Astron. Nachr. / AN 325, No. 6–8, 659 (2004) / DOI 10.1002/asna.200410305

ATOM - an Automatic Telescope for Optical Monitoring

M. HAUSER� , C. MOLLENHOFF� , G. PUHLHOFER� , S. J. WAGNER� , H.-J. HAGEN� , andM. KNOLL�

� Landessternwarte Heidelberg-Konigstuhl, Konigstuhl 12, 69117 Heidelberg, Germany� Hamburger Sternwarte, Gojenbergsweg 112, 21029 Hamburg, Germany

Received 12 July 2004; accepted 16 August 2004; published online 31 October 2004

1. Introduction

ATOM (Automatic Telescope for Optical Monitoring) is a75 cm telescope which is currently being automated to en-able a fully robotic observation mode. ATOM will be partof the H.E.S.S. project and will be installed at the H.E.S.S.site. H.E.S.S. (High Energy Stereoscopic System) is an ar-ray of four Imaging Atmospheric Cherenkov Telescopes forthe investigation of cosmic �-rays above 100 GeV. H.E.S.S. islocated in the Khomas Highland of Namibia, about 100 kmsouth-west of Windhoek at an altitude of 1800 m asl. Themain tasks for ATOM will be optical observations simultane-ous with �-ray observations performed by H.E.S.S., and mon-itoring of high energy sources (e.g. AGN) to provide triggersfor H.E.S.S. observations of flaring sources.

The automation of the telescope is done in a col-laboration between Landessternwarte Heidelberg-Konigstuhl(LSW) and Hamburger Sternwarte (HS). After commission-ing the system will consist of a 75 cm telescope with AltAzmount, an imaging CCD camera with filter wheel and controlcomputers which run an autonomous robotic control, observ-ing scheduling, and online data analysis software.

2. TelescopeThe telescope was built by the Zeiss company as a prototypefor computer controlled azimuthal mounting. It was operatedat LSW for a decade and successfully used for many kinds ofastronomical projects. Upon the start of the H.E.S.S. projectin 2000, it became apparent that multifrequency observationswould best be conducted on-site, resulting in a project to au-tomate and relocate this telescope.While the mechanical components only required mod-est redesign for automatic operations, the control elec-tronics were replaced completely, following the strategiesused for automating the Oskar-Luhning-Teleskop (OLT, seewww.hs.uni-hamburg.de/EN/Ins/Olt/). In particular,ATOM will be operated using industrial approved pro-grammable logic controllers (PLCs), resulting in a very stablesystem.

Correspondence to: M.Hauser@LSW.Uni-Heidelberg.de

3. Instrument and detector

The instrument of ATOM will consist of an imager with filterwheel, feeding a peltier-cooled CCD camera, mounted in theCassegrain focus. Closed-cycle LN2 cooling will not be used,since ATOM will be placed at a site without infrastructure forthat type of cooling.

Since fast temporal monitoring is a major goal, we cur-rently investigate the use of L3 technology. Tests of L3-typeCCD chips with arrays of 512x512 pixels are currently con-ducted at LSW. When mounted on ATOM, it will provide afield of view (FOV) of about 5x5 arcmin with a resolution of0.58”/pixel. This FOV is sufficiently large to monitor pointsources; even in fields with low star density, a couple of com-parison stars will be in the FOV to do differential photometry.

4. Scientific motivation and goals

ATOM will be placed at the H.E.S.S. site and will act as aslave to the H.E.S.S. telescope array whenever requested. Thiswill allow the H.E.S.S. collaboration to perform simultaneousTeV - optical multiwavelength observations on variable TeV�-ray sources with an on-site telescope that experiences thesame weather conditions as the Cherenkov Telescopes.

During periods when no simultaneous optical monitor-ing is required, ATOM will automatically perform a moni-toring program of point sources, mainly AGN. The systemsoftware will carry out on-line data analysis and thus pro-vide triggers for observations in other wavelength regimes ifa source is flaring (primarily TeV observations with H.E.S.S.,but extended multiwavelength campaigns are also possible).Both of these observing modes will be conducted on fieldswhich include secondary photometric standards, and henceprovide continuous monitoring of atmospheric extinction.This will serve as an additional input to the analysis ofCerenkov signals studied with H.E.S.S.

Acknowledgements. We thank the EC for supporting this workthrough the network ENIGMA under contract HPRN-CT-2002-00321 as well as the BMBF Forderschwerpunkt Astroteilchen-physik (05 CH2VOA/2).

c�2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim