Atomic carbon ([CI]) is a key species in the carbon chemistry of the interstellar medium (ISM). Using the Submillimeter Wave Astronomy Satellite (SWAS), we conduct a [CI](3P1 → 3P0) 492 GHz survey covering approximately 4 deg2 of the L1688 and L1689 regions in the ρ Oph molecular cloud, achieving a spatial resolution of 4.25′. The derived [CI] column densities, N([CI), range from 4.85 × 1014 to 6.29 × 1017 cm−2, corresponding to an abundance ratio N([CI])/N(H2) of 2.24 × 10−7 to 2.39 × 10−4, with a median value of 1.8 × 10−5. Combining observations with photodissociation region (PDR) modeling, we find that [CI] abundance varies less than that of CO in regions with Ultraviolet intensity G0 > 16 and N(H2) < 4.6 × 1021 cm−2, suggesting [CI] is a more reliable tracer of molecular hydrogen in low-density, high-radiation environments where the [CI]-to-CO transition occurs. Utilizing [CI] as a direct H2 tracer, the CO-dark gas fraction is estimated to be 0.43, meaning that 43

Using new Institut de Radioastronomie Millim & eacute;trique 30 m telescope N2H+, C18O J = 1-0 and Atacama Pathfinder Experiment telescope 13CO and C18O J = 2-1 maps together with archival far-infrared continuum data, and 12CO, and 13CO J = 1-0 data, we present a comprehensive analysis of the massive filament CFG024.00+0.48 (G24) across clump-to-cloud scales. Our results show that G24 is an similar to 80 pc giant filament with a total mass of similar to 105 M circle dot. In the different tracers the filament width is measured to be about similar to 2 times the beam size of the observations, as expected for power-law density distributions, giving beam-deconvolved widths in the range from 0.8 to 2.8 pc. We determine a line-of-sight thickness of similar to 2.2 pc demonstrating that G24 is not an edge-on, flattened structure. The virial parameter obtained from line mass (alpha line,vir = Mline,vir/Mline) from the C18O (1-0) data is 0.85, and that obtained from Herschel-based H2 column density is 0.52, suggesting G24 is globally close to virial equilibrium. The distribution of the 40 dust clumps appears to have a "two-tier" fragmentation pattern. For the clump groups, the separation, with a mean/median of 3.68/3.46 pc, is very close to expected length associated with the maximum fragmentation growth rate of lambda max=3.55 +/- 0.32 pc estimated for the dust. However, the longitudinal centroid velocity profiles of C18O and N2H+ show oscillation patterns with wavelengths of 9.8 +/- 0.1 pc and 9.9 +/- 0.1 pc, respectively. This is similar to 2 times larger than the corresponding values of lambda max of 4.96 +/- 0.63 pc and 4.65 +/- 1.34 pc, respectively. This suggests that the velocity structure is not dominated by flows directly associated with the fragmentation seen in the dust emission.

For over a century, the origin of low-energy cosmic rays (LECRs), the dominant heaters and ionizers of dense interstellar gas, has remained elusive owing to solar modulation and uncertain transport processes. In this study, we introduce a new astrophysical approach based on H i narrow self-absorption (HINSA) to obtain spatially resolved measurements of LECR ionization rates using high-fidelity H i observations toward the Orion region from the FAST telescope. The LECR ionization rate is found to scale with local star formation rate as log10 zeta=(1.4 +/- 0.70)log10SFR+(-10.5 +/- 2.9) . Moreover, it increases with visual extinction, and is found to exceed, toward active star-forming regions, the value predicted for diffuse regions based on Voyager measurements and an external propagation model. These findings demonstrate that LECRs are generated in situ by star-forming activities rather than penetrating from the broader Galactic cosmic-ray population. This is further supported by Fermi-LAT gamma-ray observations toward the Orion region. Together, these results resolve a key uncertainty in cosmic-ray origin and establish a new avenue for quantifying the energetic feedback that regulates the interstellar medium.

By combining multi-band data from Gaia DR3, MWISP CO, and LAMOST DR11 LSR/MSR, we investigate the co-evolution of stars and their parent molecular cloud in a snake-like stellar structure, named Snake III. Based on 5-D phase-space selection, we identified 5683 member stars (median age 7.6 Myr) across approximately 300 × 500 × 175 pc^3 volume, along with 12 embedded open clusters. Then we use BEEP distances combined with ^12CO velocities to clearly identify the molecular clouds associated with the stellar complex in spatial and kinematics. The molecular cloud density increases with Galactic longitude, with older open clusters forming in cavities near higher-density regions (except ASCC 125), while young field stars currently form preferentially in present-day high-density environments, indicating that cloud density regulates the star-formation sequence. ^12CO excitation temperature, centroid velocity, velocity dispersion and Hα emission reveal that early feedback first compresses cloud edges to trigger new stars, then sweeps and disperses the parent clouds. The extremely young cluster (ASCC 125, 4.4 Myr) lies near the densest region yet is surrounded by a shell with bidirectional density-velocity perturbations, consistent with a delayed-triggering scenario under the combined influence of UBC 178 stellar-wind feedback and a suspected supernova blast. Our results naturally demonstrate that snake-like stellar structures are filamentary relics of hierarchical star formation within giant molecular clouds. They provide direct observational evidence that cloud density and early feedback jointly modulate the progression of star formation, offering a clear and young laboratory for studying star-cloud co-evolution.

Infrared dark clouds (IRDCs) contains cold dense gas at the earliest stage of massive star and cluster formation. In studying the IRDCs, a universal and fundamental task is to resolve their internal hierarchical structures. Various packages and algorithms were developed for this purpose, but with most of them mainly focused on certain individual steps in data processing. In this work, we build a more automatic procedure for multi-band structure measurement HONKAI (Hierarchical cOre ideNtification and Kinematic property AssIgnment), which can resolve the elemental components including cores and clumps, disentangle the velocity components in spectral data, measure their physical properties, and generate a catalogue for all the measured properties. We use honkai for a joint study towards three IRDCs observed in 850 μm dust continuum with James Clerk Maxwell Telescope (JCMT) and the ^13CO (1-0) data cube with the Purple Mount Observatory 14-m telescope. 193 dense cores in 16 clumps are identified. As major dynamical properties, a large amount of the cores (136 out of 193) are measured to have large virial ratio of R_ vir>1, but their mass-size relation is bellow the threshold for massive star formation. Meanwhile, core mass function (CMF) also exhibits a steeper slope towards high-mass end compared to more evolved core samples. These three properties in accordance suggest that although many IRDC cores are self-gravitating, only a small fraction are seemingly possible to form high-mass stars. In subsequent core evolution, some further mass assembly trend may be involved to facilitate the high-mass star formation.

We present the first Galactic-scale validation of flux scaling relations among CO isotopologues, using an enlarged sample from the Milky Way Imaging Scroll Painting Phase I survey. We identified 10,843 ^13 CO-emitting clouds and 746 C ^18 O-emitting clouds using a stacking algorithm from the ^12 CO cloud sample of Q.-Z. Yan et al. We obtained flux scaling relations ${F}_{{}^{13}{\rm{CO}}}=0.11\,{F}_{{}^{12}{\rm{CO}}}$ within the ^12 CO-bright region and ${F}_{{}^{13}{\rm{CO}}}=0.16\,{F}_{{}^{12}{\rm{CO}}}$ within the ^13 CO-bright region. Additionally, we found the relation ${F}_{{{\rm{C}}}^{18}{\rm{O}}}\,=\,0.11\,{F}_{{}^{13}{\rm{CO}}}$ in C ^18 O-emitting regions, which indicates their abundance ratio ${X}_{{}^{13}{\rm{CO}}}/{X}_{{{\rm{C}}}^{18}{\rm{O}}}\sim 8.0$ . It suggests large-scale chemical homogeneity in molecular clouds. Flux ratios within individual clouds demonstrate a general pattern that gradually decreases outward. The cumulative distributions of flux in ^12 CO, ^13 CO, and C ^18 O are all close to “top heavy,” suggesting that a small number of high-flux molecular clouds dominate the total flux in the Galaxy.

We present the first data release (DR1) of the Milky Way Imaging Scroll Painting (MWISP) survey, a mapping in the J = 1 -> 0 transition lines of 12CO, 13CO, and C18O toward the northern Galactic plane during 2011-2022. The MWISP survey was conducted using the Purple Mountain Observatory 13.7 m telescope at a spatial resolution of approximately 50 '' and a velocity resolution of 0.16 km s-1 at 115 GHz. DR1 fully covered 2310 deg2 within the Galactic longitude (l) and latitude (b) range of 9 .degrees 75 <= l <= 229 .degrees 75 and divided by b divided by <= 5 .degrees 25. The surveyed area was divided into cell units of 30 ' x30 ' for practical purposes and on-the-fly mapping was performed toward each target cell unit. The data were regridded into a regular three-dimensional data cube in l-b-VLSR with a pixel size of 30 '' in l-b axes and 0.16 km s-1 in the VLSR axis. The median rms noise is 0.47, 0.25, and 0.25 K for 12CO, 13CO, and C18O, respectively. The equivalent 3 sigma sensitivity in 12CO luminosity is approximately 0.23 K km s-1, making MWISP the most sensitive survey of its kind. In this paper, we describe the survey data, including the calibration, data cleaning, data mosaic processes, and the data products. The final mosaicked data cubes contain about 3.33 x 107 spectra (pixels) for each CO isotopologue line. Color composite images, made from the intensities of the isotopologue lines, and some concise descriptions are provided. We constructed a molecular cloud catalog based on the mosaicked 12CO data cube using the clustering algorithm DBSCAN, detecting 103,517 molecular clouds, 10,790 of which exhibit 13CO emission and 304 of which show C18O emission. Based on the histogram of voxel brightness temperature, we estimated a total 12CO flux of 7.69 +/- 0.38 x 107 K km s-1 arcmin2, 82% of which is captured by the DBSCAN algorithm. The properties of molecular clouds show a large dynamic range, facilitating more accurate statistics. The data, together with the cloud sample, provide unique information on molecular gas in the northern Milky Way.

The axion is a well-motivated dark matter candidate, which can convert into narrow radio spectral lines via the Primakoff effect in the strongly magnetized magnetospheres of neutron stars. This provides a novel astrophysical probe for axion searches that is complementary to laboratory experiments. Using FAST, the world's most sensitive single-dish radio telescope, we observed two X-ray dim isolated neutron stars (RXJ1605.3+3249 and RXJ1308.6+2127) within its sky coverage, which are predicted to yield the strongest axion-conversion spectral lines (ACL). Although no significant signal was detected at the 5 sigma confidence level, we establish new upper limits on the axion-photon coupling constant g_{a gamma gamma} less than or similar to 5 x 10^{-12} GeV^{-1} for axion masses ranging from 4.14 to 6.20 micro-eV corresponding to the 1.0-1.5 GHz observational band. This result constitutes the tightest constraint in this axion mass range among all existing studies employing the same ACL-based method.

Most massive stars reside in binary systems, and binary interactions can profoundly alter the properties of both stellar components. In young open clusters, such interactions can produce multiple main-sequence populations, despite the coeval nature of the stellar population. In this work, we extend our previous studies on the role of binary evolution in shaping main-sequence morphologies by performing a more detailed and systematic analysis. We investigate the progenitor properties of different main-sequence populations from 10 to 100 Myr using detailed binary models computed with MESA, assuming SMC-like metallicity, and initial primary masses of 3–100 M _⊙ . We provide physical explanations for the features identified in our earlier work. We focus especially on post–Case A mass-transfer systems, which produce a prominent “bridge-like” feature connecting the reddest Be stars and the bluest blue stragglers. We show that the positions of these stars are sensitive to surface helium enrichment and rotation. We further perform quantitative comparisons with observed clusters aged 30–90 Myr whose turn-off masses are from approximately 9 to 5 M _⊙ . We find that our models broadly reproduce the observed stellar distributions. However, we underpredict the fraction of Be stars, suggesting that a larger fraction of binaries may undergo stable mass transfer. We also overpredict the number of stars on the redder side of the unresolved-binary sequence, indicating that the initial mass-ratio distribution may deviate from a flat distribution. Overall, this work provides a comprehensive analysis of how binary evolution produces diverse main-sequence populations and lays the foundation for future population-synthesis studies.

Infrared Dark Clouds are ideal sites for investigating the initial conditions of massive star and cluster formation. The A Lei Of the Habitat and Assembly of Infrared Dark Clouds (ALOHA IRDCs), a James Clerk Maxwell Telescope (JCMT) Large Program, has mapped nearby IRDCs with SCUBA-2. Complementary molecular line observations are needed to characterise the physical, kinematic, and chemical properties of the dense gas. We aim to determine the thermal, kinematic, and chemical properties of clumps identified in the ALOHA IRDCs, and to assess their evolutionary status and level of star-forming activity. We performed single-pointing K-band and W-band observations towards 56 ALOHA IRDCs clumps using the Effelsberg 100-m and Yebes 40-m telescopes, respectively. We derived NH3 kinetic temperatures using the hyperfine group ratio (HFGR) method and identified infall and shock signatures from HCO+, H13CO+, SiO, and HNCO profiles. Water masers and NH2D emission were used as complementary tracers of chemical evolution and star formation. The clumps exhibit kinetic temperatures of 15-29 K. We detect NH2D emission towards 18 sources, with NH2D centroid velocities consistent with NH3, indicating both species trace the same dense gas component. More than half of the clumps display blue-asymmetric HCO+ profiles, identifying them as infall candidates. Water masers are detected in 22 sources, with prominent velocity ranges and variability. Broad SiO emission (> 20 km/s) indicates strong shocks, while narrower extents (< 6km/s) likely trace large-scale interactions or low-velocity shocks. The widespread infall signatures, shock tracers, masers, and NH2D emission suggest that relatively quiescent, chemically young material can coexist with dynamically active gas affected by early protostellar feedback, providing insight into the coupled physical and chemical evolution of massive IRDC clumps.

To ensure the reliability of the analysis results from Insight-HXMT scanning observations, particle event (PE) generated by high-energy charged particles must be masked from the raw light curves of scanning observations. PEs typically manifest as bumps on the light curve with timescales ranging from tens to thousands of seconds, and their significant impact on the analysis process leads to incorrect flux estimates for known sources and even the mis-identification of fake sources. Insight-HXMT is actually equipped with plastic scintillator detectors, including anti-coincidence detectors and particle monitors, that are sensitive to high-energy particles. However, a large amount of data analyses indicate that relying solely on these detectors is insufficient for the effective PE masking in the scanning data. Using extensive archival observations, we obtain the peak-to-duration ratios and similarity coefficients of detected PEs and X-ray sources. Based on their distinct behaviors in the two-dimensional distribution of these parameters, we develop a new PE masking method. An empirical function is used to parameterize the boundary of this two-dimensional distribution. At a fixed PE-identification rate of 99.7%, the non-PE mis-identification rates under the optimal parameters are 0.32%, 0.15% and 0.002% for the low-, medium-, and high-energy telescopes, respectively. This method is validated under more complex conditions using simulated data, with mis-identification rates of 1.65%, 0.16%, and 1.62%, respectively

Searching for fleeting radio transients like fast radio bursts (FRBs) with wide-field radio telescopes has become a common challenge in data-intensive science. Conventional algorithms normally cost enormous time to seek candidates by finding the correct dispersion measures, of which the process is so-called dedispersion. Here we present a novel scheme to identify FRB signals from raw data without dedispersion using Machine Learning (ML). Under the data environment for multibeam receivers, we train the EfficientNet model and achieve both exceeding 92

report the results of the first 2-year observations of LEIA in the Galactic plane and demonstrate its excellent performance. We select 34 sources for detailed analysis of their flux and spectral variability. Systematic errors calculated and the observational performance differences between CMOS15 and CMOS16 are corrected. During analysis of these sources, excess variance and standard chi 2 tests are applied to characterize flux and spectral variability, respectively, and the distributions and their interrelations are analyzed. A variable flux is observed most sources, with a more significant difference in flux variability observed closer to the Galactic Center. methods are employed to characterize spectral variability: fluctuations in the Hardness Ratio (HR) derived count rates in the high-to-low energy bands, and variability in the photon index (Gamma) obtained from spectral fitting. results from both methods are broadly consistent. The findings suggest that the spectra of most XRBs variable. Statistical analysis of flux and spectral variability for the sample sources reveals no significant correlation between the two. As a result, the first 2-year XRBs catalog of LEIA in the Galactic plane is presented. At the same time, the analysis of the sources indicate that the observation data of LEIA are usable and valuable, fulfilling mission as the pathfinder of lobster-eye Wide-field X-ray Telescope onboard the Einstein Probe mission.

We present the calibration procedures and validation of source measurement with the data of the Commensal Radio Astronomy FAST Survey for H i intensity mapping by the Five-hundred-meter Aperture Spherical Radio Telescope. Using a 70 hr drift-scan observation with the L -band (1.05–1.45 GHz) 19 beam receiver, we obtain the data covering a 270 deg ^2 sky area. We employ both the pulsar backend and the spectrum backend to calibrate the spectral time-ordered data (TOD) before projecting them onto HEALPix maps. We produce calibrated TOD with a frequency resolution of 30 kHz and time resolution of 1 s and the map data cube with a frequency resolution of 30 kHz and spatial resolution of 2.95 arcmin ^2 . We examine the pointing errors, noise overflow, radio-frequency interference (RFI) contamination, and their effect on the data quality. The resulting noise level is ∼5.7 mJy for the calibrated TOD and 1.6 mJy for the map, consistent with the theoretical predictions within 5% at RFI-free channels. We also validate the data by principal component analysis and find that the residual map looks thermal noise dominated after removing 30 modes. We identify 447 isolated bright continuum sources in our data matching the NRAO VLA Sky Survey catalog, with relative flux error of 8.3% for TOD and 6.6% for the map level. We also measure the H i emission of 90 galaxies with redshift z < 0.07 and compare them with H i -MaNGA spectra, yielding an overall relative H i integral flux error of 16.7%. These results provide an important first step in assessing the feasibility of conducting cosmological H i detection with CRAFTS.

Pulsar observation is a critical tool for exploring the universe, necessitating advanced digital backends to efficiently capture and process faint pulsar signals. This paper introduces a 4-channel wideband digital backend for pulsar observation, with each channel featuring dual polarization and a maximum bandwidth of 2 GHz. The system is capable of simultaneously processing multiple signal bands, with a total bandwidth up to 8 GHz, and employs Bartlett’s method for power spectrum estimation. The design divides 8 high-speed data streams from ADCs into 32 low-speed data streams to reduce power, while a specialized combined Fast Fourier Transform (FFT) unit with bit-reversed order is utilized to minimize resource consumption. This approach yields a compact and power-efficient solution integrated into a single Radio Frequency System on Chip (RFSoC). The backend fully utilizes the hardware resources and supports multiple observation modes, offering flexible bandwidth and frequency resolution options. The system’s performance has been validated through on-site telescope observations, confirming its capability to reliably acquire and process pulsar signals.

The vast majority of massive binary systems in the universe is evidently unsuited to produce merging binary black holes. However, several narrow evolutionary paths of isolated massive binaries towards this goal have recently been identified. Due to the high degree of simplification and assumptions applied in previous modelling of these paths, conclusions remained vague so far. For one of these paths, the stable mass transfer channel, we now construct detailed binary evolution models which include internal differential rotation as well as mass and angular momentum transfer between the stars, all the way from the zero-age main sequence to the formation of the black holes, only skipping the rapid late burning stages. This allows us to follow the mass and chemical structure evolution of the mass accreting component, which turns out to have a key influence on the phase of reverse mass transfer, that allows the obtained black hole spins and mass ratios to naturally fall into the regime observed for the gravitational-wave source in the 10–25M_⊙ primary black hole mass range. As for this channel, also a large number of progenitor binaries are known, we conclude that it likely contributes to the observed population of gravitational wave sources.

Supernovae, the explosive deaths of massive stars, create heavy elements and form black holes and neutron stars. These compact objects often receive a velocity at formation, a "kick" whose physical origin remains debated. We investigate kicks in Be X-ray binaries, containing a neutron star and a rapidly spinning companion. We identify two distinct populations: one with kicks below 10 km s^-1, much lower than theoretical predictions, and another with kicks around 100 km s^-1, that shows evidence for being aligned within 5 degrees of the progenitor's rotation axis. The distribution of progenitor masses for the two populations have medians around 2.3 M_⊙ and 4.9 M_⊙, corresponding to stars with birth masses of about 10 M_⊙ and 15 M_⊙. The second component matches the low-velocity mode observed in isolated pulsars. Combined with the known high-velocity component, which dominates isolated pulsars, this suggests three distinct kick modes. These results reveal previously unrecognized diversity in neutron-star formation.

In this work, we report a study on the relationship between flux and intensity for molecular clouds. Our analysis is established on high-quality CO images from the Milky Way Imaging Scroll Painting project. The new flux–intensity relation characterizes the flux variation of molecular clouds above specific intensity levels. We found that the flux–intensity relation exhibits two prominent features. First, the flux–intensity relation generally follows exponential shapes; second, hierarchical structures of molecular clouds are imprinted on flux–intensity relations. Specifically, ^12 CO flux–intensity relations are composed of one or more exponential segments, and for molecular clouds with segmented flux–intensity relations, the edge and the flux of the high-temperature component are strikingly consistent with ^13 CO emission. Further analysis shows that a similar relationship also exists between ^13 CO flux–intensity relations and C ^18 O emission. The mean brightness temperature of molecular clouds is tightly associated with the decay rate of flux, the break temperature of exponential segments, and, to a certain extent, the flux fraction of the high-temperature component. Broadly, the flux–intensity relation of a molecular tracer, either in optically thick or in optically thin cases, has the capability to outline the silhouette of internal structures of molecular clouds, proving to be a potent tool for probing structures of molecular clouds.

Filaments are believed to play a key role in high-mass star formation. We present a systematic study of the filaments and their hosting clumps in the G35 molecular complex using James Clerk Maxwell Telescope SCUBA-2 850 mu m continuum data. We identified five clouds in the complex and 91 filaments within them, some of which form 10 hub-filament systems (HFSs), each with at least three hub-composing filaments. We also compiled a catalog of 350 dense clumps, 183 of which are associated with the filaments. We investigated the physical properties of the filaments and clumps, such as mass, density, and size, and their relation to star formation. We find that the global mass-length trend of the filaments is consistent with a turbulent origin, while the hub-composing filaments of high line masses (ml >230 M-circle dot pc(-1)) in HFSs deviate from this relation, possibly due to feedback from massive star formation. We also find that the most massive and densest clumps (R >0.2 pc, M >35 M-circle dot, Sigma>0.05gcm(2)) are located in the filaments and in the hubs of HFSs, with the latter bearing a higher probability of the occurrence of high-mass star-forming signatures, highlighting the preferential sites of HFSs for high-mass star formation. We do not find significant variation in the clump mass surface density across different evolutionary environments of the clouds, which may reflect the balance between mass accretion and stellar feedback.