First Chemical Analysis of Stars in The Triangulum-Andromeda Star Cloud

TL;DR

This study presents the first high-resolution spectroscopic analysis of stars in the Triangulum-Andromeda star cloud, revealing its likely origin as a dwarf galaxy and distinguishing it from the Monoceros Stream.

Contribution

It provides the first chemical abundance measurements of TriAnd stars, supporting its origin in a dwarf galaxy and clarifying its independence from the Monoceros Stream.

Findings

TriAnd stars show chemical patterns similar to dwarf galaxies.

TriAnd is chemically distinct from the Monoceros Stream.

Supports TriAnd as a dwarf galaxy remnant.

Abstract

We undertake the first high resolution spectroscopic study of the Triangulum-Andromeda (TriAnd) star cloud --- an extended, mid-latitude Milky Way halo substructure about 20 kpc away in the second Galactic quadrant --- through six M giant star candidates selected to be both spatially and dynamically associated with this system. The abundance patterns of [Ti/Fe], [Y/Fe] and [La/Fe] as a function of [Fe/H] for these stars support TriAnd as having an origin in a dwarf galaxy with a chemical enrichment history somewhat similar to that of the Sagittarius dwarf spheroidal (dSph) galaxy. We also investigate the previously proposed hypothesis that TriAnd is an outlying, dynamically older piece of the Monoceros Stream (also known as the Galactic Anticenter Stellar Structure, "GASS") under the assumption that both features come from the tidal disruption of the same accreted Milky Way satellite and find that net differences in the above abundance patterns between the TriAnd and GASS stars studied suggest that these two systems are independent and unrelated.