Precision of Radial Velocity Surveys using Multiobject Spectrographs — Experiences with Hectochelle

Abstract

There are two multiobject spectrographs at the 6.5m MMT telescope (Arizona, USA), sharing the same fiber feed and fiber positioner. A robotic positioner places all 300 fibers over the 600 mm (1 degree wide field [1]) focal surface in five minutes with an accuracy of 25μm or better. The fiber diameter is 250μm, or 1.5 arcsec at the MMT f/5 plate scale. The 30m long fiber run ends in a room accommodating two bench mounted spectrographs, the moderate resolution Hectospec and the high resolution (R=34,000) Hectochelle [2]. As there is no cross disperser, the orders of Hectochelle are separated by interference filters in front of the pseudo-slit, one order being ∼ 150 Å wide. Efficiency peaks at ∼ 7%, at a wavelength ∼ 5200 Å.