Research in Astronomy and Astrophysics

The Large sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST) general survey is a spectroscopic survey that will eventually cover approximately half of the celestial sphere and collect 10 million spectra of stars, galaxies and QSOs. Objects in both the pilot survey and the first year regular survey are included in the LAMOST DR1. The pilot survey started in October 2011 and ended in June 2012, and the data have been released to the public as the LAMOST Pilot Data Release in August 2012. The regular survey started in September 2012, and completed its first year of operation in June 2013. The LAMOST DR1 includes a total of 1202 plates containing 2 955 336 spectra, of which 1 790 879 spectra have observed signal-to-noise ratio (SNR) ≥ 10. All data with SNR ≥ 2 are formally released as LAMOST DR1 under the LAMOST data policy. This data release contains a total of 2 204 696 spectra, of which 1 944 329 are stellar spectra, 12 082 are galaxy spectra and 5017 are quasars. The DR1 not only includes spectra, but also three stellar catalogs with measured parameters: late A,FGK-type stars with high quality spectra (1061 918 entries), A-type stars (100 073 entries), and M-type stars (121 522 entries). This paper introduces the survey design, the observational and instrumental limitations, data reduction and analysis, and some caveats. A description of the FITS structure of spectral files and parameter catalogs is also provided.

In order to evaluate how much Total Solar Irradiance (TSI) has influenced Northern Hemisphere surface air temperature trends, it is important to have reliable estimates of both quantities. Sixteen different estimates of the changes in TSI since at least the 19^th century were compiled from the literature. Half of these estimates are "low variability" and half are "high variability". Meanwhile, five largely-independent methods for estimating Northern Hemisphere temperature trends were evaluated using: 1) only rural weather stations; 2) all available stations whether urban or rural (the standard approach); 3) only sea surface temperatures; 4) tree-ring widths as temperature proxies; 5) glacier length records as temperature proxies. The standard estimates which use urban as well as rural stations were somewhat anomalous as they implied a much greater warming in recent decades than the other estimates, suggesting that urbanization bias might still be a problem in current global temperature datasets – despite the conclusions of some earlier studies. Nonetheless, all five estimates confirm that it is currently warmer than the late 19^th century, i.e., there has been some "global warming" since the 19^th century. For each of the five estimates of Northern Hemisphere temperatures, the contribution from direct solar forcing for all sixteen estimates of TSI was evaluated using simple linear least-squares fitting. The role of human activity on recent warming was then calculated by fitting the residuals to the UN IPCC's recommended "anthropogenic forcings" time series. For all five Northern Hemisphere temperature series, different TSI estimates suggest everything from no role for the Sun in recent decades (implying that recent global warming is mostly human-caused) to most of the recent global warming being due to changes in solar activity (that is, that recent global warming is mostly natural). It appears that previous studies (including the most recent IPCC reports) which had prematurely concluded the former, had done so because they failed to adequately consider all the relevant estimates of TSI and/or to satisfactorily address the uncertainties still associated with Northern Hemisphere temperature trend estimates. Therefore, several recommendations on how the scientific community can more satisfactorily resolve these issues are provided.

Since 2007, the Intergovernmental Panel on Climate Change (IPCC) has heavily relied on the comparison between global climate model hindcasts and global surface temperature (ST) estimates for concluding that post-1950s global warming is mostly human-caused. In Connolly et al., we cautioned that this approach to the detection and attribution of climate change was highly dependent on the choice of Total Solar Irradiance (TSI) and ST data sets. We compiled 16 TSI and five ST data sets and found by altering the choice of TSI or ST, one could (prematurely) conclude anything from the warming being "mostly human-caused" to "mostly natural." Richardson and Benestad suggested our analysis was "erroneous" and "flawed" because we did not use a multilinear regression. They argued that applying a multilinear regression to one of the five ST series re-affirmed the IPCC's attribution statement. They also objected that many of the published TSI data sets were out-of-date. However, here we show that when applying multilinear regression analysis to an expanded and updated data set of 27 TSI series, the original conclusions of Connolly et al. are confirmed for all five ST data sets. Therefore, it is still unclear whether the observed warming is mostly human-caused, mostly natural or some combination of both.

The Large Sky Area Multi-Object Fiber Spectroscopic Telescope (LAMOST, also called the Guo Shou Jing Telescope) is a special reflecting Schmidt telescope. LAMOST's special design allows both a large aperture (effective aperture of 3.6 m–4.9 m) and a wide field of view (FOV) (5°). It has an innovative active reflecting Schmidt configuration which continuously changes the mirror's surface that adjusts during the observation process and combines thin deformable mirror active optics with segmented active optics. Its primary mirror (6.67 m × 6.05 m) and active Schmidt mirror (5.74m × 4.40m) are both segmented, and composed of 37 and 24 hexagonal sub-mirrors respectively. By using a parallel controllable fiber positioning technique, the focal surface of 1.75 m in diameter can accommodate 4000 optical fibers. Also, LAMOST has 16 spectrographs with 32 CCD cameras. LAMOST will be the telescope with the highest rate of spectral acquisition. As a national large scientific project, the LAMOST project was formally proposed in 1996, and approved by the Chinese government in 1997. The construction started in 2001, was completed in 2008 and passed the official acceptance in June 2009. The LAMOST pilot survey was started in October 2011 and the spectroscopic survey will launch in September 2012. Up to now, LAMOST has released more than 480000 spectra of objects. LAMOST will make an important contribution to the study of the large-scale structure of the Universe, structure and evolution of the Galaxy, and cross-identification of multi-waveband properties in celestial objects.

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) is the most sensitive telescope at the L-band (1.0–1.5 GHz) and has been used to carry out the FAST Galactic Plane Pulsar Snapshot (GPPS) survey in the last 5 yr. Up to now, the survey has covered one-fourth of the planned areas within ±10^∘ from the Galactic plane visible by FAST, and discovered 751 pulsars. After the first publication of the discovery of 201 pulsars and one rotating radio transient (RRAT) in 2021 and 76 RRATs in 2023, here we report the discovery of 473 new pulsars from the FAST GPPS survey, including 137 new millisecond pulsars and 30 new RRATs. We find 34 millisecond pulsars discovered by the GPPS survey which can be timed with a precision better than 3 μs by using FAST 15 minute observations and can be used for pulsar timing arrays. The GPPS survey has discovered eight pulsars with periods greater than 10 s including one with 29.77 s. The integrated profiles of pulsars and individual pulses of RRATs are presented. During the FAST GPPS survey, we also detected previously known pulsars and updated parameters for 52 pulsars. In addition, we discovered two fast radio bursts plus one probable case with high dispersion measures indicating their extragalactic origin.

As the second step of relativistic time transfer for a Mars lander, we investigate the transformation between Areocentric Coordinate Time (TCA) and Barycentric Coordinate Time (TCB) in the framework of IAU Resolutions. TCA is a local time scale for Mars, which is analogous to the Geocentric Coordinate Time (TCG) for Earth. This transformation has two parts: contributions associated with gravitational bodies and those depending on the position of the lander. After setting the instability of an onboard clock to 10⁻¹³ and considering that the uncertainty in time is about 3.2 microseconds after one Earth year, we find that the contributions of the Sun, Mars, Jupiter and Saturn in the leading term associated with these bodies can reach a level exceeding the threshold and must be taken into account. Other terms can be safely ignored in this transformation for a Mars lander.

Magnetic fields play a key role in driving a broad range of dynamic phenomena in the atmospheres of the Sun and other stars. Routine and accurate measurements of the magnetic fields at all the atmospheric layers are of critical importance to understand these magnetic activities, but in the solar and stellar coronae such a measurement is still a challenge due to the weak field strength and the high temperature. Recently, a magnetic-field-induced transition (MIT) of Fe x at 257.26 Å has been proposed for the magnetic field measurements in the solar and stellar coronae. In this review, we present an overview of recent progresses in the application of this method in astrophysics. We start by introducing the theory underlying the MIT method and reviewing the existing atomic data critical for the spectral modeling of Fe x lines. We also discuss the laboratory measurements that verify the potential capability of the MIT technique as a probe for diagnosing the plasma magnetic fields. We then continue by investigating the suitability and accuracy of solar and stellar coronal magnetic field measurements based on the MIT method through forward modeling. Furthermore, we discuss the application of the MIT method to the existing spectroscopic observations obtained by the Extreme-ultraviolet Imaging Spectrometer onboard Hinode. This novel technique provides a possible way for routine measurements of the magnetic fields in the solar and stellar coronae, but still requires further efforts to improve its accuracy. Finally, the challenges and prospects for future research on this topic are discussed.

Observing and timing a group of millisecond pulsars with high rotational stability enables the direct detection of gravitational waves (GWs). The GW signals can be identified from the spatial correlations encoded in the times-of-arrival of widely spaced pulsar-pairs. The Chinese Pulsar Timing Array (CPTA) is a collaboration aiming at the direct GW detection with observations carried out using Chinese radio telescopes. This short article serves as a "table of contents" for a forthcoming series of papers related to the CPTA Data Release 1 (CPTA DR1) which uses observations from the Five-hundred-meter Aperture Spherical radio Telescope. Here, after summarizing the time span and accuracy of CPTA DR1, we report the key results of our statistical inference finding a correlated signal with amplitude $\mathrm{log}{A}_{{\rm{c}}}=-14.4{\,}_{-2.8}^{+1.0}$ for spectral index in the range of α ∈ [ − 1.8, 1.5] assuming a GW background (GWB) induced quadrupolar correlation. The search for the Hellings–Downs (HD) correlation curve is also presented, where some evidence for the HD correlation has been found that a 4.6σ statistical significance is achieved using the discrete frequency method around the frequency of 14 nHz. We expect that the future International Pulsar Timing Array data analysis and the next CPTA data release will be more sensitive to the nHz GWB, which could verify the current results.

Type Ia supernovae (SNe Ia) play a key role in the fields of astrophysics and cosmology. It is widely accepted that SNe Ia arise from thermonuclear explosions of white dwarfs (WDs) in binary systems. However, there is no consensus on the fundamental aspects of the nature of SN Ia progenitors and their actual explosion mechanism. This fundamentally flaws our understanding of these important astrophysical objects. In this review, we outline the diversity of SNe Ia and the proposed progenitor models and explosion mechanisms. We discuss the recent theoretical and observational progress in addressing the SN Ia progenitor and explosion mechanism in terms of the observables at various stages of the explosion, including rates and delay times, pre-explosion companion stars, ejecta–companion interaction, early excess emission, early radio/X-ray emission from circumstellar material interaction, surviving companion stars, late-time spectra and photometry, polarization signals and supernova remnant properties. Despite the efforts from both the theoretical and observational sides, questions of how the WDs reach an explosive state and what progenitor systems are more likely to produce SNe Ia remain open. No single published model is able to consistently explain all observational features and the full diversity of SNe Ia. This may indicate that either a new progenitor paradigm or an improvement in current models is needed if all SNe Ia arise from the same origin. An alternative scenario is that different progenitor channels and explosion mechanisms contribute to SNe Ia. In the next decade, the ongoing campaigns with the James Webb Space Telescope, Gaia and the Zwicky Transient Facility, and upcoming extensive projects with the Vera C. Rubin Observatory's Legacy Survey of Space and Time and the Square Kilometre Array will allow us to conduct not only studies of individual SNe Ia in unprecedented detail but also systematic investigations for different subclasses of SNe Ia. This will advance theory and observations of SNe Ia sufficiently far to gain a deeper understanding of their origin and explosion mechanism.

Searching for primordial gravitational waves in the cosmic microwave background (CMB) polarization signal is one of the key topics in modern cosmology. Cutting-edge CMB telescopes require thousands of pixels to maximize mapping speed. Using a modular design, the telescope focal plane is simplified to several detector modules. Each module has hundreds of pixels including antenna arrays, detector arrays, and readout arrays. The antenna arrays, as the beam defining component, determine the overall optical response of the detector module. In this article, we present the developments of 6 inch broadband antenna arrays from 80 to 170 GHz for the future IHEP focal plane module. The arrays are fabricated from 42 6 inch silicon wafers including 456 antennas, 7% more pixels than the usual design. The overall in-band cross polarization is smaller than −20 dB and the in-band beam asymmetry is smaller than 10%, fulfilling the requirements for primordial gravitational wave search.

Solar magnetic field measurements mainly use the Zeeman effect, but this method has two problems, namely, low accuracy of the transverse magnetic field components and a 180° ambiguity. Multi-perspective observations can increase the measurement accuracy and resolve the ambiguity. This study investigates how combined observations from the Sun-Earth L5 point, Sun-Earth line, and solar polar-orbiting satellites improve the accuracy of the transverse solar magnetic field under different satellite positional configurations. A three-satellite model is developed using spherical trigonometry to establish coordinate relationships, and the error propagation formulas are applied to correct transverse field measurement errors. The magnetic field measurement error distribution of the Helioseismic and Magnetic Imager is analyzed, and the magnetograms from the three satellites are simulated. The improvement to the transverse field accuracy under various satellite configurations is then assessed based on simulation results. The results show that multi-perspective measurements can reduce transverse component errors ΔB_x to approximately 10% and ΔB_y to about 15% compared to the error from a single satellite. An optimally designed polar orbit can decrease the transverse field error by nearly an order of magnitude for 80% of its operation time.

I present the results of échelle spectroscopy of a bright H ii region in the irregular galaxy IC 4662 and their comparison with results from long-slit spectroscopy of the same region. All observations were obtained with the standard spectrographs of the Southern African Large Telescope: (1) low and medium spectral resolution spectrograph Robert Stobie Spectrograph (R ≈ 800) and (2) échelle spectrograph HRS (R = 16,000–1,7000). In both types of data the intensities of most of the emission lines were measured and abundances of oxygen and N, Ne, S, Ar, Cl and Fe were determined as well as physical parameters of the H ii region. The chemical abundances were obtained from both types of data with the T_e-method. Abundances calculated from both types of data agree to within the cited uncertainties. The analysis of the échelle data revealed three distinct kinematic subsystems within the studied H ii region: a narrow component (NC, σ ≈ 12 km s⁻¹), a broad component (BC, σ ≈ 40 km s⁻¹), and a very broad component (VBC, σ ≈ 60–110 km s⁻¹, detected only in the brightest emission lines). The elemental abundances for the NC and BC subsystems were determined using the T_e-method. The velocity dispersion dependence on the ionization potential of elements showed no correlation for the NC, indicating a well-mixed turbulent medium, while the BC exhibited pronounced stratification, characteristic of an expanding shell. Based on a detailed analysis of the kinematics and chemical composition, it was concluded that the BC is associated with the region surrounding a Wolf-Rayet (WR) star of spectral type WN7-8. The stellar wind from this WR star interacts with a shell ejected during an earlier evolutionary stage (either as a red supergiant or a luminous blue variable, LBV), which is enriched in nitrogen. These findings highlight the importance of high spectral resolution for detecting small-scale (∼25 pc) chemical inhomogeneities and for understanding the feedback mechanisms of massive stars in low-metallicity environments.

White dwarfs (WDs) are the final stage for most low and intermediate mass stars, which play an important role in understanding stellar evolution and galactic history. Here we performed an asteroseismological analysis on TIC 231277791 based on 10 independent modes reported by Romero et al. Two groups of modes were identified with frequency splitting: mode identification_1 with one l = 1, m = 0 mode, two l = 2, m = 0 modes, and three l = 1 or 2, m = 0 modes, and mode identification_2 with one l = 1, m = 0 mode, three l = 2, m = 0 modes, and one l = 1 or 2, m = 0 mode. The rotation period is derived to be 41.64 ± 2.73 hr for TIC 231277791. We established a large sample (7,558,272) of DAV star models using the White Dwarf Evolution Code (WDEC; 2018, v16), resulting of optimal models with model_1 (mode identification_1): M_* = 0.570 ± 0.005 M_⊙, T_eff = 11300 ± 10 K, −log(M_H/M_*) = 9.15 ± 0.01, −log(M_He/M_*) = 4.94 ± 0.01, and σ_rms = 0.06 s, and model_2 (mode identification_2): M_* = 0.720 ± 0.005 M_⊙, T_eff = 1910 ± 10 K, −log(M_H/M_*) = 6.11 ± 0.01, −log(M_He/M_*) = 3.09 ± 0.01, and σ_rms = 0.04 s. The central oxygen abundances are 0.71 (optimal model_1) and 0.72 (optimal model_2), respectively, which are consistent with the results of stellar structure and evolution theory.

The China Space Station Telescope (CSST) is a 2 m three-mirror anastigmat equipped with a Fast Steering Mirror (FSM), which is part of its precision image stabilization system. The FSM is used to compensate for residuals from the previous stage of the image stabilization system. However, a new type of image stabilization residual caused by image rotation and projection distortion is introduced when the FSM performs tip-tilt adjustments, reducing both the image stabilization accuracy and the absolute pointing accuracy of the CSST. In this paper, we propose a scheme to compute the image stabilization residuals across the full field of view (FOV) by using a reference star as the target for stabilization control, which can be utilized for subsequent image position correction. To achieve this, we developed a linear optical model for image point displacement by simplifying an existing image point displacement model and incorporating more readily available parameters. The computational accuracy of the new model is equivalent to that of the original, with computational differences of less than 0.03 μm. Based on this linear model, we established a calculation model for image stabilization residuals, including those due to image rotation and projection distortion caused by FSM tip-tilt adjustments. This model provides a theoretical foundation for quantifying such residuals during the image stabilization process. Finally, the results of testing using this scheme are provided. Experimental results demonstrate that within the observation FOV of the CSST, when the FSM tilts by (1'', 1''), the maximum absolute value of the image stabilization residuals accounts for 20% of the total image stabilization accuracy requirement. This finding underscores the necessity of computing and correcting these residuals to meet performance requirements.

The next generation of very long baseline interferometry (VLBI) is stepping into the era of microarcsecond (μas) astronomy, and pushing astronomy, especially astrometry, to new heights. VLBI with the Square Kilometre Array (SKA), SKA-VLBI, will increase current sensitivity by an order of magnitude, and reach astrometric precision routinely below 10 μas, even challenging 1 μas. This advancement allows precise parallax and proper motion measurements of various celestial objects. Such improvements can be used to study objects (including isolated objects, and binary or multiple systems) in different stellar stages (such as star formation, main-sequence stars, asymptotic giant branch stars, pulsars, black holes, white dwarfs, etc.), unveil the structure and evolution of complex systems (such as the Milky Way), benchmark the international celestial reference frame, and reveal cosmic expansion. Furthermore, the theory of general relativity can also be tested with SKA-VLBI using precise measurements of light deflection under the gravitational fields of different solar system objects and the perihelion precession of solar system objects.

Density functional theory (DFT) is the most versatile electronic structure method used in quantum chemical calculations, and is increasingly applied in astrochemical research. This mini-review provides an overview of the applications of DFT calculations in understanding the chemistry that occurs in star-forming regions. We survey investigations into the formation of biologically relevant compounds such as nucleobases in the interstellar medium, and also cover the formation of both achiral and chiral amino acids, as well as biologically relevant molecules such as sugars, and nitrogen-containing polycyclic aromatic hydrocarbons. Additionally, DFT calculations are used to estimate the potential barriers for chemical reactions in astronomical environments. We conclude by noting several areas that require more research, such as the formation pathways of chiral amino acids, complex sugars, and other biologically important molecules, and the role of environmental factors in the formation of interstellar biomolecules.

Type Ia supernovae (SNe Ia) play a key role in the fields of astrophysics and cosmology. It is widely accepted that SNe Ia arise from thermonuclear explosions of white dwarfs (WDs) in binary systems. However, there is no consensus on the fundamental aspects of the nature of SN Ia progenitors and their actual explosion mechanism. This fundamentally flaws our understanding of these important astrophysical objects. In this review, we outline the diversity of SNe Ia and the proposed progenitor models and explosion mechanisms. We discuss the recent theoretical and observational progress in addressing the SN Ia progenitor and explosion mechanism in terms of the observables at various stages of the explosion, including rates and delay times, pre-explosion companion stars, ejecta–companion interaction, early excess emission, early radio/X-ray emission from circumstellar material interaction, surviving companion stars, late-time spectra and photometry, polarization signals and supernova remnant properties. Despite the efforts from both the theoretical and observational sides, questions of how the WDs reach an explosive state and what progenitor systems are more likely to produce SNe Ia remain open. No single published model is able to consistently explain all observational features and the full diversity of SNe Ia. This may indicate that either a new progenitor paradigm or an improvement in current models is needed if all SNe Ia arise from the same origin. An alternative scenario is that different progenitor channels and explosion mechanisms contribute to SNe Ia. In the next decade, the ongoing campaigns with the James Webb Space Telescope, Gaia and the Zwicky Transient Facility, and upcoming extensive projects with the Vera C. Rubin Observatory's Legacy Survey of Space and Time and the Square Kilometre Array will allow us to conduct not only studies of individual SNe Ia in unprecedented detail but also systematic investigations for different subclasses of SNe Ia. This will advance theory and observations of SNe Ia sufficiently far to gain a deeper understanding of their origin and explosion mechanism.

Magnetic fields play a key role in driving a broad range of dynamic phenomena in the atmospheres of the Sun and other stars. Routine and accurate measurements of the magnetic fields at all the atmospheric layers are of critical importance to understand these magnetic activities, but in the solar and stellar coronae such a measurement is still a challenge due to the weak field strength and the high temperature. Recently, a magnetic-field-induced transition (MIT) of Fe x at 257.26 Å has been proposed for the magnetic field measurements in the solar and stellar coronae. In this review, we present an overview of recent progresses in the application of this method in astrophysics. We start by introducing the theory underlying the MIT method and reviewing the existing atomic data critical for the spectral modeling of Fe x lines. We also discuss the laboratory measurements that verify the potential capability of the MIT technique as a probe for diagnosing the plasma magnetic fields. We then continue by investigating the suitability and accuracy of solar and stellar coronal magnetic field measurements based on the MIT method through forward modeling. Furthermore, we discuss the application of the MIT method to the existing spectroscopic observations obtained by the Extreme-ultraviolet Imaging Spectrometer onboard Hinode. This novel technique provides a possible way for routine measurements of the magnetic fields in the solar and stellar coronae, but still requires further efforts to improve its accuracy. Finally, the challenges and prospects for future research on this topic are discussed.

I review studies of core collapse supernovae (CCSNe) and similar transient events that attribute major roles to jets in powering most CCSNe and in shaping their ejecta. I start with reviewing the jittering jets explosion mechanism that I take to power most CCSN explosions. Neutrino heating does play a role in boosting the jets. I compare the morphologies of some CCSN remnants to planetary nebulae to conclude that jets and instabilities are behind the shaping of their ejecta. I then discuss CCSNe that are descendants of rapidly rotating collapsing cores that result in fixed-axis jets (with small jittering) that shape bipolar ejecta. A large fraction of the bipolar CCSNe are superluminous supernovae (SLSNe). I conclude that modeling of SLSN light curves and bumps in the light curves must include jets, even when considering energetic magnetars and/or ejecta interaction with the circumstellar matter (CSM). I connect the properties of bipolar CCSNe to common envelope jets supernovae (CEJSNe) where an old neutron star or a black hole spirals-in inside the envelope and then inside the core of a red supergiant. I discuss how jets can shape the pre-explosion CSM, as in Supernova 1987A, and can power pre-explosion outbursts (precursors) in binary system progenitors of CCSNe and CEJSNe. Binary interaction also facilitates the launching of post-explosion jets.

In this study, we used the \( f(T) \) gravity framework with the energy-momentum tensor for a perfect fluid to derive key cosmological parameters, including the Hubble parameter \( H \), deceleration parameter \( q \) and Statefinder diagnostics. Model parameters were optimized using an \( R^2 \) test, resulting in \( \beta = 1.312^{+0.013}_{-0.014} \), \( \xi = 1.273^{+0.0065}_{-0.0071} \), and \( H_0 = 72.60^{+0.50}_{-0.49} \), with an \( R^2 \) of 0.9527. Our model aligns closely with the \(\Lambda\)CDM model and shows good performance based on AIC and BIC criteria. Analyzing the \( q(z) \) curve revealed the transition from deceleration to acceleration in the universe's expansion. Additionally, we examined pressure, energy density, and equation of state parameter for two models, \( f(T) = \lambda T \) and \( f(T) = T + \beta T^2 \), both aligning well with observational data. The \( r \)-\( s \) and \( r \)-\( q \) diagnostics further confirm our model's consistency with \(\Lambda\)CDM, making it a strong alternative for explaining cosmic expansion. The evolution of \(\Omega(z)\) shows strong consistency with the \(\Lambda\)CDM model, with the Om parameter approaching 0.3 at lower redshifts and parameter uncertainties highlighting the model's reliability.

We analyze the absorption features in the public $73$~ks XMM-Newton spectra of the Seyfert~1 galaxy PG 0052+251. Our analysis reveals the presence of a warm absorber (WA) intrinsic to the source and the hot circumgalactic medium (CGM) at zero redshift. The identified WA is inflowing toward the central black hole, with a velocity shift of $1178^{+156}_{-171}$~km\,s$^{-1}$. The ionization parameter of the WA is $\log (\xi / {\rm erg~cm~s}^{-1})=-1.14^{+0.17}_{-0.19}$, showing strong O II and O III absorption lines, along with a significant absorption of the spectral continuum at $\gtrsim10$~\AA. The line of sight toward PG 0052+251 intersects the halo of M 31 at an impact parameter of approximately $218$~kpc. Several local ($z\sim0$) absorption lines were also detected. The density of the derived hydrogen column is $2.2-2.6\,\sigma$ higher than those estimated with several models of the Galactic hot halo, suggesting a likely contribution from the M31 halo. We also find two potential intervening absorption features at $24.305$~\AA\ and $21.410$~\AA, showing a similar redshift of $z\sim0.125-0.129$ if they are \osv He$\alpha$ and \oeit Ly$\alpha$ lines, respectively. The temperature of this intervening hot-gas structure is estimated to be $1.9\times10^6$~K, assuming collisional ionization equilibrium.

In this manuscript, we report evidence to support the dependence of D{\it n}4000 (4000\AA~ break strength to trace stellar ages) on central AGN activity traced by narrow emission line properties in local Type-2 AGN in SDSS DR16. Based on the measured D{\it n}4000 and flux ratios of [O~{\sc iii}] to narrow H$\beta$ (O3HB) and [N~{\sc ii}] to narrow H$\alpha$ (N2HA) and narrow H$\alpha$ line luminosity $L_{H\alpha}$, linear dependence of the D{\it n}4000 on the O3HB, N2HA and $L_{H\alpha}$ in the local Type-2 AGN can provide clues to support the dependence of D{\it n}4000 on properties of narrow emission lines. Linear correlations between the Dn4000 and the O3HB and N2HA can be found in the local Type-2 AGN, with Spearman rank correlations about -0.39 and 0.53. Meanwhile, stronger dependence of the Dn4000 on the $L_{H\alpha}$ can be confirmed in Type-2 AGN, with Spearman rank correlation coefficient about -0.7. Moreover, combining the $L_{H\alpha}$ and the N2HA, a more robust and stronger linear correlation can be confirmed between the D{\it n}4000 and the new parameter $LR=0.2\log(L_{H\alpha})-0.5\log({\rm N2HA})$, with Spearman rank correlation coefficient about -0.76 and with smaller RMS scatters. After considering necessary effects, the dependence of D{\it n}4000 on $LR$ is stable and robust enough for the local Type-2 AGN, indicating the $LR$ on the narrow emission lines can be treated as a better indicator to statistically trace stellar ages of samples of more luminous AGN with weaker host galaxy absorption features.

We present the first high-precision model for the group-scale strong lensing system CASSOWARY 19 (CSWA19), utilising images from the Hubble Space Telescope (HST). Sixteen member galaxies identified via the red-sequence method, and the main halo, all modelled as the dual Pseudo Isothermal Elliptical profile (dPIE), are incorporated into a parametric lens model alongside an external shear field. To model the system, we adopt the \textsc{PyAutoLens} software package, employing a progressive search chain strategy for realizing the transition of source model from multiple S'ersic profiles to a brightness-adaptive pixelization, which uses 1000 pixels in the source plane to reconstruct the background source corresponding to 177,144 image pixels in the image plane. 
Our results indicate that the total mass within the Einstein radius is $M_{\theta_\mathrm{E}}$ $\approx 1.41\times10^{13}$~M$_{\odot}$ and the average slope of the total mass density $\rho (r)\propto r^{-\gamma}$ is $\tilde{\gamma}=1.33$ within the effective radius. This slope is shallower than those measured in galaxies and groups but is closer to those of galaxy clusters. 
In addition, our approach successfully resolves the two merging galaxies in the background source and yields a total magnification of $\mu=103.18^{+0.23}_{-0.19}$, which is significantly higher than the outcomes from previous studies of CSWA19.
In summary, our research demonstrates the effectiveness of the brightness-adaptive pixelization source reconstruction technique for modelling group-scale strong lensing systems. It can serve as a technical reference for future investigations into pixel-level modelling of the group- and cluster-scale strong lensing systems.

Galaxy groups are essential for studying the distribution of matter on a large scale in redshift surveys and for deciphering the link between galaxy traits and their associated halos. In this work, we propose a model-independent method for identifying groups through machine learning techniques in real space taking into account the impact of redshift distortion. Our methodology involves two neural networks: one is a classification model for identifying central galaxy groups, and the other is a regression model for predicting the mass of these groups. Both models input observable galaxy traits, allowing future applicability to real survey data. Testing on simulated datasets indicates our method accurately identifies over $92\%$ of groups with $\mathrm{M}_{vir} \geq 10^{11}\hMass$, with $80\%$ achieving a membership completeness of at least $80\%$. The predicted group masses vary by less than 0.3 dex across different mass scales, even in the absence of a priori data. Our network adapts seamlessly to expand to sparse samples with a flux limit of $m_{r} < 14$, to high redshift samples at $z=1.08$, and to galaxy samples from the TNG300 hydrodynamical simulation without further training. Furthermore, the framework can easily adjust to real space samples by training on redshift space data without needing parameter changes. Careful consideration of different observational effects in redshift space makes it promising that this method will be applicable to real actual galaxy surveys.