Astronomy & Astrophysics最新文献

{"title":"Reduced or westward hotspot offset explained by dynamo action in atmospheres of ultrahot Jupiters","authors":"Vincent G. A. Böning, Wieland Dietrich, Johannes Wicht","doi":"10.1051/0004-6361/202553695","DOIUrl":"https://doi.org/10.1051/0004-6361/202553695","url":null,"abstract":"Hot Jupiters are tidally locked, Jupiter-sized planets in close proximity to their host star, exhibiting equilibrium temperatures exceeding 1000 K. Photometric observations often reveal that the hotspot - the hottest location in the atmosphere - has shifted with respect to the substellar point. While both eastward and westward offsets have been observed, hydrodynamic simulations typically predict an eastward offset due to advection by a characteristic eastward flow. In ultrahot Jupiters, where equilibrium temperatures surpass 2000 K, increased ionization has enhanced the electrical conductivity, leading to substantial Lorentz forces that can significantly influence the atmospheric dynamics. Here we present magnetohydrodynamic numerical simulations of atmospheres in ultrahot Jupiters that fully capture nonlinear electromagnetic induction effects. Our study identifies a novel magnetic instability that profoundly alters the dynamics, characterized by the disruption of the well-known laminar mean flows. This instability is triggered by a sufficiently strong background magnetic field with a realistic amplitude of around 1 G, assumed to originate from a deep-seated dynamo. Upon increasing the background field to 2.5 G, a subcritical dynamo mechanism emerges, capable of sustaining itself even when the external background field is removed. While hydrodynamic models exhibit a typical eastward offset, the magnetic instability results in either a vanishing or a westward hotspot displacement. Our results suggest that radial flow patterns associated with the instability play a significant role in modifying the hotspot position, providing a new mechanism to explain the diversity of observed hotspot shifts.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"277 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144652431","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":"No apparent forbidden or permitted narrow emission lines in the broad-line quasar SDSS J1251+0613","authors":"XueGuang Zhang","doi":"10.1051/0004-6361/202555051","DOIUrl":"https://doi.org/10.1051/0004-6361/202555051","url":null,"abstract":"Strong broad and narrow emission lines from central broad emission line regions (BLRs) and narrow emission line regions (NLRs) are fundamental spectroscopic characteristics of broad-line active galactic nuclei (BLAGNs). The unique subclass of the true Type 2 AGNs can be identified without central hidden BLRs, which provides clues on the formation and/or the suppression of AGN BLRs. Whether were there BLAGNs that lack the central NLRs is still an open question. In the blue quasar SDSS J1251+0613, blue continuum emission and broad emission lines are both clearly detected in its SDSS spectrum, but there are no apparently detected narrow emission lines in the optical/near-UV bands, which leads to no central normal NLRs in the blue quasar SDSS J1251+0613. In order to explain the lack of NLRs, evolving NLRs are proposed in which the radial outflows carry material from BLRs to NLRs, and the current narrow line emission material lies closer to the outer side of the central BLRs in SDSS J1521+0613. Our results indicate a new unique subclass of BLAGNs, that is, BLAGNs without central normal NLRs. They might provide clues on the physical origin and/or evolution of AGN NLRs.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"7 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144652426","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":"Radio emission from flaring stars and brown dwarfs","authors":"K. Perger, B. Seli, K. Vida","doi":"10.1051/0004-6361/202555032","DOIUrl":"https://doi.org/10.1051/0004-6361/202555032","url":null,"abstract":"<i>Context<i/>. The vicinities of intermediate-to-late type dwarf stars are considered as an adequate terrain to host planets suitable for life to form. However, they oftentimes show increased stellar activity, which should be taken into consideration when seeking potential habitable planetary systems.<i>Aims<i/>. With the aim to reveal the effects of the magnetic field to the multi-band activity of dwarf stars, we search for associated radio emission for an extensive list of 14 915 brown dwarfs and 15 124 flaring stars.<i>Methods<i/>. We utilised the first and second epoch catalogues and radio maps from all three epochs of the VLASS, supplemented with X-ray catalogues based on observations by the <i>ROSAT<i/>, <i>eROSITA<i/>, and <i>XMM-Newton<i/> space telescopes, and 2-minute cadence optical light curves from the <i>TESS<i/> mission. The radio-detected sub-sample was queried for concurrent <i>TESS<i/> observations, and sources with coinciding light-curves were studied individually.<i>Results<i/>. We found no associated radio emission for brown dwarfs, and found 55 radio counterparts for the sample of flaring stars, out of which seven have coincident <i>TESS<i/> observations. The radio-detected sample follows both the radio-X-ray and the period-activity relations. We found a strong correlation between the radio powers and the stellar parameters of surface gravity, radius, and mass. We found no connection between the flare rate and the radio variability. For radio-detected stars with available effective temperatures and rotational periods, we estimated gyrochronological ages, which resulted in values of <i>T<i/><sub>gyro<sub/> ≲ 1 Gyr, with the majority of the sample being younger than 150 Myr. We found no strong connection between the occurrence of optical flares and radio variability for the individually studied stars.<i>Conclusions<i/>. We conclude that radio emission from intermediate-to-late type flaring stars is of synchrotron nature, and shares a common origin with X-ray processes. It is created by a predominantly young stellar population, and is the collective contribution of stellar flares, accretion, and coronal heating.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"20 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144652427","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":"Post-common envelope evolution of helium-core white dwarfs⋆","authors":"Leandro G. Althaus, Leila M. Calcaferro, Alejandro H. Córsico, Warren R. Brown","doi":"10.1051/0004-6361/202554891","DOIUrl":"https://doi.org/10.1051/0004-6361/202554891","url":null,"abstract":"<i>Context.<i/> Helium-core white dwarfs (He WDs) from the common envelope (CE) channel offer insights into binary evolution and compact remnant formation. Their cooling rates influence their detectability and affect age estimates of close binaries. Compared with those from stable Roche-lobe overflow (SRLOF), CE He WDs experience a distinct mass-loss history, leading to fundamental differences in the post-CE evolution of the resulting WDs.<i>Aims.<i/> We investigate how the H-envelope mass (<i>M<i/><sub>H<sub/>) affects the cooling evolution of CE He WDs. In particular, we analyze how the bifurcation point, which separates the degenerate He core from the envelope, determines the remaining <i>M<i/><sub>H<sub/> and the presence of residual H burning.<i>Methods.<i/> We computed evolutionary sequences for He WDs of 0.20 <i>M<i/><sub>⊙<sub/> to 0.42 <i>M<i/><sub>⊙<sub/>, from a 1 <i>M<i/><sub>⊙<sub/> progenitor on the red giant branch. Using the La Plata stellar evolution code (LPCODE), we followed their evolution from the post-CE phase to the cooling track, identifying two pathways depending on the remaining H: (i) non-flashing sequences, in which WDs cool without prior nuclear burning, and (ii) flashing sequences, in which H shell flashes reshape the envelope before cooling.<i>Results.<i/> CE He WDs with minimal <i>M<i/><sub>H<sub/> cool rapidly after formation, with negligible residual H burning. For a sample with <i>T<i/><sub>eff<sub/> between 12 000 and 27 000 K, our models predict ages of 5–130 Myr, increasing to slightly above 300 Myr for <i>T<i/><sub>eff<sub/><10 000 K, which is much younger than those from SRLOF sequences. In contrast, WDs with more <i>M<i/><sub>H<sub/> sustain residual nuclear burning, delaying cooling. At <i>T<i/><sub>eff<sub/><10 000 K, these models predict ages of several Gyr, far exceeding those from SRLOF and minimal-envelope sequences. Flashing sequences significantly extend the pre-WD phase compared to non-flashing sequences, but this phase remains much shorter than in SRLOF evolution. The amount of <i>M<i/><sub>H<sub/> also affects mass and surface gravity estimates, introducing systematic differences from SRLOF WDs at a given <i>T<i/><sub>eff<sub/>.<i>Conclusions.<i/> The evolutionary paths of CE He WDs differ significantly from those of SRLOF-produced WDs. Minimal-envelope CE WDs cool rapidly and merge at lower temperatures, while those with sustained H burning remain bright for longer and merge at higher temperatures. These differences with SRLOF WDs are critical for understanding the evolutionary history and final fate of He WDs in compact binaries.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"12 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144652236","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":"Navigating AGN variability with self-organizing maps","authors":"Ylenia Maruccia, Demetra De Cicco, Stefano Cavuoti, Giuseppe Riccio, Paula Sánchez-Sáez, Maurizio Paolillo, Noemi Lery Borrelli, Riccardo Crupi, Massimo Brescia","doi":"10.1051/0004-6361/202553866","DOIUrl":"https://doi.org/10.1051/0004-6361/202553866","url":null,"abstract":"<i>Context.<i/> The classification of active galactic nuclei (AGNs) is a challenge in astrophysics. Variability features extracted from light curves offer a promising avenue for distinguishing AGNs and their subclasses. This approach would be very valuable in sight of the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST).<i>Aims.<i/> Our goal is to utilize self-organizing maps (SOMs) to classify AGNs based on variability features and investigate how the use of different subsets of features impacts the purity and completeness of the resulting classifications.<i>Methods.<i/> We derived a set of variability features from light curves, similar to those employed in previous studies, and applied SOMs to explore the distribution of AGNs subclasses. We conducted a comparative analysis of the classifications obtained with different subsets of features, focusing on the ability to identify different AGNs types.<i>Results.<i/> Our analysis demonstrates that using SOMs with variability features yields a relatively pure AGNs sample, though completeness remains a challenge. In particular, Type 2 AGNs are the hardest to identify, as can be expected. These results represent a promising step toward the development of tools that may support AGNs selection in future large-scale surveys such as LSST.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"96 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144652237","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 Sagittarius stellar stream embedded in a fermionic dark matter halo","authors":"Santiago Collazo, Martín F. Mestre, Carlos R. Argüelles","doi":"10.1051/0004-6361/202450867","DOIUrl":"https://doi.org/10.1051/0004-6361/202450867","url":null,"abstract":"<i>Context<i/>. Stellar streams are essential tracers of the gravitational potential of the Milky Way, with key implications for the problem of dark matter model distributions, either within or beyond phenomenological ΛCDM halos.<i>Aims<i/>. For the first time in the literature, a dark matter (DM) halo model based on first physical principles such as (quantum) statistical mechanics and thermodynamics is used to try to reproduce the 6D observations of the Sagittarius (Sgr) stream. Thus, we aim to extract quantitative and qualitative conclusions on how well our assumptions stand with respect to the observations. We model both DM halos, the one of the Sgr dwarf and the one of its host, with a spherical self-gravitating system of neutral fermions that accounts for the effects of particle escape and fermion degeneracy (due to the Pauli exclusion principle), the latter causing a high-density core at the center of the halo. Full baryonic components for each galaxy are also considered.<i>Methods<i/>. We used a spray algorithm with ∼ 10<sup>5<sup/> particles to generate the Sgr tidal debris, which evolves in the combined gravitational potential of the host-progenitor system, to then make a direct comparison with the full phase-space data of the stream. We repeated this kind of simulation for different parameter setups of the fermionic model including the particle mass, with special attention to testing different DM halo morphologies allowed by the physics, including polytropic density tails as well as power-law-like trends.<i>Results<i/>. We find that the fermionic halo models considered can only reproduce the trailing arm of the Sgr stream. Within the observationally allowed span of enclosed masses where the stream moves, neither the power-law-like nor the polytropic behavior of the fermionic halo models can answer for the observed trend of the leading tail – a conclusion that is shared by former analyses using other types of spherically symmetric halos. Thus, we conclude that further model improvements, such as abandoning spherical symmetry and including the Large Magellanic Cloud perturber, are needed for the proper modeling of the overall Milky Way potential within this kind of first-principle halo model.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"662 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144652467","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":"Unlocking the mystery of strontium synthesis in the early Galaxy through analysis of barium isotopes in very metal-poor stars★","authors":"T. M. Sitnova, L. Lombardo, L. I. Mashonkina, F. Rizzuti, G. Cescutti, C. J. Hansen, P. Bonifacio, E. Caffau, A. Koch-Hansen, G. Meynet, R. Fernandes de Melo","doi":"10.1051/0004-6361/202555073","DOIUrl":"https://doi.org/10.1051/0004-6361/202555073","url":null,"abstract":"<i>Aims<i/>. We determine the contributions of the rapid (r) and slow (s) neutron capture processes to the Ba isotope mixture, along with Ba, Eu, and Sr NLTE abundances, in a sample of very metal-poor stars. The selected stars formed before the contribution from the main s-process in low- and intermediate-mass stars became significant. Some of our sample stars are enhanced in Sr, with [Sr/Ba] reaching up to 0.7. These stars gained their high Sr abundance from a poorly understood process, sometimes referred to in the literature as a light element primary process, which may appear to be a weak s-process or a weak r-process. Our aim is to uncover the nature of this additional Sr source.<i>Methods<i/>. The abundances derived from the resonance Ba II 4554 and 4934 Å lines are influenced by the adopted Ba isotope mixture. We computed Ba isotope mixtures corresponding to different r- to s-process contributions (pure r-process, 80%/20%, 50%/50% and 12%/88%, i.e. solar ratio) and determined the corresponding abundances from the Ba II resonance lines in each sample star. Additionally, we determined Ba abundances from weak subordinate Ba II lines, which are unaffected by the adopted Ba isotope mixture. We then compared the Ba abundances derived from the subordinate lines with those from the Ba II resonance lines.<i>Results<i/>. We find a higher s-process contribution to Ba isotopes in stars with greater [Sr/Eu] and [Sr/Ba] overabundances, suggesting that the additional Sr synthesis was due to the early s-process occurring in massive stars. Using Sr-enhanced stars, we estimate the [Sr/Ba] ratio produced by the early s-process and obtain [Sr/Ba]<sub>earlyS<sub/> = 1.1 ± 0.2. The derived value should be regarded as an upper limit, as we cannot definitively exclude the possibility of a contribution to Sr from the weak r-process, which produces Sr but not Ba. Regarding the potential synthesis of Sr and Ba in the i-process in massive stars, our results for Ba isotopes and element abundances argue that there was no detectable contribution from this process within the error bars in our sample stars.<i>Conclusions<i/>. In the early Galaxy, before significant main s-process enrichment, barium and strontium were produced primarily by the main r-process and the early s-process, which occurred in rapidly rotating massive stars.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"6 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144652234","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":"Planetary edge trends","authors":"Meng-Fei Sun, Ji-Wei Xie, Ji-Lin Zhou, Beibei Liu, Nikolaos Nikolaou, Sarah C. Millholland","doi":"10.1051/0004-6361/202553671","DOIUrl":"https://doi.org/10.1051/0004-6361/202553671","url":null,"abstract":"<i>Context<i/>. Recent advancements in exoplanet detection have led to over 5900 confirmed detections. The planetary systems hosting these exoplanets exhibit remarkable diversity.<i>Aims<i/>. The position of the innermost planet (i.e., the inner edge) in a planetary system provides important information about the relationship of the entire system to its host star properties, offering potentially valuable insights into planetary formation and evolution processes.<i>Methods<i/>. In this work, based on the <i>Kepler<i/> Data Release 25 catalog combined with LAMOST and <i>Gaia<i/> data, we investigate the correlation between stellar mass and the inner edge position across different populations of small planets in multi-planetary systems, such as super-Earths and sub-Neptunes. By correcting for the influence of stellar metallicity and analyzing the impact of observational selection effects, we confirm the trend that as stellar mass increases, the position of the inner edge shifts outward.<i>Results<i/>. Our results reveal a stronger correlation between the inner edge and stellar mass (<i>a<i/><sub>in<sub/> ∝ <i>M<i/><sub>⋆<sub/><sup>γ1<sup/>), with a power-law index of <i>γ<i/><sub>1<sub/> = 0.6-1.1, which is larger compared to previous studies. The stronger correlation in our findings is primarily attributed to two factors: first, the metallicity correction applied in this work enhances the correlation; second, the previous use of occurrence rates to trace the inner edge weakens the observed correlation.<i>Conclusions<i/>. Through comparison between observed statistical results and current theoretical models, we find that the pre-main-sequence dust sublimation radius of the protoplanetary disk best matches the observed inner edge-stellar mass. Therefore, we conclude that the inner dust disk likely limits the innermost orbits of small planets, contrasting with the inner edges of hot Jupiters, which are associated with the magnetospheres of gas disks, as suggested by previous studies. This highlights that the inner edges of different planetary populations are likely regulated by distinct mechanisms.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"24 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144652235","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":"Gravitational influence of the globular cluster NGC 7078 (M 15) flyby of the Oort cloud system","authors":"Maryna Ishchenko, Peter Berczik","doi":"10.1051/0004-6361/202555028","DOIUrl":"https://doi.org/10.1051/0004-6361/202555028","url":null,"abstract":"<i>Context<i/>. It is crucial to understand the interaction between globular clusters (GCs) and the Oort cloud, as close flybys of such massive objects can significantly disturb the cloud’s structure and redirect comets towards the inner Solar System. This increases the risk of impacts on Earth. Studying such events can teach us about the evolution and stability of the Solar System, as well as the effect of external gravitational forces on its dynamics over time.<i>Aims<i/>. In our study of the gravitational effects of the flyby of the NGC 7078 or M 15 GC on the Oort cloud, we focus on two types of approximation. First, we investigate the impact on the Sun’s orbit during close passages, treating the GC as a point mass. At the second stage, we use a complete <i>N<i/>-body system representation of the GC comprising over one million particles. The ultimate goal of the research is to quantify the number of particles stripped from the Oort cloud, and to understand the conditions under which this occurs.<i>Methods<i/>. We carried out a dynamical study of the gravitational interaction between Oort cloud particles and galactic GCs within the time-varying galactic external potential. Initially, the GCs are represented as point masses orbiting the Galaxy alongside the Sun and the Oort cloud system. This study was also extended to include the case of NGC 7078, for which full <i>N<i/>-body long-term dynamical modelling of the GC itself was used.<i>Results<i/>. Our study reveals significant variations in the impact of NGC 7078 on the Oort cloud, depending on whether it is modelled as a point mass or a complete <i>N<i/>-body system. The <i>N<i/>-body system results in much greater stripping of Oort cloud particles, with over 52° stripped during a close pass, compared to a few percent in the point mass model for a flyby at a large distance (>200 pc) and 36° for a closer 10 pc point mass flyby. The <i>N<i/>-body system also causes substantial expansion, with particles spreading over 50 pc from the Sun within 30 Myr after the GC’s crossing. This creates a twisted and flattened cloud structure with extended outer tails. These stripped cloud particles (more than 10°) spread across the galaxy, reaching distances of up to 16 kpc from the Sun. These differences emphasise the importance of using detailed <i>N<i/>-body simulations to accurately evaluate the gravitational influence of GCs on the Oort cloud and shed light on the varying effects of simple versus complex system representations.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"29 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144652421","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":"Water vapour masers in long-period variable stars","authors":"J. Brand, D. Engels, A. Zanichelli, S. Etoka","doi":"10.1051/0004-6361/202554822","DOIUrl":"https://doi.org/10.1051/0004-6361/202554822","url":null,"abstract":"&lt;i&gt;Context&lt;i/&gt;. We carry out decades-long single-dish monitoring of the variation in water-maser emission associated with the circumstellar envelopes (CSEs) of different types of evolved stars.&lt;i&gt;Aims&lt;i/&gt;. We follow the variation in the maser emission over long time intervals (multiple optical periods) to understand the structure and kinematics of the stellar wind that drives the maser clouds away from the star. We also determine how this may depend on the stellar properties.&lt;i&gt;Methods&lt;i/&gt;. We carried out monitoring campaigns with single-dish telescopes of water-maser emission at 22 GHz in the CSEs of four stars: o Cet, R Leo, χ Cyg, and R Cas. The observations took place with some interruptions between 1987 and 2023. The exact time interval differed from one star to the next, but no star was monitored for fewer than 15 years.&lt;i&gt;Results&lt;i/&gt;. The variability in integrated flux in the masers in R Cas and o Cet followed the variability in the optical with the same period, but with a lag of about one-third in phase. R Leo was too often below our sensitivity threshold for us to determine a radio period. Remarkably, no maser at all was detected in χ Cyg. The variability in the masers in R Cas has a distinctive pattern. The total flux, modulated by the pulsations of the star, gradually increases to a maximum, which is followed by a similar decrease. This takes about 20 years. The pattern is repeated after an interval of quiescence of several years. Our observations have covered about one and a half cycle of this pattern so far. During its decline from a maximum, the variation in the flux resembles a damped harmonic oscillator. There are two dominant emission components that move almost tangentially on either side of the star with respect to the observer. The redshifted component likely originates from a single cloud and seems to be falling back towards the star. The blue component, moving in the CSE hemisphere nearest to us, has no drift in the line-of-sight velocity and appears to originate in a time series of short-living clouds with line-of-sight velocities within ~1 km s&lt;sup&gt;−1&lt;sup/&gt; of each other. No systematic velocity drifts are found in R Leo and o Cet. A few bursts of emission were detected at infrequent times in R Cas and R Leo that lasted about a year and caused an increase in the flux density by 1-2 orders of magnitude. The velocity range of the maser emission is ≲10 kms&lt;sup&gt;−1&lt;sup/&gt;, which is narrower than the majority of the Miras and semi-regular variables we studied so far. In particular, in the stars with a low bolometric luminosity, o Cet and R Leo, only the brightest maser components from a limited part of the CSE are visible.&lt;i&gt;Conclusions&lt;i/&gt;. The existence of a zone in the CSE with favourable conditions for maser excitation is confirmed most clearly in the case of R Cas through the unique pattern of its maser variability. The bolometric luminosity of a star and the velocity range of its water-maser emission, that is, the number of ","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"84 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-07-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"144652466","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}