449 research outputs found
Weinberg propagator of a free massive particle with an arbitrary spin from the BFV-BRST path integral
The transition amplitude is obtained for a free massive particle of arbitrary
spin by calculating the path integral in the index-spinor formulation within
the BFV-BRST approach. None renormalizations of the path integral measure were
applied. The calculation has given the Weinberg propagator written in the
index-free form with the use of index spinor. The choice of boundary conditions
on the index spinor determines holomorphic or antiholomorphic representation
for the canonical description of particle/antiparticle spin.Comment: 31 pages, Latex, version published in Class. Quantum Gra
An asteroseismic study of the beta Cephei star 12 Lacertae: multisite spectroscopic observations, mode identification and seismic modelling
We present the results of a spectroscopic multisite campaign for the beta
Cephei star 12 (DD) Lacertae. Our study is based on more than thousand
high-resolution high S/N spectra gathered with 8 different telescopes in a time
span of 11 months. In addition we make use of numerous archival spectroscopic
measurements. We confirm 10 independent frequencies recently discovered from
photometry, as well as harmonics and combination frequencies. In particular,
the SPB-like g-mode with frequency 0.3428 1/d reported before is detected in
our spectroscopy. We identify the four main modes as (l1,m1) = (1, 1), (l2,m2)
= (0, 0), (l3,m3) = (1, 0) and (l4,m4) = (2, 1) for f1 = 5.178964 1/d, f2 =
5.334224 1/d, f3 = 5.066316 1/d and f4 = 5.490133 1/d, respectively. Our
seismic modelling shows that f2 is likely the radial first overtone and that
the core overshooting parameter alpha_ov is lower than 0.4 local pressure scale
heights.Comment: 16 pages, 11 figures, accepted in MNRA
Fault Tolerance Middleware for a Multi-Core System
Fault Tolerance Middleware (FTM) provides a framework to run on a dedicated core of a multi-core system and handles detection of single-event upsets (SEUs), and the responses to those SEUs, occurring in an application running on multiple cores of the processor. This software was written expressly for a multi-core system and can support different kinds of fault strategies, such as introspection, algorithm-based fault tolerance (ABFT), and triple modular redundancy (TMR). It focuses on providing fault tolerance for the application code, and represents the first step in a plan to eventually include fault tolerance in message passing and the FTM itself. In the multi-core system, the FTM resides on a single, dedicated core, separate from the cores used by the application. This is done in order to isolate the FTM from application faults and to allow it to swap out any application core for a substitute. The structure of the FTM consists of an interface to a fault tolerant strategy module, a responder module, a fault manager module, an error factory, and an error mapper that determines the severity of the error. In the present reference implementation, the only fault tolerant strategy implemented is introspection. The introspection code waits for an application node to send an error notification to it. It then uses the error factory to create an error object, and at this time, a severity level is assigned to the error. The introspection code uses its built-in knowledge base to generate a recommended response to the error. Responses might include ignoring the error, logging it, rolling back the application to a previously saved checkpoint, swapping in a new node to replace a bad one, or restarting the application. The original error and recommended response are passed to the top-level fault manager module, which invokes the response. The responder module also notifies the introspection module of the generated response. This provides additional information to the introspection module that it can use in generating its next response. For example, if the responder triggers an application rollback and errors are still occurring, the introspection module may decide to recommend an application restart
PHOEBE 2.0 – Where no model has gone before
phoebe 2.0 is an open source framework bridging the gap between stellar observations and models. It allows to create and fit models simultaneously and consistently to a wide range of observational data such as photometry, spectroscopy, spectrapolarimetry, interferometry and astrometry. To reach the level of precision required by the newest generation of instruments such as Kepler, GAIA and the arrays of large telescopes, the code is set up to handle a wide range of phenomena such as multiplicity, rotation, pulsations and magnetic fields, and to model the involved physics to a new level
Asteroseismology with the WIRE satellite. I. Combining Ground- and Space-based Photometry of the Delta Scuti Star Epsilon Cephei
We have analysed ground-based multi-colour Stromgren photometry and
single-filter photometry from the star tracker on the WIRE satellite of the
delta scuti star Epsilon Cephei. The ground-based data set consists of 16
nights of data collected over 164 days, while the satellite data are nearly
continuous coverage of the star during 14 days. The spectral window and noise
level of the satellite data are superior to the ground-based data and this data
set is used to locate the frequencies. However, we can use the ground-based
data to improve the accuracy of the frequencies due to the much longer time
baseline. We detect 26 oscillation frequencies in the WIRE data set, but only
some of these can be seen clearly in the ground-based data. We have used the
multi-colour ground-based photometry to determine amplitude and phase
differences in the Stromgren b-y colour and the y filter in an attempt to
identify the radial degree of the oscillation frequencies. We conclude that the
accuracies of the amplitudes and phases are not sufficient to constrain
theoretical models of Epsilon Cephei. We find no evidence for rotational
splitting or the large separation among the frequencies detected in the WIRE
data set. To be able to identify oscillation frequencies in delta scuti stars
with the method we have applied, it is crucial to obtain more complete coverage
from multi-site campaigns with a long time baseline and in multiple filters.
This is important when planning photometric and spectroscopic ground-based
support for future satellite missions like COROT and KEPLER.Comment: 13 pages, 12 figures, 4 tables. Fig. 4 reduced in quality. Accepted
by A&
An asteroseismic study of the Delta Scuti star 44 Tau
In this paper we investigate theoretical pulsation models for the delta Scuti
star 44 Tau. The star was monitored during several multisite campaigns which
confirmed the presence of radial and nonradial oscillations. Moreover, its
exceptionally low rotational velocity makes 44 Tau particulary interesting for
an asteroseismic study. Due to the measured log g value of 3.6 +/- 0.1, main
sequence and post-main sequence models have to be considered. We perform mode
identification based on photometric and spectroscopic data. A nonadiabatic
pulsation code is used to compute models that fit the identified modes. The
influence of different opacity tables and element mixtures on the results is
tested. The observed frequencies of 44 Tau can be fitted in both the main
sequence and the post-main sequence evolutionary stage. Post-main sequence
models are preferable as they fulfill almost all observational constraints (fit
of observed frequencies, position in the HRD and instability range). These
models can be obtained with normal chemical composition which is in agreement
with recent spectroscopic measurements. The efficiency of envelope convection
(in the framework of the mixing-length theory) is predicted to be very low in
44 Tau. We show that the results are sensitive to the choice between the OPAL
and OP opacities. While the pulsation models of 44 Tau computed with OP
opacities are considerably too cool and too faint, the use of OPAL opacities
results in models within the expected temperature and luminosity range.Comment: 9 pages, 15 figures, 2 tables, accepted for publication in A&
Close-up of primary and secondary asteroseismic CoRoT targets and the ground-based follow-up observations
To optimise the science results of the asteroseismic part of the CoRoT
satellite mission a complementary simultaneous ground-based observational
campaign is organised for selected CoRoT targets. The observations include both
high-resolution spectroscopic and multi-colour photometric data. We present the
preliminary results of the analysis of the ground-based observations of three
targets. A line-profile analysis of 216 high-resolution FEROS spectra of the
delta Sct star HD 50844 reveals more than ten pulsation frequencies in the
frequency range 5-18 c/d, including possibly one radial fundamental mode (6.92
c/d). Based on more than 600 multi-colour photometric datapoints of the beta
Cep star HD180642, spanning about three years and obtained with different
telescopes and different instruments, we confirm the presence of a dominant
radial mode nu1=5.48695 c/d, and detect also its first two harmonics. We find
evidence for a second mode nu2=0.3017 c/d, possibly a g-mode, and indications
for two more frequencies in the 7-8 c/d domain. From Stromgren photometry we
find evidence for the hybrid delta Sct/gamma Dor character of the F0 star HD
44195, as frequencies near 3 c/d and 21 c/d are detected simultaneously in the
different filters.Comment: 7 pages, 6 figures, HELAS II International Conference
"Helioseismology, Asteroseismology and MHD Connections", 2008, J.Phys.: Conf.
Ser. 118, 01207
Ground-based observations of the beta Cephei CoRoT main target HD 180642: abundance analysis and mode identification
The known beta Cephei star HD 180642 was observed by the CoRoT satellite in
2007. From the very high-precision light curve, its pulsation frequency
spectrum could be derived for the first time (Degroote and collaborators). In
this paper, we obtain additional constraints for forthcoming asteroseismic
modeling of the target. Our results are based on both extensive ground-based
multicolour photometry and high-resolution spectroscopy. We determine T_eff =
24 500+-1000 K and log g = 3.45+-0.15 dex from spectroscopy. The derived
chemical abundances are consistent with those for B stars in the solar
neighbourhood, except for a mild nitrogen excess. A metallicity Z =
0.0099+-0.0016 is obtained. Three modes are detected in photometry. The degree
l is unambiguously identified for two of them: l = 0 and l = 3 for the
frequencies 5.48694 1/d and 0.30818 1/d, respectively. The radial mode is
non-linear and highly dominant with an amplitude in the U-filter about 15 times
larger than the strongest of the other modes. For the third frequency of
7.36673 1/d found in photometry, two possibilities remain: l = 0 or 3. In the
radial velocities, the dominant radial mode presents a so-called stillstand but
no clear evidence of the existence of shocks is observed. Four low-amplitude
modes are found in spectroscopy and one of them, with frequency 8.4079 1/d, is
identified as (l,m)=(3,2). Based on this mode identification, we finally deduce
an equatorial rotational velocity of 38+-15 km/s.Comment: Accepted for publication in Astronomy and Astrophysic
- …