scholarly journals Superflares and variability in solar-type stars with TESS in the Southern hemisphere

2020 ◽  
Vol 494 (3) ◽  
pp. 3596-3610 ◽  
Author(s):  
L Doyle ◽  
G Ramsay ◽  
J G Doyle
Keyword(s):  
Statistical Analysis ◽  
Solar Flare ◽  
Southern Hemisphere ◽  
Solar Flares ◽  
Photometric Data ◽  
Light Curves ◽  
Stellar Flares ◽  
Close Relationship ◽  
Solar Type ◽  
Rotational Phase

ABSTRACT Superflares on solar-type stars have been a rapidly developing field ever since the launch of Kepler. Over the years, there have been several studies investigating the statistics of these explosive events. In this study, we present a statistical analysis of stellar flares on solar-type stars made using photometric data in 2-min cadence from Transiting Exoplanet Survey Satellite of the whole Southern hemisphere (sectors 1–13). We derive rotational periods for all the stars in our sample from rotational modulations present in the light curve as a result of large star-spot(s) on the surface. We identify 1980 stellar flares from 209 solar-type stars with energies in the range of 1031–1036 erg (using the solar flare classification, this corresponds to X1–X100 000) and conduct an analysis into their properties. We investigate the rotational phase of the flares and find no preference for any phase, suggesting the flares are randomly distributed. As a benchmark, we use GOES data of solar flares to detail the close relationship between solar flares and sunspots. In addition, we also calculate approximate spot areas for each of our stars and compare this to flare number, rotational phase, and flare energy. Additionally, two of our stars were observed in the continuous viewing zone with light-curves spanning 1 yr; as a result we examine the stellar variability of these stars in more detail.

scholarly journals Hydrodynamic Models of Solar and Stellar Flares

1989 ◽  
Vol 104 (1) ◽  
pp. 289-298
Author(s):  
Giovanni Peres
Keyword(s):  
High Resolution ◽  
Light Curve ◽  
Solar Flares ◽  
Impulsive Phase ◽  
Light Curves ◽  
Physical Parameters ◽  
The Sun ◽  
Hydrodynamic Models ◽  
X Ray ◽  
Stellar Flares

AbstractThis paper discusses the hydrodynamic modeling of flaring plasma confined in magnetic loops and its objectives within the broader scope of flare physics. In particular, the Palermo-Harvard model is discussed along with its applications to the detailed fitting of X-ray light curves of solar flares and to the simulation of high-resolution Caxix spectra in the impulsive phase. These two approaches provide complementary constraints on the relevant features of solar flares. The extension to the stellar case, with the fitting of the light curve of an X-ray flare which occurred on Proxima Centauri, demonstrates the feasibility of using this kind of model for stars too. Although the stellar observations do not provide the wealth of details available for the Sun, and, therefore, constrain the model more loosely, there are strong motivations to pursue this line of research: the wider range of physical parameters in stellar flares and the possibility of studying further the solar-stellar connection.

scholarly journals Electrons and X-Ray Emission of Solar Flares

1990 ◽  
Vol 142 ◽  
pp. 409-413
Author(s):  
V. G. Kurt
Keyword(s):  
Solar Activity ◽  
Statistical Analysis ◽  
Solar Flare ◽  
Frequency Dependence ◽  
Power Law ◽  
Solar Flares ◽  
X Rays ◽  
Fast Electrons ◽  
X Ray ◽  
Flare Frequency

A statistical analysis of solar flare X-rays and interplanetary particle fluxes, measured onboard VENERA-13, 14 Spacecraft, was performed. The correlation of fluences for different manifestations of solar flares is strong, especially for fast electrons and hard and soft X-ray emissions. Frequency dependence on fluence value ϵi for practically all Kinds of solar flare emission can be described by power law ν (ϵ > ϵO) ∼ ϵ−0.45±0.15 which does not change significantly with solar activity. For different Hα flare importances the values of ϵi were obtained. It is proposed that appearance of certain energy flare frequency is strongly dependent on some scale factor.

scholarly journals Preflare very long-periodic pulsations observed in Hα emission before the onset of a solar flare

2020 ◽  
Vol 639 ◽  
pp. L5
Author(s):  
Dong Li ◽  
Song Feng ◽  
Wei Su ◽  
Yu Huang
Keyword(s):  
Solar Flare ◽  
Light Curve ◽  
Solar Flares ◽  
Extreme Ultraviolet ◽  
Light Curves ◽  
Trigger Mechanism ◽  
X Ray ◽  
Hα Emission ◽  
Plasma Loop ◽  
Full Disk

Context. Very long-periodic pulsations during preflare phases (preflare-VLPs) have been detected in the full-disk solar soft X-ray (SXR) flux. They may be regarded as precursors to solar flares and may help us better understand the trigger mechanism of solar flares. Aims. In this Letter, we report a preflare-VLP event prior to the onset of an M1.1 circular-ribbon flare on 2015 October 16. It was simultaneously observed in Hα, SXR, and extreme ultraviolet (EUV) wavelengths. Methods. The SXR fluxes in 1−8 Å and 1−70 Å were recorded by the Geostationary Operational Environmental Satellite (GOES) and Extreme Ultraviolet Variability Experiment, respectively; the light curves in Hα and EUV 211 Å were integrated over a small local region, which were measured by the 1 m New Vacuum Solar Telescope and the Atmospheric Imaging Assembly (AIA), respectively. The preflare-VLP is identified as the repeat and quasi-periodic pulses in light curves during preflare phase. The quasi-periodicity can be determined from the Fourier power spectrum with Markov chain Monte Carlo-based Bayesian. Results. Seven well-developed pulses are found before the onset of an M1.1 circular-ribbon flare. They are firstly seen in the local light curve in Hα emission and then discovered in full-disk SXR fluxes in GOES 1−8 Å and ESP 1−70 Å, as well as the local light curve in AIA 211 Å. These well-developed pulses can be regarded as the preflare-VLP, which might be modulated by LRC-circuit oscillation in the current-carrying plasma loop. The quasi-period is estimated to be ∼9.3 min. Conclusions. We present the first report of a preflare-VLP event in the local Hα line and EUV wavelength, which could be considered a precursor of a solar flare. This finding should therefore prove useful for the prediction of solar flares, especially for powerful flares.

scholarly journals The Magnetic Corona: Magnetic Reconnection in Solar Flares

2004 ◽  
Vol 219 ◽  
pp. 91-102
Author(s):  
Harry P. Warren
Keyword(s):  
Spatial Resolution ◽  
Solar Flares ◽  
Light Curves ◽  
Small Scale ◽  
Flare Loop ◽  
X Ray ◽  
Stellar Flares ◽  
Emission Models ◽  
Reconnection Model ◽  
High Cadence

The ability of the Transition Region and Coronal Explorer (TRACE) to image the Sun at high spatial resolution and high cadence over a very broad range of temperatures makes it a unique instrument for observing solar flare plasma. TRACE observations have confirmed the reconnection model for solar flares, at least qualitatively. TRACE flare observations show impulsive footpoint brightenings that are followed by the formation of high-temperature loops in the corona. These loops then cool to lower temperatures, forming post-flare loop arcades. Comparisons between TRACE and lower spatial resolution Yohkoh Soft X-Ray Telescope (SXT) observations have revealed that solar flares are composed of a multitude of fine coronal loops. Detailed hydrodynamic modeling of flare light curves shows that this fine scale structuring is crucial to understanding the evolution of the observed emission. Models based on single, isothermal loops are not consistent with the TRACE observations. Models based on the sequential heating of small-scale loops, in contrast, are able to reproduce many of the salient features of the observed light curves. We will discuss the implication of these results for more energetic stellar flares as well as smaller-scale events that may be responsible for the heating of solar active region loops.

scholarly journals A statistical analysis of the soft X-ray profiles of solar flares

1989 ◽  
Vol 104 (2) ◽  
pp. 161-164
Author(s):  
G. Pearce ◽  
R.A. Harrison
Keyword(s):  
Statistical Analysis ◽  
Solar Flare ◽  
Solar Flares ◽  
Intensity Profile ◽  
Imaging Spectrometer ◽  
X Ray ◽  
X Ray Imaging ◽  
Selection Of

We undertake a statistical analysis of the soft X-ray (3.5 – 5.5 keV) profiles of solar flares as observed with the Hard X-ray Imaging Spectrometer on the SMM. The durations, maximum intensities and intensity profiles of the flares are examined. The properties of the “typical” solar flare are discussed. The distributions of the measured parameters with respect to one another reveal some interesting results. In common with past studies, we conclude that there is no evidence to suggest that more than one type of event is being viewed, despite a desire evident in the literature to place events into distinct groups. We also conclude that commonly held views about the relatonships between flare duration and intensity, profile asymmetries and intensity etc.. are in error. For more details of the flare events, the selection of data and the method of analysis, the reader is referred to Pearce and Harrison (1988).

scholarly journals Solar and stellar flares and their impact on planets

2015 ◽  
Vol 11 (S320) ◽  
pp. 3-24
Author(s):  
Kazunari Shibata
Keyword(s):  
Solar Flare ◽  
Total Energy ◽  
Solar Flares ◽  
Magnetic Energy ◽  
Slow Rotation ◽  
The Sun ◽  
Stellar Flare ◽  
Terrestrial Environment ◽  
The Earth ◽  
Stellar Flares

AbstractRecent observations of the Sun revealed that the solar atmosphere is full of flares and flare-like phenomena, which affect terrestrial environment and our civilization. It has been established that flares are caused by the release of magnetic energy through magnetic reconnection. Many stars show flares similar to solar flares, and such stellar flares especially in stars with fast rotation are much more energetic than solar flares. These are called superflares. The total energy of a solar flare is 1029 − 1032 erg, while that of a superflare is 1033 − 1038 erg. Recently, it was found that superflares (with 1034 − 1035 erg) occur on Sun-like stars with slow rotation with frequency once in 800 - 5000 years. This suggests the possibility of superflares on the Sun. We review recent development of solar and stellar flare research, and briefly discuss possible impacts of superflares on the Earth and exoplanets.

scholarly journals Superflares and “Hot-Jupiters”

2004 ◽  
Vol 202 ◽  
pp. 112-114
Author(s):  
Eric P Rubenstein
Keyword(s):  
Magnetic Reconnection ◽  
Solar Flares ◽  
Hot Jupiters ◽  
Stellar Flares ◽  
Solar Type ◽  
Jovian Planet

Schaefer, King & Deliyannis (2000) reported the discovery of powerful stellar flares on single, solar-type stars. The outbursts on these F8-G8 stars were 102–107 times more powerful than the largest solar flares. The observed properties are similar to the magnetic reconnection driven events of RS CVn binaries. Rubenstein & Schaefer (2000) suggested that superflares may be magnetic reconnection events mediated by the interaction between the magnetospheres of a close-in jovian planet and the star. Stars exhibiting superflares may therefore harbor detectable planets.

scholarly journals Energy Release in Stellar Flares

1990 ◽  
Vol 142 ◽  
pp. 77-92
Author(s):  
R. Pallavicini
Keyword(s):  
Solar Flares ◽  
Convincing Evidence ◽  
Fundamental Question ◽  
M Dwarfs ◽  
Physical Mechanisms ◽  
Physical Conditions ◽  
Stellar Flares ◽  
Model Predictions ◽  
Different Types ◽  
Solar Type

Flare-like events similar to those observed on the Sun occur on many different types of stars, particularly on late K and M dwarfs. Although the physical mechanisms responsible for these events remain largely unknown, it is likely that the flare energy derives from dissipation of magnetic fields as is the case for solar flares. We review the basic observational facts that suggest an analogy between solar and stellar flares and we discuss how the different physical conditions occurring on stars may affect the application of current solar-type models to the stellar case. We show that, in spite of a qualitative agreement found between model predictions and observations, there is still no convincing evidence that stellar flares are simply scaled-up versions of solar flares. Major advances in the observations of stellar flares are required before this fundamental question can be safely addressed.

scholarly journals Probing the origin of stellar flares on M dwarfs using TESS data sectors 1–3

2019 ◽  
Vol 489 (1) ◽  
pp. 437-445 ◽  
Author(s):  
L Doyle ◽  
G Ramsay ◽  
J G Doyle ◽  
K Wu
Keyword(s):  
Solar Flares ◽  
Mass Star ◽  
M Dwarfs ◽  
Low Mass Stars ◽  
Rotational Modulation ◽  
Stellar Flares ◽  
Low Mass ◽  
Band Pass ◽  
The Relationship ◽  
Rotational Phase

ABSTRACT Detailed studies of the Sun have shown that sunspots and solar flares are closely correlated. Photometric data from Kepler/K2 has allowed similar studies to be carried out on other stars. Here, we utilize Transiting Exoplanet Survey Satellite (TESS) photometric 2-min cadence of 167 low-mass stars from Sectors 1 to 3 to investigate the relationship between star-spots and stellar flares. From our sample, 90 per cent show clear rotational modulation likely due to the presence of a large, dominant star-spot and we use this to determine a rotational period for each star. Additionally, each low-mass star shows one or more flares in its light curve and using Gaia Data Release 2 parallaxes and SkyMapper magnitudes we can estimate the energy of the flares in the TESS band-pass. Overall, we have 1834 flares from the 167 low-mass stars with energies from 6.0 × 1029 to 2.4 × 1035 erg. We find none of the stars in our sample show any preference for rotational phase, suggesting the lack of a correlation between the large, dominant star-spot, and flare number. We discuss this finding in greater detail and present further scenarios to account for the origin of flares on these low-mass stars.

Phase difference between long-term magnetic feature activity and flare activity of solar-type stars

2018 ◽  
Vol 13 (S340) ◽  
pp. 217-220 ◽  
Author(s):  
Han He ◽  
Huaning Wang ◽  
Mei Zhang ◽  
Ahmad Mehrabi ◽  
Yan Yan ◽  
...  
Keyword(s):  
Light Curve ◽  
Phase Difference ◽  
Light Curves ◽  
Magnetic Feature ◽  
Flare Activity ◽  
Source Regions ◽  
Rotational Modulation ◽  
Stellar Flares ◽  
Solar Type

AbstractIn the light curves of some solar-type stars, both rotational modulation (caused by corotating bright or dark magnetic features) and flare phenomena can be seen simultaneously. Based on these light curve observations, the relation between stellar magnetic feature activity (reflected by the rotational modulation component of the light curves) and flare activity can be investigated. Here, we analyze the light curve data of a flare-abundant solar-type star, KIC 6034120, observed with Kepler space telescope, and describe magnetic feature activity property by fluctuation range of light curves and flare activity property by time occupation ratio of flares. Distinct phase difference between long-term magnetic feature activity and flare activity is found for this star, which indicates that the source regions of stellar flares (e.g., starspots) on this star do not dominate the rotational modulation of light curves, yet they might be related to a same stellar dynamo process.

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