Julio Chanamé, Jason Curtis, Simon Schuler, Marcel Agüeros, Kevin Covey, Marina Kounkel

jeffrey.andrews@northwestern.edu

Theia 456: A New Milky Way Stellar Stream

Jeff J. Andrews Northwestern University

AAS 237, 407. Star Clusters: Galactic & Extragalactic

Our Evolving Picture of the Milky Way

Credit: Gaia

Our Evolving Picture of the Milky WayPleiades Open Cluster

Omega Cen Globular Cluster

Credit: Gaia

Credit: Gaia

Our Evolving Picture of the Milky WayPleiades Open Cluster

Omega Cen Globular Cluster

Belokurov et al. (2006), Bonaca et al. (2012), and many, many others

Gaia

Structure and Dynamics

“Theia” objects identified by Kounkel & Covey (2019, 2020)

Gaia

• Spans 25 degrees across the sky • Nearly 200 pc long • Distance of 500 pc

Structure and Dynamics

“Theia” objects identified by Kounkel & Covey (2019, 2020)

MoonPleiades

Gaia

• Spans 25 degrees across the sky • Nearly 200 pc long • Distance of 500 pc • Part of the Local Arm

Structure and Dynamics

Gaia

• Spans 25 degrees across the sky • Nearly 200 pc long • Distance of 500 pc • Part of the Local Arm • Orbits within the disk

Structure and Dynamics

Gaia

• Spans 25 degrees across the sky • Nearly 200 pc long • Distance of 500 pc • Part of the Local Arm • Orbits within the disk • The stars appear to have

a common origin

Structure and Dynamics

Gaia

• Spans 25 degrees across the sky • Nearly 200 pc long • Distance of 500 pc • Part of the Local Arm • Orbits within the disk • The stars appear to have

a common origin

Structure and Dynamics

But were they born together?

LAMOST

Metallicity

MoonPleiades

LAMOST

Theia stars have similar iron abundances:

[Fe/H] = -0.08

Metallicity

MoonPleiades

TESS

ZTF

Gyrochronology

Gyrochronology is a way to date stars based on their rotation

Gyrochronology

TESS

ZTF

Gyrochronology

TESS

ZTF

Gyrochronology

TESS

ZTF

Gyrochronology

TESS

ZTF

Gyrochronology

Theia 456 has an age similar to the Pleiades, ~100 Myr

TESS

ZTF

LAMOST

Gaia

NASA

NSF

Chinese Academy Of Sciences

European Space Agency

Science is Collaborative!

TESS

ZTF

Conclusions

•New stellar structure in the Milky Way disk • Spans 200 pc • 25 degrees across the sky

•Most Likely has a common origin • Consistent age • Consistent Metallicity

•Theia 456 is just the beginning • Just one “Theia” object from Kounkel & Covey (2019, 2020)