Astrophysics and Space Science最新文献

{"title":"General relativistic analysis of the periodicity uncovered by Leibowitz in X-ray flare sequences from Sgr A*","authors":"Bertrand Chauvineau,&nbsp;Armando Domiciano de Souza,&nbsp;Nicholas Radulescu","doi":"10.1007/s10509-024-04363-x","DOIUrl":"10.1007/s10509-024-04363-x","url":null,"abstract":"<div><p>In a recent series of papers, Leibowitz revealed two pacemaker frequencies associated with flares observed near the Sgr A* location: one for X-ray flares and the other for IR (infrared) flares. He proposed an astrophysical model to account for these two frequencies, involving a unique body orbiting the Sgr A* black hole (supposed nonrotating) close to its last stable circular orbit. In the framework of this model, the Roche lobe contacts the star’s surface near the periastrons, which generates matter pullouts. The resulting X events are then separated by time intervals that are close to integer multiples of the radial orbital frequency, which explains the X pacemaker. One revisits this X sequence orbiting-body interpretation but in a full general relativistic framework, which is more appropriate than the pseudo-Newtonian Paczyński-Wiita potential approach used by Leibowitz. One concludes that no main sequence (or giant) star can survive the tidal effects, whereas no pullout matter is possible for white dwarfs (or neutron stars), on the orbits compatible with the X pacemaker frequency, even if large eccentricities are allowed. This confirms the result obtained by Leibowitz (on the impossibility of a main sequence or usual compact star, since the only solution he found involves an “unusual internal structure star”) but (1) in the framework of full relativistic calculations and (2) extending the result to the eccentric case.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"369 10","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142409653","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Unveiling bar structures in galaxy triplets: a comprehensive study of isolated galaxy triplets in the local universe","authors":"Amira A. Tawfeek","doi":"10.1007/s10509-024-04361-z","DOIUrl":"10.1007/s10509-024-04361-z","url":null,"abstract":"<div><p>A comprehensive analysis of barred galaxies in triplet systems, drawn from the SDSS-based catalog of isolated galaxy triplets composed of 315 triplet systems (945 galaxy members) is presented. The primary objective for this study is to investigate the bar fraction (<span>(f_{bar})</span>) within these systems and explore its correlation with various intrinsic and extrinsic properties of the triplets. Our final sample, after excluding highly inclined and merging galaxies, comprises 427 galaxy members embedded in 232 triplet systems. The final sample reveals a bar fraction of 42<span>(%)</span> with a bar fraction that significantly increases in nearby systems (with smaller redshift) characterized by higher virial mass (<span>(M_{vir})</span>), lower radial velocities (<span>(sigma )</span>) among their members, and larger angular separations (<span>(r_{p})</span>) and harmonic projected distances (<span>(r_{h})</span>) between the triplet members. Additionally, it has been noticed that the large-scale structure (LSS) influences the bar fraction, with <span>(f_{bar})</span> decreasing as the distance from the primary galaxy (G1) to the first neighborhood increases (<span>(d_{NN})</span>). Furthermore, <span>(f_{bar})</span> decreases as tidal strength generated by the galaxies in the <span>(LSS)</span> (<span>(Q_{LSS})</span>)increases. These findings suggest that both the dynamical environment and the local interactions within triplet systems significantly impact the abundance of barred structures. This study provides valuable insights into the role of environmental factors in shaping galaxy morphology, particularly in systems with complex gravitational interactions.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"369 10","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-10-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142409616","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Real-time automated detection of multi-category solar radio bursts","authors":"Jingyu Deng,&nbsp;Guowu Yuan,&nbsp;Hao Zhou,&nbsp;Hao Wu,&nbsp;Chengming Tan","doi":"10.1007/s10509-024-04364-w","DOIUrl":"10.1007/s10509-024-04364-w","url":null,"abstract":"<div><p>Accurate real-time solar radio burst (SRB) detection is crucial for solar physics research and space weather forecasting. Currently, most studies on solar radio burst detection focus on single-category identification and simple discrimination of bursts. There are limited existing studies on multi-category detection. This paper proposes a real-time multi-category solar radio burst detection method to meet the requirements of real-time detection, detection accuracy, and classification accuracy in solar radio bursts. First, solar radio burst spectrums were collected from e-CALLISTO. The spectrums are labeled using LabelImg, and a dataset containing solar radio bursts of Type II, Type III, Type IIIs, Type IV, and Type V was established. Second, a full-dimensional dynamic convolution was introduced in the backbone module of the YOLOv8n model, enhancing the model’s feature extraction capability. Third, a multi-scale feature fusion network based on ConvNeXt was created to prevent feature information loss and optimize the loss function. The experimental results show that the proposed method achieves an average detection accuracy of 82.4% on the established solar radio burst dataset. Compared with the original YOLOv8n model, the accuracy increased by 3.5%. Additionally, the model operates at 140.9 frames per second, with each frame representing a spectrum of 15 minutes duration. Thus, the improved YOLOv8n model enhances the detection accuracy and speed of solar radio bursts, enabling automatic detection and localization of solar radio bursts of Type II, Type III, Type IIIs, Type IV, and Type V.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"369 10","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-10-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142409482","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Fractional stars","authors":"Hooman Moradpour,&nbsp;Shahram Jalalzadeh,&nbsp;Mohsen Javaherian","doi":"10.1007/s10509-024-04362-y","DOIUrl":"10.1007/s10509-024-04362-y","url":null,"abstract":"<div><p>This study examines the possibility of starting the process of collapsing and forming stars from a fractional molecular cloud. Although the Verlinde’s approach is employed to derive the corresponding gravitational potential, the results are easily generalizable to other gravitational potential proposals for fractional systems. It is due to the fact that the different methods, despite the difference in the details of results, all obtain power forms for the potential in terms of radius. An essential result of this analysis is the derivation of the corresponding Jeans mass limit, which is a crucial parameter in understanding the formation of stars. The study shows that the Jeans mass of a cloud in fractional gravity is much smaller than the traditional value. In addition, the study also determines the burning temperature of the resulting star using the Gamow theory. This calculation provides insight into the complex processes that govern the evolution of these celestial bodies. Finally, the study briefly discusses the investigation of hydrostatic equilibrium, a crucial condition that ensures the stability of these fractional stars. It also addresses the corresponding Lane–Emden equation, which is pivotal in understanding this equilibrium.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"369 9","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-09-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142414081","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Exploring the physics of relativistic compact stars: an anisotropic model with quadratic equation of state in buchdahl geometry","authors":"Mahesh Kumar,&nbsp;Jitendra Kumar,&nbsp;Puja Bharti,&nbsp;Amit Kumar Prasad","doi":"10.1007/s10509-024-04360-0","DOIUrl":"10.1007/s10509-024-04360-0","url":null,"abstract":"<div><p>By using the quadratic equation of state and the anisotropic energy-momentum tensor for compact stars in spherically symmetric spacetime in hydrostatic static equilibrium to solve Einstein’s field equation, we are able to create a new class of models for compact stars. We developed new solutions by solving the field equations for the distribution of matter using a well-known Buchdahl metric potential (Buchdahl in Phys. Rev. D 116:1027, 1959). The resulting anisotropic solutions exhibit good behavior and obey the energy conditions. By analyzing the TOV equation, we have confirmed the stability of the produced model, Harrison-Zeldovik-Novikov criterion, and the adiabatic index for the solution. The fulfillment of all these criteria makes this model to be utilized for the study of realistic compact objects. Also, we measured the masses and radii of star candidates like “4U 1820-30”, “PSR J1903+327”, “4U 1608-52”, “Vela X-1”, “PSR J1614-2230”, and “Cyg X-2” through this model and found these values compatible with observational values of corresponding stars. For each of the considered compact stars, we have obtained the approximate value of the moment of inertia via the obtained solution.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"369 9","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-09-23","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142413405","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Thin accretion disk images of rotating hairy Horndeski black holes","authors":"Mohaddese Heydari-Fard,&nbsp;Malihe Heydari-Fard,&nbsp;Nematollah Riazi","doi":"10.1007/s10509-024-04359-7","DOIUrl":"10.1007/s10509-024-04359-7","url":null,"abstract":"<div><p>By considering the steady-state Novikov-Thorne model, we study thin accretion disk processes for rotating hairy black holes in the framework of the Horndeski gravity. We obtain the electromagnetic properties of accretion disk around such black holes and investigate the effects of the hair parameter <span>(h)</span> on them. We find that by decreasing the hair parameter from the Kerr limit, <span>(hrightarrow 0)</span>, the radius of the innermost stable circular orbit decreases which makes thin accretion disks around rotating hairy black holes in Horndeski gravity more efficient than that for the Kerr black hole in general relativity. Furthermore, using the numerical ray-tracing method, we plot thin accretion disk images around these black holes and investigate the effects of hair parameter on the central shadow area of accretion disk.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"369 9","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-09-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142175538","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"On the age and metallicity of planet-hosting triple star systems","authors":"M. Cuntz,&nbsp;S. D. Patel","doi":"10.1007/s10509-024-04351-1","DOIUrl":"10.1007/s10509-024-04351-1","url":null,"abstract":"<div><p>We present a statistical analysis of the ages and metallicities of triple stellar systems that are known to host exoplanets. With controversial cases disregarded, so far 27 of those systems have been identified. Our analysis, based on an exploratory approach, shows that those systems are on average notably younger than stars situated in the solar neighborhood. Though the statistical significance of this result is not fully established, the most plausible explanation is a possible double selection effect due to the relatively high mass of planet-hosting stars of those systems (which spend less time on the main-sequence than low-mass stars) and that planets in triple stellar systems may be long-term orbitally unstable. The stellar metallicities are on average solar-like; however, owing to the limited number of data, this result is not inconsistent with the previous finding that stars with planets tend to be metal-rich as the deduced metallicity distribution is relatively broad.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"369 9","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142175539","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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 implications of the superposed effect of cosmic ray diurnal anisotropy on weak Forbush Events at Apatity and Moscow Neutron Monitors","authors":"F. M. Menteso,&nbsp;A. E. Chukwude,&nbsp;O. Okike,&nbsp;J. A. Alhassan","doi":"10.1007/s10509-024-04358-8","DOIUrl":"10.1007/s10509-024-04358-8","url":null,"abstract":"<div><p>Low-magnitude (FD(%) <span>(geq -3%)</span>) Forbush decreases (FDs) and their space weather linkages are recently becoming popular in the literature. Accurate timing and correct magnitude measurement of weak FDs are a desideratum. This demands disentangling the effects of the ever present cosmic ray (CR) diurnal wave that exerts undesirable influence on CR data. An enhanced version of a recently developed algorithm has been deployed to decompose raw CR data at Apatity (APTY) and Moscow (MOSC) neutron monitor (NM) stations into low and high frequency signals. A subroutine in the Fast Fourier transform software simultaneously calculates the magnitude and the epoch time of the events from the transformed data. The software selected 335 and 359 low magnitude FDs respectively for APTY and MOSC observatories. The large catalogues of low-amplitude FDs selected compared to those in literature may be attributed to the efficiency of the present algorithm. We carried out a regression analysis on the magnitude of these events and the corresponding solar wind disturbance agents. The analysis shows that for the APTY NM station, the correlation coefficient results <span>(r)</span> for FD-interplanetary magnetic field (IMF) and FD-planetary geomagnetic activity index (ap) relations are statistically significant at 95% confidence level. At the MOSC station, we find <span>(r)</span> ∼ −0.41 statistically significant at 95% confidence level for FD-solar wind speed (SWS) relation (after removing events due to co-rotating interaction regions). Analyzing all (low- and high-amplitude) FDs, <span>(r)</span> is relatively strong and statistically significant at 95% confidence level. The implications of these findings are discussed.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"369 9","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-09-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142175542","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Unravelling features of the peculiar galaxy ESO 287-IG50.","authors":"P. Freitas-Lemes,&nbsp;P. C. da Rocha-Poppe,&nbsp;M. Faúndez-Abans,&nbsp;M. de Oliveira-Abans,&nbsp;I. Rodrigues,&nbsp;J. Tello,&nbsp;V. A. Fernandes-Martin","doi":"10.1007/s10509-024-04350-2","DOIUrl":"10.1007/s10509-024-04350-2","url":null,"abstract":"<div><p>This observational study investigates the effects of interaction on the kinematics and chemical abundance of the peculiar galaxy ESO 287-IG50, which may be a polar ring galaxy in an ongoing formation process. The study utilized BVRI broad band imagery and longslit spectroscopy in the wavelength range of 4240-8700 Å. The <span>STARLIGHT</span> stellar population synthesis code was used to analyze the data, and standard diagnostic diagrams were employed to classify the main ionizing source of selected emission-line regions. Image analysis using filtering techniques revealed an inner ring with perpendicular structures at both ends, which could be the inner part of a bisymmetric spiral structure. Photometric analysis showed dusty filaments crossing the central structure, which was identified as the redder region of the galaxy, dominated by a non-negligible amount of dust. Shell-like structures, which could be remnants of a galaxy merging process, were also found. Image analysis through filtering revealed what appears to be an inner ring, with perpendicular structures at both ends, which could be the inner part of a bisymmetric spiral structure. Photometric analysis shows dusty filaments crossing the central structure. This region would be dominated by a non negligible amount of dust, identified as the redder region of the galaxy. A heliocentric radial velocity of 17 689±45 km s⁻¹ was measured, and the velocity profile exhibited a clear rotational behavior, with peak velocities of 110 km s⁻¹ to the SW and 80 km s⁻¹ to the other side. The analysis of the nuclear region using the <span>STARLIGHT</span> code revealed a stellar population consisting of approximately one-third young stars and two-thirds old stars. The predominance of an aged stellar population, a distinctive feature in galaxies undergoing interaction processes, can be attributed to the prolonged evolutionary period of this galaxy, as evidenced by the shell structures we identified as indicators of this interaction process. The [NII]<span>(lambda )</span>6584Å/H<span>(alpha )</span> ratio suggests that ESO 287-IG50 may be an AGN due to the excess of Nitrogen relative to Hydrogen in the residual spectrum, a feature not yet reported in the literature. Studying the line ratios and EW(H<span>(alpha )</span>), we notice that this galaxy exhibits a peculiar AGN, with a non-stellar origin ionization mechanism.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"369 9","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-09-03","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142175544","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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":"Enhanced astronomical source classification with integration of attention mechanisms and vision transformers","authors":"Srinadh Reddy Bhavanam,&nbsp;Sumohana S. Channappayya,&nbsp;Srijith P. K,&nbsp;Shantanu Desai","doi":"10.1007/s10509-024-04357-9","DOIUrl":"10.1007/s10509-024-04357-9","url":null,"abstract":"<div><p>Accurate classification of celestial objects is essential for advancing our understanding of the universe. MargNet is a recently developed deep learning-based classifier applied to the Sloan Digital Sky Survey (SDSS) Data Release 16 (DR16) dataset to segregate stars, quasars, and compact galaxies using photometric data. MargNet utilizes a stacked architecture, combining a Convolutional Neural Network (CNN) for image modelling and an Artificial Neural Network (ANN) for modelling photometric parameters. Notably, MargNet focuses exclusively on compact galaxies and outperforms other methods in classifying compact galaxies from stars and quasars, even at fainter magnitudes. In this study, we propose enhancing MargNet’s performance by incorporating attention mechanisms and Vision Transformer (ViT)-based models for processing image data. The attention mechanism allows the model to focus on relevant features and capture intricate patterns within images, effectively distinguishing between different classes of celestial objects. Additionally, we leverage ViTs, a transformer-based deep learning architecture renowned for exceptional performance in image classification tasks. We enhance the model’s understanding of complex astronomical images by utilizing ViT’s ability to capture global dependencies and contextual information. Our approach uses a curated dataset comprising 240,000 compact and 150,000 faint objects. The models learn classification directly from the data, minimizing human intervention. Furthermore, we explore ViT as a hybrid architecture that uses photometric features and images together as input to predict astronomical objects. Our results demonstrate that the proposed attention mechanism augmented CNN in MargNet marginally outperforms the traditional MargNet and the proposed ViT-based MargNet models. Additionally, the ViT-based hybrid model emerges as the most lightweight and easy-to-train model with classification accuracy similar to that of the best-performing attention-enhanced MargNet. This advancement in deep learning will contribute to greater success in identifying objects in upcoming surveys like the Vera C. Rubin Large Synoptic Survey Telescope.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":"369 8","pages":""},"PeriodicalIF":1.8,"publicationDate":"2024-08-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"142175545","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"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}