The Pristine Inner Galaxy Survey (PIGS) III: Carbon-enhanced metal-poor stars in the bulge

Anke Arentsen*, Else Starkenburg, David S. Aguado, Nicolas F. Martin, Vinicius M. Placco, Raymond Carlberg, Jonay I. González Hernández, Vanessa Hill, Pascale Jablonka, Georges Kordopatis, Carmela Lardo, Lyudmila I. Mashonkina, Julio F. Navarro, Kim A. Venn, Sven Buder, Geraint F. Lewis, Zhen Wan, Daniel B. Zucker

*Corresponding author for this work

Research output: Contribution to journalArticleAcademicpeer-review

7 Citations (Scopus)
20 Downloads (Pure)


The most metal-deficient stars hold important clues about the early build-up 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 ([C/Fe] > +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 ([Fe/H] < -2.0); this is more than a ten-fold increase compared to the seven previously known bulge CEMP stars. The cumulative fraction of CEMP stars in PIGS is $42^{\,+14\,}_{\,-13} \%$ for stars with [Fe/H] < -3.0, and decreases to $16^{\,+3\,}_{\,-3} \%$ for [Fe/H] < -2.5 and $5.7^{\,+0.6\,}_{\,-0.5} \%$ for [Fe/H] < -2.0. The PIGS inner Galaxy CEMP fraction for [Fe/H] < -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.
Original languageEnglish
Pages (from-to)1239–1253
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Early online date12-May-2021
Publication statusPublished - Jul-2021


  • Astrophysics - Astrophysics of Galaxies
  • Astrophysics - Solar and Stellar Astrophysics

Cite this