Early type stars at high galactic latitudes II. Four evolved B-type stars of unusual chemical composition

We present the result of differential spectral analyses of a further four apparently normal B-type stars. Abundance anomalies (e.g. He, C, N enrichment), slow rotation and/or high gravities suggest that the programme stars are evolved low-mass B-type stars. In order to trace their evolutionary status several scenarios are discussed. Post-AGB evolution can be ruled out. PG 0229+064 and PG 1400+389 could be horizontal branch (HB) stars, while HD 76431 and SB 939 have already evolved away from the extreme HB (EHB). The low helium abundance of HD 76431 is consistent with post-EHB evolution. The enrichment in helium, carbon and nitrogen of the remaining stars can be explained either by deep mixing of nuclearly processed material to the surface or by diffusion processes modified by magnetic fields and/or stellar winds. A kinematic study of their galactic orbits indicates that the stars belong to an old disk population

Short stature, hyperkalemia and acidosis: A defect in renal transport of potassium

Short stature, hyperkalemia, and acidosis: A defect in renal transport of potassium. An eleven-year-old boy presented with short stature, hyperkalemia, and metabolic acidosis. No endocrine cause for a short stature could be demonstrated. Renal function, as assessed by inulin and PAH clearances, concentrating and diluting capacity, and ability to acidify the urine and to excrete net acid, was normal. No defect was detected in adrenal secretion of, or renal responsiveness to, aldosterone. A low renal threshold for bicarbonate was documented which apparently explained the acidosis. However, correction of the acidosis by administration of sodium bicarbonate did not influence the hyperkalemia, making it unlikely that an abnormality in bicarbonate reabsorption was the primary defect. Chlorothiazide induced a fall in serum potassium and a rise in serum bicarbonate to normal levels. During bicarbonate loading the rates of excretion of potassium in urine were consistently below those observed in control subjects. It appeared, therefore, that the patient had a primary abnormality in potassium excretion. The resulting hyperkalemia caused urinary loss of bicarbonate and systemic acidosis. Correction of both the acidosis and hyperkalemia by chronic administration of chlorothiazide and sodium bicarbonate has resulted in resumption of normal growth.Retard de croissance, hyperkaliéme et acidose: Un déficit du transport rénal du potassium. Un enfant de 11 ans avait un retard de croissance, une hyperkaliémie et une acidose métabolique. Aucune cause endocrine du retard de croissance n'a été trouvée. La fonction rénale, estimée par les clearances de l'inuline et du PAH, la capacité de concentration et de dilution et la capacité d'acidifier l'urine, était normales. Aucun déficit de la secrétion d'aldostérone ou de la réponse rénale à l'aldostérone n'a été mis en évidence. Un seuil rénal bas des bicarbonates a été découvert, qui explique apparemment l'acidose. Cependant la correction de l'acidose par l'administration de bicarbonate de sodium n'a pas influencé l'hyperkaliémie, ce qui rend peu probable que le déficit de la réabsorption de bicarbonate soit la cause de l'ensemble. Le Chlorothiazide a déterminé une baisse de la kaliéme et une augmentation du bicarbonate plasmatique jusqu'à des valeurs normales. Pendant une charge en bicarbonate les débits d'excretion du potassium dans les urines ont été nettement inférieurs à ceux obtenus chez des sujets témoins. Il apparaît donc que le malade a une anomalie primitive de l'excrétion de potassium. L'hyperkaliémie qui en est la conséquence a déterminé une perte de bicarbonate dans les urines et une acidose systémique. La correction de l'acidose et de l'hyperkaliémie par l'administration permanente de Chlorothiazide et de bicarbonate de sodium a eu pour résultat une reprise de la croissance normale

High resolution spectroscopy of bright subdwarf B stars - I. Radial velocity variables

Radial velocity curves for 15 bright subdwarf B binary systems have been measured using high precision radial velocity measurements from high S/N optical high-resolution spectra. In addition, two bright sdB stars are discovered to be radial velocity variable but the period could not yet be determined. The companions for all systems are unseen. The periods range from about 0.18 days up to more than ten days. The radial velocity semi amplitudes are found to lie between 15 and 130 km/s. Using the mass functions, the masses of the unseen companions have been constrained to lower limits of 0.03 up to 0.55 M_sun, and most probable values of 0.03 up to 0.81 M_sun. The invisible companions for three of our program stars are undoubtedly white dwarfs. In the other cases they could be either white dwarfs or main sequence stars. For two stars the secondaries could possibly be brown dwarfs. As expected, the orbits are circular for most of the systems. However, for one third of the program stars we find slightly eccentric orbits with small eccentricities of e~0.02-0.06. This is the first time that non-circular orbits have been found in sdB binaries. No correlation with the orbital period can be found.Comment: Accepted for publication in A&A, 10 pages, 5 figures, quality of Fig.2 is downgraded to fit in the astroph requirement

Nuclear shadowing in polarized DIS on ^6LiD at small x and its effect on the extraction of the deuteron spin structure function g_{1}^{d}(x,Q^2)

We consider the effect of nuclear shadowing in polarized deep inelastic scattering (DIS) on ^6LiD at small Bjorken x and its relevance to the extraction of the deuteron spin structure function g_{1}^{d}(x,Q^2). Using models, which describe nuclear shadowing in unpolarized DIS, we demonstrate that the nuclear shadowing correction to g_{1}^{d}(x,Q^2) is significant.Comment: 17 pages, 2 figure

HE 0437-5439 -- an unbound hyper-velocity main-sequence B-type star

We report the discovery of a 16th magnitude star, HE0437-5439, with a heliocentric radial velocity of +723+-3km/s. A quantitative spectral analysis of high-resolution optical spectra obtained with the VLT and the UVES spectrograph shows that HE0437-5439 is a main sequence B-type star with Teff=20350K, log g=3.77, solar within a factor of a few helium abundance and metal content, rotating at v sin i=54km/s. Using appropriate evolutionary tracks we derive a mass of 8 Msun and a corresponding distance of 61 kpc. Its galactic rest frame velocity is at least 563km/s, almost twice the local Galactic escape velocity, indicating that the star is unbound to the Galaxy. Numerical kinematical experiments are carried out to constrain its place of birth. It has been suggested that such hyper-velocity stars can be formed by the tidal disruption of a binary through interaction with the super-massive black hole at the Galactic center (GC). HE0437-5439 needs about 100Myrs to travel from the GC to its presentposition, much longer than its main sequence lifetime of 25Myrs. This can only be reconciled if HE0437-5439 is a blue straggler star. In this case, the predicted proper motion is so small that it can only be measured by future space missions. Since the star is much closer to the Large Magellanic Cloud (LMC, 18kpc) than to the GC, it can reach its position from the center of the LMC. The proper motion predicted in this case is about 2mas/y (relative to the LMC), large enough to be measurable with conventional techniques from the ground. The LMC origin could also be tested by a high-precision abundance analysis.Comment: 13 pages, 4 figures. Astrophysical Journal Letters, accepte

Impact of propofol on mid-latency auditory-evoked potentials in children†

Background Propofol is increasingly used in paediatric anaesthesia, but can be challenging to titrate accurately in this group. Mid-latency auditory-evoked potentials (MLAEPs) can be used to help titrate propofol. However, the effects of propofol on MLAEP in children are unclear. Therefore, we investigated the relationship between propofol and MLAEP in children undergoing anaesthesia. Methods Fourteen healthy children aged 4-16 yr received anaesthesia for elective surgery. Before surgery, propofol was administered in three concentrations (3, 6, 9 µg ml−1) through a target-controlled infusion pump using Kataria and colleagues' model. MLAEPs were recorded 5 min after having reached each target propofol concentration at each respective concentration. Additionally, venous propofol blood concentrations were assayed at each measuring time point. Results Propofol increased all four MLAEP peak latencies (peaks Na, Pa, Nb, P1) in a dose-dependent manner. In addition, the differences in amplitudes were significantly smaller with increasing propofol target concentrations. The measured propofol plasma concentrations correlated positively with the latencies of the peaks Na, Pa, and Nb. Conclusions Propofol affects MLAEP latencies and amplitudes in children in a dose-dependent manner. MLAEP measurement might therefore be a useful tool for monitoring depth of propofol anaesthesia in childre