arXiv subjects

D. Geisler

Publications and source records attributed to D. Geisler.

At least 73 records · Page 4Linked to original sources

arXiv2014

Gaia-ESO Survey: The analysis of high-resolution UVES spectra of FGK-type stars

The Gaia-ESO Survey is obtaining high-quality spectroscopic data for about 10^5 stars using FLAMES at the VLT. UVES high-resolution spectra are being collected for about 5000 FGK-type stars. These UVES spectra are analyzed in parallel by several state-of-the-art methodologies. Our aim is to present how these analyses were implemented, to discuss their results, and to describe how a final recommended parameter scale is defined. We also discuss the precision (method-to-method dispersion) and accuracy (biases with respect to the reference values) of the final parameters. These results are part of the Gaia-ESO 2nd internal release and will be part of its 1st public release of advanced data products. The final parameter scale is tied to the one defined by the Gaia benchmark stars, a set of stars with fundamental atmospheric parameters. A set of open and globular clusters is used to evaluate the physical soundness of the results. Each methodology is judged against the benchmark stars to define weights in three different regions of the parameter space. The final recommended results are the weighted-medians of those from the individual methods. The recommended results successfully reproduce the benchmark stars atmospheric parameters and the expected Teff-log g relation of the calibrating clusters. Atmospheric parameters and abundances have been determined for 1301 FGK-type stars observed with UVES. The median of the method-to-method dispersion of the atmospheric parameters is 55 K for Teff, 0.13 dex for log g, and 0.07 dex for [Fe/H]. Systematic biases are estimated to be between 50-100 K for Teff, 0.10-0.25 dex for log g, and 0.05-0.10 dex for [Fe/H]. Abundances for 24 elements were derived: C, N, O, Na, Mg, Al, Si, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Zr, Mo, Ba, Nd, and Eu. The typical method-to-method dispersion of the abundances varies between 0.10 and 0.20 dex.

astro-ph.SR↗

arXiv2014

The Gaia-ESO Survey: Stellar content and elemental abundances in the massive cluster NGC 6705

Chemically inhomogeneous populations are observed in most globular clusters, but not in open clusters. Cluster mass seems to play a key role in the existence of multiple populations. Studying the chemical homogeneity of the most massive open clusters is necessary to better understand the mechanism of their formation and determine the mass limit under which clusters cannot host multiple populations. Here we studied NGC6705, that is a young and massive open cluster located towards the inner region of the Milky Way. This cluster is located inside the solar circle. This makes it an important tracer of the inner disk abundance gradient. This study makes use of BVI and ri photometry and comparisons with theoretical isochrones to derive the age of NGC6705. We study the density profile of the cluster and the mass function to infer the cluster mass. Based on abundances of the chemical elements distributed in the first internal data release of the Gaia-ESO Survey, we study elemental ratios and the chemical homogeneity of the red clump stars. Radial velocities enable us to study the rotation and internal kinematics of the cluster. The estimated ages range from 250 to 316Myr, depending on the adopted stellar model. Luminosity profiles and mass functions show strong signs of mass segregation. We derive the mass of the cluster from its luminosity function and from the kinematics, finding values between 3700 M$_{\odot}$ and 11 000 M$_{\odot}$. After selecting the cluster members from their radial velocities, we obtain a metallicity of [Fe/H]=0.10$\pm$0.06 based on 21 candidate members. Moreover, NGC6705 shows no sign of the typical correlations or anti-correlations between Al, Mg, Si, and Na, that are expected in multiple populations. This is consistent with our cluster mass estimate, which is lower than the required mass limit proposed in literature to develop multiple populations.

astro-ph.SR↗

arXiv2014

New galactic star clusters discovered in the VVV survey. Candidates projected on the inner disk and bulge

VISTA Variables in the Vía Láctea (VVV) is one of six ESO Public Surveys using the 4 meter Visible and Infrared Survey Telescope for Astronomy (VISTA). The VVV survey covers the Milky Way bulge and an adjacent section of the disk, and one of the principal objectives is to search for new star clusters within previously unreachable obscured parts of the Galaxy. The primary motivation behind this work is to discover and analyze obscured star clusters in the direction of the inner Galactic disk and bulge. Regions of the inner disk and bulge covered by the VVV survey were visually inspected using composite JHKs color images to select new cluster candidates on the basis of apparent overdensities. DR1, DR2, CASU, and PSF photometry of 10x10 arcmin fields centered on each candidate cluster were used to construct color-magnitude and color-color diagrams. Follow-up spectroscopy of the brightest members of several cluster candidates was obtained in order to clarify their nature. We report the discovery of 58 new infrared cluster candidates. Fundamental parameters such as age, distance, and metallicity were determined for 20 of the most populous clusters.

astro-ph.GA↗

arXiv2014

The metallicity spread and the age-metallicity relation of Omega Centauri

Omega Centauri is a peculiar Globular Cluster formed by a complex stellar population. To shed light on this, we studied 172 stars belonging to the 5 SGBs that we can identify in our photometry, in order to measure their [Fe/H] content as well as estimate their age dispersion and the age-metallicity relation. The first important result is that all of these SGBs has a distribution in metallicity with a spread that exceeds the observational errors and typically displays several peaks that indicate the presence of several sub-populations. We were able to identified at least 6 of them based on their mean [Fe/H] content. These metallicity-based sub-populations are seen to varying extents in each of the 5 SGBs. Taking advantage of the age-sensitivity of the SGB we showed that, first of all, at least half of the sub-populations have an age spread of at least 2 Gyrs. Then we obtained an age-metallicity relation that is the most complete up to date for this cluster. The interpretation of the age-metallicity relation is not straightforward, but it is possible that the cluster (or what we can call its progenitor) was initially composed of two populations having different metallicities. Because of their age, it is very unlikely that the most metal-rich derives from the most metal-poor by some kind of chemical evolution process, so they must be assumed as two independent primordial objects or perhaps two separate parts of a single larger object, that merged in the past to form the present-day cluster.

astro-ph.GA↗

arXiv2014

Uncovering Multiple Populations with Washington Photometry: I. The Globular Cluster NGC 1851

The analysis of multiple populations (MPs) in globular clusters (GCs) has become a forefront area of research in astronomy. Multiple red giant branches (RGBs), subgiant branches (SGBs), and even main sequences (MSs) have now been observed photometrically in many GCs. UV photometry has been crucial in discovering and analyzing these MPs, but the Johnson U and the Stromgren and Sloan u filters that have generally been used are relatively inefficient and very sensitive to reddening and atmospheric extinction. In contrast, the Washington C filter is much broader and redder than these competing UV filters. Here we investigate the use of the Washington system to uncover MPs using only a 1-meter telescope. Our analysis of the well-studied GC NGC 1851 finds that the C filter is both very efficient and effective at detecting its previously discovered MPs in the RGB and SGB. Remarkably, we have also detected an intrinsically broad MS best characterized by two distinct but heavily overlapping populations that cannot be explained by binaries, field stars, or photometric errors. The MS distribution is in very good agreement with that seen on the RGB, with ~30% of the stars belonging to the second population. There is also evidence for two sequences in the red horizontal branch, but this appears to be unrelated to the MPs in this cluster. Neither of these latter phenomena have been observed previously in this cluster. The redder MS stars are also more centrally concentrated than the blue MS. This is the first time MPs in a MS have been discovered from the ground, and using only a 1-meter telescope. The Washington system thus proves to be a very powerful tool for investigating MPs, and holds particular promise for extragalactic objects where photons are limited.

astro-ph.SR↗

arXiv2014

Massive open star clusters using the VVV survey III: A young massive cluster at the far edge of the Galactic bar

Context: Young massive clusters are key to map the Milky Way's structure, and near-IR large area sky surveys have contributed strongly to the discovery of new obscured massive stellar clusters. Aims: We present the third article in a series of papers focused on young and massive clusters discovered in the VVV survey. This article is dedicated to the physical characterization of VVV CL086, using part of its OB-stellar population. Methods: We physically characterized the cluster using $JHK_S$ near-infrared photometry from ESO public survey VVV images, using the VVV-SkZ pipeline, and near-infrared $K$-band spectroscopy, following the methodology presented in the first article of the series. Results: Individual distances for two observed stars indicate that the cluster is located at the far edge of the Galactic bar. These stars, which are probable cluster members from the statistically field-star decontaminated CMD, have spectral types between O9 and B0V. According to our analysis, this young cluster ($1.0$ Myr $<$ age $< 5.0$ Myr) is located at a distance of $11^{+5}_{-6}$ kpc, and we estimate a lower limit for the cluster total mass of $(2.8^{+1.6}_{-1.4})\cdot10^3 {M}_{\odot}$. It is likely that the cluster contains even earlier and more massive stars.

astro-ph.GA↗

arXiv2014

Age Determination of Fifteen Old to Intermediate-Age Small Magellanic Cloud Star Clusters

We present CMDs in the V and I bands for fifteen star clusters in the Small Magellanic Cloud (SMC) based on data taken with the Very Large Telescope (VLT, Chile). We selected these clusters from our previous work, wherein we derived cluster radial velocities and metallicities from Calcium II infrared triplet (CaT) spectra also taken with the VLT. We discovered that the ages of six of our clusters have been appreciably underestimated by previous studies, which used comparatively small telescopes, graphically illustrating the need for large apertures to obtain reliable ages of old and intermediate-age SMC star clusters. In particular, three of these clusters, L4, L6 and L110, turn out to be amongst the oldest SMC clusters known, with ages of 7.9 +- 1.1, 8.7 +- 1.2 and 7.6 +- 1.0 Gyr, respectively, helping to fill a possible "SMC cluster age gap" (Glatt et al. 2008). Using the present ages and metallicities from Parisi et al. (2009), we analyze the age distribution, age gradient and age metallicity relation (AMR) of a sample of SMC clusters measured homogeneously. There is a suggestion of bimodality in the age distribution but it does not show a constant slope for the first 4 Gyr (Piatti 2011), and we find no evidence for an age gradient. Due to the improved ages of our cluster sample, we find that our AMR is now better represented in the intermediate/old period than that we derived in Parisi et al. (2009), where we simply took ages available in the literature. Additionally, clusters younger than aprox. 4 Gyr now show better agreement with the bursting model, but we confirm that this model is not a good representation of the AMR during the intermediate-age/old period. A more complicated model is needed to explain the SMC chemical evolution in that period.

astro-ph.SR↗

arXiv2014

Photometric Metallicities in Bootes I

We present new Stromgren and Washington data sets for the Bootes I dwarf galaxy, and combine them with the available SDSS photometry. The goal of this project is to refine a ground-based, practical, accurate method to determine age and metallicity for individual stars in Bootes I that can be selected in an unbiased imaging survey, without having to take spectra. We produce photometric metallicities from Stromgren and Washington photometry, for stellar systems with a range of $-1.0>[Fe/H]>-3.5$. To avoid the decrease in sensitivity of the Stromgren metallicity index on the lower red-giant branch, we replace the Stromgren v-filter with the broader Washington C-filter; we find that $CT_1by$ is the most successful filter combination, for individual stars with $[Fe/H]<-2.0$, to maintain ~0.2 dex $[Fe/H]$-resolution over the whole red-giant branch. We demonstrate that we can break the isochrones' age-metallicity degeneracy with these filters, using stars with log g=2.5-3.0, which have less than a 2% change in their $(C-T_1)$-colour due to age, over a range of 11-14 Gyr.

astro-ph.GA↗

arXiv2013

Deriving Metallicities from Calcium Triplet Spectroscopy in combination with Near Infrared Photometry

Context. [...] One of the most efficient methods is the measurement of the equivalent width (EW) of the Calcium II Triplet (CaT), corrected for the luminosity and temperature effects via magnitude differences from the horizontal branch (HB). Methods. We use the Ks magnitude difference between the star and the reddest part of the HB (RHB) to generate reduced equivalent widths (rEW) from the datasets presented in Saviane et al. (2012) and Rutledge et al. (1997). Subsequently we calibrated these rEW against three different metellicity (met) scales: the one presented in Carretta et al. (2009), the met values given in Harris (2010) and a version of the former corrected via high-resolution spectroscopic met. Results. We calculated the calibration relations for the two datasets and the three met scales and found that they are approximately equivalent, with differences almost negligible. We compared our nIR calibrations with the corresponding optical ones, and found them to be equivalent, establishing that the luminosity-corrected rEW using the Ks magnitude is compatible with the one obtained from the V magnitude. We then used the met obtained from the calibration to investigate the internal met distributions of the GCs. Conclusions. We have established that the ([Fe/H]:rEW) relation is independent from the mag used for the luminosity correction and find that the calibration relations only change slightly for different met scales. The CaT technique using NIR photometry is thus a powerful tool to derive met. In particular, it can be used to study the internal met spread of a GC. We confirm the presence of at least two met populations in NGC 6656 and find that several other GCs present peculiar met distributions.

astro-ph.SR↗

arXiv2013

The Gaia-ESO Survey: Abundance ratios in the inner-disk open clusters Trumpler 20, NGC 4815, NGC 6705

Open clusters are key tools to study the spatial distribution of abundances in the disk and their evolution with time. Using the first release of stellar parameters and abundances of the Gaia-ESO Survey, we analyse the chemical properties of stars in three old/intermediate-age open clusters, namely NGC 6705, NGC 4815, and Trumpler 20, all located in the inner part of the Galactic disk at Galactocentric radius R$_{GC}\sim$7 kpc, aiming at proving their homogeneity and at comparing them with the field population. We study the abundance ratios of elements belonging to two different nucleosynthetic channels: $α$-elements and iron-peak elements. The main results can be summarised as follows: i) cluster members are chemically homogeneous within 3-$σ$ in all analysed elements; ii) the three clusters have comparable [El/Fe] patters within $\sim$1-$σ$, but they differ in their global metal content [El/H], with NGC 4815 having the lowest metallicity. Their [El/Fe] ratios show differences and analogies with those of the field population, both in the solar neighbourhood and in the bulge/inner disk; iii) comparing the abundance ratios with the results of two chemical evolution models and with field star abundance distributions, we find that the abundance ratios of Mg, Ni, Ca in NGC 6705 might require an inner birthplace, implying a subsequent variation of its R$_{GC}$ during its lifetime, consistent with previous orbit determination. The full dataset of the Gaia-ESO Survey will be a superlative tool to constrain the chemical evolution of our Galaxy by disentangling different formation and evolution scenarios.

astro-ph.GA↗

arXiv2013

The Gaia-ESO Survey: Reevaluation of the parameters of the open cluster Trumpler 20 using photometry and spectroscopy

Trumpler 20 is an old open cluster (OC) located toward the Galactic centre, at about 3 kpc from the Sun and $\sim$7 kpc from the Galactic centre. Its position makes this cluster particularly interesting in the framework of the chemical properties of the Galactic disc because very few old OCs reside in the inner part of the disc. For this reason it has been selected as a cluster target of the Gaia-ESO Survey, and spectra of many stars in the main sequence and red clump phases are now available. Moreover, although it has been studied by several authors in the past, no consensus on the evolutionary status of Tr 20 has been reached. The heavy contamination of field stars (the line of sight of Tr 20 crosses the Carina spiral arm) complicates a correct interpretation. Another interesting aspect of the cluster is that it shows a broadened main-sequence turn-off and a prominent and extended red-clump, characteristics that are not easily explained by classical evolutionary models. Exploiting both spectroscopic information from the Gaia-ESO Survey (and the ESO archive) and literature photometry, we obtain a detailed and accurate analysis of the properties of the cluster. We make use of the first accurate metallicity measurement ever obtained from several spectra of red clump stars, and of cluster membership determination using radial velocities. According to the evolutionary models adopted, we find that Tr 20 has an age in the range 1.35-1.66 Gyr, an average reddening $E(B-V)$ in the range 0.31-0.35 mag, and a distance modulus $(m-M)_0$ between 12.64 and 12.72 mag. The spectroscopic metallicity is [Fe/H]=+0.17 dex. We discuss the structural properties of the object and constrain possible hypotheses for its broadened upper main sequence by estimating the effect of differential reddening and its extended red clump.

astro-ph.SR↗

arXiv2013

Ruprecht 106: the first single population Globular Cluster?

All old Galactic Globular Clusters studied in detail to date host at least two generations of stars, where the second is formed from gas polluted by processed material produced by massive stars of the first. This process can happen if the initial mass of the cluster exceeds a threshold above which ejecta are retained and a second generation is formed. A determination of this mass-threshold is mandatory in order to understand how GCs form. We analyzed 9 RGB stars belonging to the cluster Ruprecht 106. Targets were observed with the UVES@VLT2 spectrograph. Spectra cover a wide range and allowed us to measure abundances for light (O,Na,Mg,Al), alpha (Si,Ca,Ti), iron-peak (Sc,V,Cr,Mn,Fe,Co,Ni,Cu,Zn) and neutron-capture (Y,Zr,Ba,La,Ce,Pr,Nd,Sm,Eu,Dy,Pb) elements. Based on these abundances we show that Ruprecht 106 is the first convincing example of a single population GC (i.e. a true simple stellar population), although the sample is relatively small. This result is supported also by an independent photometric test and by the HB morphology and the dynamical state. It is old (~12 Gyrs) and, at odds with other GCs, has no alpha-enhancement. The material it formed from was contaminated by both s- and r- process elements. The abundance pattern points toward an extragalactic origin. Its present day mass (M=10^4.83 Msun) can be assumed as a strong lower limit for the initial mass threshold below which no second generation is formed. Clearly, its initial mass must have been significantly greater but we have no current constraints on the amount of mass loss during its evolution.

astro-ph.GA↗

arXiv2013

Spectroscopy of blue horizontal branch stars in NGC 6656 (M22)

Recent investigations revealed very peculiar properties of blue horizontal branch (HB) stars in ωCentauri, which show anomalously low surface gravity and mass compared to other clusters and to theoretical models. ωCentauri, however, is a very unusual object, hosting a complex mix of multiple stellar populations with different metallicity and chemical abundances. We measured the fundamental parameters (temperature, gravity, and surface helium abundance) of a sample of 71 blue HB stars in M22, with the aim of clarifying if the peculiar results found in ωCen are unique to this cluster. M22 also hosts multiple sub-populations of stars with a spread in metallicity, analogous to ωCen. The stellar parameters were measured on low-resolution spectra fitting the Balmer and helium lines with a grid of synthetic spectra. From these parameters, the mass and reddening were estimated. Our results on the gravities and masses agree well with theoretical expectations, matching the previous measurements in three "normal" clusters. The anomalies found in ωCen are not observed among our stars. A mild mass underestimate is found for stars hotter than 14\,000 K, but an exact analogy with ωCen cannot be drawn. We measured the reddening in the direction of M22 with two independent methods, finding E(B-V)=0.35 \pm 0.02 mag, with semi-amplitude of the maximum variation Δ(E(B-V))=0.06 mag, and an rms intrinsic dispersion of σ(E(B-V))=0.03 mag.

astro-ph.SR↗

arXiv2013

Milky Way Demographics with the VVV Survey II. Color Transformations and Near-Infrared Photometry for 136 Million Stars in the Southern Galactic Disk

The new multi-epoch near-infrared VVV survey (VISTA Variables in the Via Lactea) is sampling 562 sq. deg of the Galactic bulge and adjacent regions of the disk. Accurate astrometry established for the region surveyed allows the VVV data to be merged with overlapping surveys (e.g., GLIMPSE, WISE, 2MASS, etc.), thereby enabling the construction of longer baseline spectral energy distributions for astronomical targets. However, in order to maximize use of the VVV data, a set of transformation equations are required to place the VVV JHKs photometry onto the 2MASS system. The impetus for this work is to develop those transformations via a comparison of 2MASS targets in 152 VVV fields sampling the Galactic disk. The transformation coefficients derived exhibit a reliance on variables such as extinction. The transformed data were subsequently employed to establish a mean reddening law of E_{J-H}/E_{H-Ks}=2.13 +/- 0.04, which is the most precise determination to date and merely emphasizes the pertinence of the VVV data for determining such important parameters.

astro-ph.GA↗

arXiv2013

The Araucaria Project. A Distance Determination to the Local Group Spiral M33 from Near-Infrared Photometry of Cepheid Variables

Motivated by an amazing range of reported distances to the nearby Local Group spiral galaxy M33, we have obtained deep near-infrared photometry for 26 long-period Cepheids in this galaxy with the ESO VLT. From the data we constructed period-luminosity relations in the J and K bands which together with previous optical VI photometry for the Cepheids by Macri et al. were used to determine the true distance modulus of M33, and the mean reddening affecting the Cepheid sample with the multiwavelength fit method developed in the Araucaria Project. We find a true distance modulus of 24.62 for M33, with a total uncertainty of +- 0.07 mag which is dominated by the uncertainty on the photometric zero points in our photometry. The reddening is determined as E(B-V)=0.19 +- 0.02, in agreement with the value used by the HST Key Project of Freedman et al. but in some discrepancy with other recent determinations based on blue supergiant spectroscopy and an O-type eclipsing binary which yielded lower reddening values. Our derived M33 distance modulus is extremely insensitive to the adopted reddening law. We show that the possible effects of metallicity and crowding on our present distance determination are both at the 1-2% level and therefore minor contributors to the total uncertainty of our distance result for M33.

astro-ph.CO↗

arXiv2013

Anchors for the Cosmic Distance Scale: the Cepheid QZ Normae in the Open Cluster NGC 6067

Cepheids are key to establishing the cosmic distance scale. Therefore it's important to assess the viability of QZ Nor, V340 Nor, and GU Nor as calibrators for Leavitt's law via their purported membership in the open cluster NGC 6067. The following suite of evidence confirms that QZ Nor and V340 Nor are members of NGC 6067, whereas GU Nor likely lies in the foreground: (i) existing radial velocities for QZ Nor and V340 Nor agree with that established for the cluster (-39.4+-1.2 km/s) to within 1 km/s, whereas GU Nor exhibits a markedly smaller value; (ii) a steep velocity-distance gradient characterizes the sight-line toward NGC 6067, thus implying that objects sharing common velocities are nearly equidistant; (iii) a radial profile constructed for NGC 6067 indicates that QZ Nor is within the cluster bounds, despite being 20' from the cluster center; (iv) new BVJH photometry for NGC 6067 confirms the cluster lies d=1.75+-0.10 kpc distant, a result that matches Wesenheit distances computed for QZ Nor/V340 Nor using the Benedict et al. (2007, HST parallaxes) calibration. QZ Nor is a cluster Cepheid that should be employed as a calibrator for the cosmic distance scale.

astro-ph.GA↗

arXiv2013

The Origin and Chemical Evolution of the Exotic Globular Cluster NGC3201

NGC3201 is a globular cluster (GC) which shows very peculiar kinematic characteristics including an extreme radial velocity and a highly retrograde orbit, strongly suggesting an extraGalactic origin. Our aims are to study NGC3201 in the context of multiple populations (MPs), hoping to constrain possible candidates for the self-enrichment by studying the chemical abundance pattern, as well as adding insight into the origin of this intriguing cluster. We present a detailed chemical abundance analysis of eight red giant branch (RGB) stars using high resolution spectroscopy. We measured 29 elements and found [Fe/H]=-1.53+/-0.01, we cannot rule out a metallicity spread of ~0.12 dex, and an alpha-enhancement typical of halo GCs. However significant spreads are observed in the abundances of all light elements except for Mg. We confirm the presence of an extended Na-O anticorrelation. n-capture elements generally are dominated by the r-process, in good agreement with the bulk of Galactic GCs. The total (C+N+O) abundance is slightly supersolar and requires a small downward correction to the isochrone age, yielding 11.4 Gyr. Kinematically, NGC3201 appears likely to have had an extraGalactic origin but its chemical evolution is similar to most other, presumably native, Galactic GCs.

astro-ph.GA↗

arXiv2012

Elemental Abundances and their Implications for the Chemical Enrichment of the Boötes~I Ultra-Faint Galaxy

We present a double-blind analysis of high-dispersion spectra of seven red giant members of the Boötes I ultra-faint dwarf spheroidal galaxy, complemented with re-analysis of a similar spectrum of an eighth member star. The stars cover [Fe/H] from -3.7 to -1.9, and include a CEMP-no star with [Fe/H] = -3.33. We conclude from our chemical abundance data that Boötes I has evolved as a self-enriching star-forming system, from essentially primordial initial abundances. This allows us uniquely to investigate the place of CEMP-no stars in a chemically evolving system, in addition to limiting the timescale of star formation. The elemental abundances are formally consistent with a halo-like distribution, with enhanced mean [alpha/Fe] and small scatter about the mean. This is in accord with the high-mass stellar IMF in this low-stellar-density, low-metallicity system being indistinguishable from the present-day solar neighborhood value. There is a non-significant hint of a decline in [alpha/Fe] with [Fe/H]; together with the low scatter, this requires low star formation rates, allowing time for SNe ejecta to be mixed over the large spatial scales of interest. One star has very high [Ti/Fe], but we do not confirm a previously published high value of [Mg/Fe] for another star. We discuss the existence of CEMP-no stars, and the absence of any stars with lower CEMP-no enhancements at higher [Fe/H], a situation which is consistent with knowledge of CEMP-no stars in the Galactic field. We show that this observation requires there be two enrichment paths at very low metallicities: CEMP-no and "carbon-normal".

astro-ph.GA↗