Astronomers explore the properties of a particular stellar stream

Using ESA’s Gaia satellite and the MMT Observatory, astronomers have investigated a special stream of stars in our galaxy called Theia 456. The results of the study, published on May 21 on the server ahead of print arXivprovides important insights into the properties and origins of this stellar stream.

Discovered in 2019, Theia 456 (also known as COIN-Gaia-13) is a stellar stream in the thin disk of the Milky Way, consisting of about 320 loosely bound stars. The stream extends about 400 light years in longitude and 20 degrees across the sky in the Northern Hemisphere.

Previous observations of Theia 456 have revealed it to be a kinematically, chemically and gyrochronically coherent stellar stream. However, many properties of Theia 456 still remain uncertain and its dynamical history is not well understood.

That’s why a team of astronomers led by Kyle Tregoning of the University of Florida decided to conduct follow-up observations of Theia 456 using Gaia’s multi-object spectrograph and the MMT Hectochelle.

“In this work, we combine Gaia astrometric quantities with radial velocities derived from MMT-Hectochelle to present a detailed dynamical history of Theia 456, a stellar stream located in the thin disk of the Milky Way,” the researchers write.

Tregoning’s team managed to produce a catalog of 321 stars in Theia 456-43 with full space information in the 6D phase and the other 278 with 5D Gaia astrometry. They found that, overall, the stream consists of about 2,100 stars contributing to a total mass of about 900 solar masses.

The observations revealed that Theia 456 formed as a low-density open cluster, and its kinematic age is estimated to be 245 million years. Initially, the cluster had a half-light radius of about 29 light-years and a velocity distribution of 0.14 km/s.

The images obtained show that Theia 456 has two distinct lobes, which may be indicative of a substructure in the east. However, astronomers noted that other processes, such as the interaction with a passing giant molecular cloud and the spiral arms of the Milky Way, may be responsible for this.

Based on the collected data, the authors of the paper predict that Theia 456 will become more dispersed in the future, so that it will eventually be undetectable as a stellar structure of common origin. They hypothesize that the flow will likely become undetectable to our current cluster-finding methods in less than 100 million years.

“Within another ~100 Myr, the extent of Theia 456 should roughly double in right ascension, making this structure impossible to identify by the current generation of clustering algorithms,” the scientists concluded.

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