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Detection Of Silver In Metal-Poor Stars, James L. Crawford, Christopher Sneden, Jeremy R. King, Ann M. Boesgaard, Contantine P. Deliyannis
Detection Of Silver In Metal-Poor Stars, James L. Crawford, Christopher Sneden, Jeremy R. King, Ann M. Boesgaard, Contantine P. Deliyannis
Publications
The resonance lines of neutral silver appearing at 3280, 3382 Å in the near-ultraviolet spectral region have been identified on Keck I HIRES spectra of four halo stars with metallicities -1.3 ≥ [Fe/H] ≥ -2.2. This represents the first detection in metal-poor stars of an element in the atomic number range 41 ≤ Z ≤ 55. The mean relative silver abundance is [Ag/Fe] +0.2, with little star-to-star variation. Silver abundance upper limits in three other metal-poor stars are consistent with this mean value. The modest overabundance of silver is similar to the overabundances in this metallicity range exhibited by other …
The Problem Of Hipparcos Distances To Open Clusters. I. Constraints From Multicolor Main-Sequence Fitting, Marc H. Pinsonneault, John Stauffer, David Soderblom, Jeremy R. King, Robert B. Hanson
The Problem Of Hipparcos Distances To Open Clusters. I. Constraints From Multicolor Main-Sequence Fitting, Marc H. Pinsonneault, John Stauffer, David Soderblom, Jeremy R. King, Robert B. Hanson
Publications
Parallax data from the Hipparcos mission allow the direct distance to open clusters to be compared with the distance inferred from main-sequence (MS) Ðtting. There are surprising differences between the two distance measurements, indicating either the need for changes in the cluster compositions or reddening, underlying problems with the technique of MS Ðtting, or systematic errors in the Hipparcos parallaxes at the 1 mas level. We examine the di†erent possibilities, focusing on MS fitting in both metallicity-sensitive B[V and metallicity-insensitive V [I for five well-studied systems (the Hyades, Pleiades, a Per, Praesepe, and Coma Ber). The Hipparcos distances to the …
Lithium In The Young Cluster Ngc 2264, Jeremy R. King
Lithium In The Young Cluster Ngc 2264, Jeremy R. King
Publications
We use moderate-resolution, moderate signal-to-noise ratio spectroscopy to derive Li abundances for six F and G stars in the young (few Myr) cluster NGC 2264. These are combined with consistently determined abundances of five NGC 2264 G and K stars having published Li data. The mean non-LTE abundance, calculated with photometric temperatures, is log N(Li) = 3.27 ± 0.05. This is essentially identical to the meteoritic value, providing no evidence of Galactic Li enrichment over the past 4.6 Gyr—at least to the extent that the meteoritic value represents a typical "cosmic" value at that time. The scatter of 0.16 dex …
High Resolution Spectroscopy Of Some Very Active Southern Stars, David R. Soderblom, Jeremy R. King, Todd J. Henry
High Resolution Spectroscopy Of Some Very Active Southern Stars, David R. Soderblom, Jeremy R. King, Todd J. Henry
Publications
We have obtained high-resolution echelle spectra of 18 solar-type stars that an earlier survey showed to have very high levels of Ca II H and K emission. Most of these stars belong to close binary systems, but five remain as probable single stars or well-separated binaries that are younger than the Pleiades on the basis of their lithium abundances and Hα emission. Three of these probable single stars also lie more than 1 mag above the main sequence in a color-magnitude diagram, and appear to have ages of 10 to 15 Myr. Two of them, HD 202917 and HD 222259, …
Keck Hires Spectroscopy Of M92 Subgiants: Surprising Abundances Near The Turnoff, Jeremy R. King, Alex Stephens, Ann Merchant Boesgaard, Constantine P. Deliyannis
Keck Hires Spectroscopy Of M92 Subgiants: Surprising Abundances Near The Turnoff, Jeremy R. King, Alex Stephens, Ann Merchant Boesgaard, Constantine P. Deliyannis
Publications
Using high-resolution, moderate signal-to-noise ratio spectroscopy obtained with the 10 m Keck I Telescope and efficient HIRES echelle spectrograph, we derive abundances of several elements in subgiants near the M92 turnoff. As a consistency check, we also analyze the metal-poor field star HD 140283 and find an Fe abundance in fine agreement with many previous determinations. However, our M92 value ([Fe/H] = -2.52) is a factor of 2 lower than the abundance derived from its red giant members. Differences in model atmospheres, gf-values, and instrumental effects might account for this difference, but whether they in fact do so is unclear. …
Primordial Lithium: Keck Observations In M92 Turnoff Stars, Ann Merchant Boesgaard, Constantine Deliyannis, Alex Stephens, Jeremy R. King
Primordial Lithium: Keck Observations In M92 Turnoff Stars, Ann Merchant Boesgaard, Constantine Deliyannis, Alex Stephens, Jeremy R. King
Publications
We present new Keck I/HIRES observations at R\45,000 (\3 pixels) of seven stars near the turno† of the old, metal-poor globular cluster M92. In three of these stars, we have signal-to-noise ratios (S/Ns) of 40 pixel~1, and in the other four, the S/N is near 20. The Li abundance in star 18 is high compared with the halo Ðeld-star plateau and is similar to that in the remarkable Li-rich halo Ðeld star BD ]23¡3912. In addition to the high Li abundance in star 18, there is a dispersion in Li abundance in our seven stars covering the full range of …