National Radio
Astronomy Observatory

componentlist.asciitocomponentlist - Function

1.2.1 Create a componentlist from an ascii file (Not implemented yet)


Description

This constructor allows conversion of a number of ascii-file-based formats to componentlists. The formats currently supported are the AIPS star file format, the Caltech model format, and the WENSS, FIRST, and NVSS surveys.

AIPS ST file

The AIPS star file describes positions of “stars” that one might wish to plot overlaid on some other display. It does not contain source strength information. In the AIPS help file for STARS, the format of the star file is described as follows:

    The text file contains one line per star and each line has  
up to 7 logical columns containing, in order:  
   1. X position (Right Ascension 00 00 00.00)  
   2. Y position (Declination +/-00 00 00.0)  
   3. Major axis (Full width in arc seconds on sky)  
   4. Minor axis (Full width in arc seconds on sky)  
   5. Position Angle (E of N, degrees)  
   6. Star Type  (-1 to 20, integer )  
   7. Star label (up to 24 character string)  
If X and Y are not RA-DEC or DEC-RA, then the logical columns  
are also 7 actual columns and the units are in AIPS standard  
units (e.g. degrees, m/s etc. ).  In this case the position  
angle should be given as 0.0, the major axis is the width in the  
Y coordinate and the minor axis is the width in the X  
coordinate.  For RA and DEC positions, the sexagesimal notation  
is used (e.g. HH MM SS.SSS -DD MM SS.S) for the positions and  
arc seconds on the sky are used for the Deltas.  
The last 5 columns are not required.  If the last 5 columns are  
not given, a value of 1 cell is assumed for the deltas.  
If the position angle is not included, the default is 0 degrees.  
If the star type is not included, the default type is a cross.  
The default is no label string.  
There are currently 22 different types of star marks.  
 < 0: No Mark, only the star label is printed  
   0: Cross             10: Five pointed star  
   1: Ellipse           11: Star of David  
   2: Box               12: Seven pointed star  
   3: Triangle          13: Eight pointed star  
   4: Diamond           14: Nine  pointed star  
   5: Pentagon          15: Ten   pointed star  
   6: Hexagon           16: 11    pointed star  
   7: Septagon          17: 12    pointed star  
   8: Octagon           18: 13    pointed star  
   9: Nine-gon          19: 14    pointed star  
  20: Cross with gap   >20: Ellipse  
The Box (type=2) is different from the diamond in that the  
star size is the half height and width of the box dimensions.  
The Box and the Null (<0) are labeled at RA and Dec plus Delta  
RA and Delta Dec.  The other marks are labeled at the right  
edge of the of the Rotated RA axis.  The CROSS WITH GAP  
(type=20) has the inner third of the cross removed so the  
marked object is not over written.

For more information, see the AIPS help file for STARS.

Caveats:

• In AIPS, the following are supported: 1: 1900; 2: B1950; 3: J2000; 4: Galactic 5: OHLSSON Gal.; 6: VAN TULDER Galactic; 7: Super Galactic; if ¿ 1000 then year assumed. Currently, CASA can support 2 (refer=’b1950’), 3 (refer=’j2000’), 4 (refer=’gal’), 7 (refer=’supergal’). If you need any of the others, please contact us.
• The Caltech package uses a format for specifying positions relative to an undefined position. In the documentation for modelfit, the format is described as follows:

     Model files are text files that can be typed or printed directly;  
they  can  be  modified or created using the standard text editors.  A  
model file consists of one line for each component of the model,  with  
up to 7 numbers on each line (in free format):  
 
     1.  Component flux density (Jy)  
 
     2.  Distance of center of component  from  origin  (milliarcsec),  
         "radius"  
 
     3.  Position angle of center of component  with  respect  to  the  
         origin (degrees, North through East), "theta"  
 
     4.  Major axis of component (milliarcsec), "axis"  
 
     5.  Axial ratio (minor/major, i.e.  < 1), "ratio"  
 
     6.  Position angle of major axis (degrees, North  through  East),  
         "phi"  
 
     7.  Type:  
             0 or 1:  elliptical Gaussian  (major  axis  is  FWHM)  or  
             delta-function (major axis = 0)  
             2:  uniform elliptical disk (major axis is diameter)  
             3:  optically thin spheroid or tapered disk  (major  axis  
             is diameter)  
             4:  elliptical ring (major axis is diameter)  
             5:  line (major axis is length)  
 
For Gaussians and  delta-functions,  the  Type  can  be  omitted;  for  
delta-functions, the major-axis, axial-ratio, position- angle and type  
can be omitted.  (Not all the  programs  understand  types  2-5.)  The  
"origin" is an arbitrary phase-reference point.  The maximum number of  
components varies from 600  to  10000,  depending  on  the  individual  
program.

Caveats:

• In CASA, directions in componentlist are currently absolute only. Hence one must specify the reference direction.
• The Westerbork Northern Sky Survey (WENSS) is a low-frequency radio survey that covers the whole sky north of delta=30 degree at a wavelength of 92cm to a limiting flux density of approximately 18 mJy (5 sigma). This survey has a resolution of 54” x 54” cosec (delta) and a positional accuracy for strong sources of 1.5”. The WSRT Northern Sky Survey catalog is available via a Web interface. Use this interface to search for sources, choose the plain text output, capture the output into a file and then convert.
• Faint Images of the Radio Sky at Twenty-cm – is a project designed to produce the radio equivalent of the Palomar Observatory Sky Survey over 10,000 square degrees of the North and South Galactic Caps. Using the NRAO Very Large Array (VLA) and an automated mapping pipeline, they produce images with 1.8” pixels, a typical rms of 0.15 mJy, and a resolution of 5”. At the 1 mJy source detection threshold, there are ~90 sources per square degree, ~35% of which have resolved structure on scales from 2-30”. Go to the FIRST catalog search page, search for the sources that you want, cut out only the lines that include the sources, put in a file and then convert.
• The NRAO VLA Sky Survey The NRAO VLA Sky Survey (NVSS) is a radio continuum survey covering the sky north of -40 deg declination. A detailed description appears in the 1998 May issue of The Astronomical Journal (Condon, J. J., Cotton, W. D., Greisen, E. W., Yin, Q. F., Perley, R. A., Taylor, G. B., & Broderick, J. J. 1998, AJ, 115, 1693). Go to the NVSS catalog search page, search for the sources that you want, cut out only the lines that include the sources (you can leave in the alternating lines with error information), put in a file and then convert.

Caveats:

• The catalog contains upper limits on some scale sizes. We have chosen to represent these as actual sizes.

Arguments

Example

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