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Search Results: 1 - 10 of 191459 matches for " D. Branch "
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Spectroscopically Peculiar Type Ia Supernovae and Implications for Progenitors
D. Branch
Physics , 2000, DOI: 10.1086/318614
Abstract: In a recent paper Li et al. (2000) reported that 36 percent of 45 Type Ia supernovae (SNe Ia) discovered since 1997 in two volume-limited supernova searches were spectroscopically peculiar, and they suggested that because this peculiarity rate is higher than that reported for an earlier observational sample by Branch et al. (1993), it is now more likely that SNe Ia are produced by more than one kind of progenitor. In this paper I discuss and clarify the differences between the results of Li et al. and Branch et al. and I suggest that multiple progenitor systems are now less likely than they were before.
Type Ia Supernovae and the Hubble Constant
D. Branch
Physics , 1998, DOI: 10.1146/annurev.astro.36.1.17
Abstract: The focus of this review is the work that has been done during the 1990s on using Type Ia supernovae (SNe Ia) to measure the Hubble constant ($H_0$). SNe Ia are well suited for measuring $H_0$. A straightforward maximum-light color criterion can weed out the minority of observed events that are either intrinsically subluminous or substantially extinguished by dust, leaving a majority subsample that has observational absolute-magnitude dispersions of less than $\sigma_{obs}(M_B) \simeq \sigma_{obs}(M_V) \simeq 0.3$ mag. Correlations between absolute magnitude and one or more distance-independent SN Ia or parent-galaxy observables can be used to further standardize the absolute magnitudes to better than 0.2 mag. The absolute magnitudes can be calibrated in two independent ways --- empirically, using Cepheid-based distances to parent galaxies of SNe Ia, and physically, by light curve and spectrum fitting. At present the empirical and physical calibrations are in agreement at $M_B \simeq M_V \simeq -19.4$ or -19.5. Various ways that have been used to match Cepheid-calibrated SNe Ia or physical models to SNe Ia that have been observed out in the Hubble flow have given values of $H_0$ distributed throughout the range 54 to 67 km/s Mpc$^{-1}$. Astronomers who want a consensus value of $H_0$ from SNe Ia with conservative errors could, for now, use $60 \pm 10$ km/s Mpc^{-1}$.
Direct Analysis of Spectra of Type Ic Supernovae
D. Branch
Physics , 1999,
Abstract: Synthetic spectra generated with the parameterized supernova synthetic-spectrum code SYNOW are compared with observed photospheric-phase optical spectra of the normal Type Ic SN 1994I and the peculiar Type Ic SNe 1997ef and 1998bw. The observed spectra can be matched fairly well with synthetic spectra that are based on spherical symmetry and that include lines of just a few ions that are expected to appear on the basis of LTE calculations. Spectroscopic estimates of the mass and kinetic energy of the line-forming layers of the ejected matter give conventional values for SN 1994I but high kinetic energy ($\sim 30 \times 10^{51}$ erg) for SN 1997ef and even higher ($\sim 60 \times 10^{51}$ erg) for SN 1998bw. It is likely that even if SNe 1997ef and 1998bw were non-spherical, they also were hyper-energetic.
Determination of the Hubble Constant Using a Two-Parameter Luminosity Correction for Type Ia Supernovae
R. Tripp,D. Branch
Physics , 1999, DOI: 10.1086/307883
Abstract: In this paper, we make a comprehensive determination of the Hubble constant $H_0$ by using two parameters - the B-V color and the rate of decline $\Delta m_{15}$ - to simultaneously standardize the luminosities of all nearby Cepheid-calibrated type Ia supernovae (SNe Ia) and those of a larger, more distant sample of 29 SNe Ia. Each group is treated in as similar a manner as possible in order to avoid systematic effects. A simultaneous $\chi ^2$ minimization yields a standardized absolute luminosity of the Cepheid-calibrated supernovae as well as the Hubble constant obtained from the more distant sample. We find $H_0 = 62 km/s Mpc^{-1}$ and a standardized absolute magnitude of -19.46. The sensitivity of $H_0$ to a metallicity dependence of the Cepheid-determined distances is investigated. The total uncertainty $\delta H_0$, dominated by uncertainties in the primary Cepheid distance indicator, is estimated to be 5 km/s Mpc^{-1}.
Corrección de bordes en imágenes de rango por medio de un algoritmo genético
Idanis B. Díaz,John W. Branch
Ingeniería y Desarrollo , 2005,
Abstract: En este artículo se propone un método que permite completar y mejorar los bordes definidos para imágenes de rango de superficies planas. El método parte de un mapa inicial de bordes gruesos, fragmentados y con píxeles bordes mal ubicados, obtenidos a partir de la localización de cambios de profundidad y orientación entre las superficies. El mapa de bordes inicial es mejorado empleando un algoritmo genético cuya tarea es a adir y desechar píxeles bordes, para encontrar una buena delimitación de las superficies de la imagen.
The Effects of Inhomogeneities on Evaluating the Deceleration Parameter q$_0$
R. Kantowski,T. Vaughan,D. Branch
Physics , 1995, DOI: 10.1086/175854
Abstract: Analytic expressions for distance-redshift relations which have been corrected for the effects of some inhomogeneities in the Friedmann-Robertson-Walker (FRW) mass density are used to illustrate the significance of inhomogeneities on a determination of $q_0$ made by using Type Ia supernovae. The value of $q_0$ inferred from a given set of observations depends on the fractional amount of matter in inhomogeneities and is up to 50 percent larger than that obtained by using the standard Mattig $m$-$z$ result for pure dust FRW models.
Extinction and the Radial Distribution of Supernova Properties in Their Parent Galaxies
K. Hatano,D. Branch,J. Deaton
Physics , 1997, DOI: 10.1086/305903
Abstract: We use a Monte Carlo technique and assumed spatial distributions of dust and supernova (SN) progenitors in a simple model of a characteristic SN--producing disk galaxy to explore the effects of extinction on the radial distributions of SN properties in their parent galaxies. The model extinction distributions and projected radial number distributions are presented for various SN types. Even though the model has no core-collapse SNe within three kpc of the center, a considerable fraction of the core-collapse SNe are projected into the inner regions of inclined parent galaxies owing to their small vertical scale height. The model predicts that because of extinction, SNe projected into the central regions should on average appear dimmer and have a much larger magnitude scatter than those in the outer regions. In particular, the model predicts a strong deficit of bright core-collapse events inside a projected radius of a few kpc. Such a deficit is found to be present in the observations. It is a natural consequence of the characteristic spatial distributions of dust and core-collapse SNe in galaxies, and it leads us to offer an alternative to the conventional interpretation of the Shaw effect.
Supernova Resonance-Scattering Profiles in the Presence of External Illumination
D. Branch,D. J. Jeffery,M. Blaylock,K. Hatano
Physics , 1999, DOI: 10.1086/316510
Abstract: We discuss a simple model for the formation of a supernova spectral line by resonance scattering in the presence of external illumination of the line-forming region by light from circumstellar interaction (toplighting). The simple model provides a clear understanding of the most conspicuous toplighting effect: a rescaling or, as we prefer, a ``muting'' of the line profile relative to the continuum. This effect would be present in more realistic models, but would be harder to isolate. An analytic expression for a muting factor for a P-Cygni line is derived that depends on the ratio E of the toplighting specific intensity to the specific intensity from the supernova photosphere. If E<1, the line profile is reduced in scale or ``muted''. If E=1, the line profile vanishes altogether. If E>1, the line profile flips vertically: then having an absorption component near the observer-frame line center wavelength and a blueshifted emission component.
On the Spectrum and Nature of the Peculiar Type Ia Supernova 1991T
A. Fisher,D. Branch,K. Hatano,E. Baron
Physics , 1998, DOI: 10.1046/j.1365-8711.1999.02299.x
Abstract: A parameterized supernova synthetic-spectrum code is used to study line identifications in the photospheric-phase spectra of the peculiar Type Ia SN 1991T, and to extract some constraints on the composition structure of the ejected matter. The inferred composition structure is not like that of any hydrodynamical model for Type Ia supernovae. Evidence that SN 1991T was overluminous for an SN Ia is presented, and it is suggested that this peculiar event probably was a substantially super-Chandrasekhar explosion that resulted from the merger of two white dwarfs.
Synthetic Spectra of Hydrodynamic Models of Type Ia Supernovae
P. Nugent,E. Baron,D. Branch,A. Fisher,Peter Hauschildt
Physics , 1996, DOI: 10.1086/304459
Abstract: We present detailed NLTE synthetic spectra of hydrodynamic SNe Ia models. We make no assumptions about the form of the spectrum at the inner boundary. We calculate both Chandrasekhar-mass deflagration models and sub-Chandrasekhar ``helium detonators.'' Gamma-ray deposition is handled in a simple, accurate manner. We have parameterized the storage of energy that arises from the time dependent deposition of radioactive decay energy in a reasonable manner, that spans the expected range. We find that the Chandrasekhar-mass deflagration model W7 of Nomoto etal shows good agreement with the observed spectra of SN 1992A and SN 1994D, particularly in the UV, where our models are expected to be most accurate. The sub-Chandrasekhar models do not reproduce the UV deficit observed in normal SNe Ia. They do bear some resemblance to sub-luminous SNe Ia, but the shape of the spectra (i.e. the colors) are opposite to that of the observed ones and the intermediate mass element lines such as Si II, and Ca II are extremely weak, which seems to be a generic difficulty of the models. Although the sub-Chandrasekhar models have a significant helium abundance (unlike Chandrasekhar-mass models), helium lines are not prominent in the spectra near maximum light and thus do not act as a spectral signature for the progenitor.
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