19,069 research outputs found
Nebular Spectra and Explosion Asymmetry of Type Ia Supernovae
The spectral signatures of asymmetry in Type Ia Supernova (SN Ia) explosions
are investigated, using a sample of late-time nebular spectra. First, a
kinematical model is constructed for SN Ia 2003hv, which can account for the
main features in its optical, Near-Infrared (NIR), and Mid-Infrared (Mid-IR)
late-time spectra. It is found that an asymmetric off-center model can explain
the observed characteristics of SN 2003hv. This model includes a relatively
high density, Fe-rich region which displays a large velocity off-set, and a
relatively low density, extended 56Ni-rich region which is more spherically
distributed. The high density region consists of the inner stable Fe-Ni region
and outer 56Ni-rich region. Such a distribution may be the result of a
delayed-detonation explosion, in which the first deflagration produces the
global asymmetry in the innermost ejecta, while the subsequent detonation can
lead to the bulk spherical symmetry. This configuration, if viewed from the
direction of the off-set, can consistently explain the blueshift in some of the
emission lines and virtually no observed shift in other lines in SN 2003hv. For
this model, we then explore the effects of different viewing angles and the
implications for SNe Ia in general. The model predicts that a variation of the
central wavelength, depending on the viewing angle, should be seen in some
lines (e.g., [Ni II]7378), while the strongest lines (e.g., [Fe III] blend at
4700A) will not show this effect. By examining optical nebular spectra of 12
SNe Ia, we have found that such a variation indeed exists. We suggest that the
global asymmetry in the innermost ejecta, as likely imprint of the deflagration
flame propagation, is a generic feature of SNe Ia (abridged).Comment: 14 pages, 11 figures, 4 tables. Accepted for publication in the
Astrophysical Journal. Minor correction
Measurement of the Kerr Spin Parameter by Observation of a Compact Object's Shadow
A black hole casts a shadow as an optical appearance because of its strong
gravitational field. We study how to determine the spin parameter and the
inclination angle by observing the apparent shape of the shadow, which is
distorted mainly by those two parameters. Defining some observables
characterizing the apparent shape (its radius and distortion parameter), we
find that the spin parameter and inclination angle of a Kerr black hole can be
determined by the observation. This technique is also extended to the case of a
Kerr naked singularity.Comment: 9 pages, 11 figures; v2: references added, typos corrected; v3:
accepted for publication in Physical Review
Introdução de cultivares e linhagens de soja em Porto Velho-RO.
Face a inexistência de dados sobre a cultura de soja (Glycine max (L) Merrill) em Porto Velho, instalou-se na Estação Experimental da UEPAE de Porto Velho, um ensaio com o objetivo de se obter informações sobre o comportamento da cultura. Esta publicação tem como objetivo apresentar os primeiros resultados obtidos.bitstream/item/43851/1/PA-13-820001.pd
Discrete derivatives and symmetries of difference equations
We show on the example of the discrete heat equation that for any given
discrete derivative we can construct a nontrivial Leibniz rule suitable to find
the symmetries of discrete equations. In this way we obtain a symmetry Lie
algebra, defined in terms of shift operators, isomorphic to that of the
continuous heat equation.Comment: submitted to J.Phys. A 10 Latex page
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