Elemental Abundance Ratios in Stars of the Outer Galactic Disk. III. Cepheids

Abstract

We present metallicities, [Fe/H], and elemental abundance ratios, [X/Fe], for a sample of 24 Cepheids in the outer Galactic disk. The sample have Galactocentric distances covering 12 < R_GC (kpc) < 17.2 making them the most distant Galactic Cepheids upon which detailed abundance analyses have been performed. We find sub-solar ratios of [Fe/H] and overabundances of [alpha/Fe], [La/Fe], and [Eu/Fe]. All abundance ratios exhibit a dispersion that exceeds the measurement uncertainties. As seen in our previous studies of old open clusters and field giants, enhanced ratios of [alpha/Fe] and [Eu/Fe] reveal that recent star formation has taken place in the outer disk. The outer disk Cepheids appear to exhibit a bimodal distribution for [Fe/H] and [alpha/Fe]. Most of the Cepheids continue the trends with Galactocentric distance exhibited by Andrievsky's larger Cepheid sample and we refer to these stars as the "Galactic Cepheids". A minority of the Cepheids show considerably lower [Fe/H] and higher [alpha/Fe] and we refer to these stars as the "Merger Cepheids". One signature of a merger event would be composition differences between the "Galactic" and "Merger" Cepheids. The Cepheids satisfy this requirement and we speculate that the distinct compositions suggest that the "Merger Cepheids" may have formed under the influence of significant merger or accretion events. The short lifetimes of the Cepheids reveal that the merger event may be on-going with the Monoceros ring and Canis Major galaxy being possible merger candidates. [Abridged]

Accepted for publication in AJ

References in corpus (27)

• Maps of Dust IR Emission for Use in Estimation of Reddening and CMBR Foregrounds
• Color Transformations for the 2MASS Second Incremental Data Release
• Stellar Chemical Signatures And Hierarchical Galaxy Formation
• The Chemical Compositions of Galactic Disk F and G Dwarfs
• The Ghost of Sagittarius and Lumps in the Halo of the Milky Way
• Abundance Gradients and the Formation 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
• A dwarf galaxy remnant in Canis Major: the fossil of an in-plane accretion onto the Milky Way
• One Ring to Encompass them All: A giant stellar structure that surrounds the Galaxy
• Elemental Abundance Ratios in Stars of the Outer Galactic Disk. I. Open Clusters
• Abundances in Stars from the Red Giant Branch Tip to Near the Main Sequence Turn Off in M71: III. Abundance Ratios
• Galactic Metallicity Gradients Derived from a Sample of OB Stars
• A comprehensive model for the Monoceros tidal stream
• Using Cepheids to determine the galactic abundance gradient I. The solar neighbourhood
• Classical Cepheid Pulsation Models. X. The Period-Age Relation
• Sulfur, Chlorine, and Argon Abundances in Planetary Nebulae. IV: Synthesis and the Sulfur Anomaly
• Using Cepheids to determine the galactic abundance gradient II. Towards the galactic center
• Using Cepheids to determine the galactic abundance gradient. III.First results for the outer disc
• The MACHO Project LMC Variable Star Inventory: I. Beat Cepheids - Conclusive Evidence for the Excitation of the Second Overtone in Classical Cepheids
• Mean JHK Magnitudes of Fundamental-Mode Cepheids from Single-Epoch Observations
• Detection of the Canis Major galaxy at (l;b)=(244;-8) and in the background of Galactic open clusters
• The Shape and Scale of Galactic Rotation from Cepheid Kinematics
• A radial velocity survey of low Galactic latitude structures: I. Kinematics of the Canis Major dwarf galaxy
• The Effect of Thermal Conduction on the Virgo Cluster
• Elemental Abundance Ratios in Stars of the Outer Galactic Disk. II. Field Red Giants
• UVES observations of the Canis Major overdensity

Cited by in corpus (65)

• The Gaia-ESO Survey: the Galactic Thick to Thin Disc transition
• The Distribution of the Elements in the Galactic Disk III. A Reconsideration of Cepheids from l = 30 to 250 Degrees
• A First Constraint on the Thick Disk Scale Length: Differential Radial Abundances in K Giants at Galactocentric Radii 4, 8, and 12 kpc
• Stellar Population gradients in galaxy discs from the CALIFA survey
• The flat oxygen abundance gradient in the extended disk of M83
• HII Region Metallicity Distribution in the Milky Way Disk
• On the fine structure of the Cepheid metallicity gradient in the Galactic thin disk
• 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
• Old open clusters in the outer Galactic disk
• Abundance gradients in the Milky Way for alpha elements, Iron peak elements, Barium, Lanthanum and Europium
• The Distribution of the Elements in the Galactic Disk II. Azimuthal and Radial Variation in Abundances from Cepheids
• 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
• Tombaugh 2: The First Open Cluster with a Significant Abundance Spread or Embedded in a Cold Stellar Stream?
• 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 abundance patterns in the inner Galaxy: the Scutum Red Supergiant Clusters
• Cepheids in Open Clusters: An 8-D All-sky Census
• Cepheids in external galaxies. I. The maser-host galaxy NGC 4258 and the metallicity dependence of P-L and P-W relations
• 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
• Observational studies of Cepheid amplitudes. I - Period-amplitude relationships for Galactic Cepheids and interrelation of amplitudes
• The Distances to Open Clusters from Main-Sequence Fitting. IV. Galactic Cepheids, the LMC, and the Local Distance Scale
• NGC 2579 and the carbon and oxygen abundance gradients beyond the solar circle
• Baade-Wesselink distances to Galactic and Magellanic Cloud Cepheids and the effect of metallicity
• On the alpha-element gradients of the Galactic thin disk using Cepheids
• Cepheid Variables in the Flared Outer Disk of our Galaxy
• The Abundance Gradient in the Extremely Faint Outer Disk of NGC 300
• Chemical gradients in the Milky Way from the RAVE data. II. Giant stars
• On the Origin of Dynamically Cold Rings Around the Milky Way
• The influence of metallicity on the Leavitt Law from geometrical distances of Milky Way and Magellanic Clouds Cepheids
• On the metallicity distribution of classical Cepheids in the Galactic inner disk
• Metallicity gradients in Local Universe galaxies: time evolution and effects of radial migration
• Baade-Wesselink distances and the effect of metallicity in classical cepheids
• On the Application of Wesenheit Function in Deriving Distance to Galactic Cepheids
• Tracing the Milky Way warp and spiral arms with classical Cepheids
• The Chemical Evolution of the Monoceros Ring/Galactic Anticenter Stellar Structure
• On the neutron-capture elements across the Galactic thin disk using Cepheids
• The Structure and Metallicity Gradient in the Extreme Outer Disk of NGC 7793
• Detailed chemical composition of classical Cepheids in the LMC cluster NGC 1866 and in the field of the SMC
• Abundances and kinematics for ten anticentre open clusters
• A new and homogeneous metallicity scale for Galactic classical Cepheids II. The abundance of iron and alpha elements
• Chemical evolution of disc galaxies from cosmological simulations
• Study of the stellar population properties in the discs of ten spiral galaxies
• Effects of the selection function on metallicity trends in spectroscopic surveys of the Milky Way
• First metallicity determination from Near-Infrared spectra for five obscured Cepheids discovered in the inner Disk
• Evidence of Early Enrichment of the Galactic Disk by Large-Scale Winds
• Modeling the Stellar Populations in the Canis Major Over-Density: the Relation Between the Old and Young Populations
• The First Metallicity Study of M83 using the integrated UV light of Star Clusters
• Gas-phase metallicity break radii of star-forming galaxies in IllustrisTNG
• Deep secrets of intermediate-mass giants and supergiants: Models with rotation seem to overestimate mixing effects on the surface abundances of C, N, and Na
• Gamma-ray bursts and terrestrial planetary atmospheres
• Galactic structure in the outer disk: the field in the line of sight to the intermediate-age open cluster Tombaugh 1
• The Science Case for PILOT III: the Nearby Universe
• Properties of the open cluster Tombaugh 1 from high resolution spectroscopy and uvbyCaH$\beta$ photometry
• Constraints on the history of Galactic spiral arms revealed by Gaia GSP-Spec alpha-elements
• A Monte Carlo based simulation of the galactic chemical evolution of the Milky Way galaxy
• Outer Spiral Disks as Clues to Galaxy Formation and Evolution
• The flux-weighted gravity-luminosity relation of Galactic classical Cepheids
• Stellar Populations in the Galactic Center
• Stellar Population Astrophysics (SPA) with the TNG: NLTE atmospheric parameters and abundances of giant stars in 33 Open Clusters
• Triangulum-Andromeda overdensity: a region with a complex stellar population
• Study of the effect of metallicity on the amplitudes of Cepheids