8,200 research outputs found
High resolution charge-exchange spectroscopic measurements of aluminum impurity ions in a high temperature plasma
Charge-exchange recombination spectroscopy, which is generally used to measure low-Z impurities in fusion devices, has been used for measuring Al+11 and Al+13 impurities in the Madison Symmetric Torus reversed field pinch. To obtain the impurity ion temperature, the experimental emission spectrum is fitted with a model which includes fine structure in the atomic transition. Densities of these two ionization states, calculated from charge-exchange emission brightness, are used in combination with a collisional radiative model to estimate the abundance of all other charge states of aluminum in the plasma and the contribution of aluminum to the effective ionic charge of the plasma
The kinematic footprints of five stellar streams in Andromeda's halo
(abridged) We present a spectroscopic analysis of five stellar streams (`A',
`B', `Cr', `Cp' and `D') as well as the extended star cluster, EC4, which lies
within streamC, all discovered in the halo of M31 from our CFHT/MegaCam survey.
These spectroscopic results were initially serendipitous, making use of our
existing observations from the DEep Imaging Multi-Object Spectrograph mounted
on the Keck II telescope, and thereby emphasizing the ubiquity of tidal streams
that account for ~70% of the M31 halo stars in the targeted fields. Subsequent
spectroscopy was then procured in streamCr/p and streamD to trace the velocity
gradient along the streams. For the cluster EC4, candidate member stars with
average [Fe/H]~-1.4 (Fe/H_spec=-1.6), are found at v_{hel}=-285 km/s suggesting
it could be related to streamCp. No similarly obvious cold kinematic candidate
is found for streamD, although candidates are proposed in both of two
spectroscopic pointings along the stream (both at -400 km/s). Spectroscopy near
the edge of streamB suggests a likely kinematic detection, while a candidate
kinematic detection of streamA is found (plausibly associated to M33 rather
than M31). The low dispersion of the streams in kinematics, physical thickness,
and metallicity makes it hard to reconcile with a scenario whereby these stream
structures as an ensemble are related to the giant southern stream. We conclude
that the M31 stellar halo is largely made up of multiple kinematically cold
streams.Comment: 19 pages, 12 figures, accepted in MNRAS. High resolution version,
with fig10 here: http://www.ast.cam.ac.uk/~schapman/streams.pd
A Keck/DEIMOS spectroscopic survey of the faint M31 satellites And IX, And XI, And XII, and And XIII
We present the first spectroscopic analysis of the faint M31 satellite
galaxies, AndXI and AndXIII, and a reanalysis of existing spectroscopic data
for two further faint companions, And IX and AndXII. By combining data obtained
using the DEIMOS spectrograph mounted on the Keck II telescope with deep
photometry from the Suprime-Cam instrument on Subaru, we have calculated global
properties for the dwarfs, such as systemic velocities, metallicites and
half-light radii.We find each dwarf to be very metal poor ([Fe/H] -2 both
photometrically and spectroscopically, from their stacked spectrum), and as
such, they continue to follow the luminosity-metallicity relationship
established with brighter dwarfs. We are unable to resolve a dispersion for And
XI due to small sample size and low S/N, but we set a one sigma upper limit of
sigma-v <5 km/s. For And IX, And XII and And XIII we resolve velocity
dispersions of v=4.5 (+3.4,-3.2), 2.6(+5.1,-2.6) and 9.7(+8.9,-4.5) km/s, and
derive masses within the half light radii of 6.2(+5.3,-5.1)x10^6 Msun, 2.4
(+6.5,-2.4)x10^6 Msun and 1.1(+1.4,-0.7)x10^7 Msun respectively. We discuss
each satellite in the context of the Mateo relations for dwarf spheroidal
galaxies, and the Universal halo profiles established for Milky Way dwarfs
(Walker et al. 2009). For both galaxies, this sees them fall below the
Universal halo profiles of Walker et al. (2009). When combined with the
findings of McConnachie & Irwin (2006a), which reveal that the M31 satellites
are twice as extended (in terms of both half-light and tidal radii) as their
Milky Way counterparts, these results suggest that the satellite population of
the Andromeda system could inhabit halos that are significantly different from
those of the Milky Way in terms of their central densities (abridged).Comment: 26 pages, 18 figures, MNRAS submitte
A trio of new Local Group galaxies with extreme properties
We report on the discovery of three new dwarf galaxies in the Local Group.
These galaxies are found in new CFHT/MegaPrime g,i imaging of the south-western
quadrant of M31, extending our extant survey area to include the majority of
the southern hemisphere of M31's halo out to 150 kpc. All these galaxies have
stellar populations which appear typical of dwarf spheroidal (dSph) systems.
The first of these galaxies, Andromeda XVIII, is the most distant Local Group
dwarf discovered in recent years, at ~1.4 Mpc from the Milky Way (~ 600 kpc
from M31). The second galaxy, Andromeda XIX, a satellite of M31, is the most
extended dwarf galaxy known in the Local Group, with a half-light radius of r_h
~ 1.7 kpc. This is approximately an order of magnitude larger than the typical
half-light radius of many Milky Way dSphs, and reinforces the difference in
scale sizes seen between the Milky Way and M31 dSphs (such that the M31 dwarfs
are generally more extended than their Milky Way counterparts). The third
galaxy, Andromeda XX, is one of the faintest galaxies so far discovered in the
vicinity of M31, with an absolute magnitude of order M_V ~ -6.3. Andromeda
XVIII, XIX and XX highlight different aspects of, and raise important questions
regarding, the formation and evolution of galaxies at the extreme faint-end of
the luminosity function. These findings indicate that we have not yet sampled
the full parameter space occupied by dwarf galaxies, although this is an
essential pre-requisite for successfully and consistently linking these systems
to the predicted cosmological dark matter sub-structure.Comment: 32 pages, 7 figures (ApJ preprint format). Accepted for publication
in Ap
Boltzmann equation and hydrodynamic fluctuations
We apply the method of invariant manifolds to derive equations of generalized
hydrodynamics from the linearized Boltzmann equation and determine exact
transport coefficients, obeying Green-Kubo formulas. Numerical calculations are
performed in the special case of Maxwell molecules. We investigate, through the
comparison with experimental data and former approaches, the spectrum of
density fluctuations and address the regime of finite Knudsen numbers and
finite frequencies hydrodynamics.Comment: This is a more detailed version of a related paper: I.V. Karlin, M.
Colangeli, M. Kroger, PRL 100 (2008) 214503, arXiv:0801.2932. It contains
comparison between predictions and experiment, in particular. 11 pages, 6
figures, 2 table
Resolved diffraction patterns from a reflection grating for atoms
We have studied atomic diffraction at normal incidence from an evanescent
standing wave with a high resolution using velocity selective Raman
transitions. We have observed up to 3 resolved orders of diffraction, which are
well accounted for by a scalar diffraction theory. In our experiment the
transverse coherence length of the source is greater than the period of the
diffraction grating.Comment: 8 pages, 4 figure
An HST/ACS View of the Inhomogeneous Outer Halo of M31
We present a high precision photometric view of the stellar populations in
the outer halo of M31, using data taken with the Hubble Space Telescope
Advanced Camera for Surveys (HST/ACS). We analyse the field populations
adjacent to 11 luminous globular clusters which sample the galactocentric
radial range 18 < R < 100 kpc and reach a photometric depth of ~2.5 magnitudes
below the horizontal branch (m_F814W ~27 mag). The colour-magnitude diagrams
(CMDs) are well populated out to ~60 kpc and exhibit relatively metal-rich red
giant branches, with the densest fields also showing evidence for prominent red
clumps. We use the Dartmouth isochrones to construct metallicity distribution
functions (MDFs) which confirm the presence of dominant populations with
= -0.6 to -1.0 dex and considerable metallicity dispersions of 0.2 to
0.3 dex (assuming a 10 Gyr population and scaled-Solar abundances). The average
metallicity over the range 30 - 60 kpc is [Fe/H] = -0.8 +/- 0.14 dex, with no
evidence for a significant radial gradient. Metal-poor stars ([Fe/H] <= -1.3)
typically account for < 10-20 % of the population in each field, irrespective
of radius. Assuming our fields are unbiased probes of the dominant stellar
populations in these parts, we find that the M31 outer halo remains
considerably more metal-rich than that of the Milky Way out to at least 60 kpc.Comment: Accepted for publication in MNRAS. 10 pages, 6 figure
The outer halo globular cluster system of M31 - II. Kinematics
We present a detailed kinematic analysis of the outer halo globular cluster
(GC) system of M31. Our basis for this is a set of new spectroscopic
observations for 78 clusters lying at projected distances between Rproj ~20-140
kpc from the M31 centre. These are largely drawn from the recent PAndAS
globular cluster catalogue; 63 of our targets have no previous velocity data.
Via a Bayesian maximum likelihood analysis we find that GCs with Rproj > 30 kpc
exhibit coherent rotation around the minor optical axis of M31, in the same
direction as more centrally- located GCs, but with a smaller amplitude of
86+/-17 km s-1. There is also evidence that the velocity dispersion of the
outer halo GC system decreases as a function of projected distance from the M31
centre, and that this relation can be well described by a power law of index ~
-0.5. The velocity dispersion profile of the outer halo GCs is quite similar to
that of the halo stars, at least out to the radius up to which there is
available information on the stellar kinematics. We detect and discuss various
velocity correlations amongst subgroups of GCs that lie on stellar debris
streams in the M31 halo. Many of these subgroups are dynamically cold,
exhibiting internal velocity dispersions consistent with zero. Simple Monte
Carlo experiments imply that such configurations are unlikely to form by
chance, adding weight to the notion that a significant fraction of the outer
halo GCs in M31 have been accreted alongside their parent dwarf galaxies. We
also estimate the M31 mass within 200 kpc via the Tracer Mass Estimator,
finding (1.2 - 1.6) +/- 0.2 10^{12}M_sun. This quantity is subject to
additional systematic effects due to various limitations of the data, and
assumptions built in into the TME. Finally, we discuss our results in the
context of formation scenarios for the M31 halo.Comment: 24 pages, 12 figures, 7 tables; Accepted for publication in MNRA
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