2,159 research outputs found
Asteroseismology of the GW Virginis stars SDSS J0349-0059 and VV 47
We present an asteroseismological study of SDSS J0349-0059 and VV 47 aimed
mainly at deriving their total mass on the basis of state-of-the-art PG 1159
evolutionary models. We compute adiabatic nonradial -mode pulsation periods
for PG 1159 evolutionary models with stellar masses ranging from to
0.741\ M_{\sun}, that take into account the complete evolution of the
progenitor stars. We first estimate a mean period spacing for both SDSS
J0349-0059 and VV 47. By comparing the observed period spacing with the
asymptotic period spacing we obtain M_{\star}\sim 0.569\ M_{\sun} for SDSS
J0349-0059 and M_{\star}\sim 0.523\ M_{\sun} for VV 47. If we compare the
observed period spacing with the average of the computed period spacings we
found M_{\star}\sim 0.535\ M_{\sun} for SDSS J0349-0059 and M_{\star}\sim
0.528 M_{\sun} for VV 47. Searching for the best period fit we found, in the
case of SDSS J0349-0059, an asteroseismological model with $M_{\star}= 0.542\
M_{\sun}T_{\rm eff}= 91\, 255\ P_{\rm rot}= 1/\Omega \sim 0.407$
days. The results presented in this work constitute a further step in the study
of GW Vir stars through asteroseismology in the frame of fully evolutionary
models of PG 1159 stars. In particular, once again it is shown the potential of
asteroseismology to derive stellar masses of PG 1159 stars with an
unprecedented precision.Comment: 13 pages, 16 figures, 6 tables. To be published in Astronomy and
Astrophysic
New evolutionary sequences for extremely low mass white dwarfs: Homogeneous mass and age determinations, and asteroseismic prospects
We provide a fine and homogeneous grid of evolutionary sequences for He-core
white dwarfs with masses 0.15-0.45 Msun, including the mass range for ELM white
dwarfs (<0.20Msun). The grid is appropriate for mass and age determination, and
to study their pulsational properties. White dwarf sequences have been computed
by performing full evolutionary calculations that consider the main energy
sources and processes of chemical abundance changes during white dwarf
evolution. Initial models for the evolving white dwarfs have been obtained by
computing the non-conservative evolution of a binary system consisting of a
Msun ZAMS star and a 1.4 Msun neutron star for various initial orbital periods.
To derive cooling ages and masses for He-core white dwarf we perform a least
square fitting of the M(Teff, g) and Age(Teff, g) relations provided by our
sequences by using a scheme that takes into account the time spent by models in
different regions of the Teff-g plane. This is useful when multiple solutions
for cooling age and mass determinations are possible in the case of
CNO-flashing sequences. We also explore the adiabatic pulsational properties of
models near the critical mass for the development of CNO flashes (~0.2 Msun).
This is motivated by the discovery of pulsating white dwarfs with stellar
masses near this threshold value. We obtain reliable and homogeneous mass and
cooling age determinations for 58 very low-mass white dwarfs, including 3
pulsating stars. Also, we find substantial differences in the period spacing
distributions of g-modes for models with stellar masses ~ 0.2 Msun, which could
be used as a seismic tool to distinguish stars that have undergone CNO flashes
in their early cooling phase from those that have not. Finally, for an easy
application of our results, we provide a reduced grid of values useful to
obtain masses and ages of He-core white dwarf.Comment: 12 pages, 9 figures, to be published in Astronomy and Astrophysic
Efeito do cultivo de milho, braquiária, crotalária e soja sobre a população do nematoide reniforme (Rotylenchulus reniformis) em solo naturalmente infestado.
Efeito do consórcio de soja com forrageiras sobre a população do nematoide reniforme (Rotylenchulus reniformis) no solo.
White dwarf evolutionary sequences for low-metallicity progenitors: The impact of third dredge-up
We present new white dwarf evolutionary sequences for low-metallicity
progenitors. White dwarf sequences have been derived from full evolutionary
calculations that take into account the entire history of progenitor stars,
including the thermally-pulsing and the post-asymptotic giant branch phases. We
show that for progenitor metallicities in the range 0.00003--0.001, and in the
absence of carbon enrichment due to the occurrence of a third dredge-up
episode, the resulting H envelope of the low-mass white dwarfs is thick enough
to make stable H burning the most important energy source even at low
luminosities. This has a significant impact on white dwarf cooling times. This
result is independent of the adopted mass-loss rate during the
thermally-pulsing and post-AGB phases, and the planetary nebulae stage. We
conclude that in the absence of third dredge-up episodes, a significant part of
the evolution of low-mass white dwarfs resulting from low-metallicity
progenitors is dominated by stable H burning. Our study opens the possibility
of using the observed white dwarf luminosity function of low-metallicity
globular clusters to constrain the efficiency of third dredge up episodes
during the thermally-pulsing AGB phase of low-metallicity progenitors.Comment: To be published in Astronomy and Astrophysics. 12 pages, 11 figure
Constraining the neutrino magnetic dipole moment from white dwarf pulsations
Pulsating white dwarf stars can be used as astrophysical laboratories to
constrain the properties of weakly interacting particles. Comparing the cooling
rates of these stars with the expected values from theoretical models allows us
to search for additional sources of cooling due to the emission of axions,
neutralinos, or neutrinos with magnetic dipole moment. In this work, we derive
an upper bound to the neutrino magnetic dipole moment using an estimate of the
rate of period change of the pulsating DB white dwarf star PG 1351+489. By
comparing the theoretical rate of change of period expected for this star with
the rate of change of period with time of PG 1351+489, we assess the possible
existence of additional cooling by neutrinos with magnetic dipole moment. Our
models suggest the existence of some additional cooling in this pulsating DB
white dwarf, consistent with a non-zero magnetic dipole moment. Our upper limit
for the neutrino magnetic dipole moment is somewhat less restrictive than, but
still compatible with, other limits inferred from the white dwarf luminosity
function or from the color-magnitude diagram of the Globular cluster M5.
Further improvements of the measurement of the rate of period change of the
dominant pulsation mode of PG 1351+489 will be necessary to confirm our bound.Comment: 18 pages, 10 figures, 3 tables. Accepted for publication in Journal
of Cosmology and Astroparticle Physic
A Lightweight Regression Method to Infer Psycholinguistic Properties for Brazilian Portuguese
Psycholinguistic properties of words have been used in various approaches to
Natural Language Processing tasks, such as text simplification and readability
assessment. Most of these properties are subjective, involving costly and
time-consuming surveys to be gathered. Recent approaches use the limited
datasets of psycholinguistic properties to extend them automatically to large
lexicons. However, some of the resources used by such approaches are not
available to most languages. This study presents a method to infer
psycholinguistic properties for Brazilian Portuguese (BP) using regressors
built with a light set of features usually available for less resourced
languages: word length, frequency lists, lexical databases composed of school
dictionaries and word embedding models. The correlations between the properties
inferred are close to those obtained by related works. The resulting resource
contains 26,874 words in BP annotated with concreteness, age of acquisition,
imageability and subjective frequency.Comment: Paper accepted for TSD201
Dimensionality effects in the LDOS of ferromagnetic hosts probed via STM: spin-polarized quantum beats and spin filtering
We theoretically investigate the local density of states (LDOS) probed by a
STM tip of ferromagnetic metals hosting a single adatom and a subsurface
impurity. We model the system via the two-impurity Anderson Hamiltonian. By
using the equation of motion with the relevant Green functions, we derive
analytical expressions for the LDOS of two host types: a surface and a quantum
wire. The LDOS reveals Friedel-like oscillations and Fano interference as a
function of the STM tip position. These oscillations strongly depend on the
host dimension. Interestingly, we find that the spin-dependent Fermi wave
numbers of the hosts give rise to spin-polarized quantum beats in the LDOS.
While the LDOS for the metallic surface shows a damped beating pattern, it
exhibits an opposite behavior in the quantum wire. Due to this absence of
damping, the wire operates as a spatially resolved spin filter with a high
efficiency.Comment: revised tex
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