Modeling Ultraviolet Wind Line Variability in Massive Hot Stars

We model the detailed time-evolution of Discrete Absorption Components (DACs) observed in P Cygni profiles of the Si IV lam1400 resonance doublet lines of the fast-rotating supergiant HD 64760 (B0.5 Ib). We adopt the common assumption that the DACs are caused by Co-rotating Interaction Regions (CIRs) in the stellar wind. We perform 3D radiative transfer calculations with hydrodynamic models of the stellar wind that incorporate these large-scale density- and velocity-structures. We develop the 3D transfer code Wind3D to investigate the physical properties of CIRs with detailed fits to the DAC shape and morphology. The CIRs are caused by irregularities on the stellar surface that change the radiative force in the stellar wind. In our hydrodynamic model we approximate these irregularities by circular symmetric spots on the stellar surface. We use the Zeus3D code to model the stellar wind and the CIRs, limited to the equatorial plane. We constrain the properties of large-scale wind structures with detailed fits to DACs observed in HD 64760. A model with two spots of unequal brightness and size on opposite sides of the equator, with opening angles of 20 +/- 5 degr and 30 +/- 5 degr diameter, and that are 20 +/- 5 % and 8 +/- 5 % brighter than the stellar surface, respectively, provides the best fit to the observed DACs. The recurrence time of the DACs compared to the estimated rotational period corresponds to spot velocities that are 5 times slower than the rotational velocity. The mass-loss rate of the structured wind model for HD 64760 does not exceed the rate of the spherically symmetric smooth wind model by more than 1 %. The fact that DACs are observed in a large number of hot stars constrains the clumping that can be present in their winds, as substantial amounts of clumping would tend to destroy the CIRs.Comment: 58 pages, 16 figures, 1 animation. Accepted for publication in The Astrophysical Journal, Main Journal. More information and animations are available at http://alobel.freeshell.org/hotstars.htm

Magnetic Properties of Epitaxial and Polycrystalline Fe/Si Multilayers

Fe/Si multilayers with antiferromagnetic interlayer coupling have been grown via ion-beam sputtering on both glass and single-crystal substrates. High-angle x-ray diffraction measurements show that both sets of films have narrow Fe peaks, implying a large crystallite size and crystalline iron silicide spacer layers. Low-angle x-ray diffraction measurements show that films grown on glass have rougher interfaces than those grown on single-crystal substrates. The multilayers grown on glass have a larger remanent magnetization than the multilayers grown on single-crystal substrates. The observation of magnetocrystalline anisotropy in hysteresis loops and $(hkl)$ peaks in x-ray diffraction demonstrates that the films grown on MgO and Ge are epitaxial. The smaller remanent magnetization in Fe/Si multilayers with better layering suggests that the remanence is not an intrinsic property.Comment: 9 pages, RevTex, 4 figures available by fax. Send email to [email protected] for more info. Submitted to '95 MMM proceeding

Properties of Galactic early-type O-supergiants: A combined FUV-UV and optical analysis

We aim to constrain the properties and evolutionary status of early and mid-spectral type supergiants (from O4 to O7.5). These posses the highest mass-loss rates among the O stars, and exhibit conspicuous wind profiles. Using the non-LTE wind code CMFGEN, we simultaneously analyzed the FUV-UV and optical spectral range to determine the photospheric properties and wind parameters. We derived effective temperatures, luminosities, surface gravities, surface abundances, mass-loss rates, wind terminal velocities, and clumping filling factors. The supergiants define a very clear evolutionary sequence, in terms of ages and masses, from younger and more massive stars to older stars with lower initial masses. O4 supergiants cluster around the 3 Myr isochrone and are more massive than 60 Msun, while the O5 to O7.5 stars have masses in the range 50 - 40 Msun and are 4 +/- 0.3 Myr old. The surface chemical composition is typical of evolved O supergiants (nitrogen-rich, carbon- and oxygen-poor). While the observed ranges of carbon and nitrogen mass-fractions are compatible with those expected from evolutionary models for the measured stellar masses, the N/C ratios as a function of age are inconsistent with the theoretical predictions for the four earliest (O4 spectral type) stars of the sample. We question the efficiency of rotational mixing as a function of age for these stars and suggest that another mechanism may be needed to explain the observed abundance patterns. Mass-loss rates derived with clumped-models range within a factor of three of the theoretical mass-loss rates. The corresponding volume-filling factors associated with small-scale clumping are 0.05 +/- 0.02. Clumping is found to start close to the photosphere for all but three stars, two of which are fast rotators.Comment: 30 pages, 11 figures, accepted for publication in A&A 201

{\it Ab initio} calculations of magnetic structure and lattice dynamics of Fe/Pt multilayers

The magnetization distribution, its energetic characterization by the interlayer coupling constants and lattice dynamics of (001)-oriented Fe/Pt multilayers are investigated using density functional theory combined with the direct method to determine phonon frequencies. It is found that ferromagnetic order between consecutive Fe layers is favoured, with the enhanced magnetic moments at the interface. The bilinear and biquadratic coupling coefficients between Fe layers are shown to saturate fast with increasing thickness of nonmagnetic Pt layers which separate them. The phonon calculations demonstrate a rather strong dependence of partial iron phonon densities of states on the actual position of Fe monolayer in the multilayer structure.Comment: 7 pages, 8 figure

The EXPLORE Project I: A Deep Search for Transiting Extrasolar Planets

(Abridged) We discuss the design considerations of the EXPLORE (EXtra-solar PLanet Occultation REsearch) project, a series of transiting planet searches using 4-m-class telescopes to continuously monitor a single field of stars in the Galactic Plane in each ~2 week observing campaign. We discuss the general factors which determine the efficiency and the number of planets found by a transit search, including time sampling strategy and field selection. The primary goal is to select the most promising planet candidates for radial velocity follow-up observations. We show that with very high photometric precision light curves that have frequent time sampling and at least two detected transits, it is possible to uniquely solve for the main parameters of the eclipsing system (including planet radius) based on several important assumptions about the central star. Together with a measured spectral type for the star, this unique solution for orbital parameters provides a powerful method for ruling out most contaminants to transiting planet candidates. For the EXPLORE project, radial velocity follow-up observations for companion mass determination of the best candidates are done on 8-m-class telescopes within two or three months of the photometric campaigns. This same-season follow-up is made possible by the use of efficient pipelines to produce high quality light curves within weeks of the observations. We conclude by presenting early results from our first search, EXPLORE I, in which we reached <1% rms photometric precision (measured over a full night) on ~37,000 stars to I <= 18.2.Comment: accepted by ApJ. Main points unchanged but more thorough discussion of some issues. 36 pages, including 14 figure

Active Management of Third Stage of Labour Saves Facility Costs in Guatemala and Zambia

This study calculated the net benefit of using active management of the third stage of labour (AMTSL) rather than expectant management of the third stage of labour (EMTSL) for mothers in Guatemala and Zambia. Probabilities of events were derived from opinions of experts, publicly available data, and published literature. Costs of clinical events were calculated based on national price lists, observation of resources used in AMTSL and EMTSL, and expert estimates of resources used in managing postpartum haemorrhage and its complications, including transfusion. A decision tree was used for modelling expected costs associated with AMTSL or EMTSL. The base case analysis suggested a positive net benefit from AMTSL, with a net cost-saving of US$18,000 in Guatemala (with 100 lives saved) and US$ 145,000 in Zambia (with 467 lives saved) for 100,000 births. Facilities have strong economic incentives to adopt AMTSL if uterotonics are available

The Discordance of Mass-Loss Estimates for Galactic O-Type Stars

We have determined accurate values of the product of the mass-loss rate and the ion fraction of P^{4+}, Mdot q(P^{4+}), for a sample of 40 Galactic O-type stars by fitting stellar-wind profiles to observations of the P V resonance doublet obtained with FUSE, ORFEUS/BEFS, and Copernicus. When P^{4+} is the dominant ion in the wind, Mdot q(P^{4+}) approximates the mass-loss rate to within a factor of 2. Theory predicts that P^{4+} is the dominant ion in the winds of O7-O9.7 stars, though an empirical estimator suggests that the range from O4-O7 may be more appropriate. However, we find that the mass-loss rates obtained from P V wind profiles are systematically smaller than those obtained from fits to Halpha emission profiles or radio free-free emission by median factors of about 130 (if P^{4+} is dominant between O7 and O9.7) or about 20 (if P^{4+} is dominant between O4 and O7). These discordant measurements can be reconciled if the winds of O stars in the relevant temperature range are strongly clumped on small spatial scales. We use a simplified two-component model to investigate the volume filling factors of the denser regions. This clumping implies that mass-loss rates determined from "density squared" diagnostics have been systematically over-estimated by factors of 10 or more, at least for a subset of O stars. Reductions in the mass-loss rates of this size have important implications for the evolution of massive stars and quantitative estimates of the feedback that hot-star winds provide to their interstellar environments.Comment: 26 pages, 4 figures; accepted for publication in Ap

Stroke impact on mortality and psychologic morbidity within the Childhood Cancer Survivor Study.

BackgroundPoor socioeconomic and health-related quality of life (HRQOL) outcomes in survivors of childhood cancer can lead to distress and overall negatively impact the lives of these individuals. The current report has highlighted the impact of stroke and stroke recurrence on mortality, psychological HRQOL, and socioeconomic outcomes within the Childhood Cancer Survivor Study (CCSS).MethodsThe CCSS is a retrospective cohort study with longitudinal follow-up concerning survivors of pediatric cancer who were diagnosed between 1970 and 1986. Mortality rates per 100 person-years were calculated across 3 periods: 1) prior to stroke; 2) after first stroke and before recurrent stroke; and 3) after recurrent stroke. Socioeconomic outcomes, the standardized Brief Symptoms Inventory-18, the Medical Outcomes Study 36-Item Short Form Health Survey, and the CCSS-Neurocognitive Questionnaire also were assessed.ResultsAmong 14,358 participants (median age, 39.7&nbsp;years), 224 had a stroke after their cancer diagnosis (single stroke in 161 patients and recurrent stroke in 63 patients). Based on 2636 deaths, all-cause late mortality rates were 0.70 (95% CI, 0.68-0.73) prior to stroke, 1.03 (95% CI, 0.73-1.46) after the first stroke, and 2.42 (95% CI, 1.48-3.94) after the recurrent stroke. Among 7304 survivors, those with stroke were more likely to live with a caregiver (single stroke odds ratio [OR], 2.3 [95% CI, 1.4-3.8]; and recurrent stroke OR, 5.3 [95% CI, 1.7-16.8]) compared with stroke-free survivors. Stroke negatively impacted task efficiency (single stroke OR, 2.4 [95% CI, 1.4-4.1] and recurrent stroke OR, 3.3 [95% CI, 1.1-10.3]) and memory (single stroke OR, 2.1 [95% CI, 1.2-3.7]; and recurrent stroke OR, 3.5 [95% CI, 1.1-10.5]).ConclusionsStroke and stroke recurrence are associated with increased mortality and negatively impact HRQOL measures in survivors of pediatric cancer