Promoting sustainable Indian textiles: final report to the Department for Environment, Food and Rural Affairs (Defra), London, UK

In 2009, the Department for Environment, Food and Rural Affairs (Defra), through the Sustainable Development Dialogue (SDD) fund, backed the Centre for Sustainable Fashion (CSF) at London College of Fashion and Pearl Academy of Fashion (PAF), New Delhi to run a project to promote Indian sustainable textiles. Improving patterns of sustainable consumption and production (SCP) in India and the UK is one of the agreed areas for collaboration under the UK-India Sustainable Development Dialogue. The project is also part of a body of work taking place under the Defra Sustainable Clothing Roadmap, which aims to improve the sustainability of clothing. Defra has identified that ‘while an economic success story (globally worth over £500 billion) the industry has a significant environmental and social footprint across its supply chain.’ The Roadmap aims to improve the sustainability of clothing by gathering a robust evidence base of impacts and working with a wide range of stakeholders, to build on existing interventions. For more details on the roadmap see: http://www.defra.gov.uk/environment/business/products/roadmaps/clothing/index.htm This report is only one of the dissemination tools associated with the project. The project film, images and website should be viewed in conjunction with this report

On the angular momentum evolution of merged white dwarfs

We study the angular momentum evolution of binaries containing two white dwarfs which merge and become cool helium-rich supergiants. Our object is to compare predicted rotation velocities with observations of highly evolved stars believed to have formed from such a merger, including RCrB and extreme helium stars. The principal study involves a binary containing a 0.6 solar mass CO white dwarf, and a 0.3 solar mass He white dwarf. The initial condition for the angular momentum distribution is defined where the secondary fills its Roche Lobe. We assume conservation of angular momentum to compute the angular momentum distribution in a collisionless disk and subsequently in the giant envelope. At the end of shell-helium burning, the giant contracts to form a white dwarf. We derive the surface rotation velocity during this contraction. The calculation is repeated for a range of initial mass ratios, and also for the case of mergers between two helium white dwarfs; the latter will contract to the helium main-sequence rather than the white dwarf sequence. Assuming complete conservation of angular momentum, we predict acceptable angular rotation rates for cool giants and during the initial subsequent contraction. However such stars will only survive spin-up to reach the white dwarf sequence (CO+He merger) if the initial mass ratio is close to unity. He+He merger products must lose angular momentum in order to reach the helium main sequence. Minimum observed rotation velocities in extreme helium stars are lower than our predictions by at least one half, indicating that CO+He mergers must lose at least one half of their angular momentum.Comment: 11 pages, 11 figures, MNRAS in pres

Evolution of Rotating Accreting White Dwarfs and the Diversity of Type Ia Supernovae

Type Ia supernovae (SNe Ia) have relatively uniform light curves and spectral evolution, which make SNe Ia useful standard candles to determine cosmological parameters. However, the peak brightness is not completely uniform, and the origin of the diversity has not been clear. We examine whether the rotation of progenitor white dwarfs (WDs) can be the important source of the diversity of the brightness of SNe Ia. We calculate the structure of rotating WDs with an axisymmetric hydrostatic code. The diversity of the mass induced by the rotation is ~0.08 Msun and is not enough to explain the diversity of luminosity. However, we found the following relation between the initial mass of the WDs and their final state; i.e., a WD of smaller initial mass will rotate more rapidly before the supernova explosion than that of larger initial mass. This result might explain the dependence of SNe Ia on their host galaxies.Comment: 7 pages, 6 figure

Chandra View of DA 530: A Sub-Energetic Supernova Remnant with a Pulsar Wind Nebula?

Based on a Chandra ACIS observation, we report the detection of an extended X-ray feature close to the center of the remnant DA 530 with 5.3 sigma above the background within a circle of 20'' radius. This feature, characterized by a power-law with the photon index gamma=1.6+-0.8 and spatially coinciding with a nonthermal radiosource, most likely represents a pulsar wind nebula. We have further examined the spectrum of the diffuse X-ray emission from the remnant interior with a background-subtracted count rate of ~0.06 counts s^-1 in 0.3-3.5 keV. The spectrum of the emission can be described by a thermal plasma with a temperature of ~0.3-0.6 keV and a Si over-abundance of >~7 solar. These spectral characteristics, together with the extremely low X-ray luminosity, suggest that the remnant arises from a supernova with an anomalously low mechanical energy (<10^50 ergs). The centrally-filled thermal X-ray emission of the remnant may indicate an early thermalization of the SN ejecta by the circum-stellar medium. Our results suggest that the remnant is likely the product of a core-collapsed SN with a progenitor mass of 8-12 Msun. Similar remnants are probably common in the Galaxy, but have rarely been studied.Comment: 23 pages, 7 figures, accepted for publication in ApJ; complete the abstract on astro-ph and correct some typo

A Five-year Spectroscopic and Photometric Campaign on the Prototypical alpha Cygni Variable and A-type Supergiant Star Deneb

Deneb is often considered the prototypical A-type supergiant, and is one of the visually most luminous stars in the Galaxy. A-type supergiants are potential extragalactic distance indicators, but the variability of these stars needs to be better characterized before this technique can be considered reliable. We analyzed 339 high resolution echelle spectra of Deneb obtained over the five-year span of 1997 through 2001 as well as 370 Stromgren photometric measurements obtained during the same time frame. Our spectroscopic analysis included dynamical spectra of the H-alpha profile, H-alpha equivalent widths, and radial velocities measured from Si II 6347, 6371. Time-series analysis reveals no obvious cyclic behavior that proceeds through multiple observing seasons, although we found a suspected 40 day period in two, non-consecutive observing seasons. Some correlations are found between photometric and radial velocity data sets, and suggest radial pulsations at two epochs. No correlation is found between the variability of the H-alpha profiles and that of the radial velocities or the photometry. Lucy (1976) found evidence that Deneb was a long period single-lined spectroscopic binary star, but our data set shows no evidence for radial velocity variations caused by a binary companion.Comment: 49 pages, 9 figures, 5 tables, accepted for publication in the Astronomical Journa

The Progenitors of Subluminous Type Ia Supernovae

We find that spectroscopically peculiar subluminous SNe Ia come from an old population. Of the sixteen subluminous SNe Ia known, ten are found in E/S0 galaxies, and the remainder are found in early-type spirals. The probability that this is a chance occurrence is only 0.2%. The finding that subluminous SNe Ia are associated with an older stellar population indicates that for a sufficiently large lookback time (already accessible in current high redshift searches) they will not be found. Due to a scarcity in old populations, hydrogen and helium main sequence stars and He red giant stars that undergo Roche lobe overflow are unlikely to be the progenitors of subluminous SNe Ia. Earlier findings that overluminous SNe Ia (dM15(B) < 0.95) come from a young progenitor population are confirmed. The fact that subluminous SNe Ia and overluminous SNe Ia come from different progenitor populations and also have different properties is a prediction of the CO white dwarf merger progenitor scenario.Comment: 7 pages, 1 figure, Accepted to ApJ Letter

R-mode oscillations and rocket effect in rotating superfluid neutron stars. I. Formalism

We derive the hydrodynamical equations of r-mode oscillations in neutron stars in presence of a novel damping mechanism related to particle number changing processes. The change in the number densities of the various species leads to new dissipative terms in the equations which are responsible of the {\it rocket effect}. We employ a two-fluid model, with one fluid consisting of the charged components, while the second fluid consists of superfluid neutrons. We consider two different kind of r-mode oscillations, one associated with comoving displacements, and the second one associated with countermoving, out of phase, displacements.Comment: 10 page

Differential rotation of nonlinear r-modes

Differential rotation of r-modes is investigated within the nonlinear theory up to second order in the mode amplitude in the case of a slowly-rotating, Newtonian, barotropic, perfect-fluid star. We find a nonlinear extension of the linear r-mode, which represents differential rotation that produces large scale drifts of fluid elements along stellar latitudes. This solution includes a piece induced by first-order quantities and another one which is a pure second-order effect. Since the latter is stratified on cylinders, it cannot cancel differential rotation induced by first-order quantities, which is not stratified on cylinders. It is shown that, unlikely the situation in the linearized theory, r-modes do not preserve vorticity of fluid elements at second-order. It is also shown that the physical angular momentum and energy of the perturbation are, in general, different from the corresponding canonical quantities.Comment: 9 pages, revtex4; section III revised, comments added in Introduction and Conclusions, references updated; to appear in Phys. Rev.

On the evolution of rapidly rotating massive white dwarfs towards supernovae or collapses

A recent study by Yoon & Langer (2004a) indicated that the inner cores of rapidly accreting (Mdot > 10^{-7} M_sun/yr) CO white dwarfs may rotate differentially, with a shear rate near the threshold value for the onset of the dynamical shear instability. Such differentially rotating white dwarfs obtain critical masses for thermonuclear explosion or electron-capture induced collapse which significantly exceed the canonical Chandrasekhar limit. Here, we construct two-dimensional differentially rotating white dwarf models with rotation laws resembling those of the one-dimensional models of Yoon & Langer (2004a). We derive analytic relations between the white dwarf mass, its angular momentum, and its rotational-, gravitational- and binding energy. We show that these relations are applicable for a wide range of angular velocity profiles, including solid body rotation. We demonstrate that pre-explosion and pre-collapse conditions of both, rigidly and differentially rotating white dwarfs are well established by the present work, which may facilitate future multi-dimensional simulations of Type Ia supernova explosions and studies of the formation of millisecond pulsars and gamma-ray bursts from collapsing white dwarfs.Our results lead us to suggest various possible evolutionary scenarios for progenitors of Type Ia supernovae, leading to a new paradigm of a variable mass of exploding white dwarfs, at values well above the classical Chandrasekhar mass. Based on our 2D-models, we argue for the supernova peak brightness being proportional to the white dwarf mass, which could explain various aspects of the diversity of Type Ia supernovae, such as their variation in brightness, the dependence of their mean luminosity on the host galaxy type, and the weak correlation between ejecta velocity and peak brightness.Comment: Based on 2-D white dwarf models: 19 pages, 13 figures, A&A, accepte

A numerical study of the r-mode instability of rapidly rotating nascent neutron stars

The first results of numerical analysis of classical r-modes of {\it rapidly} rotating compressible stellar models are reported. The full set of linear perturbation equations of rotating stars in Newtonian gravity are numerically solved without the slow rotation approximation. A critical curve of gravitational wave emission induced instability which restricts the rotational frequencies of hot young neutron stars is obtained. Taking the standard cooling mechanisms of neutron stars into account, we also show the `evolutionary curves' along which neutron stars are supposed to evolve as cooling and spinning-down proceed. Rotational frequencies of $1.4M_{\odot}$ stars suffering from this instability decrease to around 100Hz when the standard cooling mechanism of neutron stars is employed. This result confirms the results of other authors who adopted the slow rotation approximation.Comment: 4 pages, 2 figures; MNRAS,316,L1(2000