Planet detection and characterization
through high contrast imaging
Raffaele Gratton
INAF – Osservatorio Astronomico di
Padova
La ricerca sui pianeti extrasolari in Italia,
Roma, 5-7 novembre 2014
Content
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The difficulty of HCI
Extrasolar planets may be detected in HCI!
Struggling against speckles: the principles of HCI
High contrast imagers: first and second gen’s
What we can do with HCI?
– Detection
– Characterization
• Photometry
• Astrometry
• Spectroscopy
La ricerca sui pianeti extrasolari in Italia,
Roma, 5-7 novembre 2014
Problematic
Planets are faint and close ….
But better for young giant planets
10 = 1 billion
6
Contrast ~10 in NIR
9
106 = 1 million
Reflected light
Thermal emission
Required high contrast performances are equivalent to
those required to see a moth flying around a street-lamp
from a satellite at 500 km height
Systems with quite large mass ratio are
being discovered…
Fomalhaut
< 3 MJ
120 AU
HR8799 b
7 MJ
68 AU
HR8799 c
10 MJ
38 AU
HR8799 d
10 MJ
24 AU
Systems with quite large mass ratio are
being discovered…
Fomalhaut
< 3 MJ
120 AU
HR8799 b
7 MJ
68 AU
HR8799 c
10 MJ
38 AU
HR8799 d
10 MJ
24 AU
First generation HCI
• These discoveries were made using first
generation HCI systems such as NACO, NIRC,
or Hi-CIAO
• These instruments used moderately high
order AO systems (<200 actuators, sampling
the pupil at ~50 cm  SR(H)~0.5) available
since early 2000s, and were not specially
designed to fully exploit the potential of HCI
La ricerca sui pianeti extrasolari in Italia,
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State-of-the-art HCI
• Combines various techniques to provide high
contrast imaging, with excellent stellar PSF
suppression and stability:
– a high density high frequency AO system that
corrects turbulence and static optical aberrations
(WFE~100 nm, SR(H)~0.9, 5-σ contrast at 0.5
arcsec: ~10-3)
– coronagraphy (gain by a factor of 10)
– differential imaging, in which images at different
wavelengths or polarization states are observed
simultaneously (further gain by a factor of 100)
Angular Differential Imaging
• ADI exploits the fact that the field and the
pupil rotate with respect to each other
• In pupil stabilized mode, most speckles are
caused by instrumental artifacts and are
locked up in the pupil plane, whereas the
object of interest, a companion or a disk, will
rotate as the field rotates (see video_adi.avi )
• This allows distinguishing the stellar halo
from the object (provided instrument is
stable)
Spectral deconvolution
• Simultaneous observation of several
monochromatic images can be used to reduce the
impact of speckles (Sparks and Ford, 2002)
• For a given observation, the location of a
companion around a star is constant while the
location of speckles from the star increases with
wavelength and their intensity decreases (see
video_spectrum.avi )
• For a wide enough wavelength range this allows
subtraction of the speckles. This process is known
as spectral deconvolution (Thatte et al. 2007)
High contrast imaging pillars
High-order AO:
Contrast ~103
Coronagraphy:
Contrast ~104
Differential imaging:
Contrast ~106
First and second generation HCI
NACO
SPHERE
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Second generation (XAO based) HCI
Instrument
Telescope
Year of
operation
Wavelength
range (µm)
IFS
P1640
Palomar
2012
1.0-2.5
Yes
LMIRCam
LBT
2013
2.0-5.0
No
CLIO2
Magellan
2013
1-5
No
GPI
Gemini South
2013
1.0-2.5
Yes
SPHERE
VLT UT3
2014
0.6-2.5
Yes
Hi-CIAO
upgrade
Subaru
2014
Y-K
Yes
La ricerca sui pianeti extrasolari in Italia,
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What is SPHERE?
• SPHERE is the new high contrast imager for
the VLT
• It just passed commissioning and is offered in
P95
• SPHERE also provides narrow-field (few
arcsec), very high quality diffraction-limited
imaging over the wavelength range 0.6-2.5
micron
• It requires a bright NGS (I<14-16)
First new detection with SPHERE:
HR7581B (an M dwarf companion to
a K-giant)
Photometric accuracy: <0.02 mag
La ricerca sui pianeti extrasolari in Italia,
Roma, 5-7 novembre 2014
Spectra of HR8799 planets (Pueyo et
al. 2014)
See talk by Anne-Lise Maire
La ricerca sui pianeti extrasolari in Italia,
Roma, 5-7 novembre 2014
Comparison between transmission
and high contrast imaging spectra
Transmission spectrum
HD189733 (Pont et al. 2013)
High contrast imaging spectrum
HR8799c (Pueyo et al. 2014)
La ricerca sui pianeti extrasolari in Italia,
Roma, 5-7 novembre 2014
Astrometry of HR8799 planets (Pueyo
et al. 2014)
La ricerca sui pianeti extrasolari in Italia,
Roma, 5-7 novembre 2014