Asiago 1.82m telescope

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The Asiago 1.82m telescope, operated by the National Institute of Astrophysics (INAF), is located 1375 meters above the sea-level in the pre-Alps (longitude E11° 34' 08.4" — latitude 45° 50' 54.9"), opened in 1973, has a classic Cassegrain design on a fork mount, and several focus stations are available (Cassegrain, Naismith, Coude). It is operated only remotely (with site staff for maintenance). The telescope has unobstructed access to any position on the sky, with a limit of 20deg on the height above the local horizon (which permits reaching -24deg in declination on the meridian) and no within-fork pointing allowed.

A REOSC Echelle spectrograph is mounted at the Cassegrain focus for about 10 nights around each Full Moon; it can be rotated to any angle, with the slit usually oriented along the parallactic angle for optimal flux calibration. The Echelle grating is an R2 79 ln/mm, and the cross-dispersion is achieved by a 300 ln/mm reflection grating (blazed to 5000 Ang). A filter can be inserted to choose 1st or 2nd order at wavelengths of overlap.

The slit can be widened continuously from 100micron to 1mm (usually set at 200micron). The slit is viewed by a high-sensitivity TV camera, which allows both on-slit and off-slit auto-guiding. A resolving power of 20,000 is obtained with a 200micron slit width, and 27,000 by closing it to 100micron which is a fair match to the 1.0 arcsec seeing that the telescope enjoys on good nights when the atmosphere is steady.

The CCD camera is an ANDOR DW436-BV with an CCD42-40 AIMO back illuminated chip, with an active pixel matrix 2048x2048 (2100x2100 including overs-can) corresponding to 27.6 x 27.6 mm, pixel size 13.5x13.5 micron, Peltier cooled to -75 °C (absolute), readout noise 3 e- rms, gain 1.9 e-/ADU, and a dark current (@-75°C) 0.001e-/pix/sec. The chip size allows to cover the normal operating range of 3525-7360 Ang without gaps in wavelength among the 32 Echelle orders.

Low and high intensity beams illuminating a dome screen are used for flat-fielding, while for wavelength calibration a Thorium lamp is adopted. A pre-slit decker allows to select the length of the long-slit, with 25arcsec avoiding overlap of adjacent orders.