Eclipse mapping with SPIRou reveals first CO signal on WASP-33b’s dayside

Star system: WASP-33 | Distance from the Sun: 378 light years

WASP-33b is an ultra-hot Jupiter, a giant planet orbiting very close to its star. Scientists used high-resolution spectroscopy with the SPIRou instrument to observe eight eclipses of WASP-33b, focusing on the moments when the planet passes behind its star (ingress and egress). This technique, called eclipse mapping, can reveal details about the planet’s dayside atmosphere. The team analyzed the data using advanced software and combined it with previous observations to search for signals from molecules in the planet’s atmosphere.

The study reports the first tentative detection of carbon monoxide (CO) from in-eclipse data alone, showing that stacking multiple eclipse observations can improve the chances of detecting atmospheric features. When combined with longer observations of the planet’s dayside, the eclipse data also help to better constrain the planet’s rotation speed. The researchers performed tests by adding artificial signals to the data, confirming that their method works as expected for a planet rotating in sync with its orbit. They estimate that about 15 more eclipse observations would be needed to measure WASP-33b’s rotation directly using this approach.

This work demonstrates the potential of Doppler eclipse mapping for studying exoplanet atmospheres and highlights the challenges that remain, such as processing short time series and observing planets with slow changes in velocity. The results pave the way for future studies with next-generation telescopes.

Key findings
- First tentative detection of CO in WASP-33b’s dayside atmosphere using eclipse mapping.
- Stacking multiple eclipse observations boosts detection sensitivity.
- Eclipse data help constrain the planet’s rotation speed.
- About 15 more eclipses are needed for a direct rotation measurement.
- The method shows promise for future exoplanet studies with advanced telescopes.

Scientific study

Towards Doppler eclipse mapping of hot Jupiters. An observational perspective on WASP-33 b with SPIRou (external link)