Showing papers by "Peter Nugent published in 1995"

Evidence for a Spectroscopic Sequence among Type Ia Supernovae

Abstract: In this Letter we present evidence for a spectral sequence among Type Ia supernovae (SN Ia's). The sequence is based on the systematic variation of several features seen in the near-maximum light spectrum. This sequence is analogous to the recently noted photometric sequence among SN Ia's which shows a relationship between the peak brightness of a SN Ia and the shape of its light curve. In addition to the observational evidence we present a partial theoretical explanation for the sequence. This has been achieved by producing a series of non-LTE synthetic spectra in which only the effective temperature is varied. The synthetic sequence nicely reproduces most of the differences seen in the observed one and presumably corresponds to the amount of 56Ni produced in the explosion.

Evidence for a Spectroscopic Sequence Among SNe Ia

Abstract: In this Letter we present evidence for a spectral sequence among Type Ia supernovae (SNe Ia). The sequence is based on the systematic variation of several features seen in the near-maximum light spectrum. This sequence is analogous to the recently noted photometric sequence among SNe Ia which shows a relationship between the peak brightness of a SN Ia and the shape of its light curve. In addition to the observational evidence we present a partial theoretical explanation for the sequence. This has been achieved by producing a series of non-LTE synthetic spectra in which only the effective temperature is varied. The synthetic sequence nicely reproduces most of the differences seen in the observed one and presumably corresponds to the amount of 56Ni produced in the explosion.

Low Hubble constant from the physics of type Ia supernovae.

Abstract: Two physical methods for determining luminosities and distances of type Ia supernovae, the spectral fitting expanding atmosphere method and the ${}^{56}\mathrm{Ni}$ radioactivity method, depend on the interval between the times of explosion and maximum brightness, but in differing ways. By requiring consistency between the two methods we derive blue and visual absolute magnitudes ${M}_{B}\ensuremath{\simeq}{M}_{V}\ensuremath{\simeq}\ensuremath{-}19.74\ifmmode\pm\else\textpm\fi{}0.45\mathrm{mag}$ which, together with the ridge line of type Ia supernovae in the magnitude-redshift diagram, constrain the Hubble constant to be ${50}_{\ensuremath{-}10}^{+12}\mathrm{km}{\mathrm{s}}^{\ensuremath{-}1}{\mathrm{Mpc}}^{\ensuremath{-}1}$.

Spectrum synthesis of the Type Ia supernovae SN 1992A and SN 1981B

Abstract: We present non-local thermodynamic equilibrium (non-LTE) synthetic spectra for the Type Ia supernovae SN 1992A and SN 1981B, near maximum light. At this epoch both supernovae were observed from the UV through the optical. This wide spectral coverage is essential for determining the density structure of a SN Ia. Our fits are in good agreement with observation and provide some insight as to the differences between these supernovae. We also discuss the application of the expanding photosphere method to SNe Ia which gives a distance that is independent of those based on the decay of Ni-56 and Cepheid variable stars.

Design technique for wideband optical couplers

Abstract: In this paper a new design technique for wideband optical couplers is presented. The structure is composed by an asymmetrical coupler sandwiched between two symmetrical ones. Wideband operation is obtained thanks to the compensation of the wavelength variation of the various coupling lengths. The design is based on coupled mode theory and is validated through a BPM simulation.