High-resolution spectroscopy reveals gaseous silicon in the atmosphere of brown dwarf TWA 5 B

Star system: TWA 5 A | Distance from the Sun: 162 light years

TWA 5 B is a directly imaged sub-stellar companion, a type of object often categorized as a gas giant or brown dwarf. Understanding the chemical composition of these atmospheres is essential for learning how they formed. Silicon is a particularly important element, as it is a refractory material — a substance that remains solid at relatively high temperatures — and it plays a major role in the formation of magnesium-silicate clouds, which are similar to rock clouds in the atmospheres of hot planets.

Researchers conducted the first results of the CRIMSON survey using the CRIRES+ instrument, which specializes in high-resolution spectroscopy in the M-band, an infrared range. This approach allowed them to observe gas-phase silicon monoxide (SiO) at 4 micrometers. The study successfully detected gaseous SiO in the atmosphere of TWA 5 B, along with volatile species like carbon monoxide and water.

The high abundance of detected silicon monoxide indicates that significant amounts of silicon are remaining in the gas phase, which suggests that magnesium-silicate clouds are not condensing in the upper atmosphere to a significant degree. By comparing the ratios of refractory materials like silicon to volatile materials like carbon and oxygen, the scientists determined that this object's atmospheric composition is consistent with formation processes like core-accretion beyond the snowline, or gravitational instability followed by the enrichment of solid materials.

Key findings
- Strong detection of gaseous silicon monoxide (SiO) in the atmosphere of the companion TWA 5 B.
- Measured atmospheric silicon abundance implies minimal cloud condensation of magnesium silicates.
- Simultaneous detection of carbon monoxide, water, and silicon monoxide allows for detailed atmospheric modeling.
- The results indicate that the object formed through core-accretion beyond the CO snowline or through gravitational instability with solid enrichment.

Scientific study

The CRIMSON survey I: super-stellar SiO in the directly imaged companion TWA 5 B from high-resolution M-band spectroscopy (external link)