56 research outputs found
Absolute dimensions of eclipsing binaries. XXVI, Setting a new standard : masses, radii, and abundances for the F-type systems ADâBootis, VZâHydrae, and WZâOphiuchi
Context. Accurate mass, radius, and abundance determinations from binaries provide important information on stellar evolution, fundamental to central fields in modern astrophysics and cosmology.
Aims. We aim to determine absolute dimensions and abundances for the three F-type main-sequence detached eclipsing binaries ADBoo, VZHya, and WZOph and to perform a detailed comparison with results from recent stellar evolutionary models.
Methods. uvby light curves and uvbyÎČ standard photometry were obtained with the Strömgren Automatic Telescope at ESO, La Silla, radial velocity observations at CfA facilities, and supplementary high-resolution spectra with ESOâs FEROS spectrograph. State-ofthe-art methods were applied for the analyses: the EBOP andWilson-Devinney binary models, two-dimensional cross-correlation and
disentangling, and the VWA abundance analysis tool.
Results. Masses and radii that are precise to 0.5â0.7% and 0.4â0.9%, respectively, have been established for the components, which span the ranges of 1.1 to 1.4 M and 1.1 to 1.6 R. The [Fe/H] abundances are from â0.27 to +0.10, with uncertainties between 0.07 and 0.15 dex. We find indications of a slight α-element overabundance of [α/Fe] ⌠+0.1 for WZOph. The secondary component of ADBoo and both components of WZOph appear to be slightly active. Yale-Yonsai and Victoria-Regina evolutionary models fit the
components of ADBoo and VZHya almost equally well, assuming coeval formation, at ages of about 1.75/1.50 Gyr (ADBoo) and
1.25/1.00 Gyr (VZHya). BaSTI models, however, predict somewhat different ages for the primary and secondary components. For WZOph, the models from all three grids are significantly hotter than observed. A low He content, decreased envelope convection coupled with surface activity, and/or higher interstellar absorption would remove the discrepancy, but its cause has not been definitively identified.
Conclusions. We have demonstrated the power of testing and comparing recent stellar evolutionary models using eclipsing binaries, provided their abundances are known. The strongest limitations and challenges are set by Teff and interstellar absorption determinations, and by their effects on and correlation with abundance results
Four-colour photometry of eclipsing binaries. XLI uvby light curves for AD Bootis, HW Canis Majoris, SW Canis Majoris, V636 Centauri, VZ Hydrae, and WZ Ophiuchi
CONTEXT: Accurate mass, radius, and abundance determinations from binaries
provide important information on stellar evolution, fundamental to central
fields in modern astrophysics and cosmology.
AIMS: Within the long-term Copenhagen Binary Project, we aim to obtain
high-quality light curves and standard photometry for double-lined detached
eclipsing binaries with late A, F, and G type main-sequence components, needed
for the determination of accurate absolute dimensions and abundances, and for
detailed comparisons with results from recent stellar evolutionary models.
METHODS: Between March 1985 and July 2007, we carried out photometric
observations of AD Boo, HW CMA, SW CMa, V636 Cen, VZ Hya, and WZ Oph at the
Str"omgren Automatic Telescope at ESO, La Silla.
RESULTS: We obtained complete uvby light curves, ephemerides, and standard
uvby\beta indices for all six systems.For V636 Cen and HW CMa, we present the
first modern light curves, whereas for AD Boo, SW CMa, VZ Hya, and WZ Oph, they
are both more accurate and more complete than earlier data. Due to a high
orbital eccentricity (e = 0.50), combined with a low orbital inclination (i =
84.7), only one eclipse, close to periastron, occurs for HW CMa. For the two
other eccentric systems, V636 Cen (e = 0.134) and SW CMa (e = 0.316), apsidal
motion has been detected with periods of 5270 +/- 335 and 14900 +/- 3600 years,
respectively.Comment: Only change is: Bottom lines (hopefully) not truncated anymore.
Accepted for publication in Astonomy & Astrophysic
Reanalysis of two eclipsing binaries: EE Aqr and Z Vul
We study the radial-velocity and light curves of the two eclipsing binaries
EE Aqr and Z Vul. Using the latest version of the Wilson & Van Hamme (2003)
model, absolute parameters for the systems are determined. We find that EE Aqr
and Z Vul are near-contact and semi-detached systems, respectively. The primary
component of EE Aqr fills about 96% of its 'Roche lobe', while its secondary
one appears close to completely filling this limiting volume. In a similar way,
we find fill-out proportions of about 72 and 100% of these volumes for the
primary and secondary components of Z Vul respectively. We compare our results
with those of previous authors.Comment: 13 pages, 8 figures, 10 table
Local structure study about Co in YBa(CuCo)O thin films using polarized XAFS
We have studied the local structure around Co in
YBa(CuCo)O thin films with three different
concentrations: x=0.07, 0.10, 0.17, and in a
PrBa(CuCo)O thin film of concentration x=0.05
using the X-ray Absorption Fine Structure (XAFS) technique. Data were collected
at the Co -edge with polarizations both parallel and perpendicular to the
film surface. We find that the oxygen neighbors are well ordered and shortened
in comparison with YBCO Cu-O values to 1.80 \AA{} and 1.87 \AA{} in the
-axis and -plane, respectively. A comparison of further neighbors in the
thin film and powder data show that these peaks in the film are suppressed in
amplitude relative to the powder samples, which suggests there is more disorder
and/or distortions of the Co environment present in the thin films.Comment: 14 pages; To be submitted to Phys. Rev.
Role and task allocation framework for Multi-Robot Collaboration with latent knowledge estimation
In this work a novel framework for modeling role and task allocation in Cooperative Heterogeneous Multi-Robot Systems (CHMRSs) is presented. This framework encodes a CHMRS as a set of multidimensional relational structures (MDRSs). This set of structure defines collaborative tasks through both temporal and spatial relations between processes of heterogeneous robots. These relations are enriched with tensors which allow for geometrical reasoning about collaborative tasks. A learning schema is also proposed in order to derive the components of each MDRS. According to this schema, the components are learnt from data reporting the situated history of the processes executed by the team of robots. Data are organized as a multirobot collaboration treebank (MRCT) in order to support learning. Moreover, a generative approach, based on a probabilistic model, is combined together with nonnegative tensor decomposition (NTD) for both building the tensors and estimating latent knowledge. Preliminary evaluation of the performance of this framework is performed in simulation with three heterogeneous robots, namely, two Unmanned Ground Vehicles (UGVs) and one Unmanned Aerial Vehicle (UAV)
ESCA studies of sputtered amorphous Co-Nb-Zr film
Detailed ESCA studies of sputtered amorphous Co-Nb-Zr film, carried out after a period of one year, reveal that Zr oxidises violently and migrates to the surface. Oxidation of Nb is limited to top layers (~ 300 Ă
) while Co remains metallic through out the film. The film beyond 600 Ă
down to the substrate interface is quite homogeneous. Such information could be of importance in some applications of these materials
Evolution of magnetic ground state in Ce<SUB>1−x</SUB>La<SUB>x</SUB>Ni
This article does not have an abstract
Relative strengths of the competing multipoles in the K and L series x-ray spectra in theNR limit
Reply to the comments of Krill and Kappler in relation to our XPS work on CeNi<SUB>2</SUB>
The XPS spectrum of CeNi2, which the authors published recently (see ibid., vol.14, p.L93, 1981), is in disagreement with those reported by Krill et al. (see ibid., vol.14, p.L515, 1981). This led them to repeat their measurements, and the spectrum obtained using freshly prepared samples of CeNi2 is in good agreement with that of Krill et al. (1981). This discrepancy was perhaps due to the surface contamination in their old samples during measurement
- âŠ