FRAM

Introduction

The calibration of the whole detector is crucial issue. Because the precise energetic reconstruction of cosmic ray showers is one of the main goals of the project, for the purposes of fluorescence telescopes we need to know very precisely the immediate status of the atmosphere, especially its extinction - to able to determine how much fluorescence light was lost on its way from the shower to the telescope.

The atmospheric conditions are very variable and have to be carefully monitored all the time and if possible, the measured parameters of atmosphere have to be cross-checked using different methods and different instruments. Within Auger, this task is taken extremely carefully and many independent atmospheric monitoring devices was developed. The basic instruments for extinction evaluation are LIDARs and CLF (Central Laser Facility). Furthermore, HAM (Horizontal Attenuation Monitor) and APF (Attenuation Phase Function monitor) are working, molecular atmosphere is measured using balloon flights and clouds are detected with infra-red cloud cameras. The most recent addendum to the set of atmospheric monitoring device are two different star monitors - and one of them is our photometric robotic telescope, called FRAM. Its short description follows. (The name was chosen not only as little grammatically crippled acronym Fotometric Robotic Atmospheric Monitor, but also in honor of pioneering Fridtjof Nansen's polar vessel - FRAM. "Fram" means "onward" in Norwegian.)

Telescope

[Photo from the site at Ondrejov observatory, near Prague, Czech Republic.]

Our telescope is primarily dedicated to frequent photometric observations of bright standard stars. We use Cassegrain type telescope, with diameter 200 mm and focal length 3000 mm. Telescope is attached to the equatorial mount Losmandy G-11 with Gemini electronic GOTO system. Main instrument on the telescope is photometer Optec SSP5-A. For determination of extinction we use Strömgren uvby filters, in near future we plan to add Johnson U filter for direct comparison with data from FD telescope and several narrowband filters in the spectral range 300 - 400 nm. Furthermore, the telescope is equipped with CCD camera - wide-field Starlight XPress MX516 used for astrometry and narrow-field Starlight XPress MX 716 used mainly for main telescope guiding and focusing. The narrow-field camera has field of view of about 20' and is attached directly to the main telescope. The remotely-driven movable mirror with motor chooses, whether the light goes into photometer or into narrow-field CCD. The wide-field camera has FOV of about 2° and is attached to the pointer telescope; in fact to the ordinary camera lens Sonnar. It has diameter 80 mm and focal length 200 mm. For calibration purposes have both cameras installed Johnson R filters.

The telescope is fully controlled by the Linux computer (including the roof opening and closing) running the RTS-2 (Robotic Telescope) system. This system was developed at Ondrejov for the robotic telescope BART (key author is Petr Kubanek) and was modified for our purposes.

Telescope house

Computer model of our telescope house by the fence in the vicinity of Los Leones FD building.

The design of the house was inspired by the house of Spanish robotic telescope BOOTES. This design was changed and adapted for our purposes. It is composed of laminate pyramidal roof and laminate walls. This light-weight, but resistant house should be situated on concrete foundations. The roof is splitting into two pieces during opening; for the opening is used hydraulic engine with two valves on both sides of the roof.

[Click onto picture to get it in much better resolution]
Technical drawing of the telescope house, including concrete foundations. All important dimensions and sizes are included.

Telescope house with opened roof on its test site in Ondrejov, November 2004.

M.P. 11 FEB 2005