Optical Interferometry of early-type stars with PAVO@CHARA. I. Fundamental stellar properties

We present interferometric observations of 7 main-sequence and 3 giant stars with spectral types from B2 to F6 using the PAVO beam combiner at the CHARA array. We have directly determined the angular diameters for these objects with an average precision of 2.3%. We have also computed bolometric fluxes using available photometry in the visible and infrared wavelengths, as well as space-based ultraviolet spectroscopy. Combined with precise \textit{Hipparcos} parallaxes, we have derived a set of fundamental stellar properties including linear radius, luminosity and effective temperature. Fitting the latter to computed isochrone models, we have inferred masses and ages of the stars. The effective temperatures obtained are in good agreement (at a 3% level) with nearly-independent temperature estimations from spectroscopy. They validate recent sixth-order polynomial (B-V)-$T_\mathrm{eff}$ empirical relations \citep{Boyajian2012a}, but suggest that a more conservative third-order solution \citep{vanBelle2009} could adequately describe the (V-K)-$T_\mathrm{eff}$ relation for main-sequence stars of spectral type A0 and later. Finally, we have compared mass values obtained combining surface gravity with inferred stellar radius (\textit{gravity mass}) and as a result of the comparison of computed luminosity and temperature values with stellar evolutionary models (\textit{isochrone mass}). The strong discrepancy between isochrone and gravity mass obtained for one of the observed stars, $\gamma$\,Lyr, suggests that determination of the stellar atmosphere parameters should be revised.Comment: 13 pages, 9 figures, accepted for publication in MNRA

Interferometric radii of bright Kepler stars with the CHARA Array: {\theta} Cygni and 16 Cygni A and B

We present the results of long-baseline optical interferometry observations using the Precision Astronomical Visual Observations (PAVO) beam combiner at the Center for High Angular Resolution Astronomy (CHARA) Array to measure the angular sizes of three bright Kepler stars: {\theta} Cygni, and both components of the binary system 16 Cygni. Supporting infrared observations were made with the Michigan Infrared Combiner (MIRC) and Classic beam combiner, also at the CHARA Array. We find limb-darkened angular diameters of 0.753+/-0.009 mas for {\theta} Cyg, 0.539+/-0.007 mas for 16 Cyg A and 0.490+/-0.006 mas for 16 Cyg B. The Kepler Mission has observed these stars with outstanding photometric precision, revealing the presence of solar-like oscillations. Due to the brightness of these stars the oscillations have exceptional signal-to-noise, allowing for detailed study through asteroseismology, and are well constrained by other observations. We have combined our interferometric diameters with Hipparcos parallaxes, spectrophotometric bolometric fluxes and the asteroseismic large frequency separation to measure linear radii ({\theta} Cyg: 1.48+/-0.02 Rsun, 16 Cyg A: 1.22+/-0.02 Rsun, 16 Cyg B: 1.12+/-0.02 Rsun), effective temperatures ({\theta} Cyg: 6749+/-44 K, 16 Cyg A: 5839+/-42 K, 16 Cyg B: 5809+/-39 K), and masses ({\theta} Cyg: 1.37+/-0.04 Msun, 16 Cyg A: 1.07+/-0.05 Msun, 16 Cyg B: 1.05+/-0.04 Msun) for each star with very little model dependence. The measurements presented here will provide strong constraints for future stellar modelling efforts.Comment: 9 pages, 4 figures, and 5 tables, accepted for publication in Monthly Notices of the Royal Astronomical Societ

Beam test calibration of the balloon-borne imaging calorimeter for the CREAM experiment

CREAM (Cosmic Ray Energetics And Mass) is a multi-flight balloon mission designed to collect direct data on the elemental composition and individual energy spectra of cosmic rays. Two instrument suites have been built to be flown alternately on a yearly base. The tungsten/Sci-Fi imaging calorimeter for the second flight, scheduled for December 2005, was calibrated with electron and proton beams at CERN. A calibration procedure based on the study of the longitudinal shower profile is described and preliminary results of the beam test are presented.Comment: 4 pages, 4 figures. To be published in the Proceedings of 29th International Cosmic Ray Conference (ICRC 2005), Pune, India, August 3-10, 200

Analisi scientifiche sulle tempere murali di Villa Pace

International audienceThe morphology, mineralogy, and solid-liquid phase separation of the Cu and Zn precipitates formed with sulfide produced in a sulfate-reducing bioreactor were studied at pH 3, 5, and 7. The precipitates formed at pH 7 display faster settling rates, better dewaterability, and higher concentrations of settleable solids as compared to the precipitates formed at pH 3 and 5. These differences were linked to the agglomeration of the sulfidic precipitates and coprecipitation of the phosphate added to the bioreactor influent. The Cu and Zn quenched the intensity of the dissolved organic matter peaks identified by fluorescence-excitation emission matrix spectroscopy, suggesting a binding mechanism that decreases supersaturation, especially at pH 5. X-ray absorption fine structure spectroscopy analyses confirmed the precipitation of Zn-S as sphalerite and Cu-S as covellite in all samples, but also revealed the presence of Zn sorbed on hydroxyapatite. These analyses further showed that CuS structures remained amorphous regardless of the pH, whereas the ZnS structure was more organized at pH 5 as compared to the ZnS formed at pH 3 and 7, in agreement with the cubic sphalerite-type structures observed through scanning electron microscopy at pH 5

Elemental energy spectra of cosmic rays measured by CREAM-II

We present new measurements of the energy spectra of cosmic-ray (CR) nuclei from the second flight of the balloon-borne experiment CREAM (Cosmic Ray Energetics And Mass). The instrument (CREAM-II) was comprised of detectors based on different techniques (Cherenkov light, specific ionization in scintillators and silicon sensors) to provide a redundant charge identification and a thin ionization calorimeter capable of measuring the energy of cosmic rays up to several hundreds of TeV. The data analysis is described and the individual energy spectra of C, O, Ne, Mg, Si and Fe are reported up to ~ 10^14 eV. The spectral shape looks nearly the same for all the primary elements and can be expressed as a power law in energy E^{-2.66+/-0.04}. The nitrogen absolute intensity in the energy range 100-800 GeV/n is also measured.Comment: 4 pages, 3 figures, presented at ICRC 2009, Lodz, Polan

Cosmic-Ray Proton and Helium Spectra from the First CREAM Flight

Cosmic-ray proton and helium spectra have been measured with the balloon-borne Cosmic Ray Energetics And Mass experiment flown for 42 days in Antarctica in the 2004-2005 austral summer season. High-energy cosmic-ray data were collected at an average altitude of ~38.5 km with an average atmospheric overburden of ~3.9 g cm$^{-2}$. Individual elements are clearly separated with a charge resolution of ~0.15 e (in charge units) and ~0.2 e for protons and helium nuclei, respectively. The measured spectra at the top of the atmosphere are represented by power laws with a spectral index of -2.66 $\pm$ 0.02 for protons from 2.5 TeV to 250 TeV and -2.58 $\pm$ 0.02 for helium nuclei from 630 GeV/nucleon to 63 TeV/nucleon. They are harder than previous measurements at a few tens of GeV/nucleon. The helium flux is higher than that expected from the extrapolation of the power law fitted to the lower-energy data. The relative abundance of protons to helium nuclei is 9.1 $\pm$ 0.5 for the range from 2.5 TeV/nucleon to 63 TeV/nucleon. This ratio is considerably smaller than the previous measurements at a few tens of GeV/nucleon.Comment: 20 pages, 4 figure

Measurements of cosmic-ray energy spectra with the 2nd CREAM flight

During its second Antarctic flight, the CREAM (Cosmic Ray Energetics And Mass) balloon experiment collected data for 28 days, measuring the charge and the energy of cosmic rays (CR) with a redundant system of particle identification and an imaging thin ionization calorimeter. Preliminary direct measurements of the absolute intensities of individual CR nuclei are reported in the elemental range from carbon to iron at very high energy.Comment: 4 pages, 3 figures, presented at XV International Symposium on Very High Energy Cosmic Ray Interactions (ISVHECRI 2008