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We have analyzed high-dispersion spectra in the Li 6708 Angstrom region for 167 stars within the anticenter cluster, NGC 2204. From 105 probable members, abundance analysis of 45 evolved stars produces [Fe/H] = -0.40 +/- 0.12, [Si/Fe] = 0.14 +/- 0.12, [Ca/Fe] = 0.29 +/- 0.07, and [Ni/Fe] = -0.12 +/- 0.10, where quoted errors are standard deviations. With E(B-V) = 0.07 and (m-M)_0 = 13.12, appropriate isochrones provide an excellent match from the main sequence through the tip of the giant branch for an age of 1.85 +/- 0.05 Gyr. Li spectrum synthesis produces A(Li) below 1.4 at the base of the red giant branch to a detectable value of -0.4 at the tip. Six probable AGB stars and all but one red clump star have only Li upper limits. A rapidly rotating red giant is identified as a possible Li-rich giant, assuming it is a red clump star. Main sequence turnoff stars have a well-defined A(Li) = 2.83 +/- 0.03 (sem) down to the Li-dip wall at the predicted mass of 1.29 solar masses. Despite the same isochronal age as the more metal-rich NGC 2506, the red giant luminosity distribution reflects a younger morphology similar to NGC 7789, possibly indicating a deeper metallicity impact on stellar structure and A(Li) than previously assumed. As in NGC 2506 and NGC 7789, the NGC 2204 turnoff exhibits a broad range of rotation speeds, making abundance estimation impossible for some stars. The cluster place within Galactic A(Li) evolution is discussed., Comment: Accepted for publication in the Astronomical Journal; 24 pages, 8 figures

During Big Bang nucleosynthesis (BBN) in the first 15 minutes of the Universe some $^7$Li was created along with isotopes of H and He. The determination of that primordial value of Li can help constrain the conditions at that time. The oldest stars with known ages can be found in globular clusters which have well-determined ages through stellar evolution models. High-resolution spectra have been obtained with the Keck I telescope and HIRES of Li in several unevolved stars in the clusters M13 and M71 with V magnitudes of 17.6 -- 17.9. Abundances of Li have been determined with spectrum synthesis techniques and show a range of a factor of 4. We attribute that spread to differences in initial angular momentum resulting in different amounts of spin-down, related mixing, and destruction of Li. Our results are compared with similar results for main-sequences and turn-off stars in other globular clusters. The range in age of these clusters is 11.2 to 14.2 Gyr for an age span of 3 Gyr. These clusters range in [Fe/H] from $-$0.75 to $-$2.24 corresponding to a factor of 30 in metallicity. The maximum in the Li abundance for these unevolved stars in all eight clusters is the same corresponding to Li/H = 3.16 x 10$^{-10}$ while the predicted Li abundance, based on the deuterium abundance and the BBN predictions, is 5.24 x 10$^{-10}$., Comment: 19 pages, 4 tables, 5 figures Accepted for ApJ

The light element lithium is formed by nucleosynthesis during the Big Bang. Its abundance can help to define the parameters of the early universe. To find this primordial value, it is necessary to determine Li abundances in the oldest stars because it is readily destroyed by nuclear reactions in stellar interiors. We have made high-resolution (~45,000) spectroscopic observations of five identical unevolved turn-off stars in the 13 Gyr old globular cluster M5. In our analysis we find a range in Li abundance of a factor of two; the spread is five times the individual error. The comparison of these results with those for turn-off stars from five other globular clusters reveals similarly large range in Li. Lithium in M5 and the other clusters all have stars above the field star Li plateau, but none are as high as the predictions for primordial Li. The maximum values for Li are the same in all six clusters. Multiple generations of stars are found in many globular clusters; those later generations are expected to have formed from Li-depleted gas. Such second- and later-generation stars would have no Li. However, only one of the six clusters has a few unevolved stars with upper limits on the Li abundance., Comment: Accepted for Ap.J. 19 pages including 5 figures and 4 tables

We consider WIYN/Hydra spectra of 329 photometric candidate members of the 420-Myr-old open cluster M48, and report Lithium detections or upper limits for 234 members and likely members. The 171 single members define a number of notable Li-mass trends, some delineated even more clearly than in Hyades/Praesepe: The giants are consistent with subgiant Li dilution and prior MS Li depletion due to rotational mixing. A dwarfs (8600-7700K) have upper limits higher than the presumed initial cluster Li abundance. Two of five late A dwarfs (7700- 7200K) are Li-rich, possibly due to diffusion, planetesimal accretion, and/or engulfment of hydrogen-poor planets. Early F dwarfs already show evidence of Li depletion seen in older clusters. The Li-$T_{\rm eff}$ trends of the Li Dip (6675-6200K), Li Plateau (6200-6000K), and G and K dwarfs (6000-4000K) are very clearly delineated and are intermediate to those of the 120-Myr-old Pleiades and 650-Myr-old Hyades/Praesepe, which suggests a sequence of Li depletion with age. The cool side of the Li Dip is especially well-defined with little scatter. The Li-$T_{\rm eff}$ trend is very tight in the Li Plateau and early G dwarfs, but scatter increases gradually for cooler dwarfs. These patterns support and constrain models of the universally dominant Li depletion mechanism for FGK dwarfs, namely rotational mixing due to angular momentum loss; we discuss how diffusion and gravity-wave driven mixing may also play roles. For late-G/K dwarfs, faster rotators show higher Li than slower rotators, and we discuss possible connections between angular momentum loss and Li depletion., Comment: 29 pages, 10 figures, 5 tables, accepted for publication in the Astrophysical Journal

Precision CCD uvbyCaHbeta photometry is presented of the old cluster, M67, covering one square degree with typical internal precision at the 0.005-0.020 mag level to V~17. The photometry is calibrated using standards over a wide range in luminosity and temperature from NGC 752 and zeroed to the standard system via published photoelectric observations. Relative to NGC 752, differential offsets in reddening and metallicity are derived using astrometric members, supplemented by radial-velocity information. From single-star members, offsets in the sense (M67 - NGC 752) are Delta E(b-y) = -0.005 +/-0.001 (sem) mag from 327 F/G dwarfs and Delta [Fe/H] = 0.062 +/- 0.006 (sem) dex from the combined m1 and hk indices of 249 F dwarfs, leading to E(b-y) = 0.021 +/- 0.004 (sem), and [Fe/H] = +0.030 +/- 0.016 (sem) for M67, assuming [Fe/H]{Hyades} = +0.12. With probable binaries eliminated using c1,(b-y) indices, 83 members with relative parallax errors < 0.02 generate (m-M)_0 = 8.220 +/- 0.005 (sem) for NGC 752 and an isochronal age of 1.45 +/- 0.05 Gyr. Using the same parallax restriction for 312 stars, M67 has (m-M) = 9.77 +/- 0.02 (sem), leading to an age tied solely to the luminosity of the subgiant branch of 3.70 +/- 0.03 Gyr. The turnoff color spread implies +/- 0.1 Gyr, but the turnoff morphology defines a younger age/higher mass for the stars, consistent with recent binary analysis and broad-band photometry indicating possible missing physics in the isochrones. Anomalous stars positioned blueward of the turnoff are discussed., Comment: 36 pages, 8 figures. Accepted for Astronomical Journal

We present analyses of improved photometric and spectroscopic observations for two detached eclipsing binaries at the turnoff of the open cluster NGC 752: the 1.01 day binary DS And and the 15.53 d BD $+$37 410. For DS And, we find $M_1 = 1.692\pm0.004\pm0.010 M_\odot$, $R_1 = 2.185\pm0.004\pm0.008 R_\odot$, $M_2 = 1.184\pm0.001\pm0.003 M_\odot$, and $R_2 = 1.200\pm0.003\pm0.005 R_\odot$. We either confirm or newly identify unusual characteristics of both stars in the binary: the primary star is found to be slightly hotter than the main sequence turn off and there is a more substantial discrepancy in its luminosity compared to models (model luminosities are too large by about 40%), while the secondary star is oversized and cooler compared to other main sequence stars in the same cluster. The evidence points to non-standard evolution for both stars, but most plausible paths cannot explain the low luminosity of the primary star. BD $+$37 410 only has one eclipse per cycle, but extensive spectroscopic observations and the TESS light curve constrain the stellar masses well: $M_1 = 1.717\pm0.011 M_\odot$ and $M_2 = 1.175\pm0.005 M_\odot$. The radius of the main sequence primary star near $2.9R_\odot$ definitively requires large convective core overshooting ($> 0.2$ pressure scale heights) in models for its mass, and multiple lines of evidence point toward an age of $1.61\pm0.03\pm0.05$ Gyr (statistical and systematic uncertainties). Because NGC 752 is currently undergoing the transition from non-degenerate to degenerate He ignition of its red clump stars, BD $+$37 410 A directly constrains the star mass where this transition occurs., Comment: 34 pages, 23 figures, accepted for Astronomical Journal

The surface content of lithium (Li) and beryllium (Be) in stars can reveal important information about the temperature structure and physical processes in their interior regions. This study focuses on solar-type stars with a sample that is more precisely defined than done previously. Our selection of stars studied for Be is constrained by five parameters: mass, temperature, surface gravity, metallicity, and age to be similar to the Sun and is focussed on stars within +-0.02 of 1 M_sun. We have used the Keck I telescope with HIRES to obtain spectra of the Be II spectral region of 52 such stars at high spectral resolution ($\sim$45,000) and high signal-to-noise ratios. While the spread in Li in these stars is greater than a factor of 400, the spread in Be is only 2.7 times. Two stars were without any Be, perhaps due to a merger or a mass transfer with a companion. We find a steep trend of Li with temperature but little for Be. While there is a downward trend in Li with [Fe/H] from -0.4 to +0.4 due to stellar depletion, there is a small increase in Be with Fe from Galactic Be enrichment. While there is a broad decline in Li with age, there may be a small increase in Be with age, though age is less well-determined. In the subset of stars closest to the Sun in temperature and other parameters we find that the ratio of the abundances of Be to Li is much lower than predicted by models; there may be other mixing mechanisms causing additional Li depletion., Comment: total 29 pages including 12 figures, 5 tables Accepted for Astrophysical Journal

We present WIYN/Hydra spectra of 34 red giant candidate members of NGC 188, which, together with WOCS and Gaia data yield 23 single members, 6 binary members, 4 single nonmembers, and 1 binary nonmember. We report [Fe/H] for 29 members and derive [Fe/H]$_{\rm{NGC188}}$ = +0.064 $\pm$ 0.018 dex ($\sigma_{\mu}$) (sky spectra yield A(Fe)$_{\odot}$ = 7.520 $\pm$ 0.015 dex ($\sigma_{\mu}$)). We discuss effects on the derived parameters of varying Yale-Yonsei isochrones to fit the turnoff. We take advantage of the coolest, lowest-gravity giants to refine the line list near Li 6707.8 \AA. Using synthesis we derive detections of A(Li) = 1.17, 1.65, 2.04, and 0.60 dex for stars 4346, 4705, 5027, and 6353, respectively, and 3$\sigma$ upper-limits for the other members. Whereas only two of the detections meet the traditional criterion for "Li-richness" of A(Li) > 1.5 dex, we argue that since the cluster A(Li) vanish as subgiants evolve to the base of the RGB, all four stars are Li-rich in this cluster's context. An incidence of even a few Li-rich stars in a sample of 29 stars is far higher than what recent large surveys have found in the field. All four stars lie either slightly or substantially away from the cluster fiducial sequence, possibly providing clues about their Li-richness. We discuss a number of possibilities for the origin for the Li in each star, and suggest potentially discriminating future observations., Comment: 20 pages, 16 figures, 7 tables, accepted for publication in MNRAS

The surface abundances of the light elements lithium (Li) and beryllium (Be) reveal information about the physical processes taking place in stellar interiors. The investigation of the amount of these two elements in stars in open clusters shows the effect of age on those mechanisms. We have obtained spectra of both Li and Be in main-sequence stars in NGC 752 at high spectral resolution and high signal-to-noise ratios with HIRES on the Keck I telescope. In order to make meaningful comparisons with other clusters, we have determined the stellar parameters on a common scale. We have found abundances of Li and Be by spectral synthesis techniques. NGC 752 is twice the age of the well-studied Hyades cluster. We find that 1) The Li dip centered near 6500 K is wider in NGC 752, having expanded toward cooler temperatures; 2) The Be dip is deeper in the older NGC 752; 3) The Li "peak" near 6200 K is lower by about 0.3 dex; 4) Although there is little Be depletion in the cooler stars, it is possible that Be may be lower in NGC 752 than in the Hyades; 5) The Li content in both clusters declines with decreasing temperature, but there is less Li in NGC 752 at a given temperature by $\sim$0.4 dex. These differences are consistent with the transport of the light-element nuclei below the surface convection zone as predicted by theory. That connection to rotational spin-down is indicated by the pattern of rotation with temperature in the two clusters., Comment: 12 pages, 11 color figures, 5 tables Accepted for publication in Ap.J

New fibre spectroscopy and radial velocities from the WIYN telescope are used to measure photospheric lithium in 242 high-probability, zero-age-main-sequence (ZAMS) F- to K-type members of the rich cluster M35. Combining these with published rotation periods, the connection between lithium depletion and rotation is studied in unprecedented detail. At $T_{\rm eff}<5500$ K there is a strong relationship between faster rotation and less Li depletion, although with a dispersion larger than measurement uncertainties. Components of photometrically identified binary systems follow the same relationship. A correlation is also established between faster rotation rate (or smaller Rossby number), decreased Li depletion and larger stellar radius at a given $T_{\rm eff}$. These results support models where starspots and interior magnetic fields lead to inflated radii and reduced Li depletion during the pre main sequence (PMS) phase for the fastest rotators. However, the data are also consistent with the idea that all stars suffered lower levels of Li depletion than predicted by standard PMS models, perhaps because of deficiencies in those models or because saturated levels of magnetic activity suppress Li depletion equally in PMS stars of similar $T_{\rm eff}$ regardless of rotation rate, and that slower rotators subsequently experience more mixing and post-PMS Li depletion., Comment: Accepted version, for publication in MNRAS

We present $UBVRI$ photometry of 8702 stars in a $0.5 ^\circ\times0.5 ^\circ$ field in the direction of NGC 7142, taken with the Half Degree Imager (HDI) at the WIYN 0.9-meter telescope, to improve knowledge of this cluster's basic parameters. Our photometry spans the ranges 10.6 - 20.4 mag in $U$, 10.6 - 22.0 mag in $B$, 10.0 - 21.8 mag in $V$, 9.2 - 20.7 mag in $R$, and 8.5 - 19.9 mag in $I$. Using color-color diagrams that employ all four color combinations that include $U$, versus $B-V$, we derive a reddening-metallicity relation for the cluster, with preferred values $E(B-V$) = 0.338 $\pm$ 0.031 mag for the left-edge fiducial of the main sequence and [Fe/H] = 0.0 $\pm$ 0.1 dex, where the Hyades cluster has been used as an unreddened reference cluster, the extinction relations of Cardelli have been employed, and the metallicity dependence of the Yonsei-Yale ($Y^2$) isochrones has been assumed. Comparison of our data to the $Y^2$ isochrones in multiple color-magnitude diagrams (CMDs) yields distance-metallicity and age-metallicity relations, with preferred values of $m-M\ =\ 12.65\ \pm\ 0.23$ mag and age = $4.0 ^{-0.7}_{+1.3}$ Gyr. Re-evaluation of the parameters of M67 using Stetson's $UBVI$ photometry yields [Fe/H] = -0.02 $\pm$ 0.05 dex, $E(B-V$) = 0.04 $\pm$ 0.01 mag, $m-M$ = 9.75 $\pm$ 0.03 mag, and age = 3.85 $\pm$ 0.17 Gyr; we thus find the metallicity and age of the two clusters to be indistinguishable. A semi-independent analysis adopting the parameters of M67 and shifting the fiducials of the two clusters in six CMDs until they match strongly corroborates the values listed above. The differences between our inferred parallaxes and the Gaia DR2 values are $87\ \pm\ 60$ $\mu$as for NGC 7142 and 48 $\pm$ 15 $\mu$as for M67, consistent with previous studies., Comment: 20 pages, 15 figures, 6 tables, and accepted in the Astronomical Journal

WIYN/Hydra spectra (R $\sim$ 13,500, signal-to-noise pixel$^{-1}$ = 50-1000) of a 400 $\unicode{x212B}$ region around Li 6708 $\unicode{x212B}$ are used to determine radial and rotational velocities for 287 photometrically selected candidate members of the open cluster M48. The sample ranges from turnoff A stars to late-K dwarfs and eight giants. We combine our $V_{\rm{RAD}}$ measurements and power spectrum analysis with parallax and proper motion data from Gaia DR2 to evaluate membership and multiplicity. We classify 152 stars as single cluster members, 11 as binary members, 16 as members of uncertain multiplicity, 56 as single nonmembers, 28 as single "likely" nonmembers, two as single "likely" members, one as a binary "likely" member, five as binary nonmembers, 10 as "likely" members of uncertain multiplicity, three as nonmembers of uncertain multiplicity, and three as "likely" nonmembers of uncertain multiplicity. From a subsample of 95 single members, we derive $V_{\rm{RAD}}$ = 8.512 $\pm$ 0.087 km s$^{-1}$ ($\sigma_{\mu}$, and $\sigma$ = 0.848 km s$^{-1}$). Using 16 isolated Fe I lines for a subsample of 99 single members (that have $\sigma_{T_{\rm{eff}}}$ $<$ 75 K (from 10 colors from $UBVRI$), $v$ sin $i$ $<$ 25 km s$^{-1}$, and well-behaved Fe I lines), [Fe/H]$_{\rm{M48}}$ = -0.063 $\pm$ 0.007 dex ($\sigma_{\mu}$). [Fe/H] is independent of $T_{\rm{eff}}$ over an unprecedentedly large range of 2500 K. The minimum cluster binary fraction is 11%-21%. M48 exhibits a clear but modest broadening of the main-sequence turnoff, and there is no correlation between color and $v$ sin $i$., Comment: 17 pages, 11 figures, accepted in the Astronomical Journal

The surface content of lithium (Li) and beryllium (Be) provide insights into the mixing and circulation mechanisms in stellar interiors. The old open cluster, M 67, has been well-studied for Li abundances in both main-sequence and evolved stars. The Be abundances give us a probe to a deeper level in stars. We have taken high-resolution spectra with Keck I with HIRES to determine Be abundances along the subgiant branch of M 67, where there are dramatic depletions of Li. These subgiants range in mass from 1.26 to 1.32 M$_{\odot}$ and have evolved from main-sequence stars that would have occupied the region of the Li-Be dip found in younger clusters. Lithium abundances have been adjusted to the same scale for 103 stars in M 67 by Pace et al. The more massive stars $-$ now the coolest and furthest-evolved from the main-sequence $-$ show a drop in Li by a factor of 400 across the subgiant branch. Our new Be abundances also show a decline, but by a factor of $\sim$50. The two elements decline together with Li showing a steeper decline in these subgiants than it does in the Li-Be dip stars. The relative decline in Be abundance compared to Li is remarkably well fit by the models of Sills & Deliyannis, made specifically for the subgiants in M 67. Those models include the effects of mixing induced by stellar rotation. These M 67 subgiants show the effects of both main-sequence depletion and post-main-sequence dilution of both Li and Be., Comment: 31 pages with 3 tables, 13 figures Accepted by Ap. J. 10/7/2019

Rotation periods from Kepler K2 are combined with projected rotation velocities from the WIYN 3.5-m telescope, to determine projected radii for fast-rotating, low-mass ($0.15 \leq M/M_{\odot} \leq 0.6$) members of the Praesepe cluster. A maximum likelihood analysis that accounts for observational uncertainties, binarity and censored data, yields marginal evidence for radius inflation -- the average radius of these stars is $6\pm4$ per cent larger at a given luminosity than predicted by commonly-used evolutionary models. This over-radius is smaller (at 2-sigma confidence) than was found for similar stars in the younger Pleiades using a similar analysis; any decline appears due to changes occurring in higher mass ($>0.25 M_{\odot}$) stars. Models incorporating magnetic inhibition of convection predict an over-radius, but do not reproduce this mass dependence unless super-equipartition surface magnetic fields are present at lower masses. Models incorporating flux-blocking by starspots can explain the mass dependence but there is no evidence that spot coverage diminishes between the Pleiades and Praesepe samples to accompany the decline in over-radius. The fastest rotating stars in both Praesepe and the Pleiades are significantly smaller than the slowest rotators for which a projected radius can be measured. This may be a selection effect caused by more efficient angular momentum loss in larger stars leading to their progressive exclusion from the analysed samples. Our analyses assume random spin-axis orientations; any alignment in Praesepe, as suggested by Kovacs (2018), is strongly disfavoured by the broad distribution of projected radii., Comment: Accepted version for publication in MNRAS, 14 pages

Rotation periods obtained with the Kepler satellite have been combined with precise measurements of projected rotation velocity from the WIYN 3.5-m telescope to determine the distribution of projected radii for several hundred low-mass ($0.1 \leq M/M_{\odot} \leq 0.8$), fast-rotating members of the Pleiades cluster. A maximum likelihood modelling technique, that takes account of observational uncertainties, selection effects and censored data, and considers the effects of differential rotation and unresolved binarity, has been used to find that the average radius of these stars is $14 \pm 2$ per cent larger at a given luminosity than predicted by the evolutionary models of Dotter et al. (2008) and Baraffe et al. (2015). The same models are a reasonable match to the interferometric radii of older, magnetically inactive field M-dwarfs, suggesting that the over-radius may be associated with the young, magnetically active nature of the Pleiades objects. No evidence is found for any change in this over-radius above and below the boundary marking the transition to full convection. Published evolutionary models that incorporate either the effects of magnetic inhibition of convection or the blocking of flux by dark starspots do not individually explain the radius inflation, but a combination of the two effects might. The distribution of projected radii is consistent with the adopted hypothesis of a random spatial orientation of spin axes; strong alignments of the spin vectors into cones with an opening semi-angle $<30^{\circ}$ can be ruled out. Any plausible but weaker alignment would increase the inferred over-radius., Comment: Accepted version, to appear in MNRAS

WIYN/Hydra spectroscopy (at R~15,000) of the moderately metal-rich Praesepe and Hyades open clusters was used to study their main sequence (MS) iron ([Fe/H]) and lithium (A(Li)) abundances. Self-consistent [Fe/H] and Li analyses of these clusters of consistent age, which we re-evaluate, confirms they have consistent [Fe/H] and provides a foundation to investigate the poorly understood G-dwarf and F-dwarf Li-depletions. Neither phenomenon agrees with standard stellar evolution theory, but possible explanations abound. We supplement our A(Li) with previously published results placed on a uniform abundance scale. This creates the largest self-consistently analyzed sample of A(Li) in both the Hyades (90) and Praesepe (110). For each star, high-precision UBVRI photometry was used to determine a ten color-based Teff and then to test for photometric peculiarities indicated by a large sigma-Teff (> 75 K). The stars with large sigma-Teff were predominantly found to be binaries or stars with peculiar (apparent) A(Li). When considering only proper-motion members that have low sigma-Teff and are also photometrically consistent with the cluster MS fiducial, each cluster has a more tightly defined Li morphology than previously observed and the two clusters' A(Li) are indistinguishable. This suggests that clusters of consistent age and metallicity may have consistent Li-depletion trends across a broad range of Teff; no additional major parameters are required, at least for these two clusters. We propose that the combined Hyades and Praesepe data offer more rigorous constraints than does either cluster alone, and we discuss newly-revealed features of the combined Li-Teff trend., Comment: 36 Pages, 15 Figures, and accepted in the Astronomical Journal

High-dispersion spectra of 333 stars in the open cluster NGC 6819, obtained using the HYDRA spectrograph on the WIYN 3.5m telescope, have been analyzed to determine the abundances of iron and other metals from lines in the 400 A region surrounding the Li 6708 A line. Our spectra, with signal-to-noise per pixel (SNR) ranging from 60 to 300, span the luminosity range from the tip of the red giant branch to a point two magnitudes below the top of the cluster turnoff. We derive radial and rotational velocities for all stars, as well as [Fe/H] based on 17 iron lines, [Ca/H], [Si/H], and [Ni/H] in the 247 most probable, single members of the cluster. Input temperature estimates for model atmosphere analysis are provided by (B-V) colors merged from several sources, with individual reddening corrections applied to each star relative to a cluster mean of E(B-V) = 0.16. Extensive use is made of ROBOSPECT, an automatic equivalent width measurement program; its effectiveness on large spectroscopic samples is discussed. From the sample of likely single members, [Fe/H] = -0.03 +/- 0.06, where the error describes the median absolute deviation about the sample median value, leading to an internal precision for the cluster below 0.01 dex. The final uncertainty in the cluster abundance is therefore dominated by external systematics due to the temperature scale, surface gravity, and microturbulent velocity, leading to [Fe/H] = -0.02 +/- 0.02 for a sub-sample restricted to main sequence and turnoff stars. This result is consistent with our recent intermediate-band photometric determination of a slightly subsolar abundance for this cluster. [Ca/Fe], [Si/Fe], and [Ni/Fe] are determined to be solar within the uncertainties. NGC 6819 has an abundance distribution typical of solar metallicity thin disk stars in the solar neighborhood., Comment: WIYN Open Cluster Study LXV; accepted to Astronomical Journal. 16 pages, 5 figures, 3 tables

The study of star clusters has advanced our understanding of stellar evolution, Galactic chemical evolution and nucleosynthesis. Here we investigate the composition of turn-off stars in the intriguing open cluster, NGC 6791, which is old, but super-metal-rich with high-resolution (46,000) Keck/HIRES spectra. We find [Fe/H] = +0.30 +/-0.02 from measurements of some 40 unblended, unsaturated lines of both Fe I and Fe II in eight turn-off stars. Our O abundances come from the O I triplet near 7774 A and we do a differential analysis relative to the Sun from our Lunar spectrum also obtained with Keck/HIRES. The O results are corrected for small nLTE effects. We find consistent ratios of [O/Fe]n with a mean of $-$0.06 +/-0.02. This continues the trend of decreasing [O/Fe] with increasing [Fe/H] found in field stars that are also both old and metal-rich. The small range in our oxygen abundances is consistent with a single population of stars. Our results for the alpha elements [Mg/Fe], [Si/Fe], [Ca/Fe], and [Ti/Fe] are near solar and compare well with those of the old, metal-rich field stars. The two Fe-peak elements, Cr and Ni, are consistent with Fe. These turn-off-star abundances provide benchmark abundances to investigate changes in the giants that might arise from nuclear-burning and dredge-up processes. Determinations of upper limits were found for Li by spectrum synthesis and these results support the prediction from standard theory that higher-metallicity stars deplete more Li. Probably no stars in NGC 6791 have retained their initial Li., Comment: Accepted by The Astrophysical Journal 14 pages, 10 figures, 10 tables

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)

WIYN/HYDRA spectra in the Li 6708 Angstrom region have been obtained for 332 probable members of the old open cluster, NGC 6819. Preliminary analysis shows a pattern of Li depletion from the top of the turnoff to the base of the giant branch. Starting one magnitude below the level of the clump, all brighter giants have A(Li) below 1.0, with most having upper limits below 0.5. Star W007017, located BELOW the first-ascent red giant bump is Li-rich with A(Li) = 2.3. As a highly probable single-star astrometric and radial-velocity cluster member, its discrepant asteroseismic membership could be a by-product of the processes that triggered Li-enhancement. Its color-magnitude diagram location is consistent with only one proposed enhanced mixing process among first-ascent red giants., Comment: 12 pages, 3 figures, accepted for ApJ Letters

We present a comprehensive photometric study of the old open cluster, NGC 6819 using 1x1 degree field VI MOSAIC CCD imaging taken with the WIYN 0.9m telescope. The resultant color-magnitude diagram (CMD) shows a well developed main sequence (MS) extending from V~14.5 mag down to our photometric limit of V~21 mag. Fitting theoretical isochrones with adopted values of the reddening and metallicity (E(B-V)=0.14, [Fe/H]=+0.09 dex) to the observed CMD yields a distance modulus of (m-M)_{0}=11.93+/-0.10 and an age of ~2.6 Gyr for NGC 6819. Our wide-field imaging reveals that NGC 6819 is larger in areal extent (R=13') than previously thought. The wide-field also benefits our estimate of the degree of field star contamination, and ultimately yields improved measurements of the structural parameters (r_c=2.80', r_t=38.2', and r_h=7') and tidal mass of the cluster (M_{tid}=3542.4 M(sun)). The flattened luminosity and mass functions indicate that NGC 6819 has experienced mass segregation as a result of its dynamical evolution. Our variability study of the cluster blue straggler star (BSS) population using the Welch-Stetson variability index (I_{WS}) has revealed a number of variable BSS candidates., Comment: 11 pages, 13 figures, accepted for publication in ApJ

High-resolution CTIO 4-m/HYDRA spectroscopy of the super-metal-rich open cluster NGC 6253 ([Fe/H]=+0.43+/-0.01) has been used to study the stellar lithium (Li) abundances near the cluster's turnoff. NGC 6253 greatly expands the range of [Fe/H] for clusters that have a Li abundance analysis. This is important for studying the complicated effects of, and potential correlations with, stellar Fe abundance on surface Li abundance. Comparisons to the younger and less-metal-rich Hyades and to the similarly-aged but solar-metallicity M67 show that NGC 6253's Li abundances are qualitatively consistent with the prediction, from Standard Stellar Evolution Theory, that higher-metallicity stars have a greater Li depletion. Comparison with M67 provides evidence that the more-metal-rich NGC 6253 had a higher initial Li, which is consistent with expectations from models of Galactic Li production. NGC 6253 is also compared to the intermediate-aged NGC 3680, NGC 752, and IC 4651 open clusters. Comparison of the Li-gap positions in all six clusters shows: a) the gap's position in Teff is independent of metallicity, but b) higher-metallicity clusters have their gaps in higher-mass stars. In addition, the Li gap's position is shown not to evolve with age, which provides an important constraint for the non-standard depletion mechanisms that may create the Li gap.

Employing photometric rotation periods for solar-type stars in NGC 1039 [M 34], a young, nearby open cluster, we use its mass-dependent rotation period distribution to derive the cluster's age in a distance independent way, i.e., the so-called gyrochronology method. We present an analysis of 55 new rotation periods,using light curves derived from differential photometry, for solar type stars in M 34. We also exploit the results of a recently-completed, standardized, homogeneous BVIc CCD survey of the cluster in order to establish photometric cluster membership and assign B-V colours to each photometric variable. We describe a methodology for establishing the gyrochronology age for an ensemble of solar-type stars. Empirical relations between rotation period, photometric colour and stellar age (gyrochronology) are used to determine the age of M 34. Based on its position in a colour-period diagram, each M 34 member is designated as being either a solid-body rotator (interface or I-star), a differentially rotating star (convective or C-star) or an object which is in some transitory state in between the two (gap or g-star). Fitting the period and photometric colour of each I-sequence star in the cluster, we derive the cluster's mean gyrochronology age. 47/55 of the photometric variables lie along the loci of the cluster main sequence in V/B-V and V/V-I space. We are further able to confirm kinematic membership of the cluster for half of the periodic variables [21/55], employing results from an on-going radial velocity survey of the cluster. For each cluster member identified as an I-sequence object in the colour-period diagram, we derive its individual gyrochronology age, where the mean gyro age of M 34 is found to be 193 +/- 9 Myr, formally consistent (within the errors) with that derived using several distance-dependent, photometric isochrone methods (250 +/- 67 Myr)., Comment: accepted for publication in Astronomy & Astrophysics

Open clusters have long been used to illuminate both stellar evolution and Galactic evolution. The oldest clusters, though rather rare, can reveal the chemical and nucleosynthetic processes early in the history of the Galaxy. We have studied two turn-off stars in the old, metal-rich open cluster, NGC 6791. The Keck + HIRES spectra have a resolution of 45,000 and signal-to-noise ratios of 40 per pixel. We confirm the high value for [Fe/H] finding +0.30 $\pm$0.08, in agreement with earlier results from evolved stars in other parts of the HR diagram. We have also determined abundances for Na, Si, Ca, Ti, Cr, Ni, Y and Ba. These are compared to a sample of old, metal-rich field stars. With the probable exception of enhanced Ni in the cluster stars, the field and cluster stars show similar abundances of the elements. Model predictions show that the Ni enhancement could result from enrichment of the pre-cluster gas by SN Ia. Orbital evidence indicates that NGC 6791 could have originated near the inner regions of the Galaxy where the metallicity is generally higher than it is in the disk or halo. Subsequent perturbations and migrations may have resulted in its current heliocentric distance of 4 kpc and 1 kpc above the Galactic plane., Comment: 10 pages, 4 figures, 7 tables accepted by The Astronomical Journal for June, 2009

We use high-signal-to-noise ($\sim$150-450), high resolution ($R{\sim}45,000$) Keck HIRES spectroscopy of 13 candidate post T Tauri stars to derive basic physical parameters, lithium abundances and radial velocities. We place our stars in the M$_v$-T$_{eff}$ plane for use in determining approximate ages from pre-main sequence isochrones, and confirm these using three relative age indicators in our analysis: Li abundances, chromospheric emission and the kinematic {\it U-V} plane. Using the three age criteria we identify 5 stars (HIP 54529, HIP 62758, HIP 63322, HIP 74045, and HIP 104864) as probable post T Tauri stars with ages between 10 and 100 Myr. We confirm HIP 54529 as an SB2 and HIP 63322 as an SB1 star. We also examine irregular photometric variability of PTTs using the {\it HIPPARCOS} photometry annex. Two of our PTT stars exhibit near-IR excesses compared to Kurucz model flux; while recent work suggests classical T Tauri stars evince similar {\it JHK} excesses presumably indicative of non-photospheric (disk) emission, our results may be illusory artifacts of the chosen {\it I}-band normalization. Near-IR excesses we see in a literature-based sample of PTTs appear to be artifacts of previous spectral type-based $T_{\rm eff}$ values. Indeed, comparison of the homology of their observed and model photospheric SED's suggests that photometric temperatures are more reliable than temperatures based on spectral standards for the cooler temperature ranges of the stars in this sample. We conclude that our age oriented analysis is a robust means to select samples of nearby, young, isolated post T Tauri stars that otherwise masquerade as normal field stars., Comment: Accepted to AJ, 35 pages, 12 figures

We report broadband UBV and/or BVRI CCD photometry for a total of 1857 stars in the thick-disk and halo populations of the Galaxy. The majority of our targets were selected as candidate field horizontal-branch or other A-type stars (FHB/A, N = 576), or candidate low-metallicity stars (N = 1221), from the HK and Hamburg/ESO objective-prism surveys. Similar data for a small number of additional stars from other samples are also reported. These data are being used for several purposes. In the case of the FHB/A candidates they are used to accurately separate the lower-gravity FHB stars from various higher-gravity A-type stars, a subsample that includes the so-called Blue Metal Poor stars, halo and thick-disk blue stragglers, main-sequence A-type dwarfs, and Am and Ap stars. These data are also being used to derive photometric distance estimates to high-velocity hydrogen clouds in the Galaxy and for improved measurements of the mass of the Galaxy. Photometric data for the metal-poor candidates are being used to refine estimates of stellar metallicity for objects with available medium-resolution spectroscopy, to obtain distance estimates for kinematic analyses, and to establish initial estimates of effective temperature for analysis of high-resolution spectroscopy of the stars for which this information now exists., Comment: 22 pages, including 3 figures, 5 tables, and two ascii files of full data, accepted for publication in the Astrophysical Journal (Supplements)

We have determined Li abundances in 55 metal-poor (3.6 < [Fe/H] < -0.7) stars with extreme orbital kinematics. We find the Li abundance in the Li-plateau stars and examine its decrease in low-temperature, low-mass stars. The Li observations are primarily from the Keck I telescope with HIRES (spectral resolution of ~48,000 and median signal-to-noise per pixel of 140). Abundances or upper limits were determined for Li for all the stars with typical errors of 0.06 dex. Our 14 stars on the Li plateau give A(Li) = log N(Li)/N(H) + 12.00 of 2.215 +-0.110, consistent with earlier results. We find a dependence of the Li abundance on metallicity as measured by [Fe/H] and the Fe-peak elements [Cr/H] and [Ni/H], with a slope of ~0.18. We also find dependences of A(Li) with the alpha elements, Mg, Ca, and Ti. For the n-capture element, Ba, the relation between A(Li) and [Ba/H] has a shallower slope of 0.13; over a range of 2.6 dex in [Ba/H], the Li abundance spans only a factor of two. We examined the possible trends of A(Li) with the characteristics of the orbits of our halo stars, but find no relationship with kinematic or dynamic properties. The stars cooler than the Li plateau are separated into three metallicity subsets. The decrease in A(Li) sets in at hotter temperatures at high metallicities than at low metallicities; this is in the opposite sense of the predictions for Li depletion from standard and non-standard models., Comment: 29 pages including 3 tables and 12 figures Accepted by The Astrophysical Journal, for the 1 November 2005 issue, v. 633

We have made observations with the Keck I telescope and HIRES at a resolution of $\sim$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/Fe], [Ca/Fe] and [Ti/Fe] -- like the red giants. Our [Mg/Fe] ratio is somewhat lower than that suggested by other studies. We compare our mean abundances for the five M 71 stars with field stars of similar [Fe/H] -- 8 with halo kinematics and 17 with disk kinematics. The abundances of the alpha-fusion products (Mg, Si, Ca, Ti) agree with both samples, but seem a closer match to the disk stars. The Mg abundance in M71 is at the lower edge of the disk and halo samples. The neutron-capture elements, Y and Ba, are enhanced relative to solar in the M71 turn-off stars. Our ratio [Ba/Fe] is similar to that of the halo field stars but a factor of two above that for the disk field stars. The important [Ba/Y] ratio is significantly lower than M71 giant values. The Na content of the M71 turn-off stars is remarkably similar to that in the disk field stars, but more than a factor of two higher than the halo field star sample. We find [Na/Fe] = +0.14 $\pm$0.04 with a spread less than half of that found in the red giants in M71. Excluding Mg, the lack of intracluster $\alpha$-element variations (turn-off vs giants) suggests the polluting material arose in a more traditional $s$-process environment such as AGB stars., Comment: Accepted for Ap.J. August 20, 2005 issue 25 pages, 9 figures, 9 tables

Boron provides a special probe below the stellar surface as it survives to greater depths than do Li and Be. To search for B depletions we have observed B in 13 F and G dwarfs with large Be depletions; for comparison we also obtained spectra of five stars which are undepleted in Li and Be. We have used HST with STIS to obtain spectra of the B I resonance line at 2497 \AA. The spectral resolution is 30,000 or 114,000 and the median signal-to-noise ratio is 70 per pixel. New Be and Li spectra have been obtained at Keck I with HIRES of four of the five standard stars at $\sim$48,000 resolution. Abundances have been determined by the spectrum synthesis method with MOOG. A comparison between the standard stars and those with severe Be depletions shows a distinct difference in the B abundances between the two groups of 0.22 dex. We have discovered a correlation between the Be and B abundances. The slope between A(Be) and A(B)$_{NLTE}$ is 0.22 $\pm$0.05 (where A(element) = log N(element)/N(H) + 12.00) which, as expected, is shallower than the slope between A(Li) and A(Be) of 0.38. We have normalized the light element abundances to account for the observation that the initial abundances are somewhat lower in lower metallicity stars by employing recently published empirical relations between Be and [Fe/H] and between B and [Fe/H] (Boesgaard et al). The correlation between the normalized A(Be) and A(B)$_{NLTE}$ has a slope of 0.18 $\pm$0.06. The star with the largest Be depletion, HR 107 a main sequence Ba star, also has the largest B depletion with the B abundance lower by a factor of 3.5 relative to the standard stars., Comment: 12 pages, 6 figures, 5 tables

We report discovery of significant depletion of Li on the surfaces of F dwarf stars in the 150-Myr-old open cluster M35, analagous to a feature in the 700-Myr-old Hyades cluster that has been referred to as the ``Li gap.'' We have caught the gap in the act of forming: using high resolution, high S/N, WIYN/Hydra observations, we detect Li in all but a few M35 F stars; the maximum depletion lies at least 0.6-0.8 dex below minimally depleted (or undepleted) stars. The M35 Li depletion region, a) is quite wide, with clear depletion seen from 6000K to 6700K or hotter; b) shows a significant dispersion in Li abundance at all T_eff, even with stars of the same T_eff; and c) contains undepleted stars (as well as depleted ones) in the (narrow) classical Hyades gap region, which itself shows no undepleted stars. All of these M35 Li depletion properties support rotationally-induced slow mixing as the primary physical mechanism that forms the gap, and argues against other proposed mechanisms, particularly diffusion and steady main sequence mass loss. When viewed in the context of the M35 Li depletion properties, the Hyades Li gap may well be wider than is usually recognized., Comment: 14 Pages, 3 figures. Accepted to ApJ Letters

We present deep BVI observations of the core of M35 and a nearby comparison field obtained at the WIYN 3.5m telescope under excellent seeing. These observations display the lower main sequence in BV and VI CMDs down to V = 23.3 and 24.6, respectively. At these faint magnitudes background field stars are far more numerous than the cluster stars, yet by using a smoothing technique and CMD density distribution subtraction we recover the cluster fiducial main sequence and luminosity function to V = 24.6. We find the location of the main sequence in these CMDs to be consistent with earlier work on other open clusters, specifically NGC 188, NGC 2420, and NGC 2477. We compare these open cluster fiducial sequences to stellar models by Baraffe et al. (1998), Siess et al. (2000), Girardi et al. (2000), and Yi et al. (2001) and find that the models are too blue in both B-V and V-I for stars below ~0.4 Mo. M35 contains stars to the limit of the extracted main sequence, at M ~ 0.10-0.15 Mo, suggesting that M35 may harbor a large number of brown dwarfs, which should be easy targets for near-IR instrumentation on 8-10m telescopes. We also identify a new candidate white dwarf in M35 at V = 21.36 +- 0.01. Depending on which WD models are used to interpret this cluster candidate, it is either a very high mass WD (1.05 +- 0.05 Mo) somewhat older (0.19-0.26 Gyr, 3-4 sigma) than our best isochrone age (150 Myr), or it is a modestly massive WD (0.67-0.78 Mo) much too old (0.42-0.83 Gyr) to belong to the cluster., Comment: 28 pages + 24 figures; to be published in the Sept, 2002 AJ

We present an analysis of high quality spectra of members of the young cluster M35. By using a multi-fiber spectrograph, we are able to collect high signal-to-noise, high resolution spectra of a sample of photometric candidate members. Accurate radial velocities are used to establish the membership status and rotational velocities are measured using cross-correlation. We also derive the metal content of the cluster, [Fe/H]= -0.21$\pm$0.10, based on spectral synthesis. Finally, we derive the lithium abundances of the bona fide cluster members and compare the results with members of other clusters. For example, M35 shows a smaller range in both rotation rates and lithium abundances as compared to the Pleiades. We discuss possible roles of various parameters. Our high quality M35 database of lithium abundances and rotational velocities are perfectly suited to be used as a laboratory to test theoretical models dealing with the lithium depletion phenomenon., Comment: Accepted ApJ (Feb 20, 2001 issue)

The fragile light elements lithium, beryllium, and boron are easily destroyed in stellar interiors, and are thus superb probes of physical processes occuring in the outer stellar layers. The light elements are also excellent tracers of the chemical evolution of the Galaxy, and can test big bang nucleosynthesis (BBN). These inter-related topics are reviewed with an emphasis on stellar physics. In Part I (presented by CPD), an overview is given of the physical processes which can modify the surface abundances of the light elements, with emphasis on Population I dwarfs - convection; gravitational settling, thermal diffusion, and radiative levitation; slow mixing induced by gravity waves or rotation. We will discuss the increasingly large body of data which begin to enable us to discern the relative importance of these mechanisms in Population I main sequence stars. In Part II (presented by MHP), discussion is extended to the issue of whether or not the halo Li plateau is depleted, and includes the following topics: Li dispersion in field and globular cluster stars, Li production vs. destruction in Li-rich halo stars, and constraints from 6Li. Also discussed are trends with metal abundance and Teff and implications for chemical evolution and BBN. In Part III (presented by CC), evidence is reviewed that suggests that in situ mixing occurs in evolved low mass Population I and Population II stars. Theoretical mechanisms that can create such mixing are discussed, as well as their implications in stellar yields., Comment: IAU Symp. 198, "The Light Elements and their Evolution", Natal, Brazil (nov.1999), three-part review

The fragile light elements lithium, beryllium, and boron are easily destroyed in stellar interiors, and are thus superb probes of physical processes occuring in the outer stellar layers. The light elements are also excellent tracers of the chemical evolution of the Galaxy, and can test big bang nucleosynthesis (BBN). These inter-related topics are reviewed with an emphasis on stellar physics. In Part I (presented by CPD), an overview is given of the physical processes which can modify the surface abundances of the light elements, with emphasis on Population I dwarfs - convection; gravitational settling, thermal diffusion, and radiative levitation; slow mixing induced by gravity waves or rotation. We will discuss the increasingly large body of data which begin to enable us to discern the relative importance of these mechanisms in Population I main sequence stars. In Part II (presented by MHP), discussion is extended to the issue of whether or not the halo Li plateau is depleted, and includes the following topics: Li dispersion in field and globular cluster stars, Li production vs. destruction in Li-rich halo stars, and constraints from 6Li. Also discussed are trends with metal abundance and Teff and implications for chemical evolution and BBN. In Part III (presented by CC), evidence is reviewed that suggests that in situ mixing occurs in evolved low mass Population I and Population II stars. Theoretical mechanisms that can create such mixing are discussed, as well as their implications in stellar yields., Comment: IAU Symp. 198, "The Light Elements and their Evolution", Natal, Brazil (nov. 1999), three-part review

Short duration flares are well known to occur on cool main-sequence stars as well as on many types of `exotic' stars. Ordinary main-sequence stars are usually pictured as being static on time scales of millions or billions of years. Our sun has occasional flares involving up to $\sim 10^{31}$ ergs which produce optical brightenings too small in amplitude to be detected in disk-integrated brightness. However, we identify nine cases of superflares involving $10^{33}$ to $10^{38}$ ergs on normal solar-type stars. That is, these stars are on or near the main-sequence, are of spectral class from F8 to G8, are single (or in very wide binaries), are not rapid rotators, and are not exceedingly young in age. This class of stars includes many those recently discovered to have planets as well as our own Sun, and the consequences for any life on surrounding planets could be profound. For the case of the Sun, historical records suggest that no superflares have occurred in the last two millennia., Comment: 16 pages, accepted for publication in ApJ