planet detection and characterization through high contrast imaging raffaele gratton inaf –...
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![Page 1: Planet detection and characterization through high contrast imaging Raffaele Gratton INAF – Osservatorio Astronomico di Padova La ricerca sui pianeti extrasolari](https://reader036.vdocuments.us/reader036/viewer/2022062621/551c2f74550346a34f8b6298/html5/thumbnails/1.jpg)
La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014
Planet detection and characterization through high contrast imaging
Raffaele GrattonINAF – Osservatorio Astronomico di
Padova
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La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014
Content
• 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
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ProblematicPlanets are faint and close ….
109 = 1 billion
106 = 1 million
Reflected light Thermal emission
But better for young giant planetsContrast ~106 in NIR
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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
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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…
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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…
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La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014
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
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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)
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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)
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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)
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High contrast imaging pillars
High-order AO:Contrast ~103
Coronagraphy:Contrast ~104
Differential imaging:Contrast ~106
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La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014
First and second generation HCI
NACO
SPHERE
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La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014
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
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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)
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First new detection with SPHERE: HR7581B (an M dwarf companion to a K-giant)
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La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014
Photometric accuracy: <0.02 mag
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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
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La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014
Comparison between transmission and high contrast imaging spectra
Transmission spectrumHD189733 (Pont et al. 2013)
High contrast imaging spectrumHR8799c (Pueyo et al. 2014)
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La ricerca sui pianeti extrasolari in Italia, Roma, 5-7 novembre 2014
Astrometry of HR8799 planets (Pueyo et al. 2014)