An analysis of the peculiar A star HD 204411

Spectrum analysis of cool Ap star HD 20441

Analysis of F and G Subdwarfs. I. The Location of Subdwarfs in the Theoretical H-R Diagram

Spectrum scans and model stellar atmospheres have been used to locate in the (L/L_⊙, T_(eff)) plane F and G subdwarfs having known parallax A comparison is made between their position on the H-R diagram and the evolutionary tracks for Population II models of low- and high-helium content recently computed by Faulkner and Iben. The lower helium-content models are found to give somewhat more plausible ages than the high-helium models. Nevertheless, for both the low- and high-helium-content models, we find several subdwarfs with ages apparently greater than 10 X 10^9 years

PhEMaterialism: Response-able Research & Activism

This Special Issue offers PhEmaterialisms as a way to explore the world asvital and complex, while simultaneously being response-able to the multiple ethical imperatives of late-stage capitalism. We argue that PhEmaterialist thinking and practices can help us grapple with growing educational complexities, enabling strategies toresist and create alternatives to the patterns of injustice occurring across the world, from burgeoning ethno-nationalist and neo-fascist political movements, to rising global poverty levels, to massive population displacements, to environmental degradation, to toxic internet movements grounded in misogyny, homophobia, transphobia, and xenophobia (Strom & Martin, 2017a). To understand, enquire into, and generate action worthy of the complexity of our times requires a fundamental shift in our thinking and research practice. This shift disrupts the foundational logic on which dominant thinking in education (and indeed, all Western society) is based—humanism and anthropocentrism (Braidotti, 2013; Murris, 2016; Snaza et al, 2014). Instead, we argue that we need to put theories/concepts to work in education and educational research which can better account for the multiple, entangled, ever-shifting, difference-rich nature of processes of teaching, learning, schooling, and activism. For this work, we also draw on a rich feminist legacy attentive to unequal power relations (e.g., Ahmed, 1998; Anzaldua, 1999; hooks, 1994; Spivak, 1978), and our critical approach to rethinking Vitruvian “man” is especially informed by posthuman/new materialist feminist thinkings and thinkers, including Rosi Braidotti, Donna Haraway, and Karen Barad

PhEmaterialism: Response-able Research & Pedagogy

This Special Issue offers PhEmaterialisms as a way to explore the world asvital and complex, while simultaneously being response-able to the multiple ethical imperatives of late-stage capitalism. We argue that PhEmaterialist thinking and practices can help us grapple with growing educational complexities, enabling strategies toresist and create alternatives to the patterns of injustice occurring across the world, from burgeoning ethno-nationalist and neo-fascist political movements, to rising global poverty levels, to massive population displacements, to environmental degradation, to toxic internet movements grounded in misogyny, homophobia, transphobia, and xenophobia (Strom & Martin, 2017a). To understand, enquire into, and generate action worthy of the complexity of our times requires a fundamental shift in our thinking and research practice. This shift disrupts the foundational logic on which dominant thinking in education (and indeed, all Western society) is based—humanism and anthropocentrism (Braidotti, 2013; Murris, 2016; Snaza et al, 2014). Instead, we argue that we need to put theories/concepts to work in education and educational research which can better account for the multiple, entangled, ever-shifting, difference-rich nature of processes of teaching, learning, schooling, and activism. For this work, we also draw on a rich feminist legacy attentive to unequal power relations (e.g., Ahmed, 1998; Anzaldua, 1999; hooks, 1994; Spivak, 1978), and our critical approach to rethinking Vitruvian “man” is especially informed by posthuman/new materialist feminist thinkings and thinkers, including Rosi Braidotti, Donna Haraway, and Karen Barad

Oscillation Effects On Neutrinos From The Early Phase Of a Nearby Supernova

Neutrinos emitted during stellar core collapse leading to a supernova are primarily of the electron neutrino type at source which may undergo oscillation between flavor eigenstates during propagation to an earth-bound detector. Although the number of neutrinos emitted during the pre-bounce collapse phase is much smaller than that emitted in the post-bounce phase (in which all flavors of neutrinos are emitted), a nearby supernova event may nevertheless register a substantial number of detections from the pre-bounce phase at SuperKamiokande (SK) and the Sudbury Neutrino Observatory (SNO). The calorimetric measurement of the supernova neutrino fluence from this stage via the charge current and neutral current detection channels in SNO and the corresponding distortion of detected spectrum in SK over the no-oscillation spectrum, can probe information about neutrino mass difference and mixing which are illustrated here in terms of two- and three-flavor oscillation models

A High Fraction of Ly-alpha-Emitters Among Galaxies with Extreme Emission Line Ratios at z ~ 2

Star-forming galaxies form a sequence in the [OIII]/H-beta vs. [NII]/H-alpha diagnostic diagram, with low metallicity, highly ionized galaxies falling in the upper left corner. Drawing from a large sample of UV-selected star-forming galaxies at z~2 with rest-frame optical nebular emission line measurements from Keck-MOSFIRE, we select the extreme ~5% of the galaxies lying in this upper left corner, requiring log([NII]/H-alpha) = 0.75. These cuts identify galaxies with 12 + log(O/H) <~ 8.0, when oxygen abundances are measured via the O3N2 diagnostic. We study the Ly-alpha properties of the resulting sample of 14 galaxies. The mean (median) rest-frame Ly-alpha equivalent width is 39 (36) A, and 11 of the 14 objects (79%) are Ly-alpha-emitters (LAEs) with W_Lya > 20 A. We compare the equivalent width distribution of a sample of 522 UV-selected galaxies at 2.0<z<2.6 identified without regard to their optical line ratios; this sample has mean (median) Ly-alpha equivalent width -1 (-4) A, and only 9% of these galaxies qualify as LAEs. The extreme galaxies typically have lower attenuation at Ly-alpha than those in the comparison sample, and have ~50% lower median oxygen abundances. Both factors are likely to facilitate the escape of Ly-alpha: in less dusty galaxies Ly-alpha photons are less likely to be absorbed during multiple scatterings, while the harder ionizing spectrum and higher ionization parameter associated with strong, low metallicity star formation may reduce the covering fraction or column density of neutral hydrogen, further easing Ly-alpha escape. The use of nebular emission line ratios may prove useful in the identification of galaxies with low opacity to Ly-alpha photons across a range of redshifts.Comment: 12 pages, 5 figures, 2 tables. Accepted for publication in Ap

Analysis of F and G Subdwarfs. I. The Location of Subdwarfs in the Theoretical H-R Diagram

Spectrum scans and model stellar atmospheres have been used to locate in the (L/L_⊙, T_(eff)) plane F and G subdwarfs having known parallax A comparison is made between their position on the H-R diagram and the evolutionary tracks for Population II models of low- and high-helium content recently computed by Faulkner and Iben. The lower helium-content models are found to give somewhat more plausible ages than the high-helium models. Nevertheless, for both the low- and high-helium-content models, we find several subdwarfs with ages apparently greater than 10 X 10^9 years

Massive star formation in NGC 6946

H-alpha measurements of the late-type spiral galaxy NGC 6946 are presented. Assuming an initial mass function, the H-alpha data are used to calculate the total star formation rate and efficiency of massive star formation as a function of galactocentric radius. An attempt is made to determine the factors influencing these quantities by comparing them to the surface densities of H I and H 2 and the degree of compression suffered by the gas in spiral density wave theory. The rate of star formation is very closely correlated with the first power of the surface density of H2, and somewhat less correlated with the degree of compression of the gas predicted by density wave theory. In contrast, the efficiency of massive star formation is roughly constant across the face of the galaxy

Instabilities and Clumping in Type Ia Supernova Remnants

We present two-dimensional high-resolution hydrodynamical simulations in spherical polar coordinates of a Type Ia supernova interacting with a constant density interstellar medium. The ejecta are assumed to be freely expanding with an exponential density profile. The interaction gives rise to a double-shocked structure susceptible to hydrodynamic instabilities. The Rayleigh-Taylor instability initially grows, but the Kelvin-Helmholtz instability takes over, producing vortex rings. The nonlinear instability initially evolves toward longer wavelengths and eventually fades away when the reverse shock front is in the flatter part of the supernova density distribution. Based on observations of X-ray knots and the protrusion in the southeast outlin of Tycho's supernova remnant, we include clumping in the ejecta. The clump interaction with the reverse shock induces Rayleigh-Taylor and Kelvin-Helmholtz instabilities on the clump surface that facilitate fragmentation. In order to survive crushing and to have a bulging effect on the forward shock, the clump's initial density ratio to the surrounding ejecta must be at least 100 for the conditions in Tycho's remnant. The 56Ni bubble effect may be important for the development of clumpiness in the ejecta. The observed presence of an Fe clump would then require a non-radioactive origin for this Fe, possibly 54Fe. The large radial distance of the X-ray emitting Si and S ejecta from the remnant center indicates that they were initially in clumps.Comment: 27 pages, 4 postscript figures, 5 GIF figures submitted to Astrophysical Journa