Seeing measurements for the Guoshoujing Telescope (LAMOST) site with DIMM

Abstract

We present seeing measurements of the Guoshoujing Telescope (formerly named the Large Sky Area Multi-Object Fiber Spectroscopic Telescope-LAMOST) site at Xinglong station during the period from 2007 March 12 to April 25. The measurements were carried out with the Differential Image Motion Monitor (DIMM), and a total of 9259 data sets was obtained. The median seeing was measured to be 1.1 ′′ , with 25% being better than 0.8 ′′ and 75% better than 1.5 ′′. The experiment shows that the DIMM exposure time has significant effects on the results of seeing measurements. An SBIG Polaris seeing monitor, which had been planned to be installed on the LAMOST site for long-term monitoring, was also employed during the DIMM observations. The results show that the SBIG seeing monitor is easily affected by gusty wind, resulting in larger seeing values. Considering the previous seeing measurements at Xinglong station over the last 15 yr, we conclude that an acceptable seeing condition at Xinglong station is around 1 ′′-2 ′′ .

Optical turbulence characterization at LAMOST site: observations and models

“…Although the results includes many influence factors, such as the dome seeing, image quality, and tracking accuracy of the telescope, however, the data collection for over a decade is useful to understand more about the seasonal seeing conditions. Liu et al (2010) performed DIMM seeing measurements on the top of LAMOST building in 2007, and obtained a better seeing with higher elevation than that at the 2.16m telescope. In this work, we selected an open flat roof for the measurements, and for the first time, we obtained whole night optical turbulence profiles; this work should provide more reliable results to characterize the site condition at Xinglong observatory.…”

“…Based on the photometry dataset in 1995-2001 of Beijing-Arizona-Taipei-Connecticut(BATC) telescope, Liu et al (2003) analyzed the Polaris images by measuring the Full Width at Half Maximum(FWHM) to understand seasonal features of seeing condition. Liu et al (2010) performed DIMM seeing measurements on the top of LAMOST building, in order to optimize the slit width of LAMOST spectrometer. Yao et al(2012) analyzed the seeing conditions with the BATC photometric data in 1995-2011, and their results could be referred as the long-term (more than 15 years) seeing variation at Xinglong observatory.…”

OUP accepted manuscript

“…The Tibet Ali site is considered to be one of the best sites in east Asia (Liu et al 2015a;Ye et al 2016) and has been selected as one of the potential sites for the LOT. The site-testing data are obtained with the method discussed in Liu et al (2010), Liu et al (2013) and Liu et al (2015b). Because this method does not allow ground-layer turbulence measurement, we will set the GLAO system telescope to 100 m lower than the lowest layer of measured turbulence-profile data, and randomly select two nights of site-testing data with different seeing conditions to show the performance variation in these conditions.…”

Optical Observing Conditions at Delingha Station

“…It can be easily noticed the DIMM seeing values are lower than the SBIG seeing. This is because the SBIG seeing monitor uses a star trail method which can be easily affected by equipment jitter (Liu et al 2010).…”