Ultra-high precision radial velocity spectrometer

We are developing a new instrument for McDonald Observatory designed to allow measurement of stellar radial velocity variations to a precision of ±1 m/s. The prime scientific use of the instrument will be a search for planets around other stars, but it will also be extremely useful for studies of binary stars and for analysis of stellar atmospheric motions including the more complex modes of pulsation now being discovered in the sun and a few other stars. A pair of ultra stable Fabry-Perot etalons, used in reflection, will impose a set of fixed reference absorption lines on the stellar spectrum before it enters the coudé spectrograph of the McDonald Observatory 2.7m telescope. The spectrum, covering 1500 Å at 0.132 Å resolution, will be recorded by the Octicon detector. The etalons and optical isolator system will be rigidly mounted in an evacuated, thermostated chamber to prevent movement of the interference orders exceeding the desired precision. A double cross-correlation technique will be used to measure the shift of stellar spectral lines will respect to the artifical absorption lines introduced by the Fabry-Perot orders. Calibration methods have been developed to measure any motion of the etalons which might occur.