More planetary candidates from K2 Campaign 5 using TRAN_K2

Abstract

Context. The exquisite precision of space-based photometric surveys and the unavoidable presence of instrumental systematics and intrinsic stellar variability call for the development of sophisticated methods that distinguish these signal components from those caused by planetary transits. Aims. Here, we introduce the standalone Fortran code tran_k2 to search for planetary transits under the colored noise of stellar variability and instrumental effects. We use this code to perform a survey to uncover new candidates. Methods. Stellar variability is represented by a Fourier series and, when necessary, by an autoregressive model aimed at avoiding excessive Gibbs overshoots at the edges. For the treatment of systematics, a cotrending and an external parameter decorrelation were employed by using cotrending stars with low stellar variability as well as the chip position and the background flux level at the target. The filtering was done within the framework of the standard weighted least squares, where the weights are determined iteratively, to allow a robust fit and to separate the transit signal from stellar variability and systematics. Once the periods of the transit components are determined from the filtered data by the box-fitting least squares method, we reconstruct the full signal and determine the transit parameters with a higher accuracy. This step greatly reduces the excessive attenuation of the transit depths and minimizes shape deformation. Results. We tested the code on the field of Campaign 5 of the K2 mission. We detected 98% of the systems with all their candidate planets as previously reported by other authors. We then surveyed the whole field and discovered 15 new systems. An additional three planets were found in three multiplanetary systems, and two more planets were found in a previously known single-planet system.

Near infrared and optical emission of WASP-5 b

“…The model time series constituted two multiplicative parts: the transit and a 36 th -order polynomial. For the transit we adopted the simple model of Kovacs (2020), representing the ingress/egress phases as linear flux depressions with the same steepness and duration. The limb darkening was modeled by a scalable U-shaped function.…”

“…In the standard least squares fit we employed Cauchy weights, adjusted iteratively to the processed time series -see, e.g.,Kovacs (2020).…”

TFAW survey II: six newly validated planets and 13 planet candidates fromK2

“…We visually inspect the transits positions in the light curves and require that they are at least 0.5 days away from the beginning or end of any gaps in their light curves to avoid false positives, especially in the case of long period candidates. 6) we cross-match our candidates with the most up-to-date (March 2022) lists of confirmed or candidate exoplanets from the NASA Exoplanet Archive 4 or in the Vizier database (Adams et al 2016;Barros et al 2016;Crossfield et al 2016;Vanderburg et al 2016;Crossfield et al 2018;Hirano et al 2018;Livingston et al 2018;Mayo et al 2018;Dattilo et al 2019;Kruse et al 2019;Castro González et al 2020;Kovacs 2020;Zink et al 2020;Adams et al 2021;Castro-González et al 2021;de Leon et al 2021;Zink et al 2021;Christiansen et al 2022). 7) we run EDI-Vetter Unplugged 5 , a simplified version of EDI-Vetter (Zink et al 2020), that uses the output from TLS to identify false-positive transit-like signals using a battery of tests: transit outliers, individual transit, even/odd transit, secondary transit, phase coverage, period and transit duration limits, period alias, and flux contamination checks.…”

“…These have provided the best photometric precision for K2 light curves and can return photometric precisions very similar to the ones from ★ E-mail: danieldelser@icc.ub.edu the original Kepler mission to K p =15 mag. Most planet searches in K2 campaigns used these EVEREST 2.0-corrected light curves, yielding an appreciable fraction of the currently confirmed planets and candidates (Mayo et al 2018;Kovacs 2020;Zink et al 2020;Adams et al 2021;de Leon et al 2021;Castro-González et al 2021;Zink et al 2021;Christiansen et al 2022). The development of new transit search tools has also helped increase the number of planets detected.…”

Near-infrared and optical emission of WASP-5 b

“…We employed Cauchy weights in the standard least-squares fit, which were adjusted iteratively to the processed time series; see, e.g.,Kovacs (2020). A47, page 3 of 13 A&A 664, A47(2022) …”