Noise properties of the CoRoT data^*

A planet-finding perspective

¹ School of Physics, University of Exeter, Exeter, EX4 4QL, UK e-mail: suz@astro.ex.ac.uk
² Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138, US
³ LAM, Université de Provence, 13388 Marseille, France
⁴ LESIA, Observatoire de Paris, 92195 Meudon, France
⁵ IAS, Université Paris XI, 91405 Orsay, France
⁶ Observatoire de Haute-Provence, 04870 St Michel l'Observatoire, France
⁷ IAC, 38205 La Laguna, Spain
⁸ ON/MCT, 20921-030, Rio de Janeiro, Brazil
⁹ IfA, University of Vienna, 1180 Vienna, Austria
¹⁰ Institute of Planetary Research, DLR, 12489 Berlin, Germany
¹¹ RSSD, ESA/ESTEC, 2200 Noordwijk, The Netherlands
¹² IWF, Austrian Academy of Sciences, 8042 Graz, Austria
¹³ IAG, Université de Liège, Liège 1, Belgium
¹⁴ Sch. Physics & Astronomy, Tel Aviv Univ., Tel Aviv 69978, Israel
¹⁵ RIU, Universität zu Köln, 50931 Köln, Germany
¹⁶ Observatoire de Genève, 1290 Sauverny, Switzerland
¹⁷ ZAA, TU Berlin, 10623 Berlin, Germany
¹⁸ LUTH, Observatoire de Paris, 92195 Meudon, France
¹⁹ Thüringer Landessternwarte, 07778 Tautenburg, Germany
²⁰ Dept. Geophysics & Planetary Sciences, Tel Aviv Univ., Tel Aviv 69978, Israel

Received: 19 February 2009
Accepted: 9 March 2009

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 time scales 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 time scales of interest. The behaviour of the noise on 2 h time scales is described well by a power-law with index 0.25 in R-magnitude, ranging from 0.1 mmag at to 1 mmag at , 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 of slight degradation in the performance over time. We find clear evidence of enhanced variability on hour time scales (at the level of 0.5 mmag) in stars identified as likely giants from their R magnitude and  colour, which represent approximately 60 and 20% of the observed population in the directions of Aquila and Monoceros, respectively. On the other hand, median correlated noise levels over 2 h for dwarf stars are extremely low, reaching 0.05 mmag at the bright end.