Brown Dwarf Discovery Orbits Star in Hyades, Advancing Understanding of Exoplanets in Astronomy

An international group of astronomers, with the aid of NASA's TESS (Transiting Exoplanet Survey Satellite), has identified a new warm brown dwarf named HIP 33609 b. It orbits around a bright, fast-spinning star, and the discovery was reported in a study released on January 23rd in arXiv.

Brown dwarfs (BDs) are celestial bodies that occupy the mass range between 13 to 80 Jupiter masses (0.012 to 0.076 solar masses), residing between planets and stars. Despite numerous detections of brown dwarfs, it is rare to find one orbiting around another star.

The researchers in this study announced the finding of a benchmark transiting brown dwarf in the HIP 33609 system. They utilized a combination of spectroscopic and photometric data from ground and space-based resources to characterize the host star and transiting brown dwarf.

Brown Dwarf in Space Dark

The recently discovered brown dwarf is larger, with a radius approximately 58% larger than Jupiter, while its weight is calculated to be approximately 68 times that of Jupiter. The research shows that HIP 33609 b has an elliptical orbit with an eccentricity of 0.56 and takes 39.47 days to complete one orbit. The equilibrium temperature of the brown dwarf was determined to be 1,237 K.

The star HIP 33609 has a radius of about 1.86 times that of the sun and is 2.38 times more massive. It rotates rapidly, with a rotation period of approximately 55.6 km/s. The effective temperature of the star is estimated to be 10,400 K, as reported by Phys.

The astronomers observed the unusual characteristics of HIP 33609 b, particularly its extended orbital period, and stated that it could further our understanding of transiting companions around hot stars. As a result, HIP 33609 b is considered a benchmark for evolutionary models of substellar objects. They also mentioned that all previously discovered transiting companions around B- and A-type stars have orbital periods shorter than ten days.

(Photo: Vowell et al., 2023)
The TESS and ground-based follow-up transits for HIP 33609 b.

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Intermediary Space Objects

The authors of the study stated that the HIP 33609 system is a suitable subject for evaluating substellar evolutionary models and for conducting a comparative analysis with the large population of highly irradiated, short-period brown dwarfs and giant planets.

Furthermore, the observations carried out by Vowell's team led to the identification of a young stellar association, estimated to be about 150 million years old, named MELANGE-6. HIP 33609 appears to be a member of this association. Last August, a team of scientists from around the world discovered a new, distant, cold, and dim brown dwarf with the help of the James Webb Space Telescope (JWST). The newly found object, GLASS-JWST-BD1, has a mass approximately 31 times that of Jupiter.

Brown dwarfs are considered to be intermediary objects between stars and planets, with masses usually ranging from 13 to 80 Jupiter masses. The T dwarf subtype, in particular, has effective temperatures ranging from 500 to 1,500 K and are the least bright and coldest substellar objects found to date. The discovery was documented in a paper published on arXiv.org on July 29.