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No one has yet observed the first stars that formed in the Milky Way. In all likelihood, they will never be directly observed, because the first stars are massive, ending their lives only a few millions years after their birth.
But, astronomers can study those oldest stars by examining the elements these stars produced through nuclear fusion and the supernova explosions that mark the spectacular ends of their short lives.
Timothy Beers, the Notre Dame Chair in Astrophysics at the University of Notre Dame, is part of a team that has used the Cosmic Origins Spectrograph (COS) on the Hubble Space Telescope to study key regions of the ultraviolet (UV) spectrum of a star thought to have been enriched by elements from one of the first generation of stars. This star, named BD+44 493, is the brightest known second-generation star in the sky. While examining its UV spectrum, Beers and his team detected several elements that had never been seen before in such a star. Their findings were published Monday (June 20) in the Astrophysical Journal Letters.
Beers and his team detected phosphorus and sulphur, which had never been seen previously, and zinc, which had only been seen in one such second-generation star. They compared the amounts of each element to model predictions to learn about the nature of one of the first stars.
Their work is the first to use COS on the Hubble Space Telescope to study the elements in ancient stars. These never-before-seen products of one of the first stars reveal that the particular star that introduced these atoms into space was likely massive, probably more than 20 times more massive than our own Sun, and exploded as a relatively faint supernova.
At present, only the Hubble Space Telescope can collect the UV spectra needed to study these elements in ancient stars. These results foreshadow the exciting possibility of studying dozens or even hundreds of these ancient stars with the next generation of UV spectrographs on space telescopes, like the High Definition Space Telescope now under consideration by NASA.
Quelle: University of Notre Dame
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Authors of the study are Ian U. Roederer at the University of Michigan, and Beers and Vinicius M. Placco at the University of Notre Dame. The paper is available online here: http://iopscience.iop.org/article/10.3847/2041-8205/824/2/L19.:
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The Astrophysical Journal Letters
American Astronomical Society
A publishing partnership
DETECTION OF PHOSPHORUS, SULPHUR, AND ZINC IN THE CARBON-ENHANCED METAL-POOR STAR BD+44 493*
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Abstract
The carbon-enhanced metal-poor star BD+44°493 ([Fe/H] = −3.9) has been proposed as a candidate second-generation star enriched by metals from a single Pop III star. We report the first detections of P and S and the second detection of Zn in any extremely metal-poor carbon-enhanced star, using new spectra of BD+44°493 collected by the Cosmic Origins Spectrograph on the Hubble Space Telescope. We derive [P/Fe] = −0.34 ± 0.21, [S/Fe] = +0.07 ± 0.41, and [Zn/Fe] = −0.10 ± 0.24. We increase by 10-fold the number of Si i lines detected in BD+44°493, yielding [Si/Fe] = +0.15 ± 0.22. The [S/Fe] and [Zn/Fe] ratios exclude the hypothesis that the abundance pattern in BD+44°493 results from depletion of refractory elements onto dust grains. Comparison with zero-metallicity supernova (SN) models suggests that the stellar progenitor that enriched BD+44°493 was massive and ejected much less than 0.07 M ⊙ of 56Ni, characteristic of a faint SN.
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