426 research outputs found
Burst Neutrinos from Nitrogen Flash
Neutrinos give a novel probe to explore deep interior of astrophysical
objects, which otherwise is not accessible with optical observations; among
notable examples are solar and supernova neutrinos. We show that there is a new
class of strong neutrino emission from helium burning, N + alpha --> 18F gamma
followed by beta decay 18F --> 18O + e+ + nu_e, that gives a maximum neutrino
luminosity of 10^8 times the solar bolometric luminosity at the helium-core
flash of a 1 M_sun star, whereas the flash is not observable by optical means.
This means that the neutrino flux, of average energy of 0.382 MeV, will be 10%
the solar CNO neutrino flux on Earth if the star is located at 10pc.Comment: Accepted to ApJ Letters. Replaced version with extended discussion.
Some additional references adde
Bayesian mass and age estimates for transiting exoplanet host stars
The mean density of a star transited by a planet, brown dwarf or low mass
star can be accurately measured from its light curve. This measurement can be
combined with other observations to estimate its mass and age by comparison
with stellar models. Our aim is to calculate the posterior probability
distributions for the mass and age of a star given its density, effective
temperature, metallicity and luminosity. We computed a large grid of stellar
models that densely sample the appropriate mass and metallicity range. The
posterior probability distributions are calculated using a Markov-chain
Monte-Carlo method. The method has been validated by comparison to the results
of other stellar models and by applying the method to stars in eclipsing binary
systems with accurately measured masses and radii. We have explored the
sensitivity of our results to the assumed values of the mixing-length
parameter, , and initial helium mass fraction, Y. For a star
with a mass of 0.9 solar masses and an age of 4 Gyr our method recovers the
mass of the star with a precision of 2% and the age to within 25% based on the
density, effective temperature and metallicity predicted by a range of
different stellar models. The masses of stars in eclipsing binaries are
recovered to within the calculated uncertainties (typically 5%) in about 90% of
cases. There is a tendency for the masses to be underestimated by about 0.1
solar masses for some stars with rotation periods Pd. Our method
makes it straightforward to determine accurately the joint posterior
probability distribution for the mass and age of a star eclipsed by a planet or
other dark body based on its observed properties and a state-of-the art set of
stellar models.Comment: Accepted for publication in A&A. 9 pages, 4 figures. Source code for
the software described is available from
http://sourceforge.net/projects/bagemas
New DA white dwarf evolutionary models and their pulsational properties
In this letter we investigate the pulsational properties of ZZ Ceti stars on
the basis of new white dwarf evolutionary models calculated in a
self-consistent way with the predictions of time dependent element diffusion
and nuclear burning. In addition, full account is taken of the evolutionary
stages prior to the white dwarf formation. Emphasis is placed on the trapping
properties of such models. By means of adiabatic, non-radial pulsation
calculations, we find, as a result of time dependent diffusion, a much weaker
mode trapping effect, particularly for the high-period regime of the pulsation
g-spectrum. This result is valid at least for models with massive hydrogen-rich
envelopes. Thus, mode trapping would not be an effective mechanism to explain
the fact that all the high periods expected from standard models of stratified
white dwarfs are not observed in the ZZ Ceti stars.Comment: 3 pages, 5 figures, accepted for publication in Astronomy &
Astrophysics Letter
PENGARUH ATRIBUT PRODUK TERHADAP SIKAP KONSUMEN INEZ KOSMETIK (Studi Kasus di Pusaka Indah Swalayan Kebumen Tahun 2013)
Penelitian ini bertujuan untuk mengetahui (1) Ada tidaknya pengaruh
atribut produk secara simultan terhadap sikap konsumen Inez kosmetik di Pusaka
Indah Swalayan, (2) Ada tidaknya pengaruh atribut produk terhadap sikap
konsumen Inez kosmetik di Pusaka Indah Swalayan.
Jenis penelitian yang digunakan oleh penulis untuk memenuhi tujuan
tersebut adalah menggunakan metode deskriptif kuantitatif dengan teknik
pengumpulan data berupa kuesioner. Populasi penelitian ini adalah orang yang
membeli dan menggunakan Inez Kosmetik atau konsumen yang memiliki minat
terhadap Inez Kosmetik di Pusaka Indah Swalayan. Jumlah sampel yang
digunakan dalam penelitian ini sebanyak 100 responden. Teknis analisis data yang
digunakan adalah teknik analisis regresi linier berganda.
Berdasarkan hasil penelitian tersebut dapat disimpulkan bahwa (1) terdapat
pengaruh atribut produk terhadap sikap konsumen Inez kosmetik di Pusaka Indah
Swalayan. Hal tersebut tercermin dari hasil uji F diperoleh nilai probabilitas
sebesar 0,000. Sehubungan dengan nilai probabilitas 0,000 lebih kecil dari 0,05,
maka Ho ditolak dan Ha diterima, sehingga dapat disimpulkan bahwa variabel
atirbut produk yang terdiri dari yang terdiri dari : kualitas, merek, kemasan, label
dan harga berpengaruh secara simultan terhadap sikap konsumen. (2) hasil
perhitungan data untuk variabel kualitas memiliki tingkat signifikansi sebesar
0,035, variabel merek memiliki tingkat signifikansi sebesar 0,027, variabel
kemasan memiliki tingkat signifikansi sebesar 0,039, variabel label memiliki
tingkat signifikansi sebesar 0,038, variabel harga memiliki tingkat signifikansi
sebesar 0,023 . Oleh karena probabilitas variabel kualitas, merek, kemasan, label,
dan harga lebih kecil dari 0,05 maka dapat dikemukakan bahwa variabel variabel
kualitas, merek, kemasan, label, dan harga berpengaruh secara parsial terhadap
keputusan pembelian konsumen.
Kata kunci: Atribut produk, sikap konsumen, kosmeti
The ages and colours of cool helium-core white dwarf stars
The purpose of this work is to explore the evolution of helium-core white
dwarf stars in a self-consistent way with the predictions of detailed non-gray
model atmospheres and element diffusion. To this end, we consider helium-core
white dwarf models with stellar masses of 0.406, 0.360, 0.327, 0.292, 0.242,
0.196 and 0.169 solar masses and follow their evolution from the end of mass
loss episodes during their pre-white dwarf evolution down to very low surface
luminosities. We find that when the effective temperature decreases below
4000K, the emergent spectrum of these stars becomes bluer within time-scales of
astrophysical interest. In particular, we analyse the evolution of our models
in the colour-colour and colour-magnitude diagrams and we find that helium-core
white dwarfs with masses ranging from approx. 0.18 to 0.3 solar masses can
reach the turn-off in their colours and become blue again within cooling times
much less than 15 Gyr and then remain brighter than M_V approx. 16.5. In view
of these results, many low-mass helium white dwarfs could have had time enough
to evolve to the domain of collision-induced absorption from molecular
hydrogen, showing blue colours.Comment: 11 pages, 9 figures. Accepted for publication in MNRA
Evolution and colours of helium-core white dwarf stars: the case of low metallicity progenitors
The present work is designed to explore the evolution of helium-core white
dwarf (HeWD) stars for the case of metallicities much lower than the solar one
(Z=0.001 and Z=0.0002). Evolution is followed in a self-consistent way with the
predictions of detalied and new non-grey atmospheres, time-dependent element
diffusion and the history of the white dwarf progenitor. Reliable initial
models for low mass HeWDs are obtained by applying mass loss rates to a 1msun
stellar model. The loss of angular momentum caused by gravitational wave
emission and magnetic stellar wind braking are considered. Model atmospheres,
based on a detailed treatment of the microphysics entering the WD atmosphere
enable us to provide accurate colours and magnitudes at both early and advanced
evolutionary stages. We find that most of our evolutionary sequences experience
several episodes of hydrogen thermonuclear flashes. In particular, the lower
the metallicity, the larger the minimum stellar mass for the occurrence fo
flashes induced by CNO cycle reactions. The existence of a mass-threshold for
the occurrence of diffusion-induced CNO flashes leadss to a marked dichotomy in
the age of our models. Another finding of this study is that our HeWD models
experience unstable hydrogen burning via PP nuclear reactions at late cooling
stages as a result of hydrogen chemically diffusing inwards. Such PP flashes
take place in models with very low metal content. We also find that models
experiencing CNO flashes exhibit a pronouncede turn-off in most of their
colours at M_V=16 approximately. Finally, colour-magnitude diagrams for our
models are presented and compared with recent observational data of HeWD
candidates in the globular clusters NGC 6397 and 47 Tucanae.Comment: 14 pages, 10 figures. Accepted for publication in MNRA
CN-Cycle Solar Neutrinos and Sun's Primordial Core Metalicity
We argue that it may be possible to exploit neutrinos from the CN cycle and
pp chain to determine the primordial solar core abundances of C and N at an
interesting level of precision. Such a measurement would allow a comparison of
the Sun's deep interior composition with it surface, testing a key assumption
of the standard solar model (SSM), a homogeneous zero-age Sun. It would also
provide a cross-check on recent photospheric abundance determinations that have
altered the once excellent agreement between the SSM and helioseismology. As
further motivation, we discuss a speculative possibility in which photospheric
abundance/helioseismology puzzle is connected with the solar-system metal
differentiation that accompanied formation of the gaseous giant planets.
The theoretical relationship between core C and N and the 13N and 15O solar
neutrino fluxes can be made more precise (and more general) by making use of
the Super-Kamiokande and SNO 8B neutrino capture rates, which calibrate the
temperature of the solar core. The primordial C and N abundances can then be
obtained from these neutrino fluxes and from a product of nuclear rates, with
little residual solar model dependence. We describe some of the recent
experimental advances that could allow this comparison to be made
(theoretically) at about the 9% level, and note that this uncertainty may be
reduced further due to ongoing work on the S-factor for 14N(p,gamma). The
envisioned measurement might be possible in deep, large-volume detectors using
organic scintillator, e.g., Borexino or SNO+Comment: 33 pages, 4 figure
The influence of planetary engulfment on stellar rotation in metal-poor main-sequence stars
The method of gyrochronology relates the age of its star to its rotation
period. However, recent evidence of deviations from gyrochronology relations
was reported in the literature. Here, we study the influence of tidal
interaction between a star and its companion on the rotation velocity of the
star, in order to explain peculiar stellar rotation velocities. The interaction
of a star and its planet is followed using a comprehensive numerical framework
that combines tidal friction, magnetic braking, planet migration, and detailed
stellar evolution models from the GARSTEC grid. We focus on close-in companions
from 1 to 20 M orbiting low-mass, 0.8 and 1 M, main-sequence
stars with a broad metallicity range from [Fe/H] = -1 to solar. Our simulations
suggest that the dynamical interaction between a star and its companion can
have different outcomes, which depend on the initial semi-major axis and the
mass of the planet, as well as the mass and metallicity of its host star. In
most cases, especially in the case of planet engulfment, we find a catastrophic
increase in stellar rotation velocity from 1 kms to over 40 kms,
while the star is still on the main-sequence. The main prediction of our model
is that low-mass main-sequence stars with abnormal rotation velocities should
be more common at low-metallicity, as lower [Fe/H] favours faster planet
engulfment, provided occurrence rate of close in massive planets is similar at
all metallicities. Our scenario explains peculiar rotation velocities of
low-mass main-sequence stars by the tidal interaction between the star and its
companion. Current observational samples are too small and incomplete, and thus
do not allow us to test our model.Comment: 10 pages, 6 figures, accepted for publication in A&
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