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Observations of binary system V455 Car suggest a possible third companion

Chinese astronomers have employed NASA's Transiting Exoplanet Survey Satellite (TESS) to observe an eclipsing binary of the Algol-type, designated V455 Car. Results of the observational campaign are in the journal New Astronomy.

Algol-type binaries are semi-detached systems whose less-massive component transfers mass to the more massive component due to filling its Roche lobe, causing mass and angular momentum loss. They are a class of eclipsing binary stars related to the prototype member of this class, known as Beta Persei or Algol.

V455 Car is an oscillating eclipsing Algol-type binary with an orbital period of approximately 5.133 days. Its effective temperature is estimated to be about 18,000 K and the mass of the primary star in the system is assumed to be around 3.5 solar masses.

Given that the pulsating characteristic of V455 Car is still unknown, a team of astronomers led by Zhao-Long Deng of the Yunnan Observatories in China, decided to investigate this system with TESS. Their study was complemented by data from ESA's Gaia satellite and from the Fiber-fed Extended Range Optical Spectrograph (FEROS).

The observations found that V455 Car is a semi-detached binary with a mass ratio of 0.298, in which the secondary star almost fills its Roche lobe. The masses of the primary and secondary stars were measured to be 5.3 and 1.58 solar masses, respectively.

According to the paper, the primary star in V455 Car has a radius of 3.17 solar radii, luminosity at a level of 659 solar luminosities, and an effective temperature of 16,427 K. When it comes to its companion, it is about 6.66 times larger than the sun, has a luminosity of about 40 solar luminosities and its effective temperature is estimated to be 5,619 K.

Furthermore, it was found that the system has a semi-major axis of 23.81 solar radii and detected a periodic variation of approximately 26.62 years. The astronomers suppose that such variation indicates the presence of a third body in the system with a minimum mass of 0.59 solar masses.

Summing up the results, the authors of the paper conclude that V455 Car is an Algol-type system that experienced a rapid mass transfer stage, composed most likely of a slowly pulsating B star (SPB) exhibiting a stochastic low-frequency (SLF) variability, and a red giant star.

"V455 Car represents an example of a binary system with an SPB/SLF primary star. Because the secondary star of V455 Car almost fills its Roche lobe, but the filling factors of the primary star is extremely low, we speculate that it is an Algol-type system that has just experienced a rapid mass transfer stage, the periodic variation may be attributed to the presence of a third body, and the specific mass transfer mechanism and process can be further studied in future," the researchers explain.