Managing shortleaf pine in Missouri

Cover title.Includes bibliographical references (pages 33-35)

The Chandra LETGS high resolution X-ray spectrum of the isolated neutron star RX J1856.5-3754

We present the Chandra LETGS X-ray spectrum of the nearby (~60 pc) neutron star RX J1856.5-3754. Detailed spectral analysis of the combined X-ray and optical data rules out the nonmagnetic neutron star atmosphere models with hydrogen, helium, iron and solar compositions. We also conclude that strongly magnetized atmosphere models are unable to represent the data. The data can be explained with a two-component blackbody model. The harder component with temperature of kT_bb~63 eV and a radius R_bb~2.2 km of the emitting region well fits the X-ray data and can be interpreted as radiation from a hot region on the star's surface.Comment: 4 pages, 3 color figures; acceped by A&A Letters; http://www.xray.mpe.mpg.de/~burwitz/burwitz_refereed.htm

Coronal density diagnostics with Helium-like triplets: CHANDRA--LETGS observations of Algol, Capella, Procyon, Eps Eri, Alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR1099

We present an analysis of ten cool stars (Algol, Capella, Procyon, Eps Eri, Alpha Cen A&B, UX Ari, AD Leo, YY Gem, and HR1099) observed with the Low Energy Transmission Grating Spectrometer (LETGS) on board the Chandra X-ray Observatory. This sample contains all cools stars observed with the LETGS presently available to us with integration times sufficiently long to warrant a meaningful spectral analysis. Our sample comprises inactive, moderately active, and hyperactive stars and samples the bulk part of activity levels encountered in coronal X-ray sources. We use the LETGS spectra to carry out density and temperature diagnostics with an emphasis on the H-like and the He-like ions. We find a correlation between line flux ratios of the Lyman-Alpha and He-like resonance lines with the mean X-ray surface flux. We determine densities using the He-like triplets. For active stars we find no significant deviations from the low-density limit for the ions of Ne, Mg, and Si, while the measured line ratios for the ions of C, N, and O do show evidence for departures from the low-density limit in the active stars, but not in the inactive stars. Best measurements can be made for the OVII triplet where we find significant deviations from the low-density limit for the stars Algol, Procyon, YY Gem, Eps Eri, and HR1099. We discuss the influence of radiation fields on the interpretation of the He-like triplet line ratios in the low-Z ions, which is relevant for Algol, and the influence of dielectronic satellite lines, which is relevant for Procyon. For the active stars YY Gem, Eps Eri, and HR1099 the low f/i ratios can unambiguously be attributed to high densties in the range 1--3 10^10 cm^-3 at OVII temperatures. We find our LETGS spectra to be an extremely useful tool for plasma diagnostics of stellar coronae.Comment: 17 pages, Latex2e, 12 figures. accepted for A&A under MS262

A WZW model based on a non-semi-simple group

We present a conformal field theory which desribes a homogeneous four dimensional Lorentz-signature space-time. The model is an ungauged WZW model based on a central extension of the Poincar\'e algebra. The central charge of this theory is exactly four, just like four dimensional Minkowski space. The model can be interpreted as a four dimensional monochromatic plane wave. As there are three commuting isometries, other interesting geometries are expected to emerge via $O(3,3)$ duality.Comment: 8 pages, phyzzx, IASSNS-HEP-93/61 Texable versio

Development of FuGO: An ontology for functional genomics investigations

The development of the Functional Genomics Investigation Ontology (FuGO) is a collaborative, international effort that will provide a resource for annotating functional genomics investigations, including the study design, protocols and instrumentation used, the data generated and the types of analysis performed on the data. FuGO will contain both terms that are universal to all functional genomics investigations and those that are domain specific. In this way, the ontology will serve as the “semantic glue” to provide a common understanding of data from across these disparate data sources. In addition, FuGO will reference out to existing mature ontologies to avoid the need to duplicate these resources, and will do so in such a way as to enable their ease of use in annotation. This project is in the early stages of development; the paper will describe efforts to initiate the project, the scope and organization of the project, the work accomplished to date, and the challenges encountered, as well as future plans

Hidden Quantum Critical Point in a Ferromagnetic Superconductor

We consider a coexistence phase of both Ferromagnetism and superconductivity and solve the self-consistent mean-field equations at zero temperature. The superconducting gap is shown to vanish at the Stoner point whereas the magnetization doesn't. This indicates that the para-Ferro quantum critical point becomes a hidden critical point. The effective mass in such a phase gets enhanced whereas the spin wave stiffness is reduced as compared to the pure FM phase. The spin wave stiffness remains finite even at the para-Ferro quantum critical point.Comment: 4 pages, Phys. Rev. B (Rapid) accepte

First Light Measurements of Capella with the Low Energy Transmission Grating Spectrometer aboard the Chandra X-ray Observatory

We present the first X-ray spectrum obtained by the Low Energy Transmission Grating Spectrometer (LETGS) aboard the Chandra X-ray Observatory. The spectrum is of Capella and covers a wavelength range of 5-175 A (2.5-0.07 keV). The measured wavelength resolution, which is in good agreement with ground calibration, is $\Delta \lambda \simeq$ 0.06 A (FWHM). Although in-flight calibration of the LETGS is in progress, the high spectral resolution and unique wavelength coverage of the LETGS are well demonstrated by the results from Capella, a coronal source rich in spectral emission lines. While the primary purpose of this letter is to demonstrate the spectroscopic potential of the LETGS, we also briefly present some preliminary astrophysical results. We discuss plasma parameters derived from line ratios in narrow spectral bands, such as the electron density diagnostics of the He-like triplets of carbon, nitrogen, and oxygen, as well as resonance scattering of the strong Fe XVII line at 15.014 A.Comment: 4 pages (ApJ letter LaTeX), 2 PostScript figures, accepted for publication in ApJ Letters, 200