Examinando por Autor "Gieren, Wolfgang"

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    The Araucaria Project. First Cepheid Distance to the Sculptor Group Galaxy NGC 7793 from Variables discovered in a Wide-Field Imaging Survey
    (2010) Pietrzynski, Grzegorz; Gieren, Wolfgang; Hamuy, Mario; Pignata, Giuliano; Soszynski, Igor; Udalski, Andrzej; Walker, Alistair; Fouque, Pascal; Bresolin, Fabio; Kudritzki, Rolf-Peter
    We have detected, for the first time, Cepheid variables in the Sculptor Group spiral galaxy NGC 7793. From wide-field images obtained in the optical V and I bands on 56 nights in 2003-2005, we have discovered 17 long-period (24-62 days) Cepheids whose periods and mean magnitudes define tight period-luminosity relations. We use the (V-I) Wesenheit index to determine a reddening-free true distance modulus to NGC 7793 of 27.68 ± 0.05 mag (internal error) ± 0.08 mag (systematic error). The comparison of the reddened distance moduli in V and I with the one derived from the Wesenheit magnitude indicates that the Cepheids in NGC 7793 are affected by an average total reddening of E(B-V)=0.08 mag, 0.06 of which is produced inside the host galaxy. As in the earlier Cepheid studies of the Araucaria Project, the reported distance is tied to an assumed LMC distance modulus of 18.50. The quoted systematic uncertainty takes into account effects like blending and possible inhomogeneous filling of the Cepheid instability strip on the derived distance. The reported distance value does not depend on the (unknown) metallicity of the Cepheids according to recent theoretical and empirical results. Our Cepheid distance is shorter, but within the errors consistent with the distance to NGC 7793 determined earlier with the TRGB and Tully-Fisher methods.The NGC 7793 distance of 3.4 Mpc is almost identical to the one our project had found from Cepheid variables for NGC 247, another spiral member of the Sculptor Group located close to NGC 7793 on the sky. Two other conspicuous spiral galaxies in the Sculptor Group, NGC 55 and NGC 300, are much nearer (1.9 Mpc), confirming the picture of a very elongated structure of the Sculptor Group in the line of sight put forward by Jerjen et al. and others.
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    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.
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    The Orbit and Mass of the Cepheid AW Per
    (Institute of Physics, 2024-09) Evans, Nancy Remage; Gallenne, Alexandre; Kervella, Pierre; Mérand, Antoine; Monnier, John; Anderson, Richard I; Günther, H. Moritz; Proffitt, Charles; Winston, Elaine M.; Pietrzynski, Grzegorz; Gieren, Wolfgang; Kuraszkiewicz, Joanna; Anugu, Narsireddy; Roettenbacher, Rachael M.; Lanthermann, Cyprien; Gutierrez, Mayra; Schaefer, Gail; Setterholm, Benjamin R.; Ibrahim, Noura; Kraus, Stefan
    The Cepheid AW Per is a component in a multiple system with a long-period orbit. The radial velocities of Griffin cover the 38 yr orbit well. An extensive program of interferometry with the Center for High Angular Resolution Astronomy array is reported here, from which the long-period orbit is determined. In addition, a Hubble Space Telescope high-resolution spectrum in the ultraviolet demonstrates that the companion is itself a binary with nearly equal-mass components. These data combined with a distance from Gaia provide a mass of the Cepheid (primary) of M 1 = 6.79 ± 0.85 M ⊙. The combined mass of the secondary is M S = 8.79 ± 0.50 M ⊙. The accuracy of the mass will be improved after the fourth Gaia data release, expected in approximately two years.