An international team of astronomers has reported the discovery of a new variable system using NASA’s Transiting Exoplanet Survey Satellite (TESS). The newly discovered object, named TIC 378898110, is the binary star AM Canum Venaticorum, a rare type of catastrophic variable. The discovery was presented in a paper published on the preprocessing server on November 2. arXiv.

Cataclysmic variables (CVs) are close binary star systems consisting of (usually) a primary white dwarf (WD) accumulating material from a main sequence star. Their brightness increases significantly, unevenly, and then they return to their resting state.

AM Canum Venaticorum (AM CVn) systems are a rare type of CVn named after AM Canum Venaticorum, a double cataclysmic hydrogen-deficient variant found in the constellation Canis Venaticus. In general, AM CVn type systems are ultracompact mass transfer binaries with orbital periods between 5 and 68 minutes. They form from a white dwarf accumulating matter dominated by helium from a degenerate or semi-degenerate donor star. Only 56 AM CVs have been detected to date.

Now, a team of astronomers led by Matthew J. Green of the Max Planck Institute for Astronomy in Heidelberg, Germany, has discovered a new object belonging to this rare class. They first identified TIC 378898110 as a short-period variant based on TESS photometric data. Later ground observations allowed them to classify this variable as AM CV.

“TIC 378898110 is a bright system that exhibits photometric modulation for 23.07 minutes, first detected in two TESS spin minimum observations. Its spectrum, photometric period, and accumulation-based photometric scintillation support its classification as a high-state AM CVn binary system,” the researchers explained. .

According to the article, TIC 378898110 is the third brightest AM CVn known to date, with an apparent magnitude of 14.3. The system is approximately 1000 light-years away, making it the twelfth closest AM CVn to Earth.

The mass of the main star in TIC 378898110 was determined to be 0.8 times that of the Sun, and the mass of the secondary star was 0.125 times that of the Sun. The system’s rotation period is estimated to be approximately 22-23 minutes, and the measured orbital inclination is approximately 74 degrees. Therefore, TIC 378898110 is the shortest binary detected by TESS.

Additionally, observations revealed that TIC 378898110 shows a photometric modulation with a period of 23.07 minutes; this is most likely the superhump period. According to astronomers, TIC 378898110’s spectrum, photometric period, and accretion-induced photometric jitter indicate that it is a high-state AM CVn binary system.

The study also found that TIC 378898110 recently experienced an unusual illumination event of magnitude 0.3 that lasted about a year. It can be seen that during this illumination the dominant photometric period decreases from 23.07 minutes to approximately 18.5-22.5 minutes.