Observations investigate the properties of nearby brown dwarf HD 33632 Ab

Astronomers used Hawaii’s Keck II telescope to observe a nearby brown dwarf star called HD 33632 Ab. The results of the observation campaign, presented in a paper published May 14 on the preprint server arXiv, provide further insight into the properties of this substellar object and its atmosphere. Brown dwarfs (BDs) are intermediate objects between planets and stars, occupying a mass range of 13 to 80 masses of Jupiter (0.012 to 0.076 solar masses). Because BDs have similar temperature and atmospheric properties to gas giant exoplanets, they are more massive and brighter at the same age, allowing astronomers to more easily characterize their atmospheric properties. HD 33632 Ab, located 86 light-years away, is her BD companion of the solar-mass star HD 33632 A of spectral type FV8. It exhibits subsolar metallicity and is estimated to be between 1 and 2.5 billion years old. This brown dwarf has about 46 times the mass of Jupiter and is located about 20 AU from its host. A team of astronomers led by his Chih-Chun Hsu at Northwestern University in Evanston, Illinois, performed high-resolution spectroscopic analysis of this system using the Keck Planet Imager and Characterizer (KPIC). “We present high-resolution Keck/KPIC K-band spectroscopy of the brown dwarf benchmark mass companion star HD 33632 Ab, providing the companion’s radial and projected rotational velocities, as well as CO and H2O abundances.” they wrote. Observations revealed that HD 33632 Ab has an estimated rotational speed of 53 km/s and a radial velocity of -8 km/s. The orbital period of this system was measured to be approximately 74 years, and the orbital eccentricity was calculated to be 0.25. The data collected suggest that HD 33632 Ab is smaller and closer to its host than previously thought. The brown dwarf’s mass was approximately 37 times that of Jupiter, and its distance from HD 33632 was estimated to be approximately 18 astronomical units. Based on her KPIC spectrum of HD 33632 Ab, astronomers detected carbon monoxide and water vapor in its atmosphere. However, they found no trace of methane. This may be due to several factors, including the brown dwarf’s rapid rotation and the relatively low signal-to-noise ratio of the resulting spectra. The study found that HD 33632 Ab has metallicity at the level of 0.0 Dex and a carbon-oxygen ratio of 0.58, which closely matches the properties of its parent star. The researchers noted that these results are what would be expected for brown dwarfs that form due to gravitational core collapse or disk instability. In conclusion, the authors of this paper emphasized that the new results of HD 33632 Ab could help expand our knowledge about brown dwarf formation and evolution in general. However, more samples of nearby brown dwarfs are still needed to significantly improve this problem.

source: https://dx.doi.org/10.48550/arxiv.2405.08312