3,340 research outputs found
A 22 Degree Tidal Tail for Palomar 5
Using Data Release 4 of the Sloan Digital Sky Survey, we have applied an
optimal contrast, matched filter technique to trace the trailing tidal tail of
the globular cluster Palomar 5 to a distance of 18.5 degrees from the center of
the cluster. This more than doubles the total known length of the tail to some
22 degrees on the sky. Based on a simple model of the Galaxy, we find that the
stream's orientation on the sky is consistent at the 1.7 sigma level with
existing proper motion measurements. We find that a spherical Galactic halo is
adequate to model the stream over its currently known length, and we are able
to place new constraints on the current space motion of the cluster.Comment: 10 pages, 3 figures, accepted for publication in ApJ Letter
Reduction of quantum noise in optical interferometers using squeezed light
We study the photon counting noise in optical interferometers used for
gravitational wave detection. In order to reduce quantum noise a squeezed
vacuum state is injected into the usually unused input port. Here, we
specifically investigate the so called `dark port case', when the beam splitter
is oriented close to 90{\deg} to the incoming laser beam, such that nearly all
photons go to one output port of the interferometer, and only a small fraction
of photons is seen in the other port (`dark port'). For this case it had been
suggested that signal amplification is possible without concurrent noise
amplification [R.Barak and Y.Ben-Aryeh, J.Opt.Soc.Am.B25(361)2008]. We show
that by injection of a squeezed vacuum state into the second input port,
counting noise is reduced for large values of the squeezing factor, however the
signal is not amplified. Signal strength only depends on the intensity of the
laser beam.Comment: 8 pages, 1 figur
Upper Columbia United Tribes Fisheries Center Fisheries Technical Report No. 12
Predicting the Effect of Reduced Streamflow on Rainbow Trout, Brown Trout, and Sculpin Populations in Chamokane Creek Using the Instream Flow Incremental Methodology (IFIM
UKIDSS detections of cool brown dwarfs - proper motions of 14 known T5 dwarfs and discovery of three new T5.5-T6 dwarfs
AIMS: We contribute to improving the census of cool brown dwarfs (late-T and
Y dwarfs) in the immediate solar neighbourhood. METHODS: By combining
near-infrared (NIR) data of UKIDSS with mid-infrared WISE and other available
NIR (2MASS) and red optical (SDSS -band) multi-epoch data we detect high
proper motion (HPM) objects with colours typical of late spectral types
(T5). We use NIR low-resolution spectroscopy for the classification of new
candidates. RESULTS: We determined new proper motions for 14 known T5.5-Y0
dwarfs, many of them being significantly (2-10 times) more accurate than
previous ones. We detected three new candidates, ULAS J0954+0623, ULAS
J1152+0359, and ULAS J1204-0150, by their HPMs and colours. Using previously
published and new UKIDSS positions of the known nearby T8 dwarf WISE J0254+0223
we improved its trigonometric parallax to 16520 mas. For the three new
objects we obtained NIR spectroscopic follow-up with LBT/LUCIFER classifying
them as T5.5 and T6 dwarfs. With their estimated spectroscopic distances of
about 25-30 pc, their proper motions of about 430-650 mas/yr lead to tangential
velocities of about 50-80 km/s typical of the Galactic thin disk population.Comment: 5 pages, 2 figures, plus 3 pages with 5 tables (online material),
accepted for publication in Astronomy and Astrophysic
The RAVE survey: the Galactic escape speed and the mass of the Milky Way
We construct new estimates on the Galactic escape speed at various
Galactocentric radii using the latest data release of the Radial Velocity
Experiment (RAVE DR4). Compared to previous studies we have a database larger
by a factor of 10 as well as reliable distance estimates for almost all stars.
Our analysis is based on the statistical analysis of a rigorously selected
sample of 90 high-velocity halo stars from RAVE and a previously published data
set. We calibrate and extensively test our method using a suite of cosmological
simulations of the formation of Milky Way-sized galaxies. Our best estimate of
the local Galactic escape speed, which we define as the minimum speed required
to reach three virial radii , is km/s (90%
confidence) with an additional 5% systematic uncertainty, where is
the Galactocentric radius encompassing a mean over-density of 340 times the
critical density for closure in the Universe. From the escape speed we further
derive estimates of the mass of the Galaxy using a simple mass model with two
options for the mass profile of the dark matter halo: an unaltered and an
adiabatically contracted Navarro, Frenk & White (NFW) sphere. If we fix the
local circular velocity the latter profile yields a significantly higher mass
than the un-contracted halo, but if we instead use the statistics on halo
concentration parameters in large cosmological simulations as a constraint we
find very similar masses for both models. Our best estimate for , the
mass interior to (dark matter and baryons), is M (corresponding to M). This estimate is in good agreement with recently published
independent mass estimates based on the kinematics of more distant halo stars
and the satellite galaxy Leo I.Comment: 16 pages, 15 figures; accepted for publication in Astronomy &
Astrophysic
Probing two topological surface bands of Sb2Te3 by spin-polarized photoemission spectroscopy
Using high resolution spin- and angle-resolved photoemission spectroscopy, we
map the electronic structure and spin texture of the surface states of the
topological insulator Sb2Te3. In combination with density functional
calculations (DFT), we directly show that Sb2Te3 exhibits a partially occupied,
single spin-Dirac cone around the Fermi energy, which is topologically
protected. DFT obtains a spin polarization of the occupied Dirac cone states of
80-90%, which is in reasonable agreement with the experimental data after
careful background subtraction. Furthermore, we observe a strongly spin-orbit
split surface band at lower energy. This state is found at 0.8eV below the
Fermi level at the gamma-point, disperses upwards, and disappears at about
0.4eV below the Fermi level into two different bulk bands. Along the gamma-K
direction, the band is located within a spin-orbit gap. According to an
argument given by Pendry and Gurman in 1975, such a gap must contain a surface
state, if it is located away from the high symmetry points of the Brillouin
zone. Thus, the novel spin-split state is protected by symmetry, too.Comment: 8 pages, 10 figure
Evolution of displacements and strains in sheared amorphous solids
The local deformation of two-dimensional Lennard-Jones glasses under imposed
shear strain is studied via computer simulations. Both the mean squared
displacement and mean squared strain rise linearly with the length of the
strain interval over which they are measured. However, the
increase in displacement does not represent single-particle diffusion. There
are long-range spatial correlations in displacement associated with slip lines
with an amplitude of order the particle size. Strong dependence on system size
is also observed. The probability distributions of displacement and strain are
very different. For small the distribution of displacement has
a plateau followed by an exponential tail. The distribution becomes Gaussian as
increases to about .03. The strain distributions consist of
sharp central peaks associated with elastic regions, and long exponential tails
associated with plastic regions. The latter persist to the largest studied.Comment: Submitted to J. Phys. Cond. Mat. special volume for PITP Conference
on Mechanical Behavior of Glassy Materials. 16 Pages, 8 figure
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