Old open clusters in the outer Galactic disk

Abstract

The outer parts of the Milky Way disk are believed to be one of the main arenas where the accretion of external material in the form of dwarf galaxies and subsequent formation of streams is taking place. The Monoceros stream and the Canis Major and Argo over-densities are notorious examples. VLT high resolution spectra have been acquired for five distant open clusters. We derive accurate radial velocities to distinguish field interlopers and cluster members. For the latter we perform a detailed abundance analysis and derive the iron abundance [Fe/H] and the abundance ratios of several $\alpha$ elements. Our analysis confirms previous indications that the radial abundance gradient in the outer Galactic disk does not follow the expectations extrapolated from the solar vicinity, but exhibits a shallower slope. By combining the metallicity of the five program clusters with eight more clusters for which high resolution spectroscopy is available, we find that the mean metallicity in the outer disk between 12 and 21 kpc from the Galactic center is [Fe/H] $\approx -0.35$, with only marginal indications for a radial variation. In addition, all the program clusters exhibit solar scaled or slightly enhanced $\alpha$ elements, similar to open clusters in the solar vicinity and thin disk stars. We investigate whether this outer disk cluster sample might belong to an extra-galactic population, like the Monoceros ring. However, close scrutiny of their properties - location, kinematics and chemistry - does not convincingly favor this hypothesis. On the contrary, they appear more likely genuine Galactic disk clusters. We finally stress the importance to obtain proper motion measurements for these clusters to constrain their orbits.

19 pages, 9 eps figure, in press in A&A, abstract rephrased to fit in

References in corpus (31)

• Evolutionary tracks and isochrones for low- and intermediate-mass stars: from 0.15 to 7 M_sun, and from Z=0.0004 to 0.03
• A 2MASS All-Sky View of the Sagittarius Dwarf Galaxy: I. Morphology of the Sagittarius Core and Tidal Arms
• The Ghost of Sagittarius and Lumps in the Halo of the Milky Way
• A Low Latitude Halo Stream around the Milky Way
• Some Revised Observational Constraints on the Formation and Evolution of the Galactic Disk
• Abundances for metal-poor stars with accurate parallaxes I. Basic data
• Outer structure of the Galactic warp and flare: explaining the Canis Major over-density
• Improved Color-Temperature Relations and Bolometric Corrections for Cool Stars
• One Ring to Encompass them All: A giant stellar structure that surrounds the Galaxy
• The exotic chemical composition of the Sagittarius dwarf Spheroidal galaxy
• Elemental Abundance Ratios in Stars of the Outer Galactic Disk. I. Open Clusters
• Oxygen Abundances in Nearby Stars. Clues to the formation and evolution of the Galactic disk
• On the galactic disc age-metallicity relation
• A comprehensive model for the Monoceros tidal stream
• Two measures of the shape of the Milky Way's dark halo
• Exploring Halo Substructure with Giant Stars: Spectroscopy of Stars in the Galactic Anticenter Stellar Structure
• Abundance gradients in the Milky Way for alpha elements, Iron peak elements, Barium, Lanthanum and Europium
• Elemental Abundance Ratios in Stars of the Outer Galactic Disk. III. Cepheids
• Integrated Nebular Abundances of Disk Galaxies
• Spiral structure of the Third Galactic Quadrant and the solution to the Canis Major debate
• The Oort Constants Measured from Proper Motions
• Metal abundances in extremely distant Galactic old open clusters. I. Berkeley 29 and Saurer 1
• A possible age-metallicity relation in the Galactic thick disk?
• Star Clusters in the Galactic Anticenter Stellar Structure and the Origin of Outer Old Open Clusters
• A Comparison of the Chemical Evolutionary Histories of the Galactic Thin Disk and Thick Disk Stellar Populations
• Elemental Abundance Ratios in Stars of the Outer Galactic Disk. II. Field Red Giants
• Metal abundances in extremely distant Galactic old open clusters. II. Berkeley 22 and Berkeley 66
• Photometry and Spectroscopy of Old, Outer Disk Star Clusters: vdB-Hagen 176, Berkeley 29 and Saurer 1
• A photometric study of the old open clusters Berkeley 73, Berkeley 75 and Berkeley 25
• Fundamental parameters of six neglected old open clusters
• The intermediate-age open clusters Ruprecht 4, Ruprecht 7 and Pismis 15

Cited by in corpus (85)

• On the metallicity of open clusters. III. Homogenised sample
• A First Constraint on the Thick Disk Scale Length: Differential Radial Abundances in K Giants at Galactocentric Radii 4, 8, and 12 kpc
• Chemical abundance analysis of the Open Clusters Cr110, NGC2099 (M37), NGC2420, NGC7789 and M67 (NGC2682)
• Stellar Population gradients in galaxy discs from the CALIFA survey
• HII Region Metallicity Distribution in the Milky Way Disk
• On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk
• The evolution of the Galactic metallicity gradient from high-resolution spectroscopy of open clusters
• Shape of the oxygen abundance profiles in CALIFA face-on spiral galaxies
• Star formation history of barred disc galaxies
• Elemental Abundance Ratios in Stars of the Outer Galactic Disk. IV. A New Sample of Open Clusters
• The Origin of the Light Distribution in Spiral Galaxies
• Chemical abundance analysis of the Open Clusters Berkeley 32, NGC 752, Hyades and Praesepe
• A Chemical Abundance Study of 10 Open Clusters Based on WIYN-Hydra Spectroscopy
• Milky Way vs Andromeda: a tale of two disks
• On the metallicity gradient of the Galactic disk
• The Gaia-ESO Survey: radial distribution of abundances in the Galactic disc from open clusters and young field stars
• Overlapping abundance gradients and azimuthal gradients related to the spiral structure of the Galaxy
• On the metallicity of open clusters II. Spectroscopy
• Open clusters as key tracers of Galactic chemical evolution. III. Element abundances in Berkeley 20, Berkeley 29, Collinder 261, and Melotte 66
• Tombaugh 2: The First Open Cluster with a Significant Abundance Spread or Embedded in a Cold Stellar Stream?
• Metal production in M33: space and time variations
• Gaia Early Data Release 3: The Galactic anticentre
• Galactic abundance gradients from Cepheids : On the iron abundance gradient around 10-12 kpc
• Galactic abundance gradients from Cepheids: alpha and heavy elements in the outer disk
• Chemical gradients in the Milky Way from the RAVE data. I. Dwarf stars
• Origin and Evolution of the Abundance Gradient along the Milky Way Disk
• The Gaia-ESO survey: mapping the shape and evolution of the radial abundance gradients with open clusters
• The Gaia-ESO Survey: Sodium and aluminium abundances in giants and dwarfs - Implications for stellar and Galactic chemical evolution
• The Gaia-ESO Survey: Probes of the inner disk abundance gradient
• On the alpha-element gradients of the Galactic thin disk using Cepheids
• The spatially resolved Kennicutt-Schmidt relation in the HI dominated regions of spiral and dwarf irregular galaxies
• Testing the chemical tagging technique with open clusters
• The evolution of the Milky Way: New insights from open clusters
• Chemical gradients in the Milky Way from the RAVE data. II. Giant stars
• The Gaia-ESO Survey: double, triple and quadruple-line spectroscopic binary candidates
• High Spatial Resolution Galactic 3D Extinction Mapping with IPHAS
• Early-A stars from IPHAS, and their distribution in and around the Cyg OB2 association
• The Gaia-ESO Survey: CNO abundances in the open clusters Trumpler 20, NGC 4815, and NGC 6705
• The Gaia-ESO Survey: Galactic evolution of sulphur and zinc
• Chemical distribution of HII regions towards the Galactic anticentre
• On the metallicity distribution of classical Cepheids in the Galactic inner disk
• Discovery and astrophysical properties of Galactic open clusters in dense stellar fields using Gaia DR2
• A catalogue of 74 new open clusters found in Gaia Data-Release 2
• Chemical composition of clump stars in the open cluster NGC 6134
• A kinematic study of Open Clusters: implications for their origin
• The Structure of the Outer Galactic Disc as revealed by IPHAS early A Stars
• Comprehensive abundance analysis of red giants in the open clusters NGC 1342, 1662, 1912, 2354 and 2447
• 3D Extinction Mapping Using Hierarchical Bayesian Models
• The stellar metallicity gradients in galaxy discs in a cosmological scenario
• The Structure and Metallicity Gradient in the Extreme Outer Disk of NGC 7793
• Barium and Yttrium abundance in intermediate-age and old open clusters
• The relation between atomic gas and star formation rate densities in faint irregular galaxies
• Abundances and kinematics for ten anticentre open clusters
• Oxygen, sulfur, and iron radial abundance gradients of classical Cepheids across the Galactic thin disk
• Abundances and physical parameters for stars in the open clusters NGC 5822 and IC 4756
• Detailed chemical composition and orbit of the new globular cluster FSR1758: Implications for the accretion of the Sequoia dwarf galaxy onto the Milky Way
• NGC 6791: a probable bulge cluster without multiple populations
• Timing the Milky Way bar formation and the accompanying radial migration episode
• Old open clusters in the Sagittarius dSph tidal stream -- kith or kin?
• Chemical abundance analysis of the old, rich open cluster Trumpler 20
• Evidence of Early Enrichment of the Galactic Disk by Large-Scale Winds
• The old open cluster NGC 2112: updated estimates of fundamental parameters based on a membership analysis
• Open clusters and associations in the Gaia era
• Mapping radial abundance gradients with Gaia-ESO open clusters: Evidence of recent gas accretion in the Milky Way disk
• Characterisation of the Galactic thin disc with Corot targets
• NGC 7789: An Open Cluster Case Study
• Age Aspects of Habitability
• Radial Velocities of Three Poorly Studied Clusters and the Kinematics of Open Clusters
• BVRIJHK photometry and proper motion analysis of NGC 6253 and the surrounding field
• Stellar Populations in the Outer Disk and Halo of the Spiral Galaxy M101
• Disintegration of the Aged Open Cluster Berkeley 17
• An analysis of the most distant catalogued open clusters -- Re-assessing fundamental parameters with Gaia EDR3 and $\text{ASteCA}$
• CCD $UBV(RI{)}_C$ Photometry of Twenty Open Clusters
• Gemini spectroscopy of the outer disk star cluster BH176
• Old open clusters and the Galactic metallicity gradient: Berkeley 20, Berkeley 66, and Tombaugh 2
• Five old open clusters more in the outer Galactic disk
• UB CCD photometry of the old, metal rich, open clusters NGC 6791, NGC 6819 and NGC 7142
• A chemical and kinematical analysis of the intermediate-age open cluster IC 166 from APOGEE and Gaia DR2
• Stellar atmospheric parameters and chemical abundances of about 5 million stars from S-PLUS multi-band photometry
• The completeness of the open cluster census towards the Galactic anticentre
• Stellar Populations in the Galactic Center
• Photometry of the Four Anti-Galactocentric Old Open Clusters: Czernik 30, Berkeley 34, Berkeley 75, and Berkeley 76
• Open cluster age calibration from colour-magnitude morphological indices using Gaia DR3 data
• The old metal-poor open cluster ESO 92-SC05: accreted from a dwarf galaxy?
• Open clusters in the outer disc studied with MEGARA@GTC Auner 1 and Berkeley 102