The Gaia spectrophotometric standard stars survey - III. Short-term variability monitoring

TL;DR

This study monitored the short-term variability of Gaia spectrophotometric standard stars over nearly a decade, validating most candidates as stable for calibration purposes, and identifying a few with variability.

Contribution

It provides a comprehensive variability assessment of Gaia SPSS candidates, ensuring reliable calibration standards for Gaia data.

Findings

150 out of 162 candidates are stable within 10 mmag.

12 candidates, including some flux standards, showed variability and were rejected.

The monitoring campaign spanned nine instruments over nine years.

Abstract

We present the results of the short-term constancy monitoring of candidate Gaia Spectrophotometric Standard Stars (SPSS). We obtained time series of typically 1.24 hour - with sampling periods from 1-3 min to a few hours, depending on the case - to monitor the constancy of our candidate SPSS down to 10 mmag, as required for the calibration of Gaia photometric data. We monitored 162 out of a total of 212 SPSS candidates. The observing campaign started in 2006 and finished in 2015, using 143 observing nights on nine different instruments covering both hemispheres. Using differential photometry techniques, we built light curves with a typical precision of 4 mmag, depending on the data quality. As a result of our constancy assessment, 150 SPSS candidates were validated against short term variability, and only 12 were rejected because of variability including some widely used flux standards such as BD+174708, SA 105-448, 1740346, and HD 37725.