,
Chemistry of the Sagittarius Dwarf Galaxy: a Top-Light IMF, Outflows and the R-Process
(2013)cite arxiv:1309.2974Comment: 20 figures ApJ accepted. Two text files with full data for tables 2 and 4.
Аннотация
From chemical abundance analysis of stars in the Sagittarius dwarf spheroidal
galaxy (Sgr), we conclude that the alpha-element deficiencies cannot be due to
the Type Ia supernova (SNIa) time-delay scenario of Tinsley (1979). Instead,
the evidence points to low alpha/Fe ratios resulting from an initial mass
function (IMF) deficient in the highest mass stars. The critical evidence is
the 0.4 dex deficiency of O/Fe, Mg/Fe and other hydrostatic elements,
contrasting with the normal trend of r-process Eu/Fer with Fe/H. Supporting
evidence comes from the hydrostatic element (O, Mg, Na, Al, Cu) X/Fe ratios,
which are inconsistent with iron added to the Milky Way (MW) disk trends. Also,
the ratio of hydrostatic to explosive (Si, Ca, Ti) element abundances suggests
a relatively top-light IMF. Abundance similarities with the LMC, Fornax and IC
1613, suggest that their alpha-element deficiencies also resulted from IMFs
lacking the most massive SNII.
For such a top-light IMF, the normal trend of r-process Eu/Fer with Fe/H,
as seen in Sgr, indicates that massive Type II supernovae (>30Msun) cannot be
major sources of r-process elements.
High La/Y ratios, consistent with leaky-box chemical evolution, are
confirmed but ~0.3 dex larger than theoretical AGB predictions. This may be due
to the 13C pocket mass, or a difference between MW and Sgr AGB stars. Sgr has
the lowest Rb/Zr ratios known, consistent with low-mass (~2Msun) AGB stars
near Fe/H=-0.6, likely resulting from leaky-box chemical evolution.
The Cu/O trend in Sgr and the MW suggest that Cu yields increase with both
metallicity and stellar mass, as expected from Cu production by the weak
s-process in massive stars.
Finally, we present an updated hfs line list, an abundance analysis of
Arcturus, and further develop our error analysis formalism.
