Nova eruption of RS Ophiuchi in 2021 generated million-degree gas and transformed the companion red giant

Star system: RS Ophiuchi A | Distance from the Sun: 7381 light years

RS Ophiuchi is a recurrent nova system, where a white dwarf and a red giant star orbit each other closely. The dwarf sucks material from the giant which leads to repeating eruptions known as nova. In 2021, RS Ophiuchi experienced another eruption, providing astronomers with a rare chance to observe changes before, during, and after the event using near-infrared light.

Researchers collected spectra before the eruption, showing the signature of the red giant star and emission lines from its wind. During the eruption, the spectra revealed strong emission lines, including those from very hot coronal gas, and a smooth background from hot, ionized material at about 8,900 degrees Kelvin. The temperature of the coronal gas was measured at around one million degrees 11 days after the eruption, and slightly less by 31 days after. High-speed observations did not find rapid changes in a key helium line. About a year after the eruption, the data suggested the red giant’s spectral type may have changed.

Key findings
- Near-infrared spectra captured before, during, and after the 2021 eruption of RS Ophiuchi
- Coronal gas reached temperatures of about one million degrees during the eruption
- No rapid changes were detected in the helium emission line during high-speed observations
- The red giant’s spectral type may have changed after the eruption
- Emission lines in the spectra likely originate from the red giant’s wind

Scientific study

Near-infrared spectroscopy of RS Ophiuchi in 2021: the calm, the storm, and the abatement (external link)