Engineering topics

Leibundgut, Bruno

Publications and source records attributed to Leibundgut, Bruno.

8 records

NASA NTRS1994

SN 1991T: Reflections of past glory

We have obtained photometry and spectra of SN 1991T which extend more than 1000 days past maximum light, by far the longest of SN Ia has been followed. Although SN 1991T exhibited nearly photometric behavior in the first 400 days following maximum, by 600 days its decline had slowed, and by 950 days the supernova brightness was consistent with a constant apparent magnitude of m(sub B) = 21.30. Spectra near maximum showed minor variations on the SN Ia theme which grew less conspicuous during the exponential decline. At 270 days the nebular spectrum was composed of Fe and Co lines common to SN Ia. However, by 750 days past maximum light, these lines had shifted in wavelength, and were superposed on a strong blue continuum. The luminosity of SN 1991T at 950 days is more than (9.0 x 10(exp 38)(D/13 Mpc)(2) ergs/s with a rate of decline of less than 0.04 mag per 100 days. We show that this emission is likely to be light that was emitted by SN 1991T near maximum light which has reflected from foreground dust, much like the light echos observed around SN 1987A.

Schmidt, Brian P.↗

NASA NTRS1994

Evidence for Ni-56 yields Co-56 yields Fe-56 decay in type Ia supernovae

In the prevailing picture of Type Ia supernovae (SN Ia), their explosive burning produces Ni-56, and the radioactive decay chain Ni-56 yields Co-56 yields Fe-56 powers the subsequent emission. We test a central feature of this theory by measuring the relative strengths of a (Co III) emission feature near 5900 A and a (Fe III) emission feature near 4700 A. We measure 38 spectra from 13 SN Ia ranging from 48 to 310 days after maximum light. When we compare the observations with a simple multilevel calculation, we find that the observed Fe/Co flux ratio evolves as expected when the Fe-56/Co-56 abundance ratio follows from Ni-56 yields Co-56 yields Fe-56 decay. From this agreement, we conclude that the cobalt and iron atoms we observe through SN Ia emission lines are produced by the radioactive decay of Ni-56, just as predicted by a wide range of models for SN Ia explosions.

Kuchner, Marc J.↗

NASA NTRS1993

Photometric and spectroscopic observations of SN 1990E in NGC 1035 - Observational constraints for models of type II supernovae

We present 126 photometric and 30 spectral observations of SN 1990E spanning from 12 days before B maximum to 600 days past discovery. These observations show that SN 1990E was of type II-P, displaying hydrogen in its spectrum, and the characteristic plateau in its light curve. SN 1990E is one of the few SNe II which has been well observed before maximum light, and we present evidence that this SN was discovered very soon after its explosion. In the earliest spectra we identify, for the first time, several N II lines. We present a new technique for measuring extinction to SNe II based on the evolution of absorption lines, and use this method to estimate the extinction to SN 1990E, A(V) = 1.5 +/- 0.3 mag. From our photometric data we have constructed a bolometric light curve for SN 1990E and show that, even at the earliest times, the bolometric luminosity was failing rapidly. We use the late-time bolometric light curve to show that SN 1990E trapped a majority of the gamma rays produced by the radioactive decay of Co-56, and estimate that SN 1990E ejected an amount of Ni-56 virtually identical to that of SN 1987A.

Schmidt, Brian P.↗

NASA NTRS1993

SN 1991bg - A type Ia supernova with a difference

While SN 1991bg is an unusual type Ia SN in such a feature as the brief duration of the photospheric phase, which ended only two weeks after maximum, it shares with other Ia SNs strong Si II and Ca II lines near maximum light. In addition, the light and color curve slopes are almost identical with the templates at late times. The spectral evolution of SN 1991bg is also unique but not unrecognizable; nevertheless, the peculiarities associated with this event complicate the fundamental question as to whether the Ia SNs make good standard candles.

Leibundgut, Bruno↗

NASA NTRS1992

A distance-independent calibration of the luminosity of type Ia supernovae and the Hubble constant

The absolute magnitude of SNe Ia at maximum is calibrated here using radioactive decay models for the light curve and a minimum of assumptions. The absolute magnitude parameter space is studied using explosion models and a range of rise times, and absolute B magnitudes at maximum are used to derive a range of the H0 and the distance to the Virgo Cluster from SNe Ia. Rigorous limits for H0 of 45 and 105 km/s/Mpc are derived.

Leibundgut, Bruno↗

NASA NTRS1992

Analysis of the photospheric epoch spectra of type 1a supernovae SN 1990N and SN 1991T

This paper presents an LTE analysis of the photospheric epoch optical and IUE UV spectra of the recent Type Ia supernovae SN 1990N and SN 1991T. It is found that SN 1990N has matter moving as fast as 40,000 km/s, while SN 1991T has matter moving as fast as 20,000 km/s. The exponential density profile with e-folding velocity of 3160 km/s suggested by deflation and delayed/late-detonation explosion models is adequate for calculating fits to the observed spectra. Findings on the iron peak elements suggest that in both SNe some nuclear burning continues into the outer ejecta or the newly synthesized elements are mixed into the outer ejecta. The observed spectra of SN 1990N are consistent with a composition of the inner envelope like that of model W7. Intermediate-mass elements with abundances higher than solar are probably in the outer ejecta of both SNe, while silicon, sulfur, and calcium are underabundance in SN 1991T relative to SN 1990N by factors of order 3, 3, and 120, respectively.

Jeffery, David J.↗

NASA NTRS1991

Spectra of two very old supernovae - SN 1986J and SN 1980K

Spectra are presented for SN 1986J in NGC 891, observed 4 and 7 years after the explosion, and SN 1980K, observed 9 years after maximum light. A narrow-line and a broad-line component are noted in SN 1986J; these are respectively attributed to a circumstellar shell and the actual stellar interior (without hydrogen). SN 1980K continues to emit in very broad lines. Comparison with earlier observations suggests that this SN halted its exponential flux decline in the early 1980s, and is currently emitting at a constant rate. In both SNs studies, the identity of the energy source which sustains emission remains uncertain.

Leibundgut, Bruno↗

NASA NTRS1991

Premaximum observations of the type Ia SN 1990N

Spectroscopic and photometric observations of SN 1990N were obtained at ultraviolet and optical wavelengths, beginning 14 days before maximum light. The early observations reveal important differences from spectra of SN Ia's around maximum light. Photometry and spectroscopy obtained after maximum show that SN 1990N is a typical SN Ia and that most of the observed differences are due to the early epoch of the observations. The most significant characteristics are (1) the high velocities of Ca and Si up to 22,000 km/s; (2) the presence of Co and Fe 2 weeks before maximum; and (3) the more rapid increase in the UV flux compared to the optical. The most popular models for white dwarf deflagration that have provided the standard interpretation for SN Ia's at maximum light do not reproduce the high velocities of Ca II and Si II lines observed in SN 1990N.

Leibundgut, Bruno↗