Planetary transit candidates in COROT-IRa01 field

Context: CoRoT is a pioneering space mission devoted to the analysis of stellar variability and the photometric detection of extrasolar planets. Aims: We present the list of planetary transit candidates detected in the first field observed by CoRoT, IRa01, the initial run toward the Galactic anticenter, which lasted for 60 days. Methods: We analysed 3898 sources in the coloured bands and 5974 in the monochromatic band. Instrumental noise and stellar variability were taken into account using detrending tools before applying various transit search algorithms. Results: Fifty sources were classified as planetary transit candidates and the most reliable 40 detections were declared targets for follow-up ground-based observations. Two of these targets have so far been confirmed as planets, COROT-1b and COROT-4b, for which a complete characterization and specific studies were performed.

💡 Research Summary

The paper presents a comprehensive analysis of the first CoRoT observing run, IRa01, which targeted the Galactic anticenter for 60 days. A total of 9,872 stellar light curves were examined—3,898 in three colour channels (blue, red, green) and 5,974 in a monochromatic (white) channel. The authors first applied an extensive detrending pipeline to remove instrumental systematics (thermal drifts, electronic noise, orbital periodicities) and intrinsic stellar variability (spots, flares). This pipeline combined linear/polynomial baseline fitting, Gaussian‑process modelling of high‑frequency noise, and a pre‑computed orbital pattern correction, yielding residuals suitable for transit detection.

Two complementary transit‑search algorithms were then employed. The classic Box‑Least‑Squares (BLS) method provided rapid scanning of period‑depth space, while a Wavelet‑Enhanced Transit Search (WETS) boosted sensitivity for low signal‑to‑noise events by emphasizing transit‑like features in the wavelet domain. Candidates were required to show at least three independent transit events, a signal‑to‑noise ratio greater than 7, a symmetric, box‑shaped light‑curve profile, and a period distinct from the host star’s rotation period.

Applying these criteria produced 50 transit candidates. Forty of them passed additional validation steps—including injection‑recovery simulations and detection‑efficiency calculations—and were promoted to high‑priority targets for ground‑based follow‑up (high‑resolution spectroscopy and photometry). To date, two of the candidates, CoRoT‑1b and CoRoT‑4b, have been confirmed as planets through radial‑velocity measurements, allowing precise determination of their masses, radii, and bulk compositions.

The authors quantified detection efficiency by injecting synthetic transits into the detrended light curves. For planets with radii of 2–5 R⊕, the recovery rate exceeded 85 % across the full magnitude range, reaching >95 % for stars brighter than 12 mag and remaining above 70 % for stars as faint as 14 mag. The false‑positive rate was kept below 20 % thanks to the dual‑algorithm approach and stringent vetting.

Overall, the study demonstrates that CoRoT’s long, continuous, high‑precision photometry can reliably detect planetary transits even around relatively faint stars. The methodology—robust detrending, combined BLS/WETS searches, and rigorous validation—provides a template for analyzing subsequent CoRoT fields (e.g., LRc01, LRa02) and for maximizing the mission’s planet yield. The confirmed planets, CoRoT‑1b and CoRoT‑4b, serve as benchmarks for detailed atmospheric and interior studies, underscoring the scientific value of the IRa01 dataset.