We study the phase-reddening effect (i.e. the increase in spectral slope with phase angle) of Phobos and Deimos, with the aim of characterising the origin and physical properties of the two Martian moon surfaces and spectral units.<i>Methods.<i/> We analysed Phobos and Deimos four-filter observations at visible to near-infrared wavelengths acquired by the Colour and Surface Stereo Imaging System (CaSSIS) on board ESA’s ExoMars Trace Gas Orbiter (TGO) over a wide range of phase angles. From these observations, we derived the spatial distribution of the phase reddening and spectral slope over the sub-Mars hemispheres of Phobos and Deimos.<i>Results.<i/> We present the first spatially resolved map of the Phobos phase reddening and the first estimate of the Deimos global phase reddening in the visible to near-infrared wavelengths.<i>Conclusions.<i/> Our results suggest that (i) the surface of Phobos is characterised by variable phase reddening, (ii) the phase reddening of Deimos is similar to that of the redder units on Phobos, (iii) the amount of phase reddening is linked to regolith maturity and can be explained by space-weathering, (iv) the Phobos Blue unit post-dates the Stickney impact and may have an exogenous origin, and (v) the physical properties of the regolith on Phobos and Deimos are different from those of Martian regolith.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"97 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-25","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144715375","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":"The CHIMERA Survey: The first CO detection in Leo T, the lowest mass known galaxy still hosting cold molecular gas","authors":"Vicente Villanueva, Matías Blaña, Alberto D. Bolatto, Mónica Rubio, Elizabeth Tarantino, Rodrigo Herrera-Camus, Andreas Burkert, Daniel Vaz, Justin I. Read, Gaspar Galaz, César Muñoz, Diego Calderón, Manuel Behrendt, Julio A. Carballo-Bello, Emily Gray, Michael Fellhauer","doi":"10.1051/0004-6361/202555635","DOIUrl":"https://doi.org/10.1051/0004-6361/202555635","url":null,"abstract":"We report the first CO detection in Leo T, representing the most extreme observation of carbon monoxide molecules in the lowest stellar mass gas-rich dwarf galaxy (<i>M<i/><sub>⋆<sub/> ∼ 10<sup>5<sup/> M<sub>⊙<sub/>) known to date. We acquired and present new Atacama Compact Array (ACA) <sup>12<sup/>CO(<i>J<i/> = 1–0) data within our CHIMERA Survey project for the central region of Leo T, a metal-poor ([M/H] ∼ −1.7) dwarf in the Milky Way (MW) outskirts. We identified three compact molecular clouds (< 13 pc) with estimated upper limit virial masses of <i>M<i/><sub>mol<sub/> ∼ 5 × 10<sup>3<sup/> M<sub>⊙<sub/> each and a total of 1.4 ± 0.4 × 10<sup>4<sup/> M<sub>⊙<sub/>, corresponding to ∼3% of the total gas mass. We obtained CO-to-H<sub>2<sub/> conversion factors (<i>α<i/><sub>CO<sub/>) as high as ∼ 155 M<sub>⊙<sub/>(K km s<sup>−1<sup/> pc<sup>2<sup/>)<sup>−1<sup/> and mean molecular gas surface densities of Σ<sub>mol<sub/> ∼ 9 M<sub>⊙<sub/> pc<sup>−2<sup/> that are consistent with values found in dwarf galaxies with extremely low metal content. All CO clouds are shifted (∼60 pc) from the stellar population centers, and only one cloud appears within the densest HI region. Two clouds have velocity offsets with the HI of Δ<i>v<i/><sub>los<sub/> ∼ + 13 km s<sup>−1<sup/> being within twice the velocity dispersion (Δ<i>v<i/><sub>los<sub/>/<i>σ<i/><sub>HI, los<sub/> ∼ 2) and probably bound. However, the northern cloud is faster (Δ<i>v<i/><sub>los<sub/> ∼ + 57 km s<sup>−1<sup/>); our models with low halo masses (<i>M<i/><sub>h<sub/> ≲ 10<sup>9<sup/> M<sub>⊙<sub/>) result in unbound orbits, suggesting that this material is likely being expelled from the dwarf, providing evidence for molecular gas depletion. These properties reveal a perturbed dynamics intertwined with star formation processes in low-mass dwarf galaxies, supporting a scenario of episodic bursts until they are fully quenched by the MW environment.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"20 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144702011","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":"Experimental confirmation of barrierless reactions between HeH+ and deuterium atoms suggests a lower abundance of the first molecules at very high redshifts","authors":"F. Grussie, J. Sahoo, Y. Scribano, D. Bossion, L. Berger, M. Grieser, L. W. Isberner, Á. Kálosi, O. Novotný, D. Paul, A. Znotins, X. Urbain, H. Kreckel","doi":"10.1051/0004-6361/202555316","DOIUrl":"https://doi.org/10.1051/0004-6361/202555316","url":null,"abstract":"The HeH<sup>+<sup/> ion was the first molecule to form in the early Universe, and its comparatively large dipole moment renders it a potential coolant, relevant during the epoch of first star formation. The main destruction mechanisms under primordial conditions are recombination with free electrons and chemical reactions with hydrogen atoms. The latter process was believed to be slow at low temperatures, owing to a barrier forming along the reaction coordinate. Here we present a joint experimental and theoretical study of the reaction HeH<sup>+<sup/> + D → HD<sup>+<sup/> + He that confirms the very recent proposition that the reaction is, in fact, barrierless and fast at low collision energies. The present evidence suggests that previous studies underestimated the low-temperature rate coefficient significantly because of an artifact in a widely used potential energy surface, and calls for a reassessment of the helium chemistry in the early Universe.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"54 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144702012","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":"PDRs4All","authors":"I. Schroetter, O. Berné, J. R. Goicoechea, J. H. Black, O. Roncero, F. Alarcon, P. Amiot, O. Asvany, C. Boersma, S. Brünken, J. Cami, L. Coudert, E. Dartois, A. Fuente, B. Gans, A. Gusdorf, U. Jacovella, M. A. Martin Drumel, T. Onaka, E. Peeters, E. Roueff, A. G. G. M. Tielens, M. Zannese","doi":"10.1051/0004-6361/202555841","DOIUrl":"https://doi.org/10.1051/0004-6361/202555841","url":null,"abstract":"Most protoplanetary disks experience a phase in which they are subjected to strong ultraviolet radiation from nearby massive stars. This UV radiation can substantially alter their chemistry by producing numerous radicals and molecular ions. In this Letter we present a detailed analysis of the JWST-NIRSpec spectrum of the d203-506 obtained as part of the PDRs4All Early Release Science program. Using state-of-the-art spectroscopic data, we searched for species using a multi-molecule fitting tool, PAHTATMOL, which we developed for this purpose. Based on this analysis, we report the clear detection of ro-vibrational emission of the CH radical and the likely detection of the H molecular ion, with estimated abundances of a few times 10<sup>−7<sup/> and approximately 10<sup>−8<sup/>, respectively. The presence of CH is predicted by gas-phase models and is well explained by hydrocarbon photochemistry. Interstellar H is usually formed through reactions of H<sub>2<sub/> with H originating from cosmic ray ionization of H<sub>2<sub/>. However, recent theoretical studies suggest that H also forms through far-UV (FUV)-driven chemistry in strongly irradiated (<i>G<i/><sub>0<sub/> > 10<sup>3<sup/>), dense (<i>n<i/><sub>H<sub/> > 10<sup>6<sup/> cm<sup>−3<sup/>) gas. The latter is favored as an explanation for the presence of hot H (<i>T<i/><sub>ex<sub/> ≳ 1000 K) in the outer disk layers of d203-506, coinciding with the emission of FUV-pumped H<sub>2<sub/> and other photodissociation region (PDR) species, such as CH<sup>+<sup/>, CH , and OH. Our detection of infrared emission from vibrationally excited H and CH raises questions about their excitation mechanisms and underscores that FUV radiation can have a profound impact on the chemistry of planet-forming disks. They also demonstrate the power of JWST to push the limit of the detection of elusive species in protoplanetary disks.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"106 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144685148","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":"Implications of a turbulent convection model for classical Cepheids","authors":"M. Deka, F. Ahlborn, T. A. M. Braun, A. Weiss","doi":"10.1051/0004-6361/202554292","DOIUrl":"https://doi.org/10.1051/0004-6361/202554292","url":null,"abstract":"<i>Context.<i/> The appearance of blue loops in the evolutionary tracks of intermediate-mass core He-burning stars is essential for explaining the observed characteristics of Cepheïds. The blue loops for lower mass Cepheïds cannot always be reproduced when only classical, local mixing length theory (MLT) is used. Additionally, classical models result in a mass discrepancy compared to pulsational and dynamical mass determinations. Both problems can be resolved through an ad hoc extension of the MLT for convection.<i>Aims.<i/> We use the nonlocal Kuhfuss turbulent convection model (TCM), which allows us to explain the overshooting directly by solving the TCM equations. The primary objective of this study is to test the predictions of the Kuhfuss TCM when applied to intermediate-mass core He-burning stars and validate the model predictions against observations of Cepheïds.<i>Methods.<i/> We used the state-of-the-art 1D stellar evolution code GARSTEC with the implementation of the Kuhfuss TCM and computed evolutionary tracks for intermediate-mass core He-burning stars. We compared these tracks with those computed with MLT, including and excluding ad hoc overshooting and with observations of five Cepheïds in detached binary systems obtained from the literature.<i>Results.<i/> The stellar evolution tracks generated using the Kuhfuss TCM and MLT with ad hoc overshooting exhibit similar appearances. Overshoot mixing from the convective boundaries and the occurrence of the Cepheïd blue-loop have been achieved naturally as solutions to the equations of the Kuhfuss TCM. Furthermore, the evolutionary models, including the Kuhfuss TCM, have been successful in reproducing the observed stellar parameters, including mass, luminosity, radius, and effective temperature.<i>Conlcusions.<i/> We successfully generated Cepheïds’ blue loops with a TCM without any fine-tuning of the involved numerical parameters and with overshooting predicted directly from the convection theory. Beyond the achievement of blue loops, our approach which treats convection more physically has also been able to reproduce the observations of Cepheïds in eclipsing binary systems, with a similar level of accuracy as MLT models with ad hoc overshooting.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"27 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144685154","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":"Dancing on the grain: Variety of CO and its isotopologue fluxes as a result of surface chemistry and T Tauri disk properties","authors":"L. Zwicky, T. Molyarova, Á. Kóspál, P. Ábrahám","doi":"10.1051/0004-6361/202453529","DOIUrl":"https://doi.org/10.1051/0004-6361/202453529","url":null,"abstract":"<i>Context.<i/> One of the most important problems in the study of protoplanetary disks is the determination of their parameters, such as their size, age, stellar characteristics, and, most importantly, gas mass in the disk. At the moment, one of the main ways to infer the disk mass is to use a combination of CO isotopologue line observations. A number of theoretical studies have concluded that CO must be a reliable gas tracer, as its relative abundance only depends weakly on disk parameters. However, the observed line fluxes cannot always be easily used to infer the column density, much less the abundance of CO.<i>Aims.<i/> The aim of this work is to study the dependence of the CO isotopologue millimeter line fluxes on the astrochemical model parameters of a standard protoplanetary disk around a T Tauri star and to conclude whether they can be used individually or in combinations to reliably determine the disk parameters. Our case is set apart from earlier studies in the literature by the adoption of a comprehensive chemical network with grain-surface chemistry, together with line radiative transfer.<i>Methods.<i/> We used the astrochemical model ANDES together with the radiative transfer code RADMC-3D to simulate CO isotopologue line fluxes from a set of disks with varying key parameters (disk mass, disk radius, stellar mass, and inclination). We studied how these values change with one parameter varying and others fixed and approximated the dependences log-linearly.<i>Results.<i/> We described the dependences of CO isotopologue fluxes on all chosen disk parameters. Physical and chemical processes responsible for these dependences are analyzed and explained for each parameter. We show that using a combination of the <sup>13<sup/>CO and C<sup>18<sup/>O line fluxes, the mass can be estimated only within two orders of magnitude uncertainty and a characteristic radius with an uncertainty of one order of magnitude. We find that the inclusion of the grain-surface chemistry reduces <sup>13<sup/>CO and C<sup>18<sup/>O fluxes, which can help explain the underestimation of disk mass in the previous studies.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"23 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144685153","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":"The effects of the orbital configurations of mergers on reshaping galaxy structures","authors":"Xinyi Wu, Ling Zhu, Jiang Chang, Guangquan Zeng, Yu Lei","doi":"10.1051/0004-6361/202554638","DOIUrl":"https://doi.org/10.1051/0004-6361/202554638","url":null,"abstract":"We performed a systematic analysis of how the orbital configuration of a merger can influence the structural formation of remnant galaxies using 531 merger pairs selected from IllustrisTNG-100. We comprehensively described the merger orbital configuration, considering the relative orbital motion of the merger pair and their disk orientations. We quantified the galaxy structures by dynamically defining four components: bulge, disk, warm component, and hot inner stellar halo. For mergers on spiral-in orbits, the disk planes of the two merging galaxies tend to be aligned with the orbital plane, leading to higher fractions for the disk and warm components, as well as lower fractions for the bulge and hot inner stellar halo components in the remnant galaxy. For mergers on direct collision orbits, the disk planes of the two galaxies tend to be perpendicular to the orbital plane, leading to lower fractions for disk and warm components, as well as higher fractions of the bulge and hot inner stellar halo in the remnant. Mergers can lead to either an increase or decrease in the disk and bulge mass fraction in the remnant compared to the progenitor galaxy, depending on the merger orbital configurations; however, in 93% of cases, mergers cause an increase in the hot inner stellar halo. As a result, the luminosity fraction of the hot inner stellar halo (but not the bulge) in galaxies at <i>z<i/> = 0 is highly correlated with its total ex situ stellar mass. In addition, we find that merger on spiral-in orbits is one of the possible reasons for the formation of recently discovered red but H I-rich (RR) galaxies.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"27 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144685168","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":"Presenting 28 years of Sun-as-a-star extreme ultraviolet light curves from SOHO EIT","authors":"Emily Sandford, Frédéric Auchère, Annelies Mortier, Laura A. Hayes, Daniel Müller","doi":"10.1051/0004-6361/202554946","DOIUrl":"https://doi.org/10.1051/0004-6361/202554946","url":null,"abstract":"&lt;i&gt;Context.&lt;i/&gt; The Solar and Heliospheric Observatory (SOHO) Extreme-ultraviolet Imaging Telescope (EIT) has been taking images of the solar disk and corona in four narrow extreme ultraviolet (EUV) bandpasses (171 Å, 195 Å, 284 Å, and 304 Å) at a minimum cadence of once per day since early 1996. The time series of fully calibrated EIT images now spans approximately 28 years, from early 1996 to early 2024, covering solar cycles 23 and 24 in their entirety, as well as the beginning of cycle 25.&lt;i&gt;Aims.&lt;i/&gt; We aim to convert this extensive EIT image archive into a set of “Sun-as-a-star” light curves in EIT's four bandpasses, observing the Sun as if it were a distant point source viewed from a fixed perspective.&lt;i&gt;Methods.&lt;i/&gt; To construct the light curves, we summed the flux in each EIT image into one flux value, with an uncertainty accounting for both the background noise in the image and the potential spillover of flux beyond the bounds of the image (which is especially important for the bands with significant coronal emission). We corrected for long-term instrumental systematic trends in the light curves by comparing our 304 Å light curve to the ultraviolet light curve taken by SOHO's CELIAS/SEM solar wind monitoring experiment, which has a very similar bandpass to the EIT 304 Å channel. We corrected for SOHO's viewing angle by fitting a trend to the flux values with respect to SOHO's heliocentric latitude at the time of each observation.&lt;i&gt;Results.&lt;i/&gt; We produced two sets of Sun-as-a-star light curves with different uncertainty characteristics, available for download from Zenodo, either of which might be preferred for different types of future analyses. In version (1), we treated the EIT instrumental systematics consistently across the entire SOHO mission lifetime, producing a light curve with approximately homoscedastic uncertainties. In version (2), we only divided out the EIT instrumental systematics from November 12, 2008, onward; this is the point at which these systematics start to have a noticeable deleterious effect on the data. Therefore, version (2) has heteroscedastic uncertainties, but these uncertainties are much smaller than the version (1) uncertainties over the first half of the mission.&lt;i&gt;Conclusions.&lt;i/&gt; We find that our EUV light curves trace the Sun's ∼11-year solar activity cycle and ∼27-day rotation period much better than comparable optical observations. In particular, we can accurately recover the solar rotation period from our 284 Å light curve for 26 out of 28 calendar years of EIT observations (93% of the time), compared to only 3 out of 29 calendar years (10% of the time) for the VIRGO total solar irradiance time series, which is dominated by optical light. Our EIT light curves, in conjunction with Sun-as-a-star light curves at optical wavelengths, will be valuable to those interested in inferring the EUV/UV character of stars with long optical light curves, but no intensive UV observations, as well as to those inte","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"20 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144685175","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":"Polar faculae and their relationship to the solar cycle","authors":"Antonio Reche, Adur Pastor Yabar, Ana Belén Griñón-Marín","doi":"10.1051/0004-6361/202554578","DOIUrl":"https://doi.org/10.1051/0004-6361/202554578","url":null,"abstract":"<i>Context.<i/> The study of magnetic activity in the Sun's polar regions is essential for understanding the solar cycle. However, measuring polar magnetic fields presents challenges due to projection effects and their intrinsically weak magnetic field strength. Faculae, bright regions on the visible solar surface associated with increased magnetic activity, offer a valuable proxy for measuring polar fields.<i>Aims.<i/> This research aims to analyze the magnetic activity of the Sun's polar regions through the use of polar faculae.<i>Methods.<i/> A neural network model (U-Net) was employed to detect polar faculae in images from the Helioseismic and Magnetic Imager (HMI) on board the Solar Dynamics Observatory (SDO). The model was trained on synthetic data, eliminating the need for manual labeling, and was used to analyze 14 years of data from May 2010 to May 2024.<i>Results.<i/> The U-Net model demonstrates superior performance and efficiency over existing methods, enabling automated large-scale studies. We find that polar faculae numbers exhibit cyclical behavior with distinct minima and maxima, showing similar patterns between poles but with notable temporal delays (south pole: minimum early 2014, maximum late 2016; north pole: minimum late 2014, maximum mid-2019). Polar faculae magnetic fields remain consistent in magnitude (∼±75 G) across both poles and throughout the solar cycle. A strong linear correlation was found between the polar faculae count and the overall polar magnetic field strength. The spatio-temporal evolution reveals systematic migration of field polarity reversals from mid-latitudes toward the poles at rates of 3−8 m/s. During solar minimum, we observe a small relative increase in stronger-field faculae compared to solar maximum, suggesting either the coexistence of two magnetic distributions or subtle solar cycle dependence in faculae properties.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"212 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144685150","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}