37,191 research outputs found
On the bar pattern speed determination of NGC 3367
An important dynamic parameter of barred galaxies is the bar pattern speed.
Among several methods that are used for the determination of the pattern speed
the Tremaine-Weinberg method has the advantage of model independency and
accuracy. In this work we apply the method to a simulated bar including gas
dynamics and study the effect of 2D spectroscopy data quality on robustness of
the method. We added a white noise and a Gaussian random field to the data and
measured the corresponding errors in the pattern speed. We found that a signal
to noise ratio in surface density ~5 introduces errors of ~20% for the Gaussian
noise, while for the white noise the corresponding errors reach ~50%. At the
same time the velocity field is less sensitive to contamination. On the basis
of the performed study we applied the method to the NGC 3367 spiral galaxy
using H{\alpha} Fabry-Perot interferometry data. We found for the pattern speed
43 \pm 6 km/s/kpc for this galaxy.Comment: Accepted for publication in ApJ. 16 pages, 16 figure
Pair Creation of Dilaton Black Holes in Extended Inflation
Dilatonic Charged Nariai instantons mediate the nucleation of black hole
pairs during extended chaotic inflation. Depending on the dilaton and inflaton
fields, the black holes are described by one of two approximations in the
Lorentzian regime. For each case we find Euclidean solutions that satisfy the
no boundary proposal. The complex initial values of the dilaton and inflaton
are determined, and the pair creation rate is calculated from the Euclidean
action. Similar to standard inflation, black holes are abundantly produced near
the Planck boundary, but highly suppressed later on. An unusual feature we find
is that the earlier in inflation that the dilatonic black holes are created,
the more highly charged they can be.Comment: 23 pages, LaTeX, 6 figures; submitted to Phys. Rev.
On the frequency dependence of p-mode frequency shifts induced by magnetic activity in Kepler solar-like stars
The variations of the frequencies of the low-degree acoustic oscillations in
the Sun induced by magnetic activity show a dependence with radial order. The
frequency shifts are observed to increase towards higher-order modes to reach a
maximum of about 0.8 muHz over the 11-yr solar cycle. A comparable frequency
dependence is also measured in two other main-sequence solar-like stars, the
F-star HD49933, and the young 1-Gyr-old solar analog KIC10644253, although with
different amplitudes of the shifts of about 2 muHz and 0.5 muHz respectively.
Our objective here is to extend this analysis to stars with different masses,
metallicities, and evolutionary stages. From an initial set of 87 Kepler
solar-like oscillating stars with already known individual p-mode frequencies,
we identify five stars showing frequency shifts that can be considered reliable
using selection criteria based on Monte Carlo simulations and on the
photospheric magnetic activity proxy Sph. The frequency dependence of the
frequency shifts of four of these stars could be measured for the l=0 and l=1
modes individually. Given the quality of the data, the results could indicate
that a different physical source of perturbation than in the Sun is dominating
in this sample of solar-like stars.Comment: Accepted for publication in A&
A model for conservative chaos constructed from multi-component Bose-Einstein condensates with a trap in 2 dimensions
To show a mechanism leading to the breakdown of a particle picture for the
multi-component Bose-Einstein condensates(BECs) with a harmonic trap in high
dimensions, we investigate the corresponding 2- nonlinear Schr{\"o}dinger
equation (Gross-Pitaevskii equation) with use of a modified variational
principle. A molecule of two identical Gaussian wavepackets has two degrees of
freedom(DFs), the separation of center-of-masses and the wavepacket width.
Without the inter-component interaction(ICI) these DFs show independent regular
oscillations with the degenerate eigen-frequencies. The inclusion of ICI
strongly mixes these DFs, generating a fat mode that breaks a particle picture,
which however can be recovered by introducing a time-periodic ICI with zero
average. In case of the molecule of three wavepackets for a three-component
BEC, the increase of amplitude of ICI yields a transition from regular to
chaotic oscillations in the wavepacket breathing.Comment: 5 pages, 4 figure
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