36,526 research outputs found
Spectroscopic study of early-type multiple stellar systems II. New binary subsystems
Context. This work is part of a long-term spectroscopic study of a sample of
30 multiple stars with early-type components. In this second paper we present
the results of six multiple systems in which new stellar components have been
detected.
Aims. The main aim is to increase the knowledge of stellar properties and
dynamical structure of early-type multiple stellar systems.
Methods. Using spectroscopic observations taken over a time baseline of more
than 5 years we measured RVs by cross-correlations and applied a spectral
disentangling method to double-lined systems. Besides the discovery of objects
with double-lined spectra, the existence of new spectroscopic subsystems have
been inferred from the radial velocity variations of single-lined components
and through the variation of the barycentric velocity of double-lined
subsystems. Orbital elements have been calculated when possible.
Results. Seven new stellar components and two members that we expect to
confirm with new observations have been discovered in the six studied
multiples. We present orbital parameters for two double-lined binaries and
preliminary orbits for three single-lined spectroscopic binaries. Five of the
six analysed systems are quadruples, while the remaining has five components
distributed in four hierarchical levels. These multiplicity orders are in fact
lower limits, since these systems lack high-resolution visual observations and
additional hierarchical level might exist in that separation range.
Conclusions. The six analysed systems have greater multiplicity degree and a
more complex hierarchical structure than previously known, which suggests that
high-order multiple systems are significantly more frequent that it is
currently estimated. The long term spectroscopic monitoring of multiple systems
has shown to be useful for the detection of companions in intermediate
hierarchical levels.Comment: 13 pages, 9 figures. Accepted by Astronomy and Astrophysic
Room temperature ferromagnetic-like behavior in Mn-implanted and post-annealed InAs layers deposited by Molecular Beam Epitaxy
We report on the magnetic and structural properties of Ar and Mn implanted
InAs epitaxial films grown on GaAs (100) by Molecular Beam Epitaxy (MBE) and
the effect of Rapid Thermal Annealing (RTA) for 30 seconds at 750C. Channeling
Particle Induced X- ray Emission (PIXE) experiments reveal that after Mn
implantation almost all Mn atoms are subsbtitutional in the In-site of the InAs
lattice, like in a diluted magnetic semiconductor (DMS). All of these samples
show diamagnetic behavior. But, after RTA treatment the Mn-InAs films exhibit
room-temperature magnetism. According to PIXE measurements the Mn atoms are no
longer substitutional. When the same set of experiments were performed with As
as implantation ion all of the layers present diamagnetism without exception.
This indicates that the appearance of room-temperature ferromagnetic-like
behavior in the Mn-InAs-RTA layer is not related to lattice disorder produce
during implantation, but to a Mn reaction produced after a short thermal
treatment. X-ray diffraction patterns (XRD) and Rutherford Back Scattering
(RBS) measurements evidence the segregation of an oxygen deficient-MnO2 phase
(nominally MnO1.94) in the Mn-InAs-RTA epitaxial layers which might be on the
origin of room temperature ferromagnetic-like response observed.Comment: 16 pages, 5 figures. Acepted in J. Appl. Phy
Recovery of normal heat conduction in harmonic chains with correlated disorder
We consider heat transport in one-dimensional harmonic chains with isotopic
disorder, focussing our attention mainly on how disorder correlations affect
heat conduction. Our approach reveals that long-range correlations can change
the number of low-frequency extended states. As a result, with a proper choice
of correlations one can control how the conductivity scales with the
chain length . We present a detailed analysis of the role of specific
long-range correlations for which a size-independent conductivity is exactly
recovered in the case of fixed boundary conditions. As for free boundary
conditions, we show that disorder correlations can lead to a conductivity
scaling as , with the scaling exponent
being arbitrarily small (although not strictly zero), so that
normal conduction is almost recovered even in this case.Comment: 15 pages, 2 figure
Environmental sensitivity of n-i-n and undoped single GaN nanowire photodetectors
In this work, we compare the photodetector performance of single defect-free
undoped and n-in GaN nanowires (NWs). In vacuum, undoped NWs present a
responsivity increment, nonlinearities and persistent photoconductivity effects
(~ 100 s). Their unpinned Fermi level at the m-plane NW sidewalls enhances the
surface states role in the photodetection dynamics. Air adsorbed oxygen
accelerates the carrier dynamics at the price of reducing the photoresponse. In
contrast, in n-i-n NWs, the Fermi level pinning at the contact regions limits
the photoinduced sweep of the surface band bending, and hence reduces the
environment sensitivity and prevents persistent effects even in vacuum
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