Atmospheric optical turbulence at the Roque de los Muchachos Observatory: data base and recalibration of the generalized SCIDAR data

Abstract

We present the largest data base so far of atmospheric optical turbulence profiles [197 035 individual C2N(h)] for an astronomical site, the Roque de los Muchachos Observatory (La Palma, Spain). This C2N(h) data base was obtained through generalized SCIDAR observations at the 1‐m Jacobus Kapteyn Telescope from 2004 February to 2009 August, obtaining useful data for 211 nights. The overestimation of the turbulence strength induced during the generalized SCIDAR data processing has been analysed for the different observational configurations. All the individual C2N(h) have been recalibrated to compensate for the errors introduced during data treatment. Comparing the results from profiles before and after the recalibration, we analyse its impact on the calculation of relevant parameters for adaptive optics.

Recalibrated generalized SCIDAR measurements at Cerro Paranal (the site of the Very Large Telescope)

“…20 km from the ground). In previous studies in the literature (Avila et al 2004; Masciadri, Avila & Sanchez 2004; Egner et al 2007; Masciadri et al 2010; García‐Lorenzo & Fuensalida 2011a,b; Hagelin, Masciadri & Lascaux 2011) the calculation of θ 0 was done with a value of h up between 20 and 22 km from the ground. To estimate the effect of the value of h up on θ 0 and to evaluate potential differences because of this element, we calculated the integral using h up = 22 km.…”

“…Some larger errors have been observed in the study performed at the Roque de los Muchachos Observatories on the Canary Islands (García‐Lorenzo & Fuensalida 2011b) because a set of different geometric parameters (wider binary separation and deeper conjugation heights of the detector plane) has been used in combination with a smaller telescope pupil size. In the study of Roque de los Muchachos ( D = 1 m), five binaries with an angular separation wider than 10 arcsec (for a percentage of time equal to 3.39 per cent) have been selected.…”

“…To overcome this limitation, Fuchs, Tallon & Vernin (1994, 1998) proposed a generalized version of SCIDAR, called generalized SCIDAR (GS), in which the detector is virtually conjugated below the ground at a distance h gs , allowing the measurement range to be expanded to the whole atmosphere (from the ground up to ∼20–25 km). GS measurements were later performed by several authors above different astronomical sites using instruments developed by several different teams (Avila, Vernin & Masciadri 1997; Avila, Vernin & Cuevas 1998; Klueckers et al 1998; McKenna et al 2003; Avila et al 2004; García‐Lorenzo & Fuensalida 2006, 2011a,b; Egner et al 2007; Egner & Masciadri 2007; Fuensalida, García‐Lorenzo & Hoegemann 2008; Masciadri et al 2010; Avila et al 2011).…”

“…The GS PAR2007 measurements were taken from an Auxiliary Telescope (AT) of the Very Large Telescope Interferometer (VLTI) with the Cute‐SCIDAR III instrument, which has been developed by the Instituto de Astrofísica de Canarias (IAC) team (Vázquez Ramió et al 2008) to be used at the Paranal Observatory within the European project, ELT design study. This instrument is an improved version of another previously developed by the same group for the Roque de los Muchachos and Teide Observatories, which has been used since 2002 to extensively monitor the optical turbulence at both observatories (Fuensalida et al 2004; García‐Lorenzo & Fuensalida 2011a,b). The Cute‐SCIDAR III instrument provides profiles in real time without dome and mirror seeing components.…”

Coherence time and turbulence velocity at the Roque de los Muchachos Observatory from G-SCIDAR turbulence profiles and operational radiosounding wind speed.

“…The full database covers more than 200,000 profiles from 212 nights at ORM. 9 The median and mean monthly turbulence profiles for ORM with the full database are shown in Fig. 3 The C 2 n profiles were calculated from the normalized autocovariances derived from 1000 images of scintillation patterns in a displaced pupil plane, following the G-SCIDAR technique.…”