M-dwarfs are common stellar hosts of habitable-zone exoplanets. NUV radiation can severely impact the atmospheric and surface conditions of such planets, making characterization of NUV flaring ...activity a key aspect in determining habitability. We use archival data from the GALEX and XMM-Newton telescopes to study the flaring activity of M-dwarfs in the NUV. The GALEX observations form the most extensive dataset of M-dwarfs in the NUV to date, with exploitation of this data possible due to the new gPhoton2 pipeline. We run a dedicated algorithm to detect flares in the pipeline produced lightcurves and find some of the most energetic flares observed to date within the NUV bandpass, with energies of \(\sim 10^{34}\) ergs. Using GALEX data, we constrain flare frequency distributions for stars from M0 to M6 in the NUV up to \(10^5\) s in equivalent duration and \(10^{34}\) ergs in energy, orders of magnitude above any previous study in the UV. We estimate the combined effect of NUV luminosities and flare rates of stars later than M2 to be sufficient for abiogenesis on habitable zone exoplanets orbiting them. As a counterpoint, we speculate the high frequencies of energetic UV flares and associated coronal mass ejections would inhibit the formation of an ozone layer, possibly preventing genesis of complex Earth-like lifeforms due to sterilizing levels of surface UV radiation. We also provide a framework for future observations of M-dwarfs with ULTRASAT, a wide FoV NUV telescope to be launched in 2026.
A large population of intermediate-separation binaries, consisting of a
main-sequence (MS) star and a white dwarf (WD), has recently emerged from
Gaia's third data release (DR3), posing challenges to ...current models of binary
evolution. Here we examine the $s$-process element abundances in these systems
using data from GALAH DR3. Following refined sample analysis with parameter
estimates based on GALAH spectra, we find a distinct locus where enhanced
$s$-process elements depend on both the WD mass and metallicity, consistent
with loci identified in previous asymptotic giant branch (AGB) nucleosynthesis
studies with higher $s$-process yields. Notably, these enhanced abundances show
no correlation with the systems' orbital parameters, supporting a history of
accretion in intermediate-separation MS+WD systems. Consequently, our results
form a direct observational evidence of a connection between AGB masses and
$s$-process yields. We conclude by showing that the GALAH DR3 survey includes
numerous Ba dwarf stars, within and beyond the mass range covered in our
current sample, which can further elucidate $s$-process element distributions
in MS+WD binaries.
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