  The Large Ultraviolet / Optical / Infrared Surveyor (LUVOIR) is one of four
large mission concepts currently undergoing community study for consideration
by the 2020 Astronomy and Astrophysics Decadal Survey. The LUVOIR Ultraviolet
Multi-Object Spectrograph, LUMOS, is being designed to support all of the UV
science requirements of LUVOIR, from exoplanet host star characterization to
tomography of circumgalactic halos to water plumes on outer solar system
satellites. LUMOS offers point source and multi-object spectroscopy across the
UV bandpass, with multiple resolution modes to support different science goals.
The instrument will provide low (R = 8,000-18,000) and medium (R =
30,000-65,000) resolution modes across the far-ultraviolet (FUV: 100-200 nm)
and near-ultraviolet (NUV: 200-400 nm) windows, and a very low resolution mode
(R = 500) for spectroscopic investigations of extremely faint objects in the
FUV. Imaging spectroscopy will be accomplished over a 3 x 1.6 arcminute
field-of-view by employing holographically-ruled diffraction gratings to
control optical aberrations, microshutter arrays (MSA), advanced optical
coatings for high-throughput in the FUV, and next generation large-format
photon-counting detectors. The spectroscopic capabilities of LUMOS are
augmented by an FUV imaging channel (100-200nm, 13 milliarcsecond angular
resolution, 2 x 2 arcminute field-of-view) that will employ a complement of
narrow and medium-band filters. We present an overview of LUMOS' observing
modes and estimated performance curves for effective area, spectral resolution,
and imaging performance. Example "LUMOS 100-hour Highlights" observing programs
are presented to demonstrate the potential power of LUVOIR's ultraviolet
spectroscopic capabilities.
