A Massive-star Forming Infrared Loop around the Crab-like Supernova Remnant G54.1+0.3: Post Main-sequence Triggered Star Formation?

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 11 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 M⊙) 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 early 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 M⊙. The triggering must have occurred near the end of the progenitor’s life, possibly after it had evolved off the main sequence. Subject headings: ISM: individual (G54.1+0.3) — infrared: stars — stars: formation — stars: premain-sequence — supernovae: general — supernova remnants