A sophomore in the Department of Applied and Computational Mathematics and Statistics identified an intriguing light curve in a binary star that suggests a complete cessation of accretion—the movement of matter from one star to another—a phenomenon seen for only the second time in a similar star system.
Katherine Hill ’24, was the first author on a paper recently accepted for publication in the Astronomical Journal. She and collaborators including Peter Garnavich, chair of the Department of Physics, and Colin Littlefield, formerly of Notre Dame but now of the Bay Area Environmental Research Institute, based in southern Utah, used data obtained from the Kepler/Transiting Exoplanet Surveying Satellite (TESS) between December 2019 and the end of February 2020 to identify the event.
The study focused on the magnetic cataclysmic binary star YY Draconis (YY Dra). Researchers hoped to understand how matter was transferred from the cool star in the system to its compact white dwarf with a strong magnetic field. The TESS satellite data recorded the binary as it fell into a faint deep state, implying that a mass transfer stopped for more than one day before recovering.
“The star system didn’t look like anything special at first, but when you look at the 2020 data, there were hints that this system was different,” Hill said. When breaking down all of the different energy signals, all except one “died out,” which demonstrated there wasn’t any more matter transferred, she said.
“This had only been observed once before in another system, but nowhere as convincingly, I think, as Katherine reported in this paper,” Littlefield said.
In addition to the scientific discovery, the paper included a note in the appendix that likely cleared up a long-standing mystery in astrophysics, and has even has a tie-in to the current war in Ukraine.
Ukrainian-born astronomer V. Tsesevich discovered a variable star, later named YY Dra, in 1934 after he analyzed a series of photographic glass plates. However, attempts to confirm this discovery failed because there is no star at the exact coordinates he recorded. For decades, the whereabouts of YY Dra remained a mystery.
Fifty years later, a satellite identified a source of X-rays from a variable star system subsequently named DO Draconis (DO Dra), which is only a small distance from the coordinates given by Tsesevich for YY Dra. One theory had been that DO Dra and YY Dra are the same object, and that Tsesevich simply made an error when recording its position. Based on an analysis of newly available databases of variable stars, Hill’s appendix concludes that this is exactly what happened.
Hill’s paper motivated a review by two additional astrophysicists, one in Japan and one in Crimea, to find out if YY Dra and DO Dra were the same, Garnavich noted
“The authors of the review paper, Taichi Kato and Elena Pavlenko note that the uncertainty surrounding YY Dra could have been resolved by simply re-analyzing the photographic plates used by Tsesevich from his original discovery,” Garnavich wrote. “But these plates were destroyed during World War II, so that it may be impossible to ever recover the true nature of the lost star YY Dra.
“In an unusual conclusion to an astrophysics paper, Kato and Pavlenko note: ‘At the time of writing of this paper, crises are unfolding in Ukraine. As we have seen, the final conclusion on Tsesevich’s YY Dra is almost impossible to reach due to the result of World War II. The same thing also happened in various fields of science … We wish that no further destruction of our treasures should occur,’” Garnavich wrote.
It is now assumed there was no “lost” star system, and that YY Dra and DO Dra are the same, which serves as a bonus of the research, Littlefield said. In addition to the discovery within the TESS data and the researchers’ roles in deciphering it, the use of Kepler/TESS to “see” such an anomaly is also notable.
“All of these rare phenomena have basically been hiding in plain sight, which is one of the most interesting outcomes from TESS,” he said.
In addition to Hill, Littlefield and Garnavich, other collaborators on the paper included researchers from Bay Area Environmental Research Institute, Durham University, New Mexico State University, Picture Rocks Observatory, University College Cork, the University of Nevada, the University of Manchester, and University of Washington.
The work was partially funded through an NSF grant and the Irish Research Council in the form of a postdoctoral fellowship.