955 research outputs found
The CoRoT B-type binary HD50230: a prototypical hybrid pulsator with g-mode period and p-mode frequency spacings
B-type stars are promising targets for asteroseismic modelling, since their
frequency spectrum is relatively simple.
We deduce and summarise observational constraints for the hybrid pulsator,
HD50230, earlier reported to have deviations from a uniform period spacing of
its gravity modes. The combination of spectra and a high-quality light curve
measured by the CoRoT satellite allow a combined approach to fix the position
of HD50230 in the HR diagram.
To describe the observed pulsations, classical Fourier analysis was combined
with short-time Fourier transformations and frequency spacing analysis
techniques. Visual spectra were used to constrain the projected rotation rate
of the star and the fundamental parameters of the target. In a first
approximation, the combined information was used to interpret multiplets and
spacings to infer the true surface rotation rate and a rough estimate of the
inclination angle.
We identify HD50230 as a spectroscopic binary and characterise the two
components. We detect the simultaneous presence of high-order g modes and
low-order p and g-modes in the CoRoT light curve, but were unable to link them
to line profile variations in the spectroscopic time series. We extract the
relevant information from the frequency spectrum, which can be used for seismic
modelling, and explore possible interpretations of the pressure mode spectrum.Comment: 26 pages, 12+6 figures, accepted for publication in Astronomy and
Astrophysic
Non-radial oscillations in the red giant HR7349 measured by CoRoT
Convection in red giant stars excites resonant acoustic waves whose
frequencies depend on the sound speed inside the star, which in turn depends on
the properties of the stellar interior. Therefore, asteroseismology is the most
robust available method for probing the internal structure of red giant stars.
Solar-like oscillations in the red giant HR7349 are investigated. Our study is
based on a time series of 380760 photometric measurements spread over 5 months
obtained with the CoRoT satellite. Mode parameters were estimated using maximum
likelihood estimation of the power spectrum. The power spectrum of the
high-precision time series clearly exhibits several identifiable peaks between
19 and 40 uHz showing regularity with a mean large and small spacing of Dnu =
3.47+-0.12 uHz and dnu_02 = 0.65+-0.10 uHz. Nineteen individual modes are
identified with amplitudes in the range from 35 to 115 ppm. The mode damping
time is estimated to be 14.7+4.7-2.9 days.Comment: 8 pages, A&A accepte
Models of red giants in the CoRoT asteroseismology fields combining asteroseismic and spectroscopic constraints
Context. The availability of asteroseismic constraints for a large sample of
red giant stars from the CoRoT and Kepler missions paves the way for various
statistical studies of the seismic properties of stellar populations.
Aims. We use the first detailed spectroscopic study of 19 CoRoT red-giant
stars (Morel et al 2014) to compare theoretical stellar evolution models to
observations of the open cluster NGC 6633 and field stars.
Methods. In order to explore the effects of rotation-induced mixing and
thermohaline instability, we compare surface abundances of carbon isotopic
ratio and lithium with stellar evolution predictions. These chemicals are
sensitive to extra-mixing on the red-giant branch.
Results. We estimate mass, radius, and distance for each star using the
seismic constraints. We note that the Hipparcos and seismic distances are
different. However, the uncertainties are such that this may not be
significant. Although the seismic distances for the cluster members are self
consistent they are somewhat larger than the Hipparcos distance. This is an
issue that should be considered elsewhere. Models including thermohaline
instability and rotation-induced mixing, together with the seismically
determined masses can explain the chemical properties of red-giants targets.
However, with this sample of stars we cannot perform stringent tests of the
current stellar models. Tighter constraints on the physics of the models would
require the measurement of the core and surface rotation rates, and of the
period spacing of gravity-dominated mixed modes. A larger number of stars with
longer times series, as provided by Kepler or expected with Plato, would help
for ensemble asteroseismology.Comment: Accepted 03/05/201
Statistical Properties of Charmonium Spectrum and a New Mechanism of J/\psi Suppression
The statistical properties of Charmonium energy spectrum determined by the
Bethe-Salpeter equation are investigated. It is found that the regular motion
of the system can be expected at a small value of color screening
mass but the chaotic motion at a large one. It is shown that the level mixing
due to color screening serves as a new mechanism resulting in the J/
suppression. Moreover, this kind of suppression can occur before the color
screening mass reaches its critical value for J/ dissociation. It implies
that a strong J/ suppression is possible in the absence of dissociation
of J/.Comment: 13 latex pages, 2 figures. Phys. Rev. C in pres
Characteristics of solar-like oscillations in red giants observed in the CoRoT exoplanet field
Observations during the first long run (~150 days) in the exo-planet field of
CoRoT increase the number of G-K giant stars for which solar-like oscillations
are observed by a factor of 100. This opens the possibility to study the
characteristics of their oscillations in a statistical sense. We aim to
understand the statistical distribution of the frequencies of maximum
oscillation power (nu_max) in red giants and to search for a possible
correlation between nu_max and the large separation (delta_nu). The nu_max
distribution shows a pronounced peak between 20 - 40 microHz. For about half of
the stars we obtain delta_nu with at least two methods. The correlation between
nu_max and delta_nu follows the same scaling relation as inferred for
solar-like stars. The shape of the nu_max distribution can partly be explained
by granulation at low frequencies and by white noise at high frequencies, but
the population density of the observed stars turns out to be also an important
factor. From the fact that the correlation between delta_nu and nu_max for red
giants follows the same scaling relation as obtained for sun-like stars, we
conclude that the sound travel time over the pressure scale height of the
atmosphere scales with the sound travel time through the whole star
irrespective of evolution.Comment: Accepted for publication in Astronomy and Astrophysics (CoRoT special
issue), 5 pages, 7 figures and 1 tabl
Thermal Hadron Production in High Energy Heavy Ion Collisions
We provide a method to test if hadrons produced in high energy heavy ion
collisions were emitted at freeze-out from an equilibrium hadron gas. Our
considerations are based on an ideal gas at fixed temperature , baryon
number density , and vanishing total strangeness. The constituents of this
gas are all hadron resonances up to a mass of 2 GeV; they are taken to decay
according to the experimentally observed branching ratios. The ratios of the
various resulting hadron production rates are tabulated as functions of
and . These tables can be used for the equilibration analysis of any heavy
ion data; we illustrate this for some specific cases.Comment: 12 pages (not included :13 figures + tables) report CERN-TH 6523/92
and Bielefeld preprint BI-TP 92/0
Periodic mass loss episodes due to an oscillation mode with variable amplitude in the hot supergiant HD50064
We aim to interpret the photometric and spectroscopic variability of the
luminous blue variable supergiant HD\,50064 ().CoRoT space photometry
and follow-up high-resolution spectroscopy, with a time base of 137\,d and
169\,d, respectively, was gathered, analysed and interpreted using standard
time series analysis and light curve modelling methods as well as spectral line
diagnostics.The space photometry reveals one period of 37\,d, which undergoes a
sudden amplitude change with a factor 1.6. The pulsation period is confirmed in
the spectroscopy, which additionally reveals metal line radial velocity values
differing by km\,s depending on the spectral line and on the
epoch. We estimate \teff13\,500\,K, \logg1.5 from the equivalent
width of Si lines. The Balmer lines reveal that the star undergoes episodes of
changing mass loss on a time scale similar to the changes in the photometric
and spectroscopic variability, with an average value of (in M\,yr). We tentatively interpret the 37\,d
period as due to a strange mode oscillation.Comment: 4 pages, accepted for publication in Astronomy & Astrophysics Letter
Modelling J/psi production and absorption in a microscopic nonequilibrium approach
Charmonium production and absorption in heavy ion collisions is studied with
the Ultrarelativisitic Quantum Molecular Dynamics model. We compare the
scenario of universal and time independent color-octet dissociation cross
sections with one of distinct color-singlet J/psi, psi' and chi_c states,
evolving from small, color transparent configurations to their asymptotic
sizes. The measured J/psi production cross sections in pA and AB collisions at
SPS energies are consistent with both - purely hadronic - scenarios. The
predicted rapidity dependence of J/psi suppression can be used to discriminate
between the two experimentally. The importance of interactions with secondary
hadrons and the applicability of thermal reaction kinetics to J/psi absorption
are investigated. We discuss the effect of nuclear stopping and the role of
leading hadrons. The dependence of the psi' to J/psi ratio on the model
assumptions and the possible influence of refeeding processes is also studied.Comment: 35 pages, 16 figure
Antimatter and Matter Production in Heavy Ion Collisions at CERN (The NEWMASS Experiment NA52)
Besides the dedicated search for strangelets NA52 measures light
(anti)particle and (anti)nuclei production over a wide range of rapidity.
Compared to previous runs the statistics has been increased in the 1998 run by
more than one order of magnitude for negatively charged objects at different
spectrometer rigidities. Together with previous data taking at a rigidity of
-20 GeV/c we obtained 10^6 antiprotons 10^3 antideuterons and two antihelium3
without centrality requirements. We measured nuclei and antinuclei
(p,d,antiprotons, antideuterons) near midrapidity covering an impact parameter
range of b=2-12 fm. Our results strongly indicate that nuclei and antinuclei
are mainly produced via the coalescence mechanism. However the centrality
dependence of the antibaryon to baryon ratios show that antibaryons are
diminished due to annihilation and breakup reactions in the hadron dense
environment. The volume of the particle source extracted from coalescence
models agrees with results from pion interferometry for an expanding source.
The chemical and thermal freeze-out of nuclei and antinuclei appear to coincide
with each other and with the thermal freeze-out of hadrons.Comment: 12 pages, 8 figures, to appear in the proceedings of the conference
on 'Fundamental Issues in Elementary Matter' Bad Honnef, Germany, Sept.
25-29, 200
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