Intrinsic spectral blueshifts in rapidly rotating stars?

Spectroscopic radial velocities for several nearby open clusters suggest that spectra of (especially earlier-type) rapidly rotating stars are systematically blueshifted by 3 km/s or more, relative to the spectra of slowly rotating ones. Comparisons with astrometrically determined radial motions in the Hyades suggests this to be an absolute blueshift, relative to wavelengths naively expected from stellar radial motion and gravitational redshift. Analogous trends are seen also in most other clusters studied (Pleiades, Coma Berenices, Praesepe, Alpha Persei, IC 2391, NGC 6475, IC 4665, NGC 1976 and NGC 2516). Possible mechanisms are discussed, including photospheric convection, stellar pulsation, meridional circulation, and shock-wave propagation, as well as effects caused by template mismatch in determining wavelength displacements. For early-type stars, a plausible mechanism is shock-wave propagation upward through the photospheric line-forming regions. Such wavelength shifts thus permit studies of certain types of stellar atmospheric dynamics and - irrespective of their cause - may influence deduced open-cluster membership (when selected from common velocity) and deduced cluster dynamics (some types of stars might show fortuitous velocity patterns).Comment: Accepted by Astronomy & Astrophysics; 6 pages, 3 figure

Abundance analysis of prime B-type targets for asteroseismology II. B6--B9.5 stars in the field of view of the CoRoT

The CoRoT satellite is collecting precise time-resolved photometry for tens of asteroseismology targets. To ensure a correct interpretation of the CoRoT data, the atmospheric parameters, chemical compositions, and rotational velocities of the stars must be determined. The main goal of the ground-based seismology support program for the CoRoT mission was to obtain photometric and spectroscopic data for stars in the fields monitored by the satellite. These ground-based observations were collected in the GAUDI archive. High-resolution spectra of more than 200 B-type stars are available in this database, and about 45% of them is analysed here. To derive the effective temperature of the stars, we used photometric indices. Surface gravities were obtained by comparing observed and theoretical Balmer line profiles. To determine the chemical abundances and rotational velocities, we used a spectrum synthesis method, which consisted of comparing the observed spectrum with theoretical ones based on the assumption of LTE. Atmospheric parameters, chemical abundances, and rotational velocities were determined for 89 late-B stars. The dominant species in their spectra are iron-peak elements. The average Fe abundance is 7.24+/-0.45 dex. The average rotational velocity is 126 km/sec, but there are 13 and 20 stars with low and moderate Vsin i values, respectively. The analysis of this sample of 89 late B-type stars reveals many chemically peculiar (CP) stars. Some of them were previously known, but at least 9 new CP candidates, among which at least two HgMn stars, are identified in our study. These CP stars as a group exhibit Vsin i values lower than the stars with normal surface chemical composition.Comment: 21 pages, 13 figures, accepted to Astronomy and Astrophysic

Individualisation of time-motion analysis : a method comparison and case report series

© Georg Thieme Verlag KG. This study compared the intensity distribution of time-motion analysis data, when speed zones were categorized by different methods. 12 U18 players undertook a routine battery of laboratory- and field-based assessments to determine their running speed corresponding to the respiratory compensation threshold (RCT), maximal aerobic speed (MAS), maximal oxygen consumption (vVO 2max ) and maximal sprint speed (MSS). Players match-demands were tracked using 5 Hz GPS units in 22 fixtures (50 eligible match observations). The percentage of total distance covered running at high-speed (%HSR), very-high speed (%VHSR) and sprinting were determined using the following speed thresholds: 1) arbitrary; 2) individualised (IND) using RCT, vVO 2max and MSS; 3) individualised via MAS per se; 4) individualised via MSS per se; and 5) individualised using MAS and MSS as measures of locomotor capacities (LOCO). Using MSS in isolation resulted in 61 % and 39 % of player's % HSR and % VHSR, respectively, being incorrectly interpreted, when compared to the IND technique. Estimating the RCT from fractional values of MAS resulted in erroneous interpretations of % HSR in 50 % of cases. The present results suggest that practitioners and researchers should avoid using singular fitness characteristics to individualise the intensity distribution of time-motion analysis data. A combination of players' anaerobic threshold, MAS, and MSS characteristics are recommended to individualise player-tracking data

Abundance analysis of Am binaries and search for tidally driven abundance anomalies - III. HD116657, HD138213, HD155375, HD159560, HD196544 and HD204188

We continue here the systematic abundance analysis of a sample of Am binaries in order to search for possible abundance anomalies driven by tidal interaction in these binary systems. New CCD observations in two spectral regions (6400-6500, 6660-6760 AA) of HD116657, HD138213, HD155375, HD159560, HD196544 and HD204188 were obtained. Synthetic spectrum analysis was carried out and basic stellar properties, effective temperatures, gravities, projected rotational velocities, masses, ages and abundances of several elements were determined. We conclude that all six stars are Am stars. These stars were put into the context of other Am binaries with 10 < Porb < 200 days and their abundance anomalies discussed in the context of possible tidal effects. There is clear anti-correlation of the Am peculiarities with v sin i. However, there seems to be also a correlation with the eccentricity and may be with the orbital period. The dependence on the temperature, age, mass, and microturbulence was studied as well. The projected rotational velocities obtained by us were compared to those of Royer et al. (2002) and Abt & Morrell (1995).Comment: 11 pages, 3 tables, 12 figures. Accepted for publication in Monthly Notices of the Royal Astronomical Societ

Early Results from the Galactic O-Star Spectroscopic Survey: C III Emission Lines in Of Spectra

On the basis of an extensive new spectroscopic survey of Galactic O stars, we introduce the Ofc category, which consists of normal spectra with C III \lambda\lambda4647-4650-4652 emission lines of comparable intensity to those of the Of defining lines N III \lambda\lambda4634-4640-4642. The former feature is strongly peaked to spectral type O5, at all luminosity classes, but preferentially in some associations or clusters and not others. The relationships of this phenomenon to the selective C III \lambda5696 emission throughout the normal Of domain, and to the peculiar, variable Of?p category, for which strong C III \lambda\lambda4647-4650-4652 emission is a defining characteristic, are discussed. Magnetic fields have recently been detected on two members of the latter category. We also present two new extreme Of?p stars, NGC 1624-2 and CPD -28^{\circ}2561, bringing the number known in the Galaxy to five. Modeling of the behavior of these spectral features can be expected to better define the physical parameters of both normal and peculiar objects, as well as the atomic physics involved.Comment: 12 pages, 1 table, 2 figures; accepted for ApJL, vol. 71

Understanding Bottom Production

We describe calculations of b b-bar production to next-to-next-to-leading order (NNLO) and next-to-next-to-leading logarithm (NNLL) near threshold in pp interactions. Our calculations are in good agreement with the b b-bar total cross section measured by HERA-B.Comment: contribution to the proceedings of Quark Matter'02, 4 pages, 1 .eps figure, uses special included style fil

The magnetic Bp star 36 Lyncis, I. Magnetic and photospheric properties

This paper reports the photospheric, magnetic and circumstellar gas characteristics of the magnetic B8p star 36 Lyncis (HD 79158). Using archival data and new polarised and unpolarised high-resolution spectra, we redetermine the basic physical properties, the rotational period and the geometry of the magnetic field, and the photospheric abundances of various elements.}{Based on magnetic and spectroscopic measurements, we infer an improved rotational period of $3.83475\pm 0.00002$ d. We determine a current epoch of the longitudinal magnetic field positive extremum (HJD 2452246.033), and provide constraints on the geometry of the dipole magnetic field (i\geq 56\degr, $3210 {\rm G}\leq B_{\rm d}\leq 3930$ G, $\beta$ unconstrained). We redetermine the effective temperature and surface gravity using the optical and UV energy distributions, optical photometry and Balmer line profiles ($T_{\rm eff}=13300\pm 300$ K, $\log g=3.7-4.2$), and based on the Hipparcos parallax we redetermine the luminosity, mass, radius and true rotational speed ($L=2.54\pm 0.16 L_\odot, M=4.0\pm 0.2 M_\odot, R=3.4\pm 0.7 R_\odot, v_{\rm eq}=45-61.5$ \kms). We measure photospheric abundances for 21 elements using optical and UV spectra, and constrain the presence of vertical stratification of these elements. We perform preliminary Doppler Imaging of the surface distribution of Fe, finding that Fe is distributed in a patchy belt near the rotational equator. Most remarkably, we confirm strong variations of the H$\alpha$ line core which we interpret as due to occultations of the star by magnetically-confined circumstellar gas.Comment: Accepted by Astronomy and Astrophysic

QCD Structure of Leptons

The QCD structure of the electron is defined and calculated. The leading order splitting functions are extracted, showing an important contribution from $\gamma$-$Z$ interference. Leading logarithmic QCD evolution equations are constructed and solved in the asymptotic region where log$^2$ behaviour of the parton densities is observed. Corrections to the naive evolution procedure are demonstrated. Possible applications with clear manifestation of 'resolved' photon and weak bosons are discussed.Comment: 10 pages, 5 figures, revised versio

Heavy-quark correlations in deep inelastic scattering

We discuss results for heavy quark correlations in next-to-leading order QCD in deep inelastic electroproduction.Comment: Talk presented by J. Smith. To appear in proceedings of "QCD and QED in Higher Orders" 1996 Zuethen Workshop on Elementary Particle Theory, April 22-26, 1996. Latex, 5 figures, uses espcrc2.sty (included

Rotational velocities of A-type stars I. Measurement of vsini in the southern hemisphere

Within the scope of a Key Programme determining fundamental parameters of stars observed by HIPPARCOS, spectra of 525 B8 to F2-type stars brighter than V=8 have been collected at ESO. Fourier transforms of several line profiles in the range 4200-4500 A are used to derive vsini from the frequency of the first zero. Statistical analysis of the sample indicates that measurement error is a function of vsini and this relative error of the rotational velocity is found to be about 6% on average. The results obtained are compared with data from the literature. There is a systematic shift from standard values from Slettebak et al. (1975), which are 10 to 12% lower than our findings. Comparisons with other independent vsini values tend to prove that those from Slettebak et al. are underestimated. This effect is attributed to the presence of binaries in the standard sample of Slettebak et al., and to the model atmosphere they used.Comment: 17 pages, includes 18 figures, accepted in A&