Calibration of the CH and CN Variations Among Main Sequence Stars in M71 and in M13

An analysis of the CN and CH band strengths measured in a large sample of M71 and M13 main sequence stars by Cohen (1999a,b) is undertaken using synthetic spectra to quantify the underlying C and N abundances. In the case of M71 it is found that the observed CN and CH band strengths are best matched by the {\it{identical}} C/N/O abundances which fit the bright giants, implying: 1) little if any mixing is taking place during red giant branch ascent in M71, and 2) a substantial component of the C and N abundance inhomogeneities is in place before the main sequence turn-off. The unlikelihood of mixing while on the main sequence requires an explanation for the abundance variations which lies outside the present stars (primordial inhomogeneities or intra-cluster self enrichment). For M13 it is shown that the 3883\AA CN bands are too weak to be measured in the spectra for any reasonable set of expected compositions. A similar situation exists for CH as well. However, two of the more luminous program stars do appear to have C abundances considerably greater than those found among the bright giants thereby suggesting deep mixing has taken place on the M13 red giant branch.Comment: 14 pages, 4 figures, accepted for publication by A

Szego coordinates, quadrature domains, and double quadrature domains

We define Szego coordinates on a finitely connected smoothly bounded planar domain which effect a holomorphic change of coordinates on the domain that can be as close to the identity as desired and which convert the domain to a quadrature domain with respect to boundary arc length. When these Szego coordinates coincide with Bergman coordinates, the result is a double quadrature domain with respect to both area and arc length. We enumerate a host of interesting and useful properties that such double quadrature domains possess, and we show that such domains are in fact dense in the realm of bounded finitely connected domains with smooth boundaries.Comment: 19 page

Neutron electric form factor at large momentum transfer

Based on the recent, high precision data for elastic electron scattering from protons and deuterons, at relatively large momentum transfer $Q^2$, we determine the neutron electric form factor up to $Q^2=3.5$ GeV$^2$. The values obtained from the data (in the framework of the nonrelativistic impulse approximation) are larger than commonly assumed and are in good agreement with the Gari-Kr\"umpelmann parametrization of the nucleon electromagnetic form factors.Comment: 11 pages 2 figure

C and N Abundances in Stars At the Base of the Red Giant Branch in M5

We present an analysis of a large sample of moderate resolution Keck LRIS spectra of subgiant (V \sim 17.2) and fainter stars in the Galactic globular cluster M5 (NGC 5904) with the goal of deriving C and N abundances. Star-to-star stochastic variations with significant range in both [C/Fe] and [N/Fe] are found at all luminosities extending to the bottom of the RGB at M_V \sim +3. Similar variations in CH appear to be present in the main sequence turnoff spectra. There is no sign of a change in the behavior of C and N with evolutionary stage over the full range in luminosity of the RGB and SGB. The C and N abundances appear strongly anti-correlated, as would be expected from the CN-cycle processing of stellar material. Yet the present stars are considerably fainter than the RGB bump, the point at which deep mixing is believed to set in. On this basis, while the observed abundance pattern is consistent with proton capture nucleosynthesis, we infer that the site of the reactions is likely not within the present sample, but rather in a population of more massive (2 -- 5 M(Sun)) now defunct stars. The range of variation of the N abundances is very large and the sum of C+N increases as C decreases. To reproduce this requires the incorporation not only of CN but also of ON-processed material. Furthermore, the existence of this correlation is quite difficult to reproduce with an external mechanism such as ``pollution'' with material processed in a more massive AGB star, which mechanism is fundamentally stochastic in nature. We therefore suggest that although the internal mixing hypothesis has serious flaws,new theoretical insights are needed and it should not be ruled out yet. (abridged)Comment: Slightly updated version to conform to that accepted by the A

Tracing the Galactic thick disk to Solar metallicities

We show that the Galactic thick disk reaches at least solar metallicities, and that it experienced strong chemical enrichment during a period of ~3 Gyr, ending around 8-9 Gyr ago. This finding puts further constraints on the relation and interface between the thin and thick disks, and their formation processes. Our results are based on a detailed elemental abundance analysis of 261 kinematically selected F and G dwarf stars in the solar neighborhood: 194 likely members of the thick disk and 67 likely members of the thin disk, in the range -1.3<[Fe/H]<+0.4.Comment: Accepted for publication in ApJ Letter

High energy inelastic electron hadron scattering, in peripheral kinematics. Sum rules for hadron form factors

Relations between differential cross section for inelastic scattering of electrons on hadrons and hadron form factors (sum rules) are derived on the basis of analytical properties of heavy photon forward Compton scattering on hadrons. Sum rules relating the slope of form-factors at zero momentum transfer and anomalous magnetic moments of hadrons with some integrals on photo-production on a hadrons is obtained as well. To provide the convergence of these integrals we construct differences of individual sum rules for different hadrons. Universal interaction of Pomeron with nucleons is assumed. We derive the explicit formulae for processes of electro-production on proton and light isobar nuclei. Sudakov's parametrization of momenta, for peripheral kinematics relevant here, is used. The light-cone form of differential cross sections is also discussed. The accuracy of sum rules estimated in frames of point-like hadrons and it is shown to be at the level of precision achievable by experiments. Suggestions and predictions for future experiments are also given.Comment: 18 pages, 5 figure

New Abundances for Old Stars - Atomic Diffusion at Work in NGC 6397

A homogeneous spectroscopic analysis of unevolved and evolved stars in the metal-poor globular cluster NGC 6397 with FLAMES-UVES reveals systematic trends of stellar surface abundances that are likely caused by atomic diffusion. This finding helps to understand, among other issues, why the lithium abundances of old halo stars are significantly lower than the abundance found to be produced shortly after the Big Bang.Comment: 8 pages, 7 colour figures, 1 table; can also be downloaded via http://www.eso.org/messenger

On the Use of Blanketed Atmospheres as Boundary Conditions for Stellar Evolutionary Models

Stellar models have been computed for stars having [Fe/H] = 0.0 and -2.0 to determine the effects of using boundary conditions derived from the latest MARCS model atmospheres. The latter were fitted to the interior models at both the photosphere and at tau = 100, and at least for the 0.8-1.0 solar mass stars considered here, the resultant evolutionary tracks were found to be nearly independent of the chosen fitting point. Particular care was taken to treat the entire star as consistently as possible; i.e., both the interior and atmosphere codes assumed the same abundances and the same treatment of convection. Tracks were also computed using either the classical gray T(tau,T_eff) relation or that derived by Krishna Swamy (1966) to derive the boundary pressure. The latter predict warmer giant branches (by ~150 K) at solar abundances than those based on gray or MARCS atmospheres, which happens to be in good agreement with the inferred temperatures of giants in the open cluster M67 from the latest (V-K)-T_eff relations. Most of the calculations assumed Z=0.0125 (Asplund et al.), though a few models were computed for Z=0.0165 (Grevesse & Sauval) to determine the dependence of the tracks on Z_\odot. Grids of "scaled solar, differentially corrected" (SDC) atmospheres were also computed to try to improve upon theoretical MARCS models. When they were used as boundary conditions, the resultant tracks agreed very well with those based on a standard scaled-solar (e.g., Krishna Swamy) T(tau,T_eff) relation, independently of the assumed metal abundance. Fits of isochrones to the C-M diagram of the [Fe/H] = -2 globular cluster M68 were examined, as was the possibility that the mixing-length parameter varies with stellar parameters.Comment: 54 pages, including 20 figures and 3 tables; accepted (July 2007) for publication in the Astrophysical Journa

Mira's wind explored in scattering infrared CO lines

We have observed the intermediate regions of the circumstellar envelope of Mira (o Ceti) in photospheric light scattered by three vibration-rotation transitions of the fundamental band of CO, from low-excited rotational levels of the ground vibrational state, at an angular distance of beta = 2"-7" away from the star. The data were obtained with the Phoenix spectrometer mounted on the 4 m Mayall telescope at Kitt Peak. The spatial resolution is approximately 0.5" and seeing limited. Our observations provide absolute fluxes, leading to an independent new estimate of the mass-loss rate of approximately 3e-7 Msun/yr, as derived from a simple analytic wind model. We find that the scattered intensity from the wind of Mira for 2" < beta < 7" decreases as beta^-3, which suggests a time constant mass-loss rate, when averaged over 100 years, over the past 1200 years.Comment: accepted for publication in the Astrophysical Journa

New ATLAS9 And MARCS Model Atmosphere Grids for the Apache Point Observatory Galactic Evolution Experiment (APOGEE)

We present a new grid of model photospheres for the SDSS-III/APOGEE survey of stellar populations of the Galaxy, calculated using the ATLAS9 and MARCS codes. New opacity distribution functions were generated to calculate ATLAS9 model photospheres. MARCS models were calculated based on opacity sampling techniques. The metallicity ([M/H]) spans from -5 to 1.5 for ATLAS and -2.5 to 0.5 for MARCS models. There are three main differences with respect to previous ATLAS9 model grids: a new corrected H2O linelist, a wide range of carbon ([C/M]) and alpha element [alpha/M] variations, and solar reference abundances from Asplund et al. 2005. The added range of varying carbon and alpha element abundances also extends the previously calculated MARCS model grids. Altogether 1980 chemical compositions were used for the ATLAS9 grid, and 175 for the MARCS grid. Over 808 thousand ATLAS9 models were computed spanning temperatures from 3500K to 30000K and log g from 0 to 5, where larger temperatures only have high gravities. The MARCS models span from 3500K to 5500K, and log g from 0 to 5. All model atmospheres are publically available online.Comment: 8 pages, 6 figures, 5 tables, accepted for publication in The Astronomical Journa