We present a catalog of panchromatic spectral energy distributions (SEDs) for 7 M and 4 K dwarf stars that span X-ray to infrared wavelengths (5Å -5.5 µm). These SEDs are composites of Chandra or XMM-Newton data from 5 -∼50Å, a plasma emission model from ∼50 -100Å, broadband empirical estimates from 100 -1170Å, HST data from 1170 -5700Å, including a reconstruction of stellar Lyman-α emission at 1215.67Å, and a PHOENIX model spectrum from 5700 -55000Å. Using these SEDs, we computed the photodissociation rates of several molecules prevalent in planetary atmospheres when exposed to each star's unattenuated flux ("unshielded" photodissociation rates) and found that rates differ among stars by over an order of magnitude for most molecules. In general, the same spectral regions drive unshielded photodissociations both for the minimally and maximally FUV active stars. However, for O 3 visible flux drives dissociation for the M stars whereas NUV flux drives dissociation for the K stars. We also searched for an FUV continuum in the assembled SEDs and detected it in 5/11 stars, where it contributes around 10% of the flux in the range spanned by the continuum bands. An ultraviolet continuum shape is resolved for the star Eri that shows an edge likely attributable to Si II recombination. The 11 SEDs presented in this paper, available online through the Mikulski Archive for Space Telescopes, will be valuable for vetting stellar upperatmosphere emission models and simulating photochemistry in exoplanet atmospheres.

M dwarf stars are known for their vigorous flaring. This flaring could impact the climate of orbiting planets, making it important to characterize M dwarf flares at the short wavelengths that drive atmospheric chemistry and escape. We conducted a far-ultraviolet flare survey of 6 M dwarfs from the recent MUSCLES (Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems) observations, as well as 4 highly-active M dwarfs with archival data. When comparing absolute flare energies, we found the active-M-star flares to be about 10× more energetic than inactive-M-star flares. However, when flare energies were normalized by the star's quiescent flux, the active and inactive samples exhibited identical flare distributions, with a power-law index of -0.76 +0.1 −0.09 (cumulative distribution). The rate and distribution of flares are such that they could dominate the FUV energy budget of M dwarfs, assuming the same distribution holds to flares as energetic as those cataloged by Kepler and ground-based surveys. We used the observed events to create an idealized model flare with realistic spectral and temporal energy budgets to be used in photochemical simulations of exoplanet atmospheres. Applied to our own simulation of direct photolysis by photons alone (no particles), we find Corresponding author: R. O. Parke Loyd robert.loyd@colorado.edu * Based on observations made with the NASA/ESA Hubble Space Telescope, obtained from the data archive at the Space Telescope Science Institute. STScI is operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. † The scientific results reported in this article are based in part on observations made by the Chandra X-ray Observatory. ‡ Based in part on observations obtained with XMM-Newton, an ESA science mission with instruments and contributions directly funded by ESA Member States and NASA arXiv:1809.07322v2 [astro-ph.SR] 25 Sep 2018 2 the most energetic observed flares have little effect on an Earth-like atmosphere, photolyzing ∼0.01% of the total O 3 column. The observations were too limited temporally (73 h cumulative exposure) to catch rare, highly energetic flares. Those that the power-law fit predicts occur monthly would photolyze ∼1% of the O 3 column and those it predicts occur yearly would photolyze the full O 3 column. Whether such energetic flares occur at the rate predicted is an open question.

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The evolution of the 2006 outburst of the recurrent nova RS Ophiuchi was followed with 12 X-ray grating observations with Chandra and XMM-Newton. We present detailed spectral analyses using two independent approaches. From the best data set, taken on day 13.8 after outburst, we reconstruct the temperature distribution and derive elemental abundances. We find evidence for at least two distinct temperature components on day 13.8 and a reduction of temperature with time. The X-ray flux decreases as a power law, and the powerlaw index changes from −5/3 to −8/3 around day 70 after outburst. This can be explained by different decay mechanisms for the hot and cool components. The decay of the hot component and the decrease in temperature are consistent with radiative cooling, while the decay of the cool component can be explained by the expansion of the ejecta. We find overabundances of N and of α elements, which could either represent the composition of the secondary that provides the accreted material or that of the ejecta. The N overabundance indicates CNO-cycled material. From comparisons to abundances for the secondary taken from the literature, we conclude that 20%-40% of the observed nitrogen could originate from the outburst. The overabundance of the α elements is not typical for stars of the spectral type of the secondary in the RS Oph system, and white dwarf material might have been mixed into the ejecta. However, no direct measurements of the α elements in the secondary are available, and the continuous accretion may have changed the observable surface composition.

A non-radioactive cell-free assay was developed to quantitatively determine inhibition of plant-type phytoene desaturase by bleaching herbicides. A n active desaturase was prepared from an appropriately cloned E. coli transformant. Another E. coli transformant was used to produce the required phytoene. Phytofluene and t-carotene, the products of the desaturase reaction, were either determined by H PL C or optical absorption spectra. Enzyme kinetics and inhibition data for the bleaching tetrazole herbicide W L 1 10547 are presented as an example.