Astronomy and Astrophysics – Astronomy
Scientific paper
Sep 2011
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2011ess.....2.4019w&link_type=abstract
American Astronomical Society, ESS meeting #2, #40.19
Astronomy and Astrophysics
Astronomy
Scientific paper
Transmission spectroscopy is a comparison of spectra taken during transit to spectra outside of transit. Light from the star passes through the
atmosphere of the planet during transit, and some wavelengths are reduced in flux due to opacity sources in the atmosphere. These measurements contain information about the structure and composition of the atmosphere; measurements at the narrowest bandwidths probe the highest parts of the
atmosphere, and measurements at wider bandwidths probe the lower atmosphere. Atmospheres of hot Jupiter exoplanets strongly absorb sodium (Na) at 589.0 and 589.6 nm.
The interpretation of transmission spectroscopy for very narrow bandwidths must account for Doppler shifts due to the orbit of the planet and the
rotation of the star. We have developed a numerical model using IDL which predicts the changing shape of the Na absorption lines during the transit,
due to the rotation of the star - the Rossiter-McLaughlin (RM) effect. The model is called Sodium WASP (Wide Angle Search for Planets) Atmospheric Rossiter Model - SWARM. Parameters are input, and SWARM calculates orbital elements and the RM effect for the times of a set of proposed observations including a transit, and the corresponding change in shape of the Na lines. The output of SWARM is a set of synthetic spectra which include the effects of the planetary absorption signal.
These can be used in various ways. For each planetary system, the Na transit depth can be measured; the planet's orbit, and the planetary absorption signal can be plotted; and the radial velocity shifts of the altered spectra can also be measured, and the RM curve calculated and plotted. A greyscale plot clearly shows the planetary Na absorption in WASP-17b, and the calculated RM curve reproduces that obtained from observations.
PLW is supported by a Science and Technology Facilities Council postgraduate studentship.
Maxted Pierre
Wood Patricia
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