[ ESO ]
VIMOS:
calibration data

CAL | HC | refs | QC
QUALITY CONTROL
    HOME
VIMOS QC
Trending & QC1
Pipeline
Data Package
Data Management
QC links:
VIMOS CALIBRATION DATA: GENERAL

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.

TYPES OF RAW CALIBRATION DATA

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.

mode frame DPR.CATG DPR.TYPE DPR.TECH purpose N*
detector calibrations bias** CALIB BIAS IMAGE detector status, bias level, RON 5
dark** CALIB DARK IMAGE dark current 3
screen flat CALIB FLAT,LAMP IMAGE gain, lamp efficiency 5
detector linearity CALIB BIAS,DETCHECK
FLAT,LAMP,DETCHECK
IMAGE detector non-linearity, gain >=35
IMG twilight flat
CALIB FLAT,SKY
IMAGE gain variations from pixel to pixel, illumination correction variable
photometric standard star field
CALIB STD IMAGE zeropoints >=4
MOS spectroscopic flat CALIB FLAT,LAMP MOS fixed-pattern noise, fringing 3-5
arc lamp CALIB WAVE,LAMP MOS dispersion solution 1
spectroscopic standard CALIB STD MOS flux calibration 1
IFU spectroscopic flat CALIB FLAT,LAMP IFU fixed-pattern noise, fringing 5
arc lamp CALIB WAVE,LAMP IFU dispersion solution 1
spectroscopic standard CALIB STD IFU flux calibration 1

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

CALIBRATION PRODUCTS

Complete overview of calibration files and recipes

Raw frame(s) recipe description product(s) [PRO.CATG header keywords]
bias [bias_th.gif 3K] vmbias create a master bias from a set of input raw frames MASTER_BIAS
dark [dark_th.gif 3K] vmdark create a master dark from a set of input raw frames MASTER_DARK
screen flat [fmt_th1.gif, 2K] 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 [fmt_th1.gif, 2K] vmimflatsky create a master sky flat from a set of input raw frames IMG_MASTER_SKY_FLAT
IMG std [fmt_th1.gif, 2K]

vmimstandard

vmimcalphot

reduce photometric standard star field and calculate zeropoint IMG_STANDARD_REDUCED,
IMG_STAR_MATCH_TABLE,
PHOTOMETRIC_TABLE
MOS flat [mosflatraw.gif 2K] 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 [std_th.gif 2K]
MOS flat [mosflatraw.gif 2K] vmspflat (used until May 2010) create a normalized master flat from a set of input raw frames MOS_MASTER_SCREEN_FLAT
MOS arc [std_th.gif 2K] vmspcaldisp (used until May 2010) determine inverse dispersion solution EXTRACT_TABLE
MOS std [mosstd.gif 2K] 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 [mosstd.gif 2K] vmmosstandard (used until May 2010) reduce standard star observations, extract spectrum, determine response curve MOS_SPECPHOT_TABLE
IFU flat [std_th.gif 2K] vmifucalib identify fibre traces, determine relative fibre transmission, determine inverse dispersion solution IFU_IDS,
IFU_TRACE,
IFU_TRANSMISSION
IFU arc [std_th.gif 2K]
IFU std [std_th.gif 2K] 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.
The calibration cascade for MOS consists of:
  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).
The calibration cascade for IFU consists of:
  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.

PROBLEMS AND ISSUES

VIMOS pipeline problems are documented on the Data Package page.

STATIC CALIBRATION FILES

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:

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

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


 
[ESO][Index][Search][Help][News]