Probing discs around massive young stellar objects with CO first overtone emission

We present high resolution (R~50,000) spectroastrometry over the CO 1st overtone bandhead of a sample of seven intermediate/massive young stellar objects. These are primarily drawn from the red MSX source (RMS) survey, a systematic search for young massive stars which has returned a large, well selected sample of such objects. The mean luminosity of the sample is approximately 5 times 10^4 L_\odot, indicating the objects typically have a mass of ~15 solar masses. We fit the observed bandhead profiles with a model of a circumstellar disc, and find good agreement between the models and observations for all but one object. We compare the high angular precision (0.2-0.8 mas) spectroastrometric data to the spatial distribution of the emitting material in the best-fitting models. No spatial signatures of discs are detected, which is entirely consistent with the properties of the best-fitting models. Therefore, the observations suggest that the CO bandhead emission of massive young stellar objects originates in small-scale disks, in agreement with previous work. This provides further evidence that massive stars form via disc accretion, as suggested by recent simulations.Comment: Accepted for publication in MNRA

Magnetic properties of the S=1/2 quasi square lattice antiferromagnet CuF2(H2O)2(pyz) (pyz=pyrazine) investigated by neutron scattering

We have performed elastic and inelastic neutron experiments on single crystal samples of the coordination polymer compound CuF2(H2O)2(pyz) (pyz=pyrazine) to study the magnetic structure and excitations. The elastic neutron diffraction measurements indicate a collinear antiferromagnetic structure with moments oriented along the [0.7 0 1] real-space direction and an ordered moment of 0.60 +/- 0.03 muB/Cu. This value is significantly smaller than the single ion magnetic moment, reflecting the presence of strong quantum fluctuations. The spin wave dispersion from magnetic zone center to the zone boundary points (0.5 1.5 0) and (0.5 0 1.5) can be described by a two dimensional Heisenberg model with a nearest neighbor magnetic exchange constant J2d = 0.934 +/-0.0025 meV. The inter-layer interaction Jperp in this compound is less than 1.5% of J2d. The spin excitation energy at the (0.5 0.5 0.5) zone boundary point is reduced when compared to the (0.5 1 0.5) zone boundary point by ~10.3 +/- 1.4 %. This zone boundary dispersion is consistent with quantum Monte Carlo and series expansion calculations which include corrections for quantum fluctuations to linear spin wave theory.Comment: 7 pages, 6 figure

Structural Order Parameter in the Pyrochlore Superconductor Cd2Re2O7

It is shown that both structural phase transitions in Cd2Re2O7, which occur at T_{s1}=200 K and T_{s2}=120 K, are due to an instability of the Re tetrahedral network with respect to the same doubly degenerate long-wavelength phonon mode. The primary structural order parameter transforms according to the irreducible representation E_u of the point group O_h. We argue that the transition at T_{s1} may be of second order, in accordance with experimental data. We obtain the phase diagram in the space of phenomenological parameters and propose a thermodynamic path that Cd2Re2O7 follows upon cooling. Couplings of the itinerant electronic system and localized spin states in pyrochlores and spinels to atomic displacements are discussed.Comment: 5 pages. Submitted to J. Phys. Soc. Jpn. Best quality figures are available at http://www.physics.mun.ca/~isergien/pubs.htm

Prevention of diseases after menopause

AbstractWomen may expect to spend more than a third of their lives after menopause. Beginning in the sixth decade, many chronic diseases will begin to emerge, which will affect both the quality and quantity of a woman's life. Thus, the onset of menopause heralds an opportunity for prevention strategies to improve the quality of life and enhance longevity. Obesity, metabolic syndrome and diabetes, cardiovascular disease, osteoporosis and osteoarthritis, cognitive decline, dementia and depression, and cancer are the major diseases of concern. Prevention strategies at menopause have to begin with screening and careful assessment for risk factors, which should also include molecular and genetic diagnostics, as these become available. Identification of certain risks will then allow directed therapy. Evidence-based prevention for the diseases noted above include lifestyle management, cessation of smoking, curtailing excessive alcohol consumption, a healthy diet and moderate exercise, as well as mentally stimula..

Neutron and X-ray Scattering Studies of the Lightly-Doped Spin-Peierls System Cu(1-x)Cd(x)GeO3

Single crystals of the lightly-doped spin-Peierls system Cu(1-x)Cd(x)GeO3 have been studied using bulk susceptibility, x-ray diffraction, and inelastic neutron scattering techniques. We investigate the triplet gap in the magnetic excitation spectrum of this quasi-one dimensional quantum antiferromagnet, and its relation to the spin-Peierls dimerisation order parameter. We employ two different theoretical forms to model the inelastic neutron scattering cross section and chi''(Q,omega), and show the sensitivity of the gap energy to the choice of chi''(Q,omega). We find that a finite gap exists at the spin-Peierls phase transition.Comment: 15 Pages, 7 Figures, Submitted to J. Phys. :Condensed Matte

The Northern Sky Optical Cluster Survey II: An Objective Cluster Catalog for 5800 Square Degrees

We present a new, objectively defined catalog of candidate galaxy clusters based on the galaxy catalogs from the Digitized Second Palomar Observatory Sky Survey (DPOSS). This cluster catalog, derived from the best calibrated plates in the high latitude (|b|>30) Northern Galactic Cap region, covers 5,800 square degrees, and contains 8,155 candidate clusters. A simple adaptive kernel density mapping technique, combined with the SExtractor object detection algorithm, is used to detect galaxy overdensities, which we identify as clusters. Simulations of the background galaxy distribution and clusters of varying richnesses and redshifts allow us to optimize detection parameters, and measure the completeness and contamination rates for our catalog. Cluster richnesses and photometric redshifts are measured, using integrated colors and magnitudes for each cluster. An extensive spectroscopic survey is used to confirm the photometric results. This catalog, with well-characterized sample properties, provides a sound basis for future studies of cluster physics and large scale structure.Comment: 49 pages, 16 figures. Accepted to AJ; appearing in April. Version with full resolution figures, and full length tables available at http://dposs.caltech.edu:8080/NoSOCS.htm

The Aquarius Superclusters - I. Identification of Clusters and Superclusters

We study the distribution of galaxies and galaxy clusters in a 10^deg x 6^deg field in the Aquarius region. In addition to 63 clusters in the literature, we have found 39 new candidate clusters using a matched-filter technique and a counts-in-cells analysis. From redshift measurements of galaxies in the direction of these cluster candidates, we present new mean redshifts for 31 previously unobserved clusters, while improved mean redshifts are presented for 35 other systems. About 45% of the projected density enhancements are due to the superposition of clusters and/or groups of galaxies along the line of sight, but we could confirm for 72% of the cases that the candidates are real physical associations similar to the ones classified as rich galaxy clusters. On the other hand, the contamination due to galaxies not belonging to any concentration or located only in small groups along the line of sight is ~ 10%. Using a percolation radius of 10 h^{-1} Mpc (spatial density contrast of about 10), we detect two superclusters of galaxies in Aquarius, at z = 0.086 and at z = 0.112, respectively with 5 and 14 clusters. The latter supercluster may represent a space overdensity of about 160 times the average cluster density as measured from the Abell et al. (1989) cluster catalog, and is possibly connected to a 40 h^{-1} Mpc filament from z ~ 0.11 to 0.14.Comment: LateX text (21 pages) and 12 (ps/eps/gif) figures; figures 5a, 5b and 6 are not included in the main LateX text; to be published in the Astronomical Journal, March issu

The Red-Sequence Luminosity Function in Galaxy Clusters since z~1

We use a statistical sample of ~500 rich clusters taken from 72 square degrees of the Red-Sequence Cluster Survey (RCS-1) to study the evolution of ~30,000 red-sequence galaxies in clusters over the redshift range 0.35<z<0.95. We construct red-sequence luminosity functions (RSLFs) for a well-defined, homogeneously selected, richness limited sample. The RSLF at higher redshifts shows a deficit of faint red galaxies (to M_V=> -19.7) with their numbers increasing towards the present epoch. This is consistent with the `down-sizing` picture in which star-formation ended at earlier times for the most massive (luminous) galaxies and more recently for less massive (fainter) galaxies. We observe a richness dependence to the down-sizing effect in the sense that, at a given redshift, the drop-off of faint red galaxies is greater for poorer (less massive) clusters, suggesting that star-formation ended earlier for galaxies in more massive clusters. The decrease in faint red-sequence galaxies is accompanied by an increase in faint blue galaxies, implying that the process responsible for this evolution of faint galaxies is the termination of star-formation, possibly with little or no need for merging. At the bright end, we also see an increase in the number of blue galaxies with increasing redshift, suggesting that termination of star-formation in higher mass galaxies may also be an important formation mechanism for higher mass ellipticals. By comparing with a low-redshift Abell Cluster sample, we find that the down-sizing trend seen within RCS-1 has continued to the local universe.Comment: ApJ accepted. 11 pages, 5 figure

A Serendipitous Galaxy Cluster Survey with XMM: Expected Catalogue Properties and Scientific Applications

This paper describes a serendipitous galaxy cluster survey that we plan to conduct with the XMM X-ray satellite. We have modeled the expected properties of such a survey for three different cosmological models, using an extended Press-Schechter (Press & Schechter 1974) formalism, combined with a detailed characterization of the expected capabilities of the EPIC camera on board XMM. We estimate that, over the ten year design lifetime of XMM, the EPIC camera will image a total of ~800 square degrees in fields suitable for the serendipitous detection of clusters of galaxies. For the presently-favored low-density model with a cosmological constant, our simulations predict that this survey area would yield a catalogue of more than 8000 clusters, ranging from poor to very rich systems, with around 750 detections above z=1. A low-density open Universe yields similar numbers, though with a different redshift distribution, while a critical-density Universe gives considerably fewer clusters. This dependence of catalogue properties on cosmology means that the proposed survey will place strong constraints on the values of Omega-Matter and Omega-Lambda. The survey would also facilitate a variety of follow-up projects, including the quantification of evolution in the cluster X-ray luminosity-temperature relation, the study of high-redshift galaxies via gravitational lensing, follow-up observations of the Sunyaev-Zel'dovich effect and foreground analyses of cosmic microwave background maps.Comment: Accepted to ApJ. Minor changes, e.g. presentation of temperature errors as a figure (rather than as a table). Latex (20 pages, 6 figures, uses emulateapj.sty