Revisiting the impact of atmospheric dispersion and differential refraction on widefield multiobject spectroscopic observations: From VLT/VIMOS to next generation instruments

Download
  1. Get@NRC: Revisiting the impact of atmospheric dispersion and differential refraction on widefield multiobject spectroscopic observations: From VLT/VIMOS to next generation instruments (Opens in a new window)
DOIResolve DOI: http://doi.org/10.1051/0004-6361/201423459
AuthorSearch for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for: ; Search for:
TypeArticle
Journal titleAstronomy and Astrophysics
ISSN1432-0746
Volume566
Article numberA2
SubjectAtmospheric movements; Refraction; Scheduling; Surveys; Atmospheric dispersion; Atmospheric effects; Instrumentation: spectrographs; Methods:observational; Overall efficiency; Parallactic angle; Spectral distortions; Techniques: spectroscopic; Instruments
AbstractContext. Atmospheric dispersion and field differential refraction impose severe constraints on widefield, multiobject spectroscopic (MOS) observations, where the two joint effects cannot be continuously corrected. Flux reduction and spectral distortions must then be minimised by a careful planning of the observations, which is especially true for instruments that use slits instead of fibres. This is the case of VIMOS at the VLT, where MOS observations have been restricted, since the start of operations, to a narrow two-hour range from the meridian to minimise slit losses, the so-called two-hour angle rule. Aims. We revisit in detail the impact of atmospheric effects on the quality of VIMOS-MOS spectra with the aim of enhancing the instrument's overall efficiency, and improving the scheduling of observations. Methods. We model slit losses across the entire VIMOS field of view as a function of target declination. We explore two different slit orientations at the meridian: along the parallactic angle (north-south), and perpendicular to it (east-west). Results. We show that, for fields culminating at zenith distances larger than 20 degrees, slit losses are minimised with slits oriented along the parallactic angle at the meridian. The two-hour angle rule holds for these observations using north-south orientations. Conversely, for fields with zenith angles smaller than 20 degress at culmination, losses are minimised 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. In general, night-long observations of a single field will benefit from using the east-west orientation. All-sky or service mode observations, however, require a more elaborate planning that depends on the target declination, and the hour angle of the observations. Conclusions. We establish general rules for the alignment of slits in MOS observations that will increase target observability, enhance the efficiency of operations, and speed up the completion of programmes, a particularly relevant aspect for the forthcoming spectroscopic public surveys with VIMOS. Additionally, we briefly address the non-negligible impact of field differential refraction on future widefield MOS surveys. © ESO, 2014.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC); National Science Infrastructure
Peer reviewedYes
NRC publication
This is a non-NRC publication

"Non-NRC publications" are publications authored by NRC employees prior to their employment by NRC.

NPARC number21272317
Export citationExport as RIS
Report a correctionReport a correction
Record identifier645a79a9-33d8-4359-91f3-7cbc55bb6f7c
Record created2014-07-28
Record modified2016-05-09
Bookmark and share
  • Share this page with Facebook (Opens in a new window)
  • Share this page with Twitter (Opens in a new window)
  • Share this page with Google+ (Opens in a new window)
  • Share this page with Delicious (Opens in a new window)