Astrophysics and Space Science最新文献

Linear polarimetry of unresolved stars is a powerful method for discerning or constraining the geometry of a source and its environment, since spherical sources produce no net polarization. However, a general challenge to interpreting intrinsic stellar polarization is the contribution to the signal by interstellar polarization (ISP). Here, we review methodologies for distinguishing the stellar signal from the interstellar contribution in the context of massive stars. We first characterize ISP with distance using a recent compilation of starlight polarization catalogs. Several scenarios involving Thomson scattering, rapidly rotating stars, optically thick winds, and interacting binaries are considered specifically to contrast the wavelength-dependent effects of ISP in the ultraviolet versus optical bands. ISP is recognizable in the stellar polarization from Thomson scattering in the polarization position angle rotations. For hot stars with near-critical rotation rates, the ISP declines whereas the stellar continuum polarization sharply increases. In the case of quite dense winds, strong ultraviolet lines trace the ISP, which is not always the case in the optical. In the binary case, temporal and chromatic effects illustrate how the ISP displaces variable polarization with wavelength. This study clarifies the impacts of ISP in relation to new ultraviolet spectropolarimetry efforts such as Polstar and Pollux.

The infrared (IR)/X-ray correlation of GX 339−4 is investigated based on a jet model with a modification by linking the magnetic field at the jet base to the accretion rate of the inner accretion flow though the equilibrium between magnetic pressure at horizon and the ram pressure of the accretion flow. The IR flux is attributed to the synchrotron radiation of the jet, and the X-ray flux is attributed to the advective dominated accretion flow (ADAF), synchrotron radiation of the jet and synchrotron self-Compton scattering (SSC) of the jet, respectively. We find that the observed IR/X-ray correlation with a break is well reproduced with the variation of the accretion rate if the X-ray flux originates from SSC of the jet. Either a conical ballistic jet with the magnetic field parallel to the jet axis or a conical adiabatic jet with an isotropic field can account for the correlation. The power-law index of the energy distribution of electrons (psim 3), the minimum Lorentz factor of the electrons (gamma _{mathrm{min}}sim 60), the magnetic field (B_{0}sim 10^{5} {mathrm{G}}) and the jet radius (R_{0}sim 10^{10} {mathrm{cm}}) at the jet base are required for both the ballistic jet and the adiabatic jet. This study helps us clarify the complex interaction between the accretion and jet in GX 339−4, as well as the properties and geometric structure of the jet, laying the groundwork for exploring similar astrophysical systems.

Accretion disks, swirling structures of matter spiraling into black holes, play a pivotal role in our understanding of binary star systems and their intricate evolutionary processes. While current models often simplify these complex phenomena by neglecting the influence of powerful magnetic fields, particularly within warped or distorted black hole geometries, this study delves into the crucial impact of such fields. Focusing on a thin accretion disk encircling a Schwarzschild black hole, we meticulously investigate how the presence of a quadrupole moment, an inherent distortion in the black hole’s shape, affects its spectral characteristics. By analyzing key parameters like total pressure, magnetic pressure, temperature, height scale, surface density, and radiative flux – the energy emitted by the disk – we reveal significant alterations induced by incorporating both magnetic fields and a quadrupole moment. Notably, our findings demonstrate that negative quadrupoles exert a more pronounced influence on these disk properties, highlighting the intricate interplay between these factors. This comprehensive study provides invaluable insights into the dynamics of accretion disks surrounding distorted black holes with magnetic fields, paving the way for a more accurate and nuanced understanding of these fascinating astrophysical systems.

This study presents the first integrated analysis of the Bursa L6 chondrite’s thermophysical properties using 3D laser scanning, pycnometry, differential scanning calorimetry (DSC), and thermogravimetric analysis (TGA). The meteorite exhibits a bulk density of 3.476 g/cm³, a grain density of 3.69 g/cm³, and porosity of 5.80%. DSC revealed the presence of troilite (FeS) with (alpha /beta ) and (beta /gamma ) phase transition shifts across different regions, indicating a temperature gradient during atmospheric entry, with a calculated troilite content of 4.59 wt.%. Specific heat capacity was found to be 740 ± 33 Jkg⁻¹K⁻¹ at room temperature, while volumetric heat capacity ranged from 1.90 ± 0.11 MJ/(m³K) at 200 K and 2.57 1.90 ± 0.11 MJ/(m³K) at 300 K. The atom-molar heat capacity increased from 12.64 J/(molK) to 17.41 J/(molK) across the same temperature range. Thermal diffusivity was estimated to be 1.25 ± 0.36⋅10⁻⁶ m²s⁻¹ in air and 0.71 ± 0.03⋅10⁻⁶ m²s⁻¹ in a vacuum. Thermal conductivity is 2.6 ± 0.6 Wm⁻¹K⁻¹ in air and 1.8 ± 0.2 Wm⁻¹K⁻¹ in vacuum at 300 K for both. Thermal inertia predicted for vacuum is equal to 1.84 ± 0.14 ⋅ 10³ Js^−1/2K⁻¹m⁻² at 200 K, and 2.15 ± 0.18 ⋅ 10³ Js^−1/2K⁻¹m⁻² at 300 K. A minimal mass loss of 0.62% up to 1200 °C, with water and hydrogen contents of 0.32 and 0.032%, respectively, suggests low volatile content. These results provide key insights into heat transfer behavior and the parent body evolution of the Bursa meteorite.

Using (mathit{uvby}beta )-photometry, the Eddington pulsation constant can be determined for (beta ) Cephei variables, which are mostly stars B0.5-2V-III. Therefore, the known relations between the effective surface temperature and the indexes of (mathit{uvby}beta )-photometry are analyzed for B-stars. These relations were determined using the empirical data from small numbers of stars. Therefore, the representative calibration sample is formed from 104 stars B0-4V-III, for which the effective surface temperature and the indexes of (mathit{uvby}beta )-photometry ((c_{1}), ((b- y)), (m_{1}), (beta )) are known. Using this sample, for stars B0-4 the relations between (c_{0}), ((b- y)_{0}), (m_{0}), (beta ) and the effective surface temperature are determined in luminosity classes V, IV and III. It is established new indexes of ((b- y)_{0} '), (m_{0} ') and (beta ') that are (((b- y)_{0} - (b- y)_{0(mathrm{V}+mathrm{IV})})/ ((b- y)_{0(mathrm{V}+mathrm{IV})} - (b- y)_{0(mathrm{III})})), ((m_{0} - m_{0(mathrm{IV}+mathrm{V})})/(m_{0(mathrm{IV}+mathrm{V})} - m_{0(mathrm{III})})) and ((beta - beta _{(mathrm{IV}+mathrm{V})})/(beta _{(mathrm{IV}+mathrm{V})}- beta _{mathrm{III}})), respectively. Using the condition of ((b- y)_{0} ' = m_{0} ' = beta ') at a constant metallicity, the accurate relations between (c_{0}), ((b- y)_{0}), (m_{0}), (beta ), (beta ') and the surface effective temperature are determined for stars B0-4V-III. It is found that in (mathit{uvby}beta )-photometry for stars B0-4V-III the known temperature calibrations have average errors of (4 – 9)%. The new accurate temperature calibration has an error of about 1%. It is found that the Eddington pulsation constant depends very loosely on the pulsation period for (beta ) Cephei variables.

We conduct a statistical analysis on 76 ground level enhancement (GLE) events to examine the characteristics of their associated solar flares. Our analysis reveals that GLE-associated flares predominantly occur within the longitude range of 20^∘–100^∘ west and belong to higher optical and soft X-ray flare classes, with 84% being X-class. The average flare longitudes for GLEs with increase rates above 100% and 10% are found to be 53.67^∘ ± 15.31^∘ and −59.18^∘ ± 8.04^∘, respectively, with a concentration near 55^∘ west longitude for high-intensity GLEs. Statistical timing analysis shows that 69% of GLE events commence after the associated flare peaks, with an average delay of 17.18 ± 7.06 minutes. These findings underscore the impact of solar flare location and intensity on GLE production and highlight the role of interplanetary magnetic field structures in guiding energetic particle transport toward Earth. The results further suggest that both flare-driven and CME-driven acceleration mechanisms play a role in GLE initiation, with particle transport conditions influencing the observed timing relationships.

Compact Symmetric Objects (CSOs) are a distinct category of jetted active galactic nuclei (AGN) whose optical variability characteristics have not been well investigated. We present here the results of our investigation on the optical flux and colour variability properties of a bona fide sample of 38 CSOs. We used the (g)-, (r)- and (i)-bands data from the Zwicky Transient Facility survey that spans a duration of about 5 years. We also considered a comparison sub-sample of blazars that includes 5 flat spectrum radio quasars and 12 BL Lac objects with redshifts and (g)-band magnitudes similar to the limited sub-sample of 9 CSOs. These two sub-samples of AGN, chosen for this comparative study of their long-term optical variability, represent different orientations of their relativistic jets with respect to the observer. We found that both CSOs and blazars exhibit optical flux variations, although variability of CSOs is lower than that of blazars. The observed variability in both CSOs and blazars is attributed to the relativistic jets and the increased optical variations in blazars relative to CSOs are likely due to beaming effects. CSOs and blazars exhibit similar colour variations, with both of them showing a bluer when brighter trend. Such a colour variability pattern is expected due to processes associated with their relativistic jets.

Cislunar space has been attracting interest as a strategic place to connect Earth and interplanetary space. This paper extends our previous analysis on the use of retrograde periodic orbits around Earth for staging orbits. The orbit of interest is found to be linearly stable against the luni-solar gravitational perturbation, yet its Moon-grazing geometry leads to modest (Delta v) to capture into (escape from) the orbit via lunar flyby. In the analysis of capture trajectories, we globally search for transfer trajectories from the vicinity of Earth. It is found that Sun-perturbed, multi-revolutional transfer is a promising option to reduce the launch energy and insertion (Delta v). In the escape analysis, transfer from the periodic orbit toward interplanetary space via powered Earth flyby is studied. Temporal insertion into an unstable periodic orbit that is in a retrograde (1:1) mean-motion resonance is found to be a favorable option to flexibly tune the escape direction.

This study aims to provide comprehensive insights into the dynamics of retrograde co-orbital motion, contributing to our understanding of the origin and evolution of retrograde asteroids in the solar system. The paper studies retrograde co-orbital motion with Jupiter through the computation of symmetric periodic orbits in both planar and spatial circular restricted three-body problems. The research begins with an analysis of families of the planar circular problem at which there exist three main families of co-orbital motion. Starting from the vertical critical orbits of these families we extend our study to three-dimensional configurations, revealing that most spatial families exhibit instability. The phase-space structure is also explored by using dynamical stability maps under various initial conditions. These maps help identify regions of stable motion within predominantly chaotic domains. The theoretical framework is applied to asteroid (514107) Ka’epaoka’awela, demonstrating its chaotic nature with a Lyapunov time of approximately 6350 years, despite remaining in co-orbital resonance with Jupiter for many million years.

In this study, a variable cosmological constant model is created for anisotropic star structures, which satisfies the remaining physical requirements, and validates the required energy conditions (Ecs), and TOV equations. First, the Finch-Skea spacetime solution is taken into account as a static spherically symmetric metric. Moreover, external Schwarzschild geometry is taken into account to correlate our internal stellar structure and determine the values of the constants used in the Finch-Skea spacetime solution. Finally, in this paper, multiple aspects are discussed, such as the radius, compactness, stresses, stability, density profile, and masses under the variable cosmological constant model in (f(R,T)) gravity for various stars.