Abstract
Abstract Several studies have documented periodic and quasi-periodic signals from the time series of dMe flare stars and other stellar sources. Such periodic signals, observed within quiescent phases (i.e., devoid of larger-scale microflare or flare activity), range in a period from 1 to 1000 s and hence have been tentatively linked to ubiquitous p-mode oscillations generated in the convective layers of the star. As such, most interpretations for the observed periodicities have been framed in terms of magnetohydrodynamic wave behavior. However, we propose that a series of continuous nanoflares, based upon a power-law distribution, can provide a similar periodic signal in the associated time series. Adapting previous statistical analyses of solar nanoflare signals, we find the first statistical evidence for stellar nanoflare signals embedded within the noise envelope of M-type stellar lightcurves. Employing data collected by the Next Generation Transit Survey (NGTS), we find evidence for stellar nanoflare activity demonstrating a flaring power-law index of 3.25 ± 0.20, alongside a decay timescale of 200 ± 100 s. We also find that synthetic time series, consistent with the observations of dMe flare star lightcurves, are capable of producing quasi-periodic signals in the same frequency range as p-mode signals, despite being purely composed of impulsive signatures. Phenomena traditionally considered a consequence of wave behavior may be described by a number of high-frequency but discrete nanoflare energy events. This new physical interpretation presents a novel diagnostic capability, by linking observed periodic signals to given nanoflare model conditions.
Highlights
Magnetic reconnection is a process occurring throughout the outer solar atmosphere, often visible in the form of solar flares
We have employed a combination of statistical and Fourierbased analysis techniques to search for evidence of nanoflare activity in M-type stars observed by Next Generation Transit Survey (NGTS)
We examined complementary A-type non-flareactive and K-type low-activity stars, which demonstrated zero median offsets, alongside very minor Fisher skewness values, highlighting the more symmetric composition of these A- and K- type time series that are devoid of nanoflare signatures
Summary
Magnetic reconnection is a process occurring throughout the outer solar atmosphere, often visible in the form of solar flares. On the contrary to the flare frequencies predicted by the dN/dE power-law relationship, several studies have documented evidence for “periodic” brightness variability through the examination of stellar intensity fluctuations, with periods ranging between 1 and 1000 s (Andrews 1989; Rodríguez et al 2016; McLaughlin et al 2018) These periodic brightenings are of uncertain origin, but they are believed to be linked to ubiquitous p-mode oscillations or other magnetohydrodynamic (MHD) wave behavior (e.g., Aschwanden et al 1999; Nakariakov & Verwichte 2005; Nakariakov et al 2010; McLaughlin et al 2018) generated in the convective layers of stars. By combining the statistical parameterization techniques developed for solar nanoflare detection with a novel Fourier spectral analysis, here we investigate stellar nanoflare signals and their potential role in the periodic brightenings found in stellar lightcurves
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
