Flux Standards Restructuring

Last modified: 2013-07-26

For CASA 4.2 development, in order to fully support Perley-Butler 2013 standard including the time-variable sources, restructuring in the flux standard related code in casacore (under ~/comoponents/ComponentModels/) was performed.

Main changes are:

Perley-Butler 2013

The spectral flux density models from
Perley and Butler 2013, ApJS 204, 19. This includes the support for time-variable sources listed in Perley & Butler 2013.

The coefficient data : PerleyButler2013Coeffs
Stored in a Casa table in the data directory, under ~/data/nrao/VLA/standards/. Each row contains the coefficients and their errors of all the standard sources at a certain epoch. For the sources considered to be non-variable these coefficient values are identical for all the rows.
The polynomial function assumed here is,
log(S(νGHz)) = a0 + a1*log(νGHz)+a2*(log(νGHz))2 + a3*(log(νGHz))3,
where S is the flux density in Jy and νGHz is the frequency in GHz.

The current sequence diagram of the Perley-Butler 2013 standard as shown below.

Scaife-Heald 2012

The broad-band flux scale based on
Scaife and Heald 2012, A&A, 423L at low frequencies(below 500HMz). As in Perley-Butler 2013, the coefficients are read from a CASA table. Originally implemented by Huib Intema in the older CASA code and it has been merged to the current trunk.

The coefficient data : ScaifeHeald2012Coeffs
The table consists of a single row containing the coefficients and their errors.
The polynomial function assumed here is,
log(S(ν)) = log(a0) + a1*log(ν/νref) + a2*log(ν/νref)2 + a3*log(ν/νref)3 + ...,
where νref is the reference frequency, =150MHz.