SARG: the high resolution spectrograph

TL;DR

SARG is a high resolution spectrograph at TNG, capable of detailed spectral observations from 0.37 to 1 micrometer with resolutions up to 164,000, enabling precise radial velocity measurements and stable performance since 2000.

Contribution

This paper presents the design, capabilities, and initial performance results of the SARG spectrograph, highlighting its high resolution, spectral coverage, and stability features.

Findings

Achieved maximum resolution of R~164,000

Measured peak efficiency of about 13%

Radial velocity accuracy of ~5 m/s with iodine cell

Abstract

SARG is the high resolution spectrograph of TNG. It has been in operation since late spring 2000. SARG is a cross dispersed echelle spectrograph; it offers both single object and long slit (up to 26 arcsec) observing modes covering a spectral range from {\lambda}=0.37 up to 1 {\mu}m, with resolution ranging from R=29,000 up to R=164,000. Cross dispersion is provided by means of a selection of four grisms; interference filters may be used for the long slit mode (up to 26 arcsec). A dioptric camera images the cross dispersed spectra onto a mosaic of two 2048x4096 EEV CCDs (pixel size: 13.5 {\mu}m) allowing complete spectral coverage at all resolving power for {\AA} <0.8 {\mu}m. An iodine-absorbing cell allows to obtain high precision radial velocities. A Distributed Active Temperature Control System (DATCS) maintains constant the temperature of all spectrograph components at a preset value. Early results show that SARG works according to original specifications in terms of wavelength coverage, efficiency (measured peak efficiency is about 13%), resolution (maximum resolution R~164,000 using a 0.3 arcsec slit, R~144,000 using an image slicer), and stability (preliminary estimates of the radial velocity accuracy is ~5 m/s using the iodine cell and ~ 150 m/s without the cell).