Mapping the Milky Way’s Neighbors

Hi! I’m Kaleo Toguchi-Tani (she/her), a rising senior Physics-Astronomy major with an intended Data Science minor from Kailua, Hawaiʻi. This summer I’m interning at the University of Hawaiʻi at Mānoa’s (UH) Institute for Astronomy (IfA) in Honolulu, Hawaiʻi. The IfA is the research center for astronomy within UH, dedicated to research and education while respecting the local Hawaiian culture.

At the IfA, I am a part of the Stars & Planets group, where I use an observational technique called asteroseismology–the study of oscillations to probe stellar interiors–to determine distances to far away dwarf galaxies using variable stars. While most stars appear to be constantly bright pinpoints of light, most change their brightness by expanding and contracting their surface layers. With asteroseismology, we can infer mass, radius, age, and distance from a star. Applying this technique to numerous stars allows us to create dynamic maps of our galaxy, in a process known as Galactic Cartography. Accurate 3D maps of our Milky Way will enable us to probe the interactions between our galaxy and smaller satellite galaxies that have undergone assimilation with our own. 

My project focuses on how this Galactic cannibalism affects the core of the smaller satellite galaxies, specifically the nearest dwarf galaxy to us–the Sagittarius (Sgr) Dwarf Spheroidal Galaxy (dSph). The interaction between the MW’s galactic bulge and the Sgr dSph core created two tidal streams of stellar material that wrap itself around our MW.  Thus kicking off new star formation within our galaxy. Understanding the core of the Sgr dSph will open the door to understanding other dwarf galaxies and their respective tidal streams. 

A typical work week for me has a bit of an unorthodox schedule. As most of the work I do only requires me to have access to my laptop, my workday can start as late as noon, going until 8 PM. I tend to jump back and forth between working on data analysis with data from the Gaia telescope, responding to emails from collaborators at other institutions, and writing literature reviews. I have weekly in-person meetings–one on Wednesday with my advisor, the Variable Star Postdoctoral Fellow Dr. Daniel Hey, and then group meetings on Thursday with the rest of the Stars & Planets group at the IfA. 

The biggest challenge within this project was confirming star membership. For example, when looking at a constellation such as Orion, the stars appear to lie within the same plane of the sky. However, if you were to fly out to Betelgeuse (the second brightest star in Orion), you’d notice that Orion’s left shoulder star is missing! This illustrates why interpreting data from telescopes (2D) and trying to infer 3D can be difficult. There’s only so much astronomers can do to remove background and foreground stars to obtain a clean sample of stars belonging exclusively to a different galaxy. The Sgr dSph proved extra difficult due to its proximity to the galactic center, which is packed with newly forming stars. Thankfully, we can use the principle that stars formed in the same gas cloud should have the same relative motion, known as ‘proper motion.’ This was the basis of my preliminary clean sample of stars belonging to the Sgr dSph core.

This internship has been instrumental in helping me work toward my long-term goal of becoming an astrophysics professor and research scientist. Additionally, this research will be used for my senior thesis in the fall. My time at the IfA has provided me with invaluable experience in learning the building blocks for astronomical research and understanding how collaborative efforts in the scientific community. I am immensely grateful for the Whitman Internship Grant, which has made this opportunity possible!