Galactic Plane Hα\alpha Surveys: IPHAS & VPHAS+

The optical Galactic Plane H$\alpha$ surveys IPHAS and VPHAS+ are dramatically improving our understanding of Galactic stellar populations and stellar evolution by providing large samples of stars in short lived, but important, evolutionary phases, and high quality homogeneous photometry and images over the entire Galactic Plane. Here I summarise some of the contributions these surveys have already made to our understanding of a number of key areas of stellar and Galactic astronomy.Comment: 5 pages, 2 figures, refereed proceeding of the "The Universe of Digital Sky Surveys" conference, November 2014, to be published in the Astrophysics and Space Science Proceeding

Cooperativity and Frustration in Protein-Mediated Parallel Actin Bundles

We examine the mechanism of bundling of cytoskeletal actin filaments by two representative bundling proteins, fascin and espin. Small-angle X-ray studies show that increased binding from linkers drives a systematic \textit{overtwist} of actin filaments from their native state, which occurs in a linker-dependent fashion. Fascin bundles actin into a continuous spectrum of intermediate twist states, while espin only allows for untwisted actin filaments and fully-overtwisted bundles. Based on a coarse-grained, statistical model of protein binding, we show that the interplay between binding geometry and the intrinsic \textit{flexibility} of linkers mediates cooperative binding in the bundle. We attribute the respective continuous/discontinous bundling mechanisms of fascin/espin to differences in the stiffness of linker bonds themselves.Comment: 5 pages, 3 figures, figure file has been corrected in v

First results of an Hα based search of classical Be stars in the Perseus Arm and beyond

We investigate a region of the Galactic plane, between 120° ≤ l ≤ 140° and-1° ≤ b≤+4°, and uncover a population of moderately reddened (E(B-V) ~ 1) classical Be stars within and beyond the Perseus and Outer Arms. 370 candidate emission-line stars (13≲r≲16) selected from the Isaac Newton Telescope Photometric Ha Survey of the Northern Galactic plane have been followed up spectroscopically. A subset of these, 67 stars with properties consistent with those of classical Be stars, have been observed at sufficient spectral resolution (δλ ≈ 2-4 Å) at blue wavelengths to narrow down their spectral types. We determine these to a precision estimated to be ±1 subtype and then we measure reddenings via spectral energy distribution fitting with reference to appropriate model atmospheres. Corrections for contribution to colour excess from circumstellar discs are made using an established scaling to Ha emission equivalent width. Spectroscopic parallaxes are obtained after luminosity class has been constrained via estimates of distances to neighbouring A/F stars with similar reddenings. Overwhelmingly, the stars in the sample are confirmed as luminous classical Be stars at heliocentric distances ranging from 2 kpc up to ~12 kpc. However, the errors are presently too large to enable the cumulative distribution function with respect to distance to distinguish between models placing the stars exclusively in spiral arms, or in a smooth exponentially declining distribution.Peer reviewe

How Historical and Current Management Practices have Affected Milk River Riparian Habitat in Northcentral Montana

Riparian and wetland communities support the greatest concentration of plants and animals, yet only constitute 4 percent of Montana’s land cover.  Because they are more productive than surrounding uplands, they are attractive to livestock and wildlife as they provide important forms of cover and forage.  For private and public land managers interested in maintaining long-term integrity and functionality of riparian and wetland communities on their lands, management strategies that accommodate on-site resource needs must be implemented.  Determining habitat types and their associated community types on these sites can help identify historical impacts that have affected community type succession, and how current management strategies could be affecting the trend towards one seral stage or another.  Both natural and artificial disturbances can affect community type succession, yet succession from one type to another can take several years and even decades.  Thus, changes from year to year can be very subtle, and as land managers implement current management practices, they may overlook the visual cues indicating these trends, simply because these processes can be very slow.  This presentation summarizes an evaluation of a riparian area located in the Milk River Valley in Northcentral Montana. An illustration of how historical impacts have affected community type succession, and how this site has been affected by a significant change in management practices that occurred over 20 years ago, is provided. Depending on what goals are desired for this site will determine if a change in current management practices is warranted

IPHAS and the symbiotic stars. I. Selection method and first discoveries

The study of symbiotic stars is essential to understand important aspects of stellar evolution in interacting binaries. Their observed population in the Galaxy is however poorly known, and is one to three orders of magnitudes smaller than the predicted population size. IPHAS, the INT Photometric Halpha survey of the Northern Galactic plane, gives us the opportunity to make a systematic, complete search for symbiotic stars in a magnitude-limited volume, and discover a significant number of new systems. A method of selecting candidate symbiotic stars by combining IPHAS and near-IR (2MASS) colours is presented. It allows us to distinguish symbiotic binaries from normal stars and most of the other types of Halpha emission line stars in the Galaxy. The only exception are T Tauri stars, which can however be recognized because of their concentration in star forming regions. Using these selection criteria, we discuss the classification of a list of 4338 IPHAS stars with Halpha in emission. 1500 to 2000 of them are likely to be Be stars. Among the remaining objects, 1183 fulfill our photometric constraints to be considered candidate symbiotic stars. The spectroscopic confirmation of three of these objects, which are the first new symbiotic stars discovered by IPHAS, proves the potential of the survey and selection method.Comment: Accepted for publication on Astronomy and Astrophysics. 12 pages, 8 figure

K 3-22: a D-type symbiotic star

A goal of the IPHAS survey is to determine the frequency and nature of emission-line sources in the Galactic plane. According to our selection criteria, K 3-22 is a candidate symbiotic star, but it was previously classified as a planetary nebula. To determine its nature, we acquired a low-resolution optical spectrum of K 3-22. Our analysis of our spectroscopy demonstrates that K 3-22 is indeed a D-type symbiotic star, because of its high excitation nebular spectrum and the simultaneous presence of Raman-scattered O VI emission at 6825 and 7082 angstrom, which is detected primarily in symbiotic stars.Comment: 3 pages, 1 figure. Accepted for publication on Astronomy and Astrophysic

The Discovery of XY Sex Chromosomes in a \u3cem\u3eBoa\u3c/em\u3e and \u3cem\u3ePython\u3c/em\u3e

For over 50 years, biologists have accepted that all extant snakes share the same ZW sex chromosomes derived from a common ancestor [1, 2, 3], with different species exhibiting sex chromosomes at varying stages of differentiation. Accordingly, snakes have been a well-studied model for sex chromosome evolution in animals [1, 4]. A review of the literature, however, reveals no compelling support that boas and pythons possess ZW sex chromosomes [2, 5]. Furthermore, phylogenetic patterns of facultative parthenogenesis in snakes and a sex-linked color mutation in the ball python (Python regius) are best explained by boas and pythons possessing an XY sex chromosome system [6, 7]. Here we demonstrate that a boa (Boa imperator) and python (Python bivittatus) indeed possess XY sex chromosomes, based on the discovery of male-specific genetic markers in both species. We use these markers, along with transcriptomic and genomic data, to identify distinct sex chromosomes in boas and pythons, demonstrating that XY systems evolved independently in each lineage. This discovery highlights the dynamic evolution of vertebrate sex chromosomes and further enhances the value of snakes as a model for studying sex chromosome evolution

Square vortex lattice at anomalously low magnetic fields in electron-doped Nd1.85_{1.85}Ce0.15_{0.15}CuO4_{4}

We report here on the first direct observations of the vortex lattice in the bulk of electron-doped Nd$_{1.85}$Ce$_{0.15}$CuO$_{4}$ single crystals. Using small angle neutron scattering, we have observed a square vortex lattice with the nearest-neighbors oriented at 45$^{\circ}$ from the Cu-O bond direction, which is consistent with theories based on the d-wave superconducting gap. However, the square symmetry persists down to unusually low magnetic fields. Moreover, the diffracted intensity from the vortex lattice is found to decrease rapidly with increasing magnetic field.Comment: 4 pages, 4 Figures, accepted for publication in Phys. Rev. Let