The largest Czech telescope is fifty-five years old and still in top condition

Even though the largest Czech telescope with a mirror lens diameter of two metres and a total weight of over 80 tonnes is already 55 years old, it is still in excellent technical condition. It has produced plenty of results and is taking part in the largest number of observing programmes in its history. The Perek Telescope has been operated by the Astronomical Institute of the CAS in Ondřejov since August 1967.

In 2006, the Perek Telescope underwent the last upgrade of its control system, which nowadays uses industrial automation. In 2009, the controls of the spectrographs were also improved. Both of these tune-ups were carried out by ProjectSoft from Hradec Králové. In 2018, the optical system of the telescope was fundamentally rebuilt. Instead of auxiliary mirrors, optical fibres were installed. By doing so, the efficiency of the telescope was increased by up to 60%. The project was supported by the TOPTEC centre from Turnov (part of the Institute of Plasma Physics of the CAS). A CCD camera for direct imaging and photometry was newly installed in the primary focus. Changing the configuration of the instruments – fibre spectrographs and photometric camera – can be done in one minute. The date 23 August 2022 marked 55 years since the inauguration of the two-meter telescope.

The Perek Telescope – basic information

It is the largest optical astronomical instrument to be found in the Czech Republic. In 2012, it was named after Associate Professor Luboš Perek (b. 26 July 1919, d. 17 September 2020), who was the spiritual father of the instrument and head of the scientific part of the project. The telescope was designed and manufactured by the German company Carl Zeiss Jena and its chief engineer was Alfred Jensch (b. 19 June 1912, d. 6 October 2000). The instrument was put into operation in Ondřejov on 23 August 1967.

During 55 years, the telescope has undergone a gradual evolution and modernisation of its controls and the attached astronomical instruments. The control system of the telescope has been modernised three times (1982–1987, 1996–1998, 2007), and nowadays, the telescope control is connected to the spectrograph control and is fully automatic.

The Perek Telescope is used for observing stars, or, more precisely, for measuring the spectra of stars and observing erupting stars and exoplanets, and is available to students of Czech and foreign universities.

Basic technical parameters of the Perek Telescope

• the diameter of the mirror lens is two metres, the mirror weighs 2.25 tonnes
• focal length: primary focus 9 m (until the reconstruction in 2018, a coudé focus of 63.5 m was used, today the telescope is modified and more powerful)
• the tube with mirror lens, counterweight, and other moving parts (telescope, counterweight, and axes) weighs 83 tonnes
• the telescope itself weighs 33 tonnes, the counterweight weighs 27 tonnes
• the telescope dome, 21 m in diameter, is rotatable and weighs 195 tonnes
• the width of the dome slit is five metres

The construction of the telescope and the development of stellar astronomy in Czechoslovakia were the work of the prominent astronomer doc. RNDr. Luboš Perek, DrSc., Dr. h. c., who in the past was, for example, the head of the UN Office for Outer Space Affairs, and also the director of the Astronomical Institute of the CAS. To honour the esteemed scientist, the telescope was named after him in 2012 on the occasion of the 45th anniversary of the telescope.

What the Perek Telescope observes:

Stellar spectroscopy

Considering the climatic and observing conditions of the town of Ondřejov in Central Bohemia, it was decided that the instrument would be used primarily for stellar spectroscopy. The first spectrum was recorded on 13 October 1967. From the beginnings of observations until 1992, stellar spectra were recorded on photographic plates; since 1992, electronic detectors have been used to record spectra.

Spectroscopic observations with the two-metre Perek Telescope have led to a number of important scientific findings, which have been published in international astronomical journals. The most important is the confirmation of the hypothesis of a binary origin of the emission of some B[e] stars, which was the mainstay of the early spectroscopic observations in Ondřejov.

The telescope is now used for long-term studies of massive hot OB stars and stars in transitional stages of evolution, i.e., Wolf-Rayet stars (WRs), luminous blue variable stars (LBVs), blue supergiants (BSGs), and B[e] supergiants (B[e]SGs).

The Perek Telescope is involved in the international ChETEC-INFRA (Chemical Elements as Tracers of the Evolution of the Cosmos – Infrastructures for Nuclear Astrophysics) project and is also used for spectroscopic studies of the population of brighter hot sub-dwarfs in the northern hemisphere sky, i.e., objects that are not included in observations with large telescopes due to their intense brightness.

Eruptive stars

Another programme is the observation of so-called eruptive stars, mainly red dwarfs, which is carried out within the framework of joint photometric and spectroscopic campaigns by several instruments of the Astronomical Institute of the CAS and also by the community of observers associated in the Variable Stars and Exoplanets Section of the Czech Astronomical Society. The aim is to record in detail the powerful flares occurring in the atmospheres of these stars, which resemble the solar ones in many respects. The research topic is interesting in view of the occurrence of extreme flares also on solar-type stars and the effect of strong flares on the atmospheres and habitability of extrasolar planets.

Exoplanets

Today, the Perek Telescope is also involved in exoplanet research. The research group is involved in spectroscopic observations and confirmation of candidate exoplanets discovered by the Kepler / K2 space missions and the TESS mission (NASA) and, in the future, by the PLATO mission (ESA). Using the Perek Telescope, researchers determine the parameters of exoplanetary systems by measuring radial velocities. The group is also involved in the study of exoplanetary atmospheres. These atmospheres must be observed with large telescopes, but the Perek Telescope is an ideal instrument to help select interesting candidates for larger telescopes, for example at ESO observatories (European Southern Observatory).

High Energy Astrophysics

The Perek Telescope is also used by the High Energy Astrophysics Working Group, which studies galactic and extragalactic gamma-ray sources and multispectral analysis of gamma-ray bursts and their optical counterparts (outflows). The group operates its own smaller robotic telescopes at the Ondřejov Observatory. However, if the brightness of the object under study changes too quickly or is very low, the group members have also been able to use the Perek Telescope in a photometric configuration since 2018.

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