Planet detection and characterization through high contrast imaging Raffaele Gratton INAF –...

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


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

ProblematicPlanets are faint and close ….

109 = 1 billion

106 = 1 million

Reflected light Thermal emission

But better for young giant planetsContrast ~106 in NIR

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

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…


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

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


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

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


Spectra of HR8799 planets (Pueyo et al. 2014)

See talk by Anne-Lise Maire


Comparison between transmission and high contrast imaging spectra

Transmission spectrumHD189733 (Pont et al. 2013)

High contrast imaging spectrumHR8799c (Pueyo et al. 2014)


Astrometry of HR8799 planets (Pueyo et al. 2014)

Planet detection and characterization through high contrast imaging Raffaele Gratton INAF –...

Documents

Transcript of Planet detection and characterization through high contrast imaging Raffaele Gratton INAF –...