4,217 research outputs found
Clasts in the CM2 carbonaceous chondrite Lonewolf Nunataks 94101: evidence for aqueous alteration prior to complex mixing
Clasts in the CM2 carbonaceous chondrite Lonewolf Nunataks (LON) 94101 have been characterized using scanning and transmission electron microscopy and electron microprobe analysis to determine their degrees of aqueous alteration, and the timing of alteration relative to incorporation of clasts into the host. The provenance of the clasts, and the mechanism by which they were incorporated and mixed with their host material are also considered. Results show that at least five distinct types of clasts occur in LON 94101, of which four have been aqueously altered to various degrees and one is largely anhydrous. The fact that they have had different alteration histories implies that the main part of aqueous activity occurred prior to the mixing and assimilation of the clasts with their host. Further, the presence of such a variety of clasts suggests complex mixing in a dynamic environment involving material from various sources. Two of the clasts, one containing approximately 46 vol% carbonate and the other featuring crystals of pyrrhotite up to approximately 1 mm in size, are examples of unusual lithologies and indicate concentration of chemical elements in discrete areas of the parent body(ies), possibly by flow of aqueous solutions
New chemical profiles for the asteroseismology of ZZ Ceti stars
We compute new chemical profiles for the core and envelope of white dwarfs
appropriate for pulsational studies of ZZ Ceti stars. These profiles are
extracted from the complete evolution of progenitor stars, evolved through the
main sequence and the thermally-pulsing asymptotic giant branch (AGB) stages,
and from time-dependent element diffusion during white dwarf evolution. We
discuss the importance of the initial-final mass relationship for the white
dwarf carbon-oxygen composition. In particular, we find that the central oxygen
abundance may be underestimated by about 15% if the white dwarf mass is assumed
to be the hydrogen-free core mass before the first thermal pulse. We also
discuss the importance for the chemical profiles expected in the outermost
layers of ZZ Ceti stars of the computation of the thermally-pulsing AGB phase
and of the phase in which element diffusion is relevant. We find a strong
dependence of the outer layer chemical stratification on the stellar mass. In
particular, in the less massive models, the double-layered structure in the
helium layer built up during the thermally-pulsing AGB phase is not removed by
diffusion by the time the ZZ Ceti stage is reached. Finally, we perform
adiabatic pulsation calculations and discuss the implications of our new
chemical profiles for the pulsational properties of ZZ Ceti stars. We find that
the whole mode period spectrum and the mode-trapping properties of these
pulsating white dwarfs as derived from our new chemical profiles are
substantially different from those based on chemical profiles widely used in
existing asteroseismological studies. Thus, we expect the asteroseismological
models derived from our chemical profiles to be significantly different from
those found thus far.Comment: 12 pages, 11 figures, 1 table. To be published in Ap
Short-term emission line and continuum variations in Mrk110
We present results of a variability campaign of Mrk110 performed with the
9.2-m Hobby-Eberly Telescope (HET) at McDonald Observatory. The high S/N
spectra cover most of the optical range. They were taken from 1999 November
through 2000 May. The average interval between the observations was 7.3 days
and the median interval was only 3.0 days. Mrk110 is a narrow-line Seyfert 1
galaxy. During our campaign the continuum flux was in a historically low stage.
Considering the delays of the emission lines with respect to the continuum
variations we could verify an ionization stratification of the BLR. We derived
virial masses of the central black hole from the radial distances of the
different emission lines and from their widths. The calculated central masses
agree within 20%. Furthermore, we identified optical HeI singlet emission lines
emitted in the broad-line region. The observed line fluxes agree with
theoretical predictions. We show that a broad wing on the red side of the
[OIII]5007 line is caused by the HeI singlet line at 5016A.Comment: 11 pages, 16 figures, A&A Latex. Accepted for publication in A&A Main
Journa
Asteroseismology of the Kepler V777 Her variable white dwarf with fully evolutionary models
DBV stars are pulsating white dwarfs with atmospheres rich in He.
Asteroseismology of DBV stars can provide valuable clues about the origin,
structure and evolution of hydrogen-deficient white dwarfs, and may allow to
study neutrino and axion physics. Recently, a new DBV star, KIC 8626021, has
been discovered in the field of the \emph{Kepler} spacecraft. It is expected
that further monitoring of this star in the next years will enable astronomers
to determine its detailed asteroseismic profile. We perform an
asteroseismological analysis of KIC 8626021 on the basis of fully evolutionary
DB white-dwarf models. We employ a complete set of evolutionary DB white-dwarf
structures covering a wide range of effective temperatures and stellar masses.
They have been obtained on the basis of a complete treatment of the
evolutionary history of progenitors stars. We compute g-mode adiabatic
pulsation periods for this set of models and compare them with the pulsation
properties exhibited by KIC 8626021. On the basis of the mean period spacing of
the star, we found that the stellar mass should be substantially larger than
spectroscopy indicates. From period-to-period fits we found an
asteroseismological model characterized by an effective temperature much higher
than the spectroscopic estimate. In agreement with a recent asteroseismological
analysis of this star by other authors, we conclude that KIC 8626021 is located
near the blue edge of the DBV instability strip, contrarily to spectroscopic
predictions. We also conclude that the mass of KIC 8626021 should be
substantially larger than thought.Comment: 7 pages, 5 figures, 3 tables. To be published in Astronomy and
Astrophysic
New methods in conformal partial wave analysis
We report on progress concerning the partial wave analysis of higher
correlation functions in conformal quantum field theory.Comment: 16 page
The rate of cooling of the pulsating white dwarf star G117B15A: a new asteroseismological inference of the axion mass
We employ a state-of-the-art asteroseismological model of G117-B15A, the
archetype of the H-rich atmosphere (DA) white dwarf pulsators (also known as
DAV or ZZ Ceti variables), and use the most recently measured value of the rate
of period change for the dominant mode of this pulsating star to derive a new
constraint on the mass of axion, the still conjectural non-barionic particle
considered as candidate for dark matter of the Universe. Assuming that
G117-B15A is truly represented by our asteroseismological model, and in
particular, that the period of the dominant mode is associated to a pulsation
g-mode trapped in the H envelope, we find strong indications of the existence
of extra cooling in this star, compatible with emission of axions of mass m_a
\cos^2 \beta = 17.4^{+2.3}_{-2.7} meV.Comment: 9 pages, 5 figures and 3 tables. Accepted for publication in MNRA
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