2 research outputs found
Formation of Galactic Systems in Light of the Magnesium Abundance in Field Stars.III.the Halo
We analyze the relations between the relative magnesium abundances,
metallicities, and Galactic orbital elements for halo stars. We show that the
relative magnesium abundances in protodisk halo stars are virtually independent
of metallicity and lie within a fairly narrow range while presumably accreted
stars demonstrate a large spread in relative magnesium abundances up to
negative [Mg/Fe]. The mean metallicity of magnesium-poor ([Mg/Fe]<0.2 dex)
accreted stars has been found to be displaced toward the negative values when
passing from stars with low azimuthal velocities to those with high ones at
\Delta[Fe/H]=0.5dex. The mean apogalactic radii and inclinations of the orbits
also increase while their eccentricities decrease. As a result negative radial
and vertical gradients in relative magnesium abundances are observed in the
accreted halo in the absence of correlations between the [Mg/Fe] ratios and
other orbital elements, while these correlations are found at a high
significance level for genetically related Galactic stars. We surmise that as
the masses of dwarf galaxies decrease, the maximum SNII masses and hence, the
yield of \alpha-elements in them also decrease. In this case, the relation
between the [Mg/Fe] ratios and the inclinations and sizes of the orbits of
accreted stars is in complete agreement with numerical simulations of dynamical
processes during the interaction of galaxies. Thus the behavior of the
magnesium abundance in accreted stars suggests that the satellite galaxies are
disrupted and lose their stars en masse only after dynamical friction reduces
significantly the sizes of their orbits and drags them into the Galactic plane.
Less massive satellite galaxies are disrupted even before their orbits change
appreciably under tidal forces.Comment: accepted 2006, Astronomy Letters, Vol. 32 No. 8, P.545, 18 pages, 6
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