Ground-based detection of G star superflares with NGTS
Jackman, James A. G.; Wheatley, Peter J.; Günther, Maximilian N.; Eigmüller, Philipp; Erikson, Anders; Goad, Michael R.; Armstrong, David J.; Burleigh, Matthew R.; Gillen, Edward; Jenkins, James S.; McCormac, James; Udry, Stéphane; West, Richard G.; Gänsicke, Boris T.; Watson, Christopher A.; Walker, Simon; Chaushev, Alexander; Grange, Andrew; Raynard, Liam; Broomhall, Anne-Marie; Thompson, Andrew P. G.; Pugh, Chloe E.
United Kingdom, Germany, Chile, Switzerland
Abstract
We present high cadence detections of two superflares from a bright G8 star (V = 11.56) with the Next Generation Transit Survey (NGTS). We improve upon previous superflare detections by resolving the flare rise and peak, allowing us to fit a solar flare inspired model without the need for arbitrary break points between rise and decay. Our data also enables us to identify substructure in the flares. From changing star-spot modulation in the NGTS data, we detect a stellar rotation period of 59 h, along with evidence for differential rotation. We combine this rotation period with the observed ROSAT X-ray flux to determine that the star's X-ray activity is saturated. We calculate the flare bolometric energies as 5.4^{+0.8}_{-0.7}× 10^{34} and 2.6^{+0.4}_{-0.3}× 10^{34} erg and compare our detections with G star superflares detected in the Kepler survey. We find our main flare to be one of the largest amplitude superflares detected from a bright G star. With energies more than 100 times greater than the Carrington event, our flare detections demonstrate the role that ground-based instruments such as NGTS can have in assessing the habitability of Earth-like exoplanets, particularly in the era of PLATO.