Clues to the Metallicity Distribution in the Galactic Bulge: Abundances in MOA-2008-BLG310 and MOA-2008-BLG311

Abstract

We present abundance analyses based on high dispersion and high signal-to-noise ratio Magellan spectra of two highly microlensed Galactic bulge stars in the region of the main sequence turnoff with Teff ~ 5650 K. We find that MOA-2008-BLG310 has [Fe/H]= +0.41 (+,- 0.09 dex) and MOA-2008-BLG311 has +0.26 (+, - 0.09 dex). The abundance ratios for the ~20 elements for which features could be detected in the spectra of each of the two stars follow the trends with [Fe/H] found among samples of bulge giants. Combining these two bulge dwarfs with the results from previous abundance analysis of four other Galactic bulge turnoff region stars, all highly magnified by microlensing, gives a mean [Fe/H] of +0.29dex. This implies that there there is an inconsistency between the Fe-metallicity distribution of the microlensed bulge dwarfs and that derived by the many previous estimates based on surveys of cool, luminous bulge giants, which have mean [Fe/H] ~ -0.1 dex. A number of possible mechanisms for producing this difference are discussed. If one ascribes this inconsistency to systematic errors in the abundance analyses, we provide statistical arguments suggesting that a substantial systematic error in the Fe-metallicity for one or both of the two cases, bulge dwarfs vs bulge giants, is required which is probably larger than can realistically be accommodated.

arXiv commentAccepted to the ApJ, 36 pages with 7 figures. Updated to conform to the published version, two references added, other very minor changes

References in corpus (22)

• The Dartmouth Stellar Evolution Database
• The Chemical Compositions of Galactic Disk F and G Dwarfs
• alpha-, r-, and s-process element trends in the Galactic thin and thick disks
• Age and Metallicity Distribution of the Galactic Bulge from Extensive Optical and Near-IR Stellar Photometry
• The Metal Content of Bulge Field Stars from FLAMES-GIRAFFE Spectra. I. Stellar parameters and Iron Abundances
• Massive Stars in the Arches Cluster
• Abundances of Baade's Window Giants from Keck/HIRES Spectra: II. The Alpha- and Light Odd Elements
• Oxygen, Sodium, Magnesium and Aluminium as tracers of the Galactic Bulge Formation
• The colours of the Sun
• Abundances of Baade's Window Giants from Keck/HIRES Spectra: I. Stellar Parameters and [Fe/H] Values
• Stellar Proper Motions in the Galactic Bulge from deep HST ACS/WFC Photometry
• The First Detailed Abundances for M giants in Baade's Window from Infrared Spectroscopy
• Chemical Evolution of the Galactic Bulge as Derived from High-Resolution Infrared Spectroscopy of K and M Red Giants
• Detailed chemical composition of the open cluster IC 4651: The iron peak, alpha elements, and Li
• The First Detailed Abundances for M giants in the inner Bulge from Infrared Spectroscopy
• An Abundance Analysis for Five Red Horizontal Branch Stars in the Extremely Metal Rich Globular Cluster NGC 6553
• Metallicities for 13 nearby open clusters from high-resolution spectroscopy of dwarf and giant stars. Stellar metallicity, stellar mass, and giant planets
• Clues to the Metallicity Distribution in the Galactic Bulge: Abundances in OGLE-2007_BLG-349S
• A High-Resolution Spectrum of the Extremely Metal-Rich Bulge G-Dwarf OGLE-2006-BLG-265
• Abundances in Turn-off Stars in the Old, Metal-Rich Open Cluster, NGC 6791
• A High-Resolution Spectrum of the Highly Magnified Bulge G-Dwarf MOA-2006-BLG-099S
• Detailed Analysis of Nearby Bulge-like Dwarf Stars I. Stellar Parameters, Kinematics and Oxygen Abundances

Cited by in corpus (23)

• Reddening and Extinction Toward the Galactic Bulge from OGLE-III: The Inner Milky Way's Rv ~ 2.5 Extinction Curve
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. V. Evidence for a wide age distribution and a complex MDF
• The metallicity distribution of bulge clump giants in Baade's Window
• Chemical similarities between Galactic bulge and local thick disk red giants: O, Na, Mg, Al, Si, Ca and Ti
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. IV. Two bulge populations
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. VI. Age and abundance structure of the stellar populations in the central sub-kpc of the Milky Way
• Masses and Orbital Constraints for the OGLE-2006-BLG-109Lb,c Jupiter/Saturn Analog Planetary System
• Light, Alpha, and Fe-Peak Element Abundances in the Galactic Bulge
• Sub-Saturn Planet MOA-2008-BLG-310Lb: Likely To Be In The Galactic Bulge
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. II. Ages, metallicities, detailed elemental abundances, and connections to the Galactic thick disc
• Chemical Composition of Faint (I~21 mag) Microlensed Bulge Dwarf OGLE-2007-BLG-514S
• Analysis of old very metal rich stars in the solar neighbourhood
• Abundances of Refractory Elements for G-type Stars with Extrasolar Planets
• The evolution of CNO elements in galaxies
• On the variation of carbon abundance in galaxies and its implications
• WIYN Open Cluster Study. XXXIX. Abundances in NGC 6253 from HYDRA Spectroscopy of the Li 6708 A Region
• Characterizing Lenses and Lensed Stars of High-Magnification Single-lens Gravitational Microlensing Events With Lenses Passing Over Source Stars
• A Puzzle Involving Galactic Bulge Microlensing Events
• Chemical evolution of the Galactic bulge as traced by microlensed dwarf and subgiant stars. VIII. Carbon and oxygen
• The Effect of Differential Limb Magnification on Abundance Analysis of Microlensed Dwarf Stars
• The Stellar Population of the Galactic Bulge
• How galaxies form: Mass assembly from chemical abundances in the era of large surveys
• The age and abundance structure of the stellar populations in the central sub-kpc of the Milky Way