The rotation rates of massive stars: How slow are the slow ones?

Context: Rotation plays a key role in the life cycles of stars with masses above 8 Msun. Hence, accurate knowledge of the rotation rates of such massive stars is critical for understanding their properties and for constraining models of their evolution. Aims: This paper investigates the reliability of current methods used to derive projected rotation speeds v sin i from line-broadening signatures in the photospheric spectra of massive stars, focusing on stars that are not rapidly rotating. Methods: We use slowly rotating magnetic O-stars with well-determined rotation periods to test the Fourier transform (FT) and goodness-of-fit (GOF) methods typically used to infer projected rotation rates of massive stars. Results: For our two magnetic test stars with measured rotation periods longer than one year, i.e., with v sin i < 1 km/s, we derive v sin i ~ 40-50 km/s from both the FT and GOF methods. These severe overestimates are most likely caused by an insufficient treatment of the competing broadening mechanisms referred to as microturbulence and macroturbulence. Conclusions: These findings warn us not to rely uncritically on results from current standard techniques to derive projected rotation speeds of massive stars in the presence of significant additional line broadening, at least when v sin i <~ 50 km/s. This may, for example, be crucial for i) determining the statistical distribution of observed rotation rates of massive stars, ii) interpreting the evolutionary status and spin-down histories of rotationally braked B-supergiants, and iii) explaining the deficiency of observed O-stars with spectroscopically inferred v sin i ~ 0 km/s. Further investigations of potential shortcomings of the above techniques are presently under way.Comment: 4 pages, 4 figures, accepted for publication in A&A Letter

Bright OB stars in the Galaxy.II. Wind variability in O supergiants as traced by H-alpha

We investigate the line-profile variability (lpv) of H-alpha for a large sample of O-type supergiants. We used the Temporal Variance Spectrum (TVS) analysis, developed by Fullerton et al 1996 and modified by us to take into account the effects of wind emission. By means of a comparative analysis we put a number of constraints on the properties of the variability as a function of stellar and wind parameters. The results of our analysis show that all the stars in the sample show evidence of significant lpv in H-alpha, mostly dominated by processes in the wind. The variations occur between zero and 0.3 v_inf (i.e., below ~1.5 R_star), in good agreement with the results from similar studies. A comparison between observations and line-profile simulations indicates that for stars with intermediate wind densities the H-alpha variability can be explained by simple models, consisting of coherent or broken shells (blobs) uniformly distributed over the wind volume, with an intrinsic scatter in the maximum density contrast of about a factor of two. For stars at lower and higher wind densities, on the other hand, we found certain inconsistencies between observations and our predictions, most importantly concerning the mean amplitude and the symmetry properties of the TVS. This disagreement might be explained with the presence of coherent large-scale structures, partly confined in a volume close to the star. Interpreted in terms of a variable mass-loss rate, the observed variations of H-alpha indicate changes of 4% with respect to the mean value of M_dot for stars with stronger winds and of 16% for stars with weaker winds. The effect of these variations on the corresponding wind momenta is rather insignificant (<0.16 dex), increasing the local scatter without affecting the Wind Momentum Luminosity Relationship.Comment: 22 pages, 11 figures. Accepted by Astronomy and Astrophysic

Migrants with insecure legal status and access to work: the role of ethnic solidarity networks

This article explores the complexities of ethnic solidarity and ethnic capital in enabling participation on labour markets for migrants with insecure legal status in the UK. By drawing together research insights and data from a questionnaire survey of 178 Iraqi-Kurdish migrants with insecure legal status, four focus groups and ten expert interviews, this paper examines how ‘unauthorised’ migrants get access to the segmented labour market at a time of increased in-border controls in the UK. It argues that conflict-generated diasporas such as the Kurds display a distinct solidarity with their community members with insecure legal status and provide access to the labour markets against the tangible threat of in-border migration enforcement. We term this form of solidarity as stretched solidarity which emerges during risky, difficult and destitute times and it is a reluctant act of empathy and socio-political position. This paper identifies the social phenomenon of stretched solidarity and sets out a model for understanding its embeddedness within conflict-generated diasporic networks

Spectroscopic and physical parameters of Galactic O-type stars. II. Observational constraints on projected rotational and extra broadening velocities as a function of fundamental parameters and stellar evolution

Rotation is of key importance for the evolution of hot massive stars, however, the rotational velocities of these stars are difficult to determine. Based on our own data for 31 Galactic O stars and incorporating similar data for 86 OB supergiants from the literature, we aim at investigating the properties of rotational and extra line-broadening as a function of stellar parameters and at testing model predictions about the evolution of stellar rotation. Fundamental stellar parameters were determined by means of the code FASTWIND. Projected rotational and extra broadening velocities originate from a combined Ft + GOF method. Model calculations published previously were used to estimate the initial evolutionary masses. The sample O stars with Minit > 50 Msun rotate with less that 26% of their break-up velocity, and they also lack objects with v sin i 35 Msun on the hotter side of the bi-stability jump, the observed and predicted rotational rates agree quite well; for those on the cooler side of the jump, the measured velocities are systematically higher than the predicted ones. In general, the derived extra broadening velocities decrease toward cooler Teff, whilst for later evolutionary phases they appear, at the same v sin i, higher for high-mass stars than for low-mass ones. None of the sample stars shows extra broadening velocities higher than 110 km/s. For the majority of the more massive stars, extra broadening either dominates or is in strong competition with rotation. Conclusions: For OB stars of solar metallicity, extra broadening is important and has to be accounted for in the analysis. When appearing at or close to the zero-age main sequence, most of the single and more massive stars rotate slower than previously thought. Model predictions for the evolution of rotation in hot massive stars may need to be updated.Comment: 15 pages, 10 figures, accepted for publication in A &

Corporate Social Responsibility: A Case Study of San Francisco’s Apparel Procurement

The presence of sweatshops in the apparel and textile industry has been referenced in history as far back as the 1800s when the term “sweatshop” was coined to bring public attention to factories and workshops that used “sweated labor” (Micheletti & Stolle, 2007). Contemporary anti-sweatshop activism gained momentum in the 1990s with publicized scandals about Nike’s manufacturing and celebrity Kathy Lee Gifford’s child labor subcontractors. Over the last two decades U.S. consumers have become increasingly aware of how goods are produced overseas, especially in the apparel and textile industry. Consumer awareness and public activism have encouraged change. Claeson (2009) points out that activists have succeeded in raising awareness about the global sweatshop problem

Impaired response of the denervated kidney to endothelin receptor blockade in normotensive and spontaneously hypertensive rats

Impaired response of the denervated kidney to endothelin receptor blockade in normotensive and spontaneously hypertensive rats.BackgroundAs yet, there are only limited data available on the exact role of endothelin (ET) acting through endothelin-A (ETA) receptors in renal sodium and water regulation and the potential functional implications of an interaction of the renal ET system with renal nerves in normotensive and spontaneously hypertensive rats.MethodsExperiments were carried out in 64 male conscious spontaneously hypertensive rats and in 56 normotensive Wistar-Kyoto (WKY) rats. Bilateral renal denervation (BRD) was performed in 32 spontaneously hypertensive rats and 28 WKY rats 7days before the experiments. The ETA receptor antagonist, BQ-123 (16.4nmol/kg.min intravenously) or the endothelin-B (ETB) receptor antagonist, BQ-788 (25nmol/kg.min intravenously) were infused at a rate of 25 μL/min for 50 minutes.ResultsRenal papillary ET-1 concentration in intact spontaneously hypertensive rats was 67.8% lower than in intact WKY rats (154 ± 40 fmol/mg protein vs. 478 ± 62 fmol/mg protein, P < 0.01). BRD decreased papillary ET-1 by 73.5% in WKY rats to 127 ± 19 fmol/mg protein (P < 0.001), but had no effect in spontaneously hypertensive rats (122 ± 37 fmol/mg protein). BRD, BQ-123, or BQ-788 did not affect glomerular filtration rate (GFR) or renal blood flow (RBF) in any of the groups. In intact WKY, BQ-123 decreased urine flow rate (V) from 4.65 ± 0.44 μL/min.100g body weight to 2.44 ± 0.35 μL/min.100g body weight (P < 0.01), urinary excretion of sodium (UNaV) from 238.2 ± 27.4 to 100.2 ± 17.0 (P < 0.01) and potassium (UKV) from 532.1 ± 62.6nmol/min.100g body weight to 243.0 ± 34.2nmol/min.100g body weight (P < 0.001), whereas BQ-788 decreased only V and UNaV. In renal denervated WKY, BQ-123 or BQ-788 did not alter V, UNaV, or UKV. In intact spontaneously hypertensive rats BQ-123 but not BQ-788 decreased V from 3.94 ± 0.48 μL/min.100g body weight to 2.55 ± 0.44 μL/min.100g body weight (P < 0.05). In renal denervated spontaneously hypertensive rats neither BQ-123 nor BQ-788 affected V, UNaV, or UKV.ConclusionAn interaction between ET and renal nerves is involved in the control of renal function. Moreover, renal nerves participate in the regulation of ET-1 production within the kidney. Finally, decreased synthesis of ET-1 in the renal papilla of spontaneously hypertensive rats may contribute to development and/or maintenance of hypertension due to modulation of renal excretory function