There are a number of internal headers that ORAC primitives rely on to correctly reduce data. These headers are retrieved from the files and translated to be used by oracdr. These headers can be used in recipes through the ORAC::Frame::uhdr() method and prepending ORAC_ to each header. For example, to refer to the INSTRUMENT header in a primitive, you would use
my $Frm = new ORAC::Frame('filename.sdf');
my $instrument = $Frm->uhdr('ORAC_INSTRUMENT');
New internal headers can always be created, if necessary, to define some ancillary data needed by a recipe, in an instrument-independent fashion.
The following headers currently exist. Note that not all headers are defined for each instrument or recipe.
Airmass at start of the observation (for a mosaic) or integration (for a raw frame).
Airmass at end of the observation (for a mosaic) or integration (for a raw frame).
Position angle of the chop (in degrees).
Throw of the chop with respect to the middle position (in arcseconds).
Configuration index. Increments when an instrument's hardware configuration changes.
Declination (ORAC_EQUINOX equinox) at the reference position at zero offset (in degrees). The reference position is normally at the array centre, but may be displaced, for example, to avoid the intersections of abutted detector sub-arrays.
Pixel increment along declination axis (in arcsec).
Telescope declination offset with respect to the base position given by DEC_BASE (in arcseconds).
Detector bias voltage (in volts)
Position number in detector scan.
Observing mode, such as STARE, NDSTARE, CHOP.
Equinox of object position (in years). It should be 2000.
Integration time per exposure (in seconds).
Combined filter name.
Detector gain (in electrons/ADU).
Grating dispersion (in microns/pixel).
Grating name.
Grating order.
Grating wavelength (in microns).
Instrument name.
Number of scan positions in scan.
Number of exposures in integration.
Number of jitter offset positions in an observation.
Number of reads per exposure.
Object name from telescope.
Camera mode, such as imaging or spectroscopy. Used for multi-mode instruments like Michelle.
Observation number. Observation numbers normally commence at 1 for each night.
Observation type. Used to determine whether observation is of the OBJECT, DARK, or ARC, for example.
Whether or not polarimetry observations are being done. True (1) if so, false (0) otherwise.
Right Ascension (ORAC_EQUINOX equinox) at the reference position at zero offset (in degrees). See DEC_SCALE.
Pixel increment along right-ascension axis (in arcsec).
Telescope right-ascension offset with respect to the base position given by RA_BASE (in arcseconds).
Angle of declination axis with respect to the second (y) axis, measured counterclockwise (in degrees).
Increment between scan positions (in pixels).
Position angle of slit (in degrees)
Name of slit.
Readout speed. The default is Normal.
Is the target a standard-star observation?
UTC date when the observation was made.
End time of integration (for raw data) or the observation (for a mosaic).
Start time of integration (for raw data) or the observation (for a mosaic).
Polarimeter waveplate position angle (in degrees).
Number of detectors in a readout column (in pixels).
Number of detectors in a readout row (in pixels).
Start column of array readout.
End column of array readout.
Start row of array readout.
End row of array readout.
ORAC-DR -- Programmer's Guide