EFOSC2

ESO Faint Object Spectrograph and Camera

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The 3.6m Telescope

Adaptor

Weather Condition limits

Image Quality

Basic Parameters

Telescope

Mounting	Equatorial, Horseshoe
M1 Diameter	3.566 m
Cassegrain Hole diameter	0.698 m
M1 clear area	8.8564 sq. m
M2 diameter	1.200 m
Focal Ratio (for EFOSC2)	f / 8.09
Scale at Focal Plane	7.12 arcsec/mm
Pointing Accuracy	10 arcsec

Auto Guider

Detector	Technical CCD
Dynamical Range	0 - 4096 ADU
Magnitude Range	10 - 14 mag
Accuracy	< 0.1 arcsec (rms)

Adaptor

Rotation Range	0 - 360 degrees
Default position	270 degrees -> north to the top and east to the left on the CCD -> spectroscopic slit at position angle 90 degrees on the sky
Accuracy	0.1 degree
Rotation Speed	1.2 degree / second

Pointing Limit

See the telescope web info.

Note :

The dome hatch #2 has to be brought down when observing within 5 degrees of the zenith - otherwise it could result in significant vignetting
The dome hatch #1 has to be raised when observing at very low elevations to avoid vignetting.

Pointing Accuracy

See the telescope web info.

It must also be noted that there is a bad column close to the centre of the CCD and the target may fall on it. Thus to be safe, especially for long integrations it would be more appropriate to spend a couple of extra minutes taking a MoveToPixel target acquisition image rather than save those extra minutes with a simple Preset acquisition.
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Tracking & Guiding

The AutoGuider keeps the telescope tracking accurate to about 0.1 arcsec in both RA and DEC. On the few occasions when autoguiding is not possible, either because suitable stars are absent or because the observing strategy demands it, one will have to live with the telescope wander of 1 arcsec. Spectroscopy will not be possible
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Focus

The positioning accuracy of the secondary mirror (M2) is about 10 focus encoder units. Thus the telescope has to be refocussed each time the focus changes by this amount. The focus changes by about 10 units when

the telescope moves by more than 15 degrees from the previous pointing either because of a change in target or because of change in zenith-distance of the same source OR
the Serrurier temperature changed by more than 1 degree.

Focussing may be done either by setting the Focus Flag to True in an acquisition template or by explicitly executing one of the following templates : FocusWithWedge or FocusSequence. FocusWithWedge is used normally as it is faster. The focus sequence may be difficult to use in a crowded field. However it displays a plot of the PSF size v/s Focus value and so the best focus position determined by the template can be checked visually for deviant points which could vitiate the result.
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Weather Condition Limits

Weather conditions at the 3.6m telescope may be significantly different from those reported by the MeteoMonitor because the sensor tower is near the old 1mt ESO telescope.

3p6 Local conditions are shown on the sciops3p6Telemetry panel. Then with these measurement just follow the:

LaSilla Weather Conditions rules
and the weather officer actions defined on the Sciops Operation Plan section 3.1.4

Image Quality

The image quality is dependent on several factors including the site characteristics, the instrument, telescope optics and its tracking. These factors, plots of the observed image quality and tips to improve it are discussed here.

Send comments to : ls-spectro

Last modified: Sun Nov 18 04:35:13 CLST 2001