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首页> 外文期刊>PASJ: Publications of the Astronomical Society of Japan >A new off-point-less observing method for millimeter and submillimeter spectroscopy with a frequency-modulating local oscillator
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A new off-point-less observing method for millimeter and submillimeter spectroscopy with a frequency-modulating local oscillator

机译：一种新的毫米和亚麻谱利用频率调制局部振荡器的少量脱近观察方法

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摘要

We propose a new observing method for single-dish millimeter and submillimeter spectroscopy using a heterodyne receiver equipped with a frequency-modulating local oscillator (FMLO). Unlike conventional switching methods, which extract astronomical signals by subtracting the reference spectra of off-sources from those of on-sources, the FMLO method does not need to obtain any off-source spectra; rather, it estimates them from the on-source spectra themselves. The principle uses high-dump-rate (10 Hz) spectroscopy with radio frequency modulation achieved by fast sweeping of a local oscillator of a heterodyne receiver. Because sky emission (i.e., off-source) fluctuates as 1 / f and is spectrally correlated, it can be estimated and subtracted from time series spectra (a timestream) by principal component analysis. Meanwhile, astronomical signals remain in the timestream since they are modulated to a higher time-frequency domain. The FMLO method therefore achieves (1) a remarkably high observation efficiency, (2) reduced spectral baseline wiggles, and (3) software-based sideband separation. We developed an FMLO system for the Nobeyama 45 m telescope and a data reduction procedure for it. Frequency modulation was realized by a tunable and programmable first local oscillator. With observations of Galactic sources, we demonstrate that the observation efficiency of the FMLO method is dramatically improved compared to conventional switching methods. Specifically, we find that the time to achieve the same noise level is reduced by a factor of 3.0 in single-pointed observations and by a factor of 1.2 in mapping observations. The FMLO method can be applied to observations of fainter (similar to mK) spectral lines and larger (similar to deg(2)) mapping. It offers much more efficient and baseline-stable observations compared to conventional switching methods.
机译：我们提出了一种使用配备有频率调制局部振荡器（FMLO）的外差接收器的单盘毫米和亚细仪光谱的新观察方法。与传统的开关方法不同，通过从导通源的离子的​​参考光谱中取出天文信号来提取天文信号，FMLO方法不需要获得任何偏离源谱;相反，它估计它们来自源极谱本身。该原理采用高倾倒速率（10Hz）光谱通过通过快速扫描外差接收器的本地振荡器来实现射频调制。因为天空发射（即，离源源）波动为1 / f并被光谱相关，因此可以通过主成分分析从时间序列谱（TibestReam）估计和减去它。同时，天文信号留在时间集中，因为它们被调制到更高的时频域。因此，FMLO方法实现了（1）显着高的观察效率，（2）减少了频谱基线Wiggles，以及（3）基于软件的边带分离。我们为NoboMaMa 45 M望远镜开发了一个FMLO系统和数据的数据减少程序。通过可调谐和可编程的第一本地振荡器实现频率调制。通过观察银河来源，我们证明与传统的开关方法相比，FMLO方法的观察效率显着改善。具体地，我们发现在单尖观察中达到相同的噪声水平的时间在3.0的倍数下，并且在映射观察中的尺寸为1.2。 FMLO方法可以应用于昏厥（类似于MK）光谱线的观察（类似于DEG（2））映射。与传统的开关方法相比，它提供了更有效和基线稳定的观察。

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