We present the photometry of 30 globular clusters(GCs) and GC candidates in 15 intermediate-band filters covering the wavelength region from ～ 3000 to ～ 10000 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 UBV RI broad-bands.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 3.47σ for the confirmed GCs,and > 99.99% or 4.87σ for GCs and GC candidates.
We investigate the radial color gradients of galactic disks using a sample of～20 000 face-on spiral galaxies selected from the fourth data release of the Sloan Digital Sky Survey(SDSS-DR4).We combine galaxies with similar concentrations,sizes and luminosities to construct composite galaxies,and then measure their color profiles by stacking the azimuthally averaged radial color profiles of all the member galaxies. Except for the smallest galaxies(R50<3 kpc),almost all galaxies show negative diskc olor gradients with mean g-r gradientG-gr =-0.006 mag kpc-1 and r-z gradientG-rz =-0.018 mag kpc-1.The disk color gradients are independent of the morphologi-cal types of galaxies and strongly dependent on the disk surface brightnessμd,with lower surface brightness galactic disks having steeper color gradients.We quantify the intrinsic correlation between color gradients and surface brightness as G gr=-0.011μd+0.233 and Grz=-0.015μd+0.324.These quantified correlations provide tight observational constraints on the formation and evolution models of spiral galaxies.
Cheng-Ze LiuShi-Yin ShenZheng-Yi ShaoRui-Xiang ChangJin-Liang HouJun YinDa-Wei Yang
We present results of 13CO(1-0),C18O(1-0),and HCO+(1-0) map observations and N2H+(1-0) single point observations directed towards a sample of nine low-luminosity 6.7-GHz masers.N2H + line emission has been detected from six out of nine sources,C18O line emission has been detected from eight out of nine sources,and HCO + and 13CO emission has been detected in all sources.In particular,a "blue profile" of the HCO + spectrum,a signature of inflow,is found towards one source.From integrated intensity emission maps,we identified 17 cores in the sample.Among them,nine cores are closely associated with low-luminosity methanol masers.For these cores,we derive the column densities,core sizes,masses and molecular abundances.Comparison of our results with similar molecular line surveys towards the southern sky methanol masers indicates that linewidths of our sample,including only the low-luminosity masers,are smaller than the sample that includes both lowand high-luminosity masers.For the maser associated cores,their gas masses have the same order of magnitude as their virial masses,indicating that these cores are gravitationally bound systems.In addition,we have found from our observations that the low-luminosity methanol masers tend to coexist with H2O masers and outflows rather than with OH masers.
Yuan-Wei Wu,Ye Xu and Ji Yang Purple Mountain Observatory,Chinese Academy of Sciences,Nanjing 210008,China
We present metal abundance properties of 144 globular clusters associated with M81. These globulars represent the largest globular cluster sample in M81 till now. Our main results are: the distribution of metallicities is bimodal, with metallicity peaks at [Fe/H] ≈ 1.51 and 0.58, and the metal-poor globular clusters tend to be less spatially concentrated than the metal-rich ones; the metal-rich globular clusters in M81 do not demonstrate a centrally concentrated spatial distribution like the metal-rich ones in M31 do; like our Galaxy and M31, the globular clusters in M81 have a small radial metallicity gradient. These results are consistent with those obtained from a small sample of M81 globular clusters. In addition, this paper shows that there is evidence that a strong rotation of the M81 globular cluster system around the minor axis exists, and that rotation is present in the metal-rich globular cluster subsample, but the metal-poor globular cluster subsample shows no evidence of rotation. The most significant difference between the rotation of the metal-rich and metal-poor globular clusters occurs at intermediate projected galactocentric radii. Our results confirm the conclusion of Schroder et al. that M81's metal-rich globular clusters at intermediate projected radii are associated with a thick disk of M81.
We present the first photometric results in J,H and K s from 2MASS (Two Micron All Sky Survey) imaging of 10 classical globular clusters (GCs) in the far outer regions of M31.Combined with the V and I photometric data from previous literature,we constructed a color--color diagram between J K s and V I.By comparing the integrated photometric measurements with evolutionary models,we estimate the ages of these clusters.The results showed that all of these clusters are older than 3 × 10 9 yr,and among them four are older than 10 Gyr and the other six have intermediate ages between 3 8 Gyr.The masses for these outer-halo GCs are from 7.0 × 10 4 M ⊙ to 1.02 × 10 6 M ⊙.We argued that GC2 and GC3,whose ages,metallicities and distance moduli are almost the same,were accreted from the same satellite galaxy,if they did not form in situ.The statistical results show that the ages and metallicities of these 10 M31 outer-halo GCs do not vary with projected radial position,and a relationship between age and metallicity does not exist.
Jun Ma 1,21 National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100012,China 2 Key Laboratory of Optical Astronomy,National Astronomical Observatories,Chinese Academy of Sciences,Beijing 100012,China
The Chinese Small Telescope Array(CSTAR)is the first Chinese astronomical instrument on the Antarctic ice cap.The low temperature and low pressure testing of the data acquisition system was carried out in a laboratory refrigerator and on the 4500m Pamirs high plateau,respectively.The results from the final four nights of test observations demonstrated that CSTAR was ready for operation at Dome A,Antarctica.In this paper,we present a description of CSTAR and the performance derived from the test observations.
We present a multi-line study of the massive star-forming region IRAS 22506+5944.A new 6.7 GHz methanol maser was detected.12CO,13CO,C18O and HCO+ J=1-0 transition observations reveal a star-formation complex consisting mainly of two cores.The dominant core has a mass of more than 200 M⊙,while the other one is only about 35 M.Both cores are obviously at different evolutionary stages.A 12CO energetic bipolar outflow was detected with an outflow mass of about 15 M⊙.
