Calibration data for VISIR are taken for two purposes:

• assess the instrumental status
• calibrate SCIENCE data.

VISIR calibration data are taken at night (e.g. standard star observations) and as daytime calibrations. On request of the user, also nighttime calibrations can be obtained as part of the Observing Block which generates the SCIENCE data ("attached calibrations"). Since the beginning of operations all the daytime calibrations have only been used to monitor health of the instrument.

All calibration data taken in VISIR are processed by QC Garching to obtain calibration solutions. These solutions come as

• calibration product fits file frames (e.g. standard star imaging frames)
• calibration product fits tables (e.g. spectrum extracted in a form of a table)

The VISIR data format is described here.

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

Complete overview of calibration files and recipes

Raw frame(s) recipe description product(s) [PRO.CATG header keywords] dark visir_img_dark creates a master dark from a set of input raw frames of the imaging detector IMG_DARK_AVG dark visir_img_dark creates a master dark from a set of input raw frames of the spectroscopic detector SPEC_DARK_AVG flat field visir_img_ff creates a master flatfield for the imaging detector from a set of 7 input raw frames taken at different temp. of the WarmCalibrationUnit IMG_FF IMG_BPM IMG std visir_img_phot determines sensitivity, background, conversion factor, instrumental response, observing conditions, etc. IMG_PHOT_COMBINED IMG_PHOT_CONTRIB_MAP SPEC LR/MR/HR-slit std visir_spc_phot determines sensitivity, background and conversion factor as a function of wavelength, instrumental response, observing conditions, sky spectrum, etc. SPC_PHOT_COMBINED SPC_PHOT_TAB SPC_PHOT_WEIGHT SPEC ECHELLE std visir_spc_phot_ech determines sensitivity, background and conversion factor as a function of wavelength, instrumental response, observing conditions, sky spectrum, etc. SPC_PHOT_HRG_COMBINED SPC_PHOT_HRG_TAB SPC_PHOT_HRG_WEIGHT

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

At present, all sets of VISIR calibration frames are reduced independently, i.e. there is no calibration cascade. In the future the flatfield correction may be included. It's still under investigation.

VISIR pipeline limitations/problems are documented on the Data Package page.

Static calibrations include:

• catalog of imaging standard stars (PRO.CATG=IMG_STD_CATALOG)
• catalog of spectroscopic standard stars (PRO.CATG=SPEC_STD_CATALOG)
• reference arc line table (PRO.CATG=SPEC_CAL_LINES)
• quantum efficiency map (PRO.CATG=SPEC_CAL_QEFF)