PROJECT OF THE 130 cm TELESCOPE

FOR THE SKALNATÉ PLESO OBSERVATORY

Jozef Žižňovský Stakčín, December 2012

The described system consists of a 1.3m alt-az mounted Cassegrain-Nasmyth telescope with two Nasmyth focal stations.Both Nasmyth focal stations are equipped with a field derotator.

It contains a control system and a software communicating with the dome control unit and a meteostation.

In principle it is a robotic telescope.

Manufacturer and supplier: ASTELCO Systems GmbH, München

Instruments in the foci:

CCD camera for near UV, visual and red spectral region IR CCD camera for infrared region Echelle spektrograph

It will be provided in the frame of the European Regional Development Fund in three steps:

1. Telescope: till the end of 20132. Dome computerisation : 20133. Focal instruments and infrastructure: Spring 2014

Main mirror M1, free aperture ~ 1 300mm

Main mirror M1, mechanical diameter ~ 1 310mm

Main mirror M1, focal ratio F/2.8 *

System focal ratio F/8

Wave front error /6 at 633nm RMS

Field of View at Nasmyth focus > 0.5 deg

Mirror material Zero Expansion Glass (Zerodur or Astro Sitall)

Mirror coating Al (Aluminium) + protection layer

Mirror reflectivity R > 94%

1. TELESCOPE

1.1. Optics

The primary mirror is a thin low expansion glass meniscus. Its shape and optical performance therefore has to be actively controlled during the observations. The active mirror support system consists of a combination of an 18 point whiffle-tree support and 9 axial actuators. The actuators are controlled by a Shack-Hartmann sensor unit as a part of the telescope system, like the autofocus thermal control. The Shack-Hartmann unit allows checking the online alignment performance of M1 and M2 mirrors and helps to regain the collimation of the optics after recoating. The primary mirror is fixed radially by a 4 point preloaded spring pad system, which guarantees the permanent position of M1 during all telescope movements between zenith and horizon positions as well as at high slewing rates of the telescope. The surface accuracy of the optical system will be proven by interferograms at factory acceptance. At final acceptance, there will be on-sky tests carried out at the Observatory with the supplied Shack-Hartmann sensor unit available at the Nasmyth focal station.

2. Mechanics2.1 Dimensions

Maximum height (tube in vertical position)* 440 cm**

Minimum height (tubus in horizontal position)* 300 cm**

Optical tube lengths 300 cm**

Maximum radius of movement (horizontal position) 215 cm**

Required concrete foundation diameter 300 cm**

Total weight of the telescope in basic specification ~ 7 t

* Calculated from the lower surface of the telescope basis ** Dimensions after the preliminary design phase

2.2 Telescope structure

The structure of the telescope is a special, super-compact “ASTELCO Design”. The telescope tube is a welded Serrurier truss design made from steel. This guarantees a minimal and predictable bending of the tube. All welded parts of the telescope are annealed to relax tensions. This very stiff and rigid design reaches high values for the eigenfrequencies of the system and therefore allows observing at wind speeds up to 15 m/s. The telescope’s central part connects the upper and lower truss sections and holds the combined motorized M1/M3 mirror doors. This section connects the tube assembly by means of two hollow flanges to the fork arms of the mount. Through these hollow flanges the light path of the telescope is sent to one of the 2 Nasmyth foci.A motorized rotating and self-centering M3 unit is provided to reach both Nasmyth foci by software control. Rapid and precise focus change between the two Nasmyth foci gets a simple standard task to be able to use two different instruments at two foci at practically the same time.The lower Serrurier truss part holds the mirror cell with the M1 primary mirror. The mirror cell allows easy access for maintenance – for mounting and dismounting the primary mirror a special ASTELCO tool is supplied.

M1

M2

M3

2.3 Telescope mount and drives

The tube assembly is mounted between both fork arms of the alt-az mount. The fork arms are connected to the mounting base plate. On the upper end of the fork arms the bearing housings, the encoders and the motors are located. The accuracy of the perpendicularity of axes is < 10 arc sec; residual errors are corrected by the software.

Slewing speed* 20°/sec 20°/sec

Absolute pointing accuracy < 5 arcsec RMS

Differential pointing accuracy < 0.2 arcsec RMS

Tracking accuracy without autoguider < 0.5 arcsec/10 min

Tracking accuracy with autoguider < 0.25 arcsec/10 min

Effective encoder resolution 328 increments per arc sec (0.003 arc sec / increment)

FOCAL INSTRUMENTS

1. CCD camera for near UV to red spectral region

• Quantum efficiency in the interval of 400-760nm: 80%• Sensor size 10k x 10k, class: 1 • Pixel size: 8-10 µm • Interface for communication with the computer via fiber optic cable (1 Gbit) • Dark current maximum: 0.01e‐/pixel/sec • Readout noise: less than 5e- (rms) • 16 bit AD converter• Cooling with cryotiger to < -100° C

Example: Spectral Instruments 1110S

http://www.specinst.com/Brochures%20Rev%20A/1100S-camera-broch_RevA.pdf

2. IR CCD camera for near infrared region

• Quantum efficiency in the interval of 900-2 300nm: 70%• Sensor size 2k x 2k, HgCdTe technology, class 1 • Pixel size: 15 µm• Dark current maximum: 0.01e- /pixel/sec• Readout noise: less than 20e- (rms)• 16 bit AD converter• Cooling with a Stirling engine to 70° K (-203° C) without the necessity of liquid Nitrogen use

Example: Teledyne Scientific (Manufacturer and supplier of detectors for the Hubble Space Telescope and the James Webb Space Telescope)

http://www.teledyne-si.com/infrared_visible_fpas/index.html

3. Spectrograph

Hihg-dispersion échelle spectrograph to the Nasmyth focus:

• R = 40 000 for seeing 3" • Spectral region: 400-760nm • CCD camera 2k x 2k• Calibration lamps for ThAr line spectrum and continuum light • Interchangeable slits (apertures) • Software for remote control of the spectrograph and its CCD camera

Manufacturer, contractor: Lasertechnik Berlin

Subcontractor: Hamburger Sternwarte

Thank you for your attention!

Price (incl. VAT):

• Telescope 1 030 000 €• Dome automatization 53 500 €• Spectrograph 480 000 € • CCD camera 340 000 €• IR CCD camera 590 000 €• Coating unit for the 130 cm mirror 280 000 €• Fiber optic cable from Poprad 124 000 €• Data storage devices 36 000 €• Diesel-electric generator 15 000 €

∑ 2 948 500 €

Sponsored by: European Regional Development Fund, 100%