Seeing Double: WWU Undergrad Identifies Orbiting Pairs of Stars
Editor’s note: The following article was written as an assignment in Regina Barber DeGraaff and Melissa Rice’s PHYS 497: Science Communication course by senior Physics major Holly Christenson.
Western Washington University student Martin Fernandez, a graduating senior in the Department of Physics and Astronomy, uses telescopes to see what the human eye cannot: pairs of stars that orbit each other too closely to be distinguished visually.
Fernandez has spent the last several years working on this project with Kevin Covey, an assistant professor of Physics and Astronomy. He started the project in summer 2015, after taking a class entitled “Stars and Galaxies” with Covey.
“I got an email from Dr. Covey a few weeks into spring quarter, after taking Stars and Galaxies, asking if I was interested in doing astronomy research over the summer,” said Fernandez. “At the time, I didn’t even know that research as an undergraduate was a possibility.”
Fernandez’s project is centered on finding and studying stellar duos, which are referred to as binary systems. Some binary pairs can be identified visually. For example, two stars named Mizar and Alcor make up the central “star” in the handle of the Big Dipper - on a clear night, you may be able to convince yourself that there are two stars there. The famous Alpha Centauri system, our nearest stellar neighbors, are also part of a binary system.
Not all binary pairs can be identified by eye, and those that can’t be visually resolved are called spectroscopic binaries. Spectroscopic binaries are interesting to astronomers because they are often part of a larger cluster of stars that all formed at the same time from the same cloud of gas. “Spectroscopic binaries allow us to determine the physical properties of binaries across a range of separations that would be inaccessible from visual binaries,” said Fernandez. “To properly model and understand the evolution of stars and clusters of stars, we need to know about the different configurations stars evolve into.”
Studying the physical properties of stars that are the same age is one way for astronomers to study the life cycle of stars like our own sun.
Because these binary systems cannot be identified visually, astronomers must use other methods to find them. An important property of light is how much energy it has -- for example, radiation from an x-ray machine has more energy than your microwave. In terms of light we can see, blue light has more energy than red light. Fernandez measures the amount of light received by a telescope at different energies, making use of data obtained by the Apache Point Observatory Galactic Evolution Experiment, a large astronomy survey based in New Mexico. When a star is moving towards or away from us, the energy of its light as we receive it is shifted slightly higher or lower than it would be if the star were stationary, respectively. If Fernandez can measure two different shifted energies, as shown in the figure below, that indicates that there are actually two stars in the system.
“Because astronomers have learned a great deal about the chemical makeup of stars, we can build a suite of stellar models," said Fernandez. "Comparing these models to the light we observe allows us to determine how stars are moving. If we see that a star is moving in a periodic way, as if it is orbiting around something, we know there is a second star.”
The energy shift of those stars indicates how quickly they are moving towards or away from us, which makes it possible to begin understanding how the stars are moving around each other. If a binary pair was observed more than once, it is possible to estimate which star is more massive than the other and if it was observed many times, it is possible to estimate orbital parameters for the system, including how circular and how long the stars take to orbit.
Fernandez studied 104 binary pairs in total, and identified 86 of those for the first time during the course of his research. These pairs of stars are part of a larger region where stars are being formed in the Perseus Molecular Cloud. Although Fernandez is graduating, Covey and his research team are continuing to work on refining their methods for identifying binary pairs and measuring their physical properties, especially by improving automatic selection methods and criteria that can be applied by a computer. Improving the methods will make the process of identifying binary pairs faster and more accurate than is currently possible. This work will be continued by Western undergraduates Jessica Reyna, Emmanuel Harley, and Jacob Skinner.
Many of Western’s undergraduates in Physics and Astronomy conduct research in various areas, but astronomy is of particular interest to Fernandez in particular.
“I was struck by the amount of data there was in astronomy research, and the many techniques astronomers employ to get as much information out of that data as possible,” he said.
Because data analysis is such an important part of astronomy, the research itself, he says, is primarily computer-based. “Most of the time I spend on the science part of the project is coding in a programming language called IDL. There is also some pen and paper physics calculations, but other than coding, most of my research time in the last year has been spent preparing a manuscript for publication,” said Fernandez.
The project has led to several presentations, including an award-winning poster at Scholars Week, and it will culminate in the publication of Fernandez’s manuscript. Fernandez, along with his collaborators Covey and colleagues at other universities, submitted the article to the Publications of the Astronomical Society of the Pacific in late March.
“After working on this project since my sophomore summer, it’s exciting to see it finally reach the paper stage,” said Fernandez.
Fernandez recently heard back from the journal that the paper has been accepted for publication -- and publishing a lead author paper is a significant accomplishment for an undergraduate. The article is titled “Identification and Radial Velocity Extraction for 100+ Double-Lined Spectroscopic Binaries in the APOGEE/IN-SYNC Fields.”
Fernandez will graduate this spring, leaving the project in capable hands, and plans to attend graduate school at the University of California, Riverside to pursue a doctorate in Physics. He hopes to work at the intersection of physics and astronomy and is interested in studying dark matter.
About Scholars Week
Scholars Week is an annual celebration of undergraduate research and creative activities at WWU, was created by a unanimous resolution of the Faculty Senate in November 1999. What was originally envisioned as "Scholars Day" quickly became Scholars Week in order to accommodate a diverse series of events highlighting the scholarship and creativity of Western undergraduate students.
Generously supported by Western's President, Provost, The Western Foundation and many of the Colleges, Scholars Week has grown from the inaugural celebration in May 2000 that involved 100 students in 11 events to the very successful Scholars Week 2007 which involved more than 250 undergraduate students participating in over 50 different sessions from virtually every academic area of the university. Scholars Week 2005 marked the first "University Scholars Poster Session and Reception" which had participants from 13 departments and programs. The "University Scholars Poster Session and Reception" has grown and become more popular in the last few years.
From art to engineering technology, students and faculty are working closely together at WWU to explore the boundaries of knowledge. Scholars Week has become a highlight of the academic year, celebrating the contributions of undergraduate students to enriching the intellectual environment of Western, and society in general.