Phoranso User Guide

Different photometry packages use slightly different terminology for the roles that stars can play in aperture photometry. Phoranso uses the following definitions:

• Reference star 

Reference stars are used to compute  the  magnitude  of  the  Target star(s).  Phoranso  supports a single Reference star or an ensemble of Reference stars.

• Check star 

A Check star serves as a quality control star to verify stability of the observing conditions. Variations detected in the Check star indicate that changes in the Target star may not be intrinsic.

• Comparison stars

Comparison  stars perform a role similar to additional Check stars, but they are not included in AAVSO reports. Their purpose is to help validate your light curve. For instance, if variations in the Target star also appear in one or more Comparison stars, then this is a strong indication that the variability is not intrinsic to the target but caused by an external effect (e.g., clouds, tracking issues, camera noise, ....)

The following table shows how Phoranso terminology maps to the corresponding star roles in several other photometry packages.