MULTIPLEXING PRECISION RVs: SEARCHING FOR CLOSE-IN GAS GIANTS IN OPEN CLUSTERS

Abstract

We present a multiplexed high-resolution ( R ∼ 50,000 median) spectroscopic survey designed to detect exoplanet candidates in two southern star clusters (NGC 2516 and NGC 2422) using the Michigan/ Magellan Fiber System (M2FS) on the Magellan /Clay telescope at Las Campanas Observatory. With 128 available fibers in our observing mode, we are able to target every star in the core half-degree of each cluster that could plausibly be a solar-analog member. Our template-based spectral fits provide precise measurements of fundamental stellar properties— T eff (±30 K), [Fe/H] and [ α /Fe] (±0.02 dex), and (±0.3 km s −1 )—and radial velocities (RVs) by using telluric absorption features from 7160 to 7290 Å as a wavelength reference for 251 mid-F to mid-K stars (126 in NGC 2516 and 125 in NGC 2422) that comprise our survey. In each cluster, we have obtained ∼10–12 epochs of our targets. Using repeat observations of an RV standard star, we show our approach can attain a single-epoch velocity precision of 25–60 m s −1 over a broad range of signal-to-noise ratios throughout our observational baseline of 1.1 years. Our technique is suitable for nonrapidly rotating stars cooler than mid-F. In this paper, we describe our observational sample and analysis methodology and present a detailed study of the attainable precision and measurement capabilities of our approach. Subsequent papers will provide results for stars observed in the target clusters, analyze our data set of RV time series for stellar jitter and stellar and substellar companions, and consider the implications of our findings on the clusters themselves.