We present the results of a new study on the relationship between coronal X-ray emission and stellar rotation in late-type main-sequence stars. We have selected a sample of 259 dwarfs in the range 0.5–2.0, including 110 field stars and 149 members of the Pleiades, Hyades, α Persei, IC 2602 and IC 2391 open clusters. All the stars have been observed with ROSAT, and most of them have photometrically-measured rotation periods available. Our results confirm that two emission regimes exist, one in which the rotation period is a good predictor of the total X-ray luminosity, and the other in which a constant saturated X-ray to bolometric luminosity ratio is attained; we present a quantitative estimate of the critical rotation periods below which stars of different masses (or spectral types) enter the saturated regime. In this work we have also empirically derived a characteristic time scale, , which we have used to investigate the relationship between the X-ray emission level and an X-ray-based Rossby number : we show that our empirical time scale resembles the theoretical convective turnover time for , but it also has the same functional dependence on as in the color range . Our results imply that – for non-saturated coronae – the L x – P rot relation is equivalent to the vs. R e relation.

Up-regulation of hepatic delta-aminolevulinic acid synthase 1 (ALAS1), with resultant accumulation of delta-aminolevulinic acid (ALA) and porphobilinogen, is central to the pathogenesis of acute attacks and chronic symptoms in acute hepatic porphyria. Givosiran, an RNA interference therapy, inhibits ALAS1 expression.

Full evolutionary models have been built to follow the phases of asymptotic giant branch evolution with mass loss for metal mass fractions from Z=0.0002 to Z=0.004. For the first time, we find that temperatures close to or even larger than 10^8 K are achieved at low Z; the full CNO cycle operates at the base of the envelope, the Oxygen abundance for the most metal-poor models of 4 and 5 solar masses is drastically reduced, and sodium and aluminum production by by proton capture on neon and magnesium can occur. These results may be relevant for the evolution of primordial massive globular clusters: we suggest that the low-mass stars may have been polluted at the surface by accretion from the gas that was lost from the evolving intermediate-mass stars at early ages.Comment: 14 pages, 6 figure

We build on the evidence provided by our Legacy Survey of Galactic globular clusters (GC) to submit to a crucial test four scenarios currently entertained for the formation of multiple stellar generations in GCs. The observational constraints on multiple generations to be fulfilled are manifold, including GC specificity, ubiquity, variety, predominance, discreteness, supernova avoidance, p-capture processing, helium enrichment and mass budget. We argue that scenarios appealing to supermassive stars, fast rotating massive stars and massive interactive binaries violate in an irreparable fashion two or more among such constraints. Also the scenario appealing to asymptotic giant branch (AGB) stars as producers of the material for next generation stars encounters severe difficulties, specifically concerning the mass budget problem and the detailed chemical composition of second-generation stars. We qualitatively explore ways possibly allowing one to save the AGB scenario, specifically appealing to a possible revision of the cross-section of a critical reaction rate destroying sodium, or alternatively by a more extensive exploration of the vast parameter space controlling the evolutionary behaviour of AGB stellar models. Still, we cannot ensure success for these efforts and totally new scenarios may have to be invented to understand how GCs formed in the early Universe.