7,232 research outputs found
[Fe XIV] and [Fe XI] reveal the forward shock in SNR 1E0102.2-7219
Aims. We study the forward shock in the oxygen-rich young supernova remnant
(SNR) 1E0102.2-7219 (1E0102 in short) via optical coronal emission from [Fe
XIV] and [Fe XI]: emission lines which offer an alternative method to X-rays to
do so.
Methods. We have used the Multi-Unit Spectroscopic Explorer (MUSE) optical
integral field spectrograph at the Very Large Telescope (VLT) on Cerro Paranal
to obtain deep observations of SNR 1E0102 in the Small Magellanic Cloud. Our
observations cover the entire extent of the remnant with a seeing limited
spatial resolution of 0.7" = 0.2 pc at the distance of 1E 0102.
Results. Our MUSE observations unambiguously reveal the presence of [Fe XIV]
and [Fe XI] emission in 1E0102. The emission largely arises from a thin,
partial ring of filaments surrounding the fast moving O-rich ejecta in the
system. The brightest [Fe XIV] and [Fe XI] emission is found along the eastern
and north-western sides of 1E0102, where shocks are driven into denser ISM
material, while fainter emission along the northern edge reveals the location
of the forward shock in lower density gas, possibly the relic stellar wind
cavity. Modeling of the eastern shocks and the photoionization precursor
surrounding 1E0102, we derive a pre-shock density = (7.4 +-1.5)
cm, and a shock velocity 330 km/s < < 350 km/s.Comment: 4 pages, 4 figures, accepted for publications in A&A as a Letter to
the Edito
Determination of pulsation periods and other parameters of 2875 stars classified as MIRA in the All Sky Automated Survey (ASAS)
We have developed an interactive PYTHON code and derived crucial ephemeris
data of 99.4% of all stars classified as 'Mira' in the ASAS data base,
referring to pulsation periods, mean maximum magnitudes and, whenever possible,
the amplitudes among others. We present a statistical comparison between our
results and those given by the AAVSO International Variable Star Index (VSX),
as well as those determined with the machine learning automatic procedure of
Richards et al. 2012. Our periods are in good agreement with those of the VSX
in more than 95% of the stars. However, when comparing our periods with those
of Richards et al, the coincidence rate is only 76% and most of the remaining
cases refer to aliases. We conclude that automatic codes require still more
refinements in order to provide reliable period values. Period distributions of
the target stars show three local maxima around 215, 275 and 330 d, apparently
of universal validity, their relative strength seems to depend on galactic
longitude. Our visual amplitude distribution turns out to be bimodal, however
1/3 of the targets have rather small amplitudes (A 2.5) and could
refer to semi-regular variables (SR). We estimate that about 20% of our targets
belong to the SR class. We also provide a list of 63 candidates for period
variations and a sample of 35 multiperiodic stars which seem to confirm the
universal validity of typical sequences in the double period and in the
Petersen diagramsComment: 14 pages, 14 figures, and 8 tables. Accepted to The Astrophysical
Journal Supplement Series, September 201
Heavy quark effects on parton distribution functions in the unpolarized virtual photon up to the next-to-leading order in QCD
We investigate the heavy quark mass effects on the parton distribution
functions in the unpolarized virtual photon up to the next-to-leading order in
QCD. Our formalism is based on the QCD-improved parton model described by the
DGLAP evolution equation as well as on the operator product expansion
supplemented by the mass-independent renormalization group method. We evaluate
the various components of the parton distributions inside the virtual photon
with the massive quark effects, which are included through the initial
condition for the heavy quark distributions, or equivalently from the matrix
element of the heavy quark operators. We discuss some features of our results
for the heavy quark effects and their factorization-scheme dependence.Comment: 16 pages, 16 figures, version to appear in Phys. Rev.
Exploring multi-band excitations of interacting Bose gases in a 1D optical lattice by coherent scattering
We use a coherent Bragg diffraction method to impart an external momentum to
ultracold bosonic atoms trapped in a one-dimensional optical lattice. This
method is based on the application of a single light pulse, with conditions
where scattering of photons can be resonantly amplified by the atomic density
grating. An oscillatory behavior of the momentum distribution resulting from
the time evolution in the lattice potential is then observed. By measuring the
oscillating frequencies, we extract multi-band energy structures of
single-particle excitations with zero pseudo-momentum transfer for a wide range
of lattice depths. The excitation energy structures reveal the interaction
effect through the whole range of lattice depth.Comment: 6 pages, 5 figure
Target Mass Corrections for the Virtual Photon Structure Functions to the Next-to-next-to-leading Order in QCD
We investigate target mass effects in the unpolarized virtual photon
structure functions and in
perturbative QCD for the kinematical region , where
is the mass squared of the probe (target) photon and is
the QCD scale parameter. We obtain the Nachtmann moments for the structure
functions and then, by inverting the moments, we get the expressions in closed
form for up to the next-to-next-to-leading order and
for up to the next-to-leading order, both of which
include the target mass corrections. Numerical analysis exhibits that target
mass effects appear at large and become sizable near , the maximal value of , as the ratio
increases.Comment: 24 pages, LaTeX, 7 eps figures, REVTeX
Shadowing Effects on the Nuclear Suppression Factor, R_dAu, in d+Au Interactions
We explore how nuclear modifications to the nucleon parton distributions
affect production of high transverse momentum hadrons in deuteron-nucleus
collisions. We calculate the charged hadron spectra to leading order using
standard fragmentation functions and shadowing parameterizations. We obtain the
d+Au to pp ratio both in minimum bias collisions and as a function of
centrality. The minimum bias results agree reasonably well with the BRAHMS data
while the calculated centrality dependence underestimates the data and is a
stronger function of p_T than the data indicate.Comment: 18 pages, 3 figures, final version, Phys. Rev. C in pres
Dynamical Mass Estimates for the Halo of M31 from Keck Spectroscopy
The last few months have seen the measurements of the radial velocities of
all of the dwarf spheroidal companions to the Andromeda galaxy (M31) using the
spectrographs (HIRES and LRIS) on the Keck Telescope. This paper summarises the
data on the radial velocities and distances for all the companion galaxies and
presents new dynamical modelling to estimate the mass of extended halo of M31.
The best fit values for the total mass of M31 are between 7 and 10 x 10^{11}
solar masses, depending on the details of the modelling. The mass estimate is
accompanied by considerable uncertainty caused by the smallness of the dataset;
for example, the upper bound on the total mass is roughly 24 x 10^{11} solar
masses, while the lower bound is about 3 x 10^{11} solar masses. These values
are less than the most recent estimates of the most likely mass of the Milky
Way halo. Bearing in mind all the uncertainties, a fair conclusion is that the
M31 halo is roughly as massive as that of the Milky Way halo. There is no
dynamical evidence for the widely held belief that M31 is more massive -- it
may even be less massive.Comment: In press, The Astrophysical Journal (Letters
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