冰山一角：来自CoRoT空间测光的Delta Sct星HD 50844的频率含量
The tip of the iceberg: the frequency content of the Delta Sct star HD 50844 from CoRoT space photometry
摘要：
有人认为，在Delta Sct星中探测到大量的非常低振幅的模式只是一个信噪比的问题。从地面上不可能获得这一宝藏，这是法国国家空间研究中心开发和运营的CoRoT空间任务的科学目标之一。这项工作介绍了在HD 50844上获得的结果：140，016个数据点使我们能够在振幅谱中达到10^{-5}等的水平。CoRoT时间序列的频率分析揭示了频率范围0- 30 d^{-1}中的数百个项。证实了最初的猜测，三角洲Sct星有一个非常丰富的频率内容。光谱模式识别给出了理论支持，因为非常高的度模式（高达ell=14）被识别。我们还证明，消除效果是不够的，在消除与这些模式相关的磁通量变化在噪声水平的CoRoT测量。地面观测表明，HD 50844是一颗演化恒星，重元素含量略不足，位于末龄主序星。结合地面测光和光谱数据，确定了主要项（f_1=6.92 d^{-1}）为基本径向模。这项工作是基于欧洲南方天文台望远镜在大型计划LP 178.D-0361下进行的观测。
英文摘要：
It has been suggested that the detection of a wealth of very low amplitude modes in Delta Sct stars was only a matter of signal--to--noise ratio. Access to this treasure, impossible from the ground, is one of the scientific aims of the space mission CoRoT, developed and operated by CNES. This work presents the results obtained on HD 50844: the 140,016 datapoints allowed us to reach the level of 10^{-5} mag in the amplitude spectra. The frequency analysis of the CoRoT timeseries revealed hundreds of terms in the frequency range 0--30 d^{-1}. The initial guess that Delta Sct stars have a very rich frequency content is confirmed. The spectroscopic mode identification gives theoretical support since very high--degree modes (up to ell=14) are identified. We also prove that cancellation effects are not sufficient in removing the flux variations associated to these modes at the noise level of the CoRoT measurements. The ground--based observations indicate that HD 50844 is an evolved star that is slightly underabundant in heavy elements, located on the Terminal Age Main Sequence. The predominant term (f_1=6.92 d^{-1}) has been identified as the fundamental radial mode combining ground-based photometric and spectroscopic data. This work is based on observations made with ESO telescopes under the Large Programme LP 178.D-0361.
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