7,449 research outputs found
Thermoelectricity of EuCu{2}(Ge{1-x}Si{x}){2} intermetallics
The evolution of the thermopower EuCu{2}(Ge{1-x}Si{x}){2} intermetallics,
which is induced by the Si-Ge substitution, is explained by the Kondo
scattering of conduction electrons on the Eu ions which fluctuate between the
magnetic 2+ and non-magnetic 3+ Hund's rule configurations. The Si-Ge
substitution is equivalent to chemical pressure which modifies the coupling and
the relative occupation of the {\it f} and conduction states.Comment: 2 pages, Proceedings of the SCES 2005 confernece. Physica B (2006),
in pres
Mid-infrared size survey of Young Stellar Objects: Description of Keck segment-tilting experiment and basic results
The mid-infrared properties of pre-planetary disks are sensitive to the
temperature and flaring profiles of disks for the regions where planet
formation is expected to occur. In order to constrain theories of planet
formation, we have carried out a mid-infrared (wavelength 10.7 microns) size
survey of young stellar objects using the segmented Keck telescope in a novel
configuration. We introduced a customized pattern of tilts to individual mirror
segments to allow efficient sparse-aperture interferometry, allowing full
aperture synthesis imaging with higher calibration precision than traditional
imaging. In contrast to previous surveys on smaller telescopes and with poorer
calibration precision, we find most objects in our sample are partially
resolved. Here we present the main observational results of our survey of 5
embedded massive protostars, 25 Herbig Ae/Be stars, 3 T Tauri stars, 1 FU Ori
system, and 5 emission-line objects of uncertain classification. The observed
mid-infrared sizes do not obey the size-luminosity relation found at
near-infrared wavelengths and a companion paper will provide further modelling
analysis of this sample. In addition, we report imaging results for a few of
the most resolved objects, including complex emission around embedded massive
protostars, the photoevaporating circumbinary disk around MWC 361A, and the
subarcsecond binaries T Tau, FU Ori and MWC 1080.Comment: Accepted by Astrophysical Journal. 38 pages. 9 figure
Strong Near-Infrared Emission Interior to the Dust-Sublimation Radius of Young Stellar Objects MWC275 and AB Aur
Using the longest optical-interferometeric baselines currently available, we
have detected strong near-infrared (NIR) emission from inside the
dust-destruction radius of Herbig Ae stars MWC275 and AB Aur. Our
sub-milli-arcsecond resolution observations unambiguously place the emission
between the dust-destruction radius and the magnetospheric co-rotation radius.
We argue that this new component corresponds to hot gas inside the
dust-sublimation radius, confirming recent claims based on spectrally-resolved
interferometry and dust evaporation front modeling.Comment: 12 pages, 4 figures, Accepted for publication in ApJ
A Data Exchange Standard for Optical (Visible/IR) Interferometry
This paper describes the OI Exchange Format, a standard for exchanging
calibrated data from optical (visible/infrared) stellar interferometers. The
standard is based on the Flexible Image Transport System (FITS), and supports
storage of the optical interferometric observables including squared visibility
and closure phase -- data products not included in radio interferometry
standards such as UV-FITS. The format has already gained the support of most
currently-operating optical interferometer projects, including COAST, NPOI,
IOTA, CHARA, VLTI, PTI, and the Keck Interferometer, and is endorsed by the IAU
Working Group on Optical Interferometry. Software is available for reading,
writing and merging OI Exchange Format files.Comment: 26 pages, 1 figur
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