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ccdsky - lazy (cosmology) sky scaling calculator
ccdsky is a lazy sky scaling calculator. It will give you the
scaling parameters for a FITS file (which uses degrees for angles, and
m/s for velocities), to make your typical observer or astronomical software
package happy and print out values in units observers can be in awe about.
It is also useful to remind yourself how many arcseconds/minutes a given
object is at a given distance.
Although you can transform an image/cube,
the default only needs to know the distance (in AU, pc, kpc, mpc, z, ...)
and unit size (in AU, pc, kpc, mpc, ....) of the object. This will give you
the scaling factors for length and velocities.
When the distance is given
in z, Wright’s (2006) cosmology calculator is used.
parameters are recognized in any order if the keyword is also given:
Viewing a model
at a distance 1 pc, where 1 length unit represents 1 AU, the coordinates
need to be multiplied by 0.000277785 in order for FITS to view them in the
correct angular size of 1 arcsec.
- Optional input image file. Must be in image(5NEMO)
- Output image
file, only required if an input image is given. Will be in image(5NEMO)
format, with optionally scaled image values and axes coordinates.
- Distance to your object, and optionally a unit. AU, pc, Kpc, Mpc, and
Gpc are allowed. You can also specify a dimensionless number ’z’, in which
case the special cosmology calculator is used. [default: 1,pc]
- Length scale of object, and optionally a unit. km, AU, pc, Kpc, Mpc, and
Gpc are allowed. Together with a distance d=, this will convert the length
scale in your maps to degrees, required for FITS. [default: 1,AU]
- Velocity scale of object, and optionally a unit. The output units will be
the one that FITS uses, m/s. [Default: 1,km/s]
- Total flux, in Jy.km/s,
of the source. Based on the distance, it will the compute the HI and H2
(given some reasonable X factor) masses, in units of solar masses. Default:
- Scale the intensity values in the data itself. Default: 1.
the cosmology model, with up to 3 parameters. Only used when units in d=
are ’z’ were specified. The first parameter is the Hubble Constant. Optionally
followed by the WM (Omega(matter)) and WV (Omega(vacuum)), for different
cosmologies. If only H0 and WM are given, a flat universe (WV=0) is used.
See also Wright(2006). WMAP-9 values: H=71,0.27,0.73 (2011?), Planck-1 values:
H=67.15,0.317,0.683 (2013) [Default: 71,0.27,0.73]
% ccdsky d=1,pc r=1,AU v=1,km/s
rscale=0.000277785 (1.00003 arcsec)
To find out the radius of 2 pc at the distance of the galactic center:
ccdsky r=2,pc d=8.5,kpc
rscale=0.0134814 (48.5329 arcsec)
Here is an example of creating a small bar, at position angle 30, and
observed at RA=6h and DEC=30d:
% ccdgen "" map4 bar 1,10,0.5,30 size=512,512,1
% ccdsky map4 map4b
% ccdfits in=map4b out=map4b.fits radecvel=t crval=90,30 crpix=256.5,256.5
% # now switch to MIRIAD
% fits in=map4b.fits out=map4b.mir op=xyin
% cgdisp in=map4b.mir device=/xs labtyp=arcmin
and you should see a bar (possibly with a sign error position angle) of
about 1 arcmin in length, in an 8 arcmin field. Notice that ccdfits(1NEMO)
also has various options to specify a WCS which can override the one set
Although the conversion from an observed HI flux
to mass is not too controversial (sans optical depth effects), the conversion
from CO to a mass is still under debate. We use the value 2e20 cm-2/K km/s.
Calculator for the Web (E.Wright)
The CosmoCalc website
NEMO/src/image/trans ccdsky.c - source code
17-Aug-2012 V1.0 Created PJT
23-aug-2012 V1.1 added sdv= PJT
28-aug-2012 V1.2 implemented scale= PJT
28-feb-2013 V2.2 more verbose, added H= PJT
16-mar-2013 V3.0 added Wright’s cosmology calculator PJT
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