DA白矮星视向速度测量

DA白矮星光谱在光学波段主要由巴尔默线主导,谱线比较宽,且谱线轮廓不对称,传统的线心方法确定视向速度非常困难。介绍了一种基于利用白矮星的有效温度(Teff)和表面重力加速度(log g)选择理论模板,通过交叉相关方法确定DA白矮星的APP速度,减去白矮星的引力红移得到白矮星的视向速度。测试发现对于有效温度高于10 000 K且信噪比大于20的DA白矮星的低分辨率光谱(R～2000),精度在10 km/s以内。基于这种方法测量了SDSS DR7的DA白矮星观测样本的视向速度,统计发现在1 000 pc内,视向速度的平均值接近于0。     

Metal-rich carbon stars in the Sagittarius dwarf spheroidal galaxy

We present spectroscopic observations from the Spitzer Space Telescope of six carbon-rich asymptotic giant branch (AGB) stars in the Sagittarius dwarf spheroidal galaxy (Sgr dSph) and two foreground Galactic carbon stars. The band strengths of the observed C₂H₂ and SiC features are very similar to those observed in Galactic AGB stars. The metallicities are estimated from an empirical relation between the acetylene optical depth and the strength of the SiC feature. The metallicities are higher than those of the Large Magellanic Cloud, and close to Galactic values. While the high metallicity could imply an age of around 1 Gyr, for the dusty AGB stars, the pulsation periods suggest ages in excess of 2 or 3 Gyr. We fit the spectra of the observed stars using the dusty radiative transfer model and determine their dust mass-loss rates to be in the range  1.0–3.3 × 10⁻⁸ M_⊙ yr⁻¹  . The two Galactic foreground carbon-rich AGB stars are located at the far side of the solar circle, beyond the Galactic Centre. One of these two stars shows the strongest SiC feature in our present Local Group sample.     

Asymptotic giant branch stars in the Phoenix dwarf galaxy

JHK _s near-infrared photometry of stars in the Phoenix dwarf galaxy is presented and discussed. Combining these data with the optical photometry of Massey et al. allows a rather clean separation of field stars from Phoenix members. The discovery of a Mira variable ( P = 425 d), which is almost certainly a carbon star, leads to an estimate of the distance modulus of 23.10 ± 0.18 that is consistent with other estimates and indicates the existence of a significant population of age ∼2 Gyr. The two carbon stars of Da Costa have   M _bol=−3.8  and are consistent with belonging to a population of similar age; some other possible members of such a population are identified. A Da Costa non-carbon star is  Δ K _s∼ 0.3  mag brighter than these two carbon stars. It may be an asymptotic giant branch star of the dominant old population. The nature of other stars lying close to it in the   K _s, ( J − K _s)  diagram needs studying.     

Evolution of dwarf early-type galaxies – I. Spatially resolved stellar populations and internal kinematics of Virgo cluster dE/dS0 galaxies

Understanding the origin and evolution of dwarf early-type galaxies remains an important open issue in modern astrophysics. Internal kinematics of a galaxy contains signatures of violent phenomena which may have occurred, e.g. mergers or tidal interactions, while stellar population keeps a fossil record of the star formation history; therefore studying connection between them becomes crucial for understanding galaxy evolution. Here, in the first paper of the series, we present the data on spatially resolved stellar populations and internal kinematics for a large sample of dwarf elliptical (dE) and lenticular (dS0) galaxies in the Virgo cluster. We obtained radial velocities, velocity dispersions, stellar ages and metallicities out to 1–2 half-light radii by reanalysing already published long-slit and integral-field spectroscopic data sets using the nbursts full spectral fitting technique. Surprisingly, bright representatives of the dE/dS0 class (   M_B =−18.0  to −16.0 mag) look very similar to intermediate-mass and giant lenticulars and ellipticals: (1) their nuclear regions often harbour young metal-rich stellar populations always associated with the drops in the velocity dispersion profiles; (2) metallicity gradients in the main discs/spheroids vary significantly from nearly flat profiles to −0.9 dex   r ⁻¹_e  , i.e. somewhat three times steeper than for typical bulges; (3) kinematically decoupled cores were discovered in four galaxies, including two with very little, if any, large-scale rotation. These results suggest similarities in the evolutionary paths of dwarf and giant early-type galaxies and call for reconsidering the role of major mergers in the dE/dS0 evolution.     

Building Blocks of the most Luminous Galaxies

Nearby luminous galaxies serve as templates to gain insight into the building blocks of the most luminous galaxies in the distant universe. In this conference I have shown that the most luminous galaxies in the Local Universe are mergers of evolved gas-rich galaxies that radiate the bulk of their energy in the mid and far-infrared. The most important implication for future studies on the formation of galaxies at early cosmological timescales is that they will appear as luminous sub-millimeter sources. This revised version was published online in September 2006 with corrections to the Cover Date.     

Evaluating the Potential of an Airborne Laser-scanning System for Measuring Volume Changes of Glaciers

Airborne laser scanning (ALS) is well suited for the production of digital elevation models (DEM), and can, in contrast to photographic methods, be used to acquire a DEM independently of surface texture and external light sources. ALS thus serves as a tool to generate DEMs of firn areas where photogram- metric methods often fail.
The potential of an integrated ALS system – comprising a laser scanner, precise differential global positioning system, and a gyro platform – for DEM generation of firn areas is currently being assessed. The Unteraargletscher, Bernese Alps, Switzerland, has been chosen as a test site. As part of a pilot project aimed at determining the mass balance distribution of that glacier without the use of in situ information, ALS measurements were conducted in autumn 1997. The DEM derived from laser measurements is extremely sensitive to the position and attitude of the aircraft. Currently the main work focuses on assessing and improving the system's accuracy by error modelling and by the development of error-correction algorithms.
Preliminary results from Unteraargletscher are presented, and the potential of this method for the generation of DEMs of firn areas is discussed.     

青海祁连县大柳沟金矿控矿条件

金及多金属矿化破碎蚀变带与逆断层关系密切,柱状、针状白色毒砂及细微粒黄铁矿是金的重要标志性矿物,成矿带具有良好的成矿地球化学背景和成矿地质条件,良好的控矿、容矿构造条件。     

A ring-width-based reconstruction of June–July minimum temperatures since AD 1245 from white spruce stands in the Mackenzie Delta region,northwestern Canada

We present a reconstruction of June–July minimum temperatures since AD 1245 for the Mackenzie Delta region based on a 29-site network of white spruce (Picea glauca) ring-width series. Most but not all trees experienced a divergent temperature–growth response, similar to the divergence that has affected other white spruce trees across Yukon and Alaska. However, divergence in the study region began as early as AD 1900 and we have documented our methods to avoid including divergent signals in the reconstruction. Calibration/verification testing based on local temperature data, and multi-century coherence with nearby and large-scale temperature proxy records, confirm that our reconstruction is robust. The reconstruction shows cool conditions in the late 13th, early 18th and early 19th centuries, corresponding with solar minima and increased volcanism. These cool periods are interrupted by warm periods consistent with early to mid-20th century warmth. The late 20th century is the warmest interval, and the last decade is estimated to be 1.4°C warmer than any decade before the mid-20th century. The reconstructed climate history corroborates other proxy-based inferences and supports the notion that high-latitude regions such as the Mackenzie Delta have experienced rapid warming in recent decades that is exceptional in the last eight centuries.     

Ecosystem specific yield for estimating evapotranspiration and groundwater exchange from diel surface water variation

The White method, routinely used to estimate phreatophyte transpiration from diel groundwater variation, also provides measures of total evapotranspiration (ET) and groundwater fluxes in surface waters. Such applications remain rare, however, and critically require accurate representation of stage‐dependent variation in specific yield (S_y). High‐resolution stage data from three Florida swamps were used to evaluate different relationships between S_y and stage (ecosystem specific yield, ESY). A discretized form, ESY_D, assumes constant S_y near unity for inundated conditions, applying soil S_y for belowground stage and open water S_y (S_y,OW ≈ 1.0) for aboveground stage. A mixture approach, ESY_M, applies a stage‐dependent interpolation between S_y,Soil and S_y,OW using stage‐area relationships and assumes rapid lateral equilibration between inundated and non‐inundated wetland areas. Finally, an empirical formulation, ESY_RR, uses measured ratios of rain to rise to estimate stage‐specific S_y. All formulations yielded reasonable ET rates (ET ≈ PET) at high stage; ESY_D markedly overestimated ET (ET/PET > 3) at intermediate stage, whereas ESY_M and ESY_RR maintained ET/PET near 1.0. Estimated groundwater fluxes using ESY_M and ESY_RR correlated well with Darcy‐estimated flows, but were larger, likely due to uncertainties in Darcy parameters. Well transects across wetlands documented equal water elevation and diel variation across inundated and non‐inundated areas, verifying rapid equilibration that reduces S_y and explaining overestimation by ESY_D. However, equilibration area varied within and among wetlands, explaining observed differences between ESY_M and ESY_RR, and suggesting ESY_RR may be preferred. Stage histograms followed the shape of ESY_RR, highlighting reciprocal influences of ESY on stage stability. Copyright © 2012 John Wiley & Sons, Ltd.