181 research outputs found
Complex asteroseismology of the Slowly Pulsating B-type star HD74560
We present the results of complex seismic modelling of the Slowly Pulsating
B-type star HD74560. The star pulsates in five frequencies detected in
photometric observations. For all these frequencies, we identify the mode
degree, . For two of them, found also in spectroscopic data, we are able
to derived the empirical values of the complex nonadiabatic parameter . We
test effects of chemical composition and opacity data. Our results show that
the properties of seismic models of SPB stars differ significantly from those
of the more massive Cephei stars.Comment: 4 pages, 2 figures, conference proceedings, to appear in ASS
Effect of freezer storage on quality of M. longissimus lumborum from fallow deer (Dama dama L.)
The aim of this study was to analyse changes in the quality of meat (M. longissimus lumborum) from 11 fallow deer (Dama dama L.) bucks, which had been deep-frozen (-26 °C) for 10 months. The proximate chemical composition, physico-chemical properties and sensory properties of the meat were analysed. Fallow deer aged 17–18 months were hunter-harvested in north-eastern Poland in November and December of the same hunting season. The results revealed that freezer storage did not influence the proximate chemical composition of meat (protein, fat, ash) or the content of water-soluble nitrogen compounds. An analysis of the physico-chemical properties of meat revealed that long-term freezer-stored meat was characterized by higher pH, lower contribution of redness (a*) and yellowness (b*), lower chroma (C*), greater natural drip loss, lower ability to bind added water, and greater cooking loss. Freezer storage improved meat tenderness but reduced meat juiciness. The results of the study also indicated that long-term freezer storage (-26 °C) of vacuum-packaged meat allowed it to maintain its good quality, which indicates that this storage method could help meet consumer demand for fallow deer meat between hunting seasons.Keywords: Freezing, game meat, meat quality, vacuum packagin
An asteroseismic study of the Beta Cephei star Theta Ophiuchi: photometric results
We have carried out a three-site photometric campaign for the Beta Cephei
star Theta Ophiuchi from April to August 2003. 245 hours of differential
photoelectric uvy photometry were obtained during 77 clear nights. The
frequency analysis of our measurements resulted in the detection of seven
pulsation modes within a narrow frequency interval between 7.116 and 7.973 c/d.
No combination or harmonic frequencies were found. We performed a mode
identification of the individual pulsations from our colour photometry that
shows the presence of one radial mode, one rotationally split l=1 triplet and
possibly three components of a rotationally split l=2 quintuplet. We discuss
the implications of our findings and point out the similarity of the pulsation
spectrum of Theta Ophiuchi to that of another Beta Cephei star, V836 Cen.Comment: 8 pages, 6 figure
Algebraic approach to quantum field theory on a class of noncommutative curved spacetimes
In this article we study the quantization of a free real scalar field on a
class of noncommutative manifolds, obtained via formal deformation quantization
using triangular Drinfel'd twists. We construct deformed quadratic action
functionals and compute the corresponding equation of motion operators. The
Green's operators and the fundamental solution of the deformed equation of
motion are obtained in terms of formal power series. It is shown that, using
the deformed fundamental solution, we can define deformed *-algebras of field
observables, which in general depend on the spacetime deformation parameter.
This dependence is absent in the special case of Killing deformations, which
include in particular the Moyal-Weyl deformation of the Minkowski spacetime.Comment: LaTeX 14 pages, no figures, svjour3.cls style; v2: clarifications and
references added, compatible with published versio
Constraining the properties of delta Scuti stars using spectroscopic eclipsing binary systems
Many stars exhibit stellar pulsations, favoring them for asteroseismic
analyses. Interpreting the oscillations requires some knowledge of the
oscillation mode geometry (spherical degree, radial and azimuthal orders). The
delta Scuti stars (1.5 - 2.5 M_sol) often show just one or few pulsation
frequencies. Although this may promise a successful seismological analysis, we
may not know enough about either the mode or the star to use the oscillation
frequency to improve the determination of the stellar model, or probe the
star's structure. For the observed frequencies to be used successfully as
seismic probes of these objects, we need to concentrate on stars for which we
can reduce the number of free parameters in the problem, such as binary systems
or open clusters. We investigate how much our understanding of a delta Scuti
star is improved when it is in a detached eclipsing binary system instead of
being a single field star. We use singular value decomposition to explore the
precision we expect in stellar parameters (mass, age and chemical composition)
for both cases. We examine how the parameter uncertainties propagate to the
luminosity - effective temperature diagram and determine when the effort of
obtaining a new measurement is justified. We show that for the single star, a
correct identification of the oscillation mode is necessary to produce strong
constraints on the stellar model properties, while for the binary system the
observations without the pulsation mode provide the same or better constraints
on the stellar parameters. In the latter case, ...Comment: emulateapj 16 pages, accepted Ap
Asteroseismology of the Beta Cephei star 12 (DD) Lacertae: photometric observations, pulsational frequency analysis and mode identification
We report a multisite photometric campaign for the Beta Cephei star 12
Lacertae. 750 hours of high-quality differential photoelectric Stromgren,
Johnson and Geneva time-series photometry were obtained with 9 telescopes
during 190 nights. Our frequency analysis results in the detection of 23
sinusoidal signals in the light curves. Eleven of those correspond to
independent pulsation modes, and the remainder are combination frequencies. We
find some slow aperiodic variability such as that seemingly present in several
Beta Cephei stars. We perform mode identification from our colour photometry,
derive the spherical degree l for the five strongest modes unambiguously and
provide constraints on l for the weaker modes. We find a mixture of modes of 0
<= l <= 4. In particular, we prove that the previously suspected rotationally
split triplet within the modes of 12 Lac consists of modes of different l;
their equal frequency splitting must thus be accidental.
One of the periodic signals we detected in the light curves is argued to be a
linearly stable mode excited to visible amplitude by nonlinear mode coupling
via a 2:1 resonance. We also find a low-frequency signal in the light
variations whose physical nature is unclear; it could be a parent or daughter
mode resonantly coupled. The remaining combination frequencies are consistent
with simple light-curve distortions.
The range of excited pulsation frequencies of 12 Lac may be sufficiently
large that it cannot be reproduced by standard models. We suspect that the star
has a larger metal abundance in the pulsational driving zone, a hypothesis also
capable of explaining the presence of Beta Cephei stars in the LMC.Comment: 12 pages, 7 figures, MNRAS, in pres
A multisite photometric study of two unusual Beta Cep stars: the magnetic V2052 Oph and the massive rapid rotator V986 Oph
We report a multisite photometric campaign for the Beta Cep stars V2052 Oph
and V986 Oph. 670 hours of high-quality differential photoelectric Stromgren,
Johnson and Geneva time-series photometry were obtained with eight telescopes
on five continents during 182 nights. Frequency analyses of the V2052 Oph data
enabled the detection of three pulsation frequencies, the first harmonic of the
strongest signal, and the rotation frequency with its first harmonic.
Pulsational mode identification from analysing the colour amplitude ratios
confirms the dominant mode as being radial, whereas the other two oscillations
are most likely l=4. Combining seismic constraints on the inclination of the
rotation axis with published magnetic field analyses we conclude that the
radial mode must be the fundamental. The rotational light modulation is in
phase with published spectroscopic variability, and consistent with an oblique
rotator for which both magnetic poles pass through the line of sight. The
inclination of the rotation axis is 54o <i< 58o and the magnetic obliquity 58o
<beta< 66o. The possibility that V2052 Oph has a magnetically confined wind is
discussed. The photometric amplitudes of the single oscillation of V986 Oph are
most consistent with an l=3 mode, but this identification is uncertain.
Additional intrinsic, apparently temporally incoherent, light variations of
V986 Oph are reported. Different interpretations thereof cannot be
distinguished at this point, but this kind of variability appears to be present
in many OB stars. The prospects of obtaining asteroseismic information for more
rapidly rotating Beta Cep stars, which appear to prefer modes of higher l, are
briefly discussed.Comment: 12 pages, 8 figures, MNRAS, in pres
Testing the effects of opacity and the chemical mixture on the excitation of pulsations in B stars of the Magellanic Clouds
The B-type pulsators known as \beta Cephei and Slowly Pulsating B (SPB) stars
present pulsations driven by the \kappa mechanism, which operates thanks to an
opacity bump due to the iron group elements. In low-metallicity environments
such as the Magellanic Clouds, \beta Cep and SPB pulsations are not expected.
Nevertheless, recent observations show evidence for the presence of B-type
pulsator candidates in both galaxies. We seek an explanation for the excitation
of \beta Cep and SPB modes in those galaxies by examining basic input physics
in stellar modelling: i) the specific metal mixture of B-type stars in the
Magellanic Clouds; ii) the role of a potential underestimation of stellar
opacities. We first derive the present-day chemical mixtures of B-type stars in
the Magellanic Clouds. Then, we compute stellar models for that metal mixture
and perform a non-adiabatic analysis of these models. In a second approach, we
simulate parametric enhancements of stellar opacities due to different iron
group elements. We then study their effects in models of B stars and their
stability. We find that adopting a representative chemical mixture of B stars
in the Small Magellanic Cloud cannot explain the presence of B-type pulsators
there. An increase of the opacity in the region of the iron-group bump could
drive B-type pulsations, but only if this increase occurs at the temperature
corresponding to the maximum contribution of Ni to this opacity bump. We
recommend an accurate computation of Ni opacity to understand B-type pulsators
in the Small Magellanic Cloud, as well as the frequency domain observed in some
Galactic hybrid \beta Cep-SPB stars.Comment: 16 pages, 12 figures. Accepted for publication in MNRA
The 2003-4 multisite photometric campaign for the Beta Cephei and eclipsing star 16 (EN) Lacertae with an Appendix on 2 Andromedae, the variable comparison star
A multisite photometric campaign for the Beta Cephei and eclipsing variable
16 Lacertae is reported. 749 h of high-quality differential photoelectric
Stromgren, Johnson and Geneva time-series photometry were obtained with ten
telescopes during 185 nights. After removing the pulsation contribution, an
attempt was made to solve the resulting eclipse light curve by means of the
computer program EBOP. Although a unique solution was not obtained, the range
of solutions could be constrained by comparing computed positions of the
secondary component in the Hertzsprung-Russell diagram with evolutionary
tracks.
For three high-amplitude pulsation modes, the uvy and the Geneva UBG
amplitude ratios are derived and compared with the theoretical ones for
spherical-harmonic degrees l <= 4. The highest degree, l = 4, is shown to be
incompatible with the observations. One mode is found to be radial, one is l =
1, while in the remaining case l = 2 or 3.
The present multisite observations are combined with the archival photometry
in order to investigate the long-term variation of the amplitudes and phases of
the three high-amplitude pulsation modes. The radial mode shows a
non-sinusoidal variation on a time-scale of 73 yr. The l = 1 mode is a triplet
with unequal frequency spacing, giving rise to two beat-periods, 720.7 d and
29.1 yr. The amplitude and phase of the l = 2 or 3 mode vary on time-scales of
380.5 d and 43 yr.
The light variation of 2 And, one of the comparison stars, is discussed in
the Appendix.Comment: 18 pages, 19 figures, accepted for publication in MNRA
UVSat: a concept of an ultraviolet/optical photometric satellite
Time-series photometry from space in the ultraviolet can be presently done
with only a few platforms, none of which is able to provide wide-field
long-term high-cadence photometry. We present a concept of UVSat, a twin space
telescope which will be capable to perform this kind of photometry, filling an
observational niche. The satellite will host two telescopes, one for
observations in the ultraviolet, the other for observations in the optical
band. We also briefly show what science can be done with UVSat.Comment: 6 pages, 2 figures, accepted for publication in the Proceedings of
the PAS (Proc. of the 2nd BRITE Science conference, Innsbruck
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