Research in Astronomy and Astrophysics

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.

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 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.

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.

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.

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.

We present the thorium distribution on the lunar surface derived from observations by the Chang'E-2 gamma-ray spectrometer (CE-2 GRS). This new map shows a similar thorium distribution to previous observations. In combination with this new thorium map and impact cratering model, we investigate the origination of thorium on the Moon's highlands, which was previously thought to be contributed from Imbrium ejecta. We found that the Imbrium ejecta has a small contribution (∼20%–30%) to the thorium on the lunar highlands but most thorium is likely to be indigenous before the deposition of the Imbrium ejecta. This new thorium map also confirms that the eastern highlands have a relatively higher thorium concentration than the western highlands. We propose that the thin crust and large basins on the eastern highlands are responsible for this difference in thorium.

Elemental abundance patterns of globular cluster stars can provide important clues for understanding cluster formation and early chemical evolution. The origin of the abundance patterns, however, still remains poorly understood. We have studied the impact of p-capture reaction cycles on the abundances of oxygen, sodium and aluminium considering nuclear reaction cycles of carbon-nitrogen-oxygen-fluorine, neon-sodium and magnesium-aluminium in massive stars in stellar conditions of temperature range 2×10⁷ to 10×10⁷ K and typical density of 10² gm cc⁻¹. We have estimated abundances of oxygen, sodium and aluminium with respect to Fe, which are then assumed to be ejected from those stars because of rotation reaching a critical limit. These ejected abundances of elements are then compared with their counterparts that have been observed in some metal-poor evolved stars, mainly giants and red giants, of globular clusters M3, M4, M13 and NGC 6752. We observe an excellent agreement with [O/Fe] between the estimated and observed abundance values for globular clusters M3 and M4 with a correlation coefficient above 0.9 and a strong linear correlation for the remaining two clusters with a correlation coefficient above 0.7. The estimated [Na/Fe] is found to have a correlation coefficient above 0.7, thus implying a strong correlation for all four globular clusters. As far as [Al/Fe] is concerned, it also shows a strong correlation between the estimated abundance and the observed abundance for globular clusters M13 and NGC 6752, since here also the correlation coefficient is above 0.7 whereas for globular cluster M4 there is a moderate correlation found with a correlation coefficient above 0.6. Possible sources of these discrepancies are discussed.

For lots of scientific questions about lunar physics deep inside the Moon, in-situ observation on lunar physical libration is one of the most potential ways. In this paper, we propose a brand new optical telescope functioned with simultaneously observing multiple (here there are three) fields of view (FOVs) for in-situ observation of lunar physical libration. The telescope can be placed at any place with any attitude on the Moon and do not require manned install, control or operation. It passively, continuously and simultaneously observe stars in three FOVs along with rotation of the Moon. Libration is to be measured and studied from celestial motion of the directions of three FOVs from image processing. The concept and design of this telescope are firstly introduced in this paper. The principle and feasibility of the method of in-situ observation are also demonstrated. From simulation, precision of the determined lunar physical libration is expected to be several milliarcsecs, about two orders of magnitude better than the current precision of libration by lunar laser ranging observation. Libration data with milliarcsec precision level can play a valuable role in the study of the physics and dynamics of the interior of the Moon. This telescope can also be applied to observe the rotation of other terrestrial planets like Mars.

Imaging observations of solar X-ray bursts can reveal details of the energy release process and particle acceleration in flares. Most hard X-ray imagers make use of the modulation-based Fourier transform imaging method, an indirect imaging technique that requires algorithms to reconstruct and optimize images. During the last decade, a variety of algorithms have been developed and improved. However, it is difficult to quantitatively evaluate the image quality of different solutions without a true, reference image of observation. How to choose the values of imaging parameters for these algorithms to get the best performance is also an open question. In this study, we present a detailed test of the characteristics of these algorithms, imaging dynamic range and a crucial parameter for the CLEAN method, clean beam width factor (CBWF). We first used SDO/AIA EUV images to compute DEM maps and calculate thermal X-ray maps. Then these realistic sources and several types of simulated sources are used as the ground truth in the imaging simulations for both RHESSI and ASO-S/HXI. The different solutions are evaluated quantitatively by a number of means. The overall results suggest that EM, PIXON, and CLEAN are exceptional methods for sidelobe elimination, producing images with clear source details. Although MEM_GE, MEM_NJIT, VIS_WV and VIS_CS possess fast imaging processes and generate good images, they too possess associated imperfections unique to each method. The two forward fit algorithms, VF and FF, perform differently, and VF appears to be more robust and useful. We also demonstrated the imaging capability of HXI and available HXI algorithms. Furthermore, the effect of CBWF on image quality was investigated, and the optimal settings for both RHESSI and HXI were proposed.

Indirect X-ray modulation imaging has been adopted in a number of solar missions and provided reconstructed X-ray images of solar flares that are of great scientific importance. However, the assessment of the image quality of the reconstruction is still difficult, which is particularly useful for scheme design of X-ray imaging systems, testing and improvement of imaging algorithms, and scientific research of X-ray sources. Currently, there is no specified method to quantitatively evaluate the quality of X-ray image reconstruction and the point-spread function (PSF) of an X-ray imager. In this paper, we propose percentage proximity degree (PPD) by considering the imaging characteristics of X-ray image reconstruction and in particular, sidelobes and their effects on imaging quality. After testing a variety of imaging quality assessments in six aspects, we utilized the technique for order preference by similarity to ideal solution to the indices that meet the requirements. Then we develop the final quality index for X-ray image reconstruction, QuIX, which consists of the selected indices and the new PPD. QuIX performs well in a series of tests, including assessment of instrument PSF and simulation tests under different grid configurations, as well as imaging tests with RHESSI data. It is also a useful tool for testing of imaging algorithms, and determination of imaging parameters for both RHESSI and ASO-S/Hard X-ray Imager, such as field of view, beam width factor, and detector selection.

Fast Radio Bursts (FRBs) have emerged as one of the most intriguing and enigmatic phenomena in the field of radio astronomy. The key of current related research is to obtain enough FRB signals. Computer-aided search is necessary for that task. Considering the scarcity of FRB signals and massive observation data, the main challenge is about searching speed, accuracy and recall. in this paper, we propose a new FRB search method based on Commensal Radio Astronomy FAST Survey (CRAFTS) data. The CRAFTS drift survey data provide extensive sky coverage and high sensitivity, which significantly enhance the probability of detecting transient signals like FRBs. The search process is separated into two stages on the knowledge of the FRB signal with the structural isomorphism, while a different deep learning model is adopted in each stage. To evaluate the proposed method, FRB signal data sets based on FAST observation data are developed combining simulation FRB signals and real FRB signals. Compared with the benchmark method, the proposed method F-score achieved 0.951, and the associated recall achieved 0.936. The method has been applied to search for FRB signals in raw FAST data. The code and data sets used in the paper are available at github.com/aoxipo.

According to the standard "inside-out" galaxy formation scenario, galaxies first form a dense core and then gradually assemble their outskirts. This implies that galaxies with similar central stellar mass densities might have evolutionary links. We use the UVJ color–color diagram to select quiescent galaxies in the redshift interval from 0.5 to 2.5 and classify them into different subsamples based on their central stellar mass densities, stellar mass, morphological type and redshift. We then infer the intrinsic axis ratios μ_B/A and μ_C/A of different subsamples based on the apparent axis ratio q distributions, where A, B, and C refer to, respectively, the major, intermediate and minor axis of a triaxial ellipsoidal model. We find that (1) massive quiescent galaxies have typical intrinsic shapes similarly close to thick oblate structures, with μ_B/A ≳ 0.9, regardless of stellar mass, redshift, or central stellar mass densities, and (2) galaxies at higher redshift are systematically thinner than their lower-redshift counterparts, and (3) when splitting the sample into early type and late type with Sérsic indices, ETGs at higher redshift are slightly more prolate (smaller average μ_B/A) than those at lower redshift. Minor mergers of galaxies may have played important roles in the structural evolution of quiescent galaxies found in this work.

A simple orbit classification constraint extension to stellar dynamical modeling using Schwarzschild's method is demonstrated. The classification scheme used is the existing "orbit circularity" scheme (λ_z) where orbits are split into four groups—hot, warm, cold, and counter-rotating orbits. Other schemes which can be related to the orbit weights are expected to be viable as well. The results show that the classification constraint works well in modeling. However, given that orbits in external galaxies are not observable, it is not clear how the orbit classification for any particular galaxy may be determined. Perhaps range constraints for different types of galaxies determined from cosmological simulations may offer a way forward.

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 current paper, we present a study of the spatial distribution of luminous blue variables (LBVs) and various LBV candidates (cLBVs) with respect to OB associations in the M33 galaxy. The identification of blue star groups was based on the LGGS data and was carried out by two clustering algorithms with initial parameters determined during simulations of random stellar fields. We have found that the distribution of distances to the nearest OB association obtained for the LBV/cLBV sample is close to that for massive stars with M_init>20 M_⊙, and Wolf-Rayet stars. This result is in good agreement with the standard assumption that luminous blue variables represent an intermediate stage in the evolution of the most massive stars. However, some objects from LBV/cLBV sample, particularly Fe II-emission stars, demonstrated severe isolation compared to other massive stars, which, together with certain features of their spectra, implicitly indicates that the nature of these objects and other LBV/cLBV may differ radically.

Leveraging the semi-analytic method, we compute halo spins for a substantial sample of HI-bearing galaxies observed in the Arecibo Legacy Fast Alfa Survey. Our statistical analysis reveals a correlation between halo spin and environment, although the trend is subtle. On average, galaxies exhibit a decreasing halo spin tendency in denser environments. This observation contrasts with previous results from $N$-body simulations in the Lambda cold dark matter framework. The discrepancy may be attributed to environmental gas stripping, leading to an underestimation of halo spins in galaxies in denser environments, or to baryonic processes that significantly alter the original dark matter halo spins, deviating from previous $N$-body simulation findings.

The long-period comets' perihelion places them near the sun so they may exhibit activity. Before 2013 LU28 reached the perihelion, we performed a continuous observation to detect the possible activity. Using the Lijiang 2.4 m telescope with a Johnson R filter, we measured the brightness of 2013 LU28 from 2024 January 3 to April 13. The instrumental magnitudes were subsequently transformed into the Pan-STARR r system. Due to the noticeable descending trend in the absolute magnitude, we verified the cometary activity and constrained some photometric properties of 2013 LU28. Consequently, the increased cross-section area had a rate of 42.8 km$^2$ d$^{-1}$, and the corresponding mass-loss rate was 2.64 kg s$^{-1}$ with the assumption of the dust-particle size $\bar{a}~=~10~\mu m$ and the density $\rho$ = 400 kg m$^{-3}$. We estimated the nucleus radius as $0.11\lesssim r_n \lesssim0.21$ km for CO sublimation and $0.20\lesssim r_n \lesssim 0.71$ km for CO$_2$ sublimation and the grain size of 2013 LU28 was $a_c\simeq117.95~\mu$m for CO and $a_c\simeq7.57~\mu$m for CO$_2$. The long-term observations provided in this paper will offer significant value for investigating the mechanisms driving the activity of 2013 LU28.

The China Space Station Telescope (CSST) is a 2-meter 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 residuals 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 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 field
of view of the CSST, when the FSM tilts by (1 arcsec, 1 arcsec), 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 Square Kilometre Array (SKA) has the potential to revolutionize astronomical research through its unparalleled precision. A critical aspect of SKA imaging is the computation of the UVW coordinates, which must be accurate and reliable for the development of the SKA scientific data processor. Katpoint is the current method used to calculate UVW in MeerKAT. Using a pseudo-source, we employ a simple cross-product method to determine UVWs. In this study, we explore the applicability of Katpoint for SKA1-low and SKA1-mid and evaluate its precision.
The conventional method, CALC/OmniUV, and Katpoint were quantitatively assessed through simulations. The results indicate that Katpoint exhibits substantial accuracy with MeerKAT compared to traditional techniques. However, its precision is slightly inadequate for the long baselines of SKA1. We improved the precision of Katpoint by identifying optimal offset values for pseudo-sources on the SKA1 telescope through simulation, finding a 0.11-degree offset suitable for SKA1-Mid and a 0.045-degree offset for SKA1-Low. Final result validations demonstrate that these adjustments render the computational accuracy fully comparable to the standard CALC/OmniUV method, which would meet the requirements of SKA high-precision imaging and offer a solution for high-precision imaging in radio interferometers.