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HD 52961 - an extremely metal-deficient, CNO- and S-rich, pulsating star embedded in a dust cloud
Results of an LTE atmosphere analysis of the seventh-magnitude star HD52961 are presented. The iron abundance of HD 52961 is found to be aslow as -4.8; the abundances of carbon, nitrogen, oxygen, and alsosulphur are enhanced with respect to iron by several orders ofmagnitude. HD 52961 displays an infrared excess which is due tocircumstellar dust; the dust shell does not cause significantcircumstellar absorption. It is suggested that HD 52961 is a slightlycooler analog of the peculiar supergiant HR 4049. The first detection ofa metal line in the optical spectrum of the latter star is reported; theiron abundance derived from it is also -4.8. One possible explanation ofthe IR excess and the abundances in these stars is that they arepresently evolving away from the AGB. This possibility is discussedconsidering the short timescale of this phase and the lack of observedprogenitors with such extreme metallicities. It is suggested that thesulphur anomaly may have its origin in the violent core flashes thatvery-low-metallicity stars possibly undergo.
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