Ultraviolet Detection of the Binary Companion to the Type IIb SN 2001ig

We present HST/WFC3 ultraviolet imaging in the F275W and F336W bands of the Type IIb SN 2001ig at an age of more than 14 years. A clear point source is detected at the site of the explosion having $m_{\rm F275W}=25.39 \pm 0.10$ and $m_{\rm F336W}=25.88 \pm 0.13$ mag. Despite weak constraints on both the distance to the host galaxy NGC 7424 and the line-of-sight reddening to the supernova, this source matches the characteristics of an early B-type main sequence star having $19,000 < T_{\rm eff} < 22,000$ K and $\log (L_{\rm bol}/L_{\odot})=3.92 \pm 0.14$. A BPASS v2.1 binary evolution model, with primary and secondary masses of 13 M$_{\odot}$ and 9 M$_{\odot}$ respectively, is found to resemble simultaneously in the Hertzsprung-Russell diagram both the observed location of this surviving companion, and the primary star evolutionary endpoints for other Type IIb supernovae. This same model exhibits highly variable late-stage mass loss, as expected from the behavior of the radio light curves. A Gemini/GMOS optical spectrum at an age of 6 years reveals a narrow He II emission line, indicative of continuing interaction with a dense circumstellar medium at large radii from the progenitor. We review our findings on SN 2001ig in the context of binary evolution channels for stripped-envelope supernovae. Owing to the uncrowded nature of its environment in the ultraviolet, this study of SN 2001ig represents one of the cleanest detections to date of a surviving binary companion to a Type IIb supernova.Comment: 8 pages, 3 figures. Resubmitted to ApJ after minor changes requested by refere

The VLT-FLAMES Tarantula Survey XXI. Stellar spin rates of O-type spectroscopic binaries

The initial distribution of spin rates of massive stars is a fingerprint of their elusive formation process. It also sets a key initial condition for stellar evolution and is thus an important ingredient in stellar population synthesis. So far, most studies have focused on single stars. Most O stars are however found in multiple systems. By establishing the spin-rate distribution of a sizeable sample of O-type spectroscopic binaries and by comparing the distributions of binary sub-populations with one another as well as with that of presumed single stars in the same region, we aim to constrain the initial spin distribution of O stars in binaries, and to identify signatures of the physical mechanisms that affect the evolution of the massive stars spin rates. We use ground-based optical spectroscopy obtained in the framework of the VLT-FLAMES Tarantula Survey (VFTS) to establish the projected equatorial rotational velocities (\vrot) for components of 114 spectroscopic binaries in 30 Doradus. The \vrot\ values are derived from the full-width at half-maximum (FWHM) of a set of spectral lines, using a FWHM vs. \vrot\ calibration that we derive based on previous line analysis methods applied to single O-type stars in the VFTS sample. The overall \vrot\ distribution of the primary stars resembles that of single O-type stars in the VFTS, featuring a low-velocity peak (at \vrot < 200 kms) and a shoulder at intermediate velocities (200 < \vrot < 300 kms). The distributions of binaries and single stars however differ in two ways. First, the main peak at \vrot \sim100 kms is broader and slightly shifted toward higher spin rates in the binary distribution compared to that of the presumed-single stars. Second, the \vrot distribution of primaries lacks a significant population of stars spinning faster than 300 kms while such a population is clearly present in the single star sample.Comment: 16 pages, 16 figures, paper accepted in Astronomy & Astrophysic

Geologic Evaluation of Critical Production Parameters for Coalbed Methane Resources, Part II, Black Warrior Basin

Geologic evaluation of critical production parameters for coalbed-methane resources in the Black Warrior basin of Alabama employed an interdisciplinary approach that utilized structural, coal-quality, sedimentologic, hydrologic, and engineering data. Results indicate that geologic factors are a major control on the producibility of coalbed methane and that completion techniques may be used to increase recovery if tailored to specific geologic settings. Sedimentologic and coal-quality parameters may be used to locate regions for coalbed methane development by characterizing the occurrence, rank, and grade of coal resources. However, high-productivity trends within those regions are localized, and geologic data suggest that productivity trends may be predictable. Several highly productive trends occur along northeast-oriented lineaments. These lineaments are the inferred surface expression of zones of enhanced permeability which are related to fractures. Productive trends also are associated with areas of low reservoir pressure, and salinity maps indicate that fresh water has migrated toward areas with low reservoir pressure. The available data indicate that structure and hydrology are critical production parameters that may be used to identify favorable well sites within regions containing significant coalbed-methane resources.Bureau of Economic Geolog

Geologic Evaluation of Critical Production Parameters for Coalbed Methane Resources, Black Warrior Basin - Final Report

Characterization of coalbed methane occurrence and producibility in the Black Warrior basin of Alabama indicates that geologic factors are the principal controls on the occurrence and producibility of coalbed methane. Results of engineering analysis indicate that application of completion and stimulation techniques may be used to increase recovery once favorable well sites are chosen. Sedimentologic and coal-quality parameters may be used to locate regions for coalbed methane development by characterizing the occurrence, rank, and grade of coal resources. However, high-productivity trends within those regions are localized, and geologic data suggest that productivity trends may be predictable on the basis of structural and hydrologic parameters. Several highly productive trends occur along northeast-oriented lineaments. These trends evidently are the surface expression of zones of enhanced permeability which apparently are related to fractures. Productive trends also are associated with areas of low reservoir pressure, and salinity maps indicate that fresh water has migrated toward these areas from the southeast margin of the basin. The available data indicate that structure and hydrology are critical production parameters that may be used to identify favorable well sites within regions containing significant, high-quality coal resources.Bureau of Economic Geolog

The VLT-FLAMES Tarantula Survey XIX. B-type Supergiants - Atmospheric parameters and nitrogen abundances to investigate the role of binarity and the width of the main sequence

TLUSTY non-LTE model atmosphere calculations have been used to determine atmospheric parameters and nitrogen (N) abundances for 34 single and 18 binary B-type supergiants (BSGs). The effects of flux contribution from an unseen secondary were considered for the binary sample. We present the first systematic study of the incidence of binarity for a sample of BSGs across the theoretical terminal age main sequence (TAMS). To account for the distribution of effective temperatures of the BSGs it may be necessary to extend the TAMS to lower temperatures. This is consistent with the derived distribution of mass discrepancies, projected rotational velocities (vsini) and N abundances, provided that stars cooler than this temperature are post RSG objects. For the BSGs in the Tarantula and previous FLAMES surveys, most have small vsini. About 10% have larger vsini (>100 km/s) but surprisingly these show little or no N enhancement. All the cooler BSGs have low vsini of <70km/s and high N abundance estimates, implying that either bi-stability braking or evolution on a blue loop may be important. A lack of cool binaries, possibly reflects the small sample size. Single star evolutionary models, which include rotation, can account for the N enhancement in both the single and binary samples. The detailed distribution of N abundances in the single and binary samples may be different, possibly reflecting differences in their evolutionary history. The first comparative study of single and binary BSGs has revealed that the main sequence may be significantly wider than previously assumed, extending to Teff=20000K. Some marginal differences in single and binary atmospheric parameters and abundances have been identified, possibly implying non-standard evolution for some of the sample. This sample as a whole has implications for several aspects of our understanding of the evolution of BSGs. Full abstract in paperComment: 21 pages, 15 figures, 11 table

The VLT-FLAMES Tarantula Survey XVIII. Classifications and radial velocities of the B-type stars

We present spectral classifications for 438 B-type stars observed as part of the VLT-FLAMES Tarantula Survey (VFTS) in the 30 Doradus region of the Large Magellanic Cloud. Radial velocities are provided for 307 apparently single stars, and for 99 targets with radial-velocity variations which are consistent with them being spectroscopic binaries. We investigate the spatial distribution of the radial velocities across the 30 Dor region, and use the results to identify candidate runaway stars. Excluding potential runaways and members of two older clusters in the survey region (SL 639 and Hodge 301), we determine a systemic velocity for 30 Dor of 271.6 ± 12.2 kms-1 from 273 presumed single stars. Employing a 3σ criterion we identify nine candidate runaway stars (2.9% of the single stars with radial-velocity estimates). The projected rotational velocities of the candidate runaways appear to be significantly different to those of the full B-type sample, with a strong preference for either large (≥345 kms-1) or small (≤65 kms-1) rotational velocities. Of the candidate runaways, VFTS 358 (classified B0.5: V) has the largest differential radial velocity (−106.9 ± 16.2 kms-1), and a preliminary atmospheric analysis finds a significantly enriched nitrogen abundance of 12 + log (N/H) ≳ 8.5. Combined with a large rotational velocity (ve sin i = 345 ± 22 kms-1), this is suggestive of past binary interaction for this star

Mathematical stories: Why do more boys than girls choose to study mathematics at AS-level in England?

Copyright @ 2005 Taylor & FrancisIn this paper I address the question: How is it that people come to choose mathematics and in what ways is this process gendered? I draw on the findings of a qualitative research study involving interviews with 43 young people all studying mathematics in post-compulsory education in England. Working within a post-structuralist framework, I argue that gender is a project and one that is achieved in interaction with others. Through a detailed reading of Toni and Claudia’s stories I explore the tensions for young women who are engaging in mathematics, something that is discursively inscribed as masculine, while (understandably) being invested in producing themselves as female. I conclude by arguing that seeing ‘doing mathematics’ as ‘doing masculinity’ is a productive way of understanding why mathematics is so male dominated and by looking at the implications of this understanding for gender and mathematics reform work.This work is funded by the ESR

Enlightening the structure and dynamics of Abell 1942

We present a dynamical analysis of the galaxy cluster Abell 1942 based on a set of 128 velocities obtained at the European Southern Observatory. Data on individual galaxies are presented and the accuracy of the determined velocities is discussed as well as some properties of the cluster. We have also made use of publicly available Chandra X-ray data. We obtained an improved mean redshift value z = 0.22513 \pm 0.0008 and velocity dispersion sigma = 908^{+147}_{-139} km/s. Our analysis indicates that inside a radius of ~1.5 h_{70}^{-1} Mpc (~7 arcmin) the cluster is well relaxed, without any remarkable feature and the X-ray emission traces fairly well the galaxy distribution. Two possible optical substructures are seen at ~5 arcmin from the centre towards the Northwest and the Southwest direction, but are not confirmed by the velocity field. These clumps are however, kinematically bound to the main structure of Abell 1942. X-ray spectroscopic analysis of Chandra data resulted in a temperature kT = 5.5 \pm 0.5 keV and metal abundance Z = 0.33 \pm 0.15 Z_odot. The velocity dispersion corresponding to this temperature using the T_X-sigma scaling relation is in good agreement with the measured galaxies velocities. Our photometric redshift analysis suggests that the weak lensing signal observed at the south of the cluster and previously attributed to a "dark clump", is produced by background sources, possibly distributed as a filamentary structure.Comment: Accepted for publication in Astronomy & Astrophysics, 15 pages, 15 figures, table w/ positions, photometric data and redshift

The Cluster of Galaxies Abell 970

We present a dynamical analysis of the galaxy cluster Abell 970 based on a new set of radial velocities measured at ESO, Pic du Midi and Haute-Provence observatories. Our analysis indicates that this cluster has a substructure and is out of dynamical equilibrium. This conclusion is also supported by differences in the positions of the peaks of the surface density distribution and X-ray emission, as well as by the evidence of a large scale velocity gradient in the cluster. We also found a discrepancy between the masses inferred with the virial theorem and with the X-ray emission, what is expected if the galaxies and the gas inside the cluster are not in hydrostatic equilibrium. Abell 970 has a modest cooling flow, as is expected if it is out of equilibrium as suggested by Allen (1998). We propose that cooling flows may have an intermittent behavior, with phases of massive cooling flows being followed by phases without significant cooling flows after the acretion of a galaxy group massive enough to disrupt the dynamical equilibrium in the center of the clusters. A massive cooling flow will be established again, after a new equilibrium is achieved.Comment: 24 pages, 9 figures, submitted to A&