Astrophys. J., 790, 34 (2014/July-3)
Hubble Space Telescope near-ultraviolet spectroscopy of the bright CEMP-no star BD+44°493.
PLACCO V.M., BEERS T.C., ROEDERER I.U., COWAN J.J., FREBEL A., FILLER D., IVANS I.I., LAWLER J.E., SCHATZ H., SNEDEN C., SOBECK J.S., AOKI W. and SMITH V.V.
Abstract (from CDS):
We present an elemental-abundance analysis, in the near-ultraviolet (NUV) spectral range, for the extremely metal-poor star BD+44°493 a ninth magnitude subgiant with [Fe/H] =-3.8 and enhanced carbon, based on data acquired with the Space Telescope Imaging Spectrograph on the Hubble Space Telescope. This star is the brightest example of a class of objects that, unlike the great majority of carbon-enhanced metal-poor (CEMP) stars, does not exhibit over-abundances of heavy neutron-capture elements (CEMP-no). In this paper, we validate the abundance determinations for a number of species that were previously studied in the optical region, and obtain strong upper limits for beryllium and boron, as well as for neutron-capture elements from zirconium to platinum, many of which are not accessible from ground-based spectra. The boron upper limit we obtain for BD+44°493, log ε (B) ←0.70, the first such measurement for a CEMP star, is the lowest yet found for very and extremely metal-poor stars. In addition, we obtain even lower upper limits on the abundances of beryllium, log ε (Be) ←2.3, and lead, log ε (Pb) ←0.23 ([Pb/Fe] <+1.90), than those reported by previous analyses in the optical range. Taken together with the previously measured low abundance of lithium, the very low upper limits on Be and B suggest that BD+44°493 was formed at a very early time, and that it could well be a bona-fide second-generation star. Finally, the Pb upper limit strengthens the argument for non-s-process production of the heavy-element abundance patterns in CEMP-no stars.
Galaxy: halo - stars: abundances - stars: atmospheres - stars: individual: BD+44 493 - stars: Population II - techniques: spectroscopic
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