Monday, July 1, 2013

1306.6750 (R. Caimmi)

Fractional yields inferred from halo and thick disk stars    [PDF]

R. Caimmi
Linear [Q/H]-[O/H] relations, Q = Na, Mg, Si, Ca, Ti, Cr, Fe, Ni, are inferred from a sample (N=67) of recently studied FGK-type dwarf stars in the solar neighbourhood including different populations (Nissen and Schuster 2010; Ramirez et al. 2012), namely LH (N=24, low-alpha halo), HH (N=25, high-alpha halo), KD (N=16, thick disk), OL (N=2, globular cluster outliers). Regression line slope and intercept estimators and related variance estimators are determined. With regard to the straight line, [Q/H] = aQ [O/H] + bQ, sample stars display along a "main sequence", [Q,O] = [aQ, bQ, Delta bQ], leaving aside the two OL stars which, in most cases (e.g., Na), lie outside. A unit slope, aQ = 1, implies Q is a primary element synthesised via SNII progenitors in presence of universal stellar initial mass function (defined as simple primary element). To this respect, Mg, Si, Ti, show aQ = 1 within 2 sigma(aQ); Cr, Fe, Ni, within 3 sigma(aQ); Na, Ca, exceeding 3 sigma(aQ). The fractional yields are determined within the framework of simple MCBR (multistage closed box + reservoir) chemical evolution models. The generalized fractional yields are determined regardless from the chemical evolution model. A regression line slope larger than unity for the element, Q, implies the related abundance, ZQ, is growing faster with respect to its counterpart related to oxygen, ZO, as expected for secondary elements and primary elements synthesised also via SNIa progenitors (with a possible contribution from different sources such as AGB stars) or in absence of universal initial stellar mass function (defined as non-simple primary elements), which is the case for Q = Na, Cr, Fe, Ni.
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