No Transits of Proxima Centauri Planets in High-Cadence TESS Data

Abstract

Proxima Centauri is our nearest stellar neighbor and one of the most well-studied stars in the sky. In 2016, a planetary companion was detected through radial velocity measurements. Proxima Centauri b has a minimum mass of 1.3 Earth masses and orbits with a period of 11.2 days at 0.05 AU from its stellar host, and resides within the star’s Habitable Zone. While recent work has shown that Proxima Centauri b likely does not transit, given the value of potential atmospheric observations via transmission spectroscopy of the closest possible Habitable Zone planet, we reevaluate the possibility that Proxima Centauri b is a transiting exoplanet using data from the Transiting Exoplanet Survey Satellite (TESS). We use three sectors (Sectors 11, 12, and 38 at 2-min cadence) of observations from TESS to search for planets. Proxima Centauri is an extremely active M5.5 star, emitting frequent white-light flares; we employ a novel method that includes modeling the stellar activity in our planet search algorithm. We do not detect any planet signals. We injected synthetic transiting planets into the TESS and use this analysis to show that Proxima Centauri b cannot be a transiting exoplanet with a radius larger than 0.4 R⊕. Moreover, we show that it is unlikely that any Habitable Zone planets larger than Mars transit Proxima Centauri.

The strong suppression of galactic cosmic rays reaching AU Mic b, c, and Prox Cen b

“…Another important aspect to consider is that stars themselves can accelerate stellar cosmic rays during events such as flares and coronal mass ejections (Rodgers-Lee et al 2021a). Prox Cen and AU Mic are both active stars with strong surface magnetic fields (Klein et al 2021a,b) and frequent flaring activity (Gilbert et al 2021(Gilbert et al , 2022 and, as such, they should be efficient at accelerating stellar cosmic rays. As a result, for these stars, stellar cosmic ray fluxes will dominate over Galactic cosmic rays up to a certain energy.…”

Llamaradas Estelares: Modeling the Morphology of White-light Flares

“…Currently, many planet detection algorithms account for transits and flares separately (e.g., Luger et al 2017), or the flare is simply masked out (e.g., Plavchan et al 2020), which increases the uncertainty in the transit profile. More recent studies have simultaneously modeled the stellar activity within the planet search algorithm (Gilbert et al 2021); however, the flare template used in the analysis is from D14, which is improved on in this work. Our new flare template can be incorporated into existing detection and characterization tools (e.g., Günther & Daylan 2021;Gilbert et al 2022).…”

“…In addition to detectability, many teams have shown that strong magnetic activity (i.e., flares and CMEs) can affect planetary atmospheres (e.g., Segura et al 2010;Vida et al 2016;Tilley et al 2019) and thus influence potential habitability by causing runaway greenhouse effects (Shields et al 2016), atmospheric erosion (Lammer et al 2007), and hydrodynamic escape of atmospheres (Luger et al 2015). By better understanding the temporal evolution or light-curve morphology of flares on active M-type stars, we can help improve exoplanet detection and characterization (Gilbert et al 2021).…”

Null transit detections of 68 radial-velocity exoplanets observed by TESS

“…To improve the study of this kind of object, it would be necessary to account for the presence of flares when looking for transits. This topic is treated in a recent work about Proxima Centauri; the authors obtain better results when identifying and modeling the flares using a template, which they then subtract from the data, and perform the transit exploration (Gilbert et al 2021a); simi-lar processes were performed for the AU Mic system by Gilbert et al (2021b) and Szabó et al (2021).…”