Hubble Space Telescope Near-ultraviolet Spectroscopy of the Bright CEMP-no Star BD+44°493

July 2014 • 2014ApJ...790...34P

Authors • Placco, Vinicius M. • Beers, Timothy C. • Roederer, Ian U. • Cowan, John J. • Frebel, Anna • Filler, Dan • Ivans, Inese I. • Lawler, James E. • Schatz, Hendrik • Sneden, Christopher • Sobeck, Jennifer S. • Aoki, Wako • Smith, Verne V.

Abstract • 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 epsilon (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 epsilon (Be) <-2.3, and lead, log epsilon (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.

Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with program GO-12554, and we also make use of data taken in program GO-12268.

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Jennifer Sobeck

Associate Scientist