Instrument Design

FALCON is intended to replace the Inamori Magellan Areal Camera and Spectrograph (IMACS), which has been the workhorse instrument on the 6.5 meter Magellan Baade telescope since 2003. Advances in optics, detectors, and spectrograph design paradigms present an opportunity to expand on the great success of IMACS and extend the limits of scientific research for the Magellan community in the 2030s and beyond.

FALCON may operate as a spectrograph in wide field multi-object, single slit, or integral field modes.  In order to control the sizes of optics in the spectrograph cameras, the telescope field of view is split in half just past a field lens. Each half is then separated by wavelength using dichroic beamsplitters into four arms, each optimized individually. Grisms may be selected to provide full coverage optimized from 330 to 1050 nm for all field positions, or to split the wavelength coverage in half while doubling the spectral resolving power. Full wavelength coverage can then be recovered by collecting spectra with two different grisms.

By removing the field splitting mirror, a ninth arm is enabled for broadband or narrowband imaging, or low resolution spectroscopy using a zero deviation prism.

The field of view of FALCON is somewhat smaller than that of IMACS, but in moderate resolution mode, targets across FALCON's full field of view may be selected with no compromise on wavelength coverage.

In addition to the dispersion inherent to the grism designs, spectral resolving power can be set by adjusting the widths of slits cut into the aperture mask at the telescope's focal surface. The following tables describes the wavelength coverage and sample resolving powers for the four spectroscopic channels.

The FALCON optics were designed with the rigorous and demanding metric to avoid degrading the 10th percentile best seeing at Las Campanas by more than 10%.  The following plot shows that this is achieved except for the very bluest wavelengths. The theoretical performance of IMACS using the f/2 camera is shown for comparison.

One of the driving factors of the FALCON design is to maximize throughput across the full wavelength range. The efficiency from the slits to the detector are estimated in the following figure.