Spectralindex
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This page documents the spectralindex function of the linfit class in the Python module analysisUtils.
This function is designed to fit a power-law spectral index to the results output from casa's fluxscale task (using scipy.optimize.leastsq). Currently, it also requires a listobs-generated ascii file as the first argument in order to determine the center frequencies of each spectral window. (To avoid the need for this file in the future, we have submitted an improvement request for fluxscale to also print these frequencies.) By default, it estimates the uncertainties of the fitted slope and amplitude from the square root of the diagonals of the covariance matrix. Alternatively, there is an option to run a Monte-Carlo series of fits to empirically determine the uncertainties. Finally, it produces a plot summarizing the results. By default, it will use all spectral windows, but it will exclude those with an "INSUFFICIENT DATA" status from fluxscale (which can arise in high-frequency EVLA data if you have not split off the pointing spws). Note: spectralIndex is a camel-caps synonym for spectralindex.
Usage:
au.linfit().spectralindex(filename, yfilename, source="", verbose=False, maxpoints=0, trials=2000, spw="", help=False, plotdir="", labelspw=False, referenceFrame='TOPO')
filename: contains a listobs output file
yfilename: contains a fluxscale output file
source: sourcename to choose from the (possibly) multi-source fluxscale file
maxpoints: the maximum number of spws to select for the fit starting from the first one (0=no max)
trials: if > 0, use a Monte-Carlo technique estimate the fit uncertainties,
otherwise, use the sqrt(covarMatrix) from scipy.optimize.leastsq (default).
(There is a minimum number of 100 trials, and ~1000 is recommended.)
spw: the spws to use, e.g. ""=all, "1~3,5,6~8"=[1,2,3,5,6,7,8]
plotdir: the directory in which to write the plotfile (in case you don't have permission in the pwd)
labelspw: draw spw numeric labels adjacent to each point
referenceFrame: the frequency reference frame in the listobs file, if not 'TOPO'
Examples
# In CASA
au.linfit().spectralIndex('listobs.txt','fluxscale_d2_new.txt','J19',spw='1~15')
Will use spw = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15]
Skipping spw 0
Read 15 x values for J1924-2914 (avg=41706.267)
Read 15 y values for J1924-2914 (avg=13.180)
Error-weighted fit: Slope: -0.327+-0.067 Flux D. @ 40118.00MHz: 13.346+-0.011
Un-weighted fit: Slope: -0.325 Flux D. @ 40118.00MHz: 13.345
Plot saved in ./d2_fluxscale.txt.J1924-2914.png
File formats
The listobs file should look like this. It is keying off the referenceFrame string (default = "TOPO"), so there can be any number of leading or trailing comment characters on each line, and any number of unrelated lines of text at the top or bottom.
SpwID #Chans Frame Ch1(MHz) ChanWid(kHz) TotBW(kHz) Corrs 0 128 TOPO 42738 1000 128000 RR LL 1 128 TOPO 42866 1000 128000 RR LL 2 128 TOPO 42994 1000 128000 RR LL 3 128 TOPO 43122 1000 128000 RR LL 4 128 TOPO 43250 1000 128000 RR LL 5 128 TOPO 43378 1000 128000 RR LL 6 128 TOPO 43506 1000 128000 RR LL 7 128 TOPO 43634 1000 128000 RR LL 8 128 TOPO 44488 1000 128000 RR LL 9 128 TOPO 44616 1000 128000 RR LL 10 128 TOPO 44744 1000 128000 RR LL 11 128 TOPO 44872 1000 128000 RR LL 12 128 TOPO 45000 1000 128000 RR LL 13 128 TOPO 45128 1000 128000 RR LL 14 128 TOPO 45256 1000 128000 RR LL 15 128 TOPO 45384 1000 128000 RR LL
Similarly, the fluxscale file should look like this. It can contain the results for multiple sources. It is keying off of the string 'SpW', so there can be any number of leading comment characters on each line, and any number of unrelated lines of text at the top.
# Opening MS: 10C186_B_Q_d1_3s.ms for calibration. # Found reference field(s): J1331+3030 # Found transfer field(s): J1717-3342 J1924-2914 # Flux density for J1717 3342 in SpW=0 is: 2.33891 ± 0.0620232 (SNR = 37.7102, N= 44) # Flux density for J1717-3342 in SpW=1 is: 2.33168 ± 0.0608224 (SNR = 38.3358, N= 44) # Flux density for J1717-3342 in SpW=2 is: 2.33139 ± 0.0642111 (SNR = 36.3082, N= 44) # Flux density for J1717-3342 in SpW=3 is: 2.33639 ± 0.0697579 (SNR = 33.4929, N= 44) # Flux density for J1717-3342 in SpW=4 is: 2.31025 ± 0.0631668 (SNR = 36.5738, N= 44) # Flux density for J1717-3342 in SpW=5 is: 2.32929 ± 0.0667446 (SNR = 34.8986, N= 44) # Flux density for J1717-3342 in SpW=6 is: 2.35698 ± 0.0698231 (SNR = 33.7564, N= 44) # Flux density for J1717-3342 in SpW=7 is: 2.32728 ± 0.0668059 (SNR = 34.8364, N= 44) # Flux density for J1717-3342 in SpW=8 is: 2.23395 ± 0.0394774 (SNR = 56.588, N= 46) # Flux density for J1717-3342 in SpW=9 is: 2.23898 ± 0.0404523 (SNR = 55.3487, N= 46) # Flux density for J1717-3342 in SpW=10 is: 2.20212 ± 0.0408321 (SNR = 53.9311, N= 46) # Flux density for J1717-3342 in SpW=11 is: 2.18275 ± 0.0392774 (SNR = 55.5727, N= 46) # Flux density for J1717-3342 in SpW=12 is: 2.17859 ± 0.0388576 (SNR = 56.0659, N= 46) # Flux density for J1717-3342 in SpW=13 is: 2.16182 ± 0.0405544 (SNR = 53.3066, N= 46) # Flux density for J1717-3342 in SpW=14 is: 2.16303 ± 0.0413542 (SNR = 52.305, N= 46) # Flux density for J1717-3342 in SpW=15 is: 2.19681 ± 0.0400311 (SNR = 54.8777, N= 46) # Flux density for J1924-2914 in SpW=0 is: 14.6731 ± 0.138529 (SNR = 105.921, N= 44) # Flux density for J1924-2914 in SpW=1 is: 14.5996 ± 0.136761 (SNR = 106.753, N= 44) # Flux density for J1924-2914 in SpW=2 is: 14.6242 ± 0.146673 (SNR = 99.7061, N= 44) # Flux density for J1924-2914 in SpW=3 is: 14.6802 ± 0.158394 (SNR = 92.6816, N= 44) # Flux density for J1924-2914 in SpW=4 is: 14.5259 ± 0.141069 (SNR = 102.97, N= 44) # Flux density for J1924-2914 in SpW=5 is: 14.6075 ± 0.151812 (SNR = 96.2206, N= 44) # Flux density for J1924-2914 in SpW=6 is: 14.7261 ± 0.157892 (SNR = 93.2666, N= 44) # Flux density for J1924-2914 in SpW=7 is: 14.5783 ± 0.14938 (SNR = 97.5919, N= 44) # Flux density for J1924-2914 in SpW=8 is: 13.9264 ± 0.0748849 (SNR = 185.971, N= 46) # Flux density for J1924-2914 in SpW=9 is: 13.9368 ± 0.0751502 (SNR = 185.452, N= 46) # Flux density for J1924-2914 in SpW=10 is: 13.7826 ± 0.0785357 (SNR = 175.494, N= 46) # Flux density for J1924-2914 in SpW=11 is: 13.7178 ± 0.0778214 (SNR = 176.273, N= 46) # Flux density for J1924-2914 in SpW=12 is: 13.6833 ± 0.0748109 (SNR = 182.905, N= 46) # Flux density for J1924-2914 in SpW=13 is: 13.6308 ± 0.0772038 (SNR = 176.555, N= 46) # Flux density for J1924-2914 in SpW=14 is: 13.6372 ± 0.0792322 (SNR = 172.117, N= 46) # Flux density for J1924-2914 in SpW=15 is: 13.7463 ± 0.0735882 (SNR = 186.8, N= 46)
