云南天文台40米射电望远镜河外射电源观测

Observations of Extragalactic Radio Sources with the 40 m Radio Telescope of the Yunnan Observatory

为了在云南天文台40 m天线上开展射电天文研究,使用它进行了河外射电源流量试观测。通过对河外致密源进行ON/OFF跟踪观测,得到射电源的流量变化曲线。但数据质量并不理想,说明系统存在一些问题。随后,根据对该望远镜系统的稳定性及其无线电环境干扰现状的考察,以及对现存问题的分析,提出了相应的解决方法。

To open new opportunities on radio astronomical research with the recently constructed YNAO 40 m radio telescope, we carried out test observations of extragalactic radio sources. Three compact radio sources （3C273, 3C295, and 0716＋714） were observed with the ON/OFF mode. In such a mode the telescope was pointed first toward the source and then 2 degrees off the source. In each cycle there are 2 minutes on-source observation and 2 minutes off-source observation. The observational wavelength bands were alternated between the S and X bands but with short time intervals. We present here the S- and X-band flux-density curves of the three sources. There are unexpected drifts on various time scales in these curves. The sensitivity limits of the observations are about 1 Jy. Through the observation, we have identified problems of the telescope stability and environmental radio-frequency interference. By pointing the telescope to the Zenith without tracking, we found ≤ 1% per hour drifts in the flux-density curve, which are much less than the drifts observed in an ON/OFF mode for a source. In the S band, there is a strong interference signal at the frequency 2 142 MHz. This interference signal has several harmonics, so that it polluted our data severely. The frequency interference in the X band is weaker than in the S band. We finally propose measures to improve the telescope capacity. These include developing of a counter-interference system, using a radiometer for measuring the K factor to eliminate gain drifts of devices, and performing drift-scan observation without telescope tracking to avoid other unstable factors.