Two Portions of Sagittarius Stream in the LAMOST Complete Spectroscopic Survey of Pointing Area at Southern Galactic Cap

TL;DR

This study identifies and characterizes portions of the Sagittarius stream in the Southern Galactic Cap using spectroscopic and astrometric data, revealing their chemical properties and spatial distributions.

Contribution

It presents a new sample of Sagittarius stream candidates identified via clustering in combined spectroscopic and astrometric data, with detailed chemical and spatial analysis.

Findings

220 stream candidates identified with DBSCAN

106 likely members of the Sagittarius stream

No significant metallicity gradients along the stream

Abstract

We constructed a sample of 13,798 stars with $T\rm_{eff}$, log $g$, [Fe/H], radial velocity, proper motions and parallaxes from LAMOST DR5 and Gaia DR2 in the LAMOST Complete Spectroscopic Survey of Pointing Area (LaCoSSPAr) at the Southern Galactic Cap consisting of areas A and B. Using the distributions in both proper motions and radial velocity, we detected very significant overdensities in these two areas. These substructures most likely are portions of Sagittarius (Sgr) stream. With the Density-Based Spatial Clustering of Applications with Noise (DBSCAN) algorithm, 220 candidates stream members were identified. Based upon distance to the Sun and published models, 106 of these stars are likely to be the members of the Sgr stream. The abundance pattern of these members using [$\alpha$/Fe] from Xiang et al. were found to be similar to Galactic field stars with [Fe/H] $<$ -1.5 and deficient to Milky Way populations at similar metallicities with [Fe/H] $>$ -1.0. No vertical and only small radial gradients in metallicity along the orbit of Sgr stream were found in our Sgr stream candidates.