Area spectroscopy with ASPECT

ASPECT (which stands for Area SPECTrograph) is a software package which coordinates the acquisition of IPCS spectral data with telescope scanning to produce spectra of rectangular regions of the sky. The 3D data arrays it produces (`data cubes') have one wavelength dimension and (normally) two spatial dimensions, along and perpendicular to the spectrograph slit.

While Taurus produces data cubes for emission-line objects, ASPECT can be used for both absorption and emission-line work. The choice between the two depends on the size of the data cube required; generally Taurus is more efficient over a small spectral range at high resolution, while ASPECT is used when a wide wavelength coverage is needed.

ASPECT has several advantages over traditional methods of long-slit spectroscopy for extended objects, for example:

• Telescope offsetting is fast and accurate.
• Rapid scanning means that variations in transparency are averaged out.
• There is minimal dead time between telescope steps and between observations, and simultaneous recording and taking of data.
• When observing galaxies, the slit positions are evenly spaced rather than all being centred on the nucleus. This gives a more uniform spatial coverage and a higher signal-to-noise ratio in the faint outer parts.

ASPECT can also be used in a high-speed mode, without scanning the telescope, to take spectra of a rapidly varying object with high time resolution and no little or no dead time between scans.

Full details of the ASPECT package are given in AAO UM 15: ASPECT: Area spectroscopy using IPCS with AAT scanning.