CALIBRATION DATA: GENERAL

Calibration data are taken for two purposes:

• to calibrate SCIENCE data
• to measure and control the instrumental status

GIRAFFE calibration data are mostly taken as daytime calibrations. Flux standard stars and nasmyth screen flats are taken, as part of the calibration plan, for Argus data.

On request by the user, also nighttime calibrations can be obtained as part of the Observing Block which generates the SCIENCE data ("attached calibrations"). Furthermore simultaneous arclamp calibration is available, upon request, by feeding some fibres with light from the simultaneous calibration unit (SCIENCE data taken in SimCal mode).

Find information about the GIRAFFE data format, spectral format and the detector here.

The following calibration data are taken as part of the daily GIRAFFE calibration plan. The data types are identified by the DPR TYPE keyword in the FITS headers.

frame DPR.CATG DPR.TYPE DPR.TECH purpose N* FITS headers details more examples BIAS CALIB BIAS IMAGE detector status, bias level 5 bias.hdr   DARK CALIB DARK IMAGE dark current (old and new CCD); CCD glow (old CCD only) 3 dark.hdr     FLAT (robotic, taken with the calibration lamp on the robot arm; this is the regular flat) CALIB LAMP,FLAT MOS (for Medusa) or IFU (for IFU and Argus) signal localization and extraction; fix-pattern noise, fringing 3 flat.hdr more ... FLAT (taken with the nasmyth screen illuminated; this is the 'attached' flat taken during the night, useful for Argus mode because of better illumination) CALIB LAMP,FLAT,NASMYTH MOS (for Medusa) or IFU (for IFU and Argus) same as FLAT 3 nflat.hdr [nasmyth flats look like robotic flats]   IMAGE FLAT CALIB LAMP,FLAT,DETCHECK IMAGE detector monitoring 40 iflat.hdr     ARC-LAMP CALIB LAMP,WAVE MOS (for Medusa) or IFU (for IFU and Argus) dispersion relation, wavelength calibration, resolution monitoring 1 wave.hdr more ... STD (flux standard star, taken for Argus data) CALIB STD IFU (argus) relative flux calibration 1 std.hdr

* N: typical number taken per night and setting

The ARC-LAMP and FLAT frames split into five fibre system (MEDUSA1/2; IFU1/2; Argus). They also split into two different gratings (HR and LR) with a set of standard wavelengths (which are listed here).

BIAS frames are taken in unbinned (1x1) mode, normal or low gain (fast read mode).

The flux STD data are regularly taken for the Argus and IFU settings.

In addition, DARK frames are taken about monthly, to monitor the dark current level.

A series of about 40 IMAGE FLATs is also taken roughly once per month, to monitor the status of the detector. They come in pairs with exposure times increasing from 0 to about 280 sec (saturation). Both types of data are not required for science reduction.

Complete overview of calibration files and recipes

* used for processing of science files between 2007-10 (before that date the pipeline did not correct for dark structure) and 2008-03 (after that date, with the new CCD, there was no need for correction).
** for STD_ARG data ony; for STD_IFU data, no instrument response is produced.

Naming scheme

After production and certification, the calibration products are renamed with a user-friendly scheme which includes type, creation date and relevant setting parameters.

Description of naming scheme

The processing of GIRAFFE calibration frames requires a cascaded scheme where the mutual dependencies of products and raw frames are respected. The proper sequence of all these production steps is called the calibration cascade. It is described here.

Within that cascade, all products are checked with respect to their quality and their relationship in time. This means e.g. that a dispersion solution is not only generated using an arbitrary quality-checked localization solution, but that specific solution is chosen which is closest in time.

All products created by QC Garching follow the calibration cascade. On contrary, Paranal-processed science data never use the up-to-date calibration products but standard solutions manufactured by QC Garching and possibly several months old.

The following static calibration tables (the ones not being regularly processed from raw calibration data) are required for GIRAFFE data processing:

• the emission line table
• the grating tables (one for each grating: HR = high-resolution and LR = low-resolution)
• the slit geometry tables (one for each setup). They provide the fine-tuning of the dispersion solution, after the physical model has been applied.

They come as FITS tables (extension tfits). They are part of the data packages for GIRAFFE data, and they are also delivered through the calSelector archive service.

The static tables can be downloaded as gzipped tar file here [848 kB, created in April 2005].

TABLE NAME PRO_CATG PURPOSE GI_GRAT_040813A_HR_grating.fits [old name: grating_HR316.tfits] GRATING_DATA grating table: definition of setups per grating; high resolution grating (316 lines/mm) GI_GRAT_030412A_LR_grating.fits [old name: grating_LR600.tfits] low resolution grating (600 lines/mm) GI_GCAT_040421A_line_catalog.fits [old name: lcatalog_ThAr.tfits] LINE_CATALOG Thorium argon line table: wavelengths, identifications and fluxes used for wavelength calibration GI_GSGS_041207A_Medusa1_H379.0nm_o15.fits [old name: slitgeometry_medusa1_H379.0_o15.tfits] SLIT_GEOMETRY_SETUP (before 2005-04: SLIT_GEOMETRY) slit geometry table: describes fibre and button parameters per slit GI_GDIS_030610A_Medusa2_H737.nm_o8.fits REFERENCE_DISP_SOLUTION reference dispersion solution, used by the pipeline as starting point for fine-tuned solution GI_GMSK_050327A_H572.8nm_o10.fits LINE_MASK table with initial guesses for emission lines GI_GFLX_021231A_flux_standards.fits FLUX_STANDARDS list of flux standards (identical to UVES list) GI_GATM_021231A_atm_extinction.fits ATMOSPHERIC_EXTINCTION table with extinction

ACTUAL PROBLEMS AND ISSUES

Since December 2005, all but three setups are pipeline-supported (detailed overview here). Data packages delivered before that date may have received only raw data, especially in case the IFU settings have been used.