Recent Results on SN 1987A

Abstract

A b s t r a c t ! Several critical issues recently raised by observations of SN 1987A are addressed. These include: 1) the evolution of the pre-supernova star, why it was blue, what its composition and core structure were; 2) the detailed isotopic composition of the ejecta; 3) why and to what extent the supernova composition was mixed in velocity space; 4) the interpretation of recently observed infrared lines, especially their profiles and the existence of red-shifted 'wings'; and 5) what has become of the neutron star.Blue Super-giants a n d Nitrogen E n h a n c e m e n t s There is now general agreement among several groups that the star which made SN 1987A, Sk -6 9 202, only became a blue supergiant (BSG) just prior to exploding. Observationally, the evidence consists of a substantial number of red supergiants (RSGs) in the LMC (Humphreys and McElroy 1984), showing that a reasonable fraction of massive stars must spend at least a portion of their helium burning lifetimes as a red star, and observations of SN 1987A by IUE (Frannson et al. 1988) and at ESO (Wampler and Richichi 1988) showing the presence of a low velocity circumstellar shell. The narrow velocity spread (~15 km s -1 ) and heliocentric velocity (286 km s -1 ) of this shell have interesting implications. For example, the progenitor star could not have been a member of a close binary system or the orbital velocity would have contributed a greater spread to the velocity. The heliocentric velocity also gives a frame of reference in which to search for anomalous motion of the supernova itself. Perhaps most importantly, the low velocity and the anomalous nitrogen-rich composition strongly indicate ejection from a convective, extended RSG, not a radiative, compact blue one. Further the radius of the shell and some simple hydrodynamical arguments gives an approximate date for the ejection of the shell (Chevalier 1988;Chalabaev et al.

Stark halfwidth trends along the homologous sequence of doubly ionized noble gases

“…Neon has also been observed in supernova ejecta (Thieleman et al 1986;Woosley et al 1988). Ne III lines have been identified in the spectrum of solar active region (Thomas & Neupert 1994).…”

The origin and abundances of the chemical elements revisited

“…Thus you can tell at a glance that the Thielemann et al (1990) model ejected 1.48 Me of 016, 0.228 Mo of Ne 2~ 0.147 MG of Mg 24, and so forth from hydrogen to gallium. By the same token, the Woosley et al (1988) model ejected 1.6 Mo of 016, 0.18 Mo of Ne 2~ 0.096 Mo of Mg 24, and so forth from hydrogen to zinc, when the cut between neutron star and expelled envelope was drawn to give the right amount of Ni s6. Both of these are high C12(e,7)O 16 models of 20Mo stars with 6Mo helium cores at the time of collapse, and initial metallicity about 1/3 solar.…”

“…much of the cosmic ray spallation comes from lower energy particles than those directly detected at earth) are probably such that neither serious disagreement or complete confirmation can be claimed for any of them. Table 6 shows the amounts of elements from carbon to copper produced by a Nomoto et al (1984;Thielemann et al 1986) Type Ia supernova and a Woosley et al (1988) Type II. The former ejected 1.32 solar masses of heavy elements, the latter (which is a 20 Mo star model for SN 1987A) 2.67 Mo of heavy elements.…”

Confirmation of dust condensation in the ejecta of supernova 1987a.

“…The infrared luminosity continued to decline until day 1050 (Fig. 4) [3] where L. is the SIBL extrapolated to t = 0, and f(t) is the fraction of the y ray energy that can be thermalized in the ejecta;f is unity at outburst and decreases later as the ejecta become optically thin to y rays (20). The obscuring dust directly affects the UBV decline rates (Fig.…”

“…It seems possible that the condensation of water ice onto the grains could have accelerated their growth after day 700. Woosley et al (20) have shown that mixing in the outer ejecta should produce an oxygen-rich mixture where the condensation of water might be expected. (Fig.…”