The signature of orbital motion from the dayside of the planet τ Boötis b

Leiden Observatory, Leiden University, Postbus 9513, 2300RA Leiden, The Netherlands.
Nature (Impact Factor: 41.46). 06/2012; 486(7404):502-4. DOI: 10.1038/nature11161
Source: PubMed


The giant planet orbiting τ Boötis (named τ Boötis b) was amongst the first extrasolar planets to be discovered. It is one of the brightest exoplanets and one of the nearest to us, with an orbital period of just a few days. Over the course of more than a decade, measurements of its orbital inclination have been announced and refuted, and have hitherto remained elusive. Here we report the detection of carbon monoxide absorption in the thermal dayside spectrum of τ Boötis b. At a spectral resolution of ∼100,000, we trace the change in the radial velocity of the planet over a large range in phase, determining an orbital inclination of 44.5° ± 1.5° and a mass 5.95 ± 0.28 times that of Jupiter, demonstrating that atmospheric characterization is possible for non-transiting planets. The strong absorption signal points to an atmosphere with a temperature that is decreasing towards higher altitudes, in contrast to the temperature inversion inferred for other highly irradiated planets. This supports the hypothesis that the absorbing compounds believed to cause such atmospheric inversions are destroyed in τ Boötis b by the ultraviolet emission from the active host star.

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Available from: Matteo Brogi, Apr 24, 2015
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    • "Furthermore, to create broad-band spectra from the UV to the infrared we must stitch together non-simultaneous measurements, sometimes only marginally compatible with one another (e.g., Lee et al., 2012; Pont et al., 2013) due either to global variations on the planet itself (unlikely given the experience of jovians in our own solar system); peculiarities of the instrument used for the observations; or due to the variability of spots on the parent star masquerading as different transit depths. One promising groundbased technique to break the degeneracies between temperature and composition is to use high spectral resolutions to unambiguously detect molecular bands and the Doppler shift of lines with orbital phase to separate the planet signal from the stellar and terrestrial background (e.g., Snellen et al., 2010; Brogi et al., 2012; de Kok et al., 2013). Space-based spectroscopy in the coming decades from observatories dedicated to transit spectroscopy (i.e., improving on the work of Hubble and Spitzer); coupled with spectroscopy of directly imaged planets (e.g., spectroscopy of HR8799b, Lee et al., 2013), should help to rapidly expand the ensemble of EGPs available for the testing of classification systems. "
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