Astrophysics and Space Science最新文献

Stellar activity cycles on magnetically active stars can be estimated by molecular absorption bands. We have previously introduced a molecular index which compares absorptional line strength of the (TiOlambda 567nm) with its nearby continuum has previously been introduced. In this work we use this indicator to evaluation long-term activity variations for Proxima Centauri star, using spectroscopic data from HARPS. The results indicate periodicity with an activity period of (2873_{-53.9}^{+47.4}) days, which is similar to the previous measurements from other indicators.

Neutron stars (NSs) are observed with high space velocities and elliptical orbits in binaries. The magnitude of these effects points to natal kicks that originate from asymmetries during the supernova (SN) explosions. Using a growing set of long-time 3D SN simulations with the Prometheus-Vertex code, we explore the interplay of NS kicks that are induced by asymmetric neutrino emission and by asymmetric mass ejection. Anisotropic neutrino emission can arise from a large-amplitude dipolar convection asymmetry inside the proto-NS (PNS) termed LESA (Lepton-number Emission Self-sustained Asymmetry) and from aspherical accretion downflows around the PNS, which can lead to anisotropic neutrino emission (absorption/scattering) with a neutrino-induced NS kick roughly opposite to (aligned with) the kick by asymmetric mass ejection. In massive progenitors, hydrodynamic kicks can reach up to more than 1300 km s⁻¹, whereas our calculated neutrino kicks reach (55–140) km s⁻¹ (estimated upper bounds of (170–265) km s⁻¹) and only ∼(10–50) km s⁻¹, if LESA is the main cause of asymmetric neutrino emission. Therefore, hydrodynamic NS kicks dominate in explosions of high-mass progenitors, whereas LESA-induced neutrino kicks dominate for NSs born in low-energy SNe of the lowest-mass progenitors, when these explode nearly spherically. Our models suggest that the Crab pulsar with its velocity of ∼160 km s⁻¹, if born in the low-energy explosion of a low-mass, single-star progenitor, should have received a hydrodynamic kick in a considerably asymmetric explosion. Black holes, if formed by the collapse of short-lived PNSs and solely kicked by anisotropic neutrino emission, obtain velocities of only some km s⁻¹.

In this paper, we performed solar synodic period (∼27 days) and heliospheric effect for selected solar activity parameters: sunspot number (SSN), sunspot area (SSA), modified coronal index (MCI), solar radio flux (F10.7), chromospheric composite Mg II index and Galactic cosmic rays (GCRs), during the ascending phase of solar cycles 24 and 25 (2009–2012 and 2020 to 2023). The Wavelet analyses of daily data of SSN, SSA, MCI, Mg II, and F10.7, reveal a solar rotational period of ∼27 days. The R Robper method is used to validate the observed periods; near one solar rotational period during the ascending phase of solar cycles 24 and 25. We observed cross-correlation and time lag for solar activity parameters (SSN, SSA, MCI, Mg II, and F10.7) with GCRs during the ascending phase of solar cycles 24 and 25 (2009–2012 and 2020 to 2023). We found the highest time lag for SSA is ∼300 days, and for SSN is ∼270 days during the ascending phase of solar cycle 25. We also found the highest cross-correlation values are 0.998 and 0.996 for chromospheric composite Mg II index with Galactic cosmic rays (GCRs) during the ascending phase of solar cycle 24 and 25 respectively. We found the chromospheric composite Mg II index is a good indicator of solar activity indices and it is strongly correlated to SSN.

The exploration and investigation of near-Earth outer space (NES) have highlighted attention to potential threats, namely the dangers posed by asteroids and the emergence of techno-genic pollution known as space debris (SD). To address these challenges, an international initiative known as the ISON Optical Observatories Global Network was established. The International Scientific Optical Network (ISON) volunteer project commenced in 2004 intending to serve as an open repository of scientific data related to NES objects. At its zenith, the project collaborated with 33 observatories across 17 countries, operating 100 telescopes. Currently, ISON conducts its research using approximately 50 optical telescopes situated in 23 observatories across Europe, Asia, the Far East, Africa, and North & South America. The network is coordinated in conjunction with the dedicated company Research and Development Institution ISON Orbital Dynamics (RD ISON-OD), which owns 32 telescopes, observation scheduling centers, and databases focusing on SD and asteroids. ISON actively monitors the entire Geostationary Earth Orbit (GEO) region, tracking objects at GEO, Geostationary transfer orbit (GTO), High Earth Orbit (HEO), and Low Earth Orbit (LEO), while also maintaining the orbits of around 10,000 space objects. The data collected by ISON on space debris contribute to validating space debris population models and conducting conjunction assessment analyses for satellites in high orbits. Additionally, ISON is developing technology for asteroid surveys using small telescopes, providing follow-up observations, and conducting regular photometry observations of near-Earth asteroids. The project has resulted in the discovery of approximately 1600 new asteroids, obtaining 1.25 million astrometry measurements, and acquiring around 700 light curves for 300 asteroids. Space debris represents a unique subject of study, as it intersects the interests of various industries, scientific institutions, and governmental agencies.

The fraction of planetary mass objects in the Trapezium cluster that are in wide binaries is much greater than implied by extrapolation to lower masses of the fraction of stars that are wide binaries. Wide binaries may be produced by gravitational collapse of a medium with fluid vorticity. In a uniform medium with uniform vorticity the collapse criterion is independent of the size and mass of the collapsing region, which would imply a wide binary fraction independent of mass, in contradiction to observation. Angular momentum, rather than thermal pressure, may be the chief obstacle to star formation. The excess of Jupiter Mass Binary Objects in the Trapezium cluster may be attributed to cosmic ray viscosity that transports angular momentum to surrounding material. Viscosity is more effective in smaller and less massive collapsing regions, preferentially producing planetary mass wide binaries.

We present a relativistic model of anisotropic compact objects with spherically symmetric matter distribution coupled with dark energy in the framework of general theory of relativity. We assumed an ansatz for the dark energy (DE) equation of state (EoS) in addition to the baryonic matter. The interior spacetime of the compact object is described by the Finch-Skea (FS) metric and a causal domain of DE with a coupling parameter (beta ). The stellar model is employed to investigate physical features such as energy density, radial pressure, transverse pressure, anisotropy, mass-radius relation, EoS, etc. for a known pulsar, PSR J0348+0432 ((M = 2.01 pm 0.04 M_{odot }) and (R = 12.072) km) taking different (beta ). We test the stability of the stellar models for various values of (beta ) in a relativistic stellar model. The EoS of the matter configuration inside the star is determined for different (beta ) which are non-linear. The EoS obtained varying the DE coupling parameter ((beta )) indicates that the matter inside the DE star is more stiff for less (beta ). The prescription for obtaining a realistic stellar model is used to employ for other pulsars. The equation of states for those pulsars and the model parameters are determined for their observed masses and radii. The Mass-Radius (M-R) relation is independent of the coupling parameter (beta ) and the M-R relation is consistent with the observational constraints.

In this work, we investigate the phenomenologically emergent dark energy (PEDE) model and its generalized form, namely the generalized emergent dark energy (GEDE) model, which introduces a free parameter (Delta ) that can discriminate between the (Lambda )CDM model and the PEDE model. Fitting the emergent dark energy (EDE) models with the observational datasets including the cosmology-independent gamma-ray bursts (GRBs) and the observational Hubble data (OHD) at intermediate redshift, we find a large value of (H_{0}) which is close to the results of local measurement of (H_{0}) from the SH0ES Collaboration in both EDE models. In order to refine our analysis and tighten the constraints on cosmological parameters, we combine mid-redshift observations GRBs and OHD with baryon acoustic oscillations (BAOs). Finally, we constrain DE models by using the simultaneous fitting method, in which the parameters of DE models and the relation parameters of GRBs are fitted simultaneously. Our results suggest that PEDE and GEDE models can be possible alternative to the standard cosmological model, pending further theoretical explorations and observational verifications.

We consider a recently modified version of holographic dark energy, known as Barrow holographic dark energy, in the framework of (f(R, T)) gravity and consider a flat Friedmann-Lemaitre-Robertson-Walker line element for our study. We solve the field equations of the model to obtain the values of Hubble parameter and scale factor of the universe. We obtain the values of deceleration parameter and effective equation of state to discuss the evolution of the universe. Further, we constrain the model parameters using various data sets like type Ia supernova, observational Hubble data, SH0ES data etc. We use the Monte Carlo Markov Chain method to obtain the best fit values of the model parameters. We observe that the best fit present values of Hubble parameter (H_{0}=67.764_{-1.354}^{+1.274}) and (H_{0}=70.440_{-0.869}^{+0.816}), obtained for two different combinations of observational data, are in agreement with recent observations. We also constrain the case in which our model converts to the Barrow holographic dark energy model in general relativity and compare the results of both models. We compare the results with (Lambda )-CDM model wherever required. We plot deceleration parameter against redshift parameter for best fit values of the model parameters. We observe a smooth phase transition of the universe from early time decelerated expansion to accelerated expansion which shows compatibility with recent observations. The values of equation of state parameter (omega _{h}) of Barrow holographic dark energy are found to be (-0.873_{-0.078}^{+0.115}) and (-0.866_{-0.130}^{+0.156}), and age of the universe are found to be 14.09 (Gyr) and 15.43 (Gyr) for two combination of data sets for Barrow holographic dark energy model in (f(R, T)) gravity. Furthermore, we apply statefinder and (Om) diagnostic to discriminate our model from existing dark energy models.

In this work, we aim to study the consequences of presently observed accelerated expansion of the universe by assuming power-law based Starobinsky type metric (f(R)) gravity as the theory of gravity. We, here, focused on evolution of the universe by studying different cosmological parameters like Hubble parameter, Deceleration parameter and Jerk parameter etc. From our analysis, we found that the phenomenological constant of Starobinsky model ((M^{2})) has a very small value (0.6538t_{0}^{-2}), where (t_{0}) is the present age of the universe. Again, from the nature of variation of deceleration parameter and jerk parameter, we concluded that the universe has been undergoing an accelerated phase of expansion from (0.711t_{0}) and this will continue even upto the distant future.

In this manuscript we pursue tidal disruption of magnetically confined clumps of matter as candidate to interpret the twin peak high-frequency quasiperiodic oscillations (HF QPOs) seen in low-mass x-ray binaries (LMXBs). In previews works we have proposed the upper HF QPO seen in neutron star (NS) LMXBs be linked to the energy released during tidal circularization of relativistic orbits. The lower HF QPO instead might come from the energy released during spiraling and tidal stretching of the clump. The observed behavior of the coherence (Q) of the lower HF QPO was related to both the tidal stretching time-scale of the clump along the orbit and the number of turns clumps make before reaching the innermost stable bound orbit. In this paper we focus on the maximum value of (Q) across LMXBs spanning two orders of magnitudes in luminosity. We show the (Q_{max}) behavior of the lower HF QPO seen across LMXBs luminosity might be related to tidal stretching time-scale as well, giving an estimate of the magnetic field in the plasma.