NASA’s TESS Discovers Nearly 100 Quadruple Star Systems

Artist’s conception of the 30 Ari star system. The system is made up of four stars. Credit: Art by Karen Teramura, UH IfA

" data-gt-translate-attributes="[{" attribute="">NasaTransiting exoplanet study satellite (TESS) found more than 5000 candidates exoplanet candidates and 197 exoplanets confirmed since its mission began in late 2018. TESS is good at finding exoplanets, but the spacecraft is a powerful science platform, and it has made other discoveries as well. Scientists working with TESS recently announced 97 quad star candidates, nearly doubling the number of known quad systems.

The mission of TESS is to find exoplanets. More specifically, its mission is to find exoplanets around nearby bright stars. The Transiting Exoplanet Survey Satellite can also study the mass, density, size and orbit of these planets.

But TESS’s field of view is wide, far wider than its predecessor, the Kepler Space Telescope. Its network of wide-field cameras surveyed 85% of the sky and collected a huge amount of data. Scientists are using machine learning and a cohort of enthusiastic citizen scientists to sift through this data.

According to a new paper, the latest TESS data results are a catalog of 97 “…uniformly controlled candidates for quadruple stellar systems,” according to a new paper. The article is “97 eclipsing quadruple star candidates discovered in full-frame TESS images”. The article is available on the prepress site arxiv.org and will be published in The Astrophysical Journal Supplement. The lead author of the article is Veselin Kostov of NASA’s Goddard Space Flight Center.

“Candidates were identified in TESS Full Frame Image data from Sectors 1-42 through a combination of machine learning and visual examination techniques, with major contributions from a dedicated group of citizen scientists,” the authors write. authors.

TESS observation area

TESS is fitted with four CCD cameras with adjacent fields of view to produce a 4 x 1 array, or “viewing sector”, giving a combined field of view of 96x 24 degrees, as shown above. Credit: NASA

Finding these systems required collaboration between some of the usual suspects – the Astrophysical Sciences Division of NASA’s Goddard Space Flight Center (GSFC) and the MIT Kavli Institute. But the professionals at these research institutions needed help. This help came from seven experienced citizen scientists who participated in the painstaking effort of analyzing the light curves pixel by pixel. “To exclude false positives due to near field stars or systematic effects, we evaluate the pixel-by-pixel light curve of the target…” the authors write in their paper.

HD 98800 quad star system

This is an artist’s rendering of HD 98800, a quadruple star system located in the TW Hydrae Association. It is not part of the new catalog and was previously discovered. Credit: NASA/JPL-Caltech/T. Pyle (SSC)

Researchers have focused their efforts on identifying triple and quadruple star systems, but the results go beyond these multiple star systems. They also found “…the first sextuple star system with sextuple eclipses and the first transiting circumbinary planet detected from a sector of TESS data,” explain the authors.

Quadruple star systems contain two pairs of eclipsing binary stars (EBs). However, they are only EBs if they slip away from our point of view. All of these transits and eclipses can be difficult to tangle, hence the help of dedicated citizen scientists.

The researchers were only interested in specific quad star systems, and they deliberately excluded others. “We note that the targets listed in this catalog are quadruple candidates that each come from a single TESS source, i.e., two-component EBs are unresolved in the TESS data,” they write. . These quad systems are in the catalog because they present observable changes on the scale of human times. “The reason is that for the purposes of this work, our interests are in close quadruple systems that can exhibit dynamically interesting interactions on the human scale (months to years),” they explain.

This explanation is a bit wordy, but it boils down to this: the TESS pixel width can be vast. If TESS locates a pair of EBs separated by two TESS pixels, and if the EBs are 500 parsecs away from us, that means the EBs are separated from each other by up to 20,000 AU. At this great distance from each other, it could take generations of human observations to notice any interaction between the stars. Systems need to be closer together to show interesting interactions observable over months or years, so they need to be in the same TESS pixel. This required careful pixel-by-pixel analysis.

Catalog systems have survived a rigorous verification process. The team also encountered many false positives. A field star near the target often appeared to be another EB until further analysis ruled it out. Other times they detected two pairs of EBs, but they were not interconnected and were too far apart to constitute a quadruple star system. There were also triple star systems whose eclipse pattern mimicked a quadruple star system. In total, there were five false positive scenarios.

In their summary, the authors write that “target stars were identified by visual inspection and exhibit two series of eclipses with two distinct periods, each with primary eclipses and, in most cases, secondary eclipses. All targets have been uniformly checked and passed a series of tests, including pixel by pixel and
analysis of the movement of the photocenter.

Why are astronomers interested in quadruple systems?

Multiple star systems can reveal a great deal about stellar evolutionary pathways. Astronomers and astrophysicists are interested in stellar stages of evolution such as short-period binaries, common-envelope events, Type Ia supernovaeand black hole mergers.

The arrangement of stars in multiple systems is also evidence of how stars formed. “For example, the mass ratios between the individual components of a quadruple system, the period ratios between the constituent binary systems, and the mutual tilt provide important information about whether the system formed via a “downward” scenario. “via core or disk fragmentation or ‘bottom-up’ aggregation via gravitational capture,” they write.

Another exciting aspect of multiple star systems is planets. Astronomers have found planets around several star systems, but their origins and fates are unclear.

In 2015, astronomers discovered a massive planet in the quadruple star system 30 Arietis. According to this discovery, the system is home to a huge gas giant Ten times more massive than Jupiter. It was the second known planetary instance in a quadruple star system.

In 2019, researchers discovered a unique quadruple star system where the stars are at right angles to the disc of gas and dust around them. Planets will likely form from this protoplanetary disk. How unusual would a view from the surface of a planet be in this system?

The team of researchers is not yet finished. They say they detected an order of magnitude more false positives than verified detections and a full analysis is beyond the scope of this article. “…given the large number of targets inspected and assuming that many of the additional candidates turn out to be real, TESS has the potential to increase the number of known quadruple eclipsing systems by more than a factor of two. “, they write.

Originally published on Universe today.