The Pristine Inner Galaxy Survey (PIGS) III: carbon-enhanced metal-poor stars in the bulge. Issue 1 (12th May 2021)

• Record Type: Journal Article
• Authors: Arentsen, Anke; Starkenburg, Else; Aguado, David S; Martin, Nicolas F; Placco, Vinicius M; Carlberg, Raymond; González Hernández, Jonay I; Hill, Vanessa; Jablonka, Pascale; Kordopatis, Georges; Lardo, Carmela; Mashonkina, Lyudmila I; Navarro, Julio F; Venn, Kim A; Buder, Sven; Lewis, Geraint F; Wan, Zhen; Zucker, Daniel B
• Is Part Of: Monthly notices of the Royal Astronomical Society. Volume 505:Issue 1(2021)
• Page Start: 1239
• Page End: 1253
• Publication Date: 2021-05-12
• Subjects: techniques: spectroscopic -- stars: carbon -- stars: chemically peculiar -- stars: Population II -- Galaxy: bulge -- Galaxy: formation; Astronomy -- Periodicals; Periodicals; 520.5
• DOI: 10.1093/mnras/stab1343
• Languages: English
• ISSNs: 0035-8711

Abstract

ABSTRACT: The most metal-deficient stars hold important clues about the early buildup and chemical evolution of the Milky Way, and carbon-enhanced metal-poor (CEMP) stars are of special interest. However, little is known about CEMP stars in the Galactic bulge. In this paper, we use the large spectroscopic sample of metal-poor stars from the Pristine Inner Galaxy Survey (PIGS) to identify CEMP stars ($\rm {[C/Fe]} \geqslant +0.7$ ) in the bulge region and to derive a CEMP fraction. We identify 96 new CEMP stars in the inner Galaxy, of which 62 are very metal-poor ($\rm {[Fe/H]} \lt -2.0$ ); this is more than a 10-fold increase compared to the seven previously known bulge CEMP stars. The cumulative fraction of CEMP stars in PIGS is $42^{\, +14\, }_{\, -13} {{\ \rm per\ cent}}$ for stars with $\rm {[Fe/H]} \lt -3.0$, and decreases to $16^{\, +3\, }_{\, -3} {{\ \rm per\ cent}}$ for $\rm {[Fe/H]} \lt -2.5$ and $5.7^{\, +0.6\, }_{\, -0.5} {{\ \rm per\ cent}}$ for $\rm {[Fe/H]} \lt -2.0$ . The PIGS inner Galaxy CEMP fraction for $\rm {[Fe/H]} \lt -3.0$ is consistent with the halo fraction found in the literature, but at higher metallicities, the PIGS fraction is substantially lower. While this can partly be attributed to a photometric selection bias, such bias is unlikely to fully explain the low CEMP fraction at higher metallicities. Considering the typical carbon excesses and metallicity ranges for halo CEMP-s and CEMP-no stars, our results point to a possible deficiency of both CEMP-s and CEMP-no stars (especially the more metal-rich) in the inner Galaxy. The former is potentially related to a difference in the binary fraction, whereas the latter may be the result of a fast chemical enrichment in the early building blocks of the inner Galaxy.