FITS is a MIRIAD task, which converts image and uv files both from FITS to Miriad format, and from Miriad to FITS format. Note that because there is not a perfect correspondence between all information in a FITS and Miriad file, some information may be lost in the conversion step. This is particularly true for uv files.
WARNING: When writing uv FITS files, fits can only handle single source, single frequency band, single array configuration. Minimal checks are made to see that these restrictions are observed!
"uvin" Convert FITS uv file to Miriad uv file. "uvout" Convert Miriad uv file to FITS uv file. "xyin" Convert FITS image file to Miriad image file. "xyout" Convert Miriad image file to FITS image file. "print" Print out a FITS header.There is no default.
"Linetype" is either "channel", "wide" or "velocity". "Nchan" is the number of channels in the output.
compress Store the data in compressed uv format. nochi Assume that the parallactic angle of the telescope is a constant 0 (or that the data are from circularly polarised feeds and have already been corrected for parallactic angle). nolefty Assume that the FITS antenna table uses a right-handed coordinate system (rather than the WSRT left-handed system).
These options for op=uvout only.
nocal Do not apply the gains table to the data. nopol Do not apply the polarization leakage table to the data. nopass Do not apply the bandpass table correctsions to the data.
This option applies for op=xyin only.
dss Use the conventions of Digital Sky Survey FITS files, and convert (partially!) its header. nod2 Use the conventions of NOD2 FITS files.
Within each line visibility data-set, Miriad stores the velocity of the observatory wrt a rest frame. This allows account to be taken of this when determining channel velocities.
The fits task will determine the observatory velocity either by being given a velocity at a given channel (wrt a rest frame) or by using a model of Earth and solar system motion (accurate to 0.005km/s).
The "velocity" parameter can be used to specify the velocity of a particular channel. The parameter consists of three values: the velocity system of the reference value, the reference value and the reference channel, viz:
velocity=velsys,refval,refchanPossible values for the velocity system are:
lsr Velocity is the radio definition wrt the LSR frame. bary Velocity is the radio definition wrt the barycenter. optlsr Velocity is the optical definition wrt the LSR frame. optbary Velocity is the optical definition wrt the barycenter. obs Velocity wrt the observatory.The reference value gives the velocity, at the reference channel, in km/s. If the reference value and reference channel are omitted, a model of Earth and solar system motion is used to determine the appropriate information.
velocity=lsr,30,1indicates that the first channel has radio LSR velocity of 30 km/s. The observatory velocity, relative to LSR, can then be computed.
velocity=lsrindicates that fits is to determine the observatory velocity wrt the LSR frame using an appropriate model.