alpha-, r-, and s-process element trends in the Galactic thin and thick disks

By T. Bensby, S. Feltzing, I. Lundstrøm, I. Observatory, Sweden., D. Astronomy, U. Michigan, A. Arbor, Usa, Aip and 2 more. 2004

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From a detailed elemental abundance analysis of 102 F and G dwarf starswe present abundance trends in the Galactic thin and thick disks for 14elements (O, Na, Mg, Al, Si, Ca, Ti, Cr, Fe, Ni, Zn, Y, Ba, and Eu).Stellar parameters and elemental abundances (except for Y, Ba and Eu)for 66 of the 102 stars were presented in our previous studies (Bensbyet al. 2003, 2004a). The 36 stars that are new in this study extend andconfirm our previous results and allow us to draw further conclusionsregarding abundance trends. The s-process elements Y and Ba, and ther-element Eu have also been considered here for the whole sample for thefirst time. With this new larger sample we now have the followingresults: 1) Smooth and distinct trends that for the thin and thick disksare clearly separated; 2) The alpha-element trends for the thick diskshow typical signatures from the enrichment of SNIa; 3) The thick diskstellar sample is in the mean older than the thin disk stellar sample;4) The thick disk abundance trends are invariant with galactocentricradii (R_m); 5) The thick disk abundance trends appear to be invariantwith vertical distance (Z_max) from the Galactic plane. Adding furtherevidence from the literaure we argue that a merger/interacting scenariowith a companion galaxy to produce a kinematical heating of the stars(that make up today's thick disk) in a pre-existing old thin disk is themost likely formation scenario for the Galactic thick disk. (Less)

Subfields: Astronomy and Astrophysics, Instrumentation

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Dissecting simulated disc galaxies - I. The structure of mono-age populations (2014, background): “…a larger scale-height than the thin disc (Robin et al. 1996; Chen et al. 2001; Jurić et al. 2008), but it is also older, more metal-poor, and enhanced in alpha elements (Gilmore, Wyse, & Jones 1995; Fuhrmann 1998; Prochaska et al. 2000; Bensby et al. 2005; Reddy, Lambert, & Allende Prieto 2006).”
Chemical abundances of 1111 FGK stars from the HARPS GTO planet search program - Galactic stellar populations and planets (2012, methodology): “Generally, the thick disk is composed of relatively old (e.g. Bensby et al. 2005; Adibekyan et al. 2011), metal-poor and α-enhanced (Fuhrmann 1998; Prochaska et al. 2000; Feltzing et al. 2003; Mishenina et al. 2004; Reddy et al. 2006; Haywood 2008b, Lee et al. 2011) stars that move in Galactic…”
New constraints on the chemical evolution of the solar neighbourhood and galactic disc(s) - improved astrophysical parameters for the Geneva-Copenhagen Survey (2011, methodology): “To this purpose we have taken only three large surveys, namely Valenti & Fischer (2005, V05), Sousa et al. (2008, S08) and Bensby et al. (2011 in prep., B11, which includes over 600 stars in addition to 102 from Bensby et al. 2003 and Bensby et al. 2005).”
THE SEGUE STELLAR PARAMETER PIPELINE. V. ESTIMATION OF ALPHA-ELEMENT ABUNDANCE RATIOS FROM LOW-RESOLUTION SDSS/SEGUE STELLAR SPECTRA (2010, background): “Thickdisk stars have relatively higher abundance ratios ([α/Fe] ∼ +0.3 to +0.4; Bensby et al. 2003, 2005; Reddy et al. 2006) than do thin-disk stars ([α/Fe] ∼ 0.0 to +0.1).”
Accurate abundance patterns of solar twins and analogs - Does the anomalous solar chemical composition come from planet formation? (2009, result): “When compared to the abundance trends for Galactic thin-disk stars published elsewhere (e.g., Bensby et al. 2005; Reddy et al. 2006; Takeda 2007; Neves et al. 2009), we notice that the slopes and relativ scatter (between different elements) are compatible with our results (all but the two most…”
INSIDE OUT AND UPSIDE DOWN: TRACING THE ASSEMBLY OF A SIMULATED DISK GALAXY USING MONO-AGE STELLAR POPULATIONS (2013, background): “Several groups have measured a similar correlation at the solar annulus in the MW and in external galaxies (e.g., Bensby et al. 2005; Yoachim & Dalcanton 2008).”
Origin and structure of the Galactic disc(s) (2009, methodology): “Hence we consider the model’s ability to reproduce the data sets of Fuhrmann (1998), Bensby et al. (2003, 2005), Venn et al. (2004) Reddy et al. (2006), Haywood (2008), Juric et al. (2008) and Ivezic et al. (2008) is remarkable and suggests that it has a sound physical basis.”
Chemical evolution with radial mixing (2008, methodology): “Breaks in the Galaxy’s star formation history (Chiappinin et al. 1997) and accretion events (Bensby et al. 2005) have been hypothesized to account for the dichotomy between the thin and thick discs.”
THE MILKY WAY HAS NO DISTINCT THICK DISK (2011, background): “Studies of the age, kinematics, and elementalabundance ratios of probable members of the thicker disk component have revealed that it is older (e.g., Bensby et al. 2005), kinematically hotter (e.g., Chiba & Beers 2000), and metal-poor and enhanced in α elements (e.g., Fuhrmann 1998; Prochaska et…”
Through thick and thin: kinematic and chemical components in the solar neighbourhood (2010, methodology): “We have used the compilation of Venn et al. (2004), which includes abundance data for solar neighbourhood stars with good spatial motions, supplemented by data in the more recent papers of Reddy et al. (2006), Bensby et al. (2005) and Nissen & Schuster (2010).”
THE STELLAR POPULATION STRUCTURE OF THE GALACTIC DISK (2015, background): “…& Reid 1983; Jurić et al. 2008; Rix & Bovy 2013), with stars in the thicker of the two components being older, more metal-poor, and [α/Fe]enhanced with respect to stars in the thinner components (Fuhrmann 1998; Prochaska et al. 2000; Bensby et al. 2005; Reddy et al. 2006; Haywood et al. 2013).”
Using chemical tagging to redefine the interface of the Galactic disc and halo (2015, background): “Kinematically, thick disk stars co-rotate with the disk, albeit with a smaller rotational velocity and overall have hotter orbits than their thin disk counterparts (e.g. Edvardsson et al. 1993; Reddy et al. 2003; Bensby et al. 2005; Haywood et al. 2013; Kordopatis et al. 2013).”
Radial mixing and the transition between the thick and thin Galactic discs (2008, methodology): “8(a) we display [α/Fe] and [Fe/H] values from the samples of Reddy et al. (2003, 2006), Bensby et al. (2005) and Gilli et al. (2006).”
TRACING CHEMICAL EVOLUTION OVER THE EXTENT OF THE MILKY WAY'S DISK WITH APOGEE RED CLUMP STARS (2014, background): “G A ] 1 1 Se p 20 disk, because of the large velocity dispersion of its stars (Fuhrmann 1998; Prochaska et al. 2000; Bensby et al. 2005; Reddy et al. 2006; Ramı́rez et al. 2007; Lee et al. 2011).”
Numerical simulation of a possible origin of the positive radial metallicity gradient of the thick disk (2013, background): “A kinematical separation like that used by Bensby et al. (2005) has had some success as it is argued that thick disk stars can be identified by their lower rotational velocity, since near the Sun, the thick disk lags solar rotation.”