Limiting infrared magnitudes for NIR Doppler imaging. Panels a)–d) show magnitude vs. spectral type for J, H, K, and L bands for a telescope either 3.5 m (dash-dotted), 8 m (dashed), or 30 m (solid) in diameter. Points indicate objects with measured rotational periods, photometric variability, and/or v sin i. The best potential targets for Doppler imaging are indicated with black outlines, which have v sin i ≥ 15 km s^-1 and/or vary photometrically by ≥2%. As described in Sect. 3 these limits assume Doppler imaging in only a single NIR band; observing slightly fainter objects should be feasible with broader wavelength coverage. Rhombus symbols indicate known directly-imaged giant exoplanets: a small number of these may be amenable to Doppler imaging with future large-aperture telescopes.