M. Lazrek

European Extremely Large Telescope Site Characterization I: Overview

ABSTRACT.The site for the future European Extremely Large Telescope (E-ELT) is already known to be Armazones, near Paranal (Chile). The selection was based on a variety of considerations, with an important one being the quality of the atmosphere for the astronomy planned for the ELT. We present an overview of the characterization of the atmospheric parameters of candidate sites, making use of standard procedures and instruments as carried out within the Framework Programme VI (FP6) of the European Union. We have achieved full characterization of the selected sites for the parameters considered. Further details on adaptive optics results and climatology will be the subject of two forthcoming articles. A summary of the results of the FP6 site-testing campaigns at the different sites is provided.

The first optical characterization of the Oukaïmeden site with the Generalized Seeing Monitor (GSM)

The main atmospheric optical parameters (AOP) have been measured during 10 nights in April 1998 with the GSM instrument at the Moroccan site of Oukaimeden. These parameters are of interest for the optimization of high angular resolution techniques. During this campaign the temporal evolution of the AOP and their distributions have been studied. The outer scale presents a log-normal histogram with a median value of 31 m which is rather similar to the values obtained at other sites visited with GSM. The selection of the Oukaimeden site is the result of several topographical and meteorological studies on the Atlas mountain chain. Since 1988 this site has been chosen for the installation of one of the IRIS (International Research of the Interior of the Sun) stations. Here, we present the whole AOP data measured with GSM during this campaign. The main photometric and meteorological conditions of this site are also presented.

European Extremely Large Telescope Site Characterization. II. High Angular Resolution Parameters

ABSTRACT.This is the second article of a series devoted to European Extremely Large Telescope (E-ELT) site characterization. In this article we present the main properties of the parameters involved in high angular resolution observations from the data collected in the site testing campaign of the E-ELT during the design study (DS) phase. Observations were made in 2008 and 2009, in the four sites selected to shelter the future E-ELT (characterized under the ELT-DS contract): Aklim mountain in Morocco, Observatorio del Roque de los Muchachos (ORM) in Spain, Macon range in Argentina, and Cerro Ventarrones in Chile. The same techniques, instruments, and acquisition procedures were taken on each site. A multiple aperture scintillation sensor (MASS) and a differential image motion monitor (DIMM) were installed at each site. Global statistics of the integrated seeing, the free atmosphere seeing, the boundary layer seeing, and the isoplanatic angle were studied for each site, and the results are presented here. ...

A simple flux integration photometer for day time site testing at Oukaimeden

We describe here a simple irradiance photometer built at Astrophysical and Geophysical Laboratory (LAG) for the integrated photometry of sun light at Oukaimeden, a 2700m summit in the Morrocan High Atlas. The solar irradiance measurement is performed simultaneously at three wavelengths to sample different levels of the sky transparency. The total of 1182 days in the data base shows that the number of clear hours is about 3086 per year which represents 65.32% of clear sky. The extinction coefficient is computed to evaluate the quality of the sky transparency at the site. We find that there is a seasonal effect for the sky transparency, and the monthly average of the extinction coefficient has a minimum value of about 0.05 in winter (oct-nov-dec) and a maximum of about 0.15 in summer (jun-jul) at 700 nm.

Moroccan participation in the study of solar oscillations

An international program of cooperation linked Astrophysics Department of the University of Nice and the Astronomical and Geophysical Laboratory of Rabat. This program has permitted the installation of an observational instrument for the study of solar seismological phenomena in the framework of the IRIS programme, on the mountain site of Oukaïmeden, in Morocco.

First characterization of Jbel Aklim in Moroccan Anti-Atlas as a potential site for the E-ELT Meteorological parameters and seeing measurements

Context. In the framework of the European Extremely Large Telescope project (E-ELT), a survey of prospective sites was launched by the European Southern Observatory (ESO) to select a site to host the next generation of optical telescopes of 42 m diameter, i.e., the E-ELT. The Moroccan Anti-Atlas (Jbel Aklim) was selected as one of these sites. Aims. We present an analysis of meteorological parameters and seeing measurements at Aklim, the Moroccan prospective site of the E-ELT project. Methods. We initiated a preliminary campaign to measure the astronomical seeing at Jbel Aklim using a differential image motion monitor (DIMM) instrument. We installed a weather station 2 m above the ground level to measure meteorological parameters such as temperature, relative humidity, pressure, wind speed, and wind direction. Results. We present data obtained by the DIMM monitor during 105 nights. The median and mean values of the seeing for the entire period of observation are 0.72 �� and 0.79 �� , respectively, with a standard deviation of 0.31 �� . The best value of the seeing obtained during this period is 0.30 �� . A seasonal analysis of meteorological parameters are presented. We also used data from the National Center for Environmental Prediction/National Center for Atmospheric Research reanalysis database (NCEP/NCAR) to derive more information about the long-term evolution of atmospheric parameters at Aklim site. Conclusions. Our preliminary results indicate that Aklim has indeed good conditions for conducting astronomical observations and could be a site to host a future astronomical observatory, even of E-ELT dimensions.

Hierarchical fringe tracking

The limiting magnitude is a key issue for optical interferometry. Pairwise fringe trackers based on the integrated optics concepts used for example in GRAVITY seem limited to about K=10.5 with the 8m Unit Telescopes of the VLTI, and there is a general “common sense” statement that the efficiency of fringe tracking, and hence the sensitivity of optical interferometry, must decrease as the number of apertures increases, at least in the near infrared where we are still limited by detector readout noise. Here we present a Hierarchical Fringe Tracking (HFT) concept with sensitivity at least equal to this of a two apertures fringe trackers. HFT is based of the combination of the apertures in pairs, then in pairs of pairs then in pairs of groups… The key HFT module is a device that behaves like a spatial filter for two telescopes (2TSF) and transmits all or most of the flux of a cophased pair in a single mode beam. We give an example of such an achromatic 2TSF, based on very broadband dispersed fringes analyzed by grids, and show that it allows piston measures from very broadband fringes with only 3 to 5 pixels per fringe tracker. We show the results of numerical simulation indicating that our device is a good achromatic spatial filter and allowing a first evaluation of its coupling efficiency, which is similar to this of a single mode fiber on a single aperture. Our very preliminary results indicate that HFT has a good chance to be a serious candidate for the most sensitive fringe tracking with the VLTI and also interferometers with much larger number of apertures. On the VLTI the first rough estimate of the magnitude gain with regard to the GRAVITY internal FT is between 2.5 and 3.5 magnitudes in K, with a decisive impact on the VLTI science program for AGNs, Young stars and planet forming disks.

European Extremely Large Telescope Site Characterization III: Ground Meteorology

Both meteorology and optical conditions are crucial for selecting the best site to host extremely large telescopes such as the Thirty Meter Telescope (TMT) and the European project (E-ELT). For the E-ELT, a year-long meteorological campaign was performed at our two reference sites, the Observatorio del Roque de los Muchachos (ORM) and Cerro Ventarrones (very close to the VLT site at Paranal), and at other sites also considered as alternatives to the reference sites: Aklim, Macon, and Izana (Observatorio del Teide; OT). In this article, we present a statistical analysis of the ground meteorological properties recorded at these sites, making use of automatic weather stations (AWSs) equipped with standard meteorological sensors providing the air temperature, relative humidity, barometric pressure, wind speed, and wind direction, using standard procedures across all sites. Meteorology offers but one discriminant in the complicated question of where to site such a major facility as the E-ELT (other factors being seeing, local geology, the economics of the logistics, etc.), both for determining the feasibility of telescope and instrumentation design and construction and for determining the useful observing time. However, the final decision of where to locate a major telescope depends in part on all these—and other—considerations and not on any one criterion alone. In summary, for 90% of the nighttime, the wind speed is lower than 18 m s-1, the telescope operational limit at all the sites except Macon. For this reason, Macon was discarded in the final site selection as, for 25% of the time, the wind speed is greater than 17 m s-1. The smallest nighttime temperature gradient is at ORM, whereas the lowest mean relative humidity value is reached at the Ventarrones site. Izana was discarded in the site selection study from the very beginning due to lack of funding to install further site-testing equipement (e.g., Multi-Aperture Scintillation Sensor-Differential Image Motion Monitor (MASS-DIMM)). We investigate the statistical distributions of annual and monthly meteorological conditions for day and night separately. This is the third paper in a series discussing the E-ELT FP6 site characterization project.

European Extremely Large Telescope: Isopistonic angle measurements at Aklim site

As part of the Extremely Large Telescope (ELT) project, the sitetesting team at Morocco has measured from April 2008 to December 2009. The atmospheric properties at Aklim which was one of the candidates sites pre-selected. In this paper we present the isoplanatic angle 0 and the isopistonic angle p measurements at Aklim site. Statistics of the mentioned parameters are obtained from the whole data recorded using a Multi Aperture Scintillation Sensor (MASS) and a Differential Image Motion Monitor (DIMM) system. More representative results and statistics are shown hereafter.

First characterization of Jbel Aklim in Moroccan Anti-Atlas as a potential site for the E-ELT

In the framework of the E-ELT project a prospecting campaign was launched by the ESO to select the site that will host the next generation of optical telescopes of 42 m diameter. Moroccan Anti-Atlas (Jbel Aklim) was selected as well as other sites (ORM, Ventarrones and Macon) to be a possible potential location that will house the E-ELT. In this paper we first present the reasons for the choice of Jbel Aklim as a E-ELT candidate through various exploration campaigns that we have achieved. The second part concerns description of instruments used. Finally we will present the preliminary results of the meteorological and MASS-DIMM measurements.