Instances where star A is brighter than (B+C)

def A_brighter(self, band='g'):
        """
        Instances where star A is brighter than (B+C)
        """
        mA = self.stars['{}_mag_A'.format(band)]
        mBC = addmags(self.stars['{}_mag_B'.format(band)],
                     self.stars['{}_mag_C'.format(band)])
        return mA < mBC