Astronomers study the atmosphere of a nearby cold brown dwarf star

Astronomers used the James Webb Space Telescope (JWST) to observe the cool brown dwarf star WISEPA J182831.08+265037.8 (WISE 1828 for short). This observation provided important information about the composition of the object’s atmosphere. The new results were published on February 8th on the preprint server arXiv. Brown dwarfs are substellar objects with masses below the flammability limit of hydrogen (about 80 masses of Jupiter). Y dwarfs are a subclass of brown dwarfs with effective temperatures below 500 K. These are the coolest and least luminous substellar objects ever discovered. WISE 1828 is located just 32.37 light years from Earth. It is a typical Y-type brown dwarf. Previous observations have shown that WISE 1828 has a radius similar to Jupiter, and its mass is estimated to be about 10 Jupiters. The effective temperature of this brown dwarf was 378 K. Recently, a team of astronomers conducted a detailed study of WISE 1828’s atmosphere. For this purpose, the scientist used his JWST NIRSpec spectrometer. The observations revealed the presence of water, carbon monoxide, carbon dioxide, methane, ammonia, and hydrogen sulfide in WISE 1828’s atmosphere. The authors noted that their study was the first to measure hydrogen sulfide in the atmosphere of his Y dwarf star. The study found that WISE 1828’s oxygen-to-hydrogen and sulfur-to-hydrogen ratios are higher than solar levels. It is estimated that the ratio of nitrogen to hydrogen is probably close to that of the Sun. The results also show low methane levels (D1). Researchers were able to measure the metal content and carbon-oxygen ratio of WISE 1828’s atmosphere using two complementary atmospheric modeling tools. One model gives a metallicity of 0.3, and the other model gives a metallicity of -0.57. According to these two models, the ratio of carbon and oxygen contents is approximately 0.46 and 0.43, respectively. The model also allowed the team to calculate WISE 1828’s radius and effective temperature. One model suggests that the brown dwarf has a radius 1.23 times that of Jupiter and an effective temperature of 534 K. Alternative models suggest that this dwarf star is smaller and cooler at Jupiter’s radius of 1.03 and 425 K.