Testing the photometric stability of BRITE-Constellation

TL;DR

This study assesses the long-term photometric stability of the BRITE-Constellation satellites by comparing their measurements of a quiet star with those from the Kepler/K2 telescope, demonstrating their high sensitivity and stability.

Contribution

It provides the first independent validation of BRITE's photometric stability using a bright star observed simultaneously by Kepler/K2 and BRITE satellites.

Findings

BRITE instruments are stable in the low-frequency regime.

BRITE can detect sub-mmag variability in faint stars.

Residual noise levels are below 10ppm for Kepler and about 100ppm for BRITE.

Abstract

To characterise the long-term stability and true photometric sensitivity of a space-based instrument is a difficult task and can be done best with independent measurements of a relatively quiet star. A rare occasion for such a test are the complementary observations of some bright Plejades stars with the Kepler/K2 telescope and the BRITE-Austria (BAb) and UniBRITE (UBr) satellites. While most of them show a complex oscillatory behaviour, the frequency spectrum of the bright B-type star Atlas is relatively simple. From the 71 days-long K2 observations we extract the three dominant frequencies and show that the residuals have a noise level of less than 10ppm. While the BAb observations are not sensitive enough, we find the same periodicities in the 167 days-long UBr data set, which shows no additional significant signal down to a noise level of about 100ppm. This impressively demonstrates the stability of the BRITE instruments in the low-frequency regime and their capability to detect sub-mmag variability, even for stars close to the faint end of the nominal dynamic range.