  HD 141569 A is a pre-main sequence B9.5 Ve star surrounded by a prominent and
complex circumstellar disk, likely still in a transition stage from
protoplanetary to debris disk phase. Here, we present a new image of the third
inner disk component of HD 141569 A made in the L' band (3.8 micron) during the
commissioning of the vector vortex coronagraph recently installed in the
near-infrared imager and spectrograph NIRC2 behind the W.M. Keck Observatory
Keck II adaptive optics system. We used reference point spread function
subtraction, which reveals the innermost disk component from the inner working
distance of $\simeq 23$ AU and up to $\simeq 70$ AU. The spatial scale of our
detection roughly corresponds to the optical and near-infrared scattered light,
thermal Q, N and 8.6 micron PAH emission reported earlier. We also see an
outward progression in dust location from the L'-band to the H-band (VLT/SPHERE
image) to the visible (HST/STIS image), likely indicative of dust blowout. The
warm disk component is nested deep inside the two outer belts imaged by HST
NICMOS in 1999 (respectively at 406 and 245 AU). We fit our new L'-band image
and spectral energy distribution of HD 141569 A with the radiative transfer
code MCFOST. Our best-fit models favor pure olivine grains, and are consistent
with the composition of the outer belts. While our image shows a putative
very-faint point-like clump or source embedded in the inner disk, we did not
detect any true companion within the gap between the inner disk and the first
outer ring, at a sensitivity of a few Jupiter masses.
