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Short duration flares are well known to occur on cool main-sequence stars as well as on many types of 'exotic' stars. Ordinary main-sequence stars are usually pictured as being static on time scales of millions or billions of years.Our sun has occasional flares involving up to ∼ 10 31 ergs which produce optical brightenings too small in amplitude to be detected in disk-integrated brightness.However, we identify nine cases of superflares involving 10 33 to 10 38 ergs on normal solar-type stars. That is, these stars are on or near the main-sequence, are of spectral class from F8 to G8, are single (or in very wide binaries), are not rapid rotators, and are not exceedingly young in age. This class of stars includes many those recently discovered to have planets as well as our own Sun, and the consequences for any life on surrounding planets could be profound. For the case of the Sun, historical records suggest that no superflares have occurred in the last two millennia.

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Original article can be found at: http://www.iop.org/EJ/journal/aj Copyright American Astronomical Society DOI: 10.1086/300780 [Full text of this article is not available in the UHRA]We have determined the abundance of Be in stars with an array of metal abundances in order to enhance our understanding of the chemical evolution of the Galaxy, cosmic-ray theory, and cosmology. Observations of the Be II resonance lines at ??3130 and ??3131 were made at the Keck telescope with the HIRES spectrometer at a resolution of 46,000 and signal-to-noise ratios of 60???110 (per pixel) typically. Our sample includes 22 halo dwarfs and five disk stars (including the Sun). We have taken special care in determining the stellar parameters for these stars in a consistent manner. The Be abundances were found (1) from the measured equivalent width of the relatively unblended Be II line at 3131.065 ?? with an analysis that included 11 weak atomic and molecular lines near that wavelength and (2) from spectrum synthesis that included newly derived enhanced O (relative to Fe) in the synthesis calculations. The two methods are in excellent agreement. We find straight-line fits between Be and Fe: log N(Be/H) = 0.96(??0.04)[Fe/H] ??? 10.59(??0.03) ; and between Be and O: log N(Be/H) = 1.45(??0.04)[O/H] ??? 10.69(??0.04) . It seems that Be and Fe increase at the same rate during the course of the evolution of the Galaxy. But as O increases by a factor of 100, Be increases more rapidly, by a factor of 800. Traditional models in which energetic cosmic rays interact with ambient CNO nuclei in the interstellar medium to produce Be are consistent with this finding, as long as certain chemical evolution effects (such as mass outflow from the halo) are taken into account. However, models predicting a linear relationship between Be and O, such as those producing Be in the vicinity of Type II supernovae, are less consistent with our result. There is some evidence for an intrinsic spread in Be at a given [Fe/H] or [O/H]. There is currently no evidence of a primordial plateau level of Be down to log N(Be/H) = -13.5

WIYN/Hydra spectroscopy (at R∼15,000) of the moderately metal-rich Praesepe and Hyades open clusters was used to study their main sequence (MS) iron ([Fe/H]) and lithium (A(Li)) abundances. Self-consistent [Fe/H] and Li analyses of these clusters of consistent age, which we re-evaluate, confirms they have consistent [Fe/H] and provides a foundation to investigate the poorly understood G-dwarf and F-dwarf Li-depletions. Neither phenomenon agrees with standard stellar evolution theory, but possible explanations abound. We supplement our A(Li) with previously published results placed on a uniform abundance scale. This creates the largest self-consistently analyzed sample of A(Li) in both the Hyades (90) and Praesepe (110). For each star, high-precision UBVRI photometry was used to determine a ten color-based T eff and then to test for photometric peculiarities indicated by a large σ Teff (> 75 K). The stars with large σ Teff were predominantly found to be binaries or stars with peculiar (apparent) A(Li). When considering only proper-motion members that have low σ Teff and are also photometrically consistent with the cluster MS fiducial, each cluster has a more tightly defined Li morphology than previously observed and the two clusters' A(Li) are indistinguishable. This suggests that clusters of consistent age and metallicity may have consistent Li-depletion trends across a broad range of T eff ; no additional major parameters are required, at least for these two clusters. We propose that the combined Hyades and Praesepe data offer more rigorous constraints than does either cluster alone, and we discuss newly-revealed features of the combined Li-T eff trend.