Calibration data for VIMOS are taken for two purposes:

• assess the instrumental status
• calibrate SCIENCE data.

VIMOS calibration data are taken during daytime and during nigth-time, depending on the type of data. As of February 2010, only bias frames, calibrations needed to assess the instrument health, and calibrations for MOS spectro-photometric standard star observations are measured during daytime. Twilight sky flats, standard star fields, and spectro-photometric standards are taken during the night as part of the observatory calibration plan. Flat-fields and arc-lamp spectra needed to calibrate MOS and IFU science data are measured as attached calibrations directly after the corresponding science observation.

The pipeline supports all three VIMOS observing modes: imaging, MOS, and IFU. All offered settings for filters and grisms are pipeline-supported (with the exception of the MR grism in combination with the OS-blue filter). The reduction of Bezier (non-horizontal) slits in MOS masks is not supported.

The VIMOS data format is described here.

The following calibration data are taken as part of the VIMOS calibration plan and/or upon request by the user. Data types are identified by DPR keywords in FITS headers.

* N: typical number taken per night and setting
** note that bias/dark frames for imaging and MOS/IFU have different read-out modes

Complete overview of calibration files and recipes

Raw frame(s) recipe description product(s) [PRO.CATG header keywords] bias vmbias create a master bias from a set of input raw frames MASTER_BIAS dark vmdark create a master dark from a set of input raw frames MASTER_DARK screen flat vmimflatscreen create a master screen flat from a set of input raw frames IMG_MASTER_SCREEN_FLAT linearity   detmon_opt_lg calculate detector linearity and gain DET_LIN_INFO, GAIN_INFO twilight flat vmimflatsky create a master sky flat from a set of input raw frames IMG_MASTER_SKY_FLAT IMG std vmimstandard vmimcalphot reduce photometric standard star field and calculate zeropoint IMG_STANDARD_REDUCED, IMG_STAR_MATCH_TABLE, PHOTOMETRIC_TABLE MOS flat vmmoscalib (used since August 2010) combined recipe for flat-field and wavelength calibration frames; creates master flat and dispersion solution table MOS_MASTER_SCREEN_FLAT, MOS_DISP_COEFF, MOS_CURV_COEFF, MOS_SLIT_LOCATION MOS arc MOS flat vmspflat (used until May 2010) create a normalized master flat from a set of input raw frames MOS_MASTER_SCREEN_FLAT MOS arc vmspcaldisp (used until May 2010) determine inverse dispersion solution EXTRACT_TABLE MOS std vmmosscience (used since August 2010) reduce standard star observations, extract spectrum, determine response curve (same recipe as for MOS science data reduction) MOS_SPECPHOT_TABLE MOS std vmmosstandard (used until May 2010) reduce standard star observations, extract spectrum, determine response curve MOS_SPECPHOT_TABLE IFU flat vmifucalib identify fibre traces, determine relative fibre transmission, determine inverse dispersion solution IFU_IDS, IFU_TRACE, IFU_TRANSMISSION IFU arc IFU std vmifustandard reduce standard star observations, extract spectrum, determine response curve MOS_SPECPHOT_TABLE

Naming scheme

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

Description of naming scheme

CALIBRATION CASCADE

The processing of VIMOS 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.

The calibration cascade for imaging consists of:

1. create master bias
2. use master bias to create master sky flat
3. use master bias and master Flat to reduce photometric standard stars images and compute the night zeropoint
4. use master bias, master flat and night zeropoint to reduce science images.

1. create master bias
2. use master bias to create the master flat and to reduce the arc lamp frame; determine the wavelength solution
3. use master bias, master flat and inverse dispersion solution table to reduce the science frame (flux calibration is achieved by master response curves which have been averaged over several individual measurements).

1. create master bias
2. use master bias to processed flat and arc lamp exposure in one step which gives the three calibration tables for inverse dispersion solution, fiber transmission and fiber tracing
3. use master bias and the three calibration tables to reduce the science frame (flux calibration is achieved by master response curves which have been averaged over several individual measurements).

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 solution, but that specific solution is chosen which is closest in time.

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

VIMOS pipeline problems are documented on the Data Package page.

Static calibrations files like line lists are part of the pipeline installation and are also delivered within data packages. CCD tables (containing lists of bad pixels) for the old and new detectors may be downloaded here:

CCD tables for the old detectors (valid for data measured until May 2010): VIMOS_CCD_030101.tar

CCD tables for the new detectors (August 2010 and later): VIMOS_CCD_100801.tar