CHIRON - A Fiber Fed Spectrometer for Precise Radial Velocities

The CHIRON optical high-resolution echelle spectrometer was commissioned at the 1.5m telescope at CTIO in 2011. The instrument was designed for high throughput and stability, with the goal of monitoring radial velocities of bright stars with high precision and high cadence for the discovery of low-mass exoplanets. Spectral resolution of R=79,000 is attained when using a slicer with a total (including telescope and detector) efficiency of 6% or higher, while a resolution of R=136,000 is available for bright stars. A fixed spectral range of 415 to 880 nm is covered. The echelle grating is housed in a vacuum enclosure and the instrument temperature is stabilized to +-0.2deg. Stable illumination is provided by an octagonal multimode fiber with excellent light-scrambling properties. An iodine cell is used for wavelength calibration. We describe the main optics, fiber feed, detector, exposure-meter, and other aspects of the instrument, as well as the observing procedure and data reduction.Comment: 15 pages, 10 figures. Accepted by PAS

Fiber scrambling for high-resolution spectrographs. I. Lick Observatory

In this paper, we report all results obtained with a fiber scrambler on the Hamilton spectrograph at Lick Observatory. We demonstrate an improvement in the stability of the instrumental profile using this fiber scrambler. Additionally, we present data obtained with a double scrambler that further improves the stability of the instrument by a factor 2. These results show that errors related to the coupling between the telescope and the spectrograph are the dominant source of instrumental profile variability at Lick Observatory. In particular, we show a strong correlation between instrumental profile variations and hour angle, most likely due to pointing-dependent illumination of the spectrograph optics

M2K: II. A Triple-Planet System Orbiting HIP 57274

Doppler observations from Keck Observatory have revealed a triple planet system orbiting the nearby mid-type K dwarf, HIP 57274. The inner planet, HIP 57274b, is a super-Earth with \msini\ = 11.6 \mearth (0.036 \mjup), an orbital period of 8.135 $\pm$ 0.004 d, and slightly eccentric orbit $e=0.19 \pm 0.1$. We calculate a transit probability of 6.5% for the inner planet. The second planet has \msini\ = 0.4 \mjup\ with an orbital period of 32.0 $\pm 0.02$ d in a nearly circular orbit, and $e = 0.05 \pm 0.03$. The third planet has \msini\ = 0.53 \mjup\ with an orbital period of 432 $\pm 8$ d (1.18 years) and an eccentricity $e = 0.23 \pm 0.03$. This discovery adds to the number of super Earth mass planets with \msini < 12 \mearth\ that have been detected with Doppler surveys. We find that 56 $\pm 18$% super-Earths are members of multi-planet systems. This is certainly a lower limit because of observational detectability limits, yet significantly higher than the fraction of Jupiter mass exoplanets, $20 \pm 8$%, that are members of Doppler-detected, multi-planet systems.Comment: 11 figures, submitte to ApJ on Sept 10, 201

Design of the CHIRON high-resolution spectrometer at CTIO

Small telescopes coupled to high resolution spectrometers are powerful tools for Doppler planet searches. They allow for high cadence observations and flexible scheduling; yet there are few such facilities. We present an innovative and inexpensive design for CHIRON, a high resolution (R∼80.000) Echelle spectrometer for the 1.5m telescope at CTIO. Performance and throughput are very good, over the whole spectral range from 410 to 870nm, with a peak efficiency of 15% in the iodine absorption region. The spectrograph will be fibre-fed, and use an iodine cell for wavelength calibration. An image slicer permits a moderate beam size. We use commercially available, high performance optical components, which is key for quick and efficient implementation. We discuss the optical design, opto-mechanical tolerances and resulting image quality.7 page(s

Investigating spectrograph design parameters with the Yale Doppler diagnostic facility

The detection of earth-like exoplanets with the Doppler technique requires extreme precision spectrographs stable over timescales of years. The precision requirement of 10 cm/s is equivalent to a relative uncertainty of 3x10-10, and, with the typical dispersion of the Echelle spectrographs used for this purpose, translates to a shift of a few nanometers of the spectrum on the detector. Consequently, the instrument must be well understood and optimized in every component and detail. We describe the Yale Doppler diagnostic facility (YDDF), a dedicated bench mounted Echelle spectrograph in our lab at Yale University, which will be used to systematically study the influence of different components at this precision level. The spectrograph bench allows for a flexible optical configuration, high resolution and sampling, and wide spectral coverage. Further, we incorporated a turbulence and guiding simulator to realistically reproduce the situation at the telescope, enabling end-to-end tests of important parameters.10 page(s

Performance of the CHIRON high-resolution Echelle spectrograph

CHIRON is a fiber-fed Echelle spectrograph with observing modes for resolutions from 28,000 to 120,000, built primarily for measuring precise radial velocities (RVs). We present the instrument performance as determined during integration and commissioning. We discuss the PSF, the effect of glass inhomogeneity on the cross-dispersion prism, temperature stabilization, stability of the spectrum on the CCD, and detector characteristics. The RV precision is characterized, with an iodine cell or a ThAr lamp as the wavelength reference. Including all losses from the sky to the detector, the overall efficiency is about 6%; the dominant limitation is coupling losses into the fiber due to poor guiding.16 page(s