PRL advanced radial-velocity all-sky search (PARAS): An efficient fiber-fed spectrograph for planet searches

We present here the optical design of an efficient Fiber-fed, Prism Cross-dispersed, Echelle Spectrograph (Resolution ~70,000 @seeing limited ~2arcsecs conditions) which will operate in the wavelength region of 3700A to 8100A. It will be used for extra-solar planets searches down to the precision of 3m/s and as well as for follow-up observations for new transit discoveries. The spectrograph design is such that with a beam size of 100mm (4inch) it should suit the existing 1 to 2m class of telescopes available in India. The fiber-fed spectrograph will be installed with a 1.2m telescope, which is situated at Mt. Abu (5800feet), Rajasthan, India. We estimate the spectrograph to be >30% efficient from the slit to the CCD detector, and up to 15% efficient including sky, telescope, fiber-fed optics etc. We expect to reach the S/N ratio of 70 on a 10mag star for an integration time of 40mins. We aim to achieve 5m/s to 3m/s Radial Velocity accuracies on such a star using the simultaneous ThAr referencing method. Since thermal stability is absolutely necessary to achieve <5m/s RV accuracies, the whole spectrograph is planned to be kept inside a vibration free isolated tank under low vacuum (0.001 mbar) in a thermally isolated room at 28C +/- 0.01C. It should see the first light by the summer of 2009. We are guaranteed at least 120 nights per year for the planet search program, more nights are possible.