Chemical similarities between Galactic bulge and local thick disk red giants: O, Na, Mg, Al, Si, Ca, and Ti

By A. Alves-Brito, Jorge Meléndez, Martin Asplund, I. Ramírez, David Yong. 2010

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Context. The formation and evolution of the Galactic bulge and its relationship with the other Galactic populations is still poorly understood. Aims. To establish the chemical differences and similarities between the bulge and other stellar populations, we performed an elemental abundance analysis of α- (O, Mg, Si, Ca, and Ti) and Z-odd (Na and Al) elements of red giant stars in the bulge as well as of local thin disk, thick disk and halo giants. Methods. We use high-resolution optical spectra of 25 bulge giants in Baade’s window and 55 comparison giants (4 halo, 29 thin disk and 22 thick disk giants) in the solar neighborhood. All stars have similar stellar parameters but cover a broad range in metallicity (−1.5 < [Fe/H] < +0.5). A standard 1D local thermodynamic equilibrium analysis using both Kurucz and MARCS models yielded the abundances of O, Na, Mg, Al, Si, Ca, Ti and Fe. Our homogeneous and differential analysis of the Galactic stellar populations ensured that systematic errors were minimized. Results. We confirm the well-established differences for [α/Fe] at a given metallicity between the local thin and thick disks. For all the elements investigated, we find no chemical distinction between the bulge and the local thick disk, in agreement with our previous study of C, N and O but in contrast to other groups relying on literature values for nearby disk dwarf stars. For −1.5 < [Fe/H] < −0.3 exactly the same trend is followed by both the bulge and thick disk stars, with a star-to-star scatter of only 0.03 dex. Furthermore, both populations share the location of the knee in the [α/Fe] vs. [Fe/H] diagram. It still remains to be confirmed that the local thick disk extends to super-solar metallicities as is the case for the bulge. These are the most stringent constraints to date on the chemical similarity of these stellar populations. Conclusions. Our findings suggest that the bulge and local thick disk stars experienced similar formation timescales, star formation rates and initial mass functions, confirming thus the main outcomes of our previous homogeneous analysis of [O/Fe] from infrared spectra for nearly the same sample. The identical α-enhancements of thick disk and bulge stars may reflect a rapid chemical evolution taking place before the bulge and thick disk structures we see today were formed, or it may reflect Galactic orbital migration of inner disk/bulge stars resulting in stars in the solar neighborhood with thick-disk kinematics.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/c9182681f1fecc8e0beef22d587363daabb70d68

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Alpha element abundances and gradients in the Milky Way bulge from FLAMES-GIRAFFE spectra of 650 K giants (2011, background): “Later on, Alves-Brito et al. (2010) reach the same conclusions when analyzing other α-elements from the sample of Meléndez et al. (2008).”
A FIRST CONSTRAINT ON THE THICK DISK SCALE LENGTH: DIFFERENTIAL RADIAL ABUNDANCES IN K GIANTS AT GALACTOCENTRIC RADII 4, 8, AND 12 kpc (2011, methodology): “2, where they are compared to the Bensby et al. (2010a) inner disk red giant sample, and the Alves-Brito et al. (2010) sample of thin and thick disk red giants in the solar neighbourhood, and in Fig.”
FUNDAMENTAL PARAMETERS AND CHEMICAL COMPOSITION OF ARCTURUS (2011, background): “Arcturus, on the other hand, represents a much better reference for this purpose, and some studies have already taken advantage of this fact (e.g., McWilliam & Rich 1994; Worley et al. 2009; Alves-Brito et al. 2010).”
OUR MILKY WAY AS A PURE-DISK GALAXY—A CHALLENGE FOR GALAXY FORMATION (2010, unknown): “The thickened disk in the pseudobulge-forming process may have contributed to the thick disk of the Milk Way, as hinted from chemical similarities of Galactic bulge and local thick disk stars (Alves-Brito et al. 2010; Bensby et al. 2010).”
THE MOST METAL-POOR STARS. II. CHEMICAL ABUNDANCES OF 190 METAL-POOR STARS INCLUDING 10 NEW STARS WITH [Fe/H] ⩽ −3.5,, (2012, background): “The reason for separating the dwarfs from giants is that we want to compare, as best we can, stars with similar stellar parameters to minimize systematic errors (e.g., Cayrel et al. 2004; Meléndez et al. 2008; Bonifacio et al. 2009; Alves-Brito et al. 2010; Nissen & Schuster 2010)16.”
The metallicity distribution of bulge clump giants in Baade’s window (2011, background): “14, the two lower panels show that indeed our conclusions would not be altered in any way if comparing our sample to local giants (Alves-Brito et al. 2010).”
REDDENING AND EXTINCTION TOWARD THE GALACTIC BULGE FROM OGLE-III: THE INNER MILKY WAY'S RV ∼ 2.5 EXTINCTION CURVE (2012, background): “The spectroscopic metallicity distribution function of the Galactic bulge is now known to an impressive degree of accuracy (Zoccali et al. 2008; Alves-Brito et al. 2010; Hill et al. 2011; Bensby et al. 2011; Johnson et al. 2011; Rich et al. 2012).”
Chemodynamics of the Milky Way - I. The first year of APOGEE data (2013, methodology): “To highlight APOGEE’s potential in chemical mapping, we compare the APOGEE [α/Fe] vs. [Fe/H] abundance plane in different bins of Rmed with the recent high-resolution study of disc 20 Indeed, Alves-Brito et al. (2010) re-analysed the same equivalent widths of Fulbright et al. (2007) and found Solar ”
The Galaxy in Context: Structural, Kinematic, and Integrated Properties (2016, background): “…disk, the thick disk and bulge are more difficult to disentangle because they share kinematic and abundance characteristics, as observed in red giants (Alves-Brito et al. 2010, Ryde et al. 2010, Gonzalez et al. 2011b, Hill et al. 2011) and microlensed dwarf stars (Bensby et al. 2009, 2013).”
Insights on the Milky Way bulge formation from the correlations between kinematics and metallicity (2010, background): “Meléndez et al. (2008), Ryde et al. (2010), Bensby et al. (2010) and Alves-Brito et al. (2010) observed similarities between the metallicity of the bulge and the metallicity of thick disc stars for metal-poor stars.”
OXYGEN ABUNDANCES IN NEARBY FGK STARS AND THE GALACTIC CHEMICAL EVOLUTION OF THE LOCAL DISK AND HALO (2013, background): “Indeed, Alves-Brito et al. (2010) have demonstrated that the practice of combining dwarf/subgiant elemental abundance data with giant star data can lead to spurious results.”
TWO RED CLUMPS AND THE X-SHAPED MILKY WAY BULGE (2010, background): “If correct, this scenario might naturally explain the similarity of the composition of thick disk and bulge red giant stars found by Alves-Brito et al. (2010).”