[daip] problem with velocity definition in headers
Lynn D. Matthews
lmatthew at cfa.harvard.edu
Fri Feb 22 17:04:49 EST 2008
I have some GBT maps that I've converted to fits and imported into AIPS
using UVLOD (or FITLD). However, I'm having a minor problem in that AIPS
does not want seem to want to properly convert between frequency and LSR
velocity. Regardless of the velocity range of the input spectrum, the
header always lists:
Alt ref. value 0.00000E+00 wrt pixel 0.00
And then programs such as POSSM interpret the edge of the spectrum to be
V_LSR=0 km/s. I can doctor this each time, but is there some reason this
is not being interpreted correctly by UVLOD/FITLD? I think the fits header
is okay, since other software is able to interpret the velocities
correctly. A sample full aips header is appended below, and I've included
as an attachment the fits header.
Lynn
AIPS 1: Image=XHer (UV) Filename=XHer .SCANS . 1
AIPS 1: Telescope=NRAO_GBT Receiver=Rcvr1_2
AIPS 1: Observer=Lynn Mat User #= 2086
AIPS 1: Observ. date=21-FEB-2008 Map date=21-FEB-2008
AIPS 1: # visibilities 361 Sort order TB
AIPS 1: Rand axes: RA DEC BEAM TIME1 WEIGHT SCALE
AIPS 1: ----------------------------------------------------------------
AIPS 1: Type Pixels Coord value at Pixel Coord incr Rotat
AIPS 1: COMPLEX 1 1.0000000E+00 1.00 1.0000000E+00 0.00
AIPS 1: STOKES 2 -1.0000000E+00 1.00 -1.0000000E+00 0.00
AIPS 1: FREQ 231 1.4207529E+09 169.40 3.8143257E+03 0.00
AIPS 1: RA 1 16 02 38.095 1.00 3600.000 0.00
AIPS 1: DEC 1 47 14 30.458 1.00 3600.000 0.00
AIPS 1: ----------------------------------------------------------------
AIPS 1: Coordinate equinox 2000.00
AIPS 1: Rest freq 1420.406 Vel type: RADIO wrt LSR
AIPS 1: Alt ref. value 0.00000E+00 wrt pixel 0.00
AIPS 1: Maximum version number of extension files of type HI is 1
-------------- next part --------------
No bad pixels, min=0., max=0. (old)
Line storage mode, physdim [0], length of user area 3281 s.u.
Created Tue 00:00:00 01-Jan-1980, Last modified Tue 00:00:00 01-Jan-1980
Pixel file "tet_vel2_uv.fits" [NO PIXEL FILE]
EXTEND = T / FITS dataset may contain extensions
GROUPS = T / random group records are present
PCOUNT = 4 / number of random group parameters
GCOUNT = 361 / number of random groups
COMMENT FITS (Flexible Image Transport System) format defined in Astronomy and
COMMENT Astrophysics Supplement Series v44/p363, v44/p371, v73/p359, v73/p365.
COMMENT Contact the NASA Science Office of Standards and Technology for the
COMMENT FITS Definition document #100 and other FITS information.
BZERO = 0.00000000000000E+00 / Zero Level
BSCALE = 1.00000000000000E+00 / Scale value
SITELAT = 38.43312 / GBT location and pointing data
SITELONG= -79.83983 / GBT location and pointing data
SITEELEV= 824.595 / GBT location and pointing data
LPC_AZ1 = 0. / GBT location and pointing data
LPC_AZ2 = 0. / GBT location and pointing data
LPC_EL = 0. / GBT location and pointing data
ORIGIN = 'NRAO, Green Bank' / WV 24944 304-456-2011
TELESCOP= 'NRAO_GBT' / Robert C. Byrd
BUNIT = 'Ta ' / Kelvins/Beam
CTYPE2 = 'COMPLEX ' / Signal, Baseline, Weight
CRVAL2 = 1.
CDELT2 = 1.
CRPIX2 = 1.
CROTA2 = 0.
CTYPE3 = 'STOKES ' / X, Y or R, L/
CRVAL3 = -1.
CDELT3 = -1.
CRPIX3 = 1.
CROTA3 = 0.
CTYPE4 = 'FREQ ' / frequency in LSR frame
VELREF = 257 / 1 LSR, 2 HEL, 3 OBS, +256 Radio
RESTFREQ= 1420405800.
BANDWIDT= 1907162.84246738
CRVAL4 = 1420752899.25872
CDELT4 = 3814.32568493475
CRPIX4 = 439.4
CROTA4 = 0.
CDELT5 = 1.
CRPIX5 = 1.
CROTA5 = 0.
CTYPE5 = 'RA ' / Right Ascension
CTYPE6 = 'DEC ' / Declination
CDELT6 = 1.
CRPIX6 = 1.
CROTA6 = 0.
CDELT6 = 1.
CRPIX6 = 1.
CROTA6 = 0.
EPOCH = 2000. / RA Dec reference epoch
PTYPE1 = 'RA ' / RA in Degrees
PSCAL1 = 57.2957795130823 / Unit conversion factor
PZERO1 = 0. / Unit conversion factor
PTYPE2 = 'DEC ' / Declination in Degrees
PSCAL2 = 57.2957795130823 / Unit conversion factor
PZERO2 = 0. / Unit zero value
PTYPE3 = 'BEAM ' / point number*256 + Scan
PSCAL3 = 1. / Unit conversion factor
PZERO3 = 0. / Unit zero value
PTYPE4 = 'DATE ' / Date+time in Julian date (days)
PSCAL4 = 1. / Unit conversion factor
PZERO4 = 2454517.5 / Unit zero value
OBJECT = 'XHer ' / DistantCreation
IMCLASS = 'SCANS ' / WV 24944 304-456-2011
IMNAME = 'XHer ' / WV 24944 304-456-2011
SORTORD = 'TB ' / Data time sorted for efficiency
DATE-OBS= '21/02/08' / UTC Date of observation
SCAN = 8 / GBT M&C Scan Number
OBSERVER= 'Lynn Matthews' / Student of the Universe
PROJID = 'AGBT08A_032_01' / Student of the Universe
INSTRUME= 'Rcvr1_2 ' / Front End
REFRACT = 0. / Refraction model (deg)
DAZMODEL= 0. / Azimuth offset (deg) at reference pos.
DELMODEL= 0. / Elevation offset (deg) at reference pos.
COORDTYP= 'J2000 ' / Coordiante Type
CRVAL5 = 240.658727893079 / Right Ascension of Center
CRVAL6 = 47.24179384729 / Declination of Center
HISTORY SORTORD = 'TB ' / Data time sorted
HISTORY AIPS SORT ORDER = 'TB'
HISTORY UVSRT SORT = 'TB' / New sort order
HISTORY Rcvr1_2 Spectrometer SAMPLER=A13 SIDE=U SIG=T CAL=F
HISTORY writeSdfits 4.0 / Glen Langston, NRAO GB
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