We aim to reveal the nature of the Sloan Digital Sky Survey (SDSS) stars: SDSSJ100921.40+375233.9, SDSSJ015717.04+135535.9, and SDSSJ171422.43+283657.2, showing apparently high NUV excesses for their g-z colors, as expected for extremely low-metallicity stars. High resolution (R=60 000) spectra of the stars with a wide wavelength coverage were obtained to determine their chemical compositions with the Tull echelle spectrograph on the 2.7 m telescope at the McDonald Observatory. We derived the spectroscopic parameters Teff =5820+-125 K, log g =3.9+-0.2, and vt =1.1+-0.5 km/s for SDSSJ100921.40+375233.9, Teff=6250+-125 K, log g =3.7+-0.2, and vt =4.0+-0.5 km/s for SDSSJ015717.04+135535.9, and Teff=6320+-125 K, log g =4.1+-0.3, and vt =1.5+-0.5 km/s for SDSS J171422.43+283657.2, and elemental abundances were computed for 21 elements for J100921 and J171422 and for 19 elements for J015717 for the first time. We find metallicities of [Fe/H]= -1.30, -0.94, and -0.80 for SDSSJ100921.40+375233.9, J015717.04+135535.9, and J171422.43+283657.2, respectively. On the basis of calculated abundance ratios for J171422.43+283657.2 and J015717.04+135535.9, we also report that these two program stars have the expected composition of main-sequence halo turnoff stars, but with low-alpha abundances, i.e., the [alpha/Fe] ratio is ~0.0 for J171422.43+283657.2 and ~0.1 for J015717.04+135535.9. The latter one shows typical halo or thick-disk alpha-element abundances, but has a substantial rotational line broadening and vsini=40 +- 0.5 km/s.
A survey for post common-envelope binary stars using GALEX and SDSS photometry
我们报告的第一个结果，我们的计划，以获得多时代的径向速度测量的恒星具有较强的远紫外线过剩，以确定后共同包络双星（PCEBs）。已确定的目标使用光学光度法从SDSS DR 4，紫外光度法从GALEX GR 2和自行信息从SDSS DR 5。我们获得了36个目标的两个或多个历元的光谱。我们的三个目标在几小时或几天的时间尺度上显示出大的径向速度变化（> 50公里/秒），几乎可以肯定是PCEB。对于其中一个目标（SDSS J104234.77+644205.4），我们已经获得了进一步的光谱，以确认这是一个轨道周期为4.74小时，半振幅K =165 km/s的PCEB。两个目标是快速旋转的K-矮星，似乎表现出小的径向速度变化，并有很强的钙II H+K发射线。这些可能是风致快速旋转（WIRRing）星。这些结果表明，我们可以使用GALEX和SDSS测光来识别单独使用SDSS测光无法识别的PCEB，并识别新的WIRRing恒星。一个更全面的调查，使用本文开发的方法确定的恒星将导致一个更好的了解共同的信封演变。
An Ultraviolet-Optical Color-Metallicity relation for Red Clump Stars using GALEX and Gaia
虽然核心燃烧氦的红色团簇（RC）恒星在紫外线波长下很微弱，但它们的紫外光颜色是一种独特且可获得的物理性质探测器。利用GALEX全天成像巡天、Gaia数据发布2和SDSS APOGEE DR 14巡天的数据，我们发现光谱金属丰度与RC星在紫外光学色星等图中的位置密切相关。与（G $_{BP}$- G $_{RP}$）$_0$中的0.7星等范围相比，RC在（NUV-G）$_0$颜色中具有超过4星等的宽范围.我们提出了一个光度计，尘埃校正，紫外光学（NUV-G）$_0$颜色金属丰度[Fe/H]关系使用的5,175个RC星的APOGEE样本。我们发现，这种关系有一个0.28德克斯的散射，更容易获得大，宽场样品比光谱金属丰度。重要的是，这种效果可能与其他研究中归因于消光的RC颜色的扩散相当。
