The assumption of an equilibrium (Maxwellian) distribution of electron energies cannot explain observed high intensities of the Si XIId satellite lines relative to the Si XIII allowed lines during the flares. However, the presence of n-distribution with a higher and narrower shape than the Maxwellian one is able to explain this behavior. We calculated the ionization equilibrium for the non-thermal n-distributions using the latest atomic data for each element up to the proton number of 30. Significant changes in the shape and maxima of the ion abundance peak occur and can strongly influence the temperature diagnostics.

Kepler observations show that starspots and superflares are present in A stars. An analysis of Kepler short-cadence data shows that the relative number of A/F flare stars is only a factor of four smaller than K/M flare stars, which can be explained as a selection effect. The average maximum flare amplitude does not depend much on spectral type, which is to be expected if the size of the active region scales in proportion to the stellar radius. The presence of starspots and superflares in A stars suggests that these stars have magnetic fields. However, X-ray observations show that A stars do not possess coronae. I therefore conclude that convection in the stellar envelope is a necessary condition for the formation of the corona. A magnetic field may be necessary to enable coronal heating.

In this talk, we discuss the formation of the near-ultraviolet and optical continuum emission in M dwarf flares through the formation of a dense, heated chromospheric condensation. Results are used from a recent radiative-hydrodynamic model of the response of an M dwarf atmosphere to a high energy flux of nonthermal electrons. These models are used to infer the charge density and optical depth in continuum emitting flare layers from spectra covering the Balmer jump and optical wavelength regimes. Future modeling and observational directions are discussed.

Observations of flare emissions in the optical continuum are very rare. Therefore, the analysis of such observations is useful and may contribute to our understanding of the flaring chromosphere and photosphere. We study the white light continuum emission observed during the X6.9 flare. This emission comes not only from the flare ribbons but also form the nearby plage area. The main aim of this work is to disentangle the flare and plage (facula) emission. We analyzed the spatial, spectral and temporal evolution of the flare and plage properties by analyzing multi-wavelength observations. We study the morphological correlation of the white-light continuum emission observed with different instruments. We found that some active region areas which produce the continuum emission correspond rather to plages than to the flare kernels. We showed that in some cases the continuum emission from the WL flare kernels is very similar to the continuum emission of faculae.

To better understand the differences between coronal cloud prominences and channel prominences, we systematically identified and analyzed coronal cloud prominences recorded in SDO/AIA images at 304 Å from 2010 May 20 through 2012 April 28. For the 225 cases identified, their numbers vary directly with the sunspot number. Their durations are typically less than 3 days. Their most frequent maximum height is 90,000 + and - 10,000 km. We offer our hypothesis that many coronal cloud prominences originate from some of the mass of previously erupted filaments ejected high out of their filament channels; subsequently part of this mass falls and collects in leaky magnetic troughs among coronal magnetic fields which constrain the leaked mass to slowly drain downward along curved trajectories where it appears as coronal rain. Currently there is inadequate evidence for a convincing correspondence between either coronal cloud prominences or channel prominences with stellar prominences detected to date.

Solar and stellar flares due to impacts of comet nuclei and falling evaporating bodies, FEBs, with the Sun/stars are analytically considered. It is shown that impacts of sun/stargrazing comets will be accompanied by essential aerodynamic effects: nuclei crushing and expansion/ flattening of crushed mass within the chromosphere. These processes lead to impulse generation of a hot plasma, strong shock wave in the thin layer near photosphere, eruption of the hot ionized clump to the lower corona, i.e., impact-induced solar/stellar flares.

The rotational braking of magnetic stars through the extraction of angular momentum by stellar winds has been studied for decades, leading to several formulations. We recently demonstrated that the dependency of the braking law on the coronal magnetic field topology can be taken into account through a simple scalar parameter: the open magnetic flux. The Zeeman-Doppler Imaging technique has brought the community a reliable and precise description of the surface magnetic field of distant stars. The coronal structure can then be reconstructed using a potential field extrapolation, a technique that relies on a source surface radius beyond which all field lines are open, thus avoiding a computationally expensive MHD simulations. We developed a methodology to choose the best source surface radius in order to estimate open flux and magnetic torques. We apply this methodology to five K-type stars from 25 to 584 Myr and the Sun, and compare the resulting torque to values expected from spin evolution models.

Here, we present a set of time-dependent 3D RMHD simulations of a M-dwarf star representative of AD Leo, which extend from the upper convection zone into the chromosphere. The 3D model atmospheres are characterized by a very dynamic and intermittent structure on small spatial and temporal scales and a wealth of physical processes, which by nature cannot be described by means of 1D static model atmospheres. Artificial observations of these models imply that a combination of complementary diagnostics such as Ca II lines and the continuum intensity from UV to millimeter wavelengths, probe various properties of the dynamics, thermal and magnetic structure of the photosphere and the chromosphere and thus provide measures of stellar activity, which can be compared to observations. The complicated magnetic field structure and its imprint in synthetic diagnostics may have important implications for the understanding and characterization of stellar activity and with it possibly for the evaluation of planetary habitability around active M-dwarf stars.

Comparing with solar cycles 21-23, the level of solar activity in the current cycle is very low. So far, there have been only five SARs and 45 X class flares. The monthly smoothed total solar irradiance decreased sharply by 0.09% from the maximum of cycle 23 to the minima between cycles 23 and 24. In this contribution, we present new studies on SARs in Cycle 24. The SARs in the current cycle have relatively smaller flare index (Iflare) and composite vector field index (Icom) comparing with the SARs in cycles 22 and 23. There is a clearly linear relationship between Iflare and Icom. The emphasis of this contribution is put on the similarity and different behaviors of vector magnetic fields of the SARs in the current solar cycle and the previous ones. We try to get a satisfactory account for the general characteristics and relatively lower level of solar flare activity in Cycle 24.

Based on the New Vacuum Solar Telescope observations, some new results about the solar activities are obtained. (1) In the Hα line, a flux rope tracked by filament activation is detected for the first time. There may exist some mild heating during the filament activation. (2) The direct observations illustrate the mechanism of confined flares, i.e., the flares are triggered by magnetic reconnection between the emerging loops and the pre-existing loops and prevented from being eruptive by the overlying loops. (3) The solid observational evidence of magnetic reconnection between two sets of small-scale loops is reported. The successive slow reconnection changes the conditions around the reconnection area and leads to the rapid reconnection. (4) An ensemble of oscillating bright features rooted in a light bridge is observed and given a new name, light wall. The light wall oscillations may be due to the leakage of p-modes from below the photosphere.

Late-type stars with thick convective zones and rapid rotations exhibit magnetic activity phenomena, such as starspots, plages, and flares. However, in many such kinds of eclipsing binaries, the details of the active phenomena are not well understood. In order to improve our understanding of stellar magnetic activities, we are carrying out an extensive study of the magnetic activities of eclipsing binaries by multi-color CCD photometry using several telescopes (SARA 90cm at KPNO, and NAOC 85cm and 60 cm telescopes at Xinglong). In this paper, we will present our preliminary results with revised orbital parameters, starspot parameters, and stellar flare events on DV Psc and BX Tri.

The Sun drives most events of space weather in the vicinity of the Earth. Because the activities of the Sun are complicated, a visualized chart with key objects of solar activities is needed for space weather forecast. This work investigates the key objects in research during the past forty years and surveys a variety of solar observational data. We design the solar synoptic chart (SSC) that covers the key objects of solar activities, i.e., active regions, coronal holes, filaments/prominences, flares and coronal mass ejections, and synthesizes images from different heights and temperatures of solar atmosphere. The SSC is used to analyze the condition of the Sun in March 2012 and October 2014 as examples. The result shows that the SSC is timely, comprehensive, concise and easy to understand. It has the potentiality for space weather forecast and can help in improving the public education.

During the declining phase of the Solar cycle 24, a new peak appeared on January 7, 2014. The release of x-class flares, with the high energetic particles, were found to be more intense than that occurred during the main peak of the same cycle. Few X-class flares were released, lately, during the year 2014. We note that during the last 5 solar cycles, a new peak has appeared, releasing high energetic particles and X-class solar flares, which are called the secondary peak or the double peak of solar cycle. The aim of this descriptive study is to follow the morphological and magnetic changes of the active region before, during, and after the production of X-class flares according to data analysis. Furthermore, the causes of the release of such eruptive storms have been discussed for the period, year 2014, during the double peak of the solar cycle 24.

A feed-forward neural network which can account for nonlinear relationship was used to model total solar irradiance (TSI). A single layer feed-forward neural network with Levenberg-marquardt back-propagation algorithm have been implemented for modeling daily total solar irradiance from daily photometric sunspot index, and core-to-wing ratio of Mg II index data. In order to obtain the optimum neural network for TSI modeling, the root mean square error (RMSE) and mean absolute error (MAE) have been taken into account. The modeled and measured TSI have the correlation coefficient of about R=0.97. The neural networks (NNs) model output indicates that reconstructed TSI from solar proxies (photometric sunspot index and Mg II) can explain 94% of the variance of TSI. This modeled TSI using NNs further strengthens the view that surface magnetism indeed plays a dominant role in modulating solar irradiance.

Started its regular, daily operational phase in 2011, by the occasion of the Symp264 in the XXVII IAU GA at Rio de Janeiro, the results so far obtained show that the Heliometer of the Observatorio Nacional fulfilled its planed performance of single measurement to the level of few tens of milli-arcsecond, freely pivoting around the heliolatitudes without systematic deviations or error enhancement. We present and discuss the astrometric additions required on ground based astronomic programs. We also discuss instrumental and observations terms, namely the constancy of the basic heliometric angle, against which the measurements are made, and the independence to meteorological and pointing conditions.

The possibility that the Sun's radius is changing, even at a faint level, has been discussed over a long time. As the solar radius is certainly one of the most important basic pieces of astrophysical information, it is crucial to determine the physical mechanisms that may cause shrinking or expansion of the solar envelope. The wavelength dependence has been poorly inspected up to now. Here we examine recent solar radius determinations from space observations, mainly from Mercury and Venus transits, made by different teams in 2006, 2012 and 2014. Seemingly, the results are not consistent: authors interpreted the discrepancies because of the different methods of analysis used in their work. However, looking at the wavelength dependence, adding other available observations, from X-EUV up to radio, a typical relationship between the radius and the wavelength can be found, reflecting the different heights at which the lines are formed. Possible explanations are discussed. Such results can be interesting for studying solar-stellar connections.

The widths of total solar eclipse paths depends on the diameter of the Sun, so if observations are obtained near both the northern and southern limits of the eclipse path, in principle, the angular diameter of the Sun can be measured. Concerted efforts have been made to obtain contact timings from locations near total solar eclipse path edges since the mid 19th century, and Edmund Halley organized a rather successful first effort in 1715. Members of IOTA have been making increasingly sophisticated observations of the Baily's bead phenomena near central solar eclipse path edges since 1970.

The magnetic activity levels of planet host stars may differ from that of stars not known to host planets in several ways. Hot Jupiters may induce activity in their hosts through magnetic interactions, or through tidal interactions by affecting their host's rotation or convection. Measurements of photospheric, chromospheric, or coronal activity might then be abnormally high or low compared to control stars that do not host hot Jupiters, or might be modulated at the planet's orbital period. Such detections are complicated by the small amplitude of the expected signal, by the fact that the signals may be transient, and by the difficulty of constructing control samples due to exoplanet detection biases and the uncertainty of field star ages. We review these issues, and discuss avenues for future progress in the field.

One potential star-planet interaction mechanism for hot Jupiters involves planetary heating via currents set up by interactions between the stellar wind and planetary magnetosphere. Early modeling results indicate that such currents, which are analogous to the terrestrial global electric circuit (GEC), have the potential to provide sufficient heating to account for the additional radius inflation seen in some hot Jupiters. Here we present a more detailed model of this phenomenon, exploring the scale of the effect, the circumstances under which it is likely to be significant, implications for the planetary magnetospheric structure, and observational signatures.

The spectral and temporal behavior of exoplanet host stars is a critical input to models of the chemistry and evolution of planetary atmospheres. High-energy photons (X-ray to NUV) from these stars regulate the atmospheric temperature profiles and photochemistry on orbiting planets, influencing the production of potential “biomarker” gases. We report first results from the MUSCLES Treasury Survey, a study of time-resolved UV and X-ray spectroscopy of nearby M and K dwarf exoplanet host stars. This program uses contemporaneous Hubble Space Telescope and Chandra (or XMM) observations to characterize the time variability of the energetic radiation field incident on the habitable zones planetary systems at d ≲ 20 pc. We find that all exoplanet host stars observed to date exhibit significant levels of chromospheric and transition region UV emission. M dwarf exoplanet host stars display 30–7000% UV emission line amplitude variations on timescales of minutes-to-hours. The relative flare/quiescent UV flux amplitudes on weakly active planet-hosting M dwarfs are comparable to active flare stars (e.g., AD Leo), despite their weak optical activity indices (e.g., Ca II H and K equivalent widths). We also detect similar UV flare behavior on a subset of our K dwarf exoplanet host stars. We conclude that strong flares and stochastic variability are common, even on “optically inactive” M dwarfs hosting planetary systems. These results argue that the traditional assumption of weak UV fields and low flare rates on older low-mass stars needs to be revised.