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18 very metal-poor stars detected in the Sagittarius dwarf galaxy

One of the stars from the sample has extremely low metallicity, slightly below -3.0.

Satellite dwarf spheroidal (dSph) galaxies of our Milky Way are excellent places to search and study metal-poor stars. Detailed investigation of such objects could be crucial for improving our understanding of early galactic environments.

The Sagittarius Dwarf Spheroidal Galaxy (Sgr dSph for short) is the most massive among dSph of the Milky Way. So far, only a handful of very metal-poor stars have been identified in Sgr dSph, mainly due to a prominent metal-rich component of the galaxy’s stellar population.

A team of astronomers at MIT reported 18 metal-poor red giant stars in the Sagittarius dwarf galaxy. 

They found that one of the stars from the sample has extremely low metallicity, slightly below -3.0.

The detection is based on the medium-resolution spectra from the MagE spectrograph on the Magellan-Baade Telescope, metallicity-sensitive photometry from the SkyMapper DR1.1 catalog, and proper motion data from Gaia DR2.

The stars in the sample have significant temperatures ranging from 4,380 to 5,170 K and are not carbon-enhanced. Hence, none of these objects can be classified as carbon-enhanced metal-poor (CEMP) stars.

Astronomers noted, “Here, we present metallicities and carbon abundances for 18 stars with metallicities between −3.08 ≤ [Fe/H] ≤−1.47 in the Sagittarius dwarf spheroidal galaxy, using medium-resolution spectra from the MagE spectrograph on the Magellan-Baade Telescope.”

Nine stars from the sample are very metal-poor, with metallicities below -2.0. This finding more than doubles the number of known very metal-poor stars in Sgr dSph. The object with the lowest metallicity (-3.08) out of the 18 described in the paper turned out to be Sgr-180. This makes Sgr-180 one of the first known extremely metal-poor stars in this galaxy.

Journal Reference:
  1. Anirudh Chiti et al. Discovery of 18 stars with -3.10 < [Fe/H] < -1.45 in the Sagittarius dwarf galaxy. arXiv:2008.09901

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