Using radial velocity measurements, astronomers from Japan and China have detected a new exoplanet orbiting a G-type giant star. The newly discovered alien world is similar in mass to Jupiter, but much hotter than the solar system’s largest planet. The discovery is reported in a paper published Nov. 12 on the arXiv pre-print server.
The Radial Velocity Method (RV) to find a exoplanet is based on the detection of variations in the speed of the central star, due to the changing direction of the gravity of an invisible exoplanet as it orbits the star. Thanks to this technique, more than 600 exoplanets have been detected so far.
Now a group of astronomers led by Huan-Yu Teng of the Tokyo Institute of Technology in Tokyo, Japan, reports the discovery of a new giant planet as a result of RH measurements using the High Dispersion Echelle Spectrograph (HIDES) at Okayama Astrophysical Observatory (OAO) in Japan. The planet orbits a deeply evolved G-type solar mass giant star known as HD 167768, located at approximately 353 light years away.
“For HD 167768 RVs, we could find a strong signal at 20 d, indicating a regular variation in the time series,” the researchers explain.
The newly discovered exoplanet, dubbed HD 167768 b, is estimated to have a mass of at least 0.85 Jupiter masses. It orbits its host every 20.65 days, at a distance of about 0.15 AU. The equilibrium temperature of this planet was calculated to be 1874 K.
Due to its parameters, the authors of the paper classified HD 167768 b as a “warm Jupiter”. The planet was found to have one of the shortest orbital periods among those ever found around deeply evolved stars using radial velocity methods.
The host star HD 167768, estimated to be 5.3 billion years old, is of spectral type G8 III, has a mass of about 1.08 solar masses and is nearly 10 times larger than the Sun. It has a effective temperature of 4,851 K, and its metallicity is at a level of -0.75.
Considering that HD 167768 is expected to rise red giant branch, the astronomers predict that in astronomical terms, its planet will be swallowed up in a relatively short time. By analyzing the evolution of the orbit, they estimate that HD 167768 b will be engulfed by the expanding star in about 150 million years.
The researchers also assume that at least two other planets may be present in the HD 167768 system, still not detected. This assumption is based on the two additional regular variations identified in the RV measurements.
“In the periodogram of the residuals, there are two additional signals at 41 d and 95 d with FAP [false alarm probability] slightly lower than 0.1 percent, suggesting possible additional companions in the system,” the scientists note.
Huan-Yu Teng et al, a close-in planet orbiting the giant star HD 167768, arXiv (2022). DOI: 10.48550/arxiv.2211.06576
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