A Spectroscopic Analysis of the Eclipsing Short-Period Binary v505 Per and the Origin of the Lithium Dip

As a test of rotationally-induced mixing causing the well-known Li dip in older mid-F dwarfs in the local Galactic disk, we utilize high-resolution and -S/N Keck/HIRESspectroscopy to measure the Li abundance in the components of the1 Gyr, [Fe/H]=-0.15 eclipsing short-period binary V505 Per. We find A(Li)=2.7+/-0.1 and 2.4+/-0.2 in the Teff=6500 and 6450 K primary and secondary components, respectively. Previous Teff determinations and uncertainties suggest that each component is located in the midst of the Li dip. If so, their A(Li) are >=2-5 times larger than A(Li) detections and upper limits observed in the similar metallicity and intermediate-age open clusters NGC 752 and 3680, as well as the more metal-rich and younger Hyades and Praesepe. These differences are even larger if the consistent estimates of the scaling ofinitial Li with metallicity inferred from nearby disk stars, open clusters, and recent Galactic chemical evolution models are correct. Our results suggest, independently of complementary evidence based on Li/Be ratios, Be/B ratios, and Li in subgiants evolving out of the Li dip, that main-sequence angular momentum evolution is the origin of the Li dip. Specifically, our stars' A(Li) indicates tidal synchronization can be sufficiently efficient and occur early enough in short-period binary mid-F stars to reduce the effects of rotationally-induced mixing and destruction of Li occuring during the main-sequence in otherwise similar stars that are not short-period tidally-locked binaries.Comment: Accepted for publication in Publications of the Astronomical Society of the Pacific (July 2013 volume

Evidence of Higher Primordial Lithium from Keck Observations of M92

Knowledge of the primordial lithium abundance (Lip) tests and constrains models of big bang nucleosynthesis and may have implications for dark matter and the laws of physics. An apparent small dispersion in the Li abundances of field halo dwarfs had been predicted to result from differences in the Li depletion of models with rotationally induced mixing, and would imply a higher Lip than is observed today in these stars. However, this dispersion could also be explained by differential Galactic Li enrichment (from lower Lip) coupled with a halo age spread and/or incomplete mixing. To differentiate between these possibilities, we have obtained Keck/HIRES observations at R = 45,000 in one of the oldest and most metal-poor globular clusters, M92, where differential Li enrichment within the cluster is unlikely. We find some evidence for differences in the Li abundances of three otherwise apparently identical M92 subgiants in the Spite Li plateau. We provide evidence against cosmic-ray, supernova, and asymptotic giant branch star Li production as causing these Li differences, and suggest that different stellar surface Li depletion histories in these stars from a higher initial abundance is a more likely explanation (as is also the case for open clusters). This higher initial abundance may have been the Lip, or a combination of Lip plus significant pre-M92 Galactic Li. Implications are discussed

The 9Be Abundances of alpha Centauri A and B and the Sun: Implications for Stellar Evolution and Mixing

We present high-resolution, high signal-to-noise ratio spectra, obtained at the Cerro Tololo Inter-American Observatory 4 m telescope, of the Be II 3131 Å region in the metal-rich solar analog α Centauri A and its companion α Centauri B. Be abundances are derived relative to the Sun in a consistent fashion via spectrum synthesis. For α Cen A, we find [Be/H] = +0.20 ± 0.15, where the error reflects random uncertainties at the 1 σ confidence level; systematic errors of ~0.1 dex are also possible. The analysis of α Cen B is more uncertain since inadequacies in the line list, which was calibrated with solar data, may manifest themselves in cool metal-rich dwarfs. Our analysis suggests [Be/H] +0.05, which is lower than the value of A, but not significantly so given the uncertainties in the A determination alone. In order to derive a conservatively probable and larger extreme range for the solar photospheric Be abundance, we consider various uncertainties (including those in the gf-values, continuum location, non-LTE effects, model atmospheres, analysis codes, and contaminating blends) in its determination. We conclude that the probable range of depletion of photospheric Be from the meteoritic value is 0.16-0.50 dex. Our larger extreme range is 0.05-0.62 dex. Even a slight real depletion in solar photospheric Be itself would strongly contradict the standard solar model (as does the Sun\u27s Li depletion), suggesting the action of additional mechanisms. When coupled with the solar Li depletion of only ~2 dex, Be depletion would point to mixing mechanisms (possibly rotationally induced) below the surface convection zone acting on a timescale that is much longer than the convective timescale. If the difference in the Be abundances of α Cen A and B is real, it too would strongly suggest the action of additional mixing mechanisms. The study of both stars with higher resolution data and improved atomic and molecular data is clearly important. We conclude that the light-element abundances of the Sun and α Cen A (and other solar analogs) are not grossly dissimilar. The idea that standard models and the current solar photospheric Li and Be abundance are discrepant because the Sun is a lone oddball is doubtful. We also have considered the issue of the unidentified blending feature(s) in the Be II 3131.065 Å region. While a putative Mn I λ3131.037 feature has several favorable characteristics, we suggest that a single significant blending feature likely lies ~0.02 Å blueward of this position

A UvbyCa Hβ ANALYSIS OF THE OLD OPEN CLUSTER, NGC 6819

This is the published version. Copyright © 2014. The American Astronomical Society. All rights reserved.NGC 6819 is a richly populated, older open cluster situated within the Kepler field. A CCD survey of the cluster on the uvbyCaHβ system, coupled with proper-motion membership, has been used to isolate 382 highly probable, single-star unevolved main-sequence members over a 20' field centered on the cluster. From 278 F dwarfs with high precision photometry in all indices, a mean reddening of E(b – y) = 0.117 ± 0.005 or E(B – V) = 0.160 ± 0.007 is derived, where the standard errors of the mean include both internal errors and the photometric zero-point uncertainty. With the reddening fixed, the metallicity derived from the same 278 stars is [Fe/H] = –0.116 ± 0.101 from m 1 and –0.055 ± 0.033 from hk, for a weighted average of [Fe/H] = –0.06 ± 0.04, where the quoted standard errors of the mean include the internal errors from the photometric scatter plus the uncertainty in the photometric zero points. If metallicity is derived using individual reddening values for each star to account for potential reddening variation across the face of the cluster, the analogous result is unchanged. The cluster members at the turnoff of the color-magnitude diagram are used to test and confirm the recently discovered variation in reddening across the face of the cluster, with a probable range in the variation of ΔE(B – V) = 0.045 ± 0.015. With the slightly higher reddening and lower [Fe/H] compared to commonly adopted values, isochrone fitting leads to an age of 2.3 ± 0.2 Gyr for an apparent modulus of (m – M) = 12.40 ± 0.12

WIYN OPEN CLUSTER STUDY. LXXII. A uvbyCaHβ CCD ANALYSIS OF THE METAL-DEFICIENT OPEN CLUSTER NGC 2506

Precision uvbyCaHβ photometry of the metal-deficient, old open cluster NGC 2506 is presented. The survey covers an area of $20^{\prime} \times 20^{\prime}$ and extends to $V\sim 18$ for b − y and Hβ and to $V\sim 17.0$ for c 1 and hk. For V brighter than 16.0, photometric scatter among the indices leads to the recovery of six known variables within the cluster core and five new variables in the outer $5^{\prime}$ of the survey field. Proper motions, radial velocities, and precise multicolor indices are used to isolate a highly probable sample of cluster members from the very rich color–magnitude diagram. From 257 highly probable members at the cluster turnoff, we derive a reddening estimate of $E(b-y)=0.042\pm 0.001$ ($E(B-V)=0.058\pm 0.001$), where the errors refer to the internal standard errors of the mean. [Fe/H] is derived from the A/F dwarf members using both m 1 and hk, leading to [Fe/H] = −0.296 ± 0.011 (sem) and −0.317 ± 0.004 (sem), respectively. The weighted average, heavily dominated by hk, is [Fe/H] = −0.316 ± 0.033. Based on red giant members, we place an upper limit of ±0.010 on the variation in the reddening across the face of the cluster. We also identify two dozen potential red giant cluster members outside the cluster core. Victoria–Regina isochrones on the Strömgren system produce an excellent match to the cluster for an apparent modulus of $(m-M)=12.75\pm 0.1$ and an age of 1.85 ± 0.05 Gyr

Constraints on the Origin of the Remarkable Lithium Abundance in the Halo Star BD+23 3912

The Li abundance of the halo star BD+23 3912 ([Fe/H]=-1.5) lies a factor of 2 - 3 above the Spite plateau. This remarkable difference could reflect either less-than-average stellar Li depletion from a higher primordial Li abundance (as predicted by the Yale rotational stellar evolutionary models), which may have interesting implications for Big Bang nucleosynthesis, or the extraordinary action of Galactic Li production mechanisms. It is also possible that both processes have acted. We use our high resolution, high S/N Keck HIRES spectrum of BD+23 3912 to determine the s-process element abundances and 6Li/7Li ratio in this star. These values serve as signatures for two possible Li production scenarios: the 7Be transport mechanism in AGB stars, and cosmic ray interactions with the ISM. The unremarkable abundances of Y, Zr, Ba, La, Nd, and Sm that we derive argue against a significant contribution to this star\u27 S excess Li from AGB production mechanisms carrying an s-process signature. Since halo subgiants like BD+23 3912 are expected to be particularly good 6Li preservers, our conservative upper limit of 6Li/7Li\u3c=0.15 (compared to 0.25-0.50 expected from cosmic ray production) argues against cosmic ray + ISM interactions as the source for the excess Li, unless Li depletion from an even higher abundance has occurred with preferential 6Li depletion. Highly speculative RGB production scenarios also seem unlikely given the normal Na and M abundances we find and the normal C and 0 abundances determined by others. The totality of Li data on halo subgiants argues against possible diffusion scenarios, in which all such stars dredge up Li that diffused during the main sequence. While the high Li abundance in BD+23 3912 is consistent with that expected from Yale rotational models having a lower-than-average initial angular momentum, future observations of -process elements (particularly 11B) produced in supernovae should provide additional constraints on any enrichment scenarios seeking to explain the large Li abundance of this interesting star

WIYN OPEN CLUSTER STUDY. LXXII. A uvbyCaHβ CCD ANALYSIS OF THE METAL-DEFICIENT OPEN CLUSTER NGC 2506

Precision uvbyCaHβ photometry of the metal-deficient, old open cluster NGC 2506 is presented. The survey covers an area of $20^{\prime} \times 20^{\prime}$ and extends to $V\sim 18$ for b − y and Hβ and to $V\sim 17.0$ for c 1 and hk. For V brighter than 16.0, photometric scatter among the indices leads to the recovery of six known variables within the cluster core and five new variables in the outer $5^{\prime}$ of the survey field. Proper motions, radial velocities, and precise multicolor indices are used to isolate a highly probable sample of cluster members from the very rich color–magnitude diagram. From 257 highly probable members at the cluster turnoff, we derive a reddening estimate of $E(b-y)=0.042\pm 0.001$ ($E(B-V)=0.058\pm 0.001$), where the errors refer to the internal standard errors of the mean. [Fe/H] is derived from the A/F dwarf members using both m 1 and hk, leading to [Fe/H] = −0.296 ± 0.011 (sem) and −0.317 ± 0.004 (sem), respectively. The weighted average, heavily dominated by hk, is [Fe/H] = −0.316 ± 0.033. Based on red giant members, we place an upper limit of ±0.010 on the variation in the reddening across the face of the cluster. We also identify two dozen potential red giant cluster members outside the cluster core. Victoria–Regina isochrones on the Strömgren system produce an excellent match to the cluster for an apparent modulus of $(m-M)=12.75\pm 0.1$ and an age of 1.85 ± 0.05 Gyr