c ontrast i maging Raffaele Gratton INAF Osservatorio Astronomico di Padova La ricerca sui pianeti extrasolari in Italia Roma 57 novembre 2014 Content The difficulty of HCI ID: 602111
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Slide1
Planet detection and characterization through high contrast imaging
Raffaele GrattonINAF – Osservatorio Astronomico di Padova
La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014Slide2
ContentThe difficulty of HCIExtrasolar planets may be detected in HCI!Struggling against speckles: the principles of HCI
High contrast imagers: first and second gen’sWhat we can do with HCI?DetectionCharacterizationPhotometryAstrometrySpectroscopy
La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014Slide3
Problematic
Planets
are
faint
and close ….
10
9
= 1
billion
10
6
= 1 million
Reflected light
Thermal emission
But better for young giant planets
Contrast ~10
6
in NIRSlide4
Required high contrast performances are equivalent to those required to see a moth flying around a street-lamp from a satellite at 500 km heightSlide5
Fomalhaut
< 3 M
J
120 AU
HR8799 b
7 M
J
68 AU
HR8799 c
10 M
J
38 AU
HR8799 d
10 M
J
24 AU
S
ystems with quite large mass ratio are being discovered…Slide6
Fomalhaut
< 3 M
J
120 AU
HR8799 b
7 M
J
68 AU
HR8799 c
10 M
J
38 AU
HR8799 d
10 M
J
24 AU
S
ystems with quite large mass ratio are being discovered…Slide7
First generation HCIThese discoveries were made using first generation HCI systems such as NACO, NIRC, or Hi-CIAOThese 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, Roma, 5-7 novembre 2014Slide8
State-of-the-art HCICombines 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)Slide9
Angular Differential ImagingADI exploits the fact that the field and the pupil rotate with respect to each
otherIn 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)Slide10
Spectral deconvolutionSimultaneous 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) Slide11
High contrast imaging pillars
High-order AO:
Contrast ~10
3
Coronagraphy
:
Contrast ~10
4
Differential imaging:
Contrast ~106Slide12
First and second generation HCILa ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014
NACO
SPHERESlide13
Second generation (XAO based) HCI
InstrumentTelescopeYear of operationWavelength
range (µm)
IFS
P1640
Palomar
2012
1.0-2.5
YesLMIRCamLBT2013
2.0-5.0NoCLIO2
Magellan20131-5 NoGPIGemini South20131.0-2.5YesSPHEREVLT UT320140.6-2.5YesHi-CIAO upgrade
Subaru2014Y-KYes
La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014Slide14
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)Slide15
First new detection with SPHERE: HR7581B (an M dwarf companion to a K-giant)Slide16
Photometric accuracy: <0.02 magLa ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014Slide17
Spectra of HR8799 planets (Pueyo et al. 2014)La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014
See talk by Anne-
Lise
MaireSlide18
Comparison between transmission and high contrast imaging spectraTransmission 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 2014Slide19
Astrometry of HR8799 planets (Pueyo et al. 2014)La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014