CAFE: Calar Alto Fiber-fed Échelle spectrograph

Abstract

We present here CAFE, the Calar Alto Fiber-fed Échelle spectrograph, a new instrument built at the Centro Astronomico Hispano Alemán (CAHA). CAFE is a single-fiber, high-resolution (R ∼ 70 000) spectrograph, covering the wavelength range between 3650−9800 Å. It was built on the basis of the common design for Échelle spectrographs. Its main aim is to measure radial velocities of stellar objects up to V ∼ 13−14 mag with a precision as good as a few tens of m s −1 . To achieve this goal the design was simplified at maximum, removing all possible movable components, the central wavelength is fixed, as is the wavelength coverage; there is no filter wheel, etc. Particular care was taken with the thermal and mechanical stability. The instrument is fully operational and publically accessible at the 2.2 m telescope of the Calar Alto Observatory. In this article we describe (i) the design, summarizing its manufacturing phase; (ii) characterize the main properties of the instrument; (iii) describe the reduction pipeline; and (iv) show the results from the first light and commissioning runs. The preliminar results indicate that the instrument fulfills the specifications and can achieve the planned goals. In particular, the results show that the instrument is more efficient than anticipated, reaching a signalto-noise of ∼20 for a stellar object as faint as V ∼ 14.5 mag in ∼2700 s integration time. The instrument is a wonderful machine for exoplanetary research (by studying large samples of possible systems cotaining massive planets), galactic dynamics (highly precise radial velocities in moving groups or stellar associations), or astrochemistry.

2MASS 0213+3648 C: A wide T3 benchmark companion to an an active, old M dwarf binary

“…2MASS J0213+3648 AB was observed under poor conditions on 2014 November 11 UT using the Calar Alto Fibre-Fed Echelle spectrograph (CAFE; Aceituno et al 2013) on the 2.2-m telescope at Calar Alto Observatory in Almeria, Spain. A single 750 s exposure was obtained under clear skies with high, variable humidity and poor seeing (>2 arcsec).…”

WES—Weihai Echelle Spectrograph

“…The system efficiency is the ratio of photons incident at the top of the atmosphere at zenith and the detected photons on the spectrograph CCD (Aceituno et al 2013). This efficiency includes atmospheric transparency, throughput of all optical elements, and guiding losses.…”

Radial velocity confirmation of Kepler-91 b

“…High-resolution spectra were collected during the Kepler observing window of May−July 2012 with the Calar Alto Fiber-fed Echelle spectrograph (CAFE, Aceituno et al 2013), mounted on the 2.2 m telescope in Calar Alto Observatory (Almería, Spain). The instrument provides an average spectral resolution of around λ/Δλ = 63 000 across the whole spectral range between 4000 Å and 9500 Å, allowing nominal radial velocity accuracies at the level of few tens of meters per second for FGK stars.…”

“…Continuum and bias images were obtained for reduction purposes and thorium-argon (ThAr) arcs were acquired after each science spectrum to calibrate the wavelength accurately. All images were processed with the pipeline provided by the observatory (see Aceituno et al 2013, for further details on the reduction process). It uses a specific ThAr line list of several hundred features to achieve wavelength calibration with a precision at the 1 m/s level.…”