On the Galactic chemical evolution of sulphur. Sulphur abundances from the [S i] 1082 nm line in giants

Context. The Galactic chemical evolution of sulphur is still under debate. At low metallicities some studies find no correlation between [S/Fe] and [Fe/H], others find [S/Fe] increasing towards lower metallicities, and still others find a combination of the two. Each scenario has different implications for the Galactic chemical evolution of sulphur. Aims. To contribute to the discussion on the Galactic chemical evolution of sulphur by deriving sulphur abundances from non-LTE insensitive spectral diagnostics in Disk and Halo stars with homogeneously determined stellar parameters. Methods. We derive Teff from photometric colours, logg from stellar isochrones and Bayesian estimation, and [Fe/H] and [S/Fe] from spectrum synthesis. We derive [S/Fe] from the [S i] 1082 nm line in 39 mostly cool and metal-poor giants, using 1D LTE MARCS model atmospheres to model our high-resolution NIR spectra obtained with the VLT, NOT and Gemini South telescopes. Results. We derive homogeneous stellar parameters for 29 stars. Our results argue for a chemical evolution of sulphur that is typical for alpha-elements, contrary to some previous studies. Our abundances are systematically higher by about 0.1 dex in comparison to other studies that arrived at similar conclusions using other sulphur diagnostics. Conclusions. We find the [S i] line to be a valuable diagnostic of sulphur abundances in cool giants down to [Fe/H] ~ -2.3. We argue that a homogeneous determination of stellar parameters is necessary, since the derived abundances are sensitive to them. Our results ([S/Fe]) show reasonable agreement with predictions of contemporary models of Galactic chemical evolution. In these models sulphur is predominantly created in massive stars by oxygen burning, and ejected in the ISM during Type II SNe explosions. Systematic differences with previous studies likely fall within modelling uncertainties.Comment: 13 pages, 6 figures. Accepted for publication in A&

Wild And Domestic: Short Stories

Wild and Domestic is a collection of short stories set in rural northwestern Minnesota that center around themes of parenting, family, and the desire for stability and security. This desire for domestic harmony often comes into conflict with the characters’ strong desire for personal freedom, self-expression, sexual gratification, and a deeper connection to the natural world—desires that are linked to the concept of wild. The collection also invites readers to reflect on its animal characters. In many of the stories, animal characters, both wild and domestic, play a role in setting up the crisis or climax of the story by bringing the characters’ competing desires into focus. In this collection I use minimalist style to explore themes that have often been associated with sentimental writing. The minimalist techniques of bare-bones language and close attention to images allow me to create round, complex human and animal characters without resorting to sentimental manipulation of the readers’ emotional. These characters complicate the domestic-wild binary and invite the reader to reimagine their own relationship with both. Many of these stories have been published in literary journals and I anticipate its publication as a collection as well. I believe that at this time of rapidly vanishing species and social isolation due to our increased dependence on technology, humans crave a connection with animals more than ever. Wild and Domestic exposes multiple reasons behind our need to connect with our animal kin and emphasizes the importance of the connection

Vision performance enhancement with ski goggle tints

Three popular ski goggle lens tints; gold, vermilion and gray; were evaluated for their effect on vision and skiing performance. Subjects were tested for visual acuity and contrast sensitivity, timed in a Giant Slalom ski race course, and asked to complete subjective questionnaires on the effectiveness of the lens tints on their performance. A video of each run was observed by three ski professionals and ranked based on skier performance. No significant differences were found between the three tints for visual acuity, contrast performance by video analysis. There was a subjective preference of the vermilion tint over the gold or gray tints

Mass Outflow from Red Giant Stars in M13, M15, and M92

Chromospheric model calculations of the Halpha line for selected red giant branch (RGB) and asymptotic giant branch (AGB) stars in the globular clusters M13, M15, and M92 are constructed to derive mass loss rates. The model spectra are compared to the observations obtained with the Hectochelle on the MMT telescope. These stars show strong Halpha emissions and blue-shifted Halpha cores signaling that mass outflow is present in all stars. Outflow velocities of 3-19 km/s, larger than indicated by Halpha profiles, are needed in the upper chromosphere to achieve good agreement between the model spectra and the observations. The resulting mass loss rates range from 0.6*10^{-9} to 5*10^{-9} Msun/yr, which are about an order of magnitude lower than predicted from "Reimers' law" or inferred from the infrared excess of similar stars. The mass loss rate increases slightly with luminosity and with decreasing effective temperature. Stars in the more metal-rich M13 have higher mass loss rates by a factor of ~2 than in the metal-poor clusters M15 and M92. A fit to the mass loss rates is given by: M [Msun/yr] = 0.092 * L^{0.16} * Teff^{-2.02} * A^{0.37} where A=10^[Fe/H]. Multiple observations of stars revealed one object in M15, K757, in which the mass outflow increased by a factor of 6 between two observations separated by 18 months. Other stars showed changes in mass loss rate by a factor of 1.5 or less.Comment: 28 pages, 10 figures, 3 tables, Accepted in Astronomical Journa