The Quasar-frame Velocity Distribution of Narrow CIV Absorbers

We report on a survey for narrow (FWHM < 600 km/s) CIV absorption lines in a sample of bright quasars at redshifts $1.8 \le z < 2.25$ in the Sloan Digital Sky Survey. Our main goal is to understand the relationship of narrow CIV absorbers to quasar outflows and, more generally, to quasar environments. We determine velocity zero-points using the broad MgII emission line, and then measure the absorbers' quasar-frame velocity distribution. We examine the distribution of lines arising in quasar outflows by subtracting model fits to the contributions from cosmologically intervening absorbers and absorption due to the quasar host galaxy or cluster environment. We find a substantial number ($\ge 43\pm6$ per cent) of absorbers with REW $> 0.3$ \AA in the velocity range +750 km/s \la v \la +12000 km/s are intrinsic to the AGN outflow. This `outflow fraction' peaks near $v=+2000$ km/s with a value of $f_{outflow} \simeq 0.81 \pm 0.13$. At velocities below $v \approx +2000$ km/s the incidence of outflowing systems drops, possibly due to geometric effects or to the over-ionization of gas that is nearer the accretion disk. Furthermore, we find that outflow-absorbers are on average broader and stronger than cosmologically-intervening systems. Finally, we find that $\sim 14$ per cent of the quasars in our sample exhibit narrow, outflowing CIV absorption with REW $> 0.3$\AA, slightly larger than that for broad absorption line systems.Comment: 11 pages, 9 figures, accepted for publication in MNRA

Comparison of Global and Local Adaptive Coordinates for Density Functional Calculations

A globally-adaptive curvilinear coordinate formalism is shown to be easily convertible to a class of curvilinear transformations locally optimized around atom sites by a few parameters. Parameter transferability is established for a demanding test case, and the results of the two methods are shown to be comparable. Computational efficiencies realized in the local method are discussed.Comment: 21 pages, 4 figure

Combined cerebellar and bilateral cervical posterior spinal artery stroke demonstrated on MRI

Combined cerebellar and spinal ischemic stroke is a rare, critical condition. We report a patient with combined cerebellar and bilateral posterolateral cervical spinal cord infarction due to bilateral stenosis of the vertebral arteries. MRI is the method of choice for imaging this condition; diffusion-weighted imaging of the spinal cord gives reliable results

Probing the BLR in AGNs using time variability of associated absorption line

It is know that most of the clouds producing associated absorption in the spectra of AGNs and quasars do not completely cover the background source (continuum + broad emission line region, BLR). We note that the covering factor derived for the absorption is the fraction of photons occulted by the absorbing clouds, and is not necessarily the same as the fractional area covered. We show that the variability in absorption lines can be produced by the changes in the covering factor caused by the variation in the continuum and the finite light travel time across the BLR. We discuss how such a variability can be distinguished from the variability caused by other effects and how one can use the variability in the covering factor to probe the BLR.Comment: 12 pages, latex(aaspp4.sty), 2 figures, (To appear in ApJ

The Metallicity of the Redshift 4.16 Quasar BR2248-1242

We estimate the metallicity in the broad emission-line region of the redshift z=4.16 quasar, BR2248-1242, by comparing line ratios involving nitrogen to theoretical predictions. BR2248-1242 has unusually narrow emission lines with large equivalent widths, thus providing a rare opportunity to measure several line-ratio abundance diagnostics. The combined diagnostics indicate a metallicity of ~2 times solar. This result suggests that an episode of vigorous star formation occurred near BR2248-1242 prior to the observed z=4.16 epoch. The time available for this enrichment episode is only ~1.5 Gyr at z=4.16 (for H_{0}=65 km s^-1 Mpc^-1, Omega_{m}=0.3 and Omega_Lambda ~< 1). This evidence for high metallicities and rapid star formation is consistent with the expected early-epoch evolution of dense galactic nuclei.Comment: 8 pages, 3 figures. Prepared in AAStex. Submitted to the Astrophysical Journal Revised version: added 1 referenc

Spectroscopy of SMC Wolf-Rayet Stars Suggests that Wind-Clumping does not Depend on Ambient Metallicity

The mass-loss rates of hot, massive, luminous stars are considered a decisive parameter in shaping the evolutionary tracks of such stars and influencing the interstellar medium on galactic scales. The small-scale structures (clumps) omnipresent in such winds may reduce empirical estimates of mass-loss rates by an evolutionarily significant factor of >=3. So far, there has been no direct observational evidence that wind-clumping may persist at the same level in environments with a low ambient metallicity, where the wind-driving opacity is reduced. Here we report the results of time-resolved spectroscopy of three presumably single Population I Wolf-Rayet stars in the Small Magellanic Cloud, where the ambient metallicity is ~1/5 Z_Sun.We detect numerous small-scale emission peaks moving outwards in the accelerating parts of the stellar winds.The general properties of the moving features, such as their velocity dispersions,emissivities and average accelerations, closely match the corresponding characteristics of small-scale inhomogeneities in the winds of Galactic Wolf-Rayet stars.Comment: 9 pages, 3 figures; accepted by ApJ Letter

Using BBN in cosmological parameter extraction from CMB: a forecast for Planck

Data from future high-precision Cosmic Microwave Background (CMB) measurements will be sensitive to the primordial Helium abundance $Y_p$. At the same time, this parameter can be predicted from Big Bang Nucleosynthesis (BBN) as a function of the baryon and radiation densities, as well as a neutrino chemical potential. We suggest to use this information to impose a self-consistent BBN prior on $Y_p$ and determine its impact on parameter inference from simulated Planck data. We find that this approach can significantly improve bounds on cosmological parameters compared to an analysis which treats $Y_p$ as a free parameter, if the neutrino chemical potential is taken to vanish. We demonstrate that fixing the Helium fraction to an arbitrary value can seriously bias parameter estimates. Under the assumption of degenerate BBN (i.e., letting the neutrino chemical potential $\xi$ vary), the BBN prior's constraining power is somewhat weakened, but nevertheless allows us to constrain $\xi$ with an accuracy that rivals bounds inferred from present data on light element abundances.Comment: 14 pages, 4 figures; v2: minor changes, matches published versio