10 research outputs found
F.A.R.O.G. FORUM, Vol. 5 No. 5
Contains a supplément littéraire.https://digitalcommons.library.umaine.edu/francoamericain_forum/1063/thumbnail.jp
F.A.R.O.G. FORUM, Vol. 5 No. 2
https://digitalcommons.library.umaine.edu/francoamericain_forum/1060/thumbnail.jp
SUPERSHARP - Segmented Unfolding Primary for Exoplanet Research via Spectroscopic High Angular Resolution Photography
We propose to search for biosignatures in the spectra of reflected light from
about 100 Earth-sized planets that are already known to be orbiting in their
habitable zones (HZ). For a sample of G and K type hosts, most of these planets
will be between 25 and 50 milli-arcsec (mas) from their host star and 1 billion
to 10 billion times fainter. To separate the planet's image from that of its
host star at the wavelength (763nm) of the oxygen biosignature we need a
telescope with an aperture of 16 metres. Furthermore, the intensity of the
light from the host star at the position in the image of the exoplanet must be
suppressed otherwise the exoplanet will be lost in the glare.
This presents huge technical challenges. The Earth's atmosphere is turbulent
which makes it impossible to achieve the required contrast from the ground at
763nm. The telescope therefore needs to be in space and to fit the telescope in
the rocket fairing it must be a factor of 4 or more times smaller when folded
than when operational. To obtain spectroscopy of the planet's biosignature at
763nm we need to use an integral field spectrometer (IFS) with a field of view
(FOV) of 1000 x 1000 milli-arcsec (mas) and a spectral resolution of 100. This
is a device that simultaneously takes many pictures of the exoplanet each at a
slightly different wavelength which are then recorded as a data cube with two
spatial dimensions and one wavelength dimension. In every data cube wavelength
slice, the background light from the host star at the location of the planet
image must be minimised. This is achieved via a coronagraph which blocks the
light from the host star and active/adaptive optics techniques which
continuously maintain very high accuracy optical alignment to make the images
as sharp as possible. These are the technical challenges to be addressed in a
design study.Comment: A proposal in response to the ESA New Science Ideas call. Sept 2016.
25 page
F.A.R.O.G. FORUM, Vol. 5 No. 4
https://digitalcommons.library.umaine.edu/francoamericain_forum/1062/thumbnail.jp
First Light LBT AO Images of HR 8799 bcde at 1.65 and 3.3 Microns: New Discrepancies between Young Planets and Old Brown Dwarfs
As the only directly imaged multiple planet system, HR 8799 provides a unique
opportunity to study the physical properties of several planets in parallel. In
this paper, we image all four of the HR 8799 planets at H-band and 3.3 microns
with the new LBT adaptive optics system, PISCES, and LBTI/LMIRCam. Our images
offer an unprecedented view of the system, allowing us to obtain H and 3.3$
micron photometry of the innermost planet (for the first time) and put strong
upper-limits on the presence of a hypothetical fifth companion. We find that
all four planets are unexpectedly bright at 3.3 microns compared to the
equilibrium chemistry models used for field brown dwarfs, which predict that
planets should be faint at 3.3 microns due to CH4 opacity. We attempt to model
the planets with thick-cloudy, non-equilibrium chemistry atmospheres, but find
that removing CH4 to fit the 3.3 micron photometry increases the predicted L'
(3.8 microns) flux enough that it is inconsistent with observations. In an
effort to fit the SED of the HR 8799 planets, we construct mixtures of cloudy
atmospheres, which are intended to represent planets covered by clouds of
varying opacity. In this scenario, regions with low opacity look hot and
bright, while regions with high opacity look faint, similar to the patchy cloud
structures on Jupiter and L/T transition brown-dwarfs. Our mixed cloud models
reproduce all of the available data, but self-consistent models are still
necessary to demonstrate their viability.Comment: Accepted to Ap