The Kinematics, Metallicities, and Orbits of Six Recently Discovered Galactic Star Clusters with Magellan/M2FS Spectroscopy

TL;DR

This study uses Magellan/M2FS spectroscopy and Gaia data to analyze six newly discovered Galactic star clusters, revealing their kinematic and chemical properties, and providing insights into their origins and orbital dynamics.

Contribution

It presents detailed spectroscopic and astrometric analysis of six new star clusters, including their metallicities, kinematics, and orbital characteristics, enhancing the understanding of Galactic structure.

Findings

Gran 3 is an old, metal-poor globular cluster in the bulge with a retrograde orbit.

Gran 4 is an old, metal-poor globular with a halo-like orbit, possibly linked to merger streams.

Gaia 9 and Gaia 10 are among the most distant and metal-poor open clusters known.

Abstract

We present Magellan/M2FS spectroscopy of four recently discovered Milky Way star clusters (Gran 3/Patchick~125, Gran 4, Garro 01, LP 866) and two newly discovered open clusters (Gaia 9, Gaia 10) at low Galactic latitudes. We measure line-of-sight velocities and stellar parameters ([Fe/H], $\log{g}$, $T_{\rm eff}$, [Mg/Fe]) from high resolution spectroscopy centered on the Mg triplet and identify 20-80 members per star cluster. We determine the kinematics and chemical properties of each cluster and measure the systemic proper motion and orbital properties by utilizing Gaia astrometry. We find Gran 3 to be an old, metal-poor (mean metallicity of [Fe/H]=-1.84) globular cluster located in the Galactic bulge on a retrograde orbit. Gran 4 is an old, metal-poor ([Fe/H]=-1.84) globular cluster with a halo-like orbit that happens to be passing through the Galactic plane. The orbital properties of Gran 4 are consistent with the proposed LMS-1/Wukong and/or Helmi streams merger events. Garro 01 is metal-rich ([Fe/H]=-0.30) and on a near circular orbit in the outer disk but its classification as an open cluster or globular cluster is ambiguous. . Gaia 9 and Gaia 10 are among the most distant known open clusters at $R_{GC}\sim 18, 21.2~kpc$ and most metal-poor with [Fe/H]~-0.50,-0.46 for Gaia 9 and Gaia 10, respectively. LP 866 is a nearby, metal-rich open cluster ([Fe/H]$=+0.1$). The discovery and confirmation of multiple star clusters in the Galactic plane shows the power of {\it Gaia} astrometry and the star cluster census remains incomplete.