Space debris orbiting around the Earth poses a significant risk to active satellites and operational spacecraft. The growing population makes the near-Earth orbital space dramatically crowded and poses a threat to the sustainability of the space environment. Optical surveys utilizing wide-field telescopes are an important way to observe and detect space debris. Considering there is a relative motion between space debris and background stars, both streak-like images and point-like images appear in the frames. To detect faint space debris, it is better to make the images of space debris appear as points. However, under these circumstances, challenges arise in extracting the object images from the large number of long streak background images. Furthermore, it is also difficult to estimate the centroids and flux intensity of these long streak images, reducing the astrometric accuracy of the space debris. To handle these challenges, a new strategy employing the alternating exposure is developed. In detail, based on the object-tracking mode, the short exposure and long exposure are performed alternately. The short-exposure frames are used to estimate the astrometric parameters while the long-exposure frames are used to extract the object images. The astrometric solutions are interpolated to the observation epochs of the long exposures to calculate the equatorial coordinates of the object. A test was performed utilizing a 70-cm wide-field optical telescope, and 145 fields were surveyed using alternating 1-second exposure and 20-second exposures. The results demonstrate that 1633 tracklets from 547 objects were detected, with an apparent magnitude down to 18, and the position detection accuracy of space objects was better than 0.3 arcseconds. Notably, our proposed method can make great contributions to the survey and discovery of faint celestial moving objects.
Circularly polarized (CP) electromagnetic waves in the dense, degenerate plasmas of white dwarfs and neutron-star envelopes are relevant to the interpretation of their emission, yet the influence of ionization on their stability has received little attention. We use a linearized quantum hydrodynamic model that includes electron and ion Fermi pressure and an ionization source term to derive the dispersion relation and analytical growth-rate expressions for the CP and right-circularly polarized (RCP) modes. In the ionization-dominated regime described by these expressions, both growth rates are approximately equal to half the ionization frequency, and their small deviations from this value depend on the plasma frequency, the Fermi velocities, the propagation angle and the wavenumber. For the CP branch, this deviation grows quadratically with the product of the wavenumber and the Thomas--Fermi screening length and is largest for propagation closest to the reference axis. For the RCP branch, we show that part of the growth-rate expression cancels identically and that the remaining expression exhibits two narrow, sign-reversing singular features, associated with the electron and ion Fermi velocities, whose positions scale linearly with the ionization frequency and inversely with the cube root of the density. We give closed-form conditions for these positions, verify them numerically, and discuss the validity range of the model and the extensions required for a quantitative comparison with observations of compact objects.
The Einstein equivalence principle (EEP) requires identical Shapiro time delays for the two circular polarization eigenstates of light; any differential delay rotates the polarization angle of linearly polarized light by a term scaling as $1/\lambda$. We perform the first test of this effect with a gamma-ray burst (GRB) radio afterglow, using the quasi-simultaneous 9--25~GHz Karl G. Jansky Very Large Array (VLA) polarimetry of GRB~260310A at $z = 0.153$, whose single Faraday screen and single reverse-shock component suppress the astrophysical systematics of persistent sources. Fitting the polarization angle as a function of wavelength with the intrinsic angle, the EEP term ($\propto 1/\lambda$) and the Faraday term ($\propto \lambda^{2}$ ) yields a rotation measure ${\rm RM} = -6023 \pm 228$~rad~m$^{-2}$, with the Bayesian information criterion (BIC) showing no preference for the EEP term ($\Delta{\rm BIC} = -1.15$). \textbf{Using the nominal value of the Galactic potential integral, the 95\% statistical upper limit on the EEP amplitude gives $|\Delta\gamma_{p}| < 2 \times 10^{-19}$. The calibration uncertainty in the potential integral is not included in this limit and represents a separate systematic uncertainty.} This constrains the difference between the parametrized post-Newtonian parameters of the two circular states and is complementary to existing radio and $\gamma$-ray polarization bounds.
We present an optical photometric study of the Type Ia supernova SN 2019ein based on B, V, R, and I-band observations obtained with the 1.5-m AZT-22 telescope at the Maidanak Astronomical Observatory, covering -11.6 to +81.4 days relative to B-band maximum. SALT2 fitting gives t_max(B) = 58619.311 MJD (formal error 0.032 d; total uncertainty 0.19 d), x1 = -1.781 ± 0.033, Δm15(B) = 1.43 ± 0.05 mag, and M_max(B) = -18.75 ± 0.22 mag; the epoch of maximum is the zero point of all phases in this work. A joint eight-band early-rise fit gives n = 1.74 ± 0.07 and t_fl = 58603.39 ± 0.24 MJD when the power-law index is free, with t_fl ranging over 58603.39-58604.48 MJD for other early-time cutoffs. Fixing n = 2 for direct comparison with previous fireball-based results gives t_fl = 58602.56 ± 0.07(stat) MJD and a rise time of 16.75 ± 0.07(stat) days, with a 0.17-day sensitivity to the adopted early-time cutoff. The spectra-assisted optical pseudo-bolometric light curve yields L_max = (6.2 ± 1.7) x 10^42 erg/s and a model-dependent 56Ni mass of M_Ni = 0.28 ± 0.08 Msun. From archival spectra we measure a Si II λ6355 velocity of 12,900 ± 400 km/s near maximum, independently confirming the high-velocity classification, and pEW(Si II λ6355) = 122 Å, consistent with the previously reported broad-line character. The intrinsic colours near maximum remain within the normal/transitional range, but their evolution is faster than in the comparison sample. The transitional interpretation rests on the light-curve shape (the decline rate, light-curve morphology, and colour-evolution timing), not on the peak luminosity, whose placement remains limited by host-extinction and pseudo-bolometric systematics.
Understanding the evolutionary history of the Milky Way disk remains a fundamental challenge in Galactic Astronomy, and unravelling this history requires a detailed analysis of disk stars. Utilizing large samples of non‑repetitive Solar-neighborhood F-, G- and K-type dwarfs with precise atmospheric and kinematic parameters from the Large Sky Area Multi-Object Fiber Spectroscopic Telescope (\textit{LAMOST}) and the \textit{Gaia} surveys, we investigate these evolutionary mechanisms through a comprehensive chemo-kinematic analysis. We select thick- and thin-disk stars using two independent criteria (i.e., kinematic and chemical). The kinematic approach identifies 116,039 thick-disk and 1,302,598 thin-disk stars, whereas the chemical method yields 9,181 thick-disk and 1,361,453 thin-disk stars. We find that within Galactic heights of $0<|Z_{\rm GC}|<1.5\,{\rm kpc}$, thin-disk stars exhibit negative $[\rm{Fe}/\rm{H}]$ gradients, which become flatter (less negative) with increasing $|Z_{\rm GC}|$. This trend is recovered under both classification schemes. We also find that stars sharing similar kinematics do not possess identical chemical compositions across the $[\alpha/\rm{Fe}]$ versus $[\rm{Fe}/\rm{H}]$ plane, and that the orbital eccentricity distribution of thick-disk stars prominently peaks at $e = 0.2$-$0.4$. Our results indicate that radial migration contributes more to the evolution of the Galactic thin disk, while radial migration and gas-rich mergers contribute more to the thick disk.
