Mirror, dome, and natural seeing at CFHT

Racine, R.; Salmon, Derrick; Cowley, David J.; Sovka, Jerry

doi:10.1086/132920

Cited by 80 publications

(47 citation statements)

References 2 publications

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“…30,31 This corresponds to an r 0 of 250 mm, which is much higher than the average results reported here for any of the sites. An interesting question is why the r 0 average for Mana Kea is nearly twice as large as observed from Mt.…”

Section: Resultscontrasting

confidence: 57%

“…In addition, microthermal probe data collected within the 1.6-m dome showed that internal heat sources have a substantial contribution, an effect long observed at the California-France-Hawaii Telescope. 30 Only two of the sites involved data collection in large domes with other instrumentation, Mt. Haleakala, Hawaii, and McDonald Observatory, Texas.…”

Section: Resultsmentioning

confidence: 99%

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Measurements of r_0 and θ_0: two decades and 18 sites

Walters

Bradford

1997

Appl. Opt.

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We present a statistical analysis of r 0 and 0 measurements collected over the last 2 decades at 18 different sites. Although the site altitudes varied from sea level to 3 km, the major distinguishing feature between average r 0 values was the presence or absence of a turbulent, atmospheric boundary layer above the surface. For locations without a strong boundary-layer inversion, the mean coherence length, r 0 , was 93 Ϯ 6 mm and the mean isoplanatic angle, 0 , was 9.4 Ϯ 0.5 rad. Where a boundarylayer inversion was present, the corresponding values for r 0 and 0 were 53 Ϯ 2 mm and 6.5 Ϯ 0.5 rad, respectively.

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Section: Resultscontrasting

confidence: 57%

Section: Resultsmentioning

confidence: 99%

Measurements of r_0 and θ_0: two decades and 18 sites

Walters

Bradford

1997

Appl. Opt.

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“…Comments on each panel of Figure 4 are made in § 3.3. Table 2 compares the convective local-seeing coefficients in Table 1 with those of Racine et al (1991). Note that what was defined as mirror seeing by Racine et al corresponds to the 5/3 power law sum of the mirror, caisson, and tube seeing here and that their dome seeing is referred to as slit seeing here.…”

Section: Iq Resultsmentioning

confidence: 99%

“…Table 5 gives the distribution of the natural atmospheric seeing at the CFHT site. Racine et al 1991 first quantified the relation between local seeing and temperature differences at the CFHT. The present study has much refined and strengthened this relation.…”

Section: The Results Of Local Deteriorations Removal On Iq Distributionsmentioning

confidence: 99%

“…The last comprehensive study of atmosphere-related sources of image deterioration at the CFHT is by Racine et al in 1991. We considerably expand here on that effort by combining the resources of two rich data sets-the MegaCam image archive and the CFHT data logger archive-to further understand where sources of image degradation arise within the telescope's environment and how further improvements could be had. Byproducts of the exercise are an estimate of the natural atmospheric seeing at the CFHT site which, for logistical reasons, has not yet been obtained from extensive differential image motion monitor (DIMM) campaigns, and an estimate of the outer scale of turbulence.…”

Section: Introductionmentioning

confidence: 99%

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CFHT Image Quality and the Observing Environment

Salmon¹,

Cuillandre²,

Barrick³

et al. 2009

PUBL ASTRON SOC PAC

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ABSTRACT. We analyze stellar images on 36,520 exposures made in the u, g, r, i, and z bands with MegaCam at the focus of the 3.6 m Canada-France-Hawai′i Telescope between 2005 August and 2008 August. The effect on image quality (IQ) of temperature differences (ΔTs) in the telescope environment and of wind speed and direction are first examined and discussed. The contributions of the optics to image spread are then estimated and the frequency distribution of the observatory-free site seeing is obtained. The main findings are: (1) In the convective mode, the thermally-induced image full width at half-maximum intensity (FWHM) grows with the temperature gradient and path length L at the rate of ∼0:2″ · ðΔT=LÞ 6=5 · L 3=5 . (2) For a given jΔTj, thermal convection is ∼3 times more detrimental to image quality than thermal inversions. (3) The orientation of the dome slit with respect to the wind direction has important effects on IQ. (4) The median observatory induced seeing is 0.43″ FWHM. (5) The FWHM caused by the optics and slight optomechanical imperfections ranges from 0.46″ in u to 0.28″ in i. (6) The median DIMM-scale zenith atmospheric seeing at a wavelength of 500 nm and an elevation of 17 m above ground at the CFHT site is 0.55″. (7) The characteristics value of the outer scale of turbulence is 30 m. The paper addresses various issues bearing on the management of facility seeing.

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Thermalizing a telescope in Antarctica – analysis of ASTEP observations

et al. 2015

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The installation and operation of a telescope in Antarctica represent particular challenges, in particular the requirement to operate at extremely cold temperatures, to cope with rapid temperature fluctuations and to prevent frosting. Heating of electronic subsystems is a necessity, but solutions must be found to avoid the turbulence induced by temperature fluctuations on the optical paths. ASTEP 400 is a 40 cm Newton telescope installed at the Concordia station, Dome C since 2010 for photometric observations of fields of stars and their exoplanets. While the telescope is designed to spread star light on several pixels to maximize photometric stability, we show that it is nonetheless sensitive to the extreme variations of the seeing at the ground level (between about 0. 1 and 5 ) and to temperature fluctuations between −30 • C and −80 • C. We analyze both day-time and night-time observations and obtain the magnitude of the seeing caused by the mirrors, dome and camera. The most important effect arises from the heating of the primary mirror which gives rise to a mirror seeing of 0. 23 K −1 . We propose solutions to mitigate these effects.

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Mirror, dome, and natural seeing at CFHT

Cited by 80 publications

References 2 publications

Measurements of r_0 and θ_0: two decades and 18 sites

Measurements of r_0 and θ_0: two decades and 18 sites

CFHT Image Quality and the Observing Environment

Thermalizing a telescope in Antarctica – analysis of ASTEP observations

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