Stellar flares detected with the Next Generation Transit Survey

James A G Jackman ,Edward Gillen,Samuel Gill,Liam Raynard,P J Wheatley ,B T Gänsicke ,Chloe E Pugh ,Christopher A Watson ,Joshua T Briegal ,Maximilian N Günther ,Jack S Acton ,M R Burleigh ,James S Jenkins ,M R Goad ,Rosanna H Tilbrook ,D Bayliss ,D R Anderson ,Beth A Henderson ,S T Hodgkin ,Sarah L Casewell ,D Queloz ,R G West

doi:10.1093/mnras/stab979

Abstract

ABSTRACT We present the results of a search for stellar flares in the first data release from the Next Generation Transit Survey (NGTS). We have found 610 flares from 339 stars, with spectral types between F8 and M6, the majority of which belong to the Galactic thin disc. We have used the 13-s cadence NGTS light curves to measure flare properties such as the flare amplitude, duration, and bolometric energy. We have measured the average flare occurrence rates of K and early to mid-M stars and present a generalized method to measure these rates while accounting for changing detection sensitivities. We find that field age K and early M stars show similar flare behaviour, while fully convective M stars exhibit increased white-light flaring activity, which we attribute to their increased spin-down time. We have also studied the average flare rates of pre-main-sequence K and M stars, showing they exhibit increased flare activity relative to their main-sequence counterparts.

Highlights

The study of stellar flares in recent years has benefited greatly from the introduction of wide-field long-duration surveys
We present the results of a search for stellar flares in the first data release from the Generation Transit Survey (NGTS)
We find that field age K and early M stars show similar flare behaviour, while fully convective M stars exhibit increased white-light flaring activity, which we attribute to their increased spin-down time

Summary

Introduction

The study of stellar flares in recent years has benefited greatly from the introduction of wide-field long-duration surveys. Schmidt et al 2007, 2016; Gizis et al 2017) could produce flares with radiated energies hundreds to thousands of times that produced by the Sun (1032 erg for the 1859 Carrington event; Carrington 1859; Tsurutani et al 2003) These flares occur on most main-sequence (MS) stars with an outer convective envelope, with the trigger believed to be due to magnetic reconnection (Shibata 1999; Benz & Gudel 2010). Due to their likelihood to flare at least once in a given night, early ground-based observations of white-light flares typically focused on nearby magnetically active M dwarfs such as AD Leo (e.g. Oskanian 1969; Pettersen, Coleman & Evans 1984) Such campaigns have been used to study statistical distributions of flare properties

Results

Discussion

Conclusion