Gemini/GRACES spectroscopy of stars in Tri II
Résumé
The chemical abundance ratios and radial velocities for two stars in the recently discovered Triangulum II faint dwarf galaxy have been determined from high-resolution, medium signalto-noise ratio spectra from the Gemini Remote Access to CFHT ESPaDonS Spectrograph facility. These stars have stellar parameters and metallicities similar to those derived from their photometry and medium-resolution Ca II triplet spectra, and supports that Triangulum II has a metallicity spread consistent with chemical evolution in a dwarf galaxy. The elemental abundances show that both stars have typical calcium abundances and barium upper limits for their metallicities, but low magnesium and sodium. This chemical composition resembles some stars in dwarf galaxies, attributed to inhomogeneous mixing in a low star formation environment, and/or yields from only a few supernova events. One of our targets (Star40) has an enhancement in potassium, and resembles some stars in the unusual outer halo star cluster, NGC 2419. Our other target (Star46) appears to be a binary based on a change in its radial velocity (v rad = 24.5 ±2.1 km s −1). This is consistent with variations found in binary stars in other dwarf galaxies. While this serves as a reminder of the high binary fraction in these ultrafaint dwarf galaxies, this particular object has had little impact on the previous determination of the velocity dispersion in Triangulum II.
Domaines
Planète et Univers [physics]
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