Exoplanet atmospheres

Abstract:

The sub-millimetre/microwave range of the spectrum has been exploited in the field of Earth observation by many instruments over the years and has provided a plethora of information on atmospheric chemistry and dynamicshowever, this spectral range has not been fully explored in planetary science, having been exclusively employed to carry out ground-based measurements. To this end, a sub-millimetre instrument, the Orbiter Terahertz Infrared Spectrometer (ORTIS), is studied by the University of Oxford and the Rutherford Appleton Laboratory, to meet the requirements of the European Space Agency's Cosmic Visions 2015-2025 programme-in particular, the Europa Jupiter System Mission (EJSM), which has the European Space Agency and the National Aeronautics and Space Administration as partners. ORTIS is designed to measure atmospheric temperature, the abundance of stratospheric water vapour and other jovian gases, and is intended to be capable of retrieving vertical profiles of horizontal windspeed in the stratosphere for the first time, from Doppler-shifted emission lines measured at high spectral resolution. In this work, a preliminary study and implementation of the estimation of windspeed profiles on simulated spectra representative of Jupiter is presented, detailing the development of the retrieval algorithm, showing that a sub-millimetre instrument such as ORTIS should be able to retrieve windspeed profiles to an accuracy of about 15 m/s between 70 and 200 km/0.1-10 mb using a single near-limb measurement, for expected noise amplitudes. © 2010 Elsevier B.V.. All rights reserved.

Abstract:

We report the discovery of a tight substellar companion to the young solar analog PZ Tel, a member of the β Pic moving group observed with high-contrast adaptive optics imaging as part of the Gemini Near-Infrared Coronagraphic Imager Planet-Finding Campaign. The companion was detected at a projected separation of 16.4 ± 1.0 AU (0. ′33 ± 0. ′01) in 2009 April. Second-epoch observations in 2010 May demonstrate that the companion is physically associated and shows significant orbital motion. Monte Carlo modeling constrains the orbit of PZ Tel B to eccentricities >0.6. The near-IR colors of PZ Tel B indicate a spectral type of M7 ± 2 and thus this object will be a new benchmark companion for studies of ultracool, low-gravity photospheres. Adopting an age of 12+8-4 Myr for the system, we estimate a mass of 36 ± 6 MJup based on the Lyon/DUSTY evolutionary models. PZ Tel B is one of the few young substellar companions directly imaged at orbital separations similar to those of giant planets in our own solar system. Additionally, the primary star PZ Tel A shows a 70 μm emission excess, evidence for a significant quantity of circumstellar dust that has not been disrupted by the orbitalmotion of the companion. © 2010. The American Astronomical Society. All rights reserved.

Abstract:

Our team is carrying out a multi-year observing program to directly image and characterize young extrasolar planets using the Near-Infrared Coronagraphic Imager (NICI) on the Gemini-South 8.1-meter telescope. NICI is the first instrument on a large telescope designed from the outset for high-contrast imaging, comprising a high-performance curvature adaptive optics system with a simultaneous dual-channel coronagraphic imager. Combined with state-of-the-art observing methods and data processing, NICI typically achieves ~2 magnitudes better contrast compared to previous ground-based or space-based programs, at separations inside of ~2 arcsec. In preparation for the Campaign, we carried out efforts to identify previously unrecognized young stars, to rigorously construct our observing strategy, and to optimize the combination of angular and spectral differential imaging. The Planet-Finding Campaign is in its second year, with first-epoch imaging of 174 stars already obtained out of a total sample of 300 stars. We describe the Campaign's goals, design, implementation, performance, and preliminary results. The NICI Campaign represents the largest and most sensitive imaging survey to date for massive (~1 Mjup) planets around other stars. Upon completion, the Campaign will establish the best measurements to date on the properties of young gas-giant planets at ~5-10 AU separations. Finally, Campaign discoveries will be well-suited to long-term orbital monitoring and detailed spectrophotometric followup with next-generation planet-finding instruments.