Hydrogen envelope

If the star loses its hydrogen envelope in the process, and if the jet produced by accretion maintains its energy and remains focussed longer than the time required to cross the star (five to ten seconds), a vigorous gamma burst is produced. Otherwise, the result is a weaker burst, less tightly collimated, or an asymmetrical supernova. 

The spectrum in both the optical and the ultraviolet at about two days is fairly well represented by a hydrogen envelope with a power law density profile (p r11) of one-quarter solar metaiiiclty in LTE. Theoretical spectra at this early epoch tend to favor luminosities on the high side of observational estimates in order to ionize Ca II and prevent excessively strong lines at H and K and the infrared triplet, with some ramifications for distance estimates. 

Unfortunately observations of the presupernova star do not constrain the mass of the hydrogen envelope. An unknown amount of mass loss could have occurred leaving anywhere from 14 M0 to as little as a few tenths M0. Since the envelope mass greatly affects the dynamics of the explosion, the light curve, and the spectroscopic history of the supernova, its determination is of high priority. Based upon observations of the supernova one conclusion of this paper will be that the envelope mass was in the range 5 to 10 M0. 

Fig. 6 - Bolometric luminosities during the first 200 days for 4 of the models defined in Table 1 compared to data from Catchpole et al. (1987) and Hamuy et a1. (1987). All models employed the same 6 M helium core capped by hydrogen envelopes of various masses. The opacity, chiefly due to electron scattering while the gas remains ionized, was given a lower floor of 0.02 cm2 g-1 for elements heavier than helium.

Figure 10. Allowed values of explosion energy and hydrogen envelope mass are broadly delineated for 1987a. Based upon the explosion of a 6 Mg core (main sequnce mass 20 M ), the atmosphere can be no greater than 14 M0. Symbols X denote a model that can be excluded on the basis of one or more observational constraints + indicates a moderately successful model arrows indicate lower and upper bounds provided by three of the models and N a successful model recently published by Nomoto et al (1987). Explosion energies below 3 x 1050 erg lead to reimplosion of the core and loss of all 5 Co.

The star always makes a final trip back to the blue and undergoes a supernova explosion when the hydrogen envelope is reduced to a few tenths of a solar mass (assuming sufficient mass loss has occurred). Final mass is 5.5M0. 

The star shoots some of its mass into outer space. In particular, the star s outermost hydrogen envelope, which by now has lots of heavier elements, blasts into space. Electrically charged particles flow outward as a stellar wind. Deep layers are also tossed off in a tenuous shell of gas called a planetary nebula. We talked about them before. I m reviewing. Only the star s core remains—like a naked peach pit after the peach has been eaten away. ... 

Planetary Nebula (Enriched hydrogen envelope tossed into space)... 

The nuclear reaction 4He + 3 He -> 7Be also occurs at the hot base of the hydrogen envelope of red-giant AGB stars. If convection can rapidly mix that to cooler temperatures before the7Be decays to 7Li, the AGB envelope can become enriched in7Li. Such events may be responsible for much of the observed Liabundance in stars (see7Li). 

Wolf-Rayet star ahot (25 000 to 50 000 K), massive (more than 25 solar masses), luminous star in an advanced stage of evolution, which is losing mass in the form of a powerful stellar wind. Wolf-Rayets are believed to be O stars that have lost their hydrogen envelopes, leaving their helium cores exposed. 

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