First steps in direct exoplanet spectroscopy January 16, 2010
Posted by sarah in: new astronomy , trackback
Top: Image of star HR8799 and its exoplanet HR8799c (ESO/M.Janson). Bottom: The spectrum as recorded by the NACO detector, prior to extraction ; the vertical direction is spatial, horizontal is spectral (M. Janson et al, 2010)
Astronomers collaborating from both sides of the Atlantic have obtained the first direct spectrum of an exoplanet. The news here is mainly that they managed to record the spectrum and separate it reliably from that of the host star. Their short letter in ApJ, posted to astro-ph yesterday, doesn’t delve deeply into the implications of what they found but focuses more on the way they obtained, processed and analysed their data to separate the planet’s signature from that of the star.
This is not at all trivial, as the contrast required on very small spatial scales spans several orders of magnitude. Achieving this with a ground-based telescope like VLT requires adaptive optics to correct for the atmospheric blurring that would otherwise smear the starlight out over the faint planetary spectrum – as is available on infrared camera NACO.
The observations were carried out in the L-band around 3.5-4 microns, what is increasingly found to be a sweet spot for exoplanet work: the flux contrast between star and planet is lower than in the optical, the effect of atmospheric turbulence is smaller and easier to compensate, and the atmospheric thermal background is not yet so dominant to require further complex calibration observations to subtract it out.
Janson et al briefly describe their initial efforts to apply a couple exoplanet atmosphere models to the data, with not such great agreement between data and model, which they presume is due to a more complex role played by dust in the planet’s atmosphere, or non-equilibrium conditions affecting the chemistry in ways that the models don’t include.
This disagreement is perhaps not so surprising given our limited experience with direct exoplanet spectroscopy and the wide variety of exoplanets, many very different from our own Solar System bodies, astronomers have discovered in the last 15 years; and given the difficult data analysis process. Despite what some theorists believe, models do improve with the odd bit of observational input – and the next few years will undoubtedly see huge advances in our understanding of the formation, evolution and properties of extrasolar planetary systems. The authors of this particular paper already describe some further improvements to their observation technique and other targets VLT might be able to observe.
On a personal note, it was nice to see a nod to METIS in a high-profile paper. The infrared instrument I’ve been working on for the European ELT will be perfect for this kind of observations if and when it sees the light later on in the decade.
M. Janson, C. Bergfors, M. Goto, W. Brandner, & D. Lafreniere (2010). Spatially resolved spectroscopy of the exoplanet HR 8799 c accepted by A&A arXiv: 1001.2017v1
Comments»
[...] This post was mentioned on Twitter by ResearchBlogging.org, Sarah Kendrew. Sarah Kendrew said: New blog post, First steps in direct exoplanet spectroscopy – http://tinyurl.com/yedtazp [...]
[...] SarahAskew » First steps in direct exoplanet spectroscopy [...]