HI in the Outskirts of Nearby Galaxies

The HI in disk galaxies frequently extends beyond the optical image, and can trace the dark matter there. I briefly highlight the history of high spatial resolution HI imaging, the contribution it made to the dark matter problem, and the current tension between several dynamical methods to break the disk-halo degeneracy. I then turn to the flaring problem, which could in principle probe the shape of the dark halo. Instead, however, a lot of attention is now devoted to understanding the role of gas accretion via galactic fountains. The current $\rm \Lambda$ cold dark matter theory has problems on galactic scales, such as the core-cusp problem, which can be addressed with HI observations of dwarf galaxies. For a similar range in rotation velocities, galaxies of type Sd have thin disks, while those of type Im are much thicker. After a few comments on modified Newtonian dynamics and on irregular galaxies, I close with statistics on the HI extent of galaxies.Comment: 38 pages, 17 figures, invited review, book chapter in "Outskirts of Galaxies", Eds. J. H. Knapen, J. C. Lee and A. Gil de Paz, Astrophysics and Space Science Library, Springer, in pres

The origins and abundances of the chemical elements before 1957: from Prout's hypothesis to Pasadena

The 1957 papers by Burbidge, Burbidge, Fowler, and Hoyle and by Cameron are generally regarded as the foundations upon which our modern understanding of nucleosynthesis has been erected. They were, however, also the capstones of an extended period of investigation of the composition of the cosmos (earth, sun, and beyond) and of the processes that might have given rise to that composition, dating back at least as far as 1885, that is longer before 1957 than “now” is after 1957