Subject: 3D fits files ?

From: svec5 at menudo.uh.edu (T.C. Zhao)
Date: 22 Mar 1994 02:17:55 -0600

Hi,
Can someone tell me an ftp site where I can find some fits
files with NAXIS=3 ? floating point/double data would be
nice.

Thanks in advance.
-- 
T.C. - Starving Physicist

---

From: dwells at nrao.edu (Don Wells)
Date: Tue, 22 Mar 1994 17:42:36 GMT

In article <2mm9jj$kkq at menudo.uh.edu> svec5 at menudo.uh.edu (T.C. Zhao) writes:
     ".. ftp site.. fits files with NAXIS=3.."

    ftp://fits.cv.nrao.edu/fits/sampledata/cubes/ngc6503.fits

This is an 8.2 Mbyte file. Some relevant header lines are:

BITPIX  =                  -32 /
NAXIS   =                    4 /
NAXIS1  =                  256 /
NAXIS2  =                  256 /
NAXIS3  =                   31 /
NAXIS4  =                    1 /
OBJECT  = 'NGC6503 '
OBSERVER= 'WELL    '
DATE-OBS= '12/04/83'
DATE-MAP= '20/09/84'
BUNIT   = 'JY/BEAM '
DATAMAX =      2.953770570E-02 /MAX PIXEL VALUE
DATAMIN =     -1.367387734E-02 /MIN PIXEL VALUE
CTYPE1  = 'RA---SIN'
CTYPE2  = 'DEC--SIN'
CTYPE3  = 'FELO-HEL'
CRVAL3  =    2.60000000000E+04 /
CDELT3  =     -1.030761914E+04 /
CRPIX3  =      1.600000000E+01 /
CROTA3  =      0.000000000E+00 /
CTYPE4  = 'STOKES  '
CRVAL4  =    1.00000000000E+00 /

This 21cm cube is a *textbook case* of a spiral galaxy rotation curve.
NGC 6503 is a normal spiral galaxy with morphological type SA(s)cd.
The VLA observation was by me 11 years ago. It used 21 antennas in C
array, 32 channels with 48 KHz (10 km/s) spacing. Exposure time on the
galaxy was about 2 hours. The VLA has much better receivers today, and
27 antennas could now be used for such a spectral line observation.

The pixels are 32-bit IEEE floating point, ranging from -13 to +29
milli-Janskys per beam. This is a 4-dimensional matrix (NAXIS=4), but
the 4th axis (of type 'STOKES') has only one pixel.  The third axis
has 31 pixels, and they are expressed in heliocentric velocity evenly
spaced in frequency (that is what 'FELO-HEL' means). Pixel 16 (the
central channel of the spectra) has a velocity of 26 km/s (26000 m/s),
and the channel spacing is -10.3 km/s. The 26 km/s was the book value
for the redshift of 6503 ten years ago; NED (IPAC's extragalactic
database) says the current book value is "Helio. radial vel. : 44 +/-
3 km/s".

This is a fun piece of data, suitable for movie-loops and 3-D
visualization systems like AVS. Enjoy!
--
  Donald C. Wells         Associate Scientist         dwells at nrao.edu
                    http://fits.cv.nrao.edu/~dwells
  National Radio Astronomy Observatory                +1-804-296-0277
  520 Edgemont Road,   Charlottesville, Virginia       22903-2475 USA