Ra, Dec in fits headers
24sep04
The computation of the ra/dec J2000 for the fits headers
was modified on 16sep04. The new format stores the ra and dec J2000 for
each beam of the alfa array in crval2a, crval3a. The program is now interpolating
the value in scramnet memory (returned from the telescope) to better align
the header values with the data taken. It is also possible to compute
the ra,dec from the az,el value and the time stamp. The difference
between the ra/dec in the header and the ra/dec computed from the encoders
is shown in the plot below.
-
Fig 1. This is the Rafits-RaEnc for the 900 seconds of a drift scan. The
red line is the difference in the declination.
-
Fig 2. The step size in ra [asec/sec] for the fitRa values (black) and
the encRa values (red). The ra values from the header are jumping around
by about 2 arc seconds relative to the 15 Asec/sec of the sidereal drift.
The difference between the raEncoder and raFitsFile is jumping around by
about 2 arc seconds. The plot of the step size for each strip shows
that this jumping is coming from fits data and not the encoder values.
Since this was a drift scan, the step size should be constant at 15Asec/sec
(i did not multiply by the cosine of the declination).
The next step is to find the location of continuum
sources in the drift scan and see how the positions come out.
processing: x101/040924/chkRaDec_a194623sep04.pro
home_~phil