Identification of a Group III CEMP-no Star in the Dwarf Spheroidal Galaxy Canes Venatici I

Abstract

CEMP-no stars, a subclass of carbon-enhanced metal-poor (CEMP) stars, are one of the most significant stellar populations in Galactic Archaeology, because they dominate the low end of the metallicity distribution function, providing information on the early star-formation and chemical-evolution history of the Milky Way and its satellite galaxies. Here we present an analysis of medium-resolution (R ∼ 1, 800) optical spectroscopy for a CEMP giant, SDSS J132755.56+333521.7, observed with the Large Binocular Telescope (LBT), one of the brightest (g ∼ 20.5) members of the classical dwarf spheroidal galaxy, Canes Venatici I (CVn I). Many CEMP stars discovered to date have very cool effective temperatures (T eff < 4500 K), resulting in strong veiling by molecular carbon bands over their optical spectra at low/medium spectral resolution. We introduce a technique to mitigate the carbon-veiling problem to obtain reliable stellar parameters, and validate this method with the LBT medium-resolution optical spectra of the ultra metal-poor ([Fe/H] = −4.0) CEMP-no dwarf, G 77-61, and seven additional very cool CEMP stars, which have published high-resolution spectroscopic parameters. We apply this technique to the LBT spectrum of SDSS J132755.56+333521.7. We find that this star is well-described with parameters T eff = 4530 K, log g = 0.7, [Fe/H] = −3.38, and absolute carbon abundance A(C) = 7.23, indicating that it is likely the first Group III CEMP-no star identified in CVn I. The Group III identification of this star suggests that it is a member of the extremely metal-poor population in CVn I, which may have been accreted into its halo.

Forecasting Chemical Abundance Precision for Extragalactic Stellar Archaeology

“…MODS, like LRIS, operates at low resolution (R ∼ 2000) across the optical spectrum with a red and a blue arm, and modest multiplexing (Tables 2 and 3). Other than a recent study on a chemically peculiar ultra metalpoor star in the dwarf galaxy Canes Venatici I (Yoon et al 2019), MODS has not been utilized for stellar chemical abundance measurements.…”

Birds of a Feather? Magellan/IMACS Spectroscopy of the Ultra-Faint Satellites Grus II, Tucana IV, and Tucana V

“…The exceptions are one star each in Gru II (DES J220400.12−462529.0) and Tuc IV (DES J000311.46−604451.5), which resemble members in every way except that their color places them ∼ 0.1 mag redder than the RGB at their magnitude. Conceivably these stars could be members that are carbonenhanced, similar to one star in Hydrus I identified by Koposov et al (2018) and another star in Canes Venatici I studied by Zucker et al (2006) and Yoon et al (2019). Additional spectroscopy at shorter wavelengths where carbon features are prominent would be needed to test this possibility.…”