Looking Forward
In our study of WASP-12b, we achieved
comparable precision to previous Hubble
Space Telescope Wide Field Camera 3 measurements, thus proving that ground-based
studies of exoplanetary atmospheres can be
a complementary addition to space-based
observations. We are currently conducting
a National Optical Astronomy Observatory
survey program (Principal Investigator (PI)
Jean-Michel Desert) using GMOS to measure
transmission spectra of a number of transiting planets and to investigate the nature and
origins of these planets in a systematic way.
In addition, the recent commissioning of
FLAMINGOS-2 (see update on page 21)
opens up the possibility of applying the
same differential spectroscopy technique in
the near-infrared. We have some observations coming up in October 2013 (GS-2013BQ-71, PI Kevin Stevenson) to test the capabilities of the instrument for this science.
These test observations will be used to observe secondary eclipses of a different planet, WASP-18b, allowing us to to measure its
thermal emission spectrum.
References
Bean, J., et al., Nature, 468: 669, 2010
Bean, J., et al., The Astrophysical Journal, 743: 92,
2011
Bean, J., et al., The Astrophysical Journal, 771: 108,
2013
Charbonneau, D., et al., The Astrophysical Journal,
568: 377, 2002
Gibson, N., et al., Monthly Notices of the Royal Astronomical Society, 428: 3680, 2013
Madhusudhan, N., et al., Nature, 469: 64, 2011
Stevenson, K., et al., The Astrophysical Journal,
submitted, arXiv:1305.1670
October2013
Jacob Bean is an assistant professor at the University of Chicago. He can be reached at:
[email protected]
Kevin Stevenson is a postdoctoral scholar at
the University of Chicago. He can be reached at:
[email protected]
Jean-Michel Desert is an assistant professor at
the University of Colorado Boulder. He can be
reached at: [email protected]
Marcel Bergmann is an independent contract
support astronomer at the National Optical
Astronomy Observatory. He can be reached at:
[email protected]
Exoplanet Transit
Spectroscopy: A Primer
Conceptually, the simplest way to take a
spectrum of an exoplanet is to spatially resolve the light from the planet from the light
of its host star and to feed that light into a
spectrograph. However, this is extremely
challenging due to the large contrast and
small angular separations between planets
and stars.
As an alternative to the approach of direct
imaging spectroscopy, transit spectroscopy
involves resolving the light from exoplanets
and their host stars temporally rather than
spatially (e.g., Charbonneau et al., 2002).
This is possible because a subset of known
exoplanets are observed to eclipse (transit)
their host stars due to a favorable geometric
alignment of their orbital plane with our line
of sight (Figure 4).
The atmospheres of transiting planets can
be probed in transmission by examining
the wavelength-dependency of the primary transit depth. This arises because the
GeminiFocus
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