The far-ultraviolet (FUV) channel of the Cosmic Origins Spectrograph (COS) is designed to operate between 1130Å and 1850Å, limited at shorter wavelengths by the reflectivity of the MgF2 protected aluminum reflective surfaces on the Optical Telescope Assembly and on the COS FUV diffraction gratings. However, because the detector for the FUV channel is windowless, it was recognized early in the design phase that there was the possibility that COS would retain some sensitivity at shorter wavelengths due to the first surface reflection from the MgF2 coated optics. Preflight testing of the flight spare G140L grating revealed ~5% efficiency at 1066Å, and early on-orbit observations verified that the COS G140L/1230 mode was sensitive down to at least the Lyman limit with 10-20 cm^2 effective area between 912Å and 1070Å, and rising rapidly to over 1000 cm2 beyond 1150Å. Following this initial work we explored the possibility of using the G130M grating out of band to provide coverage down to 900Å. We present calibration results and ray trace simulations for these observing modes and explore additional configurations that have the potential to increase spectroscopic resolution, signal to noise, and observational efficiency below 1130Å.
Prime Focus Spectrograph on the Subaru Telescope: Overview of Science Operations
National Astronomical Observatory of Japan（日本国立天文台）；Graduate Institute for Advanced Studies, SOKENDAI（综合研究大学院大学）；Subaru Telescope, National Astronomical Observatory of Japan（昴星团望远镜，日本国立天文台）
The Unrealised Interdisciplinary Advantage of Observing High Mass Transiting Exoplanets and Brown Dwarfs -- Strategic Exoplanet Initiatives with HST and JWST White Paper
Disentangling Stellar and Airglow Emission Lines from HST-COS Spectra
H I Ly $α$（1215.67）和O I三重态（1302.17、1304.86和1306.03）是明亮的远紫外线（FUV）发射线，追踪恒星色球层。使用哈勃太空望远镜（HST）最灵敏的FUV摄谱仪，宇宙起源摄谱仪（COS）对恒星Ly $α$和O I的观测受到地冠发射或气辉的污染。这项研究表明，COS观测到的气辉发射轮廓足够稳定，可以创建气辉模板，这些模板可以从数据中可靠地减去，恢复底层的恒星通量。我们开发了一个图形用户界面来实现对COS数据档案中的171个主序列F，G，K和M型矮星的气辉减法。研究了恢复的恒星辐射和恒星活动测量之间的相关性。提出了几种预测恒星Ly $α$和O I发射的幂律关系。恒星辐射相对于气辉的视亮度是气辉扣除成功或失败的关键因素。我们开发了一个预测成功的气辉减法使用附近的色球发射线Si III（1206.51欧姆）的信噪比（SNR）。成功回收的最小衰减赖氨酸$α$通量为1.39 $\times$ 10 $^{-14}$ erg cm $^{-2}$ s $^{-1}$，我们建议将此作为COS赖氨酸$α$回收的最小通量。
