3,083 research outputs found
The radio source B 1834+620: A double-double radio galaxy with interesting properties
We present a study of the peculiar radio galaxy B 1834+620. It is
characterised by the presence of a 420-kpc large edge-brightened radio source
which is situated within, and well aligned with, a larger (1.66 Mpc) radio
source. Both sources apparently originate in the same host galaxy, which has a
R_s-magnitude of 19.7 and a redshift of 0.5194, as determined from the strong
emission-lines in the spectrum. We have determined the rotation measures
towards this source, as well as the radio spectral energy distribution of its
components. The radio spectrum of the large outer source is steeper than that
of the smaller inner source. The radio core has a spectrum that peaks at a
frequency of a few GHz. The rotation measures towards the four main components
are quite similar, within rad m of 58 rad m. They are
probably largely galactic in origin. We have used the presence of a bright
hotspot in the northern outer lobe to constrain the advance velocity of the
inner radio lobes to the range between 0.19c and 0.29c, depending on the
orientation of the source. This corresponds to an age of this structure in the
range between 2.6 and 5.8 Myr. We estimate a density of the ambient medium of
the inner lobes of \la 1.6 \times 10^{-30} gr\,cm (particle density
\la 8 \times 10^{-7} cm). A low ambient density is further supported
by the discrepancy between the large optical emission-line luminosity of the
host galaxy and the relatively low radio power of the inner lobes.Comment: Accepted for publication in MNRA
Summary of random vibration prediction procedures
Summary of random vibration prediction procedures for aerospace vehicles, with bibliograph
Molecular gas in NUclei of GAlaxies (NUGA) XV. Molecular gas kinematics in the inner 3kpc of NGC6951
Within the NUclei of GAlaxies project we have obtained IRAM PdBI and 30m
12CO(1-0) and 12CO(2-1) observations of the spiral galaxy NGC 6951. Previous
work shows that there is indirect evidence of gas inflow from 3 kpc down to
small radii: a large-scale stellar bar, a prominent starburst ring (r~580 pc)
and a LINER/Seyfert 2 nucleus. In this paper we study the gas kinematics as
traced by the CO line emission in detail. We quantify the influence of the
large-scale stellar bar by constructing an analytical model of the evolution of
gas particles in a barred potential. From this model gravitational torques and
mass accumulation rates are computed. We compare our model-based gravitational
torque results with previous observationally-based ones. The model also shows
that the large-scale stellar bar is indeed the dominant force for driving the
gas inward, to the starburst ring. Inside the ring itself a nuclear stellar
oval might play an important role. Detailed analysis of the CO gas kinematics
there shows that emission arises from two co-spatial, but kinematically
distinct components at several locations. The main emission component can
always be related to the overall bar-driven gas kinematics. The second
component exhibits velocities that are larger than expected for gas on stable
orbits, has a molecular gas mass of 1.8x10^6Msun, is very likely connected to
the nuclear stellar oval, and is consistent with inflowing motion towards the
very center. This may form the last link in the chain of gas inflow towards the
active galactic nucleus in NGC 6951.Comment: 17 pages, accepted by A&A (17 feb 2011
Symbolic computation and exact distributions of nonparametric test statistics
We show how to use computer algebra for computing exact distributions on nonparametric statistics. We give several examples of nonparametric statistics with explicit probability generating functions that can be handled this way. In particular, we give a new table of critical values of the Jonckheere-Terpstra test that extends tables known in the literature
Strain dependence of the Mn anisotropy in ferromagnetic semiconductors observed by x-ray magnetic circular dichroism
We demonstrate sensitivity of the Mn 3d valence states to strain in the
ferromagnetic semiconductors (Ga,Mn)As and (Al,Ga,Mn)As, using x-ray magnetic
circular dichroism (XMCD). The spectral shape of the Mn XMCD is
dependent on the orientation of the magnetization, and features with cubic and
uniaxial dependence are distinguished. Reversing the strain reverses the sign
of the uniaxial anisotropy of the Mn pre-peak which is ascribed to
transitions from the Mn 2p core level to p-d hybridized valence band hole
states. With increasing carrier localization, the pre-peak intensity
increases, indicating an increasing 3d character of the hybridized holes.Comment: 4 pages plus 2 figures, accepted for publication in Physical Review
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