515 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
Solar Neutrinos
The study of solar neutrinos has given since ever a fundamental contribution
both to astroparticle and to elementary particle physics, offering an ideal
test of solar models and offering at the same time relevant indications on the
fundamental interactions among particles. After reviewing the striking results
of the last two decades, which were determinant to solve the long standing
solar neutrino puzzle and refine the Standard Solar Model, we focus our
attention on the more recent results in this field and on the experiments
presently running or planned for the near future. The main focus at the moment
is to improve the knowledge of the mass and mixing pattern and especially to
study in detail the lowest energy part of the spectrum, which represents most
of solar neutrino spectrum but is still a partially unexplored realm. We
discuss this research project and the way in which present and future
experiments could contribute to make the theoretical framemork more complete
and stable, understanding the origin of some "anomalies" that seem to emerge
from the data and contributing to answer some present questions, like the exact
mechanism of the vacuum to matter transition and the solution of the so called
solar metallicity problem.Comment: 51 pages, to be published in Special Issue on Neutrino Physics,
Advances in High Energy Physics Hindawi Publishing Corporation 201
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
On constructing horizontal branch models
We investigate different methods used to construct (zero-age) horizontal
branch models and compare the resulting horizontal branch evolution with that
of models resulting from the calculation of the complete stellar evolution from
the main sequence and through the core helium flash. We show that the
approximate methods may lead to small, but discernible effects, but that some
methods, which are as simple, reproduce the complete evolution very well.Comment: accepted for publication in Astronomy & Astrophysic
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
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