The visible and near infrared (VNIR) spectrometer of EChO

The Visible and Near Infrared (VNIR) spectrometer of the EChO will cover the spectral range between 0.55 and 2.50 mu m. It has to be designed to assure a high efficiency over whole spectral range. It has to be able to observe stars with an apparent magnitude M-v= 9 divided by 12 and able to see contrasts of the order of 10(-4)divided by 10(-5) in order to measure characteristics of the exoplanets under investigation. VNIR would be a spectrometer in a cross-dispersed configuration by using a combination of a diffraction grating and a prism to spread the light in different wavelengths and in a useful number of orders of diffraction. It will use a Mercury Cadmium Telluride detector to satisfy the requirements of low thermal noise and the EChO system to operate at the working temperature of 40-45K. The instrument will be interfaced to the telescope optics by optical fibers to assure an easier coupling and an easier colocation of the instrument inside the EChO optical bench. The preliminary design of the instrument foresees a resolving power of about 330 with an entrance aperture of 2 arcsec.