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Stars: abundances

Articles 1 - 13 of 13

Full-Text Articles in Physical Sciences and Mathematics

Lithium In The Upper Centaurus Lupus And Lower Centaurus Crux Subgroups Of Scorpius-Centaurus, Eric J. Bubar, Marc Schaeuble, Jeremy R. King, Eric E. Mamajek, John R. Stauffer Dec 2011

Lithium In The Upper Centaurus Lupus And Lower Centaurus Crux Subgroups Of Scorpius-Centaurus, Eric J. Bubar, Marc Schaeuble, Jeremy R. King, Eric E. Mamajek, John R. Stauffer

Publications

We utilize spectroscopically derived model atmosphere parameters and the Li i λ6104 subordinate line and the λ6708 doublet to derive lithium abundances for 12 members of the Upper Centaurus Lupus and Lower Centaurus Crux subgroups of the Scorpius–Centaurus OB Association. The results indicate any intrinsic Li scatter in our 0.9–1.4 M stars is limited to ∼0.15 dex, consistent with the lack of dispersion in 1.0 M stars in the 100 Myr Pleiades and 30–50 Myr IC 2391 and 2602 clusters. Both ab initio uncertainty estimates and the derived abundances themselves indicate that the ...


Detailed Abundances Of The Solar Twins 16 Cygni And B Cygni: Constraining Planet Formation Models, Simon C. Schuler, Katia Cunha, Verne V. Smith, Luan Ghezzi, Jeremy R. King, Constantine P. Deliyannis, Ann Merchant Boesgaard Aug 2011

Detailed Abundances Of The Solar Twins 16 Cygni And B Cygni: Constraining Planet Formation Models, Simon C. Schuler, Katia Cunha, Verne V. Smith, Luan Ghezzi, Jeremy R. King, Constantine P. Deliyannis, Ann Merchant Boesgaard

Publications

Results of a detailed abundance analysis of the solar twins 16 Cyg A and 16 Cyg B based on high-resolution, high signal-to-noise ratio echelle spectroscopy are presented. 16 Cyg B is known to host a giant planet while no planets have yet been detected around 16 Cyg A. Stellar parameters are derived directly from our high-quality spectra, and the stars are found to be physically similar, with ΔTeff = +43 K, Δ log g =−0.02 dex, and Δξ = +0.10 km s−1 (in the sense of A − B), consistent with previous findings. Abundances of 15 elements are derived and ...


Abundances Of Stars With Planets: Trends With Condensation Temperature, Simon C. Schuler, Davin Flateau, Katia Cunha, Jeremy R. King, Luan Ghezzi, Verne V. Smith May 2011

Abundances Of Stars With Planets: Trends With Condensation Temperature, Simon C. Schuler, Davin Flateau, Katia Cunha, Jeremy R. King, Luan Ghezzi, Verne V. Smith

Publications

Precise abundances of 18 elements have been derived for 10 stars known to host giant planets from high signal-to-noise ratio, high-resolution echelle spectroscopy. Internal uncertainties in the derived abundances are typically 0.05 dex. The stars in our sample have all been previously shown to have abundances that correlate with the condensation temperature (Tc) of the elements in the sense of increasing abundances with increasing Tc; these trends have been interpreted as evidence that the stars may have accreted H-depleted planetary material. Our newly derived abundances also correlate positively with Tc, although slopes of linear least-square fits to the [m ...


Spectroscopic Abundances And Membership In The Wolf 630 Moving Group, Eric J. Bubar, Jeremy R. King Aug 2010

Spectroscopic Abundances And Membership In The Wolf 630 Moving Group, Eric J. Bubar, Jeremy R. King

Publications

The concept of kinematic assemblages evolving from dispersed stellar clusters has remained contentious since Eggen’s initial formulation of moving groups in the 1960s. With high-quality parallaxes from the Hipparcos space astrometry mission, distance measurements for thousands of nearby, seemingly isolated stars are currently available. With these distances, a high-resolution spectroscopic abundance analysis can be brought to bear on the alleged members of these moving groups. If a structure is a relic of an open cluster, the members can be expected to be monolithic in age and abundance in as much as homogeneity is observed in young open clusters. In ...


Fe I And Fe Ii Abundances Of Solar-Type Dwarfs In The Pleiades Open Cluster, Simon C. Schuler, Adele L. Plunkett, Jeremy R. King, Marc H. Pinsonneault May 2010

Fe I And Fe Ii Abundances Of Solar-Type Dwarfs In The Pleiades Open Cluster, Simon C. Schuler, Adele L. Plunkett, Jeremy R. King, Marc H. Pinsonneault

Publications

We have derived Fe abundances of 16 solar-type Pleiades dwarfs by means of an equivalent width analysis of Fe I and Fe II lines in high-resolution spectra obtained with the Hobby - Eberly Telescope and High Resolution Spectrograph. Abundances derived from Fe II lines are larger than those derived from Fe I lines (herein referred to as over-ionization) for stars with Teff < 5400 K, and the dis-crepancy (∆Fe = [Fe II/H] - [Fe I/H]) increases dramatically with decreasing Teff, reaching over 0.8 dex for the coolest stars of our sample. The Pleiades joins the open clusters M34, the Hyades, IC2602, and IC2391, and the Ursa Major moving group, demonstrating ostensible over-ionization trends. The Pleiades ∆Fe abun-dances are correlated with Ca II infrared triplet and Hα chromospheric emission indicators and relative differences therein. Oxygen abundances of our Pleiades sample derived from the high-excitation O I triplet have been previously shown to increase with decreasing Teff, and a comparison with the ∆Fe abundances sug-gests that the over-excitation (larger abundances derived from high excitation lines relative to low excitation lines) and over-ionization effects that have been observed in cool open cluster and disk field main sequence (MS) dwarfs share a common origin. Curiously, a correlation between the Pleiades O I abundances and chromospheric emission indicators does not exist. Star-to-star Fe I abun-dances have low internal scatter (< 0.11 dex), but the abundances of stars with Teff< 5400 K are systematically higher compared to the warmer stars. The cool star [Fe I/H] abundances cannot be connected directly to over-excitation effects, but similarities with the ∆Fe and O I triplet trends suggest the abundances are dubious. Using the [Fe I/H] abundances of five stars with Teff > 5400 K, we derive a mean Pleiades cluster metallicity of [Fe/H] = +0.01 ± 0.02.


Possible Identification Of A Metal-Rich Old Moving Group: High-Resolution Spectroscopy Of Candidate Members, Abigail R. Daane, Jeremy R. King, Simon C. Schuler Apr 2007

Possible Identification Of A Metal-Rich Old Moving Group: High-Resolution Spectroscopy Of Candidate Members, Abigail R. Daane, Jeremy R. King, Simon C. Schuler

Publications

Using new high-resolution spectroscopic observations from both the McDonald Observatory 2.7 m and Kitt Peak National Observatory 4 m telescopes, we observed four candidate members of the Ursa Major moving group previously suggested to instead belong to a significantly older kinematic assemblage. The Fe abundances we measure strongly suggest that these stars are not UMa members but form a more metal-rich group of stars (+0.10 ≤ [Fe/H] ≤ +0.18) with an age near 3 Gyr. Our [Ca/H] determinations corroborate this result. The apparent similarities in metallicity and previously discovered UVW space motions lend credence to prior suggestions ...


Infrared High-Resolution Spectroscopy Of Post-Agb Circumstellar Disks. I. Hr 4049: The Winnowing Flow Observed?, Kenneth H. Hinkle, Sean D. Brittain, David L. Lambert Apr 2007

Infrared High-Resolution Spectroscopy Of Post-Agb Circumstellar Disks. I. Hr 4049: The Winnowing Flow Observed?, Kenneth H. Hinkle, Sean D. Brittain, David L. Lambert

Publications

High-resolution infrared spectroscopy in the 2.3-4.6 micron region is reported for the peculiar A supergiant, single-lined spectroscopic binary HR 4049. Lines from the CO fundamental and first overtone, OH fundamental, and several H2O vibration-rotation transitions have been observed in the near-infrared spectrum. The spectrum of HR 4049 appears principally in emission through the 3 and 4.6 micron region and in absorption in the 2 micron region. The 4.6 micron spectrum shows a rich 'forest' of emission lines. All the spectral lines observed in the 2.3-4.6 micron spectrum are shown to be circumbinary in origin ...


Chemical Composition In The Globular Cluster M71 From Keck Hires Spectra Of Turnoff Stars, Ann Merchant Boesgaard, Jeremy R. King, Ann Marie Cody, Alex Stephens, Constantine P. Deliyannis Aug 2005

Chemical Composition In The Globular Cluster M71 From Keck Hires Spectra Of Turnoff Stars, Ann Merchant Boesgaard, Jeremy R. King, Ann Marie Cody, Alex Stephens, Constantine P. Deliyannis

Publications

We have made observations with the Keck I telescope and HIRES at a resolution of ∼45,000 of five nearly identical stars at the turn-off of the metal-rich globular cluster M 71. Our mean Fe abundance, [Fe/H]=-0.80 +-0.02, is in excellent agreement with previous cluster determinations from both giants and near-turnoff stars. There is no clear evidence for any star-to-star abundance differences or correlations in our sample. Abundance ratios of the Fe-peak elements (Cr, Ni) are similar to Fe. The turn-off stars in M71 have remarkably consistent enhancements of 0.2 - 0.3 dex in [Si ...


Beryllium Enhancement As Evidence For Accretion In A Lithium-Rich F Dwarf, Johanna F. Ashwell, R D. Jeffries, Barry Smalley, C P. Deliyannis, Aaron Steinhauer, Jeremy R. King Aug 2005

Beryllium Enhancement As Evidence For Accretion In A Lithium-Rich F Dwarf, Johanna F. Ashwell, R D. Jeffries, Barry Smalley, C P. Deliyannis, Aaron Steinhauer, Jeremy R. King

Publications

The early F dwarf star ``J37'' in the open cluster NGC6633 shows an unusual pattern of photospheric abundances, including an order of magnitude enhancement of lithium and iron-peak elements, but an under-abundance of carbon. As a consequence of its thin convection zone these anomalies have been attributed to either radiative diffusion or the accretion of hydrogen-depleted material. By comparing high resolution VLT/UVES spectra of J37 (and other F stars in NGC 6633) with syntheses of the Be ii doublet region at 3131 Ang, we establish that J37 also has a Be abundance (A(Be)=3.0+/-0.5) that ...


The Correlation Of Lithium And Beryllium In F And G Cluster Dwarf Stars, Ann Merchant Boesgaard, Eric Armengaud, Constantine P. Deliyannis, Alex Stephens, Jeremy R. King Oct 2004

The Correlation Of Lithium And Beryllium In F And G Cluster Dwarf Stars, Ann Merchant Boesgaard, Eric Armengaud, Constantine P. Deliyannis, Alex Stephens, Jeremy R. King

Publications

Although Li has been extensively observed in main-sequence field and cluster stars, there are relatively fewer observations of Be. We have obtained Keck HIRES spectra of 36 late F and early G dwarfs in order to study the Li-Be correlation we found previously in the temperature regime of 5900–6650 K. The sample size for this temperature range with detectable and (usually) depleted Li and Be is now 88, including Li and Be abundances in both cluster and field stars. Therefore we can now investigate the influence of other parameters such as age, temperature, and metallicity on the correlation. The ...


The Li Overabundance Of J37: Diffusion Or Accretion?, J F. Ashwell, R D. Jeffries, C P. Deliyannis, A Steinhauer, Jeremy R. King Aug 2004

The Li Overabundance Of J37: Diffusion Or Accretion?, J F. Ashwell, R D. Jeffries, C P. Deliyannis, A Steinhauer, Jeremy R. King

Publications

In September 2002 the discovery of a super Li-rich F-dwarf (J37) in NGC 6633, an iron poor analogue of the better studied Hyades and Praecepe open clusters, was announced. This unique star was thought to be the smoking gun for the action of diffusion, models of which predict a narrow ”Li-peak” at approximately the correct temperature. However, with more detailed studies into J37s abundance pattern this star provides firm evidence for the accretion of planetesimals or other material from the circumstellar environment of new born stars. Thanks to the specific predictions made about the behaviour of Be abundances, (the most ...


Beryllium Abundances In F And G Dwarfs In Praesepe And Other Young Clusters From Keck Hires Observations, Ann Merchant Boesgaard, Eric Armengaud, Jeremy R. King Apr 2004

Beryllium Abundances In F And G Dwarfs In Praesepe And Other Young Clusters From Keck Hires Observations, Ann Merchant Boesgaard, Eric Armengaud, Jeremy R. King

Publications

The study of both Be and Li gives useful clues about stellar internal structure. Of particular interest is the study of these light elements in open clusters, which have a known age and metallicity. In this paper we present a study of Be abundances in 10 F-type stars in Praesepe and a comprehensive discussion about Be abundances in other open clusters: Hyades, Pleiades, Per, Coma, and UMa. We have made observations of the doublet of Be ii around 3130 A˚ in Praesepe stars, using the Keck I telescope and the High Resolution Echelle Spectrometer (HIRES). Beryllium abundances were derived from ...


Oxygen In Open Cluster Dwarfs: Pleiades And M34, Simon C. Schuler, Jeremy R. King, L M. Hobbs, Marc H. Pinsonneault Feb 2004

Oxygen In Open Cluster Dwarfs: Pleiades And M34, Simon C. Schuler, Jeremy R. King, L M. Hobbs, Marc H. Pinsonneault

Publications

We analyze the high-excitation O I lambda7774 triplet in high-resolution, moderate signal-to-noise ratio spectra of 15 Pleiades and eight M34 open cluster dwarfs over the effective temperature range of 5048-6172 K. Relative O abundances have been derived using model atmospheres interpolated from four different sets of ATLAS9 grids. In contrast to existing non-LTE (NLTE) predictions, a dramatic increase in the O I triplet abundance with decreasing temperature is seen for both clusters, regardless of the atmospheric model. S I abundances of three Pleiades stars derived from the high-excitation lambda6053 feature mimic the O I abundance behavior. O abundances have also ...