Subjects -> ASTRONOMY (Total: 94 journals)
Showing 1 - 46 of 46 Journals sorted alphabetically
Advances in Astronomy     Open Access   (Followers: 49)
Annual Review of Astronomy and Astrophysics     Full-text available via subscription   (Followers: 50)
Annual Review of Earth and Planetary Sciences     Full-text available via subscription   (Followers: 67)
Artificial Satellites     Open Access   (Followers: 21)
Astrobiology     Hybrid Journal   (Followers: 11)
Astronomical & Astrophysical Transactions: The Journal of the Eurasian Astronomical Society     Hybrid Journal   (Followers: 7)
Astronomical Review     Open Access   (Followers: 5)
Astronomische Nachrichten     Hybrid Journal   (Followers: 4)
Astronomy & Geophysics     Hybrid Journal   (Followers: 49)
Astronomy and Astrophysics     Full-text available via subscription   (Followers: 67)
Astronomy and Computing     Hybrid Journal   (Followers: 6)
Astronomy Letters     Hybrid Journal   (Followers: 22)
Astronomy Reports     Hybrid Journal   (Followers: 22)
Astronomy Studies Development     Open Access   (Followers: 15)
Astroparticle Physics     Hybrid Journal   (Followers: 10)
Astrophysical Bulletin     Hybrid Journal   (Followers: 4)
Astrophysics     Hybrid Journal   (Followers: 35)
Astrophysics and Space Science     Hybrid Journal   (Followers: 49)
Astrophysics and Space Sciences Transactions (ASTRA)     Open Access   (Followers: 60)
Astropolitics: The International Journal of Space Politics & Policy     Hybrid Journal   (Followers: 13)
Celestial Mechanics and Dynamical Astronomy     Hybrid Journal   (Followers: 15)
Chinese Astronomy and Astrophysics     Full-text available via subscription   (Followers: 25)
Colloid Journal     Hybrid Journal   (Followers: 2)
Comptes Rendus : Physique     Open Access   (Followers: 2)
Computational Astrophysics and Cosmology     Open Access   (Followers: 6)
Earth and Planetary Science Letters     Hybrid Journal   (Followers: 143)
Earth, Moon, and Planets     Hybrid Journal   (Followers: 47)
Earth, Planets and Space     Open Access   (Followers: 77)
EAS Publications Series     Full-text available via subscription   (Followers: 8)
EPL Europhysics Letters     Partially Free   (Followers: 8)
Experimental Astronomy     Hybrid Journal   (Followers: 38)
Expert Opinion on Astronomy and Astrophysics     Open Access   (Followers: 8)
Extreme Life, Biospeology & Astrobiology - International Journal of the Bioflux Society     Full-text available via subscription   (Followers: 4)
Few-Body Systems     Hybrid Journal   (Followers: 1)
Foundations of Physics     Hybrid Journal   (Followers: 40)
Frontiers in Astronomy and Space Sciences     Open Access   (Followers: 15)
Galaxies     Open Access   (Followers: 6)
Globe, The     Full-text available via subscription   (Followers: 3)
Gravitation and Cosmology     Hybrid Journal   (Followers: 6)
Icarus     Hybrid Journal   (Followers: 71)
International Journal of Advanced Astronomy     Open Access   (Followers: 21)
International Journal of Astrobiology     Hybrid Journal   (Followers: 4)
International Journal of Astronomy     Open Access   (Followers: 22)
International Journal of Astronomy and Astrophysics     Open Access   (Followers: 36)
International Journal of Satellite Communications Policy and Management     Hybrid Journal   (Followers: 15)
International Letters of Chemistry, Physics and Astronomy     Open Access   (Followers: 8)
ISRN Astronomy and Astrophysics     Open Access   (Followers: 14)
Journal for the History of Astronomy     Full-text available via subscription   (Followers: 20)
Journal of Astrobiology & Outreach     Open Access   (Followers: 5)
Journal of Astronomical Instrumentation     Open Access   (Followers: 3)
Journal of Astrophysics     Open Access   (Followers: 33)
Journal of Astrophysics and Astronomy     Open Access   (Followers: 58)
Journal of Atmospheric and Solar-Terrestrial Physics     Hybrid Journal   (Followers: 133)
Journal of Geophysical Research : Planets     Full-text available via subscription   (Followers: 116)
Journal of Geophysical Research : Space Physics     Full-text available via subscription   (Followers: 136)
Journal of High Energy Astrophysics     Full-text available via subscription   (Followers: 25)
Kinematics and Physics of Celestial Bodies     Hybrid Journal   (Followers: 11)
KronoScope     Hybrid Journal   (Followers: 1)
Macalester Journal of Physics and Astronomy     Open Access   (Followers: 5)
Monthly Notices of the Royal Astronomical Society     Hybrid Journal   (Followers: 13)
Monthly Notices of the Royal Astronomical Society : Letters     Hybrid Journal   (Followers: 2)
Nature Astronomy     Hybrid Journal   (Followers: 14)
New Astronomy     Hybrid Journal   (Followers: 26)
New Astronomy Reviews     Full-text available via subscription   (Followers: 19)
Nonlinear Dynamics     Hybrid Journal   (Followers: 19)
NRIAG Journal of Astronomy and Geophysics     Open Access   (Followers: 4)
Physics of the Dark Universe     Open Access   (Followers: 4)
Planetary and Space Science     Hybrid Journal   (Followers: 106)
Planetary Science     Open Access   (Followers: 52)
Proceedings of the International Astronomical Union     Full-text available via subscription   (Followers: 2)
Publications of the Astronomical Society of Australia     Hybrid Journal   (Followers: 3)
Publications of the Astronomical Society of Japan     Hybrid Journal   (Followers: 4)
Research & Reviews : Journal of Space Science & Technology     Full-text available via subscription   (Followers: 20)
Research in Astronomy and Astrophysics     Full-text available via subscription   (Followers: 38)
Revista Mexicana de AstronomĂ­a y AstrofĂ­sica     Open Access   (Followers: 3)
Science China : Physics, Mechanics & Astronomy     Full-text available via subscription   (Followers: 4)
Science China Physics, Mechanics & Astronomy     Hybrid Journal   (Followers: 4)
Solar Physics     Hybrid Journal   (Followers: 29)
Solar System Research     Hybrid Journal   (Followers: 15)
Space Science International     Open Access   (Followers: 118)
Space Science Reviews     Hybrid Journal   (Followers: 92)
Space Weather     Full-text available via subscription   (Followers: 27)
Transport and Aerospace Engineering     Open Access   (Followers: 13)
Universe     Open Access   (Followers: 6)
Similar Journals
Journal Cover
Astrophysics and Space Science
Journal Prestige (SJR): 0.616
Citation Impact (citeScore): 1
Number of Followers: 49  
 
  Hybrid Journal Hybrid journal (It can contain Open Access articles)
ISSN (Print) 1572-946X - ISSN (Online) 0004-640X
Published by Springer-Verlag Homepage  [2469 journals]
  • Effect of magnetic connectivity on CubeSat needle probe measurement

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      Abstract: Abstract We investigate numerically the impact of magnetic field orientation on needle Langmuir probe (NLP) onboard nano-satellites. For this purpose, we model the interaction between the CubeSat and ionospheric plasma under realistic plasma conditions by using the 3D Particle-In-Cell code PTetra. The magnetic field and plasma parameters are estimated from the International Geomagnetic Reference Field (IGRF) and International Reference Ionosphere (IRI) models, respectively. The study demonstrates the effect of magnetic field connectivity by computing the current-voltage characteristics of the NLP on a 3U CubeSat. Three different orientations of the magnetic field are considered such that the probe-spacecraft system is either magnetically connected or magnetically disconnected. The magnetically connected case corresponds to the orientation of the magnetic field in which the magnetic field lines intersect the NLP and the satellite body. Conversely, in the magnetically disconnected case the magnetic field lines intersect the probe but do not intersect the spacecraft body. The current characteristics of the needle probe computed for the cases considered, illustrate the sensitivity of the collected current to the orientation of the magnetic field. It can be inferred that the effect of the magnetic field connectivity can also be taken in to account for the interpretation of in situ measurements of the needle Langmuir probes on CubeSats. The present study will be helpful to understand the detailed interaction between nano-satellites and the low Earth orbit plasma environment.
      PubDate: 2022-05-19
       
  • Canonical scalar field inflation in f ( T ) $f(T)$ gravity with well-known
           potentials

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      Abstract: Abstract We investigate the canonical scalar field inflation under the realm of power law \(f(T)\) gravity model by assuming Valley hybrid inflation potential ( \(V(\varphi )=M^{4} [1+(\frac{\varphi}{\mu})^{p}]\) ), exponential potential \((V(\varphi )=V_{o} e^{-\frac{\varphi}{\varphi _{o}}})\) and Woods-Saxon potential \(V(\varphi )=\frac{V_{o}}{1+\beta e^{-b \kappa \varphi}}\) . We explore slow roll parameters \((\varepsilon _{1}, \varepsilon _{2})\) , number of \(e\) -folds \((N)\) , scalar spectral index \((n_{s})\) , scalar to tensor ratio \((r)\) and running of the scalar spectral index \((\alpha )\) . We find that the results evaluated for these observable are consistent with the Planck 2018 results.
      PubDate: 2022-05-18
       
  • On counter-rotating, self-gravitating warped discs in galactic nuclei

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      Abstract: Abstract We present the results of our simulations regarding the evolution of self-gravitating, counter-rotating warped discs surrounding supermassive black holes in galactic nuclei. We assume that first, a disc forms around a central black hole and settles into a steadily precessing warped disc configuration. Then, a counter-rotating, nearly planar disc forms around the pre-existing one. Modeling a disc as a collection of concentric, circular, tilted rings of non-negligible mass, we find a steadily precessing equilibrium warped disc solution for the inner disc for a set of parameters relevant to discs in galactic nuclei. By assuming different inclination angles between the inner and the outer discs, we follow their orbital evolution and construct their position-velocity diagrams and maps. Our results suggest that when the outer disc initially lies at the equatorial plane of the inner one, but counter-rotates, the two discs evolve without loosing their coherence. However, when the outer disc is initially inclined to the inner one, the inclinations of the rings making up the discs are altered such that the outer disc looses its coherence and becomes disrupted.
      PubDate: 2022-05-17
       
  • Contrasting the bulk viscous model with the standard Λ $\Lambda$ CDM
           using Bayesian statistics

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      Abstract: Abstract The causal dissipative model is a plausible choice to explain the late accelerated epoch of the universe. At the same time, \(\Lambda\) CDM is considered the standard model to explain the cosmological data corresponding to the late evolution of the universe. We consider a bulk viscous model in which dissipation is driven by the bulk viscosity \(\zeta =\alpha \rho ^{1/2}\) , described using the full causal Israel-Stewart theory. We computed the model parameters using the latest observational data (Pantheon). We contrasted this model with \(\Lambda\) CDM model for the late accelerated phase using the Bayesian inference method. The Bayes factor was obtained by calculating the likelihood for Pantheon data. Suitable prior values were assumed for model parameters to calculate the likelihood. It shows that the evidence for \(\Lambda\) CDM against this viscous model is very strong according to the Jeffreys scale.
      PubDate: 2022-05-16
       
  • Split differential transit photometry

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      Abstract: Abstract Transit photometry is a dependable method for detecting and characterizing exoplanets. However, the usual transit detection method requires a substantial amount of signal processing since the dip in the signal detected, an indication that there is a planet in transit, is minuscule compared to the overall background signal due mainly to its host star. In this paper, we discuss how to achieve higher planetary signals and lower noises by subtracting the flux of the equal halves of a host star — a split differential detection. We derive an expression of the split differential light curve and investigate the effect of two common noises: the white Gaussian background noise and the noise due to the occurrences of sunspots. We show that in separate simulations and derivation of analytical expression, the split differential transit doubles the signal and reduces the effective noise by a factor of \(1/\sqrt {2}\) . While our idea may be simple, a split differential detection can be realizable and can provide a more precise estimation of planetary parameters.
      PubDate: 2022-05-12
       
  • Variation of ionospheric plasma density during the annular solar eclipse
           on December 26, 2019

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      Abstract: Abstract The annular solar eclipse of the previous decade that occurred on December 26, 2019, was mostly visible from most Asian countries, including India. In this manuscript, we present the variation of ionospheric plasma density profiles at different heights during the eclipse and non-eclipse days. We use both the ground- and space-based instruments to study the depletion in the electron density profile in the ionospheric D and F layers. We use the International GNSS Service (IGS)/Global Positioning System (GPS) stations and Swarm satellites outcomes to compute ionospheric Total Electron Content (TEC). We choose the IGS stations either on the path of the annularity or in the close vicinity of the annularity belt. For the first kind, we choose two IGS stations, GUUG in Guam island near the Western Pacific and CNMR in the Northern Mariana islands. We choose two Indian stations, IISC in Bangalore and HYDE in Hyderabad, that are close to the annularity belt. We observe ∼ 20–40% depletion in the diurnal profile of TEC, as estimated from the IGS stations. This depletion is validated by a NovAtel GPS station-6 instrument situated at Hyderabad. Significant depletion in the spatio-temporal profile of TEC and electron density profile as computed from Swarm satellite data. The depletion in TEC is also validated by NASA’s CDAWEB archive using Global Ionospheric Map (GIM). We try to estimate the TEC in the F layer and the electron density in the D layer using a numerical model. We compute the solar obscuration percentage by the geometrical configuration of the Sun and Moon. For TEC we use the solar irradiation model and calculate the delay of the maximum depletion compared to the maximum obscuration. To investigate the effects of the eclipse at the lower ionospheric heights (68–88 km), we use the GPI ion-chemistry model and observe depletion in the electron density profiles of around ∼ 58–73% for all the locations. We observe that the time between the maximum depletion in the electron density and the maximum obscuration decreases with increasing height, and it gets the minimum value at an altitude of 84 km. All methods give consistent outcomes with depletion of plasma density that corroborates the effects of the solar eclipse on the Earth’s ionosphere.
      PubDate: 2022-05-06
       
  • A possible origin for the very-high-energy photons from BL Lac object S4
           0954+65 as observed on Feb 14 2015

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      Abstract: Abstract An intense flare in BL Lac S4 0954+65 was detected from February to March in 2015. Very-high-energy (VHE, \(>150~\mbox{GeV}\) ) photons in the rising phase were detected by the MAGIC telescopes, while no such high energy photons were detected during other periods. The analytical particle transport model contains a variety of physical mechanisms in the jets of a blazar. Based on this model, we propose a scenario for the origin of the VHE photons. By increasing the temperature of the external Compton soft photons ranging from 800 to 45000 K, the multiwavelength spectral energy distribution containing MAGIC data points can be reproduced. The result suggests that the broad line region still may contribute to the inverse-Compton process when the emission zone is closer to the base of the jet, despite the fact that S4 0954+65 is a BL Lac type object.
      PubDate: 2022-05-03
       
  • 3D stable and weakly unstable periodic orbits around the Earth near the
           retrograde co-orbital resonance with the Moon

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      Abstract: Abstract Stable or weakly unstable orbits in cislunar space are attractive as potential locations that natural objects including dust particles may be trapped. Identifying such orbits is not straightforward especially in high-dimensional, many-body dynamical systems. The present paper adopts a strategy of limiting the search space around symmetric periodic orbits in the Earth–Moon spatial circular restricted three-body problem. We find a variety of linearly stable or weakly unstable periodic orbits near the \(1:1\) retrograde resonance with the Moon. Characteristics of the periodic orbits are explored and their stabilities under solar gravitational perturbations are assessed to understand representative behaviours of retrograde co-orbital orbits around the Earth.
      PubDate: 2022-04-27
       
  • A study of vTEC above Nepal exploring different calibration techniques,
           including a comparison with the NeQuick-2 model

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      Abstract: Abstract In this paper, we investigate the performance of the NeQuick 2 (NeQ-2) model with respect to Ciraolo’s and Gopi’s derived ionospheric vertical Total Electron Content (vTEC) during the years 2014 and 2015. GPS observables derived from dual-frequency receivers over western Nepal (Simikot, Bhimchula, and Nepalganj) are processed to obtain the experimental vTEC utilizing Gopi’s and Ciraolo’s calibration procedures. The monthly and seasonal behavior of vTEC obtained from each calibration technique is compared with the vTEC obtained from the NeQ-2 model during a quiet period. It is observed that the vTEC value obtained from all studied approaches started to increase from 00:00 Universal Time (UT = Local Time(LT) +5:45), reached a maximum around 08:00 UT (13:45 LT), followed by a decrease, attaining a minimum value around 23:00 UT (4:45 LT). Moreover, a comparative study showed that vTEC computed using the Ciraolo calibration technique overestimates GPS vTEC, calculated in all hours and months by Gopi’s approach. In the Spring and Summer, vTEC derived using Ciraolo’s TEC calibration overestimates NeQ-2 and underestimates it in the Autumn and Winter. It is found that NeQ-2 model vTEC is favorably associated with GPS vTEC obtained using the Gopi procedure in Spring and correlates with the Ciraolo technique in Autumn. Two GPS vTEC estimations demonstrate superior consistency in the Summer and Winter seasons over the region of Nepal. It is found that the mean absolute difference between NeQ-2 prediction and GPS vTEC procured through the Gopi approach is less on the storm event day. By contrast, it is discovered less by the Ciraolo technique when the storm is recovering (except for a few cases).
      PubDate: 2022-04-19
       
  • Kinematics and interplanetary characteristics of a halo Coronal Mass
           Ejection: a multi-wavelength analysis

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      Abstract: Abstract In this paper, we present the evolution and speed expansion of a shock driven by a Coronal Mass Ejection (CME) that triggered a type II radio. We combine radio analysis with a broad range of observations taken by other ground-based and space borne observatories to track the evolution of this CME/shock from Sun to 1 AU. The Halo CME studied here occurred on 22 August 2015 at 07:12 UT with a linear speed of 547 km/s derived from white-light observations obtained by the SoHO/LASCO spacecraft. The CME and its associated flare (M1 Class at 06:39 UT) originated at active region 12403 located at S14E09 on the visible solar disk. Type II radio bursts drift with the shock propagation up from the solar surface and produce emissions at the fundamental and higher harmonic frequencies which can be seen in radio dynamic spectrograms. The speed of the shock derived from radio observations was consistent with white-light observations. We combined different models to estimate the evolution of the ambient coronal magnetic field at lower corona. We present evidence that this halo CME has been detected in interplanetary space near 1 AU as a smooth rotation in the interplanetary magnetic field suggesting the passage of a magnetic cloud but no shock detected in situ. We compared the CME arrival time with the arrival time obtained from the Empirical shock arrival model and drag-based model. We discuss the importance of these findings.
      PubDate: 2022-04-13
       
  • Two dimensional clustering of Gamma-Ray Bursts using durations and
           hardness

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      Abstract: Abstract Gamma-Ray Bursts (GRBs) have been traditionally divided into two categories: “short” and “long” with durations less than and greater than two seconds, respectively. However, there is a lot of literature (with conflicting results) regarding the existence of a third intermediate class. To investigate this issue, we carry out a two-dimensional classification using the GRB hardness and duration, and also incorporating the uncertainties in both the variables, by using an extension of Gaussian Mixture Model called Extreme Deconvolution (XDGMM). We carry out this analysis on datasets from two detectors, viz. BATSE and Fermi-GBM. We consider the duration and hardness features in log-scale for each of these datasets and determine the best-fit parameters using XDGMM. This is followed by information theory criterion-based tests (AIC and BIC) to determine the optimum number of classes. For BATSE, we find that both AIC and BIC show preference for two components with close to decisive and decisive significance, respectively. For Fermi-GBM, AIC shows preference for three components with decisive significance, whereas BIC does not find any significant difference between two and three components. Our analysis codes have been made publicly available.
      PubDate: 2022-04-08
       
  • The fate of particles in the dynamical environment around Kuiper-Belt
           object (486958) Arrokoth

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      Abstract: Abstract The contact binary Kuiper-Belt object (486958) Arrokoth, targeted by the New Horizons mission, has a unique slope pattern, which is a result of its irregular bilobate surface shape and high spin period. Thus, some peculiar topographic regions on its surface are predisposed to lose or accumulate material, as a long circular depression feature, an impact crater called Maryland, on its small lobe. The equilibrium points of Arrokoth are also directly related to the structure of the environment near these surface features. In this work, we performed numerical simulations around Arrokoth to explore the fate of particles close to equilibrium points and their dynamical connection with its surface features. Our results suggest that most of these particles in a ring inside Arrokoth’s rotational Roche lobe fall near the equatorial region of the Maryland impact crater or close to the Bright spots area on the large lobe. Also, particles in a spherical cloud orbiting Arrokoth accumulate preferentially near low–midlatitude regions close to the longitudes of the Maryland crater and the Bright spots area. In contrast, a few particles will fall in regions diametrically opposite to them, as in the LL_Term boundary on the large lobe. High latitudes are those more empty of impacts, as in polar sites. In addition, particles larger than a couple of micrometers are not significantly perturbed by solar radiation pressure in the environment around Arrokoth.
      PubDate: 2022-04-05
       
  • Theoretical mass-luminosity relations in Gaia G-band

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      Abstract: Abstract We have analyzed the retrieval of the relation between mass and absolute Gaia G magnitude as obtained from theoretical models by Bressan et al. (Mon. Not. R. Astron. Soc. 427:127, 2012) for the stars of different luminosity classes. For subgiant and main-sequence stars, we provide approximate analytical direct and inverse relations based on the most probable value of G magnitude in the course of evolution within the given stage. A comparison with (albeit few) observational data confirms that our results can be used for the estimation of the stellar mass from Gaia photometry in the range of 1 to 10 solar mass. We argue that similar relations for other luminosity classes are not informative.
      PubDate: 2022-04-05
       
  • Two-component model of the X-ray emissions for Fermi $\mathit {Fermi}$
           -LAT selected blazars

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      Abstract: Abstract In a two-component model, the total observed emissions are the sum of two contributions, namely a beamed one and an unbeamed one. The observed beamed emissions from a relativistic jet are strongly boosted due to the beaming effect while the observed unbeamed emissions are the same as that in the co-moving frame. In the X-ay band, it is hard to separate the beamed and the unbeamed emissions from observations. However, it is interesting to investigate the X-ray emissions applying the two-component model as in Kembhavi (Mon. Not. R. Astron. Soc. 264:683, 1993). In this work, a sample of 397 blazars with available X-ray data and radio core-dominance parameters are compiled and the method proposed by Kembhavi et al is adopted to separate the two components in the X-ray emissions, then we also discuss the difference between BL Lac objects and FSRQs. Our results show that: (1) The beamed emissions dominate the X-ray emissions. (2) The averaged X-ray core-dominance parameter in BL Lacertae objects is greater than that in FSRQs. (3) A correlation between X-ray spectral index and X-ray core-dominance parameter is obtained, which supports the unified scheme of BL Lac objects, FR type I galaxies and FR type II with galaxy morphology, FSRQs unified with FR type two quasars.
      PubDate: 2022-03-30
       
  • Particle creation and Big Rip cosmological model in Lyra geometry

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      Abstract: Abstract The current paper is concerned with the universe evolution behavior within the framework of Lyra’s geometry. The modified Einstein’s field equations based on this geometry are solved under a specific creation function and a linearly varying deceleration parameter. The energy conditions are also discussed.
      PubDate: 2022-03-30
       
  • Modeling and prediction of TEC based on multivariate analysis and
           kernel-based extreme learning machine

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      Abstract: Abstract Radio wave propagation of Global Navigation Satellite System (GNSS) signals via an ionospheric medium offer the opportunity to monitor ionospheric weather nowcasting and forecasting services. The GPS-TEC observations of 20 years are taken into consideration over the Japan region at the GridPoint (134.05° E and 34.95° N). Multivariate Singular Spectrum Analysis (MSSA) is described in this article as a new model for nowcasting and ionospheric prediction. The MSSA algorithm includes a) Time series decomposition, b) reconstruction of approximate components that retain useful components and remove noise components and c) forecast of new data points by a kernel-based extreme learning machine (KELM). An essential modification of MSSA is to maximize the joint variance of all the variables based on Vautard and Ghil (1989) approach. The proposed MSSA achieves high-level now casting illustration at different seasons and solar activities. The first MSSA mode constitutes 99% of the overall variance and characterizes the solar activity variation of the TEC. The RMSE between observed and MSSA model TEC values is 1.52 TECU for the period (1997–2016) and the correlation coefficient is 0.99. Further, MSSA is used as a pre-processing tool for TEC prediction based on KELM. The performance of MSSA-KELM is evaluated in seven cases of different solar periods. The average error measurements during the seven cases are 0.70 (MAE), 5.23 (MAPE), and 0.99 (MSD) respectively. The model achieved higher forecasting accuracy and the lowest training time.
      PubDate: 2022-03-24
       
  • Active region and flare ribbon properties associated with X-class flares
           and CMEs of solar cycle 24

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      Abstract: Abstract The solar eruptive events and their origin are important in the context of forecasting their occurrence and their effects on the space and the earth. In this paper, a set of 45 X-class flare-associated coronal mass ejections (CMEs) and their source region characteristics are analysed. The X-ray flares and white light CMEs were observed by GOES and SOHO/LASCO, respectively during 2011 – 2015 in solar cycle 24. First, a preliminary analysis of their properties and relations between them is made. The CMEs in the present sample are fast (mean speed ∼1095 km/s), highly decelerating (mean a = −45 m/s2) and consists of 50% (22/40) of halo CMEs. Weak correlation is obtained from 0.27 to 0.36 between flare strength and CME properties. Secondly, the properties of the solar source region (sunspot classification according to Hale and McIntosh, sunspot area and the number of sunspots) and active region/flare ribbon (total unsigned magnetic flux, ribbon reconnection flux, active region area, ribbon area, and the ratio of ribbon to active region properties) are obtained for a subset of events and they are analysed to find the dependence of the flare/CME properties with the source region characteristics. It is found that many of the X-class flares were produced by \(\beta \Upsilon \delta \) Hale-type sunspot group and Fkc/Ekc/Dkc McIntosh sunspot class. The flare strength/CME speed is found to be correlated better with the flare ribbon properties (like reconnection flux and area) than the active region properties. In addition, the flare strength/CME speeds are compared with the SHARP parameters and we found moderate correlations between the flare strength/CME speed with SHARP parameters. The above results of X-class flare associated events are discussed in comparison and in contrast with others published for other sets of events.
      PubDate: 2022-03-21
       
  • Red giant branch bump brightness in 7 metal-poor globular clusters
           obtained with GAIA DR2

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      Abstract: Abstract The identification of the red giant branch bump brightness in metal-poor globular clusters is important for low-mass stellar evolution. The release of Gaia DR2 prompted us to revisit the red giant branch bump (RGBB) in galactic globular clusters. We apply a popular nonparametric density estimation approach, kernel density estimation (KDE), to explore the position of RGBB in 7 metal-poor globular clusters (GCs). The \(G\) and \(V\) magnitudes of the RGBB according to our clustering algorithm, \(G_{B,K}\) and \(V_{B,K}\) , respectively show the RGB bump magnitude detected by the KDE method in \(G\) band and \(V\) band. They show the overdensity location in the luminosity function of the RGB stars. Based on the results derived by KDE, a maximum-likelihood analysis via a Markov Chain Monte Carlo (MCMC) approach is adopted to detect the RGB bump feature and obtain more accurate RGBB brightnesses in \(G\) band and \(V\) band for the samples. We find that the red giant branch bump brightness becomes fainter as the global metallicity increases in clusters with \([\text{M}/\text{H}]\leq-1.4\) . We present the empirical relation between the global metallicity \([\text{M}/\text{H}]\) and absolute magnitude \(M_{V}\) of the red giant branch bump for clusters with \([\text{M}/\text{H}]\leq-1.4\) . We verify that discrepancies between observations and theory for metal-poor globular clusters with \([\text{M}/\text{H}]\leq-1.4\) .
      PubDate: 2022-03-15
       
  • Intensity variations of showers with different zenith angle ranges during
           thunderstorms

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      Abstract: Abstract Monte Carlo simulations have been performed to study the effects of near-earth thunderstorms electric field on the showers with different zenith angle ranges. A vertical and uniform atmospheric electric field model is used in our simulations. The counting rates of ground cosmic rays at YBJ (located at YangBaJing, Tibet, China, 4300 m a. s. l.) are found to be associated with the strength and polarity of the electric field. The variations are also strongly dependent upon the shower’s zenith angle and the distance to shower core. During thunderstorms, when the distance to shower core is less than a certain value (4 m in −1000 V/cm and 40 m in +1000 V/cm), the counting rates decrease as the distance to shower core decreases, and the decreased amplitude becomes larger with the increasing zenith angle and electric field strength, especially for that in positive fields (i.e., fields accelerating positive charges downwards). As the distance to shower core increases, an increase of ground cosmic ray intensity occurs, and the enhanced amplitude becomes lager with smaller zenith angles. However, when the distance to shower core is large enough (320 m in −1000 V/cm and 540 m in +1000 V/cm), the enhanced amplitude increases with the increasing zenith angle as well as the rising strength of the electric field. A clear relationship between the intensity variations of the ground cosmic rays from showers with different zenith angle ranges and the distances to shower core in fields is given in this paper. Our simulation results are beneficial to understand the flux variations obtained by ground-based cosmic ray detectors with scaler mode and shower mode, as well as the acceleration mechanisms of secondary charged particles caused by an atmospheric electric field.
      PubDate: 2022-03-15
       
  • Interacting Tsallis agegraphic dark energy in DGP braneworld cosmology

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      Abstract: Abstract The purpose of this paper is to study the Tsallis agegraphic dark energy with an interaction term between dark energy and dark matter in the DGP brane-world scenario. For this, we assume some initial conditions to obtain the dark energy density, deceleration, dark energy EoS, and total EoS parameters. Then, we analyze the statefinder parameters, \(\omega '{}_{DE}-\omega _{DE}\) plots, and classical stability features of the model. The results state that the deceleration parameter provides the phase transition from decelerated to accelerated phase. The \(\omega _{DE}\) graphs show the phantom behavior, while the \(\omega _{tot}\) exhibits the quintessence and phantom during the evolution of the Universe. Following the graphs, the Statefinder analysis shows the quintessence behavior of the model for the past and present. However, it tends to the \(\Lambda CDM\) in the following era. The \(\omega '{}_{DE}-\omega _{DE}\) plot indicates the thawing or freezing area depending on the type of era and different values of \(b^{2}\) , \(\delta \) , and \(m\) . By the square of the sound speed, we see the model is stable in the past, stable or unstable at the current time, and unstable in the future for selected values of \(b^{2}\) , \(\delta \) , and \(m\) . To test the model, we use the recent Hubble data. We also employ Akaike Information Criterion (AIC) and Bayesian Information Criterion (BIC) to compare the model with the \(\Lambda CDM\) as the reference model. In addition, we test the model using the \(H-z\) plot, and we see a turning point in the future time. The results from the best fit values for the \(\omega _{tot}\) plot emphasize that the Universe is in the quintessence region in the current time. It will enter the phantom phase, and then it will approach the \(\Lambda \) state in the future. But, the \(\omega _{DE}\) always stays on the phantom region. The model is unstable in the present and progressive era.
      PubDate: 2022-03-15
       
 
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