The Maximum Optical Depth Towards Bulge Stars From Axisymmetric Models of the Milky Way

It has been known that recent microlensing results towards the bulge imply mass densities that are surprisingly high given dynamical constraints on the Milky Way mass distribution. We derive the maximum optical depth towards the bulge that may be generated by axisymmetric structures in the Milky Way, and show that observations are close to surpassing these limits. This result argues in favor of a bar as a source of significantly enhanced microlensing. Several of the bar models in the literature are discussed.Comment: Latex, 6 pages, 4 figures, uses aas2pp4 and epsf style files. Accepted for publication in ApJ Letter

Intrinsic electron-doping in nominal "non-doped" superconducting (La,Y)2_2CuO4_4 thin films grown by dc magnetron sputtering

The superconducting nominal "non-doped" $La_{1.85}Y_{0.15}CuO_4$ (LYCO) thin films are successfully prepared by dc magnetron-sputtering and in situ post-annealing in vacuum. The best $T_{C0}$ more than 13K is achieved in the optimal LYCO films with highly pure c-axis oriented T'-type structure. In the normal state, the quasi-quadratic temperature dependence of resistivity, the negative Hall coefficient and effect of oxygen content in the films are quite similar to the typical Ce-doped T'-214 cuprates, suggesting that T'-LYCO shows the electron-doping nature like known n-type cuprates, and is not a band superconductor as proposed previously. The charge carriers are considered to be induced by oxygen deficiency.Comment: 5 pages, 7 figure

Tracers of chromospheric structure. I. CaII H&\&K emission distribution of 13000 F, G and K stars in SDSS DR7 spectroscopic sample

We present chromospheric activity index $S\rm_{HK}$ measurements for over 13,000 F, G and K disk stars with high signal-to-noise ratio ($>$ 60) spectra in the Sloan Digital Sky Survey (SDSS) Data Release 7 (DR7) spectroscopic sample. A parameter $\delta$S is defined as the difference between $S\rm_{HK}$ and a `zero' emission line fitted by several of the most inactive stars. The $S\rm_{HK}$ indices of subgiant stars tend to be much lower than dwarfs, which provide a way to distinguish dwarfs and giants with relatively low resolution spectra. Cooler stars are generally more active and display a larger scatter than hotter stars. Stars associated with the thick disk are in general less active than those of the thin disk. The fraction of K dwarfs that are active drops with vertical distance from the Galactic plane. Metallicity affects $S\rm_{HK}$ measurements differently among F, G and K dwarfs in this sample. Using the open clusters NGC 2420, M67 and NGC6791 as calibrations, ages of most field stars in this SDSS sample range from 3-8 Gyr.Comment: 9 pages, 11 figures, AJ, 2013, 145, 14