We present a homogeneous survey of near-ultraviolet (NUV) /optical line and continuum emission during twenty M dwarf flares with simultaneous, high cadence photometry and spectra. These data were obtained to study the white-light continuum components to the blue and red of the Balmer jump to break the degeneracy with fitting emission mechanisms to broadband colors and to provide constraints for radiative-hydrodynamic flare models that seek to reproduce the white-light flare emission. The main results from the continuum analysis are the following: 1) the detection of Balmer continuum (in emission) that is present during all flares, with a wide range of relative contribution to the continuum flux in the NUV; 2) a blue continuum at the peak of the photometry that is linear with wavelength from λ = 4000 − 4800Å, matched by the spectral shape of hot, blackbody emission with typical temperatures of 10 000 − 12 000 K; 3) a redder continuum apparent at wavelengths longer than Hβ; this continuum becomes relatively more important to the energy budget during the late gradual phase. The hot blackbody component and redder continuum component (which we call "the conundruum") have been detected in previous U BV R colorimetry studies of flares. With spectra, one can compare the properties and detailed timings of all three components. Using time-resolved spectra during the rise phase of three flares, we calculate the speed of an expanding flare region assuming a simple geometry; the speeds are found to be ∼5 -10 km s −1 and 50 -120 km s −1 , which are strikingly consistent with the speeds at

The Very Large Array Sky Survey (VLASS) is a synoptic, all-sky radio sky survey with a unique combination of high angular resolution (≈2 5), sensitivity (a 1σ goal of 70 μJy/beam in the coadded data), full linear Stokes polarimetry, time domain coverage, and wide bandwidth (2-4 GHz). The first observations began in 2017 September, and observing for the survey will finish in 2024. VLASS will use approximately 5500 hr of time on the Karl G. Jansky Very Large Array (VLA) to cover the whole sky visible to the VLA (decl. >−40°), a total of 33 885deg 2. The data will be taken in three epochs to allow the discovery of variable and transient radio sources. The survey is designed to engage radio astronomy experts, multi-wavelength astronomers, and citizen scientists alike. By utilizing an "on the fly" interferometry mode, the observing overheads are much reduced compared to a conventional pointed survey. In this paper, we present the science case and observational strategy for the survey, and also results from early survey observations.

[1] The most powerful explosions on the Sun -in the form of bright flares, intense storms of solar energetic particles (SEPs), and fast coronal mass ejections (CMEs) -drive the most severe space-weather storms. Proxy records of flare energies based on SEPs in principle may offer the longest time base to study infrequent large events. We conclude that one suggested proxy, nitrate concentrations in polar ice cores, does not map reliably to SEP events. Concentrations of select radionuclides measured in natural archives may prove useful in extending the time interval of direct observations up to ten millennia, but as their calibration to solar flare fluences depends on multiple poorly known properties and processes, these proxies cannot presently be used to help determine the flare energy frequency distribution. Being thus limited to the use of direct flare observations, we evaluate the probabilities of large-energy solar events by combining solar flare observations with an ensemble of stellar flare observations. We conclude that solar flare energies form a relatively smooth distribution from small events to large flares, while flares on magnetically active, young Sun-like stars have energies and frequencies markedly in excess of strong solar flares, even after an empirical scaling with the mean coronal activity level of these stars. In order to empirically quantify the frequency of uncommonly large solar flares extensive surveys of stars of near-solar age need to be obtained, such as is feasible with the Kepler satellite. Because the likelihood of flares larger than approximately X30 remains empirically unconstrained, we present indirect arguments, based on records of sunspots and on statistical arguments, that solar flares in the past four centuries have likely not substantially exceeded the level of the largest flares observed in the space era, and that there is at most about a 10% chance of a flare larger than about X30 in the next 30 years.

We explore the ramification of associating the energetics of extreme magnetic reconnection events with transient mass loss in a stellar analogy with solar eruptive events. We establish energy partitions relative to the total bolometric radiated flare energy for different observed components of stellar flares, and show that there is rough agreement for these values with solar flares. We apply an equipartition between the bolometric radiated flare energy and kinetic energy in an accompanying mass ejection, seen in solar eruptive events and expected from reconnection. This allows an integrated flare rate in a particular waveband to be used to estimate the amount of associated transient mass loss. This approach is supported by a good correspondence between observational flare signatures on high flaring rate stars and the Sun, which suggests a common physical origin.If the frequent and extreme flares that young solar-like stars and low-mass stars experience are accompanied by transient mass loss in the form of coronal mass ejections, then the cumulative effect of this mass loss could be large. We find that for young solar-like stars and active M dwarfs, the total mass lost due to transient magnetic eruptions could have significant impacts on disk evolution, and thus planet formation, and also exoplanet habitability. Subject headings: stars: activity -stars: flare -stars: late-type -stars: mass-loss redshifted than blue-shifted emission components, and the hetergeneous nature of the events prevents a systematic exploration. Thus, in the absence of conclusive evidence of stellar CMEs, stellar astronomers must look to the Sun to gain insight into transient stellar mass loss on magnetically active stars. The commonality of stellar flare phenomenology with solar observations suggests that an extrapolation of solar flare/CME behavior to the more distant stars should be appropriate. The Sun has a low overall rate of mass loss (Ṁ ⊙ = 2 ×10 −14 M ⊙ yr −1 ), of which transient mass loss events comprise a minor component (typically <10%; Howard et al. 1985). However, if mass loss due to CMEs scales with flare occurrence, stars with a high flaring rate ought to also show an enhanced rate of mass lost due to transient events like CMEs. Recently, Aarnio et al. (2012) used an empirical scaling between solar flareX-ray energy and associated CME mass and extrapolated to pre-main sequence stars with measured X-ray flare energies to deduce mass loss rates of putative CMEs associated with the stellar flares. They inferred high levels of CME-related mass loss in these solar-type pre-main sequence stars of 10 −12 -10 −9 M ⊙ yr −1 . Drake et al. (2013) also used an empirical relationship between solar flare X-ray energy and associated CME mass to extrapolate to observed stellar coronal X-ray luminosities and investigate the radiative and kinetic energy requirements, assuming that the stellar coronal emissions are produced by flares whose occurrence has a power-law dependence on flare energy. They likewise find a large CME mass loss rate. Th...