|Revisiting the Impact of Atmospheric Dispersion and Differential Refraction on MOS Observations: The Case of VLT/VIMOS
|507, Multi-Object Spectroscopy in the Next Decade: Big Questions, Large Surveys, and Wide Fields
|Sánchez-Janssen, R.; Mieske, S.; Selman, F.; VIMOS Instrument Operations Team
|We revisit the impact of atmospheric dispersion and differential refraction on the quality of VIMOS-MOS spectra through simulations of slit losses as a function of both target declination and slit orientation.
We show that, for fields culminating at zenith distances larger than 20 degrees, slit losses are minimized with slits oriented along the parallactic angle at the meridian. Conversely, for fields with zenith angles smaller than 20 degrees at culmination, losses are minimized with slits oriented perpendicular to the parallactic angle at the meridian; MOS observations can be effectively extended to plus/minus three hours from the meridian in these cases.
We establish general rules for the alignment of slits in MOS observations that increase target observability, enhance the efficiency of operations, and speed up the completion of programs.