Examinando por Autor "Gieren, W."
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Ítem Discovery of a pair of classical cepheids in an invisible cluster beyond the galactic bulge(Institute of Physics Publishing, 2015-01) Dékány, I.; Minniti, D.; Alonso-García, J.; Hempel, M.; Palma, T.; Catelan, M.; Gieren, W.; Majaess, D.We report the discovery of a pair of extremely reddened classical Cepheid variable stars located in the Galacticplane behind the bulge, using near-infrared (NIR) time-series photometry from the VISTA Variables in the VaLáctea Survey. This is the first time that such objects have ever been found in the opposite side of the Galacticplane. The Cepheids have almost identical periods, apparent brightnesses, and colors. From the NIR Leavitt law,we determine their distances with ∼1.5% precision and ∼8% accuracy. We find that they have a same totalextinction of A(V) ? 32 mag, and are located at the same heliocentric distance of ádn = 11.4 ± 0.9 kpc, and lessthan 1 pc from the true Galactic plane. Their similar periods indicate that the Cepheids are also coeval, with an ageof ∼48 ± 3Myr, according to theoretical models. They are separated by an angular distance of only 18?.3,corresponding to a projected separation of ∼1 pc. Their position coincides with the expected location of the Far 3kpc Arm behind the bulge. Such a tight pair of similar classical Cepheids indicates the presence of an underlyingyoung open cluster that is both hidden behind heavy extinction and disguised by the dense stellar field of the bulge.All our attempts to directly detect this invisible cluster have failed, and deeper observations are needed.Ítem THE ARAUCARIA PROJECT: A STUDY OF THE CLASSICAL CEPHEID IN THE ECLIPSING BINARY SYSTEM OGLE LMC562.05.9009 IN THE LARGE MAGELLANIC CLOUD(IOP PUBLISHING, 2015-12) Gieren, W.; Pilecki, B.; Pietrzyński, G.; Graczyk, D.; Udalski, A.; Soszyński, I.; Thompson, I.B.; Moroni, P.G.P.; Smolec, R.; Konorski, P.; Górski, M.; Karczmarek, P.; Suchomska, K.; Taormina, M.; Gallenne, A.; Storm, J.; Bono, G.; Catelan, M.; Szymański, M.; Kozłowski, S.; Pietrukowicz, P.; Wyrzykowski, Ł.; Poleski, R.; Skowron, J.; Minniti, D.; Ulaczyk, K.; Mróz, P.; Pawlak, M.; Nardetto, N.We present a detailed study of the classical Cepheid in the double-lined, highly eccentric eclipsing binary system OGLE-LMC562.05.9009. The Cepheid is a fundamental mode pulsator with a period of 2.988 days. The orbital period of the system is 1550 days. Using spectroscopic data from three 4-8-m telescopes and photometry spanning 22 years, we were able to derive the dynamical masses and radii of both stars with exquisite accuracy. Both stars in the system are very similar in mass, radius, and color, but the companion is a stable, non-pulsating star. The Cepheid is slightly more massive and bigger (M-1 = 3.70 +/- 0.03 Me-circle dot R-1 = 28.6 +/- 0.2 R-circle dot) than its companion (M-2 = 3.60. +/- 0.03 M-circle dot, R-2 = 26.6 +/- 0.2 R-circle dot). Within the observational uncertainties both stars have the same effective temperature of 6030 +/- 150 K. Evolutionary tracks place both stars inside the classical Cepheid instability strip, but it is likely that future improved temperature estimates will move the stable giant companion just beyond the red edge of the instability strip. Within current observational and theoretical uncertainties, both stars fit on a 205 Myr isochrone arguing for their common age. From our model, we determine a value of the projection factor of p = 1.37 +/- 0.07 for the Cepheid in the OGLE-LMC562.05.9009 system. This is the second Cepheid for which we could measure its p-factor with high precision directly from the analysis of an eclipsing binary system, which represents an important contribution toward a better calibration of Baade-Wesselink methods of distance determination for Cepheids.Ítem THE VVV SURVEY REVEALS CLASSICAL CEPHEIDS TRACING A YOUNG and THIN STELLAR DISK ACROSS the GALAXY'S BULGE(Institute of Physics Publishing, 2015-10) Dékány, I.; Minniti, D.; Majaess, D.; Zoccali, M.; Hajdu, G.; Alonso-García, J.; Catelan, M.; Gieren, W.; Borissova, J.Solid insight into the physics of the inner Milky Way is key to understanding our Galaxy's evolution, but extreme dust obscuration has historically hindered efforts to map the area along the Galactic mid-plane. New comprehensive near-infrared time-series photometry from the VVV Survey has revealed 35 classical Cepheids, tracing a previously unobserved component of the inner Galaxy, namely a ubiquitous inner thin disk of young stars along the Galactic mid-plane, traversing across the bulge. The discovered period (age) spread of these classical Cepheids implies a continuous supply of newly formed stars in the central region of the Galaxy over the last 100 million years. © 2015. The American Astronomical Society. All rights reserved.Ítem Using classical cepheids to study the far side of the Milky Way disk(EDP Sciences, 2020-08) Minniti, J.H.; Sbordone, L.; Rojas-Arriagada, A.; Zoccali, M.; Contreras Ramos, R.; Minniti, D.; Marconi, M.; Braga, V.F.; Catelan, M.; Duffau, S.; Gieren, W.; Valcarce, A.A.R.Context. Much of what we know about the Milky Way disk is based on studies of the solar vicinity. The structure, kinematics, and chemical composition of the far side of the Galactic disk, beyond the bulge, are still to be revealed. Aims. Classical Cepheids (CCs) are young and luminous standard candles. We aim to use a well-characterized sample of these variable stars to study the present-time properties of the far side of the Galactic disk. Methods. A sample of 45 Cepheid variable star candidates were selected from near-infrared time series photometry obtained by the VVV survey. We characterized this sample using high quality near-infrared spectra obtained with VLT/X-shooter. The spectroscopic data was used to derive radial velocities and iron abundances for all the sample Cepheids. This allowed us to separate the CCs, which are metal rich and with kinematics consistent with the disk rotation, from type II Cepheids (T2Cs), which are more metal poor and with different kinematics. Results. We estimated individual distances and extinctions using VVV photometry and period-luminosity relations, reporting the characterization of 30 CCs located on the far side of the Galactic disk, plus 8 T2Cs mainly located in the bulge region, of which 10 CCs and 4 T2Cs are new discoveries. The remaining seven stars are probably misclassified foreground ellipsoidal binaries. This is the first sizeable sample of CCs in this distant region of our Galaxy that has been spectroscopically confirmed. We use their positions, kinematics, and metallicities to confirm that the general properties of the far disk are similar to those of the well-studied disk on the solar side of the Galaxy. In addition, we derive for the first time the radial metallicity gradient on the disk’s far side. Considering all the CCs with RGC < 17 kpc, we measure a gradient with a slope of −0.062 dex kpc−1 and an intercept of +0.59 dex, which is in agreement with previous determinations based on CCs on the near side of the disk.