Search

The first stars are predicted to have formed within 200 million years after the Big Bang (1), initiating the cosmic dawn. A true first star has not yet been discovered, [...]

The element abundance ratios of four low-mass stars with extremely low metallicities (abundances of elements heavier than helium) indicate that the gas out of which the stars formed was enriched in each case by at most a few- and potentially only one--low-energy supernova (1-4). Such supernovae yield large quantities of light elements such as carbon but very little iron. The dominance of low-energy supernovae seems surprising, because it had been expected that the first stars were extremely massive, and that they disintegrated in pair-instability explosions that would rapidly enrich galaxies in iron (5). What has remained unclear is the yield of iron from the first supernovae, because hitherto no star has been unambiguously interpreted as encapsulating the yield of a single supernova. Here we report the optical spectrum of SMSS J031300.36-670839.3, which shows no evidence of iron (with an upper limit of [10.sup.-7.1] times solar abundance). Based on a comparison of its abundance pattern with those of models, we conclude that the star was seeded with material from a single supernova with an original mass about 60 times that of the Sun (and that the supernova left behind a black hole). Taken together with the four previously mentioned low-metallicity stars, we conclude that low-energy supernovae were common in the early Universe, and that such supernovae yielded light-element enrichment with insignificant iron. Reduced stellar feedback both chemically and mechanically from low-energy supernovae would have enabled first-generation stars to form over an extended period. We speculate that such stars may perhaps have had an important role in the epoch of cosmic reionization and the chemical evolution of early galaxies., Whereas the solar spectrum contains many thousands of spectral lines due to iron and other elements, the high-resolution (R = 28,000) optical spectrum of SMSS J031300.36-670839.3 (hereafter SMSS 0313 - [...]

Supernova 1998bw holds the record for the most energetic Type Ic explosion, one of the brightest radio supernovae and probably the first supernova associated with a γ-ray burst. In this paper we present spectral observations of SN 1998bw observed in a cooperative monitoring campaign using the Anglo-Australian Telescope, the UK Schmidt Telescope and the Siding Springs Observatories 2.3-m telescope. We investigate the evolution of the spectrum between 7 and 94 d after V-band maximum in comparison with well-studied examples of Type Ic SNe in order to quantify the unusual properties of this supernova event. Though the early spectra differ greatly from observations of classical Ic supernovae (SNe), we find that the evolution from the photospheric to nebular phases is slow but otherwise typical. The spectra differ predominantly in the extensive line blending and blanketing which has been attributed to the high velocity of the ejecta. We find that by day 19, the absorption line minima blueshifts are 10–50 per cent higher than other SNe and on day 94 emission lines are 45 per cent broader, as expected if the progenitor had a massive envelope. However, it is difficult to explain the extent of line blanketing entirely by line broadening, and we argue that an additional contribution from other species is present, indicating unusual relative abundances or physical conditions in the envelope. [ABSTRACT FROM AUTHOR]

ABSTRACT UBVI CCD photometry has been obtained for the intermediate-age open cluster M35 (NGC 2168). From this new photometry we derived the cluster parameters (V[sub 0] - M[sub V]= 9.60 ± 0.10 mag, E(B-V) = 0.255 ± 0.024 mag), age (log t[sub age]=8.3 ±0.3) and a photometric abundance (Z ≈ 0.008, i.e. [Fe/H] ≈ - 0.3) from comparison with theoretical isochrones of the Padova group. A minimum binary frequency (35 ± 5 per cent) was estimated from the distribution of distance moduli of unevolved proper motion members. Faint photometric members were selected by using differences in the reddening effect on colour indices. [ABSTRACT FROM AUTHOR]