Revised data changed expectations for a star pair that was supposed to merge in 2022.
Two binary stars – previously suspected to be merging – aren't going to get together in 2022. A fresh look at the data used in a 2017 study shows that one of the cited references had a typo, throwing off the calculations for binary system called KIC 9832227.
The 2017 study led by Larry Molnar (Calvin College) found that the observed orbital period between the stars shortened over time over several observation sets spanning 17 years. One of those data points was an outlier, recorded about eight years before the next dataset. The outlier — a set of observations taken between April 1999 to March 2000 — came from the Northern Sky Variability Survey, published in 2004 by Przemek Woźniak (Los Alamos National Observatory) and colleagues.
Recently, a new team led by graduate student Quentin Socia (San Diego State University) found that the 2004 catalog had different Julian dates listed in the preprint version than the final, published version. Further, the typo in the published version — the date Molnar carefully copied in his 2016 paper — put the star below the local horizon, making it an impossible observation.
Astronomers use the Julian calendar to calculate dates, but each observatory has the choice of using an adjusted Julian date to move the clock forward by 12 hours, making it easier to deal with local time zones. It was this little quirk that threw off the calculations; one version of the paper used the Julian date, while the other used the adjusted Julian date, said Molnar.
It's unclear how the date changed between preprint and publication. Molnar said he made every effort to get in touch with Woźniak to find out what happened, but couldn't find him; his coauthors said that Woźniak had likely retired. He also asked the Astronomical Journal if they had any records of e-mails or other correspondence from Woźniak related to the 2004 publication, but the journal has moved offices and publishers since then, and the records are lost.
For his own part, Molnar has many years of data he took on his own of the KIC 9832227 system, and his observations are still continuing. He says the adjusted data show the stars might be moving closer together, but he's not sure; at any rate, a merger is by no means imminent. “Even if they're not going to merge, it's still useful,” he says. “Contact binary stars are not well-understood in and of themselves.”. For example, one of his upcoming papers on KIC 9832227 will talk about hotspots observed in the binary system.
Socia's team uncovered the discrepancy using previously unpublished data from 2003 from the NASA Ames Vulcan Project. This project, using an instrument installed on Lick Observatory, was supposed to search for exoplanets in the Kepler spacecraft field of view. While no exoplanets have been found yet, Vulcan's field of view included KIC 9832227.
The team saw that the stellar eclipses were happening a half-hour later than predicted by the merger hypothesis. It was after digging into this further that the 12-hour time difference in the data from 2004 was discovered. The team even took the unusual step of asking Molnar to comment on their unpublished paper during peer review, just to make sure they understood the situation correctly. Typically, peer reviewers during publication have no affiliation with the work.
Socia initially planned to study KIC 9832227 as a summer project, but the work was so groundbreaking that it ended up being the major focus for his Master’s thesis, which he will complete next year. His future Ph.D. interest is in exoplanets. As for KIC 9832227? "That will be the end of it for me, personally," he said. "Dr. Molnar is far more knowledgeable and experienced, and I trust he knows what he's doing."
Socia's work was recently published in Astrophysical Journal Letters.