STELES Description

Instrument Description

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General Description

Two channel, VPH cross dispersed echelle spectrograph
White pupil configuration
Bench mounted
Nasmyth focus, slit fed
Resolving power - 50.000 (3 - 2.5 pixel resolution) with a 0.8" slit. Higher resolution can be achieved with narrow slits.
Wavelength range - 3000 - 8900Å (blue arm 3000-5500Å, red arm 5300-8900Å )
CCDs - two 2x4k chips are foreseen, both with 15 micron pixels, one blue optimized and the other red optimized.
Fixed configuration: the bench mounted sub-assemblies of the spectrograph contain few remotely controlled moving components. This ensures reproducibility and stability of the instrument and a less expensive operation and maintenance.
On-line data reduction software will be available for fast analysis of the acquired data.

STELES main parameters

	STELES	Blue	Red
Wavelength range in one exposure	3000-8900Å	3000-5500Å	5300-8900Å
Resolving Power	50k	max. (80 k)	max. (67 k)
Slit Entrance Aperture (arcsec)	0.8"	min. (~0.5") - 2pix	min. (~0.6") - 2pix
Fore Optics Input/Output	F / 16 - F / 7.5
Spectrograph Beam Size	100 mm
Off-axis Collimators		F / 7.5	F / 7.5
Echelles	R4	41.67 gr/mm	31.6 gr/mm
Crossdisperser VPH		1200 l/mm	600l/mm
Dioptric Cameras		F / 3.0	F / 2.5

See detailed characteristics at the Conceptual design Document

Spectral Format

The blue channel spectrum format fits a 2x4k CCD (30.7mm wide, 61.4 mm high), with 71 orders. The red channel spectrum format fits a 4x2k CCD (61.4mm wide, 30.7mm high) with about 40 orders. The orders separations are expected to be in the range of 7 arcsec to 20 arcsec in the blue channel, and 7 arcsec to 19 arcsec in the red channel, allowing good sky subtraction for a 1 arcsec seeing spot. The spectral formats are presented in the Conceptual Design document.

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