The Stability of BVRI Comparison Stars Near Selected TeV Blazars

TL;DR

This study assesses the stability of comparison stars near five TeV blazars by analyzing 25 years of photometric data, confirming most stars are stable within 0.04 magnitude, with a few identified as variable.

Contribution

It provides a long-term stability assessment of comparison stars near TeV blazars, improving the reliability of photometric measurements in these regions.

Findings

Most stars are stable at the 0.04 magnitude level.

Two stars are confirmed variable.

Two additional stars are possibly variable.

Abstract

We have measured Johnson BV and Cousins RI magnitudes for comparison stars near five TeV blazars. We compare our values with published values, spanning 25 years in some cases, to identify those stars that are most likely proven stable. To avoid zero-point offsets mimicking long-term variability, we based our analysis on the standard deviation between measurements after a mean offset between data sets was removed. We found most stars to be stable at the 0.04 magnitude level. We confirm two stars as variable and identify two others as possibly being variable. In each of the five fields there are at least two stars, and typically many more, that show no evidence of variability.