7,987 research outputs found
Sclera solar diameter observations
Focus is given to possible variations in solar luminosity and accurate methods of monitoring it. Aside from direct bolometry, one methodology for this type of research makes use of measurements of the solar diameter and limb darkening function as indirect indicators of the solar luminosity. This approach was reviewed
The Detection of a 3.5-h Period in the Classical Nova Velorum 1999 (V382 Vel) and the Long Term Behavior of the Nova Light Curve
We present CCD photometry, light curve and time series analysis of the
classical nova V382 Vel (N Vel 1999). The source was observed for 2 nights in
2000, 21 nights in 2001 and 7 nights in 2002 using clear filters. We report the
detection of a distinct period in the light curve of the nova P=0.146126(18) d
(3.5 h). The period is evident in all data sets, and we interpret it as the
binary period of the system. We also measured an increase in the amplitude
modulation of the optical light (in magnitude) by more than 55% from 2000 to
2001 and about 64% from 2001 to 2002. The pulse profiles in 2001 show
deviations from a pure sinusoidal shape which progressively become more
sinusoidal by 2002. The main cause of the variations in 2001 and 2002 can be
explained with the occultation of the accretion disk by the secondary star. We
interpret the observed deviations from a pure sinusoidal shape as additional
flux resulting from the aspect variations of the irradiated face of the
secondary star.Comment: 16 pages and 4 figures, accepted as it stands to be published in the
Astronomical Journal (AJ
Theoretical investigation of magnetic order in ReOFeAs, Re = Ce, Pr
Density functional theory (DFT) calculations are carried out on ReOFeAs, Re =
Ce, Pr, the parent compounds of the high-T superconductors
ReOFFeAs, in order to determine the magnetic order of the ground
state. It is found that the magnetic moments on the Fe sites adopt a collinear
antiferromagnetic order, similar to the case of LaOFeAs. Within the generalized
gradient approximation along with Coulomb onsite repulsion (GGA+U), we show
that the Re magnetic moments also adopt an antiferromagnetic order for which,
within the ReO layer, same spin Re sites lie along a zigzag line perpendicular
to the Fe spin stripes. While within GGA the Re 4f band crosses the Fermi
level, upon inclusion of onsite Coulomb interaction the 4f band splits and
moves away from the Fermi level, making ReOFeAs a Mott insulator.Comment: 5 pages, 4 figure
Fully broadband vAPP coronagraphs enabling polarimetric high contrast imaging
We present designs for fully achromatic vector Apodizing Phase Plate (vAPP)
coronagraphs, that implement low polarization leakage solutions and achromatic
beam-splitting, enabling observations in broadband filters. The vAPP is a pupil
plane optic, inducing the phase through the inherently achromatic geometric
phase. We discuss various implementations of the broadband vAPP and set
requirements on all the components of the broadband vAPP coronagraph to ensure
that the leakage terms do not limit a raw contrast of 1E-5. Furthermore, we
discuss superachromatic QWPs based of liquid crystals or quartz/MgF2
combinations, and several polarizer choices. As the implementation of the
(broadband) vAPP coronagraph is fully based on polarization techniques, it can
easily be extended to furnish polarimetry by adding another QWP before the
coronagraph optic, which further enhances the contrast between the star and a
polarized companion in reflected light. We outline several polarimetric vAPP
system designs that could be easily implemented in existing instruments, e.g.
SPHERE and SCExAO.Comment: 11 pages, 5 figures, presented at SPIE Astronomical Telescopes and
Instrumentation 201
Inertial range scaling of the scalar flux spectrum in two-dimensional turbulence
Two-dimensional statistically stationary isotropic turbulence with an imposed
uniform scalar gradient is investigated. Dimensional arguments are presented to
predict the inertial range scaling of the turbulent scalar flux spectrum in
both the inverse cascade range and the enstrophy cascade range for small and
unity Schmidt numbers. The scaling predictions are checked by direct numerical
simulations and good agreement is observed
Decay of scalar variance in isotropic turbulence in a bounded domain
The decay of scalar variance in isotropic turbulence in a bounded domain is
investigated. Extending the study of Touil, Bertoglio and Shao (2002; Journal
of Turbulence, 03, 49) to the case of a passive scalar, the effect of the
finite size of the domain on the lengthscales of turbulent eddies and scalar
structures is studied by truncating the infrared range of the wavenumber
spectra. Analytical arguments based on a simple model for the spectral
distributions show that the decay exponent for the variance of scalar
fluctuations is proportional to the ratio of the Kolmogorov constant to the
Corrsin-Obukhov constant. This result is verified by closure calculations in
which the Corrsin-Obukhov constant is artificially varied. Large-eddy
simulations provide support to the results and give an estimation of the value
of the decay exponent and of the scalar to velocity time scale ratio
Ferromagnetism below 10 K in Mn doped BiTe
Ferromagnetism is observed below 10 K in [Bi0.75Te0.125Mn0.125]Te. This
material has the BiTe structure, which is made from the stacking of two
Te-Bi-Te-Bi-Te blocks and one Bi-Bi block per unit cell. Crystal structure
analysis shows that Mn is localized in the Bi2 blocks, and is accompanied by an
equal amount of TeBi anti-site occupancy in the Bi2Te3 blocks. These TeBi
anti-site defects greatly enhance the Mn solubility. This is demonstrated by
comparison of the [Bi1-xMnx]Te and [Bi1-2xTexMnx]Te series; in the former, the
solubility is limited to x = 0.067, while the latter has xmax = 0.125. The
magnetism in [Bi1-xMnx]Te changes little with x, while that for
[Bi1-2xTexMnx]Te shows a clear variation, leading to ferromagnetism for x >
0.067. Magnetic hysteresis and the anomalous Hall Effect are observed for the
ferromagnetic samples.Comment: Accepted for publication in Phys. Rev.
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