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On the time scale of stellar evolution, the sun is a middle-aged star. The observed surface rotation rates of young solar-type stars are up to 50 times that of the [...], Splitting of the sun's global oscillation frequencies by large-scale flows can be used to investigate how rotation varies with radius and latitude within the solar interior. The nearly uninterrupted observations by the Global Oscillation Network Group (GONG) yield oscillation power spectra with high duty cycles and high signal-to-noise ratios. Frequency splittings derived from GONG observations confirm that the variation of rotation rate with latitude seen at the surface carries through much of the convection zone, at the base of which is an adjustment layer leading to latitudinally independent rotation at greater depths. A distinctive shear layer just below the surface is discernibie at low to mid-latitudes.

Several million resonant acoustic normal modes (eigenmodes) of the sun are excited stochastically in the subsurface turbulent layer. The frequencies v, amplitudes A, and characteristic widths γ of such modes, [...], The Global Oscillation Network Group (GONG) project estimates the frequencies, amplitudes, and linewidths of more than 250,000 acoustic resonances of the sun from data sets lasting 36 days. The frequency resolution of a single data set is 0.321 microhertz. For frequencies averaged over the azimuthal order m, the median formal error is 0.044 microhertz, and the associated median fractional error is 1.6 x 10[sup.-5]. For a 3-year data set, the fractional error is expected to be 3 x 10[sup.-6]. The GONG m-averaged frequency measurements differ from other helioseismic data sets ky 0.03 to 0.08 microhertz. The differences arise from a combination of systematic errors, random errors, and possible changes in solar structure.

Stars are born from contracting interstellar clouds. The initial rapid phases of evolution are rather uncertain; however, the protostar eventually settles down to a state where the forces of gravity [...], Data from the Global Oscillation Network Group (GONG) project and other helioseismic experiments provide a test for models of stellar interiors and for the thermodynamic and radiative properties, on which the models depend, of matter under the extreme conditions found in the sun. Current models are in agreement with the helioseismic inferences, which suggests, for example, that the disagreement between the predicted and observed fluxes of neutrinos from the sun is not caused by errors in the models. However, the GONG data reveal subtle errors in the models, such as an excess in sound speed just beneath the convection zone. These discrepancies indicate effects that have so far not been correctly accounted for; for example, it is plausible that the sound-speed differences reflect weak mixing in stellar interiors, of potential importance to the overall evolution of stars and ultimately to estimates of the age of the galaxy based on stellar evolution calculations.

One of the principal purposes of the Global Oscillation Network Group (GONG) project is to determine the internal structure of the sun. Helioseismology is used to model the stratification of [...], Global Oscillation Network Group data reveal that the internal structure of the sun can be well represented by a calibrated standard model. However, immediately beneath the convection zone and at the edge of the energy-generating core, the sound-speed variation is somewhat smoother in the sun than it is in the model. This could be a consequence of chemical inhomogeneity that is too severe in the model, perhaps owing to inaccurate modeling of gravitational settling or to neglected macroscopic motion that may be present in the sun. Accurate knowledge of the sun's structure enables inferences to be made about the physics that controls the sun; for example, through the opacity, the equation of state, or wave motion. Those inferences can then be used elsewhere in astrophysics.

Scientific research shows that solar flares cause seismic waves on the sun. Seismic data from the Solar and Heliospheric Observatory indicates that x-rays, high-speed plasma flows and particle beams cause seismic waves like those predicted in theoretical models. Graphs showing the x-ray flux from a Burst and Transient Source Experiment solar flare are illustrated.

New solar soft X-ray (SXR) and extreme ultraviolet (EUV) irradiance observations from NASA Solar Dynamics Observatory (SDO) EUV Variability Experiment (EVE) provide full coverage from 0.1 to 106 nm and continuously at a cadence of 10 seconds for spectra at 0.1 nm resolution. These observations during flares can usually be decomposed into four distinct characteristics: impulsive phase, gradual phase, coronal dimming, and EUV late phase. Over 6000 flares have been observed during the SDO mission; some flares show all four phases, and some only show the gradual phase. The focus is on the newer results about the EUV late phase and coronal dimming and its relationship to coronal mass ejections (CMEs). These EVE flare measurements are based on observing the sun-as-a-star, so these results could exemplify stellar flares. Of particular interest is that new coronal dimming measurements of stars could be used to estimate mass and velocity of stellar CMEs. [ABSTRACT FROM PUBLISHER]

Solar flare X-ray loop top sources (LTSs) are known since early observations from Skylab.They are always present accompanying long duration events (LDE), but their nature remains unclear. One of the main unknowns is spatial structure of LTSs. Observations indicate that LTSs are large and diffuse, but several authors suggested that there is present a fine, internal structure within them which should be resolved even using present space instrumentation.We present an example for the solar flare well observed by SDO/AIA and RHESSI. The LTS was dynamic with an episode of splitting into two sources. We performed detailed analysis of X-ray sources morphology using restored RHESSI images. Moreover, we conducted a number of simulations taking into account various possible spatial distributions of X-ray emission. We have found that in case of the flare investigated RHESSI should be capable to detect the fine structure if present. However it is not visible on the restored images. Some of our simulations suggest that we can also miss large, diffuse sources in the X-ray observations which may eventually lead to misinterpretation of the observed X-ray features. [ABSTRACT FROM PUBLISHER]

We carried out spectroscopic observations with Subaru/HDS of 50 solar-type superflare stars found from Kepler data. More than half (34 stars) of the target stars show no evidence of the binary system, and we confirmed atmospheric parameters of these stars are roughly in the range of solar-type stars.We then conducted the detailed analyses for these 34 stars. First, the value of the “v sin i” (projected rotational velocity) measured from spectroscopic results is consistent with the rotational velocity estimated from the brightness variation. Second, there is a correlation between the amplitude of the brightness variation and the intensity of Ca II IR triplet line. All the targets expected to have large starspots because of their large amplitude of the brightness variation show high chromospheric activities compared with the Sun. These results support that the brightness variation of superflare stars is explained by the rotation of a star with large starspots. [ABSTRACT FROM PUBLISHER]

We searched for superflares on solar-type stars using the Kepler short-cadence (1-min sampling) data in order to detect superflares with short duration. We found 187 superflares on 23 solar-type stars whose bolometric energy ranges from the order of 1032 erg to 1036 erg. Using these new data combined with the results from the data with 30-min sampling, we found the occurrence frequency (dN/dE) of superflares as a function of flare energy (E) shows the power-law distribution (dN/dE ∝ E−α) with α=1.5 for 1033 < E < 1036 erg. The upper limit of energy released by superflares is basically comparable to a fraction of the magnetic energy stored near starspots which is estimated from the amplitude of brightness variations. We also found that the duration of superflares (τ) increases with the flare energy (E) as τ ∝ E0.39±0.03. This can be explained if we assume the time-scale of flares is determined by the Alfvén time. [ABSTRACT FROM PUBLISHER]

Ultra-precise light curves from Kepler provide the best opportunity to determine rates and statistical properties of stellar flares. From 11 months of data on the active M4 dwarf, GJ 1243, we have built the largest catalog of flares for a single star: over 6100 events. Combining 885 of our most pristine flares, we generated an empirical white-light flare template. This high-fidelity template shows a rapid initial rise, and two distinct exponential cooling phases. This template is useful in constraining flare energies and for improved flare detection in many surveys. Complex, multi-peaked events are more common for higher energy flares in this sample. Using our flare template we characterize the structure of complex events. In this contributed talk, I presented results from our boutique study of GJ 1243, and described an expanded investigation of the structure of complex flares and their connection to solar events. [ABSTRACT FROM PUBLISHER]

We present estimates of cool-star X-ray flare rates determined from the XMM-Tycho survey (Pye et al. 2015, A&A, 581, A28), and compare them with previously published values for the Sun and for other stellar EUV and white-light samples. We demonstrate the importance of applying appropriate corrections, especially in regard to the total, effective size of the stellar sample. Our results are broadly consistent with rates reported in the literature for Kepler white-light flares from solar-type stars, and with extrapolations of solar flare rates, indicating the potential of stellar X-ray flare observations to address issues such as ‘space weather’ in exoplanetary systems and our own solar system. [ABSTRACT FROM PUBLISHER]

High-cadence spectroscopy of solar and stellar coherent radio bursts is a powerful diagnostic tool to study coronal conditions during magnetic reconnection in flares and to detect coronal mass ejections (CMEs). We present results from wide-bandwidth VLA observations of nearby active M dwarfs, including some observations with simultaneous VLBA imaging. We also discuss the Starburst program, which will make wide-bandwidth radio spectroscopic observations of nearby active flare stars for 20+ hours a day for multiple years, coming online in spring 2016 at the Owens Valley Radio Observatory. This program should vastly increase the diversity of observed stellar radio bursts and our understanding of their origins, and offers the potential to detect a population of CME-associated radio bursts. [ABSTRACT FROM PUBLISHER]

Recent 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. [ABSTRACT FROM PUBLISHER]

Coronal mass ejections are the most spectacular form of solar activity and they play a key role in driving space weather at the Earth. These eruptions are associated with active regions and occur throughout an active region's entire lifetime. All coronal mass ejection models invoke the presence of a twisted magnetic field configuration known as a magnetic flux rope either before or after eruption onset. The observational identification of magnetic flux ropes in the solar atmosphere using remote sensing data represents a challenging task, but theoretical models have led to the understanding that there are signatures that reveal their presence. The range of coronal mass ejection models are helping build a more complete picture of both the trigger and drivers of these eruptions. [ABSTRACT FROM PUBLISHER]

Kepler observations suggest that G-type stars produce powerful flares suggesting that the early Earth may also have been exposed to frequent and energetic solar explosive events generated by the young Sun. We show that powerful coronal mass ejection (CME) events associated with superflares impacting the Earth magnetosphere with a frequency of 1 event/day. What was the impact of superflares, CMEs and associated solar energetic particle (SEPs) events on the atmospheric erosion of the young Earth and habitability? In this paper we discuss our three-dimensional (3D) magnetohydrodynamic (MHD) simulations that show that frequent and energetic CMEs from the early Sun continuously destroyed the sub-solar parts of Earth's magnetosphere at heights < 1.25 RE. This suggests that CME shock accelerated energetic protons are capable of penetrating into the polar cap region and breaking atmospheric molecular nitrogen, the major ingredient of the early Earth atmosphere, into atomic nitrogen. Photo-collisional dissociation of molecular nitrogen and carbon dioxide creates reactive chemistry that efficiently produces nitrous oxide and hydrogen cyanide, the essential molecule in prebiotic life chemistry. This raises an possibility that frequent super-CMEs could serve as a potential catalyst for the origin of life on early Earth. [ABSTRACT FROM PUBLISHER]

Lyman-α radiation dominates the ultraviolet spectra of G, K, and M stars and is a major photodissociation source for H2O, CO2, and CH4 in the upper atmospheres of exoplanets. We obtain intrinsic Lyman-α line fluxes for late-type stars by correcting for interstellar absorption or by scaling from other spectroscopic observables. When stars flare, all emission lines brighten by large factors as shown by HST spectra. We describe photochemical models of the atmosphere of the mini-Neptune GJ 436b (Miguel et al. 2015) that show the effects of flaring Lyman-α fluxes on atmospheric chemical abundances. [ABSTRACT FROM PUBLISHER]

Abundant observations in recent years show that the flares are more complex than the 2D standard flare model presents. This proposes a challenge to the 2D flare model and 3D flare model has been developed. We report the complex evolution of flare ribbons and a flux rope in a C8.9 flare event. The two ribbons slipped in opposite directions along the neutral line and the eastern ribbon seemed a hook-like structure. The flare loops were crossed each other, composing a “bi-fan” system. The slipping magnetic reconnection is involved in the flare and leads to slipping motion of flare ribbons and complex evolution of flare loops. Overlying the flare loops, a large-scale flux rope was erupted and meanwhile the eastern end of the flux rope changed with time and slipped along the hook-like ribbon. The fine structures of the flux rope delineated a “triangle-flag” surface, which may imply one-half of the coronal quasi-separatrix layers that surrounds a flux rope. We suggest that the heating process of slipping magnetic reconnection during the flare caused the apparent motion of the flux rope ends. [ABSTRACT FROM PUBLISHER]

For the past six years, the EUV Variability Experiment (EVE) onboard the Solar Dynamics Observatory has been monitoring changes in the Sun's extreme ultraviolet output over a range of timescales. Its primary function is to provide measurements of the solar spectral irradiance that is responsible for driving fluctuations in Earth's ionosphere and thermosphere. However, despite its modest spectral resolution and lack of spatial information, the EVE spectral range contains many lines and continua that have become invaluable for diagnosing the response of the lower solar atmosphere itself to an injection of energy, particularly during a flare's impulsive phase. In addition, high temperature emission lines can also be used to track changes in temperature and density of flaring plasma in the corona. The high precision of EVE observations are therefore crucial in helping us understand particle acceleration and energy transport mechanisms during solar flares, as well as the origins of the Sun's most geoeffective emission. [ABSTRACT FROM PUBLISHER]