An example primary header is shown below:
SIMPLE = T / file does conform to FITS standard BITPIX = 8 / number of bits per data pixel NAXIS = 0 / number of data axes EXTEND = T / FITS dataset may contain extensions COMMENT FITS (Flexible Image Transport System) format is defined in 'Astronomy COMMENT and Astrophysics', volume 376, page 359; bibcode: 2001A&A...376..359H ORIGIN = 'NRAO Green Bank' / INSTRUME= 'Holography' / device or program of origin GBTMCVER= 'integration' / telescope control software release FITSVER = '2.2 ' / FITS definition version for this device DATEBLD = 'DATEBLD goes here' / time program was linked SIMULATE= 1 / Is the instrument in simulate mode? DATE-OBS= '2008-03-19T00:00:04' / Manager parameter startTime TIMESYS = 'UTC ' / time scale specification for DATE-OBS TELESCOP= 'NRAO_GBT' / Green Bank Telescope (Robert C. Byrd 100m) OBJECT = '1800+7828' / Manager parameter source PROJID = 'TREG ' / Manager parameter projectId OBSID = 'unit_test' / Manager parameter scanId SCAN = 34 / Manager parameter scanNumber UTDATE = 54544 / MJD of start time UTCSTART= 3.600000000000E+00 / Start time CYCLETIM= 1.000000000000E-01 / Switching period in seconds CYCLES = 1 / Switching periods per Integration DURATION= 1.000000000000E-01 / Integration time TESTATTN= 5 / Test input attenuation db's (0-31) REFATTEN= 2 / Reference input attenuation db's (0-31) END
The primary header keywords for the holography backend FITS files are as follows:
The first four items are mandatory FITS keywords.
ORIGIN is a reserved FITS standard keyword.
INSTRUME is the FITS standard keyword used to specify the ``instrument'' responsible for producing the data in the file. This will be set to the string Holography for all holography FITS files.
GBTMCVER, FITSVER, DATEBLD, and SIMULATE are GBT-specific keywords.
GBTMCVER refers to the version of the M&C system in use at the time the file was created.
FITSVER refers to the version of the GBT FITS definition the file conforms to. The leading number refers to the global definition version (i.e. this document), while the trailing number refers to a revision specific to this specific type of FITS file. For example, a value of 2.5 in a Spectrometer FITS file would imply the fifth revision of the Spectrometer FITS file definition conforming to the second revision of the global GBT FITS standards.
DATEBLD is generated automatically via the Unix command ``date -u +whenever the program which actually writes the FITS file is linked.
SIMULATE specifies whether the program was running in simulation mode when the file was written.
DATE-OBS is the FITS standard keyword to specify the date and time of the start of an observation. As recommended in the standard, the UTC time scale is explicitly specified using the TIMESYS keyword. This time in GBT Device files represents the nominal scheduled time and is therefore represented only to the nearest second.
TELESCOP is a reserved FITS standard keyword.
OBJECT is the FITS standard, and PROJID, OBSID and SCAN pre-existing FITS keywords used to define these quantities, and so are used here. The corresponding GBT M&C base manager parameters are indicated in the comments.
The following are additional header keywords added for the holography manager:
UTDATE is the modified Julian Day (MJD) of the start of the observation.
UTCSTART is the number of seconds since midnight UTC of the start of the observation.
CYCLETIM is the duration of the sub-integration time, in seconds.
CYCLES is the integer number of sub-integrations accumulated before passing the data onto the manager. Therefore the typical integration time is CYCLETIM*CYCLES in seconds.
DURATION is the length in seconds of the each integration time. This should be equal to the cycletime times the number of cycles per integration.
TESTATTN is the amount of input attenuation of the main (i.e. GBT) signal input.
REFATTEN is the amount of input attenuation in db of the reference signal input.