Correction Coefficients


The Correction Coefficients tab is shown below. It consists of two sections: Extinction coefficients and Transformation coefficients.



Extinction Coefficients


Extinction corrections are explained in detail in this section. You can enter your First order (k') and Second order (k") extinction coefficients for each of your UBVRI filters in the corresponding fields. Use 0 if you don't want to apply extinction correction for a given filter, or if you don't have that filter.


IMPORTANT: Phoranso will apply extinction corrections to your FITS images when the following conditions are met:


    • for First order extinction correction, the k' filter value is different from 0

    • for Second order extinction correction:

      • the color of the Target star is specified and different from 0. This value is entered when creating or editing an ID Card.

      • The k" filter value is different from 0. 

      • the color magnitudes B and V are present in the selected photometric catalog for each of the reference, check and comparison stars in your image. If the color magnitudes of one or more stars are missing, no Second order extinction will be applied.

    • the Apply corrections option for Extinction Coefficients is enabled in the Photometry settings window, accessible via the Photometry menu.




Transformation Coefficients


Transformation corrections are explained in detail in this section. You can either enter transformation coefficients manually or import them by clicking the button Import AAVSO TG Transform Export file. 


The AAVSO Transform Generator (TG) is a tool that calculates the transformation coefficients for your filter system using a set of standard stars with known magnitudes, observed through multiple filters (such as B, V, and R). TG automatically computes all transformation values.  Users can analyze each transformation by viewing plots of the raw data along with the linear fit that defines the transformation value. After reviewing the transformations, users save the complete transformation set to a file and later imported into Phoranso using the aforementioned import button.


IMPORTANT: Phoranso will apply transformation corrections to your FITS images when the following conditions are met:


    • a valid sequence of color images is selected by the user. This is further explained here.


    • the Apply corrections option for Transformation Coefficients is enabled in the Photometry settings window, accessible via the Photometry menu. For the highest accuracy in photometry, we recommend enabling both the Extinction Coefficients and Transformation Coefficients options. Once both are activated, Phoranso will first apply extinction corrections to the instrumental magnitudes of your FITS images, followed by transformation corrections. 


When applying transformation corrections, Phoranso generates two report files for each Reporting format selected in the Report Settings window of the Photometry menu. For example: if you select both AAVSO and CBA Reporting formats, Phoranso will produce a standard AAVSO and CBA report for each Target star present in your FITS images, as well as an additional set of AAVSO and CBA reports with transformed magnitudes. These reports, which include transformation corrections, are easily identifiable by the "TC" (Transformation Correction) label in their file names.