Examinando por Autor "Pietrzyński, Grzegorz"

Mostrando 1 - 2 de 2
  • No hay miniatura disponible
    Ítem
    Interstellar extinction curve variations towards the inner Milky Way: A challenge to observational cosmology
    (Oxford University Press, 2016-03) Nataf, David M.; Gonzalez, Oscar A.; Casagrande, Luca; Zasowski, Gail; Wegg, Christopher; Wolf, Christian; Kunder, Andrea; Alonso-Garcia, Javier; Minniti, Dante; Rejkuba, Marina; Saito, Roberto K.; Valenti, Elena; Zoccali, Manuela; Poleski, Radosław; Pietrzyński, Grzegorz; Skowron, Jan; Soszyński, Igor; Szymański, Michał K.; Udalski, Andrzej; Ulaczyk, Krzyszto; Wyrzykowski, Łukasz
    We investigate interstellar extinction curve variations towards ∼4 deg2 of the inner Milky Way in VIJKs photometry from the OGLE-III (third phase of the Optical Gravitational Lensing Experiment) and VVV (VISTA Variables in the Via Lactea) surveys, with supporting evidence from diffuse interstellar bands and F435W, F625W photometry. We obtain independent mea surements towards ∼2000 sightlines of AI, E(V − I), E(I − J) and E(J − Ks), with median precision and accuracy of 2 per cent. We find that the variations in the extinction ratios AI/E(V − I), E(I − J)/E(V − I) and E(J − Ks)/E(V − I) are large (exceeding 20 per cent), signifi cant and positively correlated, as expected. However, both the mean values and the trends in these extinction ratios are drastically shifted from the predictions of Cardelli and Fitzpatrick, regardless of how RV is varied. Furthermore, we demonstrate that variations in the shape of the extinction curve have at least two degrees of freedom, and not one (e.g. RV), which we confirm with a principal component analysis. We derive a median value of AV/AKs = 13.44, which is ∼60 per cent higher than the ‘standard’ value. We show that the Wesenheit magnitude WI = I − 1.61(I − J) is relatively impervious to extinction curve variations. Given that these extinction curves are linchpins of observational cosmology, and that it is generally assumed that RV variations correctly capture variations in the extinction curve, we argue that systematic errors in the distance ladder from studies of Type Ia supernovae and Cepheids may have been underestimated. Moreover, the reddening maps from the Planck experiment are shown to systematically overestimate dust extinction by ∼100 per cent and lack sensitivity to extinction curve variations.
  • No hay miniatura disponible
    Ítem
    THE ARAUCARIA PROJECT: The FIRST-OVERTONE CLASSICAL CEPHEID in the ECLIPSING SYSTEM OGLE-LMC-CEP-2532
    (Institute of Physics Publishing, 2015-06) Pilecki, Bogumił; Graczyk, Dariusz; Gieren, Wolfgang; Pietrzyński, Grzegorz; Thompson, Ian B.; Smolec, Radosław; Udalski, Andrzej; Soszyński, Igor; Konorski, Piotr; Taormina, Mónica; Gallenne, Alexandre; Minniti, Dante
    We present here the first spectroscopic and photometric analysis of the double-lined eclipsing binary containing the classical, first-overtone (FO) Cepheid OGLE-LMC-CEP-2532 (MACHO 81.8997.87). The system has an orbital period of 800 days and the Cepheid is pulsating with a period of 2.035 days. Using spectroscopic data from three high-class telescopes and photometry from three surveys spanning 7500 days, we are able to derive the dynamical masses for both stars with an accuracy better than 3%. This makes the Cepheid in this system one of a few lassical Cepheids with an accurate dynamical mass determination (M1 = 3.90 +:0.10 MM). The companion is probably slightly less massive (3.82 ±0.10 MM ), but may have the same mass within errors (M2 M1 = 0.981 ±0.015). The system has an age of about 185 million years and the Cepheid is in a more advanced evolutionary stage. For the first time precise parameters are derived for both stars in this system. Due to the lack of the secondary eclipse for many years, not much was known about the Cepheids companion. In our analysis, we used extra information from the pulsations and the orbital solution from the radial velocity curve. The best model predicts a grazing secondary eclipse shallower than 1 mmag, hence undetectable in the data, about 370 days after the primary eclipse. The dynamical mass obtained here is the most accurate known for a FO Cepheid and will contribute to the solution of the Cepheid mass discrepancy problem. © 2015. The American Astronomical Society. All rights reserved.