Translated Headers

The ORAC-DR infrastructure translates instrument metadata stored in FITS headers into internal headers. An internal header offers a common name, meaning, and units independent of the instrument, thereby makes most recipe code portable between instruments, and increases code reuse, a major theme of ORAC-DR. The internal headers are accessed through the ORAC::Frame::uhdr() and ORAC::Group::uhdr() methods (see Frame headers in SUN/233).

Below is a list of these translated internal headers and their meanings and units. Here are some notes pertaining to the table.

• In a primitive these header names have an ORAC_ prefix, for example, ORAC_DEC_SCALE.
• The abbreviations for data type are B: boolean, F: floating point, I: integer, and S: string. Of the floating point only the RA_BASE and DEC_BASE warrant double precision, but the recipes impose no restriction.
• Units are in brackets.
• Some headers retain instrument-specific values, like ORAC_SPEED until a common set of instrument-independent names is compiled.

Name	Type	Meaning
AIRMASS_START	F	Airmass at the start of the observation
AIRMASS_END	F	Airmass at the end of the observation
DEC_BASE	F	Declination (J2000) at reference position (and offset 0,0) [deg]
DEC_SCALE	F	Pixel scale along declination axis [arcsec]
DEC_TELESCOPE_OFFSET	F	Telescope declination offset with respect to the DEC_BASE position [arcsec]
DETECTOR_BIAS	F	Detector bias (only used by IRCAM) [V]
DETECTOR_MODE	S	Such as STARE, NDSTARE, CHOP
EQUINOX	F	Equinox of co-ordinates (fix at 2000.0) [y]
EXPOSURE_TIME	F	Exposure time for each co-add [s]
FILTER	S	Filter name
GAIN	F	Conversion factor [electrons/data number]
INSTRUMENT	S	Name of instrument such as IRCAM, UFTI, UIST Michelle, ISAAC but its use is deprecated
NUMBER_OF_EXPOSURES	I	Number of exposures in the integration
NUMBER_OF_OFFSETS	I	Number of jitter offset positions
NUMBER_OF_READS	I	Number of reads per exposure
OBJECT	S	Name of the object, preferably adhering to IAU standard
OBSERVATION_MODE	S	Operating mode of multi-mode instrument, imaging, spectroscopy, or ifu
OBSERVATION_NUMBER	I	Observation number (starting at 1 each night)
OBSERVATION_TYPE	S	BIAS, DARK, FLAT, LAMP, OBJECT, SKY
RA_BASE	F	Right Ascension (J2000) at reference position (and offset 0,0) [h]

RA_SCALE	F	Pixel scale along right-ascension axis [arcsec]
RA_TELESCOPE_OFFSET	F	Telescope right-ascension offset with respect to the RA_BASE position [arcsec]
READMODE	S	Such as STARE, NDSTARE, CHOP
ROTATION	F	Angle of the Declination axis with respect to the frame's y axis measured counter clockwise.
SPEED_GAIN	S	Speed and type of readout, e.g. Normal, Fast, Higain for UFTI; Standard, Fast, Deepwell for IRCAM.
TELESCOPE	S	The SLALIB SLA_OBS telescope name
STANDARD	B	Whether or not the observation is of a standard
UTDATE	S	UT date of the observation in yyyymmdd format
UTEND	F	UT of the end of the observation [h]
UTSTART	F	UT of the start of the observation [h]
WAVEPLATE_ANGLE	F	Polarimetry waveplate position angle [deg]
X_LOWER_BOUND	I	Start column of array readout
X_REFERENCE_PIXEL	F	The pixel index of the x reference position for RA_BASE and DEC_BASE
X_UPPER_BOUND	I	End column of array readout
Y_LOWER_BOUND	I	Start row of array readout
Y_REFERENCE_PIXEL	F	The pixel index of the y reference position for RA_BASE and DEC_BASE
Y_UPPER_BOUND	I	End row of array readout