The effect of red noise on planetary transit detection

Abstract

Since the discovery of short-period exoplanets a decade ago, photometric surveys have been recognized as a feasible method to detect transiting hot Jupiters. Many transit surveys are now under way, with instruments ranging from 10-cm cameras to the Hubble Space Telescope. However, the results of these surveys have been much below the expected capacity, estimated in the dozens of detections per year. One of the reasons is the presence of systematics (``red noise'') in photometric time series. In general, yield predictions assume uncorrelated noise (``white noise''). In this paper, we show that the effect of red noise on the detection threshold and the expected yields cannot be neglected in typical ground-based surveys. We develop a simple method to determine the effect of red noise on photometric planetary transit detections. This method can be applied to determine detection thresholds for transit surveys. We show that the detection threshold in the presence of systematics can be much higher than with the assumption of white noise, and obeys a different dependence on magnitude, orbital period and the parameters of the survey. Our method can also be used to estimate the significance level of a planetary transit candidate (to select promising candidates for spectroscopic follow-up). We apply our method to the OGLE planetary transit search, and show that it provides a reliable description of the actual detectionthreshold with real correlated noise. We point out in what way the presence of red noise could be at least partly responsible for the dearth of transiting planet detections from existing surveys, and examine some possible adaptations in survey planning and strategy. Finally, we estimate the photometric stability necessary to the detection of transiting ``hot Neptunes''.Comment: 14 pages, 15 figures, to appear in MNRA

A Gemini ground-based transmission spectrum of WASP-29b: a featureless spectrum from 515 to 720 nm

“…We therefore analyse the residuals of each of the best-fitting models in an effort to understand the form of the systematics. We first use the time-averaging method to obtain a simple estimate of the red noise (Pont, Zucker & Queloz 2006), following the procedure of Winn et al (2008), where the residuals are averaged into bins of width N, and the RMS is calculated as a function of N. Fig. 4 shows an example of this for one of the light curves, clearly showing that there is time-correlated noise in the light curves.…”

Precision Time-series Photometry in the Thermal Infrared with a “Wall-eyed” Pointing Mode at the Large Binocular Telescope

“…Considerable effort has gone into characterizing or decorrelating its effect, particularly on exoplanet transit or secondary eclipse light curves which often require sub-percent precision (e.g., Pont et al (2006), Carter & Winn (2009), Croll et al (2015). Indeed, red noise in our dataset involving the XO-2Nb primary transit led to light curves with variations of ∼6% at apertures comparable to the first few Airy rings, when the expected transit depth was slightly more than 1%.…”

SuperLupus: A Deep, Long Duration Transit Survey

“…The duration of a transit survey is critical to its prospects of success, and underestimating required durations may have contributed to early surveys not discovering transiting planets in the numbers expected (Pont, Zucker, & Queloz 2006).…”