AMBER, the near-infrared spectro-interferometric three-telescope VLTI instrument

Abstract

Context. Optical long-baseline interferometry is moving a crucial step forward with the advent of general-user scientific instruments that equip large aperture and hectometric baseline facilities, such as the Very Large Telescope Interferometer (VLTI). Aims. AMBER is one of the VLTI instruments that combines up to three beams with low, moderate and high spectral resolutions in order to provide milli-arcsecond spatial resolution for compact astrophysical sources in the near-infrared wavelength domain. Its main specifications are based on three key programs on young stellar objects, active galactic nuclei central regions, masses, and spectra of hot extra-solar planets. Methods. These key science goals led to scientific specifications, which were used to propose and then validate the instrument concept. AMBER uses single-mode fibers to filter the entrance signal and to reach highly accurate, multiaxial three-beam combination, yielding three baselines and a closure phase, three spectral dispersive elements, and specific self-calibration procedures. Results. The AMBER measurements yield spectrally dispersed calibrated visibilities, color-differential complex visibilities, and a closure phase allows astronomers to contemplate rudimentary imaging and highly accurate visibility and phase differential measurements. AMBER was installed in 2004 at the Paranal Observatory. We describe here the present implementation of the instrument in the configuration with which the astronomical community can access it. Conclusions. After two years of commissioning tests and preliminary observations, AMBER has produced its first refereed publications, allowing assessment of its scientific potential.

Resolving the inner disk of UX Orionis

“…1; red points). The AMBER instrument is a threebeam combiner that records spectrally dispersed three-beam interferograms (Petrov et al 2007). We recorded H-and K-band interferograms in the low spectral resolution mode (R ∼ 35) with a detector integration time (DIT) of 50 ms. For data reduction, we employed the software library amdlib v3.0.5 1 .…”

The variable stellar wind of Rigel probed at high spatial and spectral resolution

“…Rigel was observed at the ESO Paranal Observatory with the Astronomical Multi BEam Recombiner (hereafter AMBER), the near-infrared instrument of the VLTI (Petrov et al 2007). AMBER operates in the J, H, and K bands with spectral resolutions of 35, 1500, and 12000, combining either three 8.2-m Unit Telescopes (UTs) or 1.8-m Auxiliary Telescopes (ATs).…”

“…For the first time, direct measurements of the spatial extension of the circumstellar structures as function of wavelength across a wind-sensitive spectral line like Brγ become feasible. Currently only two instruments provide spectrally dispersed interferometric observables with a spectral resolution power larger than R = 10 000 and a spatial resolution around a milliarcsecond: the VEGA visible recombiner at CHARA (Mourard et al 2009) and the AMBER near-IR recombiner (Petrov et al 2007) at the VLTI. These instruments are well suited to study the wind activity of the brightest BA supergiants in our vicinity in wind-sensitive spectral lines such as Hα or Brγ (Chesneau et al 2010).…”

Interferometric observations of rapidly rotating stars

“…Sufficiently high-resolution dispersion, such as the R ∼ 12,000 available with the VLTI AMBER instrument (Petrov et al 2007), make it possible to examine spectral line profiles in a spatially resolved or even imaged sense. AMBER has already been used for spectro-interferometric observations of the Herbig Be star MWC 297 as this high spectral resolution (Weigelt et al 2011).…”