Synoptic seeing measurements at the University of Hawaii 2.2-m telescope

Abstract

We present the first results of a long-term seeing measurement program at the University of Hawaii 2.2-m telescope on Mauna Kea. During a one-year period from 1985 August 10 to 1986 August 13 the median seeing was 0788 for a wavelength of 0.7 |xm. The weak correlations of the UH 2.2-m seeing with the dome thermal environment and with the CFHT 3.6-m seeing indicate that the UH 2.2-m dome and the atmosphere make comparable contributions to the total seeing. There is no significant dependence on wavelength (over the range 0.61 |xm to 0.82 |xm), wind direction, or time of year. Increasing wind speed however does contribute negatively to the seeing. These data will be used as a baseline against which planned improvements to the dome thermal balance of the UH 2.2-m telescope will be assessed.

Atmospheric and facility seeing on Mauna Kea, Hawaii

“…The correlation between the UH and CFH seeing shown in Figure 2 ever, the spread between pairs of seeing measurement (A.D. = 0.22 arc sec) is larger than the spread of each individual distribution of seeing data. As Henry et al (1987) conclude, this indicates that the contributions of uncorrelated local effects to image spread are comparable to the presumable correlated contribution of the intrinsic site seeing. Furthermore, the fact that the mean global seeing is closely similar at the two telescopes suggests that local effects had similar amplitudes at the UH and CFHT domes when the data were obtained.…”

“…Figure 2 shows the correlation between the UH and CFH data taken within 45 minutes of each other on the average. These data were obtained between August 1985 and August 1986 and are taken from the study of Henry et al (1987). In all cases the FWHM were measured on images of high signal-to-noise ratio and individual estimates should be accurate to ±0.05 arc sec or better.…”

“…The most straightforward way to evaluate atmospheric seeing is to directly measure the size of stellar images at the focus of telescopes. However, when this is done simultaneously at two telescopes on Mauna Kea, image sizes different by a factor of two or more are frequently obtained (Racine 1984;Bely 1987;Henry et al 1987). This suggests that local perturbations, uncorrelated between facilities, contribute as much to image spread as the correlated perturbations due to the free atmosphere and the planetary boundary layer above the site.…”

“…In this paper I show that comparison of seeing data obtained quasi-simultaneously at the UH and CFH telescopes can also be used to separate and evaluate the contributions to image spread due to the telescope optics and drive, to the air within and around the facilities, and to the atmosphere above the site. Section 2 presents the data, published by Henry et al (1987), on which the analysis is based. In Section 3 a simple statistical model is introduced to interpret these data in terms of three components of the seeing spread.…”

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Seeing data obtained quasi-simultaneously at the University of Hawaii 2.2-m telescope and at the Canada-France-Hawaii 3.6-m telescope (Henry et al 1987) are compared and interpreted in terms of telescope aberrations (FWHM -0.5 arc sec), facility seeing ((FWHM) -0.6 arc sec), and atmospheric seeing ((FWHM)) -0.5 arc sec).

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