Astronomy & Astrophysics最新文献

{"title":"An isolated early-type dwarf galaxy that ran away from the group environment","authors":"Sanjaya Paudel, Cristiano G. Sabiu, Suk-Jin Yoon, Patrick R. Durrell, Nau Raj Pokhrel","doi":"10.1051/0004-6361/202556457","DOIUrl":"https://doi.org/10.1051/0004-6361/202556457","url":null,"abstract":"Understanding the quenching mechanisms in dwarf galaxies is crucial for constraining models of galaxy formation and evolution. Isolated dwarf galaxies offer valuable insight by helping disentangle the relative roles of internal and environmental processes in shutting down star formation. Here we report the discovery of a quiescent early-type dwarf galaxy (dE), SDSS J011754.86+095819.0 (hereafter dE01+09), located in a nearly isolated environment at a projected distance of approximately one megaparsec from its most likely host group, the NGC 524 group. dE01+09 has <i>M<i/><sub><i>r<i/><sub/> = −15.72 and <i>g<i/> − <i>r<i/> = 0.67 mag and its light profile is well described by a Sérsic function with an index <i>n<i/> = 1.1, consistent with typical dEs. Using optical spectroscopy from the DESI survey, we derived its simple stellar population properties, and found an intermediate luminosity-weighted age of 8.3 ± 1.4 Gyr and a subsolar metallicity of −1.19 ± 0.21 dex, characteristics comparable to those of classical quiescent dEs. We propose that NGC 524 may represent an extreme example of group dynamics, in which a member galaxy, dE01+09, was ejected from its host group and subsequently evolved as an isolated system in the field.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"20 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145043402","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":"T CrB: Overview of the accretion history, Roche-lobe filling, orbital solution, and radiative modeling","authors":"U. Munari, F. Walter, N. Masetti, P. Valisa, S. Dallaporta, A. Bergamini, G. Cherini, A. Frigo, A. Maitan, C. Marino, G. Mazzacurati, S. Moretti, F. Tabacco, S. Tomaselli, A. Vagnozzi, P. Ochner, I. Albanese","doi":"10.1051/0004-6361/202555917","DOIUrl":"https://doi.org/10.1051/0004-6361/202555917","url":null,"abstract":"<i>Context.<i/> Expectations for an imminent new outburst of the recurrent symbiotic nova T CrB are mounting, initiated by the discovery in 2015 of a new enhanced mass-transfer phase (SAP), which is reminiscent of the one preceding the last recorded outburst in 1946.<i>Aims.<i/> We aim to derive a robust estimate of the most important parameters describing the physical nature of T CrB, trace the accretion history onto its white dwarf, and account for the unexpected delay in the occurrence of the new outburst. In particular, the SAP prior to 1946 was brighter and followed by a nova eruption within six months from its conclusion. This time the 2015–2023 SAP has been fainter and although two years have passed since the end of this phase, no new eruption has taken place.<i>Methods.<i/> Between 2005–2025, the period covering the SAP and the preceding quiescence, we collected a massive amount of photometric and spectroscopic observations at optical wavelengths. We analyzed these data together with the abundant ultraviolet (UV) observations available in the archive of the <i>Swift<i/> satellite.<i>Results.<i/> Guided by the results of the orbital solution and, in particular, by the radiative modeling process we employed on the whole set of available data, we derived for T CrB a binary period of 227.5528 days, along with an inclination of 61° and masses of 1.35 M<sub>⊙<sub/> and 0.93 M<sub>⊙<sub/> for the white dwarf and the M3III companions, respectively, making the mass transfer dynamically stable. The red giant completely fills its Roche lobe and at <i>V<i/><sub>rot<sub/> sin <i>i<i/> = 4.75 ± 0.26 km s<sup>−1<sup/>, it is rotating much more slowly than the 16 km s<sup>−1<sup/> co-rotation value. The ∼20° azimuth of the hot spot, implied by the hump shaping the optical light curve in quiescence, fixes the outer radius of the disk to ∼58 R<sub>⊙<sub/>. This is the same as the canonical value expected from disk theory. In quiescence, the disk is cold and mostly neutral. The SAP was caused by an inside-out collapse of the disk, during which the mean accretion rate onto the WD was ∼28× larger than in quiescence. The SAP ended in late April 2023, but from May 2024, the mass flow has intensively resumed at disk inner radii, while the collapse wave reached the outer portions of the disk. The consequent revamp in the mass accretion could fill the gap inherited by the fainter 2015–2023 SAP and eventually lead the WD accreted shell to ignition.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"28 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145043033","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 substellar population in Corona Australis","authors":"K. Mužic´, V. Almendros-Abad, A. Baptista, A. Scholz, D. Capela, S. Pearson, B. Damian, A. doBrito-doVale, T. Rom, R. Jayawardhana","doi":"10.1051/0004-6361/202555903","DOIUrl":"https://doi.org/10.1051/0004-6361/202555903","url":null,"abstract":"<i>Context<i/>. The substellar initial mass function (IMF) and the formation mechanisms of brown dwarfs (BDs) remain key open questions in star formation theory. A detailed census and characterization of the IMF in a large number of star-forming regions are essential for constraining these processes.<i>Aims<i/>. We identify and spectroscopically confirm very low-mass members of the Corona Australis (CrA) star-forming region to refine its substellar census, determine its low-mass IMF, and compare it to other clusters.<i>Methods<i/>. Using deep <i>I<i/>-band photometry from Suprime-Cam/Subaru and data from the VISTA Hemisphere Survey (VHS), we identified low-mass BD candidates in CrA. We subsequently conducted near-infrared spectroscopic follow-up of 173 of these candidates with KMOS/VLT, and we also obtained optical spectra for eight kinematic candidate members identified via <i>Gaia<i/> data using FLOYDS/LCO.<i>Results<i/>. The kinematic candidates observed with optical spectroscopy are confirmed as low-mass stellar members with spectral types M1 to M5. In contrast, all 173 BD candidates observed with KMOS are identified as contaminants. Although the follow-up yielded no new substellar members, it places strong constraints on the number of undetected substellar objects in the region. Combined with literature data, this enables us to derive the substellar IMF, which is consistent with a single power-law slope of α = 0.95 ± 0.06 in the range 0.01–1 M<sub>⊙<sub/> or α = 0.33 ± 0.19 in the range 0.01–0.1 M<sub>⊙<sub/>. The star-to-BD ratio in CrA is ∼2. We also provide updated IMFs and star-to-BD ratios for Lupus 3 and Cha I from the SONYC survey, reflecting revised distances from <i>Gaia<i/>. Finally, we estimate surface densities and median far-ultraviolet fluxes for six star-forming regions and clusters to characterize their environments and compare their substellar populations as a function of environmental properties.<i>Conclusions<i/>. The IMF and star-to-BD ratio show no clear dependence on stellar density or ionizing flux from the massive stars. A combined effect in which one factor enhances and the other suppresses BD formation also appears unlikely.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"50 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145043031","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":"A remarkable ruby: Absorption in dense gas, rather than evolved stars, drives the extreme Balmer break of a little red dot at z = 3.5","authors":"Anna de Graaff, Hans-Walter Rix, Rohan P. Naidu, Ivo Labbé, Bingjie Wang, Joel Leja, Jorryt Matthee, Harley Katz, Jenny E. Greene, Raphael E. Hviding, Josephine Baggen, Rachel Bezanson, Leindert A. Boogaard, Gabriel Brammer, Pratika Dayal, Pieter van Dokkum, Andy D. Goulding, Michaela Hirschmann, Michael V. Maseda, Ian McConachie, Tim B. Miller, Erica Nelson, Pascal A. Oesch, David J. Setton, Irene Shivaei, Andrea Weibel, Katherine E. Whitaker, Christina C. Williams","doi":"10.1051/0004-6361/202554681","DOIUrl":"https://doi.org/10.1051/0004-6361/202554681","url":null,"abstract":"The origin of the rest-optical emission of compact, red, high-redshift sources known as little red dots (LRDs) poses a major puzzle. If interpreted as starlight, it would imply that LRDs constitute the densest stellar systems in the Universe. However, alternative models suggest active galactic nuclei (AGN) may instead power the rest-optical continuum. Here, we present JWST/NIRSpec, NIRCam, and MIRI observations from the RUBIES and PRIMER programs of <i>The Cliff<i/>: a bright LRD at <i>z<i/> = 3.55 with an exceptional Balmer break, twice as strong as that of any high-redshift source previously observed. The spectra also reveal broad hydrogen (H<i>α<i/> FWHM ∼ 1500 km s<sup>−1<sup/>) and He I emission, but no significant metal lines. We demonstrate that massive evolved stellar populations cannot explain the observed spectrum, even when considering unusually steep and strong dust attenuation or reasonable variations in the initial mass function. Moreover, the formally best-fit stellar mass and compact size (<i>M<i/><sub>*<sub/> ∼ 10<sup>10.5<sup/> M<sub>⊙<sub/>, <i>r<i/><sub>e<sub/> ∼ 40 pc) would imply densities at which near-monthly stellar collisions might lead to significant X-ray emission. We argue that the Balmer break, emission lines, and H<i>α<i/> absorption line are instead most plausibly explained by a black hole star (BH<sup>*<sup/>) scenario, in which dense gas surrounds a powerful ionising source. In contrast to recently proposed BH<sup>*<sup/> models of dust-reddened AGN, we show that spectral fits in the rest UV to near-infrared favour an intrinsically redder continuum over strong dust reddening. This may point to a super-Eddington accreting massive black hole or, possibly, the presence of (super)massive stars in a nuclear star cluster. <i>The Cliff<i/> is the clearest evidence to date that at least some LRDs are not ultra-dense massive galaxies, and are instead powered by a central ionising source embedded in dense, absorbing gas.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"341 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-10","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145043038","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":"A transformer-based generative model for planetary systems","authors":"Yann Alibert, Jeanne Davoult, Sara Marques","doi":"10.1051/0004-6361/202452297","DOIUrl":"https://doi.org/10.1051/0004-6361/202452297","url":null,"abstract":"<i>Context<i/>. Numerical calculations of planetary system formation are very demanding in terms of computing power. These synthetic planetary systems can, however, provide access to correlations, as predicted in a given numerical framework, between the properties of planets in the same system. Such correlations can, in return, be used to guide and prioritise observational campaigns aimed at discovering certain types of planets, such as Earth-like planets.<i>Aims<i/>. Our goal is to develop a generative model capable of capturing correlations and statistical relationships between planets in the same system. Such a model, trained on the Bern model, offers the possibility to generate a large number of synthetic planetary systems with little computational cost. These synthetic systems can be used, for example, to guide observational campaigns.<i>Methods<i/>. We used a training database of approximately 25 000 planetary systems, each with up to 20 planets and assuming a solar-type star, generated using the Bern model. Our generative model is based on the transformer architecture, which is well-known for efficiently capturing correlations in sequences and forms the basis of all modern large language models. To assess the validity of the generative model, we performed visual and statistical comparisons, as well as machine learning-driven tests. Lastly, as a use case, we considered the TOI-469 system, in which we aimed to predict the possible properties of planets c and d based on the properties of planet b, the first planet detected in the system.<i>Results<i/>. Using different comparison methods, we show that the properties of systems generated by our model are very similar to those of the systems computed directly by the Bern model. We also demonstrate that different classifiers cannot distinguish between the directly computed and generated populations, adding confidence that the statistical correlations between planets in the same system are similar. Lastly, we show in the case of the TOI-469 system that using the generative model allows us to predict the properties of planets not yet observed based on the properties of the already observed planet.<i>Conclusions<i/>. Our generative model, which we provide to the community on our website, can be used to study a variety of problems, such as understanding correlations between certain properties of planets in systems or predicting the composition of a planetary system given some partial information (e.g. the presence of some easier-to-observe planets). Nevertheless, it is important to note that the performance of our generative model relies on the ability of the underlying numerical model – here, the Bern model – to accurately represent the actual formation process of planetary systems. Our generative model could, on the other hand, very easily be retrained using as input other numerical models provided by the community.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"64 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025416","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":"RR Lyrae stars trace the Milky Way warp","authors":"Mauro Cabrera-Gadea, Cecilia Mateu, Pau Ramos","doi":"10.1051/0004-6361/202452736","DOIUrl":"https://doi.org/10.1051/0004-6361/202452736","url":null,"abstract":"<i>Context<i/>. The outskirts of the Milky Way disc have been known to be warped since the late 1950s. Although various stellar populations have shown an underlying warped distribution, the relation between the age of the population and the warp they trace remains an open question. Understanding this relation may shed light on the origin of the warp, which remains a puzzle to be solved.<i>Aims<i/>. Our goal in this work is to detect the presence of the warp in the RR Lyrae (RRL) population of the Milky Way disc.<i>Methods<i/>. We used a compilation of the three largest public catalogues of RRL stars, precise photometric distances (∼5%), and Gaia DR3 proper motions to kinematically select a sample of thin disc RRLs in the Galactic anti-centre, where the tangential velocity best approximates the azimuthal velocity to differentiate between those that rotate (disc) and those that do not (halo). For disc-like RRLs (321), we analysed their mean vertical height and mean vertical velocity.<i>Results<i/>. For the first time, we show that RRL stars with thin disc-like kinematics trace the warp. In the anti-centre direction, the RRL population reaches a minimum in mean vertical height of ≈0.4 ± 0.2 kpc, with a trend systematically lower than the one found with classical Cepheids. The kinematical signal of the RRL warp starts at <i>R<i/> ≈ 10 kpc and, rather than resembling that of the Cepheids, shows a similar trend to the red clump population from previous works, reaching a maximum value of ≈9 ± 5 km s<sup>−1<sup/> in vertical velocity. We also obtain an estimation of the pattern speed of the RRL warp with a prograde rotation of ≈13 ± 2 km s<sup>−1<sup/> kpc<sup>−1<sup/>, which is compatible with results obtained from classical Cepheids. Finally, we also obtain a vertical velocity dispersion ≈17 km s<sup>−1<sup/>, which is inconsistent with the kinematics of a canonical old age (>10 Gyr) disc population and, instead, favours a population dominated by intermediate age stars (3–4 Gyr), in agreement with recent works that suggest the existence of such unexpected intermediate age RRLs in the thin disc.<i>Conclusions<i/>. Our results indicate that thin disc RRL stars are a dynamical intermediate-age tracer of the warp, which opens a new window to study the dependency of the warp on stellar age in the Milky Way. The warp’s age dependency will help constrain the physical mechanism behind its origin and its role in the Milky Way dynamical history.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"14 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025414","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":"YSES 2b is a background star","authors":"Matthew Kenworthy, Tomas Stolker, Jens Kammerer, William Balmer, Arthur Vigan, Sylvestre Lacour, Gilles Otten, Eric Mamajek, Christian Ginski, Mathias Nowak, Steven Martos, Jason Wang, Emily Rickman, Markus Janson, Alexander Bohn, Mariangela Bonavita","doi":"10.1051/0004-6361/202556170","DOIUrl":"https://doi.org/10.1051/0004-6361/202556170","url":null,"abstract":"<i>Aims<i/>. We wish to confirm the nature of YSES 2b, a purportedly faint companion of the young star YSES 2.<i>Methods<i/>. We used on-sky observations from SPHERE and GRAVITY to measure the astrometric position of 2b with respect to the star YSES 2, and examined the competing hypotheses of (i) a bound substellar companion versus (ii) a distant unrelated background source with a non-zero proper motion.<i>Results<i/>. YSES 2b appears to be a late-type M-dwarf star over 2 kiloparsecs behind the star YSES 2. It has a transverse velocity of ∼300 km s<sup>−1<sup/> and is located within one of the spiral arms of the Galaxy. The main discriminant was multiple epochs of GRAVITY astrometry that identified the sub-milliarcsecond parallactic motion of the star.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"103 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025415","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 cosmological lithium problem","authors":"Oswaldo D. Miranda","doi":"10.1051/0004-6361/202554482","DOIUrl":"https://doi.org/10.1051/0004-6361/202554482","url":null,"abstract":"<i>Context.<i/> The discrepancy between the predictions of primordial nucleosynthesis and the observed lithium abundance in Spite plateau stars has been attributed either to a challenge to the standard model of nucleosynthesis or to stellar processes occurring after the stars formed. To understand the origin of this discrepancy, it is crucial to link the cosmic star formation rate with a chemical enrichment model that incorporates the yields of both Population (Pop) III and II stars. It is within this framework that the evolution of lithium can be determined.<i>Aims.<i/> The primary goal is to demonstrate that there is no discrepancy between the predictions of primordial nucleosynthesis and the observed lithium abundance.<i>Methods.<i/> By combining a standard chemical evolution model with the hierarchical structure formation scenario, it is possible to determine the lithium abundance as a function of [Fe/H]. The model’s results are compared with observational data from extremely metal-poor stars, Spite plateau stars, Gaia-Enceladus sources, the Small Magellanic Cloud, lithium abundances in Solar System meteorites, and two extremely iron-poor stars: J0023+0307 and SMSS J0313–6708.<i>Results.<i/> The Spite plateau is naturally established in the range −8.0 ≲ [Fe/H]≲ − 2.0 with <sup>7<sup/>Li/H ∼1.81 × 10<sup>−10<sup/>. We find that J0023+0307 could have formed ∼4.4 × 10<sup>5<sup/> − 1.3 × 10<sup>6<sup/> years after the explosion of the first Pop III star in the Universe, whereas for SMSS J0313–6708 this event would have occurred ∼2.2 × 10<sup>5<sup/> − 4.4 × 10<sup>5<sup/> years later.<i>Conclusions.<i/> The Spite plateau serves as an observational signature of the formation of Pop III stars. The abundances observed in J0023+0307 and SMSS J0313–6708 are consistent with Pop III progenitor stars in the mass range 10 − 100 <i>M<i/><sub>⊙<sub/>. However, if some high-redshift star formation occurs within subhalo-like structures, the contribution of stars in the mass range 140 − 260 <i>M<i/><sub>⊙<sub/> to the formation of the extended Spite plateau cannot be ruled out.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"57 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025463","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":"EWOCS-IV: 1Ms ACIS Chandra observation of the supergiant B[e] star Wd1-9","authors":"K. Anastasopoulou, M. G. Guarcello, J. J. Drake, B. Ritchie, M. De Becker, A. Bayo, F. Najarro, I. Negueruela, S. Sciortino, E. Flaccomio, R. Castellanos, J. F. Albacete-Colombo, M. Andersen, F. Damiani, F. Fraschetti, M. Gennaro, S. J. Gunderson, C. J. K. Larkin, J. Mackey, A. F. J. Moffat, P. Pradhan, S. Saracino, I. R. Stevens, G. Weigelt","doi":"10.1051/0004-6361/202555305","DOIUrl":"https://doi.org/10.1051/0004-6361/202555305","url":null,"abstract":"<i>Context<i/>. Supergiant B[e] (sgB[e]) stars are exceptionally rare objects, with only a select number of confirmed examples in the Milky Way. The evolutionary pathways leading to the sgB[e] phase remain largely debated, highlighting the need for additional observations. The sgB[e] star Wd1-9, located in the massive cluster Westerlund 1 (Wd1), is enshrouded in a dusty cocoon – likely the result of past eruptive activity – leaving its true nature enigmatic.<i>Aims<i/>. We present the most detailed X-ray study of Wd1-9 to date, using X-rays that pierce through its cocoon with the aim of uncovering its nature and evolutionary state.<i>Methods<i/>. We utilised 36 <i>Chandra<i/> observations of Wd1 from the ‘Extended Westerlund 1 and 2 Open Clusters Survey’ (EWOCS), plus eight archival datasets, totalling 1.1 Ms. We used this dataset to investigate long-term variability and periodicity in Wd1-9, and analysed X-ray colours and spectra over time to uncover patterns that shed light on its nature.<i>Results<i/>. Wd1-9 exhibits significant long-term X-ray variability, within which we identify a strong ∼14-day periodic signal. We interpret this as the orbital period, marking the first period determination for the system. The X-ray spectrum of Wd1-9 is thermal and hard (<i>kT<i/> ∼ 3.0 keV), resembling the spectra of bright Wolf-Rayet (WR) binaries in Wd1, while a strong Fe emission line at 6.7 keV indicates hot plasma from a colliding-wind X-ray binary.<i>Conclusions<i/>. Wd1-9, with evidence of past mass loss, circumbinary material, a hard X-ray spectrum, and a newly detected 14-day period, displays all the hallmarks of a binary – likely a WR+OB – that recently underwent early Case B mass transfer. Its sgB[e] classification is likely phenomenological, reflecting emission from the dense circumbinary material. This places Wd1-9 in a rarely observed phase, possibly revealing a newly formed WN star, bridging the gap between immediate precursors and later evolutionary stages in Wd1.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"11 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145025462","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":"Off-centre convective zones in mass accreting stellar models","authors":"A. Miszuda","doi":"10.1051/0004-6361/202555298","DOIUrl":"https://doi.org/10.1051/0004-6361/202555298","url":null,"abstract":"We report the physical origin of transient off-centre convective zones (oCZs) that arise in mass accreting stellar models. Using detailed MESA simulations of binary evolution, we find that these oCZs are not numerical artefacts, but emerge due to a local increase in density near the retreating edge of the convective core. The density enhancement raises the local opacity, which amplifies the radiative temperature gradient ∇<sub>rad<sub/>. If this gradient surpasses the Ledoux threshold ∇<sub>L<sub/>, defined by both thermal and compositional stratification, the region becomes convectively unstable. The resulting oCZs are detached from the convective core and transient: mixing within the oCZ erases the local gradient in mean molecular weight and leaves a sharp ∇<sub><i>μ<i/><sub/> discontinuity at the boundary, thus stabilising the adjacent layers. This mechanism naturally explains the presence and evolution of oCZs, as previously reported in massive interacting stars.","PeriodicalId":8571,"journal":{"name":"Astronomy & Astrophysics","volume":"307 1","pages":""},"PeriodicalIF":6.5,"publicationDate":"2025-09-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"145009472","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}