Phoranso uses an internal Variable Star Database to memorize all information about each variable star you process and its comparison stars. This information is captured in the Identity Card (ID Card) of the variable star, as explained in this tutorial.


To access the Variable ID Card settings, select the Settings menu item from the Variable ID Card menu of the Phoranso menu bar. It shows a window with a Magnitude transformations and ID Card tab.



Magnitude transformations



When creating a new Variable ID Card for a target variable, Phoranso extracts magnitude information for the reference, check and comparison stars from the chosen Photometric catalog. 


Depending on the selected catalog, magnitude information may be lacking for certain bands. For instance, the UCAC4 catalog contains photometric magnitudes in Johnson B and V bands, Sloan g’ r’ and i’ bands, as well as 2MASS H, J and K bands.


Phoranso provides an option to calculate magnitude values for missing bands by transforming reference magnitudes from another magnitude system1. In the above example, we compute the Sloan u' g' r' i' z'  magnitudes from the U B V R I magnitudes.


The selected transformation will be automatically applied when creating a new Variable ID Card. 

4 options are available: 


    • None to not calculate missing magnitude values, 

    • UBVRI <== u' g’ r’ i’ to calculate U B V R I magnitudes from Sloan u' g' r' i' magnitudes, 

    • UBVRI ==> u' g' r’ i’ z’ to calculate Sloan magnitudes from U B V R I magnitudes,

    • R I z' <== V r' i' to calculate APASS R I z' magnitudes from APASS V and Sloan r' and i' magnitudes. 



ID Card



The ID Card tab consists of 3 sections: DSS images, AAVSO VSX and CompStars overlays, and Star callout.


    1. DSS Images

      • ID Cards can be created from a DSS image, from an AAVSO chart or from one of your FITS images. When creating the ID Card from a DSS image, the Selected catalog option allows to select the source DSS catalog, which is one of DSS1 Blue, DSS1 Red, DSS2 Blue, DSS2 Red or DSS2 IR. We recommend to use DSS2 Red.

      • Image size specifies the size of the DSS image to be retrieved from the digitized catalog. The larger size you want, the longer the download time of the image will take.


      • Image resolution  specifies the pixel resolution of the DSS image to be downloaded.


    1. AAVSO VSX and Compstars overlays


      • When you create an ID Card starting from a FITS image, the image first will be astronomically solved. Once done, Phoranso will check the AAVSO VSX database to retrieve all VSX variable stars that appear in your FITS image. They will be labeled and annotated as an 'overlay' on top of your FITS image, as shown in the below picture. 

        Some regions in the sky are cluttered with thousands of variable stars in small fields. To avoid that your FITS image overlay gets swamped with VSX stars, the Var stars limiting mag option allows to specify an upper limit, i.e. VSX stars which are fainter than the limiting mag at their maximum will be ignored and not drawn.

      • Your ID Card FITS image is not only annotated with VSX variable stars, but also with small green circles. Stars within a green circle are considered non-variable advised comparison (or reference or check) stars. This way Phoranso helps you with the selection of comparison, check and reference stars for your photometry.

        The Advised compstars limiting mag option allow to specify an upper limit, i.e. stars which are fainter than the limiting mag will be ignored as advised comparison stars (no green circle drawn).

        The 'green' classification is done by comparing the B-V value of a star with some treshold values. The B-V value or so called Color Index  is a measurement to quantify the color of the variable star. Stars with a large positive Color Index are red stars, and are to be avoided as comparison stars. 

        If a star's Color Index B-V is in between 0.3 and 1.02, it is considered an advised comparison star. 

        Note that this method does not take into account other important criteria for comparison star selection, such as those listed here.  

    1. Star callout (pop-up)


      • This section is described here.




Example of a FITS image showing the AAVSO VSX variable stars overlay and the advised (green) comparison stars overlay




(1) Phoranso's magnitude transformations are based on the formulae provided by S. Jester et al. in "The SDSS View of the Palomar-Green Bright Quasar Survey"


(2) Based on the AAVSO Sequence Selection and Revision Guidelines