Evidence of Gunn-Peterson damping wings in high-z quasar spectra: strengthening the case for incomplete reionization

The spectra of several high-redshift (z>6) quasars have shown evidence for a Gunn-Peterson (GP) damping wing, indicating a substantial mean neutral hydrogen fraction (x_HI > 0.03) in the z ~ 6 intergalactic medium (IGM). However, previous analyses assumed that the IGM was uniformly ionized outside of the quasar's HII region. Here we relax this assumption and model patchy reionization scenarios for a range of IGM and quasar parameters. We quantify the impact of these differences on the inferred x_HI, by fitting the spectra of three quasars: SDSS J1148+5251 (z=6.419), J1030+0524 (z=6.308), and J1623+3112 (z=6.247). We find that the best-fit values of x_HI in the patchy models agree well with the uniform case. More importantly, we confirm that the observed spectra favor the presence of a GP damping wing, with peak likelihoods decreasing by factors of > few - 10 when the spectra are modeled without a damping wing. We also find that the Ly alpha absorption spectra, by themselves, cannot distinguish the damping wing in a relatively neutral IGM from a damping wing in a highly ionized IGM, caused either by an isolated neutral patch, or by a damped Ly alpha absorber (DLA). However, neutral patches in a highly ionized universe (x_HI < 0.01), and DLAs with the large required column densities (N_HI > few x 10^{20} cm^{-2}) are both rare. As a result, when we include reasonable prior probabilities for the line of sight (LOS) to intercept either a neutral patch or a DLA at the required distance of ~ 40-60 comoving Mpc away from the quasar, we find strong lower limits on the neutral fraction in the IGM, x_HI > 0.1 (at 95% confidence). This strengthens earlier claims that a substantial global fraction of hydrogen in the z~6 IGM is in neutral form.Comment: 18 pages, 7 figures, version accepted for publication in the MNRA

On the possible existence of a self-regulating hydrodynamical process in slowly rotating stars II. Lithium Plateau in Halo Stars and Primordial Abundance

The lithium plateau observed in halo stars has long appeared as a paradox in the general context of the lithium abundance behavior in stellar outer layers. First, the plateau is flat, second, the lithium abundance dispersion is extremely small. This seems in contradiction with the large lithium variations observed in younger stars. It is also difficult to understand theoretically as lithium nuclei are easily destroyed by nuclear reactions, and subject to microscopic diffusion which, in the case of halo stars, should also lead to depletion. Several ideas have been proposed to account for the lithium behavior in halo stars. The most promising possibilities were rotational-induced mixing, which could reduce lithium in the same way for all the stars, and mass-loss, which could oppose the lithium settling. In both cases however, the parameters should be tightly adjusted to prevent any dispersion in the final results. Vauclair 1999 (paper I) pointed out that the mu-gradient terms which appear in the computations of the meridional circulation velocity were not introduced in previous computations of rotationally-induced mixing. This can lead to a self-regulating process which reduces the efficiency of the meridional circulation as well as the microscopic diffusion. Here we present numerical computations of this process and its influence on the lithium abundance variations in halo stars. We show that in slowly rotating stars, under some conditions, lithium can be depleted by a factor of up to two with a dispersion smaller than 0.1 dex in the middle part of the lithium plateau. We derive a primordial lithium abundance of 2.5 +/- 0.1, consistent with the recent determinations of D/H and 4He/H.Comment: 15 pages, 10 figures. to be published in A&

Self-assembled monolayers of polyoxovanadates with phthalocyaninato lanthanide moieties on gold surfaces

The two first representatives of phthalocyaninato (Pc) lanthanide-ligated polyoxovanadate cages {[V12O32(Cl)](LnPc)n}n-5 (n = 1 or 2, Ln = Yb3+) were synthesised and fully characterised. These magnetic complexes form two-dimensional self-assembled monolayers exhibiting electrical conductivity on gold substrate surfaces, as assessed by using an EGaIn tip

Very low metallicity massive star models: Pre-SN evolution and primary nitrogen production

Two series of models were computed. The first series consists of 20 solar mass models with varying initial metallicity (Z=0.02 down to Z=10^{-8}) and rotation (V_{ini}=0-600 km/s). The second one consists of models with an initial metallicity of Z=10^{-8}, masses between 9 and 85 solar masses and fast initial rotation velocities (V_{ini}=600-800 km/s). The most interesting models are the models with Z=10^{-8} ([Fe/H]~-6.6). In the course of helium burning, carbon and oxygen are mixed into the hydrogen burning shell. This boosts the importance of the shell and causes a reduction of the CO core mass. Later in the evolution, the hydrogen shell deepens and produces large amount of primary nitrogen. For the most massive models (M>~60 solar masses), significant mass loss occurs during the red supergiant stage. This mass loss is due to the surface enrichment in CNO elements via rotational and convective mixing. The 85 solar mass model ends up as a WO type Wolf-Rayet star. Therefore the models predict SNe of type Ic and possibly long and soft GRBs at very low metallicities. The rotating 20 solar mass models can best reproduce the observed CNO abundances at the surface of extremely metal poor (EMP) stars and the metallicity trends when their angular momentum content is the same as at solar metallicity (and therefore have an increasing surface velocity with decreasing metallicity). The wind of the massive star models can also reproduce the CNO abundances of the most metal-poor carbon-rich star known to date, HE1327-2326.Comment: A&A accepted, 18 pages, 13 figures WEBLINK: http://quasar.physik.unibas.ch/~hirschi/work/lowz.pd

Lithium enhancement in X-ray binaries due to stellar rotation

We discuss the high lithium abundances in the secondary stars of X-ray binaries. We show that no lithium production in these stars is necessary, and that the abundances can be explained simply due to the tidally locked rotation of the stars, which lead naturally to slower lithium destruction rates. The differences in abundances of CVs' secondaries from those of LMXBs had previously been put forth as evidence that the compact object was related to the lithium abundance, but this scenario also accounts for the lower lithium abundances in the secondary stars in cataclysmic variable systems (CVs) than in low mass X-ray binaries (LMXBs), since these stars have typically lived much longer before becoming tidally locked short period systems. We point out that if this scenario is correct, then the globular cluster X-ray binaries' donor stars should, as a class, show less lithium enhancement relative to other stars of the same spectral type in the clusters than the field X-ray binaries' donor stars show.Comment: 5 pages, accepted to A&A research note

Magneto-Thermohaline Mixing in Red Giants

We revise a magnetic buoyancy model that has recently been proposed as a mechanism for extra mixing in the radiative zones of low-mass red giants. The most important revision is our accounting of the heat exchange between rising magnetic flux rings and their surrounding medium. This increases the buoyant rising time by five orders of magnitude, therefore the number of magnetic flux rings participating in the mixing has to be increased correspondingly. On the other hand, our revised model takes advantage of the fact that the mean molecular weight of the rings formed in the vicinity of the hydrogen burning shell has been reduced by 3He burning. This increases their thermohaline buoyancy (hence, decreases the total ring number) considerably, making it equivalent to the pure magnetic buoyancy produced by a frozen-in toroidal field with B_phi ~ 10 MG. We emphasize that some toroidal field is still needed for the rings to remain cohesive while rising. Besides, this field prevents the horizontal turbulent diffusion from eroding the mu contrast between the rings and their surrounding medium. We propose that the necessary toroidal magnetic field is generated by differential rotation of the radiative zone, that stretches a pre-existing poloidal field around the rotation axis, and that magnetic flux rings are formed as a result of its buoyancy-related instability.Comment: 31 pages, 4 figures, 2 tables, accepted by ApJ after minor change

Exploring the Universe with Metal-Poor Stars

The early chemical evolution of the Galaxy and the Universe is vital to our understanding of a host of astrophysical phenomena. Since the most metal-poor Galactic stars (with metallicities down to [Fe/H]\sim-5.5) are relics from the high-redshift Universe, they probe the chemical and dynamical conditions of the Milky Way and the origin and evolution of the elements through nucleosynthesis. They also provide constraints on the nature of the first stars, their associated supernovae and initial mass function, and early star and galaxy formation. The Milky Way's dwarf satellites contain a large fraction (~30%) of the known most metal-poor stars that have chemical abundances that closely resemble those of equivalent halo stars. This suggests that chemical evolution may be universal, at least at early times, and that it is driven by massive, energetic SNe. Some of these surviving, ultra-faint systems may show the signature of just one such PopIII star; they may even be surviving first galaxies. Early analogs of the surviving dwarfs may thus have played an important role in the assembly of the old Galactic halo whose formation can now be studied with stellar chemistry. Following the cosmic evolution of small halos in simulations of structure formation enables tracing the cosmological origin of the most metal-poor stars in the halo and dwarf galaxies. Together with future observations and additional modeling, many of these issues, including the reionization history of the Milky Way, may be constrained this way. The chapter concludes with an outlook about upcoming observational challenges and ways forward is to use metal-poor stars to constrain theoretical studies.Comment: 34 pages, 11 figures. Book chapter to appear in "The First Galaxies - Theoretical Predictions and Observational Clues", 2012 by Springer, eds. V. Bromm, B. Mobasher, T. Wiklin

RADIAL VELOCITY MONITORING OFKEPLERHEARTBEAT STARS

Heartbeat stars (HB stars) are a class of eccentric binary stars with close periastron passages. The characteristic photometric HB signal evident in their light curves is produced by a combination of tidal distortion, heating, and Doppler boosting near orbital periastron. Many HB stars continue to oscillate after periastron and along the entire orbit, indicative of the tidal excitation of oscillation modes within one or both stars. These systems are among the most eccentric binaries known, and they constitute astrophysical laboratories for the study of tidal effects. We have undertaken a radial velocity (RV) monitoring campaign of Kepler HB stars in order to measure their orbits. We present our first results here, including a sample of 22 Kepler HB systems, where for 19 of them we obtained the Keplerian orbit and for 3 other systems we did not detect a statistically significant RV variability. Results presented here are based on 218 spectra obtained with the Keck/HIRES spectrograph during the 2015 Kepler observing season, and they have allowed us to obtain the largest sample of HB stars with orbits measured using a single instrument, which roughly doubles the number of HB stars with an RV measured orbit. The 19 systems measured here have orbital periods from 7 to 90 days and eccentricities from 0.2 to 0.9. We show that HB stars draw the upper envelope of the eccentricity–period distribution. Therefore, HB stars likely represent a population of stars currently undergoing high eccentricity migration via tidal orbital circularization, and they will allow for new tests of high eccentricity migration theories

Cosmological parameters from SDSS and WMAP

We measure cosmological parameters using the three-dimensional power spectrum P(k) from over 200,000 galaxies in the Sloan Digital Sky Survey (SDSS) in combination with WMAP and other data. Our results are consistent with a ``vanilla'' flat adiabatic Lambda-CDM model without tilt (n=1), running tilt, tensor modes or massive neutrinos. Adding SDSS information more than halves the WMAP-only error bars on some parameters, tightening 1 sigma constraints on the Hubble parameter from h~0.74+0.18-0.07 to h~0.70+0.04-0.03, on the matter density from Omega_m~0.25+/-0.10 to Omega_m~0.30+/-0.04 (1 sigma) and on neutrino masses from <11 eV to <0.6 eV (95%). SDSS helps even more when dropping prior assumptions about curvature, neutrinos, tensor modes and the equation of state. Our results are in substantial agreement with the joint analysis of WMAP and the 2dF Galaxy Redshift Survey, which is an impressive consistency check with independent redshift survey data and analysis techniques. In this paper, we place particular emphasis on clarifying the physical origin of the constraints, i.e., what we do and do not know when using different data sets and prior assumptions. For instance, dropping the assumption that space is perfectly flat, the WMAP-only constraint on the measured age of the Universe tightens from t0~16.3+2.3-1.8 Gyr to t0~14.1+1.0-0.9 Gyr by adding SDSS and SN Ia data. Including tensors, running tilt, neutrino mass and equation of state in the list of free parameters, many constraints are still quite weak, but future cosmological measurements from SDSS and other sources should allow these to be substantially tightened.Comment: Minor revisions to match accepted PRD version. SDSS data and ppt figures available at http://www.hep.upenn.edu/~max/sdsspars.htm

Oral pre-exposure prophylaxis uptake, adherence, and adverse events among South African men who have sex with men and transgender women

DATA AVAILABILITY : Data that support the findings may contain identifying or sensitive patient information. To preserve participant confidentiality, these data cannot be shared publicly. The principal investigator of this study, P.S.S. (pssulli@emory. edu), can be contacted with requests to access these data.BACKGROUND : HIV prevention programmes that include pre-exposure prophylaxis (PrEP) for men who have sex with men (MSM) and transgender women (TGW) in South Africa have not been widely implemented. OBJECTIVES : The authors examined oral PrEP uptake, adherence, and adverse events among HIV-uninfected MSM and TGW to inform intervention acceptability and feasibility. METHOD : In 2015, MSM and TGW in two South African cities were offered a comprehensive package of HIV prevention services, including daily oral PrEP, and were followed for one year. Different models of PrEP delivery were used at each site. Adherence was measured using self-report and pill-count data and tenofovir-diphosphate (TFV-DP) concentrations. RESULTS : Among 135 participants who were eligible for PrEP, 82 (61%) initiated PrEP, of whom 67 (82%) were on PrEP at study end. Participants were on PrEP for a median of 294 out of 314.5 possible days (93% protected days). The median time from PrEP initiation to discontinuation or study end was 305 days (interquartile range: 232–325 days). Across the follow-up time points, 57% – 72% of participants self-reported taking protective levels of PrEP and 59% – 74% were adherent to PrEP as indicated by pill counts. Fewer (≤ 18%) achieved protective TFV-DP concentrations of ≥ 700 fmol/punch in dried blood spots. Side effects, while typically mild, were the most commonly cited reason by participants for early PrEP discontinuation. CONCLUSION : Many MSM and TGW initiated and maintained PrEP, demonstrating that PrEP can be successfully delivered to South African MSM and TGW in diverse programmatic contexts. Biologic adherence measures suggest MSM and TGW may experience challenges taking PrEP regularly. Counselling for coping with side effects and motivating daily pill taking is recommended to support South African MSM and TGW in achieving protection with PrEP.The Center for AIDS Research at Emory University and the National Institute for Allergy and Infectious Diseases.http://www.sajhivmed.org.zaam2023School of Health Systems and Public Health (SHSPH