Kate Hartman '18 Researches How Stars Measure Up

Katherine Hartman stands next to her poster. Photo by Carnegie Institution for Science.

Gazing at the stars? Try measuring the stars. That’s what Katherine Hartman ’18 did this summer as part of her 10-week research internship through the Carnegie Institution for Science. Her findings add to the growing research that helps astronomers determine the distance between stars and our galaxy. 

Looking at data on “Cepheid variables,” a type of star that periodically pulses in and out and varies in brightness over the course of a few days or weeks, Hartman studied the temperature, surface gravity and atmospheric properties of these stars.

Hartman’s key observations, presented to a crowd of astronomers on Tuesday at the American Astronomical Society Meeting (AAS), help scientists understand how the composition of Cepheids affect the Leavitt Law.

What is the Leavitt Law? About a hundred years ago, an astronomer by the name of Henrietta Leavitt discovered a relationship between the brightness of a Cepheid variable and the time it took to go through a full cycle of change – but her work was largely ignored until after death.

Leavitt’s discovery was only recently named the Leavitt Law by the AAS, in part to rectify the lack of recognition she received during her lifetime.

“My research was essentially a proof of concept project—I tested a potential analysis method to see whether it would give me accurate measurements across a Cepheid's light cycle—and since we got the results we wanted, we'll now be able to do some interesting science,” explains Hartman, who worked under the guidance of Rachael Beaton at the Carnegie Observatories. Beaton is now a Hubble and Carnegie-Princeton fellow at Princeton University.

In order to dig into this, Hartman and Beaton used data from the Sloan Digital Sky Survey’s Apache Point Galactic Evolution Experiment (APOGEE), which systematically maps the chemical compositions and motions of stars.

“Because we can make the measurements we want at any point in a Cepheid's light cycle, we'll be able to use the APOGEE survey's giant dataset of Cepheids to fine-tune the Leavitt Law,” says Hartman, who hopes that work will happen in the near future.

This research influenced Hartman to continue this type of inquiry.

“I’ve been looking at grad schools that have programs with the same kind of research that I did this summer,” she says about what’s next for her.

Hartman is thankful for the experience of working with Beaton on this significant research, an opportunity she was encouraged to apply for thanks to her academic advisor Professor of Physics Phil Choi.

She also credits the research on gamma ray bursts she did the previous two summers under the Pomona College Summer Undergraduate Research Program (SURP).

Hartman’s advice to other students looking at physics and astronomy is to start searching for research opportunities early, either on campus or off, to dive into their work.