Photometric Metallicity Research Articles

The Draco and Ursa Minor Dwarf Spheroidal Galaxies: A Comparative Study

We present (V, I) photometry of two wide (≃25 × 25 arcmin2) fields centered on the low surface brightness dwarf spheroidal galaxies Draco and Ursa Minor. New estimates of the distance to these galaxies are provided [(m-M)0(UMi) = 19.41 ± 0.12 and (m-M)0(Dra) = 19.84 ± 0.14], and a comparative study of their evolved stellar population is presented. We detect for the first time the red giant branch (RGB) bump in the luminosity function of UMi (V = 19.40 ± 0.06), while the feature is not detected in Draco. Photometric metallicity distributions are obtained for the two galaxies, and an accurate analysis to determine the intrinsic metallicity spread is performed by means of artificial star experiments. The adopted method is insensitive to stars more metal poor than [Fe/H] ∼ -2.5, and it rests on the assumption that the age spread in the considered populations is small (i.e., the impact of the actual age spread on the colors of the RGB stars is negligible). We find that while the average metallicity of the two galaxies is similar (⟨[Fe/H]⟩UMi = -1.8 and ⟨Fe/H]⟩Dra = -1.7), the metallicity distributions are significantly different, having different peak values ([Fe/H] = -1.9 and [Fe/H] = -1.6) and different maximum metallicities. We suggest that such differences may be partly responsible for the difference in horizontal-branch morphology between the two galaxies. The intrinsic metallicity 1 σ spread is σi = 0.10 in UMi and σi = 0.13 in Draco. We demonstrate that the inner region of UMi is significantly structured, at odds with what is expected for a system in dynamical equilibrium. In particular, we show that the main density peak of UMi is off-center with respect to the center of symmetry of the whole galaxy and shows a much lower ellipticity with respect to the rest of the galaxy. Moreover, UMi stars are shown to be clustered according to two different characteristic clustering scales, as opposed to Draco, which instead has a very symmetric and smooth density profile. The possible consequences of this striking structural difference on our ideas about galaxy formation are briefly discussed. Combining our distance modulus with the more recent estimates of the total luminosity of UMi, we find that the mass-to-light ratio (M/L) of this galaxy may be as low as M/L ∼ 7, a factor of 5–10 lower than current estimates.

On the metallicity of the Milky Way thin disc and photometric abundance scales

The mean metallicity of the Milky Way thin disc in the solar neighbourhood is still a matter of debate, and has recently been subject to upward revision (Haywood, 2001). Our star sample was drawn from a set of solar neighbourhood dwarfs with photometric metallicities. In a recent study, Reid (2002) suggests that our metallicity calibration, based on Geneva photometry, is biased. We show here that the effect detected by Reid is not a consequence of our adopted metallicity scale, and we confirm that our findings are robust. On the contrary, the application to Stromgren photometry of the Schuster & Nissen metallicity scale is problematic. Systematic discrepancies of about 0.1 to 0.3 dex affect the photometric metallicity determination of metal rich stars, on the colour interval 0.22< b-y <0.59, i.e including F and G stars. For F stars, it is shown that this is a consequence of a mismatch between the standard sequence m_1(b-y) of the Hyades used by Schuster & Nissen to calibrate their metallicity scale, and the system of Olsen (1993, 1994ab). It means that although Schuster & Nissen calibration and Olsen photometry are intrinsically correct, there are mutually incompatible for metal rich, F-type stars. For G stars, the discrepancy is most probably the continuation of the same problem, albeit worthen by the lack of spectroscopic calibrating stars. A corrected calibration is proposed which renders the calibration of Schuster & Nissen applicable to the catalogues of Olsen. We also give a simpler calibration referenced to the Hyades sequence, valid over the same color and metallicity ranges.

K dwarfs and the chemical evolution of the solar cylinder

K dwarfs have lifetimes older than the present age of the Galactic disc, and are thus ideal stars for investigating the chemical evolution of the disc. We have developed several photometric metallicity indicators for K dwarfs, based on a sample of accurate spectroscopic metallicities for 34 disc and halo G and K dwarfs. The photometric metallicities lead us to develop a metallicity index for K dwarfs based only on their position in the colour‐absolute-magnitude diagram. Metallicities have been determined for 431 single K dwarfs drawn from the Hipparcos catalogue, selecting the stars by absolute magnitude and removing multiple systems. The sample is essentially a complete reckoning of the metal content in nearby K dwarfs. We use stellar isochrones to mark the stars by mass, and select a subset of 220 of the stars, which is complete within a narrow mass interval. We fit the data with a model of the chemical evolution of the solar cylinder. We find that only a modest cosmic scatter is required to fit our age‐ metallicity relation. The model assumes two main infall episodes for the formation of the halo-thick disc and thin disc, respectively. The new data confirm that the solar neighbourhood formed on a long time-scale of the order of 7 Gyr.

Keck Spectroscopy of Globular Clusters in the Sombrero Galaxy

We analyze high signal-to-noise spectra for 14 globular clusters (GCs) in the Sombrero galaxy, NGC 4594 = M104, obtained with the LRIS spectrograph on the Keck I telescope. We find generally good agreement between spectroscopic metallicities and previous photometric metallicities based on V-I colors. Further, we use measurements of various Balmer line indices on co-added spectra of metal-poor and metal-rich GCs to estimate ages for the GC subpopulations and find ages of 10-15 Gyr, with preferred ages around 11-12 Gyr and no detectable differences between the metal-rich and metal-poor subpopulations. However, because of model and measurement uncertainties, age differences of a few (2-3) Gyrs cannot be be ruled out. We also measure alpha-to-iron abundance ratios from Mg and TiO features and find enhancements on the order of +0.4 dex relative to the Sun, similar to the alpha/Fe abundance ratios observed in other old stellar populations. Finally, we combined our sample with radial velocities for 34 GCs from Bridges et al. 1997 and obtain virial and projected masses for the Sombrero of M(Vir) = 8.1+/-1.8 x 10^11 M(sun) and M(P) = 5.3+/-1.0 x 10^11 Msun within 17 kpc, respectively. Using 12 clusters within the central 4.5 kpc, the corresponding numbers are M(Vir) = 2.1+/-1.1 x 10^11 Msun and M(P) = 2.0+/-1.3 x 10^11 Msun.

Photometric Abundances for G Dwarfs: A Cautionary Tale

Analysis of cluster and field star uvby data demonstrates the existence of a previously undetected discrepancy in a widely used photometric metallicity calibration for G dwarfs. The discrepancy is systematic and strongly color dependent, reducing the estimated [Fe/H] for stars above [Fe/H] ~ -0.2 by between +0.1 and +0.4 dex and creating a deficit of metal-rich stars among dwarfs of mid G and later spectral type. The source of the problem, triggered for stars with b-y greater than about 0.47, appears to be an enhanced metallicity dependence for the c1 index that increases as temperature declines. The link between c1, normally a surface gravity indicator, and metallicity produces two secondary effects. The deficit in the photometric abundance for a cool dwarf is partially compensated by some degree of evolution off the main sequence, and cool dwarfs with metallicities significantly above the Hyades are found to have c1 indices that classify them as giants. The potential impact of the problem on stellar population studies is discussed.

Keck Spectroscopy of Young and Old Star Clusters in NGC 1023

We present Keck/LRIS spectra for 11 old globular clusters in the S0-type galaxy NGC 1023 and two young blue clusters in the nearby companion NGC 1023A. Analysis of the spectra of seven old clusters with sufficient signal-to-noise ratio shows generally good agreement between spectroscopic and previous photometric metallicity estimates, but the integrated colors of two clusters are too blue for their spectroscopic metallicities. Although the cluster ages are not well constrained, they are most likely similar to those of Milky Way globular clusters and certainly older than ~5 Gyr. The brightest globular cluster in the sample shows enhanced cyanogen, possibly indicating an abundance anomaly similar to that observed in some M31 globular clusters. For the two blue clusters in NGC 1023A we estimate ages between 125 and 500 Myr on the basis of their strong Balmer lines. The total masses are about 8 × 104 M⊙ and 6 × 104 M⊙ for a Miller-Scalo initial mass function and Z = 0.004, making these objects similar to the young populous clusters in the Large Magellanic Cloud. It is suggested that the two young clusters might have formed during a period of enhanced star formation activity in NGC 1023A, stimulated by a close encounter with NGC 1023.

Globular clusters in the large magellanic cloud: An impact from GAIA photometry

The goal of this work is to assess the expected scientific output from the photometric studies of globular clusters in the Large Magellanic Cloud with ESA’s astrometric space mission GAIA. For this purpose we simulate GAIA photometry of individual stars in synthetic cluster populations, covering a large range of cluster ages and metallicities. We find that accurate effective temperatures (Δ T eff < 10%) can be obtained from GAIA photometry down to V ~ 18 for stars in populations within the studied metallicity range ([M/H] = −0.4 … −1.7). GAIA will also provide photometric metallicities (Δ[M/H] ≲ 0.3 dex) for the cluster giants brighter than V ~ 17.5. The knowledge of the effective temperatures and metallicities will allow to obtain accurate ages of stellar populations younger than about 1 Gyr using the usual procedure of main sequence turn-off point fitting. Ages of older stellar populations (≳ 1 Gyr) may be constrained from the isochrone fits to the giant branches in the observed CMDs. We conclude that GAIA will provide excellent opportunities for studying star formation histories far beyond the Milky Way, providing means for better understanding of stellar and galactic evolution in different astrophysical environments.

The helium content and age of the Hyades:

We compare the accurate empirical mass-luminosity (M-L) relation based on five Hyades binary systems to predictions of stellar models calculated with various input parameters (helium, metallicity and age) or physics (mixing-length ratio, model atmosphere, equation of state and microscopic diffusion). Models based on a helium content inferred from the enrichment law are more than 3σ beyond the observations, suggesting that the Hyades initial helium abundance is lower than expected from its supersolar metallicity. With the photometric metallicity ( = dex, Grenon [CITE]) we derive . Because of the (Y, ) degeneracy in the M-L plane, the uncertainty grows to if the metallicity from spectroscopy is adopted ( = dex, Cayrel de Strobel et al. [CITE]). We use these results to discuss the Hertzsprung-Russell (HR) diagram of the Hyades, in the (MV, ) plane, based on the very precise Hipparcos dynamical parallaxes. Present models fit the tight observed sequence very well except at low temperatures. We show that the HR diagram does not bring further constraints on the helium abundance or metallicity of the cluster. In the low mass region of the HR diagram sensitive to the mixing-length parameter (), the slope of the main sequence (MS) suggests that could decrease from a solar (or even supersolar) value at higher mass to subsolar values at low mass, which is also supported by the modeling of the vB22 M-L relation. We find that the discrepancy at low temperatures (() ) remains, even if an improved equation of state or better model atmospheres are used. Finally, we discuss the positions of the stars at turn-off in the light of their observed rotation rates and we deduce that the maximum age of the Hyades predicted by the present models is ~650 Myr.

Horizontal-Branch Morphology and Dense Environments: [ITAL]HUBBLE SPACE TELESCOPE[/ITAL][ITAL]Hubble Space Telescope[/ITAL] Observations of Globular Clusters NGC 2298, 5897, 6535, and 6626

HST observations of the core of four galactic globular clusters allowed us to obtain interesting clues about the influence of the environment on the star distribution along the horizontal branch. The chemical composition and the age of the target clusters have been derived through a detailed analysis of the (V, V-I) color-magnitude diagrams. The photometric metallicities have been found in close agreement with the recent spectroscopic determinations. The four clusters are coeval within the uncertainties. Hence, age and metallicity cannot account for the difference in the horizontal-branch morphologies, as shown by a comparison with theoretical zero-age horizontal-branch sequences and synthetic horizontal branches taken from the literature. Our analysis further supports the hypothesis according to which dense environments cause the occurrence of the so-called tails in the horizontal branches of galactic globular clusters. The use of HST, as well as of ground-based data for some clusters, enabled us to study the radial distribution of the various evolved populations, starting from the very center. We thus discovered that blue stragglers are, in general, more concentrated while the horizontal and the red giant branch do not display a markedly different trend with the distance from the cluster center, although the red giant branch of NGC 6626 is more concentrated than the horizontal branch.

Distances, Ages, and Epoch of Formation of Globular Clusters

We review the results on distances and absolute ages of galactic globular clusters (GCs) obtained after the release of the Hipparcos catalogue. Several methods for the Population II local distance scale are discussed, exploiting NEW RESULTS for RR Lyraes in the Large Magellanic Cloud (LMC). We find that the so-called Short and Long Distance Scales may be reconciled whether a consistent reddening scale is adopted for Cepheids and RR Lyrae variables in the LMC. Distances and ages for the 9 clusters discussed in Paper I are re-derived using an enlarged sample of local subdwarfs, which includes about 90% of the metal-poor dwarfs with accurate parallaxes (Delta p/p < 0.12) in the whole Hipparcos catalogue. On average, our revised distance moduli are decreased by 0.04 mag with respect to Paper I. The corresponding age of the GCs is t=11.5+-2.6 Gyr (95% confidence range). The relation between Mv(ZAHB) and metallicity for the nine programme clusters turns out to be Mv(ZAHB)=(0.18+-0.09)([Fe/H]+1.5)+(0.53+-0.12).Thanks to Hipparcos the major contribution to the total error budget associated with the subdwarf fitting technique has been moved from parallaxes to photometric calibrations, reddening and metallicity scale. This total uncertainty still amounts to about +-0.12 mag. Comparing the corresponding (true) LMC distance modulus 18.64+-0.12 mag with other existing determinations, we conclude that at present the best estimate for the distance of the LMC is: 18.54+-0.03+-0.06, suggesting that distances from the subdwarf fitting method are 1 sigma too long. Consequently, our best estimate for the age of the GCs is revised to: Age = 12.9+-2.9 Gyr (95% confidence range). The best relation between Mv(ZAHB) and [Fe/H] is: Mv(ZAHB) =(0.18+-0.09)([Fe/H]+1.5)+(0.63+-0.07).

Is the Galactic disc older than the halo?

The aim of this study is to infer the age of the Galactic disc by means of the ages of old open clusters, and comment on some recent claims that the Galactic disc may be older than the halo. To this purpose, we analyse the colour–magnitude diagrams (CMDs) of six very old open clusters, namely NGC 188, NGC 6791, Collinder 261, Melotte 66, Berkeley 39 and Berkeley 17, and determine their ages. For each cluster we use the most recent photometric and spectroscopic data and metallicity estimates. The ages are derived from the isochrone-fitting method using the stellar models of the Padua library. We find that the ages of these clusters fall in the range 4 to 9–10 Gyr: Melotte 66 is the youngest whereas NGC 6791 and Berkeley 17 have ages of about 9–10 Gyr. Previous estimates for Berkeley 17 indicated an age as great as Gyr, almost falling within the range of classical globular clusters. In our analysis, this cluster is always very old, but perhaps somewhat younger than in previous studies. However, we call attention to the fact that the above ages should be taken as provisional estimates, because of the many uncertainties still affecting stellar models in the mass range 1.0–1.5 M⊙. Despite this drawback of extant theory of stellar structure, if NGC 6791 and Berkeley 17 set a limit on the age of the Galactic disc, this component of the Milky Way can be as old as about 9–10 Gyr, but must surely be younger than the Galactic halo, at least as inferred from recent determinations of the age of globular clusters. Finally, it is worth recalling that open clusters can only provide a lower limit to the age of the Galactic disc, while other indicators – like white dwarfs – are perhaps more suited to this task.

Planetary Companions around Two Solar‐Type Stars: HD 195019 and HD 21710711Based on observations obtained at Lick Observatory, which is operated by the University of California, and on observations obtained at the W. M. Keck Observatory, which is operated jointly by the University of California and the California Institute of Technology.

ABSTRACTWe have enlarged the sample of stars in the planet search at Lick Observatory. Doppler measurements of 82 new stars observed at Lick Observatory, with additional velocities from Keck Observatory, have revealed two new planet candidates. The G3 V/IV star, HD 195019, exhibits Keplerian velocity variations with a period of 18.27 days, an orbital eccentricity of 0.03 ± 0.03, and Msin i = 3.51 MJUP. Based on a measurement of Ca ii H and K emission, this star is chromospherically inactive. We estimate the metallicity of HD 195019 to be approximately solar from ubvy photometry. The second planet candidate was detected around HD 217107, a G7 V star. This star exhibits a 7.12 day Keplerian period with eccentricity 0.14 ± 0.05 and Msin i = 1.27 MJUP. HD 217107 is also chromospherically inactive. The photometric metallicity is found to be [Fe/H] = + 0.29 ± 0.1 dex. Given the relatively short orbital period, the absence of tidal spin‐up in HD 217107 provides a theoretical constraint on the upper limit of the companion mass of less than 11 MJUP.

Metallicity of clusters from RRab pulsators: results of an automatic analysis

We apply the photometric method of Jurcsik &38; Kovacs to newly available observations of RRab pulsators in clusters, in order to determine such physical properties as metallicity [Fe/H] and absolute magnitudes MV. For this purpose we devised a fully automatic algorithm for reliable and repeatable determination of Fourier parameters from light curves without resorting to smoothing and/or interpolation, employed in the past. In this way we demonstrate that these parameters form solid foundations for the method of Jurcsik &38; Kovacs. Whether these parameters lead to reliable determination of [Fe/H] and MV for RRab stars, as postulated by Jurcsik &38; Kovacs, still remains an open question. Our photometric average cluster metallicities 〈[Fe/H]〉phot for M3, M5, M68, ω Cen and NGC 288 correlate reasonably well with their spectroscopic determinations 〈[Fe/H]〉sp, supporting Jurcsik &38; Kovacs. However, for individual RRab stars in ω Cen we were not able to reproduce expected correlations between 〈V〉 (i.e. MV), 〈[Fe/H]〉phot and 〈[Fe/H]〉sp. As chemical composition in ω Cen is known to vary, the existence of such correlations is expected.

Abundances in metal-rich stars

We have derived elemental abundances of O, Na, Mg, Al, Si, Ca, Ti, Cr, Mn, Fe, Co, Ni as well as for a number of s-elements for 47 G and K dwarf, with [Me/H] dex. The selection of stars was based on their kinematics as well as on their photometry. One sample of stars on rather eccentric orbits traces the chemical evolution interior to the solar orbit and another, on circular orbits, the evolution around the solar orbit. A few Extreme Population I stars were included in the latter sample. The stars have -0.1 dex dex. The spectroscopic [Fe/H] correlate well with the [Me/H] derived from photometry. We find that the elemental abundances of Mg, Al, Si, Ca, Ti, Cr and Ni all follow [Fe/H]. Our data put further constraints on models of galactic chemical evolution, in particular of Cr, Mn and Co which have not previously been studied for dwarf stars with dex. The increase in [Na/Fe] and [Al/Fe] as a function of [Fe/H] found previously by Edvardsson et al. (1993a) has been confirmed for [Na/Fe]. This upturning relation, and the scatter around it, are shown not to be due to a mixture of populations with different mean distances to the galactic centre. We do not confirm the same trend for aluminium, which is somewhat surprising since both these elements are thought to be produced in the same environments in the pre-supernova stars. Nor have we been able to trace any tendency for relative abundances of O, Si, and Ti relative to Fe to vary with the stellar velocities, i.e. the stars present mean distance to the galactic centre. These results imply that there is no significant difference in the chemical evolution of the different stellar populations for stars with [Me/H] dex. We find that [O/Fe] continue to decline with increasing [Fe/H] and that oxygen and europium correlate well. However [Si/Fe] and [Ca/Fe] seem to stay constant. A real ("cosmic”) scatter in [Ti/Fe] at given [Fe/H] is suggested as well as a decreasing abundance of the s-elements relative to iron for the most metal-rich dwarf stars. We discuss our results in the context of recent models of galactic chemical evolution. In our sample we have included a few very metal rich stars, sometimes called SMR (super metal rich) stars. We find these stars to be among the most iron-rich in our sample but far from as metal-rich as indicated by their photometric metallicities. SMR stars on highly eccentric orbits, alleged to trace the evolution of the chemical evolution in the galactic Bulge, have previously been found overabundant in O, Mg and Si. We have included three such stars from the study by Barbuy & Grenon (1990). We find them to be less metal rich and the other elemental abundances remain puzzling. Detailed spectroscopic abundance analyses of K dwarf stars are rare. Our study includes 5 K dwarf stars and has revealed what appears to be a striking example of overionization. The overionization is especially prominent for Ca, Cr and Fe. The origin of this apparent overionization is not clear and we discuss different explanations in some detail.

ELEMENTAL ABUNDANCES AND ATMOSPHERIC PARAMETERS OF SEVEN F-G SUPERGIANTS

ABSTRACT Spectroscopic abundance determinations for a sample of seven F-G stars have been carried out. The majority of them have large galactic latitudes. One objective in deriving spectroscopic abundances is to differentiate evolved objects seen at high galactic latitudes from the young population I supergiant stars that happened to have large galactic latitudes but actually belong to the galactic disk. Secondly, it is important to get good calibrators for photometric metallicity indices. It has been suggested in the past that many high galactic latitude F-G stars that are classified as supergiants are in reality subgiants or dwarfs. Our spectroscopically derived gravities show that two of the stars studied in this paper, HR 5165 and HD 114520, are not supergiants as classified in Bright Star Catalogue but are subgiants belonging to the solar neighbourhood. In our sample, HR 3229 and HR 8470 display solar abundances and the derived gravities support the bright giant luminosity class ascribed to them. HR 4114, HR 4912 and HR 7671 have abundances significantly different from those of young supergiants of galactic disk. The evolutionary status of these objects is discussed.

Globular Clusters in the Sombrero Galaxy (NGC 4594)

The Sombrero galaxy, NGC 4594, contains the most numerous globular cluster system of any nearby spiral. It is an ideal candidate in which to study the globular clusters and contrast them with those in Local Group spirals. Here we present B and I imaging from the CTIO Schmidt telescope which gives a field-of-view of 31' x 31'. Using DAOPHOT we have detected over 400 globular clusters and derived their magnitudes, B--I colors and photometric metallicities. We have attempted to separate our sample into disk and bulge/halo globular cluster populations, based on location in the galaxy. There is some evidence that the disk population is more metal--rich than the bulge/halo globular clusters, however contamination, dust reddening and small number statistics makes this result very tentative. We find that the median metallicity of the bulge/halo globular clusters is [Fe/H] = -0.8. This metallicity is consistent with previous estimates based on smaller samples. It is also similar to the metallicity predicted by the globular cluster metallicity -- galaxy luminosity relation. As with our Galaxy, there is no radial metallicity gradient in the halo globular clusters. This suggests that the spheriodal component of NGC 4594 did not form by a dissipational process.

High-dispersion spectroscopy of giants in metal-poor globular clusters. I - Iron abundances

High-resolution, high-SNR CCD spectra have been obtained for 16 giants in eight metal-poor Galactic globular clusters. Fe abundances accurate to 0.15 dex have been determined by a fully consistent set of model atmospheres and spectrum synthesis techniques. A metallicity scale is presented for metal-poor clusters that should prove useful for calibrating a wide variety of photometric and low-resolution spectroscopic metallicity indicators.

Galactic structure from faint Stromgren photometry - The catalog of observations

view Abstract Citations (4) References (31) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Galactic Structure From Faint Stromgren Photometry: The Catalog of Observations von Hippel, Ted A. Abstract We have initiated the faint photometric survey in the Stromgren system covering about 1 square degree and including 1238 objects in order to develop samples which best probe the thick disk population. The catalog of observations are presented here. They were acquired without kinematic or metallicity biases and are complete to V=17.3-18.5, depending on the field, for 810 early to relatively late type stars. Photometric metallicities were derived for 508 stars and indicate a metal-poor stellar population, consistent with a mixture of thick disk and halo stars. While the Stromgren u-band was not part of the survey, follow-up u-band observations of 32 survey objects indicate that intermediate color survey stars are main-sequence or slightly evolved stars, while redder survey stars are giants. Publication: The Astronomical Journal Pub Date: November 1992 DOI: 10.1086/116357 Bibcode: 1992AJ....104.1765V Keywords: Astronomical Catalogs; Astronomical Photometry; Galactic Structure; Sky Surveys (Astronomy); Stellar Color; Main Sequence Stars; Milky Way Galaxy; White Dwarf Stars; Astrophysics; GALAXY: HALO; GALAXY: KINEMATICS AND DYNAMICS full text sources ADS | data products SIMBAD (1161) GCPD (1) CDS (1)

A critical appraisal of published values of (Fe/H) for K II-IV stars

'Primary' (Fe/H) averages are presented for 373 evolved K stars of luminosity classes II-IV and (Fe/H) values beween .9 and +0.21 dex. The data define a 'consensus' zero point with a precision of + or {minus} 0.018 dex and have rms errors per datum which are typically 0.08{minus}0.16 dex. The primary data base makes recalibration possible for the large (Fe/H) catalogs of Hansen and Kjaergaard (1971) and Brown et al. (1989). A set of (Fe/H) standard stars and a new DDO calibration are given which have rms of 0.07 dex or less for the standard star data. For normal K giants, CN-based values of (Fe/H) turn out to be more precise than many high-dispersion results. Some zero-point errors in the latter are also found and new examples of continuum-placement problems appear. Thus high-dispersion results are not invariably superior to photometric metallicities. A review of high-dispersion and related work on supermetallicity in K III-IV star is also given.

SPECTROSCOPY OF UPPER-MAIN-SEQUENCE AND BLUE STRAGGLER STARS IN THE INTERMEDIATE-AGE CLUSTER NGC 2477.

ABSTRACT Spectra are obtained for nine upper-main-sequence and three blue-straggler stars in the intermediate-age cluster NGC 2477. They are then used in testing the hypothesis that rapid rotation of the turnoff stars gives rise to a discrepancy between the metal abundance given by the uvby-beta photometry of main-sequence stars and by the DDO photometry of red giants. It is found that NGC 2477 turnoff stars are not rotating unusually rapidly relative to their Hyades counterparts. Discrepancies in the photometric metallicity estimates, however, can now be explained through recent revisions in the DDO reddening ratios and through small color corrections to the beta photometry. The spectroscopic and photometric results are all consistent with NGC 2477 being slightly older and slightly metal deficient compared with the Hyades. The mean cluster radial velocity is found to be 6 + or - 10 km/s. It is confirmed spectroscopically that star 'm' is an Am star.