# Detecting the Sagittarius stream with LAMOST DR4 M giants \& Gaia DR2

## TL;DR

This study identifies Sagittarius stream stars using LAMOST DR4 M giants and Gaia DR2 data, revealing structural details and suggesting multiple stellar populations within the stream.

## Contribution

It introduces a new method combining spectral indices and Gaia data to select a pure sample of Sgr stream stars and characterizes their energy and extent.

## Key findings

- The trailing arm has higher energy than the leading arm at the same angular momentum.
- The trailing arm extends to about 130 kpc from the Sun.
- Evidence suggests the Sgr stream contains multiple stellar populations.

## Abstract

We use LAMOST DR4 M giants combined with Gaia DR2 proper motions and ALLWISE photometry to obtain an extremely pure sample of Sagittarius (Sgr) stream stars. Using TiO5 and CaH spectral indices as an indicator, we selected out a large sample of M giant stars from M dwarf stars in LAMOST DR4 spectra. Considering the position, distance, proper motion and the angular momentum distribution, we obtained 164 pure Sgr stream stars. We find that the trailing arm has higher energy than the leading arm in same angular momentum. The trailing arm we detected extends to a heliocentric distance of $\sim 130$ kpc at $\tilde\Lambda_{\odot}\sim 170^{\circ}$, which is consistent with the feature found in RR Lyrae in \citet{sgr2017}. Both of these detections of Sgr, in M giants and in RR Lyrae, imply that the Sgr stream may contain multiple stellar populations with a broad metallicity range.