Astrophysics and Space Science最新文献

There will be an unprecedented increase in the number of galaxies observed as a result of the current and upcoming surveys. Consequently, data-driven approaches have become the main tools for deciphering and evaluating this massive volume of data. Computer vision combined with deep learning has proven most effective for recognizing galaxy morphology but most of the conventional deep learning models are large in terms of parameters due to which computational cost, risk of overfitting increases. In this paper, we proposed a lightweight convolutional neural network (CNN) model using separable convolution which helps to reduce trainable parameters of the model. Further, Efficient Channel Attention (ECA) mechanism is used to focus on important features. ECA focuses on features channel wise without dimensionality reduction which reduces the computational overhead. Performance of proposed model named as “DIAT-DSCNN-ECA-Net” is evaluated on two datasets such as Galaxy Zoo 2, Galaxy Zoo DECaLS, each having seven different types of galaxies, achieved an accuracy of 90.81% and 94.17% respectively at the cost of 1.8 Mega-Byte model size, 0.13 million parameters, 1.04 Floating Point Operations (FLOPs). The outcomes of the experiments demonstrate that the proposed approach can outperform the existing CNN models.

The YangBaJing Hybrid Array (YBJ-HA) is located at the Yangbajing international cosmic ray observatory, Tibet, China. It consists of 115 scintillation detectors (SDs) and 16 underground water Cherenkov muon detectors (MDA). Its main physical goal is to observe the (gamma )-ray sources in the 100 TeV energy region, so the array must have very good pointing accuracy. To achieve this performance, the time response of the scintillator detectors must have high consistency. This paper introduces a characteristic plane method (offline calibration method) to calibrate the time of each scintillator detector and uses the moon shadow analysis results to test the time calibration accuracy.

The presence of carbon-chain molecules in the interstellar medium (ISM) has been known since the early 1970s and (>130) such species have been identified to date, making up (sim 43)% of the total of detected ISM molecules. They are prevalent not only in star-forming regions in our Galaxy but also in other galaxies. These molecules provide important information on physical conditions, gas dynamics, and evolutionary stages of star-forming regions. Larger species of polycyclic aromatic hydrocarbons (PAHs) and fullerenes (C₆₀ and C₇₀), which may be related to the formation of the carbon-chain molecules, have been detected in circumstellar envelopes around carbon-rich Asymptotic Giant Branch (AGB) stars and planetary nebulae, while PAHs are also known to be a widespread component of the ISM in most galaxies. Recently, two line survey projects toward Taurus Molecular Cloud-1 with large single-dish telescopes have detected many new carbon-chain species, including molecules containing benzene rings. These new findings raise fresh questions about carbon-bearing species in the Universe. This article reviews various aspects of carbon-chain molecules, including observational studies, chemical simulations, quantum calculations, and laboratory experiments, and discusses open questions and how future facilities may answer them.

Significant association between flux emergence and the complexity of the involved processes in the solar corona could be substantial in estimating magnetic field activities and related driving mechanisms. In this study, we analysed solar magnetic activity in the time period between 1939 and 2022, covering solar cycles 17 to the present cycle 25. Our study was principally based on green coronal intensity, which was calculated using observations collected from a global network of coronal stations. Specifically, we utilized the homogenized Fe XIV 530.3 nm coronal emission line provided by the Astronomical Institute of the Slovak Academy of Sciences, as well as of the International Sunspot number index. The analyses were carried out using the Cross-Correlation and Empirical Mode Decomposition techniques. Firstly, the study found that there are strong and positive correlations between the two indices, with high coefficients specifically during the examined solar cycles. Secondly, the empirical mode decomposition technique reveals unique properties of the intrinsic mode functions (IMFs), highlighting distinctions between the emergence of sunspots and green coronal emissions based on their various modulations. Indeed, these IMFs are most likely closely linked to the magnetic flux rope structure and indirectly connected with the emergence of sunspot events. The observed lag between MCI and the SSN could potentially be linked to the dynamics between coronal response time and the evolutions of active regions. Furthermore, there is a steady decrease observed in the green coronal index from solar cycle 17 to the current cycle 25 that could be attributed to waning behaviour of solar magnetic field strength. This decline can also be regarded as evidence of the Centennial Gleissberg solar activity cycle during the descending phase. Interestingly, the green coronal index exhibits a significant degree of phase synchronization with sunspot numbers, suggesting that the intricate relationship between green coronal intensity and sunspot numbers can be potentially driven by processes such as heating, the formation of active coronal regions, and the emergence of magnetic flux.

The main aim of this paper is to study both the Interstellar Medium (ISM) and the young stellar population in the three star-forming regions, namely IRAS 05137+3919, 05168+3634, and 19110+1045. The study of the ISM includes determination of the hydrogen column density (N(H₂)) and dust temperature (T_d) in the regions using modified blackbody fitting. The main parameters of the identified and classified young stellar objects (YSOs) belonging to the regions were determined by comparing with the radiation-transfer models. We also constructed a color–magnitude diagram to compare the parameters of the YSOs with the results of the radiative-transfer models. The three stellar populations appear to have formed under different scenarios. In the cases of IRAS 05137+3919 and IRAS 05168+3634, the age spread is considerably wider, suggesting that the stellar population likely emerged from independent condensations. In contrast, the third region comprises a pair of ultracompact HII regions (UCHIIs), G45.12+0.13 and G45.07+0.13, with a notably smaller age spread. This hints at the possibility that these clusters originated from a single triggering event.

Polarization studies in blazars are effective tools for analyzing the emission composition and the relativistic jet. In this work, we collected photometric and polarization data from the Steward Observatory Blazar Monitoring Program and performed the following studies. (1) Among the 10 target sources, 8 sources exhibit correlations between the polarization variability ((P)) and (V)-lightcurves ((F_{V})). (2) When we use the multiorder power law function to fit (P) and (F_{V}), we obtain several parameters, including the brightening timescale ((Delta T_{b})) and the dimming timescale ((Delta T_{d})). In the brightening stage, (Delta T_{P|b}) and (Delta T_{F|b}) were correlated, with a correlation coefficient of (r=0.45), and a chance probability of (p=0.30%). In the dimming stage, (Delta T_{P|d}) and (Delta T_{F|d}) exhibited weak correlations. (3) To analyze the origin of the polarization, we study the dependence of polarization on spectral index.

Abstract

Recently, we have seen a series of space missions to the Moon and asteroids, whether for exploratory or scientific purposes, with possibilities of a lot of profitability in a sustainable way. Given this scenario, the Garatéa-L Mission (from the Brazilian original people language Tupi-Guarani, “Search for Life”) stands out, a genuinely Brazilian mission, whose main objective is to place a 6U brazilian cubeSat in orbit around the Moon, in 2024 or 2025, with the aim of carrying out experiments in astrobiology and studying the Aitken Basin, a basin located at the lunar south pole. In this context, the main goal of the present work is to study the orbits that meet the needs of the mission, obeying the necessary parameters of 300 km of periselene and 3000 km of aposelene. The system is formed by the Moon (the central body) and its gravitational coefficients, (J_{2}) , (J_{3}) and (C_{22}) , the Earth as the perturbing body and a particle (cubesat). As a result, we obtained a sample of orbits that meets the requirements of the mission, their lifetimes in the region of interest and the evolution of the semi-major axis and eccentricity for each value of the inclination analysed. The results showed that the largest number of orbits with the longest lifetime have inclinations of 60° and 65°, with a semi-major axis of 3460 km and an eccentricity of approximately 0.38, remaining in the mission’s region of interest for an approximate period of 180 days.

Abstract

The Alfvén resonance is an extensively observed phenomenon in astrophysics, playing a crucial role in understanding energy transfer, macroscopic structure, and evolutionary processes within celestial environments such as the magnetospheres of stars, planets, and other astrophysical objects. In this work, we investigate the spatial and temporal distribution of the Alfvén resonance points during the evolution of Kelvin-Helmholtz instability (KHI) at Earth’s dusk-flank magnetopause in numerical MHD simulation. The results show that, there is no appearance of the Alfvén resonance points (P_{AR}) during the linear phase. In the early nonlinear phase, the Alfvén resonance points (P_{AR}) , whose duration time is approximately (Delta {t_{1}} sim 3{t_{A}}) , looks like the “eyelid” of the KH vortex. During the nonlinear growth phase, the Alfvén resonance points (P_{AR}) , whose duration time is about (Delta {t_{2}} sim 6{t_{A}}) , appear at both the “eyelid” and the outer “corner” of the KH vortex. The Alfvén resonance phenomenon disappears with the decay of KH vortex.

Purpose: The 1:1 spin-orbit resonance phenomenon is widely observed in binary asteroid systems. We aim to investigate the intrinsic dynamic mechanism behind the phenomenon under the coupled influence of the secondary’s rotation and orbital motion. Methods: The planar sphere–ellipsoid model is used to approximate the synchronous binary asteroid. The Lindstedt–Poincaré method is applied on the spin-orbit problem to find its explicit quasi-periodic solution. Results: Numerical simulations demonstrate that analytical solutions truncated at high orders are accurate enough to describe the orbital and rotational motions of the synchronous binary asteroid. With the help of the solution, we are able to identify in a more accurate way the stable region for the synchronous state by using the Lyapunov characteristic exponent. Moreover, the resonances that determine the boundary of the stability region are identified. Conclusion: The stable synchronous state requires a small eccentricity (e) of the mutual orbit but permits a large libration angle (theta ) of the secondary. The anti-correlation of (theta ) and (e) is confirmed. The stable region for a very elongated secondary is small, which helps explain the lack of such secondaries in observations (see Table 1 in Pravec et al. in Icarus 267:267–295, 2016). Findings of this study provide insights into the inherent dynamics that determine the rotational states of a synchronous binary asteroid.