HD 65949: Rosetta Stone or Red Herring

HD 65949 is a late B star with exceptionally strong Hg II at 3984[A], but it is not a typical HgMn star. The Re II spectrum is of extraordinary strength. Abundances, or upper limits are derived here for 58 elements based on a model with Teff = 13100K, and log(g) = 4.0. Even-Z elements through nickel show minor deviations from solar abundances. Anomalies among the odd-Z elements through copper are mostly small. Beyond the iron peak, a huge scatter is found. The abundance pattern of the heaviest elements resembles the N=126 r-process peak of solar material, though not in detail. We find a significant correlation of the abundance excesses with second ionization potentials for elements with Z > 30. This indicates the relevance of photospheric or near-photospheric processes. We explore a model with mass accretion of exotic material followed by the more commonly accepted differentiation by diffusion. That model leads to a number of predictions which challenge future work. Likely primary and secondary masses are near 3.3 and 1.6 M(solar), with a separation of ca. 0.25 AU. New atomic structure calculations are presented in two appendices.Comment: Accepted by MNRAS: 16 pages, 5 figure

Lifetime measurements and oscillator strengths in singly ionized scandium and the solar abundance of scandium

The lifetimes of 17 even-parity levels (3d5s, 3d4d, 3d6s and 4p2) in the region 57 743–77 837 cm−1 of singly ionized scandium (Sc II) were measured by two-step timeresolved laser induced fluorescence spectroscopy. Oscillator strengths of 57 lines from these highly excited upper levels were derived using a hollow cathode discharge lamp and a Fourier transform spectrometer. In addition, Hartree–Fock calculations where both the main relativistic and core-polarization effects were taken into account were carried out for both low- and high-excitation levels. There is a good agreement for most of the lines between our calculated branching fractions and the measurements of Lawler & Dakin in the region 9000–45 000 cm−1 for low excitation levels and with our measurements for high excitation levels in the region 23 500–63 100 cm−1. This, in turn, allowed us to combine the calculated branching fractions with the available experimental lifetimes to determine semi-empirical oscillator strengths for a set of 380 E1 transitions in Sc II. These oscillator strengths include the weak lines that were used previously to derive the solar abundance of scandium. The solar abundance of scandium is now estimated to log = 3.04 ± 0.13 using these semi-empirical oscillator strengths to shift the values determined by Scott et al. The new estimated abundance value is in agreement with the meteoritic value (logmet = 3.05 ± 0.02) of Lodders, Palme & Gail

Forces frozen: Hands-on exploration of structural ice shells

© 2016 Taylor & Francis Group, London. This paper shares the authors’ experience regarding the Forces Frozen workshop developed in MIT’s Building Technology Program, within the Department of Architecture. This one-week outdoor workshop invites students to physically explore the world of structural ice shells. Ice shells are primarily created by a procedure that takes advantage of the symmetrical behavior of tension and compression, with the following steps: (1) hanging fabric sheets into the desired inverted shape, (2) spraying the fabric with water, and (3) flip the shell upside-down once they become rigid with ice. Because the initial dry fabric was stable in tension under self weight, the flipped geometry remains stable as well, but in compression. The workshop has been found to be an efficient and effective way to teach architecture and engineering students the statics and dynamics of shells in a stimulating and joyful environment