# TOI-1338

TOI-1338 is a binary star system located in the constellation Pictor, about 1,320 light-years from Earth. It is orbited by two known circumbinary planets, TOI-1338 b, discovered by the Transiting Exoplanet Survey Satellite (TESS) and BEBOP-1c, discovered by the Binaries Escorted By Orbiting Planets project.

## Discovery and nomenclature

The circumbinary planet TOI-1338 b was found in July 2019 by Wolf Cukier, a 17-year-old high school student who joined the Goddard Space Flight Center as a summer intern. The acronym TOI stands for "TESS Objects of Interest." Cukier studied data provided by volunteers of the Planet Hunters citizen science project, looking through data that had been flagged as an eclipsing binary. Cukier and six of the Planet Hunter volunteers are co-authors of the publication regarding the planet.
The discovery of TOI-1338 b was announced in early January 2020 at the 235th American Astronomical Society meeting in Honolulu, Hawaii. In June 2023, a second circumbinary planet within the system was announced to have been discovered, named BEBOP-1c. It was the first circumbinary planet to be found using the radial velocity method.
In February 2021, a petition was launched calling for TOI-1338 b to be renamed SOPHIE in honor of late Scottish musician Sophie. It was supported by Charli XCX and Caroline Polachek. The petition was unsuccessful in renaming TOI-1338 b, but in June 2021, the International Astronomical Union announced that the minor planet 1980 RE1 was given the permanent name Sophiexeon.

## Stellar binary

TOI-1338 is a single-lined spectroscopic binary system, consisting of an F8 star and a red dwarf of spectral type M. The system has an age of 4.4 billion years. The two stars with masses of 1.13 and 0.313 M$_☉$ revolve around each other every 14.6 days. The red dwarf is about nine magnitudes fainter than the primary star and cannot be detected in the spectrum.
The orbit of the two stars is inclined at 89.7° to the plane of the sky (so edge-on) and both primary and secondary eclipses can be observed, although the brightness changes are very small. The primary eclipse occurs when the hotter primary star is partially occulted by the cooler secondary. It lasts about five hours and the brightness decreases by about 4%. The secondary eclipses occur when the cooler star is occulted by the hotter star. They also last about five hours but the brightness drops by less than half a percent.

## Planetary system

The planet TOI-1338 b is between Neptune and Saturn in size, and has an orbit that is within ~1° coplanar with the binary. Its mass is estimated to be roughly 11 times that of Earth, indicating a low density similar to that of circumbinary planet Kepler-47c.
The spin of the primary star aligns with the orbits of the binary and the planet (spin-orbit angle β = 2.8°±17.1°). This is the second time the Rossiter–McLaughlin effect was measured for a star hosting a circumbinary planet. Kepler-16 was the first system with such a measurement. The measurement of the alignment for TOI-1338 suggests that the planet formed from a single circumbinary disk.
TOI-1338 c, or BEBOP-1c, is a gas giant about 75 times the mass of Earth. It is also coplanar (or nearly so) with the binary stars and planet b.
The TOI-1338 planetary system :
| Companion (in order from star) | Mass | Semimajor axis (AU) | Orbital period (days) | Eccentricity | Inclination | Radius |
| b | 11.3±2.1 M$_🜨$ | 0.4607+0.0084 −0.0088 | 95.4001+0.0062 −0.0056 | 0.0331+0.0022 −0.0021 | 90.494+0.013 −0.014° | 7.661±0.053 R$_🜨$ |
| c | 75.4+4.0 −3.6 M$_🜨$ | 0.794±0.016 | 215.79+0.46 −0.51 | 0.037+0.032 −0.026 | 97.0+6.7 −6.8° | — |