星暴矮星系NGC 5253周围的中性氢气体分布

中性氢(HI)气体是恒星形成的基本物质,驱动着星系的演化。对于星暴矮星系NGC 5253,过去的研究利用射电干涉阵观测到的HI气体呈不对称分布,向东北方向延伸约7 kpc。这一延展结构可能表明NGC 5253与其附近的旋涡星系M 83之间存在动力学联系。为研究这两个星系之间可能存在的HI气体连接,从绿岸望远镜获得了射电L波段对NGC 5253周围的HI成图数据,探测到NGC 5253和M 83之间可能存在的7个HI气体云团。这些HI气体云团候选体主要分布在东北方向,由NGC 5253延展至距离超过60 kpc外。这些气体云团可能在触发矮星系NGC 5253剧烈的恒星形成活动中发挥重要作用。

New HⅠObservations Toward the NGC 5055 Galaxy Group with FAST

We report a new high-sensitivity HⅠmapping observation of the NGC 5055 galaxy group over an area of 1°.5×0°.75 with the Five-hundred-meter Aperture Spherical radio Telescope(FAST).Our observation reveals that the warped HⅠdisk of NGC 5055 is more extended than what was previously observed by WSRT,out to239(61.7 kpc).The total HⅠmass of NGC 5055 is determined to be~1.1×10^(10)M_Θ.We identified three HⅠclouds with HⅠmasses of the order of~10^(7)M_Θat the southeastern edge of the HⅠdisk,as well as a candidate high-velocity cloud with an HⅠmass of(1.2±0.5)×10^(6)M_Θto the north of NGC 5055.The HⅠcontent of UGCA337 is robustly detected for the first time by the FAST observations.It has a narrow HⅠlinewidth of W_(50)=17.4±3.8 km s^(-1)with a total HⅠmass of(3.5±0.3)×10^(6)M_Θ.Comparing the gas content and g-r color of UGCA 337 with typical low-mass dwarf galaxies,UGCA 337 appears relatively gas-poor despite its blue color.This suggests that UGCA 337 may have undergone gas stripping in the past.We also analyzed the possible origin of the diffuse HⅠclouds located at the outskirts of NGC 5055,and speculate that they might be the remnant features of a merger event in the past.

Isochrone Fitting of Galactic Globular Clusters—Ⅵ.High-latitude Clusters NGC 5024 (M53),NGC 5053,NGC 5272 (M3),NGC 5466,and NGC7099 (M30)

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.

A Possible γ-Ray Pulsation from PSR J1740-5340B in the Globular Cluster NGC 6397

Recently, a new radio millisecond pulsar(MSP) J1740-5340B, hosted in the globular cluster(GC) NGC 6397,was reported with a 5.78 ms spin period in an eclipsing binary system with a 1.97 days orbital period. Based on a modified radio ephemeris updated by tool tempo2, we analyze the ~15 yr γ-ray data obtained from the Large Area Telescope on board the Fermi Gamma-ray Space Telescope and detect PSR J1740-5340B's γ-ray pulsation at a confidence level of ~4σ with a weighted H-test value of ~26. By performing a phase-resolved analysis, the γ-ray luminosity in on-pulse interval of PSR J1740-5340B is L_(γ)~ 3.8 × 10^(33) erg s^(-1) using NGC 6397's distance of 2.48 kpc. And γ-rays from the on-pulse part of PSR J1740-5340B contribute ~90% of the total observed γ-ray emissions from NGC 6397. No significant γ-ray pulsation of another MSP J1740-5340A in the GC is detected.Considering that the previous four cases of MSPs in GCs, more data in γ-ray, X-ray, and radio are encouraged to finally confirm the γ-ray emissions from MSP J1740-5340B, especially starving for a precise ephemeris.

Variable Stars in the 50BiN Open Cluster Survey.Ⅲ.NGC 884

Open clusters are the basic building blocks that serve as a laboratory for the study of young stellar populations in the Milky Way.Variable stars in open clusters provide a unique way to accurately probe the internal structure,temporal and dynamical evolutionary stages of individual stars and the host cluster.The most powerful tool for such studies is time-domain photometric observations.This paper follows the route of our previous work,concentrating on a photometric search for variable stars in NGC 884.The target cluster is the companion of NGC869,forming the well-known double cluster system that is gravitationally bound.From the observation run in 2016 November,a total of 9247 B-band CCD images and 8218Ⅴ-band CCD images were obtained.We detected a total of 15 stars with variability in visual brightness,including five Be stars,three eclipsing binaries,and seven of unknown types.Two new variable stars were discovered in this work.We also compared the variable star content of NGC 884 with its companion NGC 869.

Dark Matter Density Profiles of Selected Spiral Galaxies

Understanding the dark matter distribution throughout a galaxy can provide insight into its elusive nature. Numerous density profiles, such as the Navarro, Frenk and White model, have been created in an attempt to study this distribution through analyzing orbital velocities of luminous matter and modeling dark matter distributions to explain these observations. However, we are interested in a simple model to consider the significant fluctuations in rotation curves at larger radii. Therefore, our model is much simpler compared to those previously mentioned. Our model used all the observational data available for four selected galactic rotation curves. These data present a significant variation in the orbital velocity of matter at the same distances. By running real observational data through our model, we show that the density of the dark matter within them shows real complex structure, which is not suggested by other computational models. Our aim of this paper is to model this structure and then speculate as to the cause and implications of these density fluctuations.

Chandra Observations of the Flat Spectrum Seyfert-2 Galaxies NGC 2110 and NGC 7582

Chandra observations of the Seyfert-2 galaxies NGC 2110 and NGC 7582 arepresented. With the superb spatial resolution of Chandra we found that in NGC 7582 the soft (≤2keV) and hard (2-10 keV) X-rays are emitted in different regions, consistent with the report by Xueet al. By comparing the present X-ray data with the previous infrared data, we determined that thesoft X-ray region is the site of starburst activities. We found no significant temporal variationsduring our observations. We confirm the previous finding that NGC 2110 and NGC 7582 areflat-spectrum sources. We argue that the flat spectra may result from a cold absorbing material suchas envisaged in the 'dual absorbed' model. Strong FeK_α emission feature is detected in 6～7keV.Its equivalent width is so large that it cannot be reproduced by using the Galactic column densityof ～ 10^(22) cm^(-2).

Clumpy metal concentrations in elliptical galaxies NGC 4374 and NGC 4636

We present a high spatial resolution study of metal distributions in the nearby, gas-rich elliptical galaxies NGC 4374 and NGC 4636 with the Chandra ACIS archive data. We define the hardness ratio HRFeL as the ratio of the emission in 0.65- 1.4 keV to that in 0.3-0.6 keV and 1.4-3.5 keV （after the magnesium and silicon lines are excluded）, and HRcont as the ratio of the emission in 1.4-3.5keV to that in 0.3- 0.6 keV, so that the HRFeL and HRcont maps can be used to trace the iron abundance and gas temperature distributions, respectively. By applying the a Trous wavelet algorithm to the obtained emission hardness ratio maps, we reveal that the HRFeL distributions are highly irregular, exhibiting strong spatial variations on 0.1-1 Re scales, which do not follow the HRcont distributions. Since the effect of temperature variation is small, we conclude that most of the high-HRFeL regions are very likely to possess higher abundances than the ambient gas. We also find that these high-HRFeL substructures are not associated with either the LMXB or globular cluster populations, thus their origins should be related to AGN activity or mergers.

Populations of Bright X-ray Sources in the Starburst Galaxies NGC 4038/4039

Assuming a naive star formation history, we construct synthetic X-ray source populations, using a population synthesis code, for comparison with the observed X-ray luminosity function （XLF） of the interacting galaxies NGC 4038/4039. We have included highand intermediate-mass X-ray binaries, young rotation-powered pulsars and fallback disk-fed black holes in modeling the bright X-ray sources detected. We find that the majority of the X-ray sources are likely to be intermediate-mass X-ray binaries, but for typical binary evolu- tion parameters, the predicted XLF seems to be steeper than observed. We note that the shape of the XLFs depends critically on the existence of XLF break for young populations, and suggest super-Eddington accretion luminosities or the existence of intermediate-mass black holes to account for the high luminosity end and the slope of the XLF in NGC 4038/4039.

Star formation properties in barred galaxies (SFB) Ⅱ. NGC 2903 and NGC 7080

Stellar bars are important for the secular evolution of disk galaxies because they can drive gas into the galactic central regions. To investigate the star formation properties in barred galaxies, we presented a multi-wavelength study of two barred galaxies： NGC 2903 and NGC 7080. We performed the three-component bulge-diskbar decomposition using the 3.6 μm images, and identified the bulges in the two galaxies as pseudobulges. Based on the narrowband Hα images, the star formation clumps were identified and analyzed. The clumps in the bulge regions have the highest surface densities of star formation rates in both galaxies, while the star formation activities in the bar of NGC 2903 are more intense than those in the bar of NGC 7080. Finally, we compared our results with the scenario of bar-driven secular evolution in previous studies, and discussed the possible evolutionary stages of the two galaxies.

Comptonization and Reprocessing Processes in Accretion Disks: Applications to the Seyfert 1 Galaxies NGC 5548 and NGC 4051

Simultaneous multi-wavelength observations have revealed complex variability in AGNs. To explain the variability we considered a theoretical model consisting of an inner hot comptonizing corona and an outer thin accretion disk, with interactions between the two components in the form of comptonization and reprocessing. We found that the variability of AGNs is strongly affected by the parameters of the model, namely, the truncated disk radius rmin, the corona radius rs, the temperature KTe and the optical depth TO of the corona. We applied this model to the two best observed Seyfert 1 galaxies, NGC 5548 and NGC 4051. Our model can reproduce satisfactory the observed SEDs. Our fits indicate that NGC 5548 may have experienced dramatic changes in physical parameters between 1989-1990 and 1998, and that NGC 4051 has a much larger truncated disk radius （700 Schwarzschild radii） than NGC 5548 （several tens of Schwarzschild radii）. Since we adopted a more refined treatment of the comptonization process rather than simply assuming a cut-off power law, our results should be more reasonable than the previous ones.

基于ALMA高分辨率的多谱线数据对NGC 1068核区中物理性质的研究

利用ALMA干涉阵望远镜(Atacama Large Millimeter/submillimeter Array)的高分辨(~0.2′′-0.7′′)的多谱线数据,包括CO(1-0)、CO(2-1)、CO(3-2)、HCN(1-0)、HCO^(+)(1-0)、HCN(3-2)、HCO^(+)(3-2)、HCN(4-3)和HCO^(+)(4-3),并结合连续谱数据对近邻星系NGC 1068核区的物理性质进行了研究.速度积分强度图显示核周盘(CircumNuclear Disk,CND)呈现不对称的环状结构,尺度~300 pc.各分子谱线均显示,CND上的东发射结(E-knot)比西发射结(W-knot)有着更强的发射,且E-knot处表现出的分子气体的速度比W-knot更高.致密分子气体含量占比(用HCN或HCO^(+)不同转动跃迁线与CO(1-0)的积分强度比值表示),以及致密分子气体比值(HCN/HCO^(+))均在CND的东部表现出更高的值,意味着CND东部和西部有着不同的物理环境或化学组成.CO(3-2)/CO(1-0)的积分强度比值在E-knot很高,意味着该处极端的物理环境导致分子激发增强.通过与单镜望远镜JCMT(James Clerk Maxwell Telescope)比较HCN(4-3)和HCO^(+)(4-3)的流量,得到高分辨率ALMA成图测量的致密分子气体在1 kpc尺度上的流量损失为10%~20%.各分子谱线在E-knot和W-knot的流量比为1.8~3.9,CND中E-knot和W-knot的差异可能与活动星系核(Active Galactic Nucleus,AGN)的反馈有关.此外,在AGN位置处的CO(2-1)、CO(1-0)和HCO^(+)(1-0)的谱线发现了吸收特征.这种吸收主要为其背景的强连续谱辐射导致,同时AGN附近的气体下落也可能产生自吸收现象.

The Unusual AGN Host NGC 1266:Evidence for Shocks in a Molecular Gas Rich S0 Galaxy with a Low Luminosity Nucleus

NGC 1266 is a lenticular galaxy(S0)hosting an active galactic nucleus(AGN),and known to contain a large amount of shocked gas.We compare the luminosity ratio of mid-J CO lines to IR continuum with star-forming galaxies(SFGs),and then model the CO spectral line energy distribution(SLED).We confirm that in the mid-and high-J regions(J_(up)=4-13),the C-type shock(v_(s)=25 km s^(-1),n_(H)=5×10^(4)cm^(-3))can reproduce the CO observations well.The galaxy spectral energy distribution(SED)is constructed and modeled by the code X-CIGALE and obtains a set of physical parameters including the star formation rate(SFR,1.17±0.47 M_(⊙)yr^(-1)).Also,our work provides SFR derivation of[C II]from the neutral hydrogen regions only(1.38±0.14 M_(⊙)yr^(-1)).Previous studies have illusive conclusions on the AGN or starburst nature of the NGC 1266 nucleus.Our SED model shows that the hidden AGN in the system is intrinsically low-luminosity,consequently the infrared luminosity of the AGN does not reach the expected level.Archival data from Nu STAR hard X-ray observations in the 3-79 keV band shows a marginal detection,disfavoring presence of an obscured luminous AGN and implying that a compact starburst is more likely dominant for the NGC 1266 nucleus.

Variable Star Detection in the Field of Open Cluster NGC 188

This work presents the charge-coupled device(CCD)photometric survey of the old open cluster NGC 188.Timeseries V-band photometric observations were conducted for ten nights in 2017 January using the Nanshan Onemeter Wide-field Telescope to search for variable stars in the field of the cluster.A total of 25 variable stars,including one new variable star,were detected in the target field.Among the detected variables,16 are cluster member stars,and the others are identified as field stars.The periods,radial velocities,effective temperatures,and classifications of the detected variables are discussed in this work.Most of the stars’effective temperatures are between 4200 and 6600 K,indicating their spectral types are G or K.The newly discovered variable is probably a W UMa system.In this study,a known cluster variable star(V21=V0769 Cep)is classified as an EA-type variable star based on the presence of an 0.5 mag eclipse in its light curve.

The Bar-Bulge Relation in Non-dwarf SB0 Galaxies in the Central Region of Coma Cluster

In this paper we explore the formation of bars and present the bulge and bar properties and their correlations for a sample of lenticular barred(SB0)and lenticular unbarred(S0)galaxies in the central region of the Coma Cluster using HST/ACS data.In our sample,we identified bar features using the luminosity profile decomposition software GALFIT.We classified the bulges based on Sérsic index and Kormendy relation.We found that the average mass of the bulge in SB0 galaxies is 1.48×10^(10)M☉whereas the average mass of the bulge in S0 galaxies is 4.3×10^(10)M☉.We observe that SB0 galaxies show lower bulge concentration,low mass and also smaller B/T values compared to S0 galaxies.Using the Kormendy relation,we found that among the lenticular barred galaxies,82%have classical bulges and 18%have pseudo bulges.These classical bulges have low masses compared to the classical bulges of unbarred galaxies.S0,galaxies with massive classical bulges do not host bars.We also found that for all SB0s the bulge effective radius is less than the bar effective radius.SB0 galaxies with classical bulges suggest that the bar may have formed by mergers.

河外星系NGC 0925中氢二二区的光谱观测研究

氢二区是星系中恒星形成的场所,最显著的观测特征是光谱中的一系列发射线,光谱观测和分析是研究氢二区性质的主要途径。文章呈现的是利用国家天文台2.16 m望远镜对河外星系NGC 0925中的一个氢二区进行光谱观测、数据处理和测量以及分析的工作。基于观测到的光谱发射线,采用“巴尔默减幅”法得到星系内消光并作消光改正;利用Hα发射线的光度得到恒星形成率;利用强发射线方法得到氧元素丰度。结果显示,该氢二区的尘埃消光严重(V波段的尘埃消光A(V)=0.641 mag)、恒星形成活动性强(恒星形成率面密度∑_(SFR)=0.104 M⊙/yr/kpc^(2))、金属元素丰度高(氧元素丰度12+log(O/H)=8.337 dex)。

球状星团成员星的空间相关性分析

以球状星团NGC(New General Catalogue)104、NGC 5139、NGC 6121为实验样区,选取了视差等10个恒星参数,通过引入地学中的空间分析理论和相应的分析框架为定量描述球状星团成员星的空间分布特征提出了一种基于地学的研究范式.通过计算全局和局部莫兰(Moran)指数得到球状星团成员星各恒星参数的空间分布特征.研究结果表明:球状星团NGC 104、NGC 5139、NGC 6121成员星的各恒星参数在总体上呈现出空间正相关特性,表现出空间集聚特征,但不同恒星参数之间存在差异;局部空间分布也呈现聚集特征,而不同的成员星呈现出不同的空间分布特性和趋势.总体而言,用地学空间相关分析系统地定量化描述球状星团成员星空间分布特征,能够为球状星团的研究提供新的思路.

基于DBSCAN聚类算法的疏散星团NGC 188的3维运动学成员判定

利用疏散星团NGC 188所在天区的1046颗恒星样本的高精度3维(3D)运动学数据(自行和视向速度)测试了DBSCAN(Density-Based Spatial Clustering of Applications with Noise)聚类算法的成员判定效果.为了避免自行和视向速度的单位不一致带来的影响,在数据预处理阶段将3个分量的数据统一标准化至[0,1]区间.利用第k个最近邻点距离方法分析了1046颗恒星样本在标准化无量纲3D速度空间的分布特征,再根据第k个最近邻点距离随k值的变化趋势确定了DBSCAN聚类算法的输入参数(Eps,MinPts),最后利用DBSCAN聚类算法分离出497颗3D运动学成员星.分析结果表明得到的3D运动学成员星是可靠的.

基于SDSS-DR8及2MASS数据的疏散星团NGC 6791的基本性质研究

利用斯隆数字巡天(SDSS)第8次释放数据(DR8)的恒星光谱数据及2MASS(Two Micro All Sky Survey)近红外点源测光数据研究著名的疏散星团NGC 6791,得到该星团的视向速度与金属丰度分别为V_r=-46.4±0.2 km·s^(-1)和[Fe/H]=0.32±0.11dex.利用星团中红团簇巨星作为理想"标准烛光",结合2MASS近红外点源测光数据计算了该星团的绝对距离模数为(m-M)_0=13.02±0.08 mag或4.02±0.15 kpc.与其他研究者给出的结果进行了比较,金属丰度、视向速度及绝对距离模数都符合得比较好.主要结论有3点:(1)NGC 6791是个极度富金属的星团;(2)在SDSS的光谱分辨能力以内,分离出的87颗团星之间不存在明显的金属丰度差异;(3)得到的距离模数对年龄、金属丰度及尘埃消光不敏感,是一种可靠的间接测量.

Revisit of GeV Gamma-Ray Emission from Orion B with the Fermi Large Area Telescope

We revisit the γ-ray emission above 300 Me V towards the massive star-forming region of Orion B by adopting14 yr observations with the Fermi Large Area Telescope and utilizing the updated software tools.The extended γ-ray emission region around Orion B is resolved into two components(region Ⅰ and region Ⅱ).The γ-ray spectrum of region I agrees with the predicted γ-ray spectrum assuming the cosmic ray(CR)density is the same as that of Alpha Magnetic Spectrometer(AMS-02)measured locally.Theγ-ray emissivity of region II appears to be deficit at low energy band(E<3 GeV).Through modeling we find that CR densities exhibit a significant deficit below 20 Ge V,which may be caused by a slow diffusion inside the dense region.This is probably caused by an increased magnetic field whose strength increases with the gas density.