|Figure 1: A conceptual view of SPHERE and its sub-systems at the Nasmyth focus of the VLT.|
Direct detection and spectral characterization of extrasolar planets is one of
the most exciting but also one of the most challenging areas in modern
astronomy. For its second-generation instrumentation on the VLT, ESO has
supported two phase A studies for a so-called "Planet Finder" dedicated
instrument. Based on the results of these two studies, a unique instrument,
SPHERE, is now considered for first light in 2010, including a powerful extreme
adaptive optics system, various coronagraphs, an infrared differential imaging
camera (IRDIS), an infrared integral field spectrograph (IFS) and a visible
differential polarimeter (ZIMPOL).
INAF-OAPD is responsible for the IFS channel and the Instrument Software and it has a significant role in the science group, with a special responsibility for the organization of the survey to be done in the GTO time.
|Figure 2: The scheme of the IFS|
The Integral Field Spectrograph (IFS), one of the three scientific channels
foreseen in the SPHERE design, is a very low resolution spectrograph (R~50)
which works in the near IR (950-1350 nm, with possibility to extend up to 1700
nm), an ideal wavelength range for the ground based detection of planetary
features. Adequate spectral and spatial sampling of the VLT diffraction limited
PSF with low cross talk level is provided by a micro-lens based new concept
(BIGRE), developed jointly by astronomers at OAPD and LAM (France).
The field of view is about 1.8x1.8 arcsec. SPHERE-IFS is expected to suppress speckle to a contrast of 10^7, with a goal of 10^8 , at a separation of ~0.5 arcsec from a bright star with magnitude J<8. Such performances will allow the detection of giant planets with rather extended ranges of mass, ages and separation. A wide survey of several hundreds of targets will ensure a firm derivation of the frequency of giant planets beyond 5-10 AU, fully complementing the information available from radial velocity surveys. IFS spectra will also allow the physical characterization of the planets detected with the instrument.
In 2008, SPHERE has passed the Optical Final Design Review (O-FDR) in May and the FDR in December, and has now entered the Construction Phase.