Directly Imaged Planets and Brown Dwarfs

Directly imaged exoplanets are those which we are able to spatially separate on sky from their host star. As the stars are much brighter than the planets, we generally observe very massive exoplanets which are at large orbital separations from their star in order for us to be able to distinguish their light from that of their star. Whilst a smaller number of directly imaged exoplanets have been observed, they have some of the most exciting potential for the future. It is through direct imaging that we stand the best chance of being able to characterise planets similar to our own, Earth-like planets around Sun-like stars.

Measurement of carbon and oxygen isotopes of a directly imaged planet with JWST

We used recent measurement of the atmosphere of a directly imaged companion, VHS 1256 b, with JWST to observe the atmosphere and constrain the abundances of chemical species. One of the key species we are interested in is carbon monoxide, as that has a strong signature in the spectrum. Thanks to the very high signal-to-noise data we had with JWST at very high resolution, we were able to distinguish between the different isotopes of carbon monoxide in the atmosphere. Not only this, but we were able to obtain the ratios of various carbon and oxygen isotopes using these NIRSpec observations between 4 and 5 microns. This tells us not only about how VHS 1256 b could have formed, but we can also compare with how similar these isotopes are to that of the Solar System and that measured for the inter-stellar medium. We found quite a bit of a difference in the isotope ratios for this planet, with generally stronger absorption form the weaker isotopes than we might have expected. You can find out more about it here.

Measurement of variability in the young brown dwarf companion AB Pictoris b

Using high resolution observations from the CRIRES+ spectrograph on the VLT, we were able to observe the young brown dwarf companion AB Pictoris b across 4 consecutive nights of observation. Our results showed that, across each night, some of the abundances that we measured seemed to be varying. The most significantly changing were the isotope abundances and the location of the clouds in the atmosphere. This is due to differences in the atmospheric weather patterns in the atmosphere of AB Pictoris b, where we saw cloudier regions on some nights and clearer regions on others. This in turn changed what we detected in our measurements of the abundances. We also measured the rotation rate of this planet given the very high spectral resolution allows us to measure the Doppler broadening of many thousands of individual spectral lines. This showed that AB Pictoris b was rotating very slowly, an indication that it is either facing us “pole-on” or that due to its young age it is a slow rotator, and will spin up over time as it cools and contracts. You can find out more about it here.