Metallicity and motion of GD-1 and Kshir tidal streams

¹ Shandong Provincial Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, School of Space Science and Technology, Shandong University at Weihai, Weihai 264209, China
² CAS Key Laboratory of Optical Astronomy, National Astronomical Observatories, Chinese Academy of Sciences, Beijing 100101, China
³ School of Astronomy and Space Science, University of Chinese Academy of Sciences, Beijing 100049, China

^★ Corresponding author: zjk@nao.cas.cn

Received: 2 July 2024
Accepted: 16 June 2025

Abstract

Aims. To explore the metallicity and kinematic properties of stellar streams, we selected the members of the GD-1 and Kshir streams, and conducted a detailed analysis of their member stars.

Methods. By utilizing the spectral data from LAMOST DR10 and SDSS DR16, and integrating them with astrometric data from Gaia DR3, we identified member stars of the stellar streams through an analysis of their geometric space, velocity space, and metallicity properties. Based on these identified member stars, we summarize the metallicity and kinematic properties of the stellar streams.

Results. We identified 152 members in the GD-1 stream and 68 members in the Kshir stream. The average metallicity of the GD-1 stream is [Fe/H]=−2.19 ± 0.10 dex. We confirmed the known gaps at ϕ₁=−20° and ϕ₁=−40° and identified a possible new gap at ϕ₁=−60°. For the first time, we report that the gaps form because of a large velocity difference on both sides and a reversal of velocities at both ends of the stream. These velocity characteristics may be due to the gaps being near a “turnaround” point in the stream orbit, or the stellar stream being significantly impacted by the massive Sagittarius 3 Gyr ago. The average metallicity of the Kshir stream is [Fe/H]=−1.65 ± 0.13 dex. The radial velocity and proper motion distributions along the Kshir stream are consistent with those of the GD-1 stream. They likely represent orbital wraps of the same structure.