Li-Yun Zhang

Eruptive variable stars are an important type of variable stars. We investigate the chromospheric activity and white-light flare properties of International Variable Star Index (VSX)-selected eruptive stars by combining LAMOST DR10 low-resolution spectroscopy with TESS 2 minute cadence flare measurements. The LAMOST spectroscopic parent sample contains 3099 unique VSX-selected eruptive-star targets with 9132 low-resolution spectra, and the quality-controlled H α subset contains 2913 unique targets and 8259 spectra. The adopted TESS flare catalog contains 6665 flare events from 453 TESS Input Catalog (TIC) targets, among which 6621 flare events from 450 TIC targets have successful VSX matches. The final statistical sample is treated as a magnetic-activity-dominated eruptive-star population, with RS CVn systems analyzed separately from other main-sequence eruptive stars. The H α equivalent widths used in this work are independently measured from LAMOST spectra, and the excess H α emission and normalized activity index are used to compare chromospheric activity across spectral type. The H α activity indicators show a clear temperature dependence, with cooler stars generally displaying stronger and more broadly distributed chromospheric emission, whereas earlier-type bins require cautious interpretation. Multiepoch LAMOST spectra reveal H α variability in both RS CVn systems and other main-sequence eruptive stars, although the variability indicators show substantial scatter. The TESS flare population is dominated by short-duration and low-to-moderate-amplitude events, with higher-energy flares forming a sparser extension.

We report the detection of an extended 21-cm parsec-scale H I structure toward the Mira variable V420 Vul using archival Galactic Arecibo L-band Feed Array survey data. The emission exhibits a spatially coherent but intensity-asymmetric morphology that nevertheless retains a globally symmetric kinematic profile centered near v _LSR ∼ 47.6 km s ⁻¹ . At an adopted distance of ∼1.9 kpc, the structure extends over ∼20 pc, implying a dynamical timescale on the order of 10 ⁶ yr. Although the total H I mass (∼70 M _⊙ ) indicates that the atomic gas reservoir is heavily dominated by the ambient interstellar medium rather than pristine stellar ejecta, the spatially resolved spectra and position-velocity diagrams reveal an underlying symmetric velocity framework centered on the star. We interpret this as the dynamical imprint of the stellar wind preferentially channeling through a porous ambient cloud, demonstrating that cohesive kinematic records of late-stage stellar mass loss can be preserved over parsec scales and megayear timescales despite dominant interstellar coupling.

Mildly recycled pulsars are neutron stars partially spun up through relatively short mass-transfer phases, typically with massive carbon–oxygen (CO) or oxygen–neon–magnesium (ONeMg) white dwarf companions. PSR J2338+4818, a mildly recycled pulsar, was discovered with the Five-hundred-meter Aperture Spherical Telescope (FAST). As a pilot study on the formation and evolutionary pathways of mildly recycled pulsars, we present the updated timing solution for PSR J2338+4818 and examine its single pulses and scintillation properties. Aided by the sensitivity of FAST, the single pulses of PSR J2338+4818 were systematically studied. In our observations, 27,228 single pulses with signal-to-noise ratio > 7 have been detected. For the FAST ultrawideband observation on MJD 61045, the receiver was still in the technical commissioning phase, and then only a preliminary single-pulse search was performed. Pulse nulling was examined using a Markov Chain Monte Carlo method, but no evidence for nulling was found. The possible long-term nulling reported by previous studies did not occur in any of our observations in either the 1.0–1.5 GHz band or the 300–600 MHz band. Interstellar scintillation is evident in our observations. The measured scintillation timescales and bandwidths range from 2.93 to 25.26 minutes and 1.68–27.41 MHz, respectively. In all observations, no clear scintillation arc was found in the secondary spectra of PSR J2338+4818.

To investigate the driving mechanisms of orbital evolution across different mass ratios and evolutionary stages, we present the first multi-color photometric solutions and detailed orbital period analyses for four short-period eclipsing binaries: MX Ser, AY Pup, QW And, and TZ CrA. By analyzing the light curves using the Wilson–Devinney code, we determined the absolute parameters and geometric configurations for these systems. MX Ser ( q = 4.60) and AY Pup ( q = 2.02) have been identified as W-subtype contact binaries with medium fill-out factors of f ∼ 30%. QW And ( q = 0.51) is derived as an A-subtype contact binary ( f ≈ 32%) exhibiting significant magnetic activity modeled by a cool starspot. In contrast, TZ CrA ( q = 0.31) is confirmed to be a semi-detached Algol-type system with a large temperature difference (Δ T ≈ 2175 K), where the secondary component fills its Roche lobe while the primary remains detached. The orbital period analyses based on all available minimum times reveal that all four systems are undergoing continuous secular period decreases. We attribute these variations to different physical mechanisms governed by the mass ratio ( q ). For the high mass-ratio systems MX Ser and AY Pup ( q > 1), the period decrease is dominated by conservative mass transfer from the massive secondary to the primary, consistent with the thermal relaxation oscillation (TRO) theory. For the low mass-ratio systems QW And and TZ CrA ( q < 1), the period decrease is the net result of competing mechanisms, where angular momentum loss (AML) via magnetic braking completely overwhelms the mass transfer effect. The derived evolutionary status suggests that while MX Ser, AY Pup, and QW And are evolved contact binaries, TZ CrA represents a critical “pre-contact” stage (short-period Algol). Driven by efficient AML, the detached primary of TZ CrA is expected to eventually fill its Roche lobe, evolving the system into an A-subtype W UMa contact binary.

We report the discovery and phase-connected timing solution of a second millisecond binary pulsar, PSR J1717+4308B (M92B), in the globular cluster M92 (NGC 6341) using the Five-hundred-meter Aperture Spherical radio Telescope. This new pulsar, with a spin period of 3.51 ms and a dispersion measure (DM) of 35.29 pc cm ⁻³ , was discovered through frequency-domain acceleration searches. The timing solution shows that M92B is in a binary system with an orbital period of 2.3 days, an eccentricity of ≃4.8 × 10 ⁻⁴ , and a minimum companion mass of 0.2 M _⊙ . M92B lies within the cluster core radius in projection, and its negative spin period derivative ( P ̇ ) is consistent with acceleration in the cluster potential. The measured negative P ̇ of M92B, together with a DM consistent with that of M92A (−3 ), confirms that both pulsars are members of the cluster. A Bayesian Markov Chain Monte Carlo analysis based on these two pulsars yields broad constraints on the core structural parameters of M92 that are consistent with N -body dynamical modeling. This demonstrates that pulsar timing can provide useful dynamical information in sparse pulsar samples.

We present simultaneous optical photometry in the U, B, and V bands with the 85-cm telescope at Xinglong Observatory and L-band radio spectroscopy with the Five-hundred-meter Aperture Spherical radio Telescope (FAST) for a stellar flare on the active eclipsing binary CU Cancri. The flare occurred on 2025 January 11 (UT 16:30–19:30) and lasted for about 52 min, with a bolometric flare energy of 2.6 × 1032 erg. The U-band emission reached its peak earlier than the B and V bands, indicative of wavelength-dependent flare heating. The flare blackbody temperature, estimated from the B- to V-band emission ratio during the flare, increased to 13217 K near the peak and then declined rapidly toward the quiescent photospheric value. No significant radio burst was detected in the FAST L-band dynamic spectra during the optical flare. In addition, we analyse the flare activity of CU Cancri using long-term photometric data from Kepler/K2, from which a total of 532 flare events are identified. The results show that the orbital-phase distribution of the flares is consistent with uniformity and does not exhibit statistically significant orbital-phase dependence. Meanwhile, a power-law fit based on the K2 short-cadence data shows that the flare frequency distribution of CU Cancri is overall consistent with that of typical active M dwarfs. These multi-wavelength observations provide complementary constraints on plasma heating, dynamics, and electron acceleration during stellar flares, and offer new insight into how binarity shapes magnetic activity and space-weather environments in active M-dwarf systems.

We have focused on investigating X-ray stars obtained from eROSITA Data Release 1 (eRASS1) and conducting crossmatching with the TESS and LAMOST surveys. We have employed a convolutional neural network to identify flares from TESS, and found 7229 flare events on 1430 stars, with over 95% having durations less than 2 hr, and with more than 68% having amplitudes concentrated between 0.001 and 0.01. The majority of flare stars are found to have effective temperatures below 4000 K, with most occurring on stars with masses below 1 M _⊙ . The flare occurrence percentage is higher for stars with a temperature of less than 4000 K and a rotation period of less than 4 days. The flare duration is related to its energy by the formulation τ ∝ E ^0.27−0.41 . We have obtained the value of the power-law index ( α approximately 1.51 ± 0.12) of the cumulative flare frequency distribution. Crossmatching the eROSITA X-ray star sample with the LAMOST DR11 data yielded 9907 low-resolution spectra for 7672 stars and 70244 medium-resolution spectra for 7233 stars. In medium-resolution spectra, an asymmetry was observed in the H α profile of source 1eRASS J052919.0+120930, and potentially attributed to coronal rain or chromospheric condensation. By studying stars identified through crossmatching eROSITA and TESS with LAMOST DR11, we investigate the multiwavelength properties of X-ray-emitting stars. We find that flare stars, mostly late-type, exhibit stronger chromospheric and coronal activity than nonflare stars, and that the L _X / L _bol –Rossby number relation follows a broken power law with a turning point at R ₀ ≈ 0.1, indicating a transition from saturated to declining X-ray activity.

We report the discovery of six faint millisecond pulsars (MSPs) in the globular clusters (GCs) NGC 6517 and NGC 7078 (M15) using the Five-hundred-meter Aperture Spherical radio Telescope. These discoveries were enabled by stacking power spectra from multiple observations, a method that effectively boosts the signal-to-noise ratio of faint sources. In NGC 6517, we identified four new MSPs (NGC 6517S–V) with spin periods ranging from 3.68 to 6.02 ms and dispersion measures (DMs) between 182.45 and 182.85 pc cm ⁻³ . In M15, two additional MSPs (M15M and M15N) were discovered, with spin periods of 4.83 and 9.28 ms, and DMs of 67.89 and 66.65 pc cm ⁻³ , respectively. A phase-coherent timing solution has been obtained for M15M; however, sparse detection rates currently preclude phase-connected solutions for the remaining five pulsars. Current timing parameters suggest all six MSPs are isolated, which is consistent with the expected pulsar populations in core-collapsed GCs. Notably, pulsars M15N, NGC 6517U, and NGC 6517V eluded detection by standard frequency-domain searches (e.g., PRESTO-based) and the Fast Folding Algorithm, demonstrating that the stack search technique significantly enhances detection sensitivity to inherently faint pulsar signals.

As most of the companions in double neutron star systems should be normal pulsars, the Fast Folding Algorithm (FFA), which is suitable for finding these long spin period pulsars, was used to search their possible radio signals. A time domain resampling code PYSOLATOR was used to maximize the available data length by removing the orbital modulation. We collected and processed 272.2 hr of observational data taken by the Five-hundred-meter Aperture Spherical radio Telescope for the 13 double neutron star systems in its sky. The signal-to-noise ratios of known pulsar signals are obviously improved by this search method, including the detection of a faint pulsar signal which was identified only by folding the data. Unfortunately, no companion signals were found among all the 19,7962 candidates. Geodetic precession of the orbit could enhance detectability in future observations.