In his youth, Shih-Yun Tang was more often watching Star Trek than stargazing.
“Unlike traditional astronomers who like to look in the night sky, it’s more about data analysis for me,” said Tang, a graduate student in Christopher Johns-Krull’s research group in Physics and Astronomy. “I’m drawn to programming, to how you individualize and analyze all the fascinating data.”
And with a wealth of new instruments producing massive observational datasets about distant stars and planets, Tang’s timing is opportune.
As a master’s student, he made a surprising discovery about a well-known star cluster while analyzing data from the European Space Agency’s Gaia mission. “I found that instead of being a sphere, the star cluster has tails,” comma-shaped appendages that are created by the pull of gravity from the center of the galaxy. Tang was hooked by the discovery of new knowledge, and became a Rice Ph.D. student thanks to a longstanding collaboration between his co-mentors, Johns-Krull and Lowell Observatory’s Lisa Prato.
Tang studies T Tauri stars, newborns that will evolve to be similar in mass and size to the sun. Learning how planets form around such stars is one of the best ways to gain insights into Earth’s origins.
“We have some ideas on how our solar system formed, but we want to actually find planets forming at different stages and study them,” Tang said.
The Milky Way is believed to contain millions of T Tauri stars, and Gaia and infrared survey missions like Spitzer and WISE have revealed thousands of them. But finding planets around them is a challenge. They are often shrouded by the dust and gas from the protoplanetary disks that birthed them. The dust blocks light, complicating the search for the subtle spectral patterns that can reveal orbiting planets.
For example, orbiting planets tug on their stars gravitationally, creating a slight wobble. “That can cause the spectrum of light coming from the star to be alternately blue-shifted and then red-shifted,” Tang said. “If you measure the shift in the time series, you will see it go back and forth,” he said, describing the radial velocity (RV) method of planet-finding.
T Tauri stars also frequently have sunspots and strong magnetic fields. These can also obscure planet detection via the RV method, and Tang’s research has revealed that “the spot signal is way larger than the planet signal,” he said. “Basically, that means the old methodology won’t work, because we’re looking for a tiny signal and there is too much noise.”
Tang is now creating a computational model that will simulate the effects of sunspots and provide output that can be compared with observational data.
“The model can simulate the effect of the star spots,” he said. “If you give it the size of the spots and number of spots, it will generate things like the radial velocity, light curve, brightness and temperature indicator.”
Tang has learned to be patient.
“90% of the time, when you find something interesting, you find it was because of a mistake,” he said. “It’s a constant back and forth. You find new things, go to the professor, only to find there was a mistake in your analysis. Out of 100 times, there might be one where you say, ‘Okay, this is something interesting.’”