  We report the discovery of a star-forming loop around the young, Crab-like
supernova remnant (SNR) G54.1+0.3 using the AKARI infrared satellite. The loop
consists of at least eleven young stellar objects (YSOs) embedded in a
ring-like diffuse emission of radius ~1'. The YSOs are bright in the
mid-infrared and are also visible in the Spitzer Space Telescope Galactic plane
survey images. Their Spitzer colors are similar to those of class II YSOs in
[3.6]-[5.8] but significantly redder in [8]-[24], i.e., 0<[3.6]-[5.8]<1.2 and
5<[8]-[24]<9. Most of them have near-infrared counterparts in the 2MASS JHKs
images, and some of them have an optical counterpart too. Their JHKs colors and
magnitudes indicate that the YSOs are massive (<= 10 Msun) pre-main-sequence
stars at the same distance to the SNR, i.e., 8 kpc, which supports the
association of the star-forming loop with the SNR. The dereddened spectral
energy distributions are similar to eraly Herbig Be stars, which are early
B-type pre-main-sequence stars with inner disks that have been destroyed. The
confinement to a loop structure indicates that the YSOs are young, i.e., <= 2
Myr. We propose that their formation is triggered by the progenitor star of
G54.1+0.3, which has a mass of <= 15 Msun. The triggering must have occurred
near the end of the progenitor's life, possibly after it had evolved off the
main sequence.
