2,011,378 research outputs found
DN Tauri - coronal activity and accretion in a young low-mass CTTS
We present a deep XMM-Newton observation of DN Tau, a young M0-type accreting
CTTS and investigate its X-ray properties and X-ray generating mechanisms.
Specifically we examine the presence of X-ray emission from magnetic activity
and accretion shocks and compare our new X-ray data with UV data taken
simultaneously and with X-ray/UV observations performed before. We find that
the X-ray emission from DN Tau is dominated by coronal plasma generated via
magnetic activity, but also clearly detect a contribution of the accretion
shocks to the cool plasma component at about 2 MK as consistently inferred from
density and temperature analysis. Typical phenomena of active coronae like
flaring, the presence of very hot plasma at 30 MK and an abundance pattern
showing the inverse FIP effect are seen on DN Tau. Strong variations in the
emission measure of the cooler plasma components between the 2005 and 2010 XMM
data point to accretion related changes. The UV light curve taken
simultaneously is in general not related to the X-ray brightness, but exhibits
clear counterparts during the observed X-ray flares. The X-ray properties of DN
Tau are similar to those of more massive CTTS, but its low mass and large
radius shift the accretion shocks to lower temperatures, reducing their imprint
in the X-ray regime.Comment: 11 pages, 8 figures, accepted for publication in A&
Stochastic Biasing and Galaxy-Mass Density Relation in the Weakly Non-linear Regime
It is believed that the biasing of the galaxies plays an important role for
understanding the large-scale structure of the universe. In general, the
biasing of galaxy formation could be stochastic. Furthermore, the future galaxy
survey might allow us to explore the time evolution of the galaxy distribution.
In this paper, the analytic study of the galaxy-mass density relation and its
time evolution is presented within the framework of the stochastic biasing. In
the weakly non-linear regime, we derive a general formula for the galaxy-mass
density relation as a conditional mean using the Edgeworth expansion. The
resulting expression contains the joint moments of the total mass and galaxy
distributions. Using the perturbation theory, we investigate the time evolution
of the joint moments and examine the influence of the initial stochasticity on
the galaxy-mass density relation. The analysis shows that the galaxy-mass
density relation could be well-approximated by the linear relation. Compared
with the skewness of the galaxy distribution, we find that the estimation of
the higher order moments using the conditional mean could be affected by the
stochasticity. Therefore, the galaxy-mass density relation as a conditional
mean should be used with a caution as a tool for estimating the skewness and
the kurtosis.Comment: 22 pages, 7 Encapusulated Postscript Figures, aastex, The title and
the structure of the paper has been changed, Results and conclusions
unchanged, Accepted for publication in Ap
Density Functional Theory Characterization of the Multiferroicity in Spin Spiral Chain Cuprates
The ferroelectricity of the spiral magnets LiCu2O2 and LiCuVO4 was examined
by calculating the electric polarizations of their spin spiral states on the
basis of density functional theory with spin-orbit coupling. Our work
unambiguously reveals that spin-orbit coupling is responsible for the
ferroelectricity with the primary contribution from the spin-orbit coupling on
the Cu sites, but the asymmetric density distribution responsible for the
electric polarization occurs mainly around the O atoms. The electric
polarization is calculated to be much greater for the ab- than for the bc-plane
spin spiral. The observed spin-spiral plane is found to be consistent with the
observed direction of the electric polarization for LiCuVO4, but inconsistent
for LiCu2O2.Comment: Phys. Rev. Lett., in prin
A magnetic cycle of tau Bootis? The coronal and chromospheric view
Tau Bootis is a late F-type main sequence star orbited by a Hot Jupiter.
During the last years spectropolarimetric observations led to the hypothesis
that this star may host a global magnetic field that switches its polarity once
per year, indicating a very short activity cycle of only one year duration. In
our ongoing observational campaign, we have collected several X-ray
observations with XMM-Newton and optical spectra with TRES/FLWO in Arizona to
characterize tau Boo's corona and chromosphere over the course of the supposed
one-year cycle. Contrary to the spectropolarimetric reconstructions, our
observations do not show indications for a short activity cycle.Comment: 4 pages, 2 figures, appeared in Astronomical Notes 333, 1, 26-29
(2012
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