Spectroscopy of six red giants in the Draco dwarf spheroidal galaxy

Graeme H. Smith, Michael H. Siegel, Matthew D. Shetrone, Rebeccah Winnick

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Keck Observatory LRIS-B (Low Resolution Imaging Spectrometer) spectra are reported for six red giant stars in the Draco dwarf spheroidal galaxy and several comparison giants in the globular cluster M13. Indexes that quantify the strengths of the Ca n H and K lines, the λ3883 and λ4215 CN bands, and the λ4300 G band have been measured. These data confirm evidence of metallicity inhomogeneity within Draco obtained by previous authors. The four brightest giants in the sample have absolute magnitudes in the range -2.6 < M v < -2.3. They have a range in B - V color, metallicities less than that of M13, and exhibit a dispersion in both calcium and CH indices. Our data indicate that a spread in [C/H] likely exists among the Draco tip giants and that some giants have higher [C/Fe] ratios than is typical of giants in the globular clusters M13 and M92. Several suggestions are made as to why some Draco stars may have higher [C/Fe] ratios than globular cluster red giants: deep mixing might be inhibited in these Draco stars, they may formerly have been mass-transfer binaries that acquired carbon from a more massive companion, or the Draco dwarf galaxy may have experienced relatively slow chemical evolution over a period of several billion years, allowing carbon-enhanced ejecta from intermediate-mass asymptotic giant branch stars to enrich the interstellar medium while star formation was still occurring.

Original languageEnglish (US)
Pages (from-to)1361-1372
Number of pages12
JournalPublications of the Astronomical Society of the Pacific
Issue number848
StatePublished - Oct 2006

All Science Journal Classification (ASJC) codes

  • Astronomy and Astrophysics
  • Space and Planetary Science


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