We installed two sets of Astronomical Site Monitoring Systems(ASMSs)at Lijiang Observatory(GMG),for the running of the 2.4-meter Lijiang optical telescope(LJT)and the 1.6-meter Multi-channel Photometric Survey Telesco...We installed two sets of Astronomical Site Monitoring Systems(ASMSs)at Lijiang Observatory(GMG),for the running of the 2.4-meter Lijiang optical telescope(LJT)and the 1.6-meter Multi-channel Photometric Survey Telescope(Mephisto).The Mephisto is under construction.The ASMS has been running on robotic mode since 2017.The core instruments:Cloud Sensor,All-Sky Camera and AutonomousDIMM that are developed by our group,together with the commercial Meteorological Station and Sky Quality Meter,are combined into the astronomical optical site monitoring system.The new Cloud Sensor's Cloud-Clear Relationship is presented for the first time,which is used to calculate the All-Sky cloud cover.We designed the Autonomous-DIMM located on a tower,with the same height as LJT.The seeing data have been observed for a full year.ASMS's data for the year 2019 are also analysed in detail,which are valuable to observers.展开更多
We present the optical light curves of the tidal disruption event AT 2023clx in the declining phase,observed with Mephisto.Combining our light curve with the ASAS-SN and ATLAS data in the rising phase,and fitting the ...We present the optical light curves of the tidal disruption event AT 2023clx in the declining phase,observed with Mephisto.Combining our light curve with the ASAS-SN and ATLAS data in the rising phase,and fitting the composite multi-band light curves with MOSFiT,we estimate black hole mass for AT 2023clx is between 10^(5.67)and 10^(5.82)M_(⊙).This event may be caused by either a full disruption of a 0.1M_(⊙)star,or a partial disruption of a 0.99M_(⊙) star,depending on the data adopted for the rising phase.Based on those fit results and the non-detection of soft X-ray photons in the first 90 days,we propose that the observed optical radiation is powered by stream-stream collision.We speculate that the soft X-ray photons may gradually emerge in 100-600 days after the optical peak,when the debris is fully circularized into a compact accretion disk.展开更多
Red clump(RC)stars are reliable standard candles for studying the structure and evolution of the Milky Way.In this study,we present empirical calibrations of RC absolute magnitudes in the Mephisto(v,g,r,i)and CSST(g,r...Red clump(RC)stars are reliable standard candles for studying the structure and evolution of the Milky Way.In this study,we present empirical calibrations of RC absolute magnitudes in the Mephisto(v,g,r,i)and CSST(g,r,i)photometric systems using a high-purity sample of 25,059 RC stars cross-matched between APOGEE and Gaia DR3 XP spectra.Through synthetic photometry and polynomial fitting,we find that RC absolute magnitudes exhibit strong dependencies on effective temperature and metallicity,with the strongest variations observed in bluer bands and progressively decreasing towards redder wavelengths.In particular,the Mephisto v band exhibits the highest sensitivity,with variations reaching up to 2.0 mag across the metallicity range(−1.0 dex<[Fe/H]<0.5 dex)and the temperature range(4500–5200 K).The calibrations achieve high precision for all bands,enabling accurate determination of RC absolute magnitudes and distances.Furthermore,we evaluate the metallicity estimation capabilities of both systems using a Random Forest-based method,achieving a precision of 0.12 dex for Mephisto and 0.14 dex for CSST under typical photometric uncertainties(≤0.01 mag).These results provide robust tools for distance and metallicity determinations,supporting future Galactic structure studies with Mephisto and CSST data.展开更多
Accurate determinations of metallicity for large,complete stellar samples are essential for advancing various studies of the Milky Way.In this paper,we present a data-driven algorithm that leverages photometric data f...Accurate determinations of metallicity for large,complete stellar samples are essential for advancing various studies of the Milky Way.In this paper,we present a data-driven algorithm that leverages photometric data from the KiDS and the VIKING surveys to estimate stellar absolute magnitudes,effective temperatures,and metallicities.The algorithm is trained and validated using spectroscopic data from LAMOST,SEGUE,APOGEE,and GALAH,as well as a catalog of very metal-poor stars from the literature,and Gaia EDR3 data.This approach enables us to estimate metallicities,effective temperatures,and g-band absolute magnitudes for approximately 0.8 million stars in the KiDS data set.The photometric metallicity estimates exhibit an uncertainty of around 0.28 dex when compared to spectroscopic studies,within the metallicity range of−2 dex to 0.5 dex.The photometric effective temperature estimates have an uncertainty of around 149 K,while the uncertainty in the absolute magnitudes is approximately 0.36 mag.The metallicity estimates are reliable for values down to about−2 dex.This catalog represents a valuable resource for studying the structure and chemical properties of the Milky Way,offering an extensive data set for future investigations into Galactic formation and evolution.展开更多
We present simulation results examining the presence and behavior of standing shocks in zero-energy low angular momentum advective accretion flows and explore their(in)stability properties,taking into account various ...We present simulation results examining the presence and behavior of standing shocks in zero-energy low angular momentum advective accretion flows and explore their(in)stability properties,taking into account various values of specific angular momentum,λ_(0).Within the range 10-50R_(g)(where R_(g)denotes the Schwarzschild radius),shocks are discernible forλ_(0)≥1.75.In the special relativistic hydrodynamic simulation whenλ_(0)=1.80,we find the merger of two shocks resulted in a dramatic increase in luminosity.We present the impact of external and internal flow collisions from the funnel region on luminosity.Notably,oscillatory behavior characterizes shocks within 1.70≤λ_(0)≤1.80.Using free–free emission as a proxy for analysis,we show that the luminosity oscillations between frequencies of 0.1-10 Hz forλ_(0)range as 1.7≤λ_(0)≤1.80.These findings offer insights into quasiperiodic oscillation emissions from certain black hole X-ray binaries,exemplified by GX 339-4.Furthermore,for the supermassive black hole at the Milky Way's center,Sgr A*,oscillation frequencies between 10^(-6)and 10^(-5)Hz were observed.This frequency range,translating to one cycle every few days,aligns with observational data from X-ray telescopes such as Chandra,Swift,and XMM-Newton.展开更多
The availability of large data sets containing stellar parameters,distances,and extinctions for stars in the Milky Way,particularly within the Galactic disk,is essential for advancing our understanding of the Galaxy’...The availability of large data sets containing stellar parameters,distances,and extinctions for stars in the Milky Way,particularly within the Galactic disk,is essential for advancing our understanding of the Galaxy’s stellar populations,structure,kinematics,and chemical evolution.In this study,we present a catalog of stellar parameters,including effective temperature (T_(eff)),metallicity ([Fe/H]),absolute magnitudes (M_(G)),distances (d),and reddening values (E(G_(BP)-G_(RP))),for a sample of 141 million stars from the SkyMapper Southern Survey.These parameters are derived using the SPar algorithm,which employs a fitting procedure to match multi-band photometric observations and estimate the stellar properties (T_(eff),[Fe/H],M_(G),d,and E(G_(BP)-G_(RP))) on an individual star basis,following the methodology outlined in our previous work.This study successfully determines stellar parameters and extinction values simultaneously for stars located in high and low Galactic latitudes.The resulting stellar parameters and extinction values are in good agreement with results from other studies,demonstrating the robustness of our method.We derive a temperature dispersion of 195 K and a metallicity dispersion of 0.31 dex when comparing our results with spectroscopic data.The catalog produced in this work provides a valuable resource for future research on the Galactic metallicity distribution function,the structure of the Galaxy,threedimensional extinction mapping,and other related astrophysical topics.展开更多
Photometric redshifts of galaxies obtained by multi-wavelength data are widely used in photometric surveys because of their high efficiency.Although various methods have been developed,template fitting is still adopte...Photometric redshifts of galaxies obtained by multi-wavelength data are widely used in photometric surveys because of their high efficiency.Although various methods have been developed,template fitting is still adopted as one of the most popular approaches.Its accuracy strongly depends on the quality of the spectral energy distribution(SED)templates,which can be calibrated using broadband photometric data from galaxies with known spectroscopic redshifts.Such calibration is expected to improve photometric redshift accuracy,as the calibrated templates will align with observed photometric data more closely.The upcoming China Space Station Telescope(CSST)is one of the Stage IV surveys,which is aiming for high precision cosmological studies.To improve the accuracy of photometric redshift estimation for CSST,we calibrated the CWW+KIN templates using a perturbation algorithm with broadband photometric data from the CSST mock catalog.This calibration used a training set consisting of approximately 4500 galaxies,which is 10%of the total galaxy sample.The outlier fraction and scatter of the photometric redshifts derived from the calibrated templates are 2.55%and 0.036,respectively.Compared to the CWW+KIN templates,these values are reduced by 34%and 23%,respectively.This demonstrates that SED templates calibrated with a small training set can effectively optimize photometric redshift accuracy for future large-scale surveys like CSST,especially with limited spectral training data.展开更多
Early multiwavelength observations offer crucial insights into the nature of the relativistic jets responsible for gamma-ray bursts and their interaction with the surrounding medium.We present data of GRB 240825A from...Early multiwavelength observations offer crucial insights into the nature of the relativistic jets responsible for gamma-ray bursts and their interaction with the surrounding medium.We present data of GRB 240825A from 17 space-and ground-based telescopes/instruments,covering wavelengths from NIR/optical to X-ray and GeV,and spanning from the prompt emission to the afterglow phase triggered by Swift and Fermi.The early afterglow observations were carried out by SVOM/C-GFT,and spectroscopic observations of the afterglow by GTC,VLT,and TNG determined the redshift of the burst(z=0.659)later.A comprehensive analysis of the prompt emission spectrum observed by Swift-BAT and Fermi-GBM/LAT reveals a rare and significant high-energy cutoff at 76 MeV.Assuming this cutoff is due toγγabsorption allows us to place an upper limit on the initial Lorentz factor,Γ_(0)<245.The optical/NIR and GeV afterglow light curves can be described by the standard external shock model,with early-time emission dominated by a reverse shock(RS)and a subsequent transition to forward shock(FS)emission.Our afterglow modeling yields a consistent estimate of the initial Lorentz factor(Γ_(0)∼234).Furthermore,the RS-to-FS magnetic field ratio(R 302B)indicates that the RS region is significantly more magnetized than the FS region.An isotropic-equivalent kinetic energy of E_(k,iso)=5.25×10^(54) erg is derived,and the correspondingγ-ray radiation efficiency is estimated to beη_(γ)=3.1%.On the other hand,the standard afterglow model cannot reproduce the X-ray light curve of GRB 240825A,calling for improved models to characterize all multiwavelength data.展开更多
We have investigated the feasibilities and accuracies of the identifications of RR Lyrae stars and quasars from the simulated data of the Multi-channel Photometric Survey Telescope(Mephisto)W Survey.Based on the varia...We have investigated the feasibilities and accuracies of the identifications of RR Lyrae stars and quasars from the simulated data of the Multi-channel Photometric Survey Telescope(Mephisto)W Survey.Based on the variable sources light curve libraries from the Sloan Digital Sky Survey(SDSS)Stripe 82 data and the observation history simulation from the Mephisto-W Survey Scheduler,we have simulated the uvgriz multi-band light curves of RR Lyrae stars,quasars and other variable sources for the first year observation of Mephisto W Survey.We have applied the ensemble machine learning algorithm Random Forest Classifier(RFC)to identify RR Lyrae stars and quasars,respectively.We build training and test samples and extract~150 features from the simulated light curves and train two RFCs respectively for the RR Lyrae star and quasar classification.We find that,our RFCs are able to select the RR Lyrae stars and quasars with remarkably high precision and completeness,with purity=95.4%and completeness=96.9%for the RR Lyrae RFC and purity=91.4%and completeness=90.2%for the quasar RFC.We have also derived relative importances of the extracted features utilized to classify RR Lyrae stars and quasars.展开更多
We present extensive spectroscopic observations of supernova remnant （SNR） S 147 collected with the Large sky Area Multi-Object fiber Spectroscopic Telescope （LAMOST）. The spectra were care- fully sky-subtracted t...We present extensive spectroscopic observations of supernova remnant （SNR） S 147 collected with the Large sky Area Multi-Object fiber Spectroscopic Telescope （LAMOST）. The spectra were care- fully sky-subtracted taking into account the complex filamentary structure of S 147. We have utilized all available LAMOST spectra toward S 147, including sky and stellar spectra. By measuring the prominent optical emission lines including Ha, [NII] ）λ 6584 and [S n] λλ6717, 6731, we present maps of radial velocity and line intensity ratio covering the whole nebula of S 147 with unprecedented detail. The maps spatially correlate well with the complex filamentary structure of S147. For the central 2° of S147, the radial velocity varies from - 100 to 100 krn s^-1 and has peaks between - 0 and 10 km s^-1. The intensity ratios of Hα/[S n）λλ6717,6731, [Sn] λ 6717/λ 6731 and Ha/IN Hα/λ 6584 peak at about 0.77, 1.35 and 1.48, respectively, with a scatter of 0.17, 0.19 and 0.37, respectively. The intensity ratios are consistent with the literature values. However, the range of variations of line intensity ratios estimated here, which are representative of the whole nebula, is larger than previously estimated.展开更多
To investigate the effects of massive star evolution on surrounding molecules,we select nine massive clumps previously observed with the Atacama Pathfinder Experiment(APEX) telescope and the Submillimeter Array(SMA) t...To investigate the effects of massive star evolution on surrounding molecules,we select nine massive clumps previously observed with the Atacama Pathfinder Experiment(APEX) telescope and the Submillimeter Array(SMA) telescope.Based on the observations of APEX,we obtain luminosity to mass ratios Lclump/Mclump that range from 10 to 154 L_(⊙)/M_(⊙),where some of them embedded ultra compact(UC) H Ⅱ region.Using the SMA,CH3CN(12K-11K) transitions were observed toward nine massive starforming regions.We derive the CH3CN rotational temperature and column density using the XCLASS program,and calculate its fractional abundance.We find that CH3CN temperature seems to increase with the increase of Lclump/Mclump when the ratio is between 10 to 40 L_(⊙)/M_(⊙),then decrease when L_(clump)/M_(clump)≥ 40 L_(⊙)/M_(⊙).Assuming that the CH3CN gas is heated by radiation from the central star,the effective distance of CH3CN relative to the central star is estimated.The distance ranges from - 0.003 to - 0.083 pc,which accounts for - 1/100 to - 1/1000 of clump size.The effective distance increases slightly as Lclump/Mclump increases(Reff-(L_(clump)/M_(clump))0.5±0.2).Overall,the CH3 CN abundance is found to decrease as the clumps evolve,e.g.,XCH3CN -(L_(clump)/M_(clump))-1.0±0.7.The steady decline of CH3CN abundance as the clumps evolution can be interpreted as a result of photodissociation.展开更多
We study two-dimensional low angular momentum flow around a black hole using the resistive magnetohydrodynamic module of PLUTO code.Simulations have been performed for the flows with parameters of specific angular mom...We study two-dimensional low angular momentum flow around a black hole using the resistive magnetohydrodynamic module of PLUTO code.Simulations have been performed for the flows with parameters of specific angular momentum,specific energy and magnetic field which may be expected for the flow around Sgr A*.For flows with lower resistivityη=10^(-6)and 0.01,the luminosity and shock location on the equator vary quasi-periodically.The power density spectra of luminosity variation show peak frequencies which correspond to the periods of 5×10^(5),1.4×10^(5)and 5×10^(4)s.These quasi-periodic oscillations(QPOs)occur due to interaction between the outer oscillating standing shock and the inner weak shocks occurring at the innermost hot blob.While for cases with higher resistivityη=0.1 and 1.0,the high resistivity considerably suppresses the magnetic activity such as MHD turbulence and the flows tend to be steady and symmetric with respect to the equator.The steady standing shock is formed more outward compared with the hydrodynamical flow.The low angular momentum flow model with the above flow parameters and with low resistivity has a possibility to explain long-term flares of Sgr A*with frequencies~one per day and~5-10 days in the latest observations by Chandra,Swift and XMM-Newton monitoring of Sgr A*.展开更多
The stellar halo is one of the major components in the Milky Way. Research on its age can provide critical constraints on the origin of the stellar halo and further on the formation of our Galaxy.So far, different app...The stellar halo is one of the major components in the Milky Way. Research on its age can provide critical constraints on the origin of the stellar halo and further on the formation of our Galaxy.So far, different approaches and samples have been used to estimate the age of the Galactic halo. In our previous paper, we carefully selected 63 field halo turn-off stars within 1 kpc from the literature using a kinematic approach, then estimated the age of the halo. In this following work, we not only update the data from LAMOST DR4 and Gaia DR1, but also try a different method to select a clean halo sample by combining the metallicity and orbital parameters. Then we compare this halo turn-off sample with the GARSTEC model in the B-V vs. metallicity plane. After Monte Carlo simulations are performed, the age is estimated to be 10.5±1.4 Gyr, highly consistent with our previous result and other studies. However,due to the limited common sources between LAMOST DR4 and Gaia DR1, the final sample in this paper is still quite small. The estimated age will be more robust with the much larger Gaia DR2.展开更多
In the fourth paper of this series,we present the metallicity-dependent Sloan Digital Sky Survey(SDSS)stellar color loci of red giant stars,using a spectroscopic sample of red giants in the SDSS Stripe82 region.The st...In the fourth paper of this series,we present the metallicity-dependent Sloan Digital Sky Survey(SDSS)stellar color loci of red giant stars,using a spectroscopic sample of red giants in the SDSS Stripe82 region.The stars span a range of 0.55-1.2 mag in color g-i,-0.3--2.5 in metallicity[Fe/H],and have values of surface gravity log g smaller than 3.5 dex.As in the case of main-sequence(MS)stars,the intrinsic widths of loci of red giants are also found to be quite narrow,a few mmag at maximum.There are however systematic differences between the metallicity-dependent stellar loci of red giants and MS stars.The colors of red giants are less sensitive to metallicity than those of MS stars.With good photometry,photometric metallicities of red giants can be reliably determined by fitting the u-g,g-r,r-i,and i-z colors simultaneously to an accuracy of 0.2-0.25 dex,comparable to the precision achievable with low-resolution spectroscopy for a signal-to-noise ratio of 10.By comparing fitting results to the stellar loci of red giants and MS stars,we propose a new technique to discriminate between red giants and MS stars based on the SDSS photometry.The technique achieves completeness of~70 per cent and efficiency of~80 per cent in selecting metal-poor red giant stars of[Fe/H]≤-1.2.It thus provides an important tool to probe the structure and assemblage history of the Galactic halo using red giant stars.展开更多
H Ⅱ regions made of gas ionized by radiations from young massive stars,are widely distributed in the Milky Way.They are tracers for star formation,and their distributions are correlated with the Galactic spiral struc...H Ⅱ regions made of gas ionized by radiations from young massive stars,are widely distributed in the Milky Way.They are tracers for star formation,and their distributions are correlated with the Galactic spiral structure.Radio recombination lines(RRLs) of hydrogen and other atoms allow for the most precise determination of physical parameters such as temperature and density.However,RRLs at around 1.4 GHz from HⅡ regions are weak and their detections are difficult.As a result,only a limited number of detections have been obtained yet.The 19-beam receiver on board of the Five-hundred-meter Aperture Spherical radio Telescope(FAST) can simultaneously cover 23 RRLs for Hnα,Henα,and Cnα(n=164-186),respectively.This,combined with its unparalleled collecting area,makes FAST the most powerful telescope to detect weak RRLs.In this pilot survey,we use FAST to observe nine HⅡ regions at L band.We allocate20 minutes pointing time for each source to achieve a sensitivity of around 9 mK in a velocity resolution of2.0 km s^(-1).In total,21 RRLs for Hnα and Cnα at 1.0-1.5 GHz have been simultaneously detected with strong emission signals.Overall,the detection rates for the H167α and C167α RRLs are 100%,while that for the He167α RRL is 33.3%.Using hydrogen and helium RRLs,we measure the electron density,electron temperature,and pressure for three HⅡ regions.This pilot survey demonstrates the capability of FAST in RRL measurements,and a statistically meaningful sample with RRL detection,through which knowledge about Galactic spiral structure and evolution can be obtained,is expected in the future.展开更多
To explore the potential role of gravity,turbulence and magnetic fields in high-mass star formation in molecular clouds,this study revisits the velocity dispersion–size(σ–L)and density–size(ρ–L)scalings and the ...To explore the potential role of gravity,turbulence and magnetic fields in high-mass star formation in molecular clouds,this study revisits the velocity dispersion–size(σ–L)and density–size(ρ–L)scalings and the associated turbulent energy spectrum using an extensive data sample.The sample includes various hierarchical density structures in high-mass star formation clouds,across scales of 0.01–100 pc.We observeσ∝L^(0.26)andρ∝L^(-1.54)scalings,converging toward a virial equilibrium state.A nearly flat virial parameter–mass(α_(vir)-M)distribution is seen across all density scales,withα_(vir)values centered around unity,suggesting a global equilibrium maintained by the interplay between gravity and turbulence across multiple scales.Our turbulent energy spectrum(E(k))analysis,based on theσ–L andρ–L scalings,yields a characteristic E(k)∝k^(-1.52).These findings indicate the potential significance of gravity,turbulence,and possibly magnetic fields in regulating dynamics of molecular clouds and high-mass star formation therein.展开更多
Weak gravitational lensing is a powerful tool in modern cosmology.To accurately measure the weak lensing signal,one has to control the systematic bias on a small level.One of the most difficult problems is how to corr...Weak gravitational lensing is a powerful tool in modern cosmology.To accurately measure the weak lensing signal,one has to control the systematic bias on a small level.One of the most difficult problems is how to correct the smearing effect of the Point-Spread Function(PSF)on the shape of the galaxies.The chromaticity of PSF for a broad-band observation can lead to new subtle effects.Since the PSF is wavelength-dependent and the spectrum energy distributions between stars and galaxies are different,the effective PSF measured from the star images will be different from those that smear the galaxies.Such a bias is called color bias.We estimate it in the optical bands of the Chinese Space Station Survey Telescope from simulated PSFs,and show the dependence on the color and redshift of the galaxies.Moreover,due to the spatial variation of spectra over the galaxy image,another higher-order bias exists:color gradient bias.Our results show that both color bias and color gradient bias are generally below 0.1%in CSST.Only for small-size galaxies,one needs to be careful about the color gradient bias in the weak lensing analysis using CSST data.展开更多
We present a catalogue of 3305 Hα emission-line point sources observed with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) in the vicinity fields of M31 and M33 during September 2011 and Januar...We present a catalogue of 3305 Hα emission-line point sources observed with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) in the vicinity fields of M31 and M33 during September 2011 and January 2016.The catalogue contains 1487 emission-line stars,532 emission-line nebulae including 377 likely planetary nebulae(PNe),83 H Ⅱ region candidates and 20 possible supernova remnants(SNRs) and 1286 unknown objects.Among them,24 PN candidates,19 H Ⅱ region candidates,10 SNR candidates and one symbiotic star candidate are new discoveries.Radial velocities and fluxes estimated from the Hα line and those quantities of seven other major emission lines including Hβ,[O Ⅲ] A4959,[O Ⅲ] A5007,[N Ⅱ] A6548,[N Ⅱ] A6583,[S Ⅱ] A6717 and [S Ⅱ] A6731 lines of all the catalogued sources yielded from the LAMOST spectra are also presented in our catalogue.Our catalogue is an ideal starting point to study the chemistry properties and kinematics of M 31 and M 33.展开更多
The red giant branch(RGB)of globular clusters(GCs)is home to some exotic stars,which may provide clues on the formation of multiple stellar populations in GCs.It is well known that binary interactions are responsible ...The red giant branch(RGB)of globular clusters(GCs)is home to some exotic stars,which may provide clues on the formation of multiple stellar populations in GCs.It is well known that binary interactions are responsible for many exotic stars.Thus,it is important to understand what fraction of stars on the RGB of GCs is the result of binary interactions.In this paper,we performed a binary population synthesis study to track the number of post-binary-interaction(post-BI)stars that appear on the RGB,with particular emphasis on the evolved blue straggler stars(E-BSSs).Assuming an initial binary fraction of nearly 50%,we find that about half of the objects on the RGB(called giants)underwent the binary interactions,and that E-BSSs account for around 10%of the giants in our standard simulation.We also compare the properties of post-BI giants that evolved from different channels.We find that the initial orbital period and mass ratio distributions significantly affect the fraction of post-BI giants.Our results imply that the non-standard stars from binary interactions provide a non-negligible contribution to the RGB stars in GCs,which should be considered in future investigations of the origin of multiple stellar populations.展开更多
The Central Molecular Zone(CMZ) is a ring-like structure sitting at the center of the Milky Way.Using the 870 μm continuum map from the APEX Telescope Large Area Survey of the Galaxy(ATLASGAL),we study anisotropy in ...The Central Molecular Zone(CMZ) is a ring-like structure sitting at the center of the Milky Way.Using the 870 μm continuum map from the APEX Telescope Large Area Survey of the Galaxy(ATLASGAL),we study anisotropy in the density structure of gas in the CMZ utilizing the 2 D correlation function.To quantify the spatial anisotropy,we define the critical angle θhalf,as well as the anisotropy parameter A≡(π/4θ_(half))-1.We find that the density structure is strongly anisotropic at a large scale(-100 pc),and the degree of spatial anisotropy decreases with decreasing scale.At the scale of - 10 pc,the structure is still mildly anisotropic.In our analyses,we provide a quantitative description of the anisotropic density structure of gas in the CMZ,and the formalism can be applied to different regions to study their differences.展开更多
基金the National Natural Science Foundation of China(NSFC,Grant Nos.11991051,11203073,11573067,11873092 and 11803087)the CAS“Light of West China”Program(No.Y8XB018001)。
文摘We installed two sets of Astronomical Site Monitoring Systems(ASMSs)at Lijiang Observatory(GMG),for the running of the 2.4-meter Lijiang optical telescope(LJT)and the 1.6-meter Multi-channel Photometric Survey Telescope(Mephisto).The Mephisto is under construction.The ASMS has been running on robotic mode since 2017.The core instruments:Cloud Sensor,All-Sky Camera and AutonomousDIMM that are developed by our group,together with the commercial Meteorological Station and Sky Quality Meter,are combined into the astronomical optical site monitoring system.The new Cloud Sensor's Cloud-Clear Relationship is presented for the first time,which is used to calculate the All-Sky cloud cover.We designed the Autonomous-DIMM located on a tower,with the same height as LJT.The seeing data have been observed for a full year.ASMS's data for the year 2019 are also analysed in detail,which are valuable to observers.
基金the South-Western Institute for Astronomy Research of Yunnan University(SWIFAR-YNU),funded by the“Yunnan University Development Plan for World-Class University”and“Yunnan University Development Plan for World-Class Astronomy Discipline.”The authors acknowledge support from the“Science&Technology Champion Project”(202005AB160002)from two“Team Projects”-the“Innovation Team”(202105AE160021)the“Top Team”(202305AT350002)'funded by the“Yunnan Revitalization Talent Support Program.”。
文摘We present the optical light curves of the tidal disruption event AT 2023clx in the declining phase,observed with Mephisto.Combining our light curve with the ASAS-SN and ATLAS data in the rising phase,and fitting the composite multi-band light curves with MOSFiT,we estimate black hole mass for AT 2023clx is between 10^(5.67)and 10^(5.82)M_(⊙).This event may be caused by either a full disruption of a 0.1M_(⊙)star,or a partial disruption of a 0.99M_(⊙) star,depending on the data adopted for the rising phase.Based on those fit results and the non-detection of soft X-ray photons in the first 90 days,we propose that the observed optical radiation is powered by stream-stream collision.We speculate that the soft X-ray photons may gradually emerge in 100-600 days after the optical peak,when the debris is fully circularized into a compact accretion disk.
基金partially supported by the National Natural Science Foundation of China(NSFC,Grant Nos.12173034 and 12322304)the National Natural Science Foundation of Yunnan Province 202301AV070002+1 种基金the Xingdian talent support program of Yunnan Provincethe science research grants from the China Manned Space Project with No.CMS-CSST-2021-A09,CMS-CSST-2021-A08 and CMS-CSST-2021-B03。
文摘Red clump(RC)stars are reliable standard candles for studying the structure and evolution of the Milky Way.In this study,we present empirical calibrations of RC absolute magnitudes in the Mephisto(v,g,r,i)and CSST(g,r,i)photometric systems using a high-purity sample of 25,059 RC stars cross-matched between APOGEE and Gaia DR3 XP spectra.Through synthetic photometry and polynomial fitting,we find that RC absolute magnitudes exhibit strong dependencies on effective temperature and metallicity,with the strongest variations observed in bluer bands and progressively decreasing towards redder wavelengths.In particular,the Mephisto v band exhibits the highest sensitivity,with variations reaching up to 2.0 mag across the metallicity range(−1.0 dex<[Fe/H]<0.5 dex)and the temperature range(4500–5200 K).The calibrations achieve high precision for all bands,enabling accurate determination of RC absolute magnitudes and distances.Furthermore,we evaluate the metallicity estimation capabilities of both systems using a Random Forest-based method,achieving a precision of 0.12 dex for Mephisto and 0.14 dex for CSST under typical photometric uncertainties(≤0.01 mag).These results provide robust tools for distance and metallicity determinations,supporting future Galactic structure studies with Mephisto and CSST data.
基金partially supported by the National Natural Science Foundation of China 12173034 and 12322304he National Natural Science Foundation of Yunnan Province202301AV070002+1 种基金the Xingdian talent support program of Yunnan Provincethe science research grants from the China Manned Space Project with NO.CMS-CSST-2021-A09,CMS-CSST-2021-A08 and CMS-CSST-2021-B03。
文摘Accurate determinations of metallicity for large,complete stellar samples are essential for advancing various studies of the Milky Way.In this paper,we present a data-driven algorithm that leverages photometric data from the KiDS and the VIKING surveys to estimate stellar absolute magnitudes,effective temperatures,and metallicities.The algorithm is trained and validated using spectroscopic data from LAMOST,SEGUE,APOGEE,and GALAH,as well as a catalog of very metal-poor stars from the literature,and Gaia EDR3 data.This approach enables us to estimate metallicities,effective temperatures,and g-band absolute magnitudes for approximately 0.8 million stars in the KiDS data set.The photometric metallicity estimates exhibit an uncertainty of around 0.28 dex when compared to spectroscopic studies,within the metallicity range of−2 dex to 0.5 dex.The photometric effective temperature estimates have an uncertainty of around 149 K,while the uncertainty in the absolute magnitudes is approximately 0.36 mag.The metallicity estimates are reliable for values down to about−2 dex.This catalog represents a valuable resource for studying the structure and chemical properties of the Milky Way,offering an extensive data set for future investigations into Galactic formation and evolution.
基金supported by the National Natural Science Foundation of China(NSFC,Grant No.12073021)。
文摘We present simulation results examining the presence and behavior of standing shocks in zero-energy low angular momentum advective accretion flows and explore their(in)stability properties,taking into account various values of specific angular momentum,λ_(0).Within the range 10-50R_(g)(where R_(g)denotes the Schwarzschild radius),shocks are discernible forλ_(0)≥1.75.In the special relativistic hydrodynamic simulation whenλ_(0)=1.80,we find the merger of two shocks resulted in a dramatic increase in luminosity.We present the impact of external and internal flow collisions from the funnel region on luminosity.Notably,oscillatory behavior characterizes shocks within 1.70≤λ_(0)≤1.80.Using free–free emission as a proxy for analysis,we show that the luminosity oscillations between frequencies of 0.1-10 Hz forλ_(0)range as 1.7≤λ_(0)≤1.80.These findings offer insights into quasiperiodic oscillation emissions from certain black hole X-ray binaries,exemplified by GX 339-4.Furthermore,for the supermassive black hole at the Milky Way's center,Sgr A*,oscillation frequencies between 10^(-6)and 10^(-5)Hz were observed.This frequency range,translating to one cycle every few days,aligns with observational data from X-ray telescopes such as Chandra,Swift,and XMM-Newton.
基金supported by the National Natural Science Foundation of China12203016,12173034,12322304 and 12173013Natural Science Foundation of Hebei Province No.A2022205018,A2021205006,226Z7604G+4 种基金Yunnan University grant No.C619300A034Science Foundation of Hebei Normal University No.L2022B33.W.Y.Cacknowledges the science research grants from the China Manned Space Projectthe support of Physics Postdoctoral Research Station at Hebei Normal Universitythe science research grants from the China Manned Space Project with NOs.CMS-CSST-2021-A09,CMS-CSST-2021-A08 and CMS-CSST-2021-B03。
文摘The availability of large data sets containing stellar parameters,distances,and extinctions for stars in the Milky Way,particularly within the Galactic disk,is essential for advancing our understanding of the Galaxy’s stellar populations,structure,kinematics,and chemical evolution.In this study,we present a catalog of stellar parameters,including effective temperature (T_(eff)),metallicity ([Fe/H]),absolute magnitudes (M_(G)),distances (d),and reddening values (E(G_(BP)-G_(RP))),for a sample of 141 million stars from the SkyMapper Southern Survey.These parameters are derived using the SPar algorithm,which employs a fitting procedure to match multi-band photometric observations and estimate the stellar properties (T_(eff),[Fe/H],M_(G),d,and E(G_(BP)-G_(RP))) on an individual star basis,following the methodology outlined in our previous work.This study successfully determines stellar parameters and extinction values simultaneously for stars located in high and low Galactic latitudes.The resulting stellar parameters and extinction values are in good agreement with results from other studies,demonstrating the robustness of our method.We derive a temperature dispersion of 195 K and a metallicity dispersion of 0.31 dex when comparing our results with spectroscopic data.The catalog produced in this work provides a valuable resource for future research on the Galactic metallicity distribution function,the structure of the Galaxy,threedimensional extinction mapping,and other related astrophysical topics.
基金support from the Shanghai Science and Technology Foundation Fund under grant No.20070502400the support from the Innovation Program of Shanghai Municipal Education Commission(grant No.2019-0107-00-02-E00032)+4 种基金the support from National Key R&D Program of China grant Nos.2022YFF0503404,2020SKA0110402the CAS Project for Young Scientists in Basic Research(No.YSBR-092)support from the Program for Professor of Special Appointment(Eastern Scholar)at Shanghai Institutions of Higher Learning and the Shuguang Program of Shanghai Education Development Foundation and Shanghai Municipal Education Commissionsupported by the National Natural Science Foundation of China(NSFC,Grant Nos.U1931210,12141302,12173026,and 11933002)China Manned Space Project with grant Nos.CMS-CSST-2021-A01,CMS-CSST-2025-A02,CMS-CSST2025-A03,CMS-CSST-2025-A05 and CMS-CSST-2025-A20。
文摘Photometric redshifts of galaxies obtained by multi-wavelength data are widely used in photometric surveys because of their high efficiency.Although various methods have been developed,template fitting is still adopted as one of the most popular approaches.Its accuracy strongly depends on the quality of the spectral energy distribution(SED)templates,which can be calibrated using broadband photometric data from galaxies with known spectroscopic redshifts.Such calibration is expected to improve photometric redshift accuracy,as the calibrated templates will align with observed photometric data more closely.The upcoming China Space Station Telescope(CSST)is one of the Stage IV surveys,which is aiming for high precision cosmological studies.To improve the accuracy of photometric redshift estimation for CSST,we calibrated the CWW+KIN templates using a perturbation algorithm with broadband photometric data from the CSST mock catalog.This calibration used a training set consisting of approximately 4500 galaxies,which is 10%of the total galaxy sample.The outlier fraction and scatter of the photometric redshifts derived from the calibrated templates are 2.55%and 0.036,respectively.Compared to the CWW+KIN templates,these values are reduced by 34%and 23%,respectively.This demonstrates that SED templates calibrated with a small training set can effectively optimize photometric redshift accuracy for future large-scale surveys like CSST,especially with limited spectral training data.
基金supported by the National Key R&D Program of China(grant No.2024YFA1611600)the SVOM project(a mission under the Strategic Priority Program on Space Science of the Chinese Academy of Sciences)+23 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(grant No.XDB0550401)the National Natural Science Foundation of China(NSFC,grant No.12494573)partly supported by Natural Science Foundation of Xinjiang Uygur Autonomous Region(grant No.2024D01D32)Tianshan Talent Training Program(grant No.2023TSYCLJ0053)Tianshan Innovation Team Program(grant No.2024D14015)supported by the Jiangsu Funding Program for Excellent Postdoctoral Talent(grant No.2024ZB110)the Postdoctoral Fellowship Program(grant No.GZC20241916)the General Fund(grant No.2024M763531)of the China Postdoctoral Science Foundationsupported by a Royal Society Dorothy Hodgkin Fellowship(grant Nos.DHF-R1-221175 and DHF-ERE-221005)support by a postdoctoral fellowship from the CNESsupported by the National Key R&D Program of China(grant No.2024YFA1611702)the Strategic Priority Research Program of the Chinese Academy of Sciences(grant No.XDB0550101)the support of the French Agence Nationale de la Recherche(ANR),under grant ANR-23-CE31-0011(project PEGaSUS)financial support from the GRAWITA Large Program Grant(PI P.D’Avanzo)financial support from the Italian Space Agency,contract ASI/INAF No.I/004/11/6support from the INAF project Premiale Supporto Arizona&Italiasupported by the National Natural Science Foundation of China(NSFC,grant No.12133003)supported by the National Natural Science Foundation of China(NSFC,grant No.12373042)the Bagui Scholars Program(No.GXR-6BG2424001)funded by the European Union(ERC,HEAVYMETAL,101071865,Views and opinions expressed are,however,those of the authors only and do not necessarily reflect those of the European Union or the European Research Council Neither the European Union nor the granting authority can be held responsible for them)the Cosmic Dawn Center(DAWN)is funded by the Danish National Research Foundation under grant No.DNRF140supported by the National Natural Science Foundation of China(NSFC,grant Nos.12225305 and 12321003)supported by the National Natural Science Foundation of China(NSFC,grant No.12473049)supported by the General Fund(grant No.2024M763530)of the China Postdoctoral Science Foundation。
文摘Early multiwavelength observations offer crucial insights into the nature of the relativistic jets responsible for gamma-ray bursts and their interaction with the surrounding medium.We present data of GRB 240825A from 17 space-and ground-based telescopes/instruments,covering wavelengths from NIR/optical to X-ray and GeV,and spanning from the prompt emission to the afterglow phase triggered by Swift and Fermi.The early afterglow observations were carried out by SVOM/C-GFT,and spectroscopic observations of the afterglow by GTC,VLT,and TNG determined the redshift of the burst(z=0.659)later.A comprehensive analysis of the prompt emission spectrum observed by Swift-BAT and Fermi-GBM/LAT reveals a rare and significant high-energy cutoff at 76 MeV.Assuming this cutoff is due toγγabsorption allows us to place an upper limit on the initial Lorentz factor,Γ_(0)<245.The optical/NIR and GeV afterglow light curves can be described by the standard external shock model,with early-time emission dominated by a reverse shock(RS)and a subsequent transition to forward shock(FS)emission.Our afterglow modeling yields a consistent estimate of the initial Lorentz factor(Γ_(0)∼234).Furthermore,the RS-to-FS magnetic field ratio(R 302B)indicates that the RS region is significantly more magnetized than the FS region.An isotropic-equivalent kinetic energy of E_(k,iso)=5.25×10^(54) erg is derived,and the correspondingγ-ray radiation efficiency is estimated to beη_(γ)=3.1%.On the other hand,the standard afterglow model cannot reproduce the X-ray light curve of GRB 240825A,calling for improved models to characterize all multiwavelength data.
基金funded by the National Natural Science Foundation of China(NSFC)Nos.11803029,11833006 and 12173034the National Training Program of Innovation and Entrepreneurship for Undergraduates of China No.201910673001,Yunnan University grant C176220100007+8 种基金the National Key R&D Program of China No.2019YFA0405500the science research grants from the China Manned Space Project with Nos.CMS-CSST-2021-A09,CMS-CSST-2021-A08 and CMS-CSST2021-B03Funding for SDSS-Ⅲhas been provided by the Alfred P.Sloan Foundation,the Participating Institutions,the National Science Foundation,and the U.S.Department of Energy Office of ScienceThe national facility capability for Sky Mapper has been funded through ARC LIEF grant LE130100104 from the Australian Research CouncilDevelopment and support of the Sky Mapper node of the ASVO has been funded in part by Astronomy Australia Limited(AAL)the Australian Government through the Commonwealth’s Education Investment Fund(EIF)National Collaborative Research Infrastructure Strategy(NCRIS)the National e Research Collaboration Tools and Resources(Ne CTAR)the Australian National Data Service Projects(ANDS)。
文摘We have investigated the feasibilities and accuracies of the identifications of RR Lyrae stars and quasars from the simulated data of the Multi-channel Photometric Survey Telescope(Mephisto)W Survey.Based on the variable sources light curve libraries from the Sloan Digital Sky Survey(SDSS)Stripe 82 data and the observation history simulation from the Mephisto-W Survey Scheduler,we have simulated the uvgriz multi-band light curves of RR Lyrae stars,quasars and other variable sources for the first year observation of Mephisto W Survey.We have applied the ensemble machine learning algorithm Random Forest Classifier(RFC)to identify RR Lyrae stars and quasars,respectively.We build training and test samples and extract~150 features from the simulated light curves and train two RFCs respectively for the RR Lyrae star and quasar classification.We find that,our RFCs are able to select the RR Lyrae stars and quasars with remarkably high precision and completeness,with purity=95.4%and completeness=96.9%for the RR Lyrae RFC and purity=91.4%and completeness=90.2%for the quasar RFC.We have also derived relative importances of the extracted features utilized to classify RR Lyrae stars and quasars.
基金supported by the Joint Funds of the National Natural Science Foundation of China (Grant No. U1531244)the National Key Basic Research Program of China (2014CB845700)+4 种基金support from the Young Researcher Grant of National Astronomical Observatories, Chinese Academy of Sciencessupported by Special Funding for Advanced Users, budgeted and administrated by the Center for Astronomical MegaScience, Chinese Academy of Sciences (CAMS)National Major Scientific Project built by the Chinese Academy of SciencesFunding for the project has been provided by the National Development and Reform CommissionNational Astronomical Observatories, Chinese Academy of Sciences
文摘We present extensive spectroscopic observations of supernova remnant （SNR） S 147 collected with the Large sky Area Multi-Object fiber Spectroscopic Telescope （LAMOST）. The spectra were care- fully sky-subtracted taking into account the complex filamentary structure of S 147. We have utilized all available LAMOST spectra toward S 147, including sky and stellar spectra. By measuring the prominent optical emission lines including Ha, [NII] ）λ 6584 and [S n] λλ6717, 6731, we present maps of radial velocity and line intensity ratio covering the whole nebula of S 147 with unprecedented detail. The maps spatially correlate well with the complex filamentary structure of S147. For the central 2° of S147, the radial velocity varies from - 100 to 100 krn s^-1 and has peaks between - 0 and 10 km s^-1. The intensity ratios of Hα/[S n）λλ6717,6731, [Sn] λ 6717/λ 6731 and Ha/IN Hα/λ 6584 peak at about 0.77, 1.35 and 1.48, respectively, with a scatter of 0.17, 0.19 and 0.37, respectively. The intensity ratios are consistent with the literature values. However, the range of variations of line intensity ratios estimated here, which are representative of the whole nebula, is larger than previously estimated.
基金support from the National Natural Science Foundation of China (Grant Nos.W820301904 and 12033005)。
文摘To investigate the effects of massive star evolution on surrounding molecules,we select nine massive clumps previously observed with the Atacama Pathfinder Experiment(APEX) telescope and the Submillimeter Array(SMA) telescope.Based on the observations of APEX,we obtain luminosity to mass ratios Lclump/Mclump that range from 10 to 154 L_(⊙)/M_(⊙),where some of them embedded ultra compact(UC) H Ⅱ region.Using the SMA,CH3CN(12K-11K) transitions were observed toward nine massive starforming regions.We derive the CH3CN rotational temperature and column density using the XCLASS program,and calculate its fractional abundance.We find that CH3CN temperature seems to increase with the increase of Lclump/Mclump when the ratio is between 10 to 40 L_(⊙)/M_(⊙),then decrease when L_(clump)/M_(clump)≥ 40 L_(⊙)/M_(⊙).Assuming that the CH3CN gas is heated by radiation from the central star,the effective distance of CH3CN relative to the central star is estimated.The distance ranges from - 0.003 to - 0.083 pc,which accounts for - 1/100 to - 1/1000 of clump size.The effective distance increases slightly as Lclump/Mclump increases(Reff-(L_(clump)/M_(clump))0.5±0.2).Overall,the CH3 CN abundance is found to decrease as the clumps evolve,e.g.,XCH3CN -(L_(clump)/M_(clump))-1.0±0.7.The steady decline of CH3CN abundance as the clumps evolution can be interpreted as a result of photodissociation.
基金supported by the National Natural Science Foundation of China(Grant No.12073021)support from the National Natural Science Foundation of China(Grant No.11373002)the Natural Science Foundation of Fujian Province of China(Grant No.2018J01007)。
文摘We study two-dimensional low angular momentum flow around a black hole using the resistive magnetohydrodynamic module of PLUTO code.Simulations have been performed for the flows with parameters of specific angular momentum,specific energy and magnetic field which may be expected for the flow around Sgr A*.For flows with lower resistivityη=10^(-6)and 0.01,the luminosity and shock location on the equator vary quasi-periodically.The power density spectra of luminosity variation show peak frequencies which correspond to the periods of 5×10^(5),1.4×10^(5)and 5×10^(4)s.These quasi-periodic oscillations(QPOs)occur due to interaction between the outer oscillating standing shock and the inner weak shocks occurring at the innermost hot blob.While for cases with higher resistivityη=0.1 and 1.0,the high resistivity considerably suppresses the magnetic activity such as MHD turbulence and the flows tend to be steady and symmetric with respect to the equator.The steady standing shock is formed more outward compared with the hydrodynamical flow.The low angular momentum flow model with the above flow parameters and with low resistivity has a possibility to explain long-term flares of Sgr A*with frequencies~one per day and~5-10 days in the latest observations by Chandra,Swift and XMM-Newton monitoring of Sgr A*.
基金supported by the National Natural Science Foundation of China (Grant Nos. 11473001 and 11078006)support by the National Key Basic Research Program of China (Grant No. 2014CB845700)+2 种基金supported by the China Postdoctoral Science Foundation (Grant No. 2017M610695)supported by Special Funding for Advanced Users,budgeted and administrated by the Center for Astronomical Mega-Science, Chinese Academy of Sciencesa National Major Scientific Project which is built by the Chinese Academy of Sciences,funded by the National Development and Reform Commission, and operated and managed by the National Astronomical Observatories, Chinese Academy of Sciences
文摘The stellar halo is one of the major components in the Milky Way. Research on its age can provide critical constraints on the origin of the stellar halo and further on the formation of our Galaxy.So far, different approaches and samples have been used to estimate the age of the Galactic halo. In our previous paper, we carefully selected 63 field halo turn-off stars within 1 kpc from the literature using a kinematic approach, then estimated the age of the halo. In this following work, we not only update the data from LAMOST DR4 and Gaia DR1, but also try a different method to select a clean halo sample by combining the metallicity and orbital parameters. Then we compare this halo turn-off sample with the GARSTEC model in the B-V vs. metallicity plane. After Monte Carlo simulations are performed, the age is estimated to be 10.5±1.4 Gyr, highly consistent with our previous result and other studies. However,due to the limited common sources between LAMOST DR4 and Gaia DR1, the final sample in this paper is still quite small. The estimated age will be more robust with the much larger Gaia DR2.
基金the National Natural Science Foundation of China(Nos.12173007,11603002)the National Key Basic R&D Program of China(2019YFA0405503)+5 种基金Beijing Normal University(No.310232102)the science research grants from the China Manned Space Project with No.CMS-CSST-2021-A08 and CMS-CSST2021-A09Funding for SDSS-III has been provided by the Alfred P.Sloan Foundationthe Participating Institutionsthe National Science Foundationthe U.S.Department of Energy Office of Science。
文摘In the fourth paper of this series,we present the metallicity-dependent Sloan Digital Sky Survey(SDSS)stellar color loci of red giant stars,using a spectroscopic sample of red giants in the SDSS Stripe82 region.The stars span a range of 0.55-1.2 mag in color g-i,-0.3--2.5 in metallicity[Fe/H],and have values of surface gravity log g smaller than 3.5 dex.As in the case of main-sequence(MS)stars,the intrinsic widths of loci of red giants are also found to be quite narrow,a few mmag at maximum.There are however systematic differences between the metallicity-dependent stellar loci of red giants and MS stars.The colors of red giants are less sensitive to metallicity than those of MS stars.With good photometry,photometric metallicities of red giants can be reliably determined by fitting the u-g,g-r,r-i,and i-z colors simultaneously to an accuracy of 0.2-0.25 dex,comparable to the precision achievable with low-resolution spectroscopy for a signal-to-noise ratio of 10.By comparing fitting results to the stellar loci of red giants and MS stars,we propose a new technique to discriminate between red giants and MS stars based on the SDSS photometry.The technique achieves completeness of~70 per cent and efficiency of~80 per cent in selecting metal-poor red giant stars of[Fe/H]≤-1.2.It thus provides an important tool to probe the structure and assemblage history of the Galactic halo using red giant stars.
基金support from the National Key R&D Program of China (2018YFE0202900)support by the NAOC Nebula Talents Program+2 种基金the Cultivation Project for FAST Scientific Payoff and Research Achievement of CAMS-CASthe support from the Youth Innovation Promotion Association of CASsupported by the National Natural Science Foundation of China (Grant Nos.11703040,W820301904,11988101,11933011 and 11833009)。
文摘H Ⅱ regions made of gas ionized by radiations from young massive stars,are widely distributed in the Milky Way.They are tracers for star formation,and their distributions are correlated with the Galactic spiral structure.Radio recombination lines(RRLs) of hydrogen and other atoms allow for the most precise determination of physical parameters such as temperature and density.However,RRLs at around 1.4 GHz from HⅡ regions are weak and their detections are difficult.As a result,only a limited number of detections have been obtained yet.The 19-beam receiver on board of the Five-hundred-meter Aperture Spherical radio Telescope(FAST) can simultaneously cover 23 RRLs for Hnα,Henα,and Cnα(n=164-186),respectively.This,combined with its unparalleled collecting area,makes FAST the most powerful telescope to detect weak RRLs.In this pilot survey,we use FAST to observe nine HⅡ regions at L band.We allocate20 minutes pointing time for each source to achieve a sensitivity of around 9 mK in a velocity resolution of2.0 km s^(-1).In total,21 RRLs for Hnα and Cnα at 1.0-1.5 GHz have been simultaneously detected with strong emission signals.Overall,the detection rates for the H167α and C167α RRLs are 100%,while that for the He167α RRL is 33.3%.Using hydrogen and helium RRLs,we measure the electron density,electron temperature,and pressure for three HⅡ regions.This pilot survey demonstrates the capability of FAST in RRL measurements,and a statistically meaningful sample with RRL detection,through which knowledge about Galactic spiral structure and evolution can be obtained,is expected in the future.
基金supported by the National Key R&D Program of China(No.2022YFA1603101)H.-L.L.is supported by the National Natural Science Foundation of China(NSFC,Grant No.12103045)+1 种基金by Yunnan Fundamental Research Project(grant Nos.202301AT070118 and 202401AS070121)by Xingdian Talent Support Plan-Youth Project.G.-X.L.is supported by the National Natural Science Foundation of China(NSFC,Grant No.12033005).
文摘To explore the potential role of gravity,turbulence and magnetic fields in high-mass star formation in molecular clouds,this study revisits the velocity dispersion–size(σ–L)and density–size(ρ–L)scalings and the associated turbulent energy spectrum using an extensive data sample.The sample includes various hierarchical density structures in high-mass star formation clouds,across scales of 0.01–100 pc.We observeσ∝L^(0.26)andρ∝L^(-1.54)scalings,converging toward a virial equilibrium state.A nearly flat virial parameter–mass(α_(vir)-M)distribution is seen across all density scales,withα_(vir)values centered around unity,suggesting a global equilibrium maintained by the interplay between gravity and turbulence across multiple scales.Our turbulent energy spectrum(E(k))analysis,based on theσ–L andρ–L scalings,yields a characteristic E(k)∝k^(-1.52).These findings indicate the potential significance of gravity,turbulence,and possibly magnetic fields in regulating dynamics of molecular clouds and high-mass star formation therein.
基金funded by the National Natural Science Foundation of China(NSFC)under Nos.11873006,11933002,11903082,and U1931210the science research grants from the China Manned Space Project with Nos.CMS-CSST-2021-A01,CMS-CSST-2021A12,and CMS-CSST-2021-A07。
文摘Weak gravitational lensing is a powerful tool in modern cosmology.To accurately measure the weak lensing signal,one has to control the systematic bias on a small level.One of the most difficult problems is how to correct the smearing effect of the Point-Spread Function(PSF)on the shape of the galaxies.The chromaticity of PSF for a broad-band observation can lead to new subtle effects.Since the PSF is wavelength-dependent and the spectrum energy distributions between stars and galaxies are different,the effective PSF measured from the star images will be different from those that smear the galaxies.Such a bias is called color bias.We estimate it in the optical bands of the Chinese Space Station Survey Telescope from simulated PSFs,and show the dependence on the color and redshift of the galaxies.Moreover,due to the spatial variation of spectra over the galaxy image,another higher-order bias exists:color gradient bias.Our results show that both color bias and color gradient bias are generally below 0.1%in CSST.Only for small-size galaxies,one needs to be careful about the color gradient bias in the weak lensing analysis using CSST data.
基金funded by the National Natural Science Foundation of China (NSFC, Grant Nos.11080922,11803029,11973001,U1531244, 11833006 and U1731308)the National Key R&D Program of China (No.2019YFA0405500)。
文摘We present a catalogue of 3305 Hα emission-line point sources observed with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) in the vicinity fields of M31 and M33 during September 2011 and January 2016.The catalogue contains 1487 emission-line stars,532 emission-line nebulae including 377 likely planetary nebulae(PNe),83 H Ⅱ region candidates and 20 possible supernova remnants(SNRs) and 1286 unknown objects.Among them,24 PN candidates,19 H Ⅱ region candidates,10 SNR candidates and one symbiotic star candidate are new discoveries.Radial velocities and fluxes estimated from the Hα line and those quantities of seven other major emission lines including Hβ,[O Ⅲ] A4959,[O Ⅲ] A5007,[N Ⅱ] A6548,[N Ⅱ] A6583,[S Ⅱ] A6717 and [S Ⅱ] A6731 lines of all the catalogued sources yielded from the LAMOST spectra are also presented in our catalogue.Our catalogue is an ideal starting point to study the chemistry properties and kinematics of M 31 and M 33.
基金the National Natural Science Foundation of China(Grant Nos.12073070,11733008,11873085,11521303,12073071,11873016,11903075,12003027 and 11973081)the Natural Science Foundation of Yunnan Province(Nos.2017HC018,202001AT070058 and 202001AU070054)+8 种基金Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant Nos.2018076 and 2012048)the Chinese Academy of Sciences(CASKJZDEW-M06-01)for supportsupported by CAS‘Light of West China’Programsupported by the National Key Basic R&D Program of China(2019YFA0405500)the LAMOST Fellow project,funded by China Postdoctoral Science Foundation(Grant Nos.2019M653504 and 2020T130563)Yunnan province postdoctoral Directed culture Foundationthe Cultivation Project for LAMOST Scientific Payoff and Research Achievement of CAMS-CASthe science research grants from the China Manned Space Project(No.CMS-CSST-2021-A08)。
文摘The red giant branch(RGB)of globular clusters(GCs)is home to some exotic stars,which may provide clues on the formation of multiple stellar populations in GCs.It is well known that binary interactions are responsible for many exotic stars.Thus,it is important to understand what fraction of stars on the RGB of GCs is the result of binary interactions.In this paper,we performed a binary population synthesis study to track the number of post-binary-interaction(post-BI)stars that appear on the RGB,with particular emphasis on the evolved blue straggler stars(E-BSSs).Assuming an initial binary fraction of nearly 50%,we find that about half of the objects on the RGB(called giants)underwent the binary interactions,and that E-BSSs account for around 10%of the giants in our standard simulation.We also compare the properties of post-BI giants that evolved from different channels.We find that the initial orbital period and mass ratio distributions significantly affect the fraction of post-BI giants.Our results imply that the non-standard stars from binary interactions provide a non-negligible contribution to the RGB stars in GCs,which should be considered in future investigations of the origin of multiple stellar populations.
基金supported by the National Natural Science Foundation of China (NSFC,No.U1631237)the Youth Innovation Promotion Association of CAS (id.2018075)+1 种基金supported by a starting grant from Yunnan UniversityNSFC (Nos.W820301904 and 12033005)。
文摘The Central Molecular Zone(CMZ) is a ring-like structure sitting at the center of the Milky Way.Using the 870 μm continuum map from the APEX Telescope Large Area Survey of the Galaxy(ATLASGAL),we study anisotropy in the density structure of gas in the CMZ utilizing the 2 D correlation function.To quantify the spatial anisotropy,we define the critical angle θhalf,as well as the anisotropy parameter A≡(π/4θ_(half))-1.We find that the density structure is strongly anisotropic at a large scale(-100 pc),and the degree of spatial anisotropy decreases with decreasing scale.At the scale of - 10 pc,the structure is still mildly anisotropic.In our analyses,we provide a quantitative description of the anisotropic density structure of gas in the CMZ,and the formalism can be applied to different regions to study their differences.
