Astrophysics and Space Science最新文献

{"title":"Classification and characterization using HCT/HFOSC spectra of carbon stars selected from the HES survey","authors":"Meenakshi Purandardas, Aruna Goswami","doi":"10.1007/s10509-024-04269-8","DOIUrl":"https://doi.org/10.1007/s10509-024-04269-8","url":null,"abstract":"<p>We present results from the analysis of 88 carbon stars selected from Hamburg/ESO (HES) survey using low-resolution spectra (R ∼1330 &amp; 2190). The spectra were obtained with the Himalayan Faint Object Spectrograph Camera (HFOSC) attached to the 2-m Himalayan Chandra Telescope (HCT). Using well-defined spectral criteria based on the strength of carbon molecular bands, the stars are classified into different groups. In our sample, we have identified 53 CH stars, four C-R stars, and two C-N type stars. Twenty-nine stars could not be classified due to the absence of prominent C₂ molecular bands in their spectra. We could derive the atmospheric parameters for 36 stars. The surface temperature was determined using photometric calibrations and synthesis of the H-alpha line profile. The surface gravity <span>(log mathrm{g})</span> estimates are obtained using parallax estimates from the Gaia DR3 database whenever possible. Microturbulent velocity (<span>(zeta )</span>) was derived using calibration equation of <span>(log mathrm{g})</span> &amp; <span>({zeta })</span>. We could determine metallicity for 48 objects from near-infrared Ca II triplet features using calibration equations. The derived metallicity ranges from −0.43 ≤ [Fe/H] ≤ −3.49. Nineteen objects were found to be metal-poor ([Fe/H] ≤ −1), 14 very metal-poor ([Fe/H] ≤ −2), and five extremely metal-poor ([Fe/H] ≤ −3.0) stars. Eleven objects were found to have a metallicity in the range −0.43 ≤ [Fe/H] ≤ −0.97. We could derive the carbon abundance for 25 objects using the spectrum synthesis calculation of the C₂ band around 5165 Å. The most metal-poor objects found will make important targets for follow-up detailed chemical composition studies based on high-resolution spectroscopy, and are likely to provide insight into the Galactic chemical evolution.</p>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139482245","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":"Impact of two severe geomagnetic storms on the ionosphere over Indian longitude sector during March-April 2023","authors":"Siva Sai Kumar Rajana,&nbsp;Sampad Kumar Panda,&nbsp;Sridevi Jade,&nbsp;Chiranjeevi G. Vivek,&nbsp;A. K. Upadhayaya,&nbsp;Arti Bhardwaj,&nbsp;Sonam Jorphail,&nbsp;Gopi Krishna Seemala","doi":"10.1007/s10509-024-04268-9","DOIUrl":"10.1007/s10509-024-04268-9","url":null,"abstract":"<div><p>We investigated the ionosphere response to the two severe geomagnetic storms in the ascending phase of solar cycle 25 which occurred during the 23-24 March 2023 (SYM-H_min = −169 nT) and 23-24 April 2023 (SYM-H_min = −233 nT) using a latitudinally aligned dense network of Global Navigation Satellite System (GNSS) receivers, magnetometers, and digisonde along the Indian longitude sector. The significant variations in TEC during the storm’s main and recovery phases are mainly linked to the influence of westward Disturbance Dynamo Electric Fields (DDEFs). During the initial phase of the March 23-24 geomagnetic storm, no changes in daytime TEC were observed, despite the storm occurring at noon time with a southward IMF Bz due to the influence of electron density in the top side ionosphere. Furthermore, both pre-reversal enhancement (PRE) and ionosphere irregularities are suppressed within two hours of their onset during the main phase of the March 23-24 storm, owing to the westward transition of zonal electric fields from an eastward direction. During the recovery phase of both storms, a daytime positive storm effect is observed over the dip equatorial region, while the beyond equatorial ionization anomaly (EIA) and mid-latitude regions perceived a negative ionospheric storm effect. This phenomenon is attributed to the influence of the dominant westward DDEFs during the period. Moreover, these DDEFs effectively inhibited the equinoctial manifestation of PRE effects and post-sunset ionospheric irregularities during the recovery phase of both storms. These findings are further confirmed with supporting information from TEC recorded by Swarm satellites, model-derived ionospheric electric fields, and thermospheric O/N2. The results from this study may advance the understanding of ionospheric response to severe geomagnetic storms under the prevailing westward DDEFs during the dayside recovery phase, complementing the global efforts for more reliable space weather modeling and prediction services.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-01-15","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139468188","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":"Matter creation cosmology with generalized Chaplygin gas","authors":"Yogesh Bhardwaj,&nbsp;C. P. Singh","doi":"10.1007/s10509-024-04267-w","DOIUrl":"10.1007/s10509-024-04267-w","url":null,"abstract":"<div><p>In this work, we discuss the dynamics of a spatially homogeneous and isotropic flat Friedmann-Lemaître-Robertson-Walker (FLRW) model of the Universe powered by the gravitationally induced ‘adiabatic’ matter creation with generalized Chaplygin gas (GCG) equation of state. In recent years, the CGC has been proposed successfully to unify the dark matter and dark energy by using an exotic equation of state <span>(p=-A/rho ^{alpha })</span>. Considering adiabatic matter creation cosmology, as developed by Prigogine et al, we examine the effect of matter creation in describing the unification with GCG by assuming the natural phenomenological matter creation rate <span>(Gamma =3beta H)</span>, where <span>(beta )</span> is a constant and <span>(H)</span> is the Hubble parameter. We constrain the proposed model using a joint observational dataset of Type Ia supernovae Pantheon, <span>(H(z))</span> and BAO with Markov-Chain Monte-Carlo (MCMC) method. In addition, we discuss the selection criterion (AIC and BIC) and stability criteria to analyze the dynamics and differences with the standard <span>(Lambda )</span>CDM model.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-01-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139430954","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":"Properties of relativistic hot accretion flow around a rotating black hole with radially varying viscosity","authors":"Monu Singh,&nbsp;Santabrata Das","doi":"10.1007/s10509-023-04263-6","DOIUrl":"10.1007/s10509-023-04263-6","url":null,"abstract":"<div><p>We examine the effect of the variable viscosity parameter (<span>(alpha )</span>) in relativistic, low angular momentum advective accretion flow around rotating black holes. Following the recent simulation studies of the magnetohydrodynamic disk that reveal the radial variation of <span>(alpha (r))</span>, we theoretically investigate the properties of the global transonic accretion flow considering a one-dimensional power-law prescription of the viscosity parameter as <span>(alpha (r) propto r^{theta })</span>, where the viscosity exponent <span>(theta )</span> is a constant. In doing so, we adopt the relativistic equation of state and solve the fluid equations that govern the flow motion inside the disk. We find that depending on the flow parameters, accretion flow experiences centrifugally supported shock transitions and such shocked accretion solutions continue to exist for wide ranges of the flow energy, angular momentum, accretion rate, and viscosity exponent, respectively. Due to shock compression, the hot and dense postshock flow (hereafter PSC) can produce the high-energy radiations after reprocessing the soft photons from the preshock flow via inverse Comptonization. Since PSC is usually described using shock radius (<span>(r_{s})</span>), compression ratio (<span>(R)</span>), and shock strength (<span>(S)</span>), we study the role of <span>(theta )</span> in detemining <span>(r_{s})</span>, <span>(R)</span>, and <span>(S)</span>, respectively. Moreover, we obtain the parameter space for a shock and find that the possibility of shock formation diminishes as <span>(theta )</span> is increased. Finally, we compute the limiting value of <span>(theta )</span> (<i>i.e.</i>, <span>(theta ^{mathrm{max}})</span>) that admits a shock and find that flow can sustain more viscosity when it accretes onto a rapidly rotating (<span>(a_{mathrm{k}} rightarrow 1)</span>) black hole in comparison to a weakly rotating (<span>(a_{mathrm{k}} rightarrow 0)</span>) black hole.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2024-01-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139104874","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":"From infinite to finite time stability in Celestial Mechanics and Astrodynamics","authors":"Alessandra Celletti","doi":"10.1007/s10509-023-04264-5","DOIUrl":"10.1007/s10509-023-04264-5","url":null,"abstract":"<div><p>Time scales in Celestial Mechanics and Astrodynamics vary considerably, from a few hours for the motion of Earth’s artificial satellites to millions of years for planetary dynamics. Hence, the time scales on which one needs to investigate the stability of celestial objects are different. Therefore, the methods of study are themselves different and might lead to specific definitions of stability, either in the sense of bounds on the initial conditions or rather in the sense of confinement in a given region of the phase space. In this work we concentrate on three different methods: perturbation theory, Nekhoroshev’s theorem, KAM theory. All theories are constructive in the sense that they provide explicit algorithms to give estimates on the parameters of the system and on the stability time. Perturbation theory gives results on finite time scales, Nekhoroshev’s theorem provides stability results on exponentially long times, KAM theory ensures the confinement between invariant tori in low-dimensional systems.</p><p>We recall the basic ingredients of each theory, starting with KAM theory, then presenting Nekhoroshev’s theorem and finally introducing perturbation theory. We provide examples of stability results for some objects of the Solar system. Precisely, we consider the stability of the rotational motion of the Moon (or other planetary satellites) within the spin-orbit model by means of KAM theory, we analyze the stability of asteroids, also in the triangular equilibrium Lagrangian points, using Nekhoroshev’s theorem, we study the Earth’s satellite dynamics through perturbation theory.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139060377","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":"Making waves in massive star asteroseismology","authors":"Dominic M. Bowman","doi":"10.1007/s10509-023-04262-7","DOIUrl":"10.1007/s10509-023-04262-7","url":null,"abstract":"<div><p>Massive stars play a major role not only in stellar evolution but also galactic evolution theory. This is because of their dynamical interaction with binary companions, but also because their strong winds and explosive deaths as supernovae provide chemical, radiative and kinematic feedback to their environments. Yet this feedback strongly depends on the physics of the supernova progenitor star. It is only in recent decades that asteroseismology – the study of stellar pulsations – has developed the necessary tools to a high level of sophistication to become a prime method at the forefront of astronomical research for constraining the physical processes at work within stellar interiors. For example, precise and accurate asteroseismic constraints on interior rotation, magnetic field strength and geometry, mixing and angular momentum transport processes of massive stars are becoming increasingly available across a wide range of masses. Moreover, ongoing large-scale time-series photometric surveys with space telescopes have revealed a large diversity in the variability of massive stars, including widespread coherent pulsations across a large range in mass and age, and the discovery of ubiquitous stochastic low-frequency (SLF) variability in their light curves. In this invited review, I discuss the progress made in understanding the physical processes at work within massive star interiors thanks to modern asteroseismic techniques, and conclude with a future outlook.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-12-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1007/s10509-023-04262-7.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"139060368","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}

{"title":"Single station modelling of ionospheric irregularities using artificial neural networks","authors":"Valence Habyarimana,&nbsp;John Bosco Habarulema,&nbsp;Daniel Okoh,&nbsp;Teshome Dugassa,&nbsp;Jean Claude Uwamahoro","doi":"10.1007/s10509-023-04261-8","DOIUrl":"10.1007/s10509-023-04261-8","url":null,"abstract":"<div><p>An empirical model of ionospheric irregularities over Mbarara (MBAR, 30.7^∘E geographic longitude, 0.6^∘S geographic latitude, 10.22^∘S geomagnetic latitude) based on Artificial Neural Networks (ANNs) is developed using Global Navigation Satellite System (GNSS) derived Total Electron Content (TEC) data from 2001–2022. This long term data helped to study the climatology of the trends, the diurnal, seasonal, and solar activity dependence of ionospheric irregularities. We used the rate of change of TEC index (ROTI) to quantify the strength of irregularities. The input space consisted of time of the day (Hr), day of the year (doy), z-component of the Interplanetary magnetic field (IMF Bz), symmetric horizontal component of the ring current (SYM-H), solar activity factor (F10.7P), and vertical <b>E</b>×<b>B</b> drift, all of which are thought to influence irregularity occurrence, though with different percentage contributions. Of these inputs, Hr, doy, and F10.7P constituted the primary input parameters (PIP). We investigated the contribution of each input to the ROTI changes by developing seven models adding an input to the PIP at each time. The greatest contributor to the modelling results was SYM-H with a percentage contribution of ≈2% (8%) for the model with both quiet and disturbed (only disturbed) conditions. The accuracy of the overall model during both geomagnetically quiet and disturbed (only disturbed) conditions was 0.1479 (0.1494) TECU/min with a correlation coefficient of 0.72 (0.65). The diurnal variability of ROTI was observed with higher values of ROTI existing between 1600 UT (1900 LT) and 2300 UT (0200 LT) than during other UT hours of the day. The ROTI values exhibited the semi-annual/seasonal variability with higher values during the March equinox than during the September equinox, and lower values during the solstice months. We further confirmed that irregularities depend on the solar activity. They are strong during high solar activity and minimal/weak during low/minimum solar activity periods.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138580998","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":"Correction to: The fundamental plane of FSRQs based on the black hole spin-mass energy","authors":"Xu Zhang,&nbsp;Quan-Gui Gao","doi":"10.1007/s10509-023-04244-9","DOIUrl":"10.1007/s10509-023-04244-9","url":null,"abstract":"","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-12-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138621976","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":"Two-dimensional MHD simulation of the Earth’s magnetosphere","authors":"Siska Filawati,&nbsp;Bambang Setiahadi,&nbsp;Bintoro A. Subagyo","doi":"10.1007/s10509-023-04256-5","DOIUrl":"10.1007/s10509-023-04256-5","url":null,"abstract":"<div><p>The magnetosphere is the outermost part of the Earth, formed by the interaction of the Earth’s dipole magnetic field and the solar wind. Solar wind conditions depend on solar activity, which can affect space weather. One of the solar activities that significantly impact space weather is Coronal Mass Ejection (CME). The magnetosphere is observed using satellites in space-based and using a magnetometer on earth-based. However, these observations are limited to a specific location and time. In this work, we are interested in employing magnetohydrodynamics (MHD) to investigate the interaction of solar wind in the magnetosphere. The MHD has four equations: transfer of mass, momentum, magnetic, and thermal energy, which explain the four main parameters of the solar wind: density, velocity, magnetic field, and pressure, respectively. From these four parameters, the response of Earth’s magnetosphere can be identified. Here, we used both analytical and numerical calculation via the SHASTA-FCT. The results show that the positive interplanetary magnetic field merges to Earth’s magnetic field. However, the negative interplanetary magnetic field does not merge with Earth’s magnetic field. We also observed that the higher solar wind speed results in the shorter simulation time. The bow shock as a result of the interaction of the solar wind and the Earth’s magnetic field is formed at a distance of <span>(sim {50{,}000} mathrm{{km}})</span>, and the magnetopause as a result of the equilibrium of the solar wind pressure and the pressure of the Earth’s magnetic field has a thickness of <span>(sim {5000} mathrm{{km}})</span>. In addition, we also discuss Alfvén velocity represents the motion of the magnetic field.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-12-06","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138546693","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":"Study of the ionospheric responses over African and Asian longitudes to the intense geomagnetic storm of August 2018","authors":"Sk Samin Kader,&nbsp;N. Dashora,&nbsp;K. Niranjan","doi":"10.1007/s10509-023-04259-2","DOIUrl":"10.1007/s10509-023-04259-2","url":null,"abstract":"<div><p>The third strongest geomagnetic storm of solar cycle 24 occurred from 25 to 31 August 2018 (minimum SYM-H index = –206 nT on 26 August) and was associated with a weak coronal mass ejection (CME) in the low solar activity period. The storm itself has shown some very unusual characteristics in interplanetary space, which unraveled further surprises in its ionospheric and thermospheric responses. This study provides a detailed analysis of the effects of this storm over the vast African-Asian longitude region over both hemispheres. The longitudinal differences in the equatorward boundary of the auroral oval and the ionospheric convection patterns are presented using the Special Sensor Ultraviolet Spectrographic Imager (SSUSI) onboard the Defense Meteorological Satellite Program (DMSP) satellite and SuperDARN observations, respectively. The global ionospheric map (GIM)-based hourly vertical TEC (total electron content) variations show large enhancements and depletions over different regions at different phases of storms. It is found that during the morning hours on 26 August, a large TEC enhancement in the Asian low latitude region is observed, but such an effect is not observed over the African region, establishing a clear longitudinal difference. The space-time structure of the enhanced ion-density observations from Swarm satellites is used to confirm the VTEC differences and their sustenance. Furthermore, a latitudinal variation in the [O/N2] ratio during 25-27 August is analyzed for a UT-dependent response and the north–south asymmetry in the O density during the main and recovery phases of the storm. A competing effect of the prompt penetration electric field and disturbance dynamo is found to dominantly modulate the longitudinal patterns, which created positive/negative ionospheric storms over the vast African-Asian region.</p></div>","PeriodicalId":8644,"journal":{"name":"Astrophysics and Space Science","volume":null,"pages":null},"PeriodicalIF":1.9,"publicationDate":"2023-12-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"138485072","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}