addPtSrc

 d=addPtSrc(d,flux,alpha,dra,ddec)

 Takes a data structure d, all calibrated and ready for
 conv2uvf, and adds a point source of your choosing to it.

 flux is the flux at the center of the 
 the sky frequency range.

 flux is in milliJanskys (mJy).

 alpha is the spectral index. if it's negative, 
 use a negative value

 so Flux as a function of frequency is:
 f=flux * (freq/mean(freq)).^alpha

 requires at least 2 arguments.
 assumes unassigned values = 0. 
 if you want to subtract a pt src, try negative flux.

 dra = ra, in arcsec, from the central pointing
 ddec = dec, in arcsec, from the central pointing

 tony, 30th Nov '05

0001 function d=addPtSrc(d,flux,alpha,dra,ddec)
0002 
0003 % d=addPtSrc(d,flux,alpha,dra,ddec)
0004 %
0005 % Takes a data structure d, all calibrated and ready for
0006 % conv2uvf, and adds a point source of your choosing to it.
0007 %
0008 % flux is the flux at the center of the
0009 % the sky frequency range.
0010 %
0011 % flux is in milliJanskys (mJy).
0012 %
0013 % alpha is the spectral index. if it's negative,
0014 % use a negative value
0015 %
0016 % so Flux as a function of frequency is:
0017 % f=flux * (freq/mean(freq)).^alpha
0018 %
0019 % requires at least 2 arguments.
0020 % assumes unassigned values = 0.
0021 % if you want to subtract a pt src, try negative flux.
0022 %
0023 % dra = ra, in arcsec, from the central pointing
0024 % ddec = dec, in arcsec, from the central pointing
0025 %
0026 % tony, 30th Nov '05
0027 
0028 if nargin < 3
0029   alpha=0;
0030 end
0031 
0032 if nargin < 4
0033   dra=0;
0034 end
0035 
0036 if nargin < 5
0037   ddec=0;
0038 end
0039 
0040 m=sza2uv(d,'difmap');
0041 
0042 x=dra*pi/(180*3600);
0043 y=ddec*pi/(180*3600);
0044 
0045 freqs=reshape(m.freq,[1 1 16]);
0046 
0047 f=1e-3*flux*(freqs/nanmean(m.freq)).^alpha;
0048 
0049 f=repmat(f,[size(d.vis,1) size(d.vis,2)]);
0050 
0051 d.vis=d.vis + f.*(exp(j*2*pi*(x*m.u+y*m.v)));