spectrointerferometry

Spectrointerferometry is a technique that combines spectroscopy with optical or infrared interferometry to obtain spatially resolved, wavelength-dependent information about astronomical sources. By dispersing light with a spectrograph and recording interferometric fringes across the spectrum, observers measure the complex visibility as a function of wavelength, including both amplitude and phase. This yields information about the spatial distribution of emission at each wavelength, often enabling insight into kinematics and structure within small angular scales. Differential measurements of visibility and phase across spectral features can reveal photocenter shifts and velocity fields in line-forming regions.

The method is implemented on long-baseline interferometers, where light from separate telescopes is coherently combined and dispersed spectrally. Observables typically include spectrally resolved visibilities and differential phases, and sometimes closure phases, as functions of wavelength. Differential phase, in particular, can track the relative motion of emission regions across a spectral line, providing astrometric information on velocity fields even when absolute phase is not directly recoverable. Instruments on facilities such as the Very Large Telescope Interferometer (VLTI) and other optical/infrared interferometers have been used for spectrointerferometry, with examples including historical and current instruments that provide various spectral resolutions.

Applications span a range of astrophysical contexts. Spectrointerferometry is used to study circumstellar disks around young stars and evolved stars, stellar surfaces, winds, jets, and binary systems. It enables probing of line-forming regions in H-alpha, Brackett series, CO bands, and other spectral features, yielding constraints on disk geometry, rotation, inflows and outflows, and companion positions. The technique complements imaging and spectroscopic data by delivering high-angular-resolution, wavelength-resolved information about the dynamics and structure of celestial objects.