Glossary for ALMA Data Processing

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  • Amplitude: modulus of a visibility point, measured on a flux density scale (usually in Jy)
  • Beam:
    • Primary beam: the angular sensitivity pattern on the sky of each individual antenna in the array. It defines the field of view for a given pointing in the sky. The primary beam varies as ~1.2([math]\displaystyle{ \lambda }[/math]/D), where [math]\displaystyle{ \lambda }[/math] is the observational wavelength and D is the antenna diameter.
    • Synthesized beam (beam): the effective angular resolution (~psf) of an interferometric array, for a given frequency and declination.

  • Calibrated data
  • Calibration
  • Calibration table
  • Clean
  • Continuum
  • Data Package
  • Doppler tracking
  • Execution block
  • Image, Image cube
  • Imaging
  • Mask, clean mask
  • Measurement set
  • Quality Assurance
  • Phase
  • Scan
  • Scheduling block
  • Spectral frame
  • Spectral window' : subrange of frequencies. In ALMA Cycle 0 observations, each execution block contains at most four spectral windows

  • u,v distance: distance of a point in the Fourier plane (coordinate Ux, Vx) to the phase center in the Fourier plane (coordinates 0,0). The (u,v) distance of a visibility corresponds to the projected length of the corresponding baseline. It is s expressed either in meters or wavelength number (usually k[math]\displaystyle{ \lambda }[/math]). Generally speaking, visibilities with a short (u,v) distance contain information on large angular scales on the sky.

  • 'u,v plane', Fourier plane'

  • Visibility: the cross-correlation product of signals from two antennas. The data collected from the correlator in an interferometer consists of visibilities. They are complex numbers, whose argument is the phase and modulus is the amplitude. Visibilities coordinates are expressed in the Fourier Plane.