Simon Campbell
Monash University, Australia
Carbon-deficient red giants (CDGs) are a peculiar class of stars that have eluded explanation for decades. We use asteroseismology combined with spectroscopy and astrometry to better characterise the CDGs. We discover 15 new CDGs in the Kepler field. Remarkably, we find that our CDGs are almost exclusively in the red clump (RC) phase. Asteroseismic masses reveal that our CDGs are primarily low-mass stars (M ≤ 2 M⊙), in contrast to previous studies, which suggested they are of intermediate mass based on HR diagrams. Surprisingly, a very high fraction of our CDGs (50%) are also Li-rich giants. We find a bimodal distribution of luminosity in the CDGs, with one group having normal RC luminosity and the other being a factor of 2 more
luminous than expected for their masses. Demarcations in chemical patterns and luminosities lead us to split the CDGs into three groups. We discuss various formation scenarios in light of our new dataset and conclude that a merger of a helium white dwarf with a red giant branch star is the most likely scenario for the two groups of overluminous stars. Due to the overlap with
the CDGs, Li-rich giants may have similar formation channels.
Негізгі бет ACES The carbon-deficient red giants: Discovery of a stellar merger population - Simon Campbell
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