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

Emily A Gilbert,Thomas Barclay,Lucianne M Walkowicz,Elisa V Quintana,Ethan Kruse

doi:10.3389/fspas.2021.769371

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.

Highlights

M dwarf stars’ small sizes make them advantageous when it comes to exoplanet detection via both radial velocity and transit methods
We used Sectors 11–12 in this search between it speeds up the computation very significantly, and we found that the additional sector only provided limited additional sensitivity to small planets with orbital periods shorter than 25 days
We examined two different methods, firstly we interactively sigma-clipped out data-points, and secondly we tried use the flare model but clipping out the data point that occur during times that flare occur rather than subtracting the model

Summary

Introduction

M dwarf stars’ small sizes make them advantageous when it comes to exoplanet detection via both radial velocity and transit methods. These low-mass stars are frequently highly magnetically active for long portions of their lifetimes, which can confound detection and further characterization of planets orbiting such stars. White light flares may induce radial velocity shifts, increasing noise in RV measurements and hindering planet detections (Saar and Donahue 1997; Korhonen et al, 2015; Andersen and Korhonen 2015). Proxima Centauri is an M5.5 dwarf star with an estimated age of ∼5 Gyrs (Thévenin et al, 2002). Proxima Centauri is one of the most well-studied stars in the sky, and as such, has been a prominent target for exoplanet searches for many years (e.g. Holmberg 1938; Benedict et al, 1999; Kürster et al, 1999; Endl and Kürster 2008; Lurie et al, 2014)

Objectives

Methods

Findings

Discussion

Conclusion