Habitable Zone Planet Finder supplied with mosaic echelle grating

The Habitable Zone Planet Finder (HzPF), a spectrograph developed for the Hobby-Eberly telescope at the McDonald Observatory in Texas, USA, has been supplied with a large mosaic echelle grating by Richardson Gratings. It is hoped that the HZPF will be capable of discovering low-mass planets around nearby stars.

Contracted by the Pennsylvania State University in the USA, which also developed the Planet Finder, the 214 x 840 x 125mm grating has 31.6 grooves per millimetre and a nominal blaze angle of 75 degrees. The peak unpolarised diffraction efficiency is greater than 60 per cent for diffracted orders peaking between 900 and 1,650nm. The spectral resolving power was measured to exceed 1,190,000 at 633nm, and spatial resolution was measured to exceed two seconds of arc. Moreover, the overall diffracted wavefront demonstrates irregularity less than 0.06 waves at 633nm.

Once completed, the HzPF will be capable of discovering low-mass planets around cool, nearby stars as well as determining if these planets are in orbits that allow liquid water to exist on their surfaces; the so-called ‘habitable zone’ around stars. The spectrograph will cover the wavelength range from 900 to 1,650nm to enable precise radial velocities as low as one metre per second; the same speed of a person walking.

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