Noise properties of the CoRoT data: a planet-finding perspective

TL;DR

This study analyzes the noise characteristics of CoRoT satellite light curves, focusing on planetary transit timescales, revealing noise levels close to pre-launch expectations and identifying variability differences between giant and dwarf stars.

Contribution

It provides a detailed characterization of CoRoT photometric noise properties on transit timescales, aiding statistical interpretation of its exoplanet and binary detections.

Findings

Noise on 2h timescales follows a power-law with index 0.25 in R-magnitude.

Residual jitter and hot pixel events cause noise levels 2-3 times above photon noise.

Giant stars show increased variability on hours timescales compared to dwarfs.

Abstract

In this short paper, we study the photometric precision of stellar light curves obtained by the CoRoT satellite in its planet finding channel, with a particular emphasis on the timescales characteristic of planetary transits. Together with other articles in the same issue of this journal, it forms an attempt to provide the building blocks for a statistical interpretation of the CoRoT planet and eclipsing binary catch to date. After pre-processing the light curves so as to minimise long-term variations and outliers, we measure the scatter of the light curves in the first three CoRoT runs lasting more than 1 month, using an iterative non-linear filter to isolate signal on the timescales of interest. The bevhaiour of the noise on 2h timescales is well-described a power-law with index 0.25 in R-magnitude, ranging from 0.1mmag at R=11.5 to 1mmag at R=16, which is close to the pre-launch specification, though still a factor 2-3 above the photon noise due to residual jitter noise and hot pixel events. There is evidence for a slight degradation of the performance over time. We find clear evidence for enhanced variability on hours timescales (at the level of 0.5 mmag) in stars identified as likely giants from their R-magnitude and B-V colour, which represent approximately 60 and 20% of the observed population in the direction of Aquila and Monoceros respectively. On the other hand, median correlated noise levels over 2h for dwarf stars are extremely low, reaching 0.05mmag at the bright end.