下一代帕洛马摄谱仪作为恒星视向速度测量仪的校准
Calibration of the Next Generation Palomar Spectrograph as a Stellar Speedometer
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中文总结 AI 辅助
本研究校准下一代帕洛马摄谱仪，利用大气吸收特征校正仪器挠曲，将视向速度测量偏差从数十km/s降至1.6km/s，证明其适用于高精度恒星视向速度测量。
中文摘要 AI 辅助
我们利用对24颗Gaia-ESO视向速度标准星的重复观测，对下一代帕洛马摄谱仪（NGPS）进行了校准，以实现高精度的恒星视向速度（RV）测量，这些标准星的G星等范围为11至18等。由于NGPS安装在海尔望远镜的卡塞格林焦点处，仪器挠曲的变化会导致波长解产生数十km s⁻¹的偏移，且这种偏移具有显著的时间和波长依赖性。我们开发了一套数据处理流程，直接测量每次科学曝光中的这些偏移，利用R和I通道中的大气吸收特征以及G通道中的[O I] 5577 Å天光发射线。这种方法消除了频繁进行天空电弧校准的需求。由此得到的波长相关的挠曲校正将相对于Gaia-ESO视向速度的中位绝对偏差从数十km s⁻¹降低到1.6 km s⁻¹。大气吸收提供的挠曲校准比天光发射线可靠得多，因为后者无法追踪狭缝的点源照明。I通道包含许多大气吸收线和多种光谱类型下的强光球谱线，通常能产生最稳定的视向速度。所达到的精度仍高于光子噪声极限，表明NGPS的视向速度性能目前受限于校准和建模的系统性误差。这些结果表明，NGPS非常适合在广泛的天体物理研究中实现准确且精确的恒星视向速度测量。
英文摘要
We calibrate the Next Generation Palomar Spectrograph (NGPS) for precision stellar radial-velocity (RV) measurements using repeated observations of 24 Gaia-ESO RV standards spanning $G=11$-$18$. Because NGPS is mounted at the Hale telescope's Cassegrain focus, changes in instrumental flexure produce wavelength-solution shifts of tens of km s$^{-1}$, with substantial time and wavelength dependence. We develop a pipeline that measures these shifts directly from each science exposure, using telluric absorption features in the R and I channels and the [O I] 5577 Å sky-emission line in the G channel. This approach eliminates the need for frequent on-sky arc calibrations. The resulting wavelength-dependent flexure corrections reduce the median absolute discrepancy relative to Gaia-ESO RVs from tens of km s$^{-1}$ to 1.6 km s$^{-1}$. Telluric absorption provides substantially more reliable flexure calibration than sky emission lines, which do not track point-source illumination of the slit. The I channel, which contains both many telluric lines and strong photospheric lines across a range of spectral types, generally yields the most stable RVs. The achieved precision remains above the photon-noise limit, indicating that NGPS RV performance is currently limited by calibration and modeling systematics. These results demonstrate that NGPS is well-suited for accurate and precise stellar RV measurements across a wide range of astrophysical studies.
发表机构
- California Institute of Technology（加州理工学院）
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