NEW DETECTIONS OF ARSENIC, SELENIUM, AND OTHER HEAVY ELEMENTS IN TWO METAL-POOR STARS

We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 [< or =, slant] [lambda] [< or =, slant] 2360 A wavelength range for two metal-poor stars, HD 108317 and HD 128279. We derive abundances of Cu II, Zn II, As...

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Bibliographic Details
Published in:	The Astrophysical journal 2014-08, Vol.791 (1), p.1-12
Main Authors:	Roederer, Ian U, Schatz, Hendrik, Lawler, James E, Beers, Timothy C, Cowan, John J, FREBEL, ANNA, Ivans, Inese I, Sneden, Christopher, Sobeck, Jennifer S
Format:	Article
Language:	eng
Subjects:	ARSENIC ASTROPHYSICS, COSMOLOGY AND ASTRONOMY Brackets CADMIUM Constants COPPER DETECTION ELEMENT ABUNDANCE EXTRAPOLATION Hubble Space Telescope IRON Local thermodynamic equilibrium LTE MASS METALLICITY MOLYBDENUM NUCLEOSYNTHESIS SELENIUM SPACE SPECTRA STARS TELESCOPES WAVELENGTHS ZINC
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Summary:	We use the Space Telescope Imaging Spectrograph on board the Hubble Space Telescope to obtain new high-quality spectra covering the 1900 [< or =, slant] [lambda] [< or =, slant] 2360 A wavelength range for two metal-poor stars, HD 108317 and HD 128279. We derive abundances of Cu II, Zn II, As I, Se I, Mo II, and Cd II, which have not been detected previously in either star. Abundances derived for Ge I, Te I, Os II, and Pt I confirm those derived from lines at longer wavelengths. We also derive upper limits from the non-detection of W II, Hg II, Pb II, and Bi I. The mean [As/Fe] ratio derived from these two stars and five others in the literature is unchanged over the metallicity range -2.8 < [Fe/H] < -0.6, [left angle bracket][As/Fe][right angle bracket] = +0.28 + or - 0.14 ([sigma] = 0.36 dex). The mean [Se/Fe] ratio derived from these two stars and six others in the literature is also constant, [left angle bracket][Se/Fe][right angle bracket] = +0.16 + or - 0.09 ([sigma] = 0.26 dex). The As and Se abundances are enhanced relative to a simple extrapolation of the iron-peak abundances to higher masses, suggesting that this mass region (75 [< or =, slant] A [< or =, slant] 82) may be the point at which a different nucleosynthetic mechanism begins to dominate the quasi-equilibrium alpha -rich freezeout of the iron peak. [left angle bracket][Cu II/Cu I][right angle bracket] = +0.56 + or - 0.23 in HD 108317 and HD 128279, and we infer that lines of Cu I may not be formed in local thermodynamic equilibrium in these stars. The [Zn/Fe], [Mo/Fe], [Cd/Fe], and [Os/Fe] ratios are also derived from neutral and ionized species, and each ratio pair agrees within the mutual uncertainties, which range from 0.15 to 0.52 dex.
ISSN:	0004-637X 1538-4357