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  • Resolution Enhancement of SOHO/MDI Magnetograms

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: Research on the solar magnetic field and its effects on solar dynamo mechanisms and space weather events has benefited from the continual improvements in instrument resolution and measurement frequency. The augmentation and assimilation of historical observational data timelines also play a significant role in understanding the patterns of solar magnetic field variation. Within the realm of astronomical data processing, super-resolution (SR) reconstruction refers to the process of using a substantial corpus of training data to learn the nonlinear mapping between low-resolution (LR) and high-resolution (HR) images, thereby achieving higher-resolution astronomical images. This paper is an application study in high-dimensional nonlinear regression. Deep learning models were employed to perform SR modeling on SOHO/MDI magnetograms and SDO/HMI magnetograms, thus reliably achieving resolution enhancement of full-disk SOHO/MDI magnetograms and enhancing the image resolution to obtain more detailed information. For this study, a data set comprising 9717 pairs of data from 2010 April to 2011 February was used as the training set, 1332 pairs from 2011 March were used as the validation set and 1034 pairs from 2011 April were used as the test set. After data preprocessing, we randomly cropped 128 × 128 sub-images as the LR cases from the full-disk MDI magnetograms, and the corresponding 512 × 512 sub-images as HR ones from the HMI full-disk magnetograms for model training. The tests conducted have shown that the study successfully produced reliable 4× SR reconstruction of full-disk MDI magnetograms. The MESR model's results (0.911) were highly correlated with the target HMI magnetographs as indicated by the correlation coefficient values. Furthermore, the method achieved the best PSNR, SSIM, MAE and RMSE values, indicating that the MESR model can effectively reconstruct magnetograms.

  • Pulsar Glitch Activities: The Spin Parameters Approach

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: Glitch activity refers to the mean increase in pulsar spin frequency per year due to rotational glitches. It is an important tool for studying super-nuclear matter using neutron star interiors as templates. Glitch events are typically observed in the spin frequency (ν) and frequency derivative of pulsars. The rate of glitch recurrence decreases as the pulsar ages, and the activity parameter is usually measured by linear regression of cumulative glitches over a given period. This method is effective for pulsars with multiple regular glitch events. However, due to the scarcity of glitch events and the difficulty of monitoring all known pulsars, only a few have multiple records of glitch events. This limits the use of the activity parameter in studying neutron star interiors with multiple pulsars. In this study, we examined the relationship between the activity parameters and pulsar spin parameters (spin frequency, frequency derivative, and pulsar characteristic age). We found that a quadratic function provides a better fit for the relationship between activity parameters and spin parameters than the commonly used linear functions. Using this information, we were able to estimate the activity parameters of other pulsars that do not have records of glitches. Our analysis shows that the relationship between the estimated activity parameters and pulsar spin parameters is consistent with that of the observed activity parameters in the ensemble of pulsars.

  • Optical Extinctions of Inter-Arm Molecular Clouds in M31: A Pilot Study for the Upcoming CSST Observations

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: Recent submillimeter dust thermal emission observations have unveiled a significant number of inter-arm massive molecular clouds in M31. However, the effectiveness of this technique is limited to its sensitivity, making it challenging to study more distant galaxies. This study introduces an alternative approach, utilizing optical extinctions derived from space-based telescopes, with a focus on the forthcoming China Space Station Telescope (CSST). We first demonstrate the capability of this method by constructing dust extinction maps for 17 inter-arm massive molecular clouds in M31 using the Panchromatic Hubble Andromeda Treasury data. Our analysis reveals that inter-arm massive molecular clouds with an optical extinction (AV) greater than 1.6 mag exhibit a notable AV excess, facilitating their identification. The majority of these inter-arm massive molecular clouds show an AV around 1 mag, aligning with measurements from our JCMT data. Further validation using a mock CSST RGB star catalog confirms the method's effectiveness. We show that the derived AV values using CSST z and y photometries align more closely with the input values. Molecular clouds with AV > 1.6 mag can also be identified using the CSST mock data. We thus claim that future CSST observation clouds provide an effective way for the detection of inter-arm massive molecular clouds with significant optical extinction in nearby galaxies.

  • Long-term Integration Ability of the Submillimeter Wave Astronomy Satellite (SWAS) Spectral Line Receivers

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: The Submillimeter Wave Astronomy Satellite (SWAS) was the first space telescope capable of high spectral resolution observations of terahertz spectral lines. We have investigated the integration ability of its two receivers and spectrometer during five and a half years of on-orbit operation. The C i , O2, H2O, and 13CO spectra taken toward all observed Galactic sources were analyzed. The present results are based on spectra with a total integration time of up to 2.72 × 104 hr (≃108 s). The noise in the spectra is generally consistent with that expected from the radiometer equation, without any sign of approaching a noise floor. This noise performance reflects the extremely stable performance of the passively cooled front end as well as other relevant components in the SWAS instrument throughout its mission lifetime.

  • Long Term X-Ray Spectral Variations of the Seyfert-1 Galaxy Mrk 279

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: We present the results from a long term X-ray analysis of Mrk 279 during the period 2018–2020. We use data from multiple missions – AstroSat, NuSTAR and XMM-Newton, for the purpose. The X-ray spectrum can be modeled as a double Comptonization along with the presence of neutral Fe Kα line emission, at all epochs. We determined the source's X-ray flux and luminosity at these different epochs. We find significant variations in the source's flux state. We also investigate the variations in the source's spectral components during the observation period. We find that the photon index and hence the spectral shape follow the variations only over longer time periods. We probe the correlations between fluxes of different bands and their photon indices, and found no significant correlations between the parameters.

  • The Adjustment Analysis Method of the Active Surface Antenna Based on Convolutional Neural Network

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: Active surface technique is one of the key technologies to ensure the reflector accuracy of the millimeter/submillimeter wave large reflector antenna. The antenna is complex, large-scale, and high-precision equipment, and its active surfaces are affected by various factors that are difficult to comprehensively deal with. In this paper, based on the advantage of the deep learning method that can be improved through data learning, we propose the active adjustment value analysis method of large reflector antenna based on deep learning. This method constructs a neural network model for antenna active adjustment analysis in view of the fact that a large reflector antenna consists of multiple panels spliced together. Based on the constraint that a single actuator has to support multiple panels (usually 4), an autonomously learned neural network emphasis layer module is designed to enhance the adaptability of the active adjustment neural network model. The classical 8-meter antenna is used as a case study, the actuators have a mean adjustment error of 0.00252 mm, and the corresponding antenna surface error is 0.00523 mm. This active adjustment result shows the effectiveness of the method in this paper.

  • V0405 Dra: A New Deep and Low Mass Ratio Contact Binary with Extremely Fast Decrease in the Orbital Period

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: V0405 Dra is a W UMa-type binary star. Based on the TESS data, we have conducted an orbital period study and performed a light curve analysis for the system. The orbital period study reveals that the O − C curve for V0405 Dra exhibits secular decrease at an extremely high rate of dP/dt = −2.71 × 10−6 day year−1, along with periodic variations characterized by an amplitude of A3 = 0.0032 day and a period of P3 = 1.413 years. The orbital periodic change is possibly due to the light-travel time effect resulting from an additional third body in the system, for which we estimate a minimum mass of M3 = 0.77M⊙. By employing the 2013 version of the Wilson-Devinney (W-D) method to synthesize a light curve, we derived photometric solutions indicating that V0405 Dra is a new deep (f = 68.7%) and low-mass ratio (q = 0.175) contact binary. The fast decrease in its orbital period is likely caused by mass transfer from the more massive primary star to the less massive secondary star, or due to angular momentum loss. With further mass transfer and loss of angular momentum, the binary will gradually evolve into a tighter contact configuration, eventually leading to a merger into a single star, following the evolutionary paths suggested for such deep and low mass ratio contact binaries.

  • Simulating the Escaping Atmosphere of GJ 436 b with Two-fluid Magnetohydrodynamic Models

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: Observations of transmission spectra reveal that hot Jupiters and Neptunes are likely to possess escaping atmospheres driven by stellar radiation. Numerous models predict that magnetic fields may exert significant influences on the atmospheres of hot planets. Generally, the escaping atmospheres are not entirely ionized, and magnetic fields only directly affect the escape of ionized components within them. Considering the chemical reactions between ionized components and neutral atoms, as well as collision processes, magnetic fields indirectly impact the escape of neutral atoms, thereby influencing the detection signals of planetary atmospheres in transmission spectra. In order to simulate this process, we developed a magnetohydrodynamic multi-fluid model based on MHD code PLUTO. As an initial exploration, we investigated the impact of magnetic fields on the decoupling of H+ and H in the escaping atmosphere of the hot Neptune GJ436b. Due to the strong resonant interactions between H and H+, the coupling between them is tight even if the magnetic field is strong. Of course, alternatively, our work also suggests that merging H and H+ into a single flow can be a reasonable assumption in MHD simulations of escaping atmospheres. However, our simulation results indicate that under the influence of magnetic fields, there are noticeable regional differences in the decoupling of H+ and H. With the increase of magnetic field strength, the degree of decoupling also increases. For heavier particles such as O, the decoupling between O and H+ is more pronounced. Our findings provide important insights for future studies on the decoupling processes of heavy atoms in the escaping atmospheres of hot Jupiters and hot Neptunes under the influence of magnetic fields.

  • Analysis of the Impact of the Blazhko Effect Both on the Van Hoof Effect and Radial Velocity Amplitude in the Star RR Lyr

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: The Van Hoof effect is a phase shift existing between the radial velocity curves of hydrogen and metallic lines within the atmosphere of pulsating stars. In this article, we present a study of this phenomenon through the spectra of the brightest pulsating star RR Lyr of RR Lyrae stars recorded for 22 yr. We based ourselves, on the one hand, on 1268 spectra (41 nights of observation) recorded between the years 1994 and 1997 at the Observatory of Haute Provence (OHP, France) previously observed by Chadid and Gillet, and on the other hand on 1569 spectra (46 nights of observation) recorded at our Oukaimeden Observatory (Morocco) between 2015 and 2016. Through this study, we have detected information on atmospheric dynamics that had not previously been detected. Indeed, the Van Hoof effect which results in a clear correlation between the radial velocities of hydrogen and those of the metallic lines has been observed and analyzed at different Blazhko phases. A correlation between the radial velocities of different metallic lines located in the lower atmosphere has been observed as well. For the first time, we were able to show that the amplitude of the radial velocity curves deduced from the lines of hydrogen and that of Fe ii (λ4923.921 Å) increases toward the minimum of the Blazhko cycle and decreases toward the maximum of the same Blazhko cycle. Furthermore, we found that the Van Hoof effect is also modulated by the Blazhko effect. Thus, toward the minimum of the Blazhko cycle the Van Hoof effect is more visible and at the maximum of the Blazhko cycle, this effect is minimal. We also observed the temporal evolution of the amplitudes of the radial velocities of the lower and upper atmosphere. When observed over a long time, we can interpret it as a function of the Blazhko phases.

  • The Influence of the Sun and Moon on the Observation of Very High Energy Gamma-ray Sources Using EAS Arrays

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: With great advance of ground-based extensive air shower arrays, such as LHAASO and HAWC, many very high energy (VHE) gamma-ray sources have been discovered and are being monitored regardless of the day and the night. Hence, the Sun and Moon would have some impacts on the observation of gamma-ray sources, which have not been taken into account in previous analysis. In this paper, the influence of the Sun and Moon on the observation of very high energy gamma-ray sources when they are near the line of sight of the Sun or Moon is estimated. The tracks of all the known VHE sources are scanned and several VHE sources are found to be very close to the line of sight of the Sun or Moon during some period. The absorption of very high energy gamma rays by sunlight is estimated with detailed method and some useful conclusions are achieved. The main influence is the block of the Sun and Moon on gamma rays and the shadow on the cosmic ray background. The influence is investigated considering the detector angular resolution and some strategies on data analysis are proposed to avoid the underestimation of the gamma-ray emission.

  • Feedback of Efficient Shock Acceleration on Magnetic-field Structure Inside Young Type Ia Supernova Remnants

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: Using an effective adiabatic index γeff to mimic the feedback of efficient shock acceleration, we simulate the temporal evolution of a young type Ia supernova remnant (SNR) with two different background magnetic field (BMF) topologies: a uniform and a turbulent BMF. The density distribution and magnetic-field characteristics of our benchmark SNR are studied with two-dimensional cylindrical magnetohydrodynamic simulations. When γeff is considered, we find that: (1) the two-shock structure shrinks and the downstream magnetic-field orientation is dominated by the Rayleigh–Taylor instability structures; (2) there exists more quasi-radial magnetic fields inside the shocked region; and (3) inside the intershock region, both the quasi-radial magnetic energy density and the total magnetic energy density are enhanced: in the radial direction, with γeff = 1.1, they are amplified about 10–26 times more than those with γeff = 5/3. While in the angular direction, the total magnetic energy densities could be amplified about 350 times more than those with γeff = 5/3, and there are more grid cells within the intershock region where the magnetic energy density is amplified by a factor greater than 100.

  • Temporal and Spectral Characteristics of Persistent Emission and Special Bursts of Magnetar SGR J1935+2154 Based on Insight-HXMT

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: In October 2022, the magnetar SGR J1935+2154 entered the active outburst state. During the episode, the Insight-HXMT satellite carried out a long observation that lasted for 20 days. More than 300 bursts were detected, and a certain amount of persistent radiation signals were also accumulated. This paper mainly introduces the results of persistent radiation profile folding and period search based on Insight-HXMT data. At the same time, the burst phase distribution characteristics, spectral lag results of burst, the spectral characteristics of zero-lag bursts and the time-resolved spectral evolution characteristics of high-flux bursts are reported. We found that there is no significant delay feature during different energy bands for the bursts of SGR J1935+2154. The observed zero-lag burst does not have a unique spectrum. The time-resolved spectrum of the individual burst has consistent spectral types and spectral parameters at different time periods of the burst. We also find that the burst number phase distribution and the burst photon phase distribution have the same tendency to concentrate in specific regions of the persistent emission profile.

  • Timing and Spectral Analysis of the Black Hole X-Ray Binary MAXI J1803-298 with Insight-HXMT Data

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: We present a comprehensive analysis of the 2021 outburst of MAXI J1803–298 utilizing observations of the Insight-Hard X-ray Modulation Telescope (Insight-HXMT) spanning from the low hard state to the high soft state. Within the Insight-HXMT data set, compared to the previous work, we identify a more prolonged presence of type-C quasi-periodic oscillations (QPOs) with centroid frequencies ranging from ∼0.16 to 6.3 Hz, which present correlations with the hardness ratio and the photon index of the Comptonized component. For QPO frequencies less than ∼2 Hz, the QPO phase lags are hard (photons of 10–19 keV arrive later than those of 1–4 keV), while at higher frequencies, the lags become soft at and above ∼4 Hz. Furthermore, the spectra in all Insight-HXMT observations consist of a multi-color blackbody component and a Comptonized component, as commonly observed in classical black hole X-ray binaries. We analyze state transitions and the evolution of accretion geometry in this work. The fitted inner disk radius increases abnormally during the low hard state, hypothesized to result from the corona condensing onto the inner disk. Additionally, two significant drops in flux are observed during the soft intermediate state, maybe implying changes in the corona/jet and the disk, respectively.

  • Photometric Analysis for Asteroid (81) Terpsichore using Convex Inversion and Phase Function Fitting Methods

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: The shapes and rotation states (periods and pole orientations) of main-belt asteroids are important for understanding their formation and evolution. In order to obtain sufficient photometric data covering different apparitions for asteroid (81) Terpsichore, ground-based photometric observations in 2020 and 2021 were carried out. By combining published and newly obtained photometric data, we calculated the shape and spin parameters for (81) Terpsichore using the convex inversion method. With this method, we have derived a best fitted pole orientation—with a spin period of 10.94h. Based on the derived convex shape of (81) Terpsichore, we have fitted the H, G1, G2 phase function using the calibrated TESS data and Gaia data after accounting for the lightcurve amplitude correction. As a result, we have derived its absolute magnitude H = 8.68mag with corresponding phase function parameters G1 = 0.82 and G2 = 0.02 .

  • A Possible X-ray Quasi-periodic Oscillation in the Narrow-line Seyfert 1 Galaxy Mrk 142

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: A possible quasi-periodic oscillation (QPO) at frequency 7.045 × 10−5 Hz is found in the narrow-line Seyfert 1 galaxy Mrk 142 in the data of XMM-Newton collected on 2020 April 11. We find that the QPO signal is statistically significantly larger than the 5σ level and highly coherent with quality factor Q > 5 at the 0.3–10 keV band by using the method of the Lomb–Scargle Periodogram, the Weighted Wavelet Z-transform and the REDFIT. We analyze the data in 0.3–0.6 keV, 0.6–1 keV, 1–3 keV and 3–10 keV energy bands, and find obvious QPO signals at 0.3–0.6 keV and 1–3 keV bands. We then analyze the time-average spectra and time variability at the QPO frequency of 7.045 × 10−5 Hz, and use a model to fit them. We find that the QPO signal mainly comes from the X-ray hot corona.

  • Isochrone Fitting of Galactic Globular Clusters—VI. High-latitude Clusters NGC 5024 (M53), NGC 5053, NGC 5272 (M3), NGC 5466, and NGC 7099 (M30)

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: We fit various color–magnitude diagrams (CMDs) of the high-latitude Galactic globular clusters NGC 5024 (M53), NGC 5053, NGC 5272 (M3), NGC 5466, and NGC 7099 (M30) by isochrones from the Dartmouth Stellar Evolution Database and Bag of Stellar Tracks and Isochrones for α–enrichment [α/Fe] = +0.4. For the CMDs, we use data sets from Hubble Space Telescope, Gaia, and other sources utilizing, at least, 25 photometric filters for each cluster. We obtain the following characteristics with their statistical uncertainties for NGC 5024, NGC 5053, NGC 5272, NGC 5466, and NGC 7099, respectively: metallicities [Fe/H] = −1.93 ± 0.02, −2.08 ± 0.03, −1.60 ± 0.02, −1.95 ± 0.02, and −2.07 ± 0.04 dex with their systematic uncertainty 0.1 dex; ages 13.00 ± 0.11, 12.70 ± 0.11, 11.63 ± 0.07, 12.15 ± 0.11, and 12.80 ± 0.17 Gyr with their systematic uncertainty 0.8 Gyr; distances (systematic uncertainty added) 18.22 ± 0.06 ± 0.60, 16.99 ± 0.06 ± 0.56, 10.08 ± 0.04 ± 0.33, 15.59 ±0.03 ± 0.51, and 8.29 ± 0.03 ± 0.27 kpc; reddenings E(B − V) = 0.023 ± 0.004, 0.017 ± 0.004, 0.023 ± 0.004, 0.023 ± 0.003, and 0.045 ± 0.002 mag with their systematic uncertainty 0.01 mag; extinctions AV = 0.08 ± 0.01, 0.06 ± 0.01, 0.08 ± 0.01, 0.08 ± 0.01, and 0.16 ± 0.01 mag with their systematic uncertainty 0.03 mag, which suggest the total Galactic extinction AV = 0.08 across the whole Galactic dust to extragalactic objects at the North Galactic Pole. The horizontal branch morphology difference of these clusters is explained by their different metallicity, age, mass-loss efficiency, and loss of low-mass members in the evolution of the core-collapse cluster NGC 7099 and loose clusters NGC 5053 and NGC 5466.

  • Probing the Gamma-Ray Emission Region of Five TeV Flat Spectrum Radio Quasars

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: The location of γ-ray emission of blazars remains a contested topic, inspiring the development of numerous investigative techniques to address this issue. In this work, we analyzed Fermi γ-ray light curves in the GeV and MeV bands, employing the discrete cross-correlation function method to discern time lags between the two bands. For 4C +21.35, Ton 599, B2 1420+32, and PKS 1510-089, we identified a time lag spanning several days, while for PKS 1441+25, the time lag was not statistically found. The results imply that the soft photons necessary for inverse Compton scattering predominantly originate from the dusty torus in the first four sources, whereas for PKS 1441+25, they seem to be sourced mainly from the broad-line region. Further analysis of the opacity (τγγ) and the GeV spectra study supports the conclusion that the location of the dissipation region must be beyond the BLR to avoid significant absorption. Notably, for PKS 1441+25, the emission region is also posited to lie outside yet proximate to the BLR. The parameters of describing the emission region were obtained by fitting broadband spectral energy distribution with contemporaneous observation data. Our findings suggest that for the five TeV FSRQs, during TeV flaring events, the jet appears to maintain an equilibrium between the energy density of the magnetic field and that of the particles for all investigated sources, with the exceptions of 4C +21.35 and PKS 1441+25. In terms of the overall jet power, particle energy is the dominant contributor, and the observed blazar radiation cannot be solely attributed to the magnetic field, except in the case of 4C +21.35. Consequently, magnetic reconnection is unlikely to be the primary mechanism behind particle acceleration in these systems.

  • Astronomical Knowledge Entity Extraction in Astrophysics Journal Articles via Large Language Models

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: Astronomical knowledge entities, such as celestial object identifiers, are crucial for literature retrieval and knowledge graph construction, and other research and applications in the field of astronomy. Traditional methods of extracting knowledge entities from texts face numerous challenging obstacles that are difficult to overcome. Consequently, there is a pressing need for improved methods to efficiently extract them. This study explores the potential of pre-trained Large Language Models (LLMs) to perform astronomical knowledge entity extraction (KEE) task from astrophysical journal articles using prompts. We propose a prompting strategy called Prompt-KEE, which includes five prompt elements, and design eight combination prompts based on them. We select four representative LLMs (Llama-2-70B, GPT-3.5, GPT-4, and Claude 2) and attempt to extract the most typical astronomical knowledge entities, celestial object identifiers and telescope names, from astronomical journal articles using these eight combination prompts. To accommodate their token limitations, we construct two data sets: the full texts and paragraph collections of 30 articles. Leveraging the eight prompts, we test on full texts with GPT-4 and Claude 2, on paragraph collections with all LLMs. The experimental results demonstrate that pre-trained LLMs show significant potential in performing KEE tasks, but their performance varies on the two data sets. Furthermore, we analyze some important factors that influence the performance of LLMs in entity extraction and provide insights for future KEE tasks in astrophysical articles using LLMs. Finally, compared to other methods of KEE, LLMs exhibit strong competitiveness in multiple aspects.

  • The ALMA-QUARKS Survey. II. The ACA 1.3 mm Continuum Source Catalog and the Assembly of Dense Gas in Massive Star-Forming Clumps

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: Leveraging the high resolution, sensitivity, and wide frequency coverage of the Atacama Large Millimeter/submillimeter Array (ALMA), the QUARKS survey, standing for "Querying Underlying mechanisms of massive star formation with ALMA-Resolved gas Kinematics and Structures", is observing 139 massive star-forming clumps at ALMA Band 6 (λ ∼ 1.3 mm). This paper introduces the Atacama Compact Array (ACA) 7 m data of the QUARKS survey, describing the ACA observations and data reduction. Combining multi-wavelength data, we provide the first edition of QUARKS atlas, offering insights into the multiscale and multiphase interstellar medium in high-mass star formation. The ACA 1.3 mm catalog includes 207 continuum sources that are called ACA sources. Their gas kinetic temperatures are estimated using three formaldehyde transitions with a non-LTE radiation transfer model, and the mass and density are derived from a dust emission model. The ACA sources are massive (16–84 percentile values of 6–160 M⊙), gravity-dominated (M ∝ R1.1) fragments within massive clumps, with supersonic turbulence  and embedded star-forming protoclusters. We find a linear correlation between the masses of the fragments and the massive clumps, with a ratio of 6% between the two. When considering fragments as representative of dense gas, the ratio indicates a dense gas fraction (DGF) of 6%, although with a wide scatter ranging from 1% to 10%. If we consider the QUARKS massive clumps to be what is observed at various scales, then the size-independent DGF indicates a self-similar fragmentation or collapsing mode in protocluster formation. With the ACA data over four orders of magnitude of luminosity-to-mass ratio (L/M), we find that the DGF increases significantly with L/M, which indicates clump evolutionary stage. We observed a limited fragmentation at the subclump scale, which can be explained by a dynamic global collapse process.

  • Probing the Kinematic Signatures of Planet Formation in the Gas Disk of MWC 480

    分类: 天文学 >> 天文学 提交时间: 2024-07-15 合作期刊: 《Research in Astronomy and Astrophysics》

    摘要: The disk around MWC 480 has shown multiple substructures in both dust and gas observations, possibly suggesting ongoing planet formation in situ. In this paper, we explore the gas kinematics of the MWC 480 disk by analyzing the archival Atacama Large Millimeter/submillimeter Array observations of 12CO (J = 2-1), 13CO (J = 2-1), and C18O (J = 2-1). By modeling the line-of-sight velocities, inferred from the Doppler shifts of the emission lines, we are able to decompose the three-dimensional (3D) velocity field of the disk into rotational, radial, and vertical components. Further analysis reveals the presence of large-scale gas flows in the (r, z) plane. Notably, we identify potential meridional flows across various heights as traced by all three CO isotopologues in the 80–120 au region, possibly associated with ongoing planet formation activities in this region. Moreover, we find upward flows near 200 au for all three CO isotopologues, which may point to the presence of disk winds.