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LCOGT's Network of Robotic Echelle Spectrographs (NRES) will be six identical high-resolution (R~53,000), precise (≤ 3 m/s), optical (380-860 nm) echelle spectrographs, each fiber-fed (2.58" per fiber width) simultaneously by two 1 meter telescopes and a ThAr calibration source. Thus, NRES is to be a single, globally-distributed observing facility, composed of six units (one at each of our observatory sites), using twelve 1-m telescopes. NRES will roughly double the RV planet-vetting capacity nationwide, and will achieve long-term accuracy better than 3 m/s in less than an hour for stars brighter than V = 12.
We have been fully funded with an NSF MRI grant (AST-1229720). Our first spectrograph is currently scheduled for deployment in Fall of 2014, with the full network operation of all 6 units beginning in Fall of 2015.
Like all instruments at LCOGT, scheduling, observing, and data reduction will be autonomous, and all data will be publicly available after a proprietary period.
The primary motivation for NRES is to study exoplanets. NRES will roughly double the RV planet-vetting capacity nationwide and will achieve accuracy better than 3 m/s in reasonable exposure times for stars brighter than V = 12, enabling a large variety of planetary studies.
Ground-based transiting planet searches produce hundreds of transiting planet candidates per year, but many of these are “astrophysical false positives” – binary or multiple stars masquerading as planets. In space, the CoRoT (Baglin et al., 2006) and Kepler (Borucki et al., 2003) missions have located thousands of candidates, but also produce a signiﬁcant fraction of false positives. Looking forward, the Transiting Exoplanet Survey Satellite, TESS (Ricker et al., 2010), is now undergoing a NASA Phase-A study. If TESS is successful, then starting in 2017 it will produce an all-sky catalog containing an estimated 20,000 planet candidates circling bright (V ≲ 12.5) stars in the course of a 3-year mission.
Separating planets from false positives is efﬁciently done with (and often demands) RV measurements, to distinguish the (order m/s) reﬂex velocities of planets from the (order km/s) velocities of stellar binaries. Moreover, knowing the mass, radius, and temperature of an exoplanet depends on knowing the same physical properties of its parent star. This requires spectroscopic classiﬁcation of the star to yield Tef f , log g, metallicity, and v sin i. Accurate classiﬁcation is also necessary to exclude blended false positive scenarios (Torres et al., 2011). The problem of limited high-accuracy RV was severe even before Kepler was launched. Kepler has made it a crisis – one that will become paralyzing if TESS ﬂies, unless there is signiﬁcant investment in these essential resources. Accordingly, NRES will provide an efﬁcient, uniform, automated source of spectra for stellar classiﬁcation and RV vetting, with capacity sized to match the anticipated rate of planet candidate discoveries.
The Rossiter-McLaughlin (RM) effect (Rossiter, 1924; McLaughlin, 1924) allows measurement of the inclination of planetary orbits relative to the stellar rotation axis. Because different migration mechanisms predict different distributions of the planetary orbit with respect to the stellar spin, it provides valuable constraints on the formation and orbital evolution of planetary systems (Winn et al., 2005; Gaudi and Winn, 2007; Triaud et al., 2010). NRES will be capable of observing the RM effect on a signiﬁcant sample of extrasolar planets. For favorable cases, the RM signal can exceed 50 m/s, while the smallest signal yet detected is about 1.5 m/s, corresponding to a Neptune-size body transiting the slow-rotating star HAT-P-11 (Winn et al., 2010). To properly sample a RM radial velocity curve requires time resolution comparable to transit ingress/egress times – typically 5 minutes. Results from multiple transits or multiple telescopes may however be averaged together. We therefore target 3 m/s precision in 4 x 5-min observations on a typical star with V = 10.