This paper introduces a technique for searching for bright massive stars in galaxies beyond the Local Group.To search for massive stars,we processed the results of stellar photometry from the Hubble Space Telescope(HS...This paper introduces a technique for searching for bright massive stars in galaxies beyond the Local Group.To search for massive stars,we processed the results of stellar photometry from the Hubble Space Telescope(HST)images using the DAOPHOT and DOLPHOT packages.The results of such searches are demonstrated with examples of the galaxies DDO 68,M94 and NGC 1672.In the galaxy DDO 68,the LBV star changes its brightness,and massive stars in M94 can be identified by excess in the Ha band.For the galaxy NGC 1672,we measure the distance for the first time by the TRGB method,which enabled determining the luminosities of the brightest stars,likely hypergiants,in the young star formation region.So far,we have performed stellar photometry on HST images of 320 northern sky galaxies located at a distance less than 12 Mpc.This allowed us to identify 53 galaxies with probable hypergiants.Further photometric and spectral observations of these galaxies are planned to search for massive stars.展开更多
The analysis of light variation of M87 can help us understand the disk evolution.In the past decade,M87 has experienced several short-term light variabilities related to flares.We also find that there are year-scale X...The analysis of light variation of M87 can help us understand the disk evolution.In the past decade,M87 has experienced several short-term light variabilities related to flares.We also find that there are year-scale X-ray variations in the core of M87.Their light variability properties are similar to clumpy-ADAF.By re-analyzing 56Chandra observations from 2007 to 2019,we distinguish the“non-flaring state”from“flaring state”in the light variability.After removing flaring state data,we identify four gas clumps in the nucleus and all of them can be well fitted by the clumpy-ADAF model.The average mass accretion rate is~0.16M⊙yr^(-1).We analyze the photon index(Γ)-flux(2-10 keV)correlation between the non-flaring state and flaring state.For the non-flaring states,the flux is inversely proportional to the photon index.For the flaring states,we find no obvious correlation between the two parameters.In addition,we find that the flare always occurs at a high mass accretion rate,and after the luminosity of the flare reaches the peak,it will be accompanied by a sudden decrease in luminosity.Our results can be explained as that the energy released by magnetic reconnection destroys the structure of the accretion disk,thus the luminosity decreases rapidly and returns to normal levels thereafter.展开更多
Planetary nebulae (PNe) are good tracers of the stellar populations, chemical composition and dynamics of their host galaxies. This paper reports the discovery of new PNe in the outskirts of the Andromeda Galaxy (...Planetary nebulae (PNe) are good tracers of the stellar populations, chemical composition and dynamics of their host galaxies. This paper reports the discovery of new PNe in the outskirts of the Andromeda Galaxy (M31) with the Guoshoujing Telescope (GSJT, formerly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope-LAMOST) during its early commissioning phase. In total, 36 candidates selected from SDSS photometry are confirmed in terms of their PN nature, including 17 new discoveries and another 19 previously known emission line objects. Their positions, spectra, radial velocities and m5007 magnitudes are presented. We discuss the potential for detecting more PNe in M 31 with GSJT's multi-object spectroscopy and the related applications in studies of the dynamics and chemistry of M 31 and its assemblage history.展开更多
We present preliminary analyses of spectra of quasar candidates in two Guoshoujing Telescope (GSJT, formerly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope - LAMOST) test fields near M 31 where ...We present preliminary analyses of spectra of quasar candidates in two Guoshoujing Telescope (GSJT, formerly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope - LAMOST) test fields near M 31 where one is close to the optical center of the disk and the other is towards the northeastern outskirts of the halo, obtained during the early stage of the GSJT commissioning in the last season of 2009. Both fields contain background low-redshift quasar candidates selected from the SDSS photometry. In total, 14 new quasars with redshifts up to 2 and i magnitudes between 16.7 and 19.2, are discovered, including 7 within the 2.5° central region of M 31. We briefly discuss the potential applications of these newly discovered bright quasars.展开更多
Mayall Ⅱ = G1 is one of the most luminous globular clusters (GCs) in M31. Here, we determine its age and mass by comparing multicolor photometry with theoretical stellar population synthesis models. Based on far- a...Mayall Ⅱ = G1 is one of the most luminous globular clusters (GCs) in M31. Here, we determine its age and mass by comparing multicolor photometry with theoretical stellar population synthesis models. Based on far- and near-ultraviolet GALEX photometry, broad-band UBVRI, and infrared JHKs 2MASS data, we construct the most extensive spectral energy distribution of G 1 to date, spanning the wavelength range from 1538 to 20 000A. A quantitative comparison with a variety of simple stellar population (SSP) models yields a mean age which is consistent with G1 being among the oldest building blocks of M31 and having formed within ~1.7 Gyr after the Big Bang. Irrespective of the SSP model or stellar initial mass function adopted, the resulting mass estimates (of order 10^7M⊙) indicate that GI is one of the most massive GCs in the Local Group. However, we speculate that the cluster's exceptionally high mass suggests that it may not be a genuine GC. Our results also suggest that G1 may contain, on average, (1.65±0.63) × 10^2L⊙ far-ultraviolet-bright, hot, extreme horizontal-branch stars, depending on the adopted SSP model. In addition, we demonstrate that extensive multi-passband photometry coupled with SSP analysis enables one to obtain age estimates for old SSPs that have similar accuracies as those from integrated spectroscopy or resolved stellar photometry, provided that some of the free parameters can be constrained independently.展开更多
Here we present research on an ultra-luminous X-ray source (ULX) candidate 2XMM J 140229.91+542118.8. The X-ray light curves of this ULX candidate in M 101 exhibit features of a flare star. More importantly, the Ch...Here we present research on an ultra-luminous X-ray source (ULX) candidate 2XMM J 140229.91+542118.8. The X-ray light curves of this ULX candidate in M 101 exhibit features of a flare star. More importantly, the Chandra light curve displays unusual X-ray double flares, which is comprised of two close peaks. The X-ray (0.3-11.0 keV) flux of the first peak was derived from the two-temperature APEC model as ~ 1.1 ±0.1× 10-12 ergcm-2 s-1. The observed flux at its first peak increased by about two orders of magnitude in X-ray as compared to quiescence. The slope of the second fast decay phase is steeper than the slope of the first fast decay phase, indicating that the appearance of a second flare accelerated the cooling of the first flare in a way we do not understand yet. We also observed its optical counterpart using a 2.16 m telescope administered by National Astronomical Observatories, Chinese Academy of Sciences. By optical spectral fitting, it is confirmed to be a late type dMe2.5 star. According to the spectral type and apparent magnitude of its optical counterpart, we estimate the photometric distance to be ~ 133.4 ±14.2 pc. According to the X-ray spectral fitting, a possible explanation is provided. However, more similar close double flares are needed to confirm whether this accelerated cooling event is a unique coincidence or a common physical process during double flaring.展开更多
Using multi-band photometric images of M51 and its companion NGC 5195 from ultraviolet to optical and infrared,we investigate spatially resolved stellar population properties of this interacting system with stellar po...Using multi-band photometric images of M51 and its companion NGC 5195 from ultraviolet to optical and infrared,we investigate spatially resolved stellar population properties of this interacting system with stellar population synthesis models.The observed infrared excess(IRX)is used to constrain dust extinction.Stellar mass is also inferred from the model fitting.By fitting observed spectral energy distributions(SEDs)with synthetical ones,we derive two-dimensional distributions of stellar age,metallicity,dust extinction and stellar mass.In M51,two grand-designed spiral arms extending from the bulge show young age,rich metallicity and abundant dust.The inter-arm regions are filled with older,metalpoorer and less dusty stellar populations.Except for the spiral arm extending from M51 into NGC 5195,the stellar population properties of NGC 5195 are quite featureless.NGC 5195 is much older than M51,and its core is very dusty with AV up to 1.67 mag and dense in stellar mass surface density.The close encounters might drive the dust in the spiral arm of M51 into the center of NGC 5195.展开更多
Since Baade's photographic study of M32 in the mid 1940s, it has been accepted as an established fact that M32 is a compact dwarf satellite of M31. The purpose of this paper is to report on the findings of our invest...Since Baade's photographic study of M32 in the mid 1940s, it has been accepted as an established fact that M32 is a compact dwarf satellite of M31. The purpose of this paper is to report on the findings of our investigation into the nature of the existing evidence. We find that the case for M32 being a satellite of M31 rests upon Hubble Space Telescope (HST) based stellar population studies which have resolved red-giant branch (RGB) and red clump stars in M32 as well as other nearby galaxies. Taken in isolation, this recent evidence could be considered to be conclusive in favour of the existing view. However, the conventional scenario does not explain M32's anomalously high central velocity dispersion for a dwarf galaxy (several times that of either NGC 147, NGC 185 or NGC 205) or existing planetary nebula observations (which suggest that M32 is more than twice as distant as M31) and also requires an elaborate physical explanation for M32's inferred compactness. Conversely, we find that the case for M32 being a normal galaxy, of the order of three times as distant as M31, is supported by: (1) a central velocity dispersion typical of intermediate galaxies, (2) the published planetary nebula observations, and (3) known scaling relationships for normal early-type galaxies. However, this novel scenario cannot account for the high apparent luminosities of the RGB stars resolved in the M32 direction by HST observations. We are therefore left with two apparently irreconcilable scenarios, only one of which can be correct, but both of which suffer from potentially fatal evidence to the contrary.This suggests that current understanding of some relevant fields is still very far from adequate.展开更多
In this second paper of our series, we estimate the age of 41 star clusters, which were detected by Melnick & D'odorico in the nearby spiral galaxy M33, by comparing the integrated photometric measurements wit...In this second paper of our series, we estimate the age of 41 star clusters, which were detected by Melnick & D'odorico in the nearby spiral galaxy M33, by comparing the integrated photometric measurements with theoretical stellar population synthesis models of Bruzual & Charlot. Also, we calculate the mass of these star clusters using the theoretical M/LV ratio. The results show that, these star clusters formed continuously in M33 from ~ 7 × 10<SUP>6</SUP>–10<SUP>10</SUP> years and have masses between ~ 10<SUP>3</SUP> and 2 × 10<SUP>6</SUP>M<SUB>☉</SUB>. M33 frames were observed as a part of the BATC Multicolor Survey of the sky in 13 intermediate-band filters from 3800 to 10 000?. The relation between age and mass confirms that the sample star cluster masses systematically decrease from the oldest to the youngest.展开更多
Based on the large field multicolor observations ofBeijing-Arizona-Taiwan-Connecticut (BATC) program, we obtain the spectral energy distribution (SED)for individual regions of M81. We study the structure and evolution...Based on the large field multicolor observations ofBeijing-Arizona-Taiwan-Connecticut (BATC) program, we obtain the spectral energy distribution (SED)for individual regions of M81. We study the structure and evolution of M81 with an evolutionarypopulation synthesis (EPS) model, PEGASE. We find that the exponentially deceasing star formationrate (SFR) with star formation scale 3 Gyr (hereafter Exp, τ = 3 Gyr) gives the best agreementbetween the model predictions and the observed SEDs. We then obtain the structure, age distributionand evolutionary history of M81. There is a clear age gradient between the central and outerregions. The populations in the central regions are older than 7 Gyr, those in the outer regions areyounger, at about 4.5 Gyr. The youngest components in the spiral arms have ages of about 2.5 Gyr orless.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
Elemental abundance patterns of globular cluster stars can provide important clues for understanding cluster formation and early chemical evolution.The origin of the abundance patterns,however,still remains poorly und...Elemental abundance patterns of globular cluster stars can provide important clues for understanding cluster formation and early chemical evolution.The origin of the abundance patterns,however,still remains poorly understood.We have studied the impact of p-capture reaction cycles on the abundances of oxygen,sodium and aluminium considering nuclear reaction cycles of carbon-nitrogenoxygen-fluorine,neon-sodium and magnesium-aluminium in massive stars in stellar conditions of temperature range 2×107to 10×107K and typical density of 102gm cc-1.We have estimated abundances of oxygen,sodium and aluminium with respect to Fe,which are then assumed to be ejected from those stars because of rotation reaching a critical limit.These ejected abundances of elements are then compared with their counterparts that have been observed in some metal-poor evolved stars,mainly giants and red giants,of globular clusters M3,M4,M13 and NGC 6752.We observe an excellent agreement with[O/Fe]between the estimated and observed abundance values for globular clusters M3 and M4 with a correlation coefficient above 0.9 and a strong linear correlation for the remaining two clusters with a correlation coefficient above 0.7.The estimated[Na/Fe]is found to have a correlation coefficient above 0.7,thus implying a strong correlation for all four globular clusters.As far as[Al/Fe]is concerned,it also shows a strong correlation between the estimated abundance and the observed abundance for globular clusters M13 and NGC 6752,since here also the correlation coefficient is above 0.7 whereas for globular cluster M4 there is a moderate correlation found with a correlation coefficient above 0.6.Possible sources of these discrepancies are discussed.展开更多
Based on the method proposed by Kong et al. and on the multi-color spectrophotometry by Ma et al., we estimate the metallicities of 16 old star clusters in the nearby spiral galaxy M33, ten of which are halo globula...Based on the method proposed by Kong et al. and on the multi-color spectrophotometry by Ma et al., we estimate the metallicities of 16 old star clusters in the nearby spiral galaxy M33, ten of which are halo globular clusters. These old clusters are all metal poor, the range of metallicity ([Fe/H]) is from-0.14 to-2.12. In general, our results are consistent with those derived by other methods, such as integrated spectra and photometry, and our study confirms the reliability of the method of Kong et al.展开更多
Using astrometric techniques developed by Anderson et al., we determine proper motions (PMs) in the ~ 14.60 × 16.53 arcmin^2 area of the kinematically "thick-disk" globular cluster M 12. The cluster's proxim...Using astrometric techniques developed by Anderson et al., we determine proper motions (PMs) in the ~ 14.60 × 16.53 arcmin^2 area of the kinematically "thick-disk" globular cluster M 12. The cluster's proximity and sparse nature makes it a suitable target for ground-based telescopes. Archive images with time gap of ~ 11.1 years were observed with the wide-field imager (WFI) mosaic cam-era mounted on the ESO 2.2m telescope. The median value of PM error in both components is 0.7masyr^-1 for the stars having V ≤ 20mag. PMs are used to determine membership probabil-ities and to separate field stars from the cluster sample. In electronic form, a membership catalog of 3725 stars with precise coordinates, PMs and BVRI photometry is being provided. One of the possible applications of the catalog is demonstrated by gathering the membership information of the variable stars, blue stragglers and X-ray sources reported earlier in the cluster's region.展开更多
We report the discovery of year-scale X-ray variation in the nuclear region of the M87 by reanalyze the eight Chandra observations from 2007 to 2008. The X-ray spectra are fitted and decomposed into disk and flaring c...We report the discovery of year-scale X-ray variation in the nuclear region of the M87 by reanalyze the eight Chandra observations from 2007 to 2008. The X-ray spectra are fitted and decomposed into disk and flaring components. This year-scale X-ray variability can be explained quite well by a simple clumpy accretion model. We conclude that the central super-massive black hole of M87 was accreting a cloud of ~ 0.5 M⊙at that time.展开更多
Planetary nebulae(PNe) are an important tool for studying the dynamics and chemical evolution of galaxies in the Local Universe, given their characteristic bright emission line spectra. The Andromeda Galaxy(M31) provi...Planetary nebulae(PNe) are an important tool for studying the dynamics and chemical evolution of galaxies in the Local Universe, given their characteristic bright emission line spectra. The Andromeda Galaxy(M31) provides a unique laboratory for studying PNe in the circumnuclear region,thanks to its proximity and almost uniformly low line-of-sight extinction that ensures observations with high resolution and sensitivity. Using the WIYN/Hydra multi-fiber spectrograph, we have obtained optical(4119–6882 A?) spectra of 77 PN candidates selected from Hubble Space Telescope narrow-band imaging, which are located within the central ~500 pc region of M31. Among these candidates, 49(64%) are spectroscopically observed for the first time. The spectra of 300 previously known PNe and H Ⅱ regions, which primarily reside in the disk, are also taken for comparison. All 77 circumnuclear PN candidates exhibit prominent emission lines, including [O Ⅲ] λ5007, [N Ⅱ] λ6583, Hα and Hβ,strongly suggesting that they are genuine PNe. We measured the line fluxes, radial velocities and line widths for all objects, and found that the radial velocities of the circumnuclear PNe generally trace rotation of the inner bulge. We also estimated a dynamical mass of ~6.4±0.5×10~9 M_⊙ enclosed within an effective galactocentric radius of 340 pc, which is compatible with the previously estimated total stellar mass in this region.展开更多
The Ultra Violet Imaging Telescope (UVIT) is one of the payloads on the first Indian multiwavelength satellite ASTROSAT, which is expected to be launched by the Indian Space Research Organisation (ISRO) in the yea...The Ultra Violet Imaging Telescope (UVIT) is one of the payloads on the first Indian multiwavelength satellite ASTROSAT, which is expected to be launched by the Indian Space Research Organisation (ISRO) in the year 2015. We have per- formed simulations of UV studies of old open clusters for the UVIT. The colour mag- nitude diagrams (CMDs) and spatial appearances have been created using 10 filters associated with the FUV channel (130-180 nm) and NUV channel (200-300 nm) that are available for observations on the UVIT, for the three old open clusters M67, NGC 188 and NGC 6791. The CMDs are simulated for different filter combinations, and they are used to identify the loci of various evolutionary sequences, white dwarfs, blue stragglers, red giants, subgiants, turn off stars and the main sequence of the clus- ters. The present work helps in identifying a potential area of study in the case of these three old open clusters by considering the availability of filters and the detection limits of the instrument. We also recommend filter combinations, which can be used to detect and study the above mentioned evolutionary stages. The simulations and the results presented here are essential for the optimal use of the UVIT for studies of old open clusters.展开更多
We present a catalog of 908 objects observed with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) in fields in the vicinity of M31 and M33, targeted as globular clusters(GCs) and candidates. ...We present a catalog of 908 objects observed with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) in fields in the vicinity of M31 and M33, targeted as globular clusters(GCs) and candidates. The targets include known GCs and candidates selected from the literature, as well as new candidates selected from the Sloan Digital Sky Survey(SDSS). Analysis shows that 356 of them are likely GCs with various confidence levels, while the remaining ones turn out to be background galaxies and quasars, stars and H II regions in M31 or foreground Galactic stars. The 356 likely GCs include 298 bona fide GCs and 26 candidates known in the literature. Three candidates, selected from the Revised Bologna Catalog of M31 GCs and candidates(RBC) and one possible cluster from Johnson et al., are confirmed to be bona fide clusters. We search for new GCs in the halo of the M31 among the new candidates selected from the SDSS photometry. Based on radial velocities yielded by LAMOST spectra and visual examination of the SDSS images, we find 28 objects, 5bona fide and 23 likely GCs. Among the five bona fide GCs, three have been recently discovered independently by others, and the remaining 25 are our new identifications,including two bona fide ones. The newly identified objects fall at projected distances ranging from 13 to 265 kpc from M31. Of the two newly discovered bona fide GCs,one is located near M33, probably a GC belonging to M33. The other bona fide GC falls on the Giant Stream with a projected distance of 78 kpc from M31. Of the 23 newly identified likely GCs, one has a projected distance of about 265 kpc from M31 and could be an intergalactic cluster.展开更多
We present the photometry of 30 globular clusters (GCs) and GC candidates in 15 intermediate-band filters covering the wavelength region from - 3000 to 10000A using the archival CCD images of M31 observed as part o...We present the photometry of 30 globular clusters (GCs) and GC candidates in 15 intermediate-band filters covering the wavelength region from - 3000 to 10000A using the archival CCD images of M31 observed as part of the Beijing - Arizona - Taiwan - Connecticut (BATC) Multicolor Sky Survey. We transform these intermediate-band photometric data into the photometry in the standard U BV RI broadbands. These M31 GC candidates are selected from the Revised Bologna Catalog (RBC V.3.5), and most of these candidates do not have any photometric data. Therefore, the presented photometric data are a supplement to the RBC V.3.5. We find that 4 out of 61 GCs and GC candidates in RBC V.3.5 do not show any signal on the BATC images at their locations. By applying a linear fit of the distribution in the color-magnitude diagram of blue GCs and GC candidates using data from the RBC V.3.5, in this study, we find the "blue-tilt" of blue M31 GCs with a high confidence at 99.95% or 3.47cr for the confirmed GCs, and 〉 99.99% or 4.87e for GCs and GC candidates.展开更多
B037 is of interest because it is both the most luminous and the most highly reddened cluster known in M31. Deep observations and high spatial resolution images with the Advanced Camera for Surveys on the Hubble Space...B037 is of interest because it is both the most luminous and the most highly reddened cluster known in M31. Deep observations and high spatial resolution images with the Advanced Camera for Surveys on the Hubble Space Telescope (HST) first showed that this cluster is crossed by a dust lane. Photometric data in the F606W and F814W filters obtained in this paper indicate that colors of (F606W - F814W) in the dust lane are redder-0.4 mag than ones in the other regions of B037. The HST images show that this dust lane seems to be contained in B037, instead of in the M31 disk or the Milky Way. As far as we know, the formation of dust requires gas with a rather high metallicity. However, B037 has a low metallicity of [Fe/H] =→1.07 ±0.20. So, it seems improbable that the observed dust lane is physically associated with B037. It is clear that the origin of this dust lane is worthy of future study. In addition, based on these images, we present the precise variation of ellipticity and position angle, and of surface brightness profile, and determine the structural parameters of B037 by fitting a single-mass isotropic King model. In the F606W filter, we derive the best-fitting scale radius r0 = 0.56±0.02" (= 2.16±0.08 pc), a tidal radius rt = 8.6±0.4I" (= 33.1±1.5 pc), and a concentration index c = log(rt/ro) = 1.19±0.02. In the F814W filter, we derive r0 = 0.56 4± 0.01H (_=2.16 ±0.04 pc), rt = 8.9 ±0.3" (= 34.3±1.2 pc), and c = log(rt/ro) = 1.20±0.01. The extinction-corrected central surface brightness is μ0 = 13.53±0.03 mag arcsec^-2 in the F606W filter, and 12.85±0.03 mag arcsec^-2 in the F814W filter. We also calculate the half-light radius at rh = 1.05±0.03"(= 4.04±0.12 pc) in the F606W filter and rh =1.07±0.01"(= 4.12±0.04 pc) in the F814W filter. In addition, we derived the complete magnitudes of B037 in the V and I bands by transforming the magnitudes from the ACS system to the standard system, which are in good agreement with previous ground-based broad- band photometry studies.展开更多
基金financially supported by the Russian Foundation for Basic Researchthe National Science Foundation of Bulgaria as a part of the scientific project N 19–52–18007,Grant KP–06–Russia–9/2019。
文摘This paper introduces a technique for searching for bright massive stars in galaxies beyond the Local Group.To search for massive stars,we processed the results of stellar photometry from the Hubble Space Telescope(HST)images using the DAOPHOT and DOLPHOT packages.The results of such searches are demonstrated with examples of the galaxies DDO 68,M94 and NGC 1672.In the galaxy DDO 68,the LBV star changes its brightness,and massive stars in M94 can be identified by excess in the Ha band.For the galaxy NGC 1672,we measure the distance for the first time by the TRGB method,which enabled determining the luminosities of the brightest stars,likely hypergiants,in the young star formation region.So far,we have performed stellar photometry on HST images of 320 northern sky galaxies located at a distance less than 12 Mpc.This allowed us to identify 53 galaxies with probable hypergiants.Further photometric and spectral observations of these galaxies are planned to search for massive stars.
基金supported by the National Natural Science Foundation of China(Grant Nos.11863006,U1838203,and U2038104)the Science&Technology Department of Yunnan Province—Yunnan University Joint Funding(2019FY003005)the Bureau of International Cooperation,Chinese Academy of Sciences under the grant GJHZ1864。
文摘The analysis of light variation of M87 can help us understand the disk evolution.In the past decade,M87 has experienced several short-term light variabilities related to flares.We also find that there are year-scale X-ray variations in the core of M87.Their light variability properties are similar to clumpy-ADAF.By re-analyzing 56Chandra observations from 2007 to 2019,we distinguish the“non-flaring state”from“flaring state”in the light variability.After removing flaring state data,we identify four gas clumps in the nucleus and all of them can be well fitted by the clumpy-ADAF model.The average mass accretion rate is~0.16M⊙yr^(-1).We analyze the photon index(Γ)-flux(2-10 keV)correlation between the non-flaring state and flaring state.For the non-flaring states,the flux is inversely proportional to the photon index.For the flaring states,we find no obvious correlation between the two parameters.In addition,we find that the flare always occurs at a high mass accretion rate,and after the luminosity of the flare reaches the peak,it will be accompanied by a sudden decrease in luminosity.Our results can be explained as that the energy released by magnetic reconnection destroys the structure of the accretion disk,thus the luminosity decreases rapidly and returns to normal levels thereafter.
基金The Guoshoujing Telescope(GSJT)is a National Major Scientific Project built by the Chinese Academy of SciencesFunding for the project has been provided by the National Development and Reform Commission
文摘Planetary nebulae (PNe) are good tracers of the stellar populations, chemical composition and dynamics of their host galaxies. This paper reports the discovery of new PNe in the outskirts of the Andromeda Galaxy (M31) with the Guoshoujing Telescope (GSJT, formerly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope-LAMOST) during its early commissioning phase. In total, 36 candidates selected from SDSS photometry are confirmed in terms of their PN nature, including 17 new discoveries and another 19 previously known emission line objects. Their positions, spectra, radial velocities and m5007 magnitudes are presented. We discuss the potential for detecting more PNe in M 31 with GSJT's multi-object spectroscopy and the related applications in studies of the dynamics and chemistry of M 31 and its assemblage history.
基金The Guoshoujing Telescope(GSJT)is a National Major Scientific Project built by the Chinese Academy of SciencesFunding for the project has been provided by the National Development and Reform Commission
文摘We present preliminary analyses of spectra of quasar candidates in two Guoshoujing Telescope (GSJT, formerly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope - LAMOST) test fields near M 31 where one is close to the optical center of the disk and the other is towards the northeastern outskirts of the halo, obtained during the early stage of the GSJT commissioning in the last season of 2009. Both fields contain background low-redshift quasar candidates selected from the SDSS photometry. In total, 14 new quasars with redshifts up to 2 and i magnitudes between 16.7 and 19.2, are discovered, including 7 within the 2.5° central region of M 31. We briefly discuss the potential applications of these newly discovered bright quasars.
基金Supported by the National Natural Science Foundation of China
文摘Mayall Ⅱ = G1 is one of the most luminous globular clusters (GCs) in M31. Here, we determine its age and mass by comparing multicolor photometry with theoretical stellar population synthesis models. Based on far- and near-ultraviolet GALEX photometry, broad-band UBVRI, and infrared JHKs 2MASS data, we construct the most extensive spectral energy distribution of G 1 to date, spanning the wavelength range from 1538 to 20 000A. A quantitative comparison with a variety of simple stellar population (SSP) models yields a mean age which is consistent with G1 being among the oldest building blocks of M31 and having formed within ~1.7 Gyr after the Big Bang. Irrespective of the SSP model or stellar initial mass function adopted, the resulting mass estimates (of order 10^7M⊙) indicate that GI is one of the most massive GCs in the Local Group. However, we speculate that the cluster's exceptionally high mass suggests that it may not be a genuine GC. Our results also suggest that G1 may contain, on average, (1.65±0.63) × 10^2L⊙ far-ultraviolet-bright, hot, extreme horizontal-branch stars, depending on the adopted SSP model. In addition, we demonstrate that extensive multi-passband photometry coupled with SSP analysis enables one to obtain age estimates for old SSPs that have similar accuracies as those from integrated spectroscopy or resolved stellar photometry, provided that some of the free parameters can be constrained independently.
基金the National Natural Science Foundation of China(NSFC)under grants 11333004 and11403056
文摘Here we present research on an ultra-luminous X-ray source (ULX) candidate 2XMM J 140229.91+542118.8. The X-ray light curves of this ULX candidate in M 101 exhibit features of a flare star. More importantly, the Chandra light curve displays unusual X-ray double flares, which is comprised of two close peaks. The X-ray (0.3-11.0 keV) flux of the first peak was derived from the two-temperature APEC model as ~ 1.1 ±0.1× 10-12 ergcm-2 s-1. The observed flux at its first peak increased by about two orders of magnitude in X-ray as compared to quiescence. The slope of the second fast decay phase is steeper than the slope of the first fast decay phase, indicating that the appearance of a second flare accelerated the cooling of the first flare in a way we do not understand yet. We also observed its optical counterpart using a 2.16 m telescope administered by National Astronomical Observatories, Chinese Academy of Sciences. By optical spectral fitting, it is confirmed to be a late type dMe2.5 star. According to the spectral type and apparent magnitude of its optical counterpart, we estimate the photometric distance to be ~ 133.4 ±14.2 pc. According to the X-ray spectral fitting, a possible explanation is provided. However, more similar close double flares are needed to confirm whether this accelerated cooling event is a unique coincidence or a common physical process during double flaring.
基金Major Program of National Natural Science Foundation of China(No.11890691)supported by the National Basic Research Program of China(973 Program+6 种基金Grant No.2017YFA0402600)the National Natural Science Foundation of China(NSFCGrant Nos.11433005,11673027,11733007,11973038,11320101002 and 11421303)the External Cooperation Program of Chinese Academy of Sciences(Grant No.114A11KYSB20160057)the Two Micron All Sky Survey,which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center/California Institute of Technology,funded by the National Aeronautics and Space Administration and the National Science Foundationa key project of the Telescope Access Program(TAP),which has been funded by National Astronomical Observatories,Chinese Academy of Sciences(the Strategic Priority Research Program“The Emergence of Cosmological Structures”grant No.XDB09000000)the Special Fund for Astronomy from the Ministry of Finance。
文摘Using multi-band photometric images of M51 and its companion NGC 5195 from ultraviolet to optical and infrared,we investigate spatially resolved stellar population properties of this interacting system with stellar population synthesis models.The observed infrared excess(IRX)is used to constrain dust extinction.Stellar mass is also inferred from the model fitting.By fitting observed spectral energy distributions(SEDs)with synthetical ones,we derive two-dimensional distributions of stellar age,metallicity,dust extinction and stellar mass.In M51,two grand-designed spiral arms extending from the bulge show young age,rich metallicity and abundant dust.The inter-arm regions are filled with older,metalpoorer and less dusty stellar populations.Except for the spiral arm extending from M51 into NGC 5195,the stellar population properties of NGC 5195 are quite featureless.NGC 5195 is much older than M51,and its core is very dusty with AV up to 1.67 mag and dense in stellar mass surface density.The close encounters might drive the dust in the spiral arm of M51 into the center of NGC 5195.
文摘Since Baade's photographic study of M32 in the mid 1940s, it has been accepted as an established fact that M32 is a compact dwarf satellite of M31. The purpose of this paper is to report on the findings of our investigation into the nature of the existing evidence. We find that the case for M32 being a satellite of M31 rests upon Hubble Space Telescope (HST) based stellar population studies which have resolved red-giant branch (RGB) and red clump stars in M32 as well as other nearby galaxies. Taken in isolation, this recent evidence could be considered to be conclusive in favour of the existing view. However, the conventional scenario does not explain M32's anomalously high central velocity dispersion for a dwarf galaxy (several times that of either NGC 147, NGC 185 or NGC 205) or existing planetary nebula observations (which suggest that M32 is more than twice as distant as M31) and also requires an elaborate physical explanation for M32's inferred compactness. Conversely, we find that the case for M32 being a normal galaxy, of the order of three times as distant as M31, is supported by: (1) a central velocity dispersion typical of intermediate galaxies, (2) the published planetary nebula observations, and (3) known scaling relationships for normal early-type galaxies. However, this novel scenario cannot account for the high apparent luminosities of the RGB stars resolved in the M32 direction by HST observations. We are therefore left with two apparently irreconcilable scenarios, only one of which can be correct, but both of which suffer from potentially fatal evidence to the contrary.This suggests that current understanding of some relevant fields is still very far from adequate.
基金Supported by the National Natural Science Foundation of China
文摘In this second paper of our series, we estimate the age of 41 star clusters, which were detected by Melnick & D'odorico in the nearby spiral galaxy M33, by comparing the integrated photometric measurements with theoretical stellar population synthesis models of Bruzual & Charlot. Also, we calculate the mass of these star clusters using the theoretical M/LV ratio. The results show that, these star clusters formed continuously in M33 from ~ 7 × 10<SUP>6</SUP>–10<SUP>10</SUP> years and have masses between ~ 10<SUP>3</SUP> and 2 × 10<SUP>6</SUP>M<SUB>☉</SUB>. M33 frames were observed as a part of the BATC Multicolor Survey of the sky in 13 intermediate-band filters from 3800 to 10 000?. The relation between age and mass confirms that the sample star cluster masses systematically decrease from the oldest to the youngest.
基金Supported by the National Natural Science Foundation of China
文摘Based on the large field multicolor observations ofBeijing-Arizona-Taiwan-Connecticut (BATC) program, we obtain the spectral energy distribution (SED)for individual regions of M81. We study the structure and evolution of M81 with an evolutionarypopulation synthesis (EPS) model, PEGASE. We find that the exponentially deceasing star formationrate (SFR) with star formation scale 3 Gyr (hereafter Exp, τ = 3 Gyr) gives the best agreementbetween the model predictions and the observed SEDs. We then obtain the structure, age distributionand evolutionary history of M81. There is a clear age gradient between the central and outerregions. The populations in the central regions are older than 7 Gyr, those in the outer regions areyounger, at about 4.5 Gyr. The youngest components in the spiral arms have ages of about 2.5 Gyr orless.
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.
文摘Elemental abundance patterns of globular cluster stars can provide important clues for understanding cluster formation and early chemical evolution.The origin of the abundance patterns,however,still remains poorly understood.We have studied the impact of p-capture reaction cycles on the abundances of oxygen,sodium and aluminium considering nuclear reaction cycles of carbon-nitrogenoxygen-fluorine,neon-sodium and magnesium-aluminium in massive stars in stellar conditions of temperature range 2×107to 10×107K and typical density of 102gm cc-1.We have estimated abundances of oxygen,sodium and aluminium with respect to Fe,which are then assumed to be ejected from those stars because of rotation reaching a critical limit.These ejected abundances of elements are then compared with their counterparts that have been observed in some metal-poor evolved stars,mainly giants and red giants,of globular clusters M3,M4,M13 and NGC 6752.We observe an excellent agreement with[O/Fe]between the estimated and observed abundance values for globular clusters M3 and M4 with a correlation coefficient above 0.9 and a strong linear correlation for the remaining two clusters with a correlation coefficient above 0.7.The estimated[Na/Fe]is found to have a correlation coefficient above 0.7,thus implying a strong correlation for all four globular clusters.As far as[Al/Fe]is concerned,it also shows a strong correlation between the estimated abundance and the observed abundance for globular clusters M13 and NGC 6752,since here also the correlation coefficient is above 0.7 whereas for globular cluster M4 there is a moderate correlation found with a correlation coefficient above 0.6.Possible sources of these discrepancies are discussed.
基金the Chinese Acadeinv of Sciences,the Chinese National Naturnal Science Foundation and the Ministry of sciences and technology of ChinaThe project is also supported in part by the National Science Foundation(grant IXT 93-01805)by Arizona State University,the University of Arizona and Western Connecticut State University
文摘Based on the method proposed by Kong et al. and on the multi-color spectrophotometry by Ma et al., we estimate the metallicities of 16 old star clusters in the nearby spiral galaxy M33, ten of which are halo globular clusters. These old clusters are all metal poor, the range of metallicity ([Fe/H]) is from-0.14 to-2.12. In general, our results are consistent with those derived by other methods, such as integrated spectra and photometry, and our study confirms the reliability of the method of Kong et al.
基金supported by grants from the Ministry of Science and Technology(MOST),Taiwan(MOST Nos.103-2112M-007-020-MY3,104-2811-M-007-024,105-2811-M007-038,105-2119-M-007-029-MY3,106-2112-M-007006-MY3 and 106-2811-M-007-051)
文摘Using astrometric techniques developed by Anderson et al., we determine proper motions (PMs) in the ~ 14.60 × 16.53 arcmin^2 area of the kinematically "thick-disk" globular cluster M 12. The cluster's proximity and sparse nature makes it a suitable target for ground-based telescopes. Archive images with time gap of ~ 11.1 years were observed with the wide-field imager (WFI) mosaic cam-era mounted on the ESO 2.2m telescope. The median value of PM error in both components is 0.7masyr^-1 for the stars having V ≤ 20mag. PMs are used to determine membership probabil-ities and to separate field stars from the cluster sample. In electronic form, a membership catalog of 3725 stars with precise coordinates, PMs and BVRI photometry is being provided. One of the possible applications of the catalog is demonstrated by gathering the membership information of the variable stars, blue stragglers and X-ray sources reported earlier in the cluster's region.
基金supported by the CASSACA Postdoc Grant(from the Chinese Academy of Sciences,CAS)the Visiting Scholarship Grant(administered by the CAS South America Center for Astronomy,CASSACA,NAOC)+3 种基金Science&Technology Department of Yunnan Province–Yunnan University Joint Funding(2019FY003005)the National Natural Science Foundation of China(Grant Nos.11203019 and 11863006)supported by the Young Researcher Grant of National Astronomical Observatories,Chinese Academy of Science and the National Natural Science Foundation of China(Grant No.11803044)sponsored(in part)by the Chinese Academy of Sciences(CAS),through a grant to the CAS South America Center for Astronomy(CASSACA)。
文摘We report the discovery of year-scale X-ray variation in the nuclear region of the M87 by reanalyze the eight Chandra observations from 2007 to 2008. The X-ray spectra are fitted and decomposed into disk and flaring components. This year-scale X-ray variability can be explained quite well by a simple clumpy accretion model. We conclude that the central super-massive black hole of M87 was accreting a cloud of ~ 0.5 M⊙at that time.
基金supported by the National Key Research and Development Program of China(No.2017YFA0402703)the National Natural Science Foundation of China(Grant No.11133001)+1 种基金support from the Recruitment Program of Global Youth Expertsfunding support from the European Research Council under the European Union’s Seventh Framework Programme(FP7/2007-2013)/ERC grant agreement n~⊙[614922]
文摘Planetary nebulae(PNe) are an important tool for studying the dynamics and chemical evolution of galaxies in the Local Universe, given their characteristic bright emission line spectra. The Andromeda Galaxy(M31) provides a unique laboratory for studying PNe in the circumnuclear region,thanks to its proximity and almost uniformly low line-of-sight extinction that ensures observations with high resolution and sensitivity. Using the WIYN/Hydra multi-fiber spectrograph, we have obtained optical(4119–6882 A?) spectra of 77 PN candidates selected from Hubble Space Telescope narrow-band imaging, which are located within the central ~500 pc region of M31. Among these candidates, 49(64%) are spectroscopically observed for the first time. The spectra of 300 previously known PNe and H Ⅱ regions, which primarily reside in the disk, are also taken for comparison. All 77 circumnuclear PN candidates exhibit prominent emission lines, including [O Ⅲ] λ5007, [N Ⅱ] λ6583, Hα and Hβ,strongly suggesting that they are genuine PNe. We measured the line fluxes, radial velocities and line widths for all objects, and found that the radial velocities of the circumnuclear PNe generally trace rotation of the inner bulge. We also estimated a dynamical mass of ~6.4±0.5×10~9 M_⊙ enclosed within an effective galactocentric radius of 340 pc, which is compatible with the previously estimated total stellar mass in this region.
文摘The Ultra Violet Imaging Telescope (UVIT) is one of the payloads on the first Indian multiwavelength satellite ASTROSAT, which is expected to be launched by the Indian Space Research Organisation (ISRO) in the year 2015. We have per- formed simulations of UV studies of old open clusters for the UVIT. The colour mag- nitude diagrams (CMDs) and spatial appearances have been created using 10 filters associated with the FUV channel (130-180 nm) and NUV channel (200-300 nm) that are available for observations on the UVIT, for the three old open clusters M67, NGC 188 and NGC 6791. The CMDs are simulated for different filter combinations, and they are used to identify the loci of various evolutionary sequences, white dwarfs, blue stragglers, red giants, subgiants, turn off stars and the main sequence of the clus- ters. The present work helps in identifying a potential area of study in the case of these three old open clusters by considering the availability of filters and the detection limits of the instrument. We also recommend filter combinations, which can be used to detect and study the above mentioned evolutionary stages. The simulations and the results presented here are essential for the optimal use of the UVIT for studies of old open clusters.
基金supported by the National Basic Research Program of China (973 Program, 2014CB845700)the China Postdoctoral Science Foundation (2014M560843)
文摘We present a catalog of 908 objects observed with the Large Sky Area Multi-Object Fiber Spectroscopic Telescope(LAMOST) in fields in the vicinity of M31 and M33, targeted as globular clusters(GCs) and candidates. The targets include known GCs and candidates selected from the literature, as well as new candidates selected from the Sloan Digital Sky Survey(SDSS). Analysis shows that 356 of them are likely GCs with various confidence levels, while the remaining ones turn out to be background galaxies and quasars, stars and H II regions in M31 or foreground Galactic stars. The 356 likely GCs include 298 bona fide GCs and 26 candidates known in the literature. Three candidates, selected from the Revised Bologna Catalog of M31 GCs and candidates(RBC) and one possible cluster from Johnson et al., are confirmed to be bona fide clusters. We search for new GCs in the halo of the M31 among the new candidates selected from the SDSS photometry. Based on radial velocities yielded by LAMOST spectra and visual examination of the SDSS images, we find 28 objects, 5bona fide and 23 likely GCs. Among the five bona fide GCs, three have been recently discovered independently by others, and the remaining 25 are our new identifications,including two bona fide ones. The newly identified objects fall at projected distances ranging from 13 to 265 kpc from M31. Of the two newly discovered bona fide GCs,one is located near M33, probably a GC belonging to M33. The other bona fide GC falls on the Giant Stream with a projected distance of 78 kpc from M31. Of the 23 newly identified likely GCs, one has a projected distance of about 265 kpc from M31 and could be an intergalactic cluster.
基金Supported by the National Natural Science Foundation of China (Grant Nos.10873016,10803007,10473012,10573020,10633020,10673012 and 10603006)Supported by the National Basic Research Program of China (973 Program,No.2007CB815403)
文摘We present the photometry of 30 globular clusters (GCs) and GC candidates in 15 intermediate-band filters covering the wavelength region from - 3000 to 10000A using the archival CCD images of M31 observed as part of the Beijing - Arizona - Taiwan - Connecticut (BATC) Multicolor Sky Survey. We transform these intermediate-band photometric data into the photometry in the standard U BV RI broadbands. These M31 GC candidates are selected from the Revised Bologna Catalog (RBC V.3.5), and most of these candidates do not have any photometric data. Therefore, the presented photometric data are a supplement to the RBC V.3.5. We find that 4 out of 61 GCs and GC candidates in RBC V.3.5 do not show any signal on the BATC images at their locations. By applying a linear fit of the distribution in the color-magnitude diagram of blue GCs and GC candidates using data from the RBC V.3.5, in this study, we find the "blue-tilt" of blue M31 GCs with a high confidence at 99.95% or 3.47cr for the confirmed GCs, and 〉 99.99% or 4.87e for GCs and GC candidates.
基金supported by the National Natural Science Foundation of China (Grant Nos.10873016 and 10633020)the National Basic Research Program of China (973 Program),No. 2007CB815403
文摘B037 is of interest because it is both the most luminous and the most highly reddened cluster known in M31. Deep observations and high spatial resolution images with the Advanced Camera for Surveys on the Hubble Space Telescope (HST) first showed that this cluster is crossed by a dust lane. Photometric data in the F606W and F814W filters obtained in this paper indicate that colors of (F606W - F814W) in the dust lane are redder-0.4 mag than ones in the other regions of B037. The HST images show that this dust lane seems to be contained in B037, instead of in the M31 disk or the Milky Way. As far as we know, the formation of dust requires gas with a rather high metallicity. However, B037 has a low metallicity of [Fe/H] =→1.07 ±0.20. So, it seems improbable that the observed dust lane is physically associated with B037. It is clear that the origin of this dust lane is worthy of future study. In addition, based on these images, we present the precise variation of ellipticity and position angle, and of surface brightness profile, and determine the structural parameters of B037 by fitting a single-mass isotropic King model. In the F606W filter, we derive the best-fitting scale radius r0 = 0.56±0.02" (= 2.16±0.08 pc), a tidal radius rt = 8.6±0.4I" (= 33.1±1.5 pc), and a concentration index c = log(rt/ro) = 1.19±0.02. In the F814W filter, we derive r0 = 0.56 4± 0.01H (_=2.16 ±0.04 pc), rt = 8.9 ±0.3" (= 34.3±1.2 pc), and c = log(rt/ro) = 1.20±0.01. The extinction-corrected central surface brightness is μ0 = 13.53±0.03 mag arcsec^-2 in the F606W filter, and 12.85±0.03 mag arcsec^-2 in the F814W filter. We also calculate the half-light radius at rh = 1.05±0.03"(= 4.04±0.12 pc) in the F606W filter and rh =1.07±0.01"(= 4.12±0.04 pc) in the F814W filter. In addition, we derived the complete magnitudes of B037 in the V and I bands by transforming the magnitudes from the ACS system to the standard system, which are in good agreement with previous ground-based broad- band photometry studies.