We report the discovery of a star-forming loop around the young, Crab-like supernova remnant (SNR) G54.1ϩ0.3 using the AKARI infrared satellite. The loop consists of at least 11 young stellar objects (YSOs) embedded in a ringlike diffuse emission of radius ∼1Ј. 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] Ϫ [5.8] but significantly redder in [8] Ϫ [24], i.e., 0 ! [3.6] Ϫ [5.8] ! 1.2 and 5 ! [8] Ϫ [24] ! 9. Most of them have near-infrared counterparts in the 2MASS images, and some of them have an optical counterpart too. JHK s Their colors and magnitudes indicate that the YSOs are massive (տ10 ) pre-main-sequence stars at JHK M s , 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 premain-sequence stars with inner disks that have been destroyed. The confinement to a loop structure indicates that the YSOs are young, i.e., Շ2 Myr. We propose that their formation is triggered by the progenitor star of G54.1ϩ0.3, which has a mass of Շ15 . The triggering must have occurred near the end of the progenitor's M , life, possibly after it had evolved off the main sequence.

We present the results of near-infrared imaging and spectroscopic observations of the young core-collapse supernova remnant (SNR) G11.2À0.3. In the [Fe ii] 1.644 m image, we first discover long, clumpy [Fe ii] filaments within the radio shell of the SNR, together with some faint, knotty features in the interior of the remnant. The filaments are thick and roughly symmetric with respect to the northeast-southwest elongation axis of the central pulsar wind nebula. We have detected several [Fe ii] lines and a H i Br line toward the peak position of the bright southeastern [Fe ii] filament. The derived extinction is large (A V ¼ 13 mag), and it is the brightest [Fe ii] 1.644 m filament detected toward SNRs to date. By analyzing two [Fe ii] 1.644 m images obtained 2.2 yr apart, we detect a proper motion corresponding to an expansion rate of 0:035 00 AE 0:013 00 yr À1 (830 AE 310 km s À1 ). In addition to the [Fe ii] features, we also discover two small H 2 2.122 m filaments. One is bright and along the southeastern boundary of the radio shell, while the other is faint and just outside its northeastern boundary. We have detected the H 2 (2Y1) S(3) line toward the former filament and derive an excitation temperature of 2100 K. We suggest that the H 2 filaments are dense clumps in a presupernova circumstellar wind swept up by the SNR shock, while the [Fe ii] filaments are probably composed of both shocked wind material and shocked supernova (SN) ejecta. The distribution of [Fe ii] filaments may indicate that the SN explosion in G11.2À0.3 was asymmetric, as in Cassiopeia A. Our results support the suggestion that G11.2À0.3 is a remnant of a SN IIL/b interacting with a dense red supergiant wind.

We present the results of AKARI observations of the O-rich supernova remnant G292.0+1.8 using six IRC and four FIS bands covering 2.7-26.5 µm and 50-180 µm, respectively. The AKARI images show two prominent structures; a bright equatorial ring structure along the east-west direction and an outer elliptical shell structure surrounding the remnant. The equatorial ring structure is clumpy and incomplete with its western end opened. The outer shell is almost complete and slightly squeezed along the north-south direction. The central position of the outer shell is ∼ 1 ′ northwest from the embedded pulsar and coincides with the center of the equatorial ring structure. In the northen and southwestern regions, there is also faint emission with a sharp boundary beyond the bright

We present the results of near-infrared [Fe II] and H 2 line imaging and spectroscopic observations of the supernova remnant 3C 396 using the Palomar 5 m Hale telescope. We detect long, filamentary [Fe II] emission delineating the inner edge of the radio emission in the western boundary of the remnant in imaging observations, together with a bright [Fe II] emission clump close to the remnant center. There appears to be faint, diffuse [Fe II] emission between the central clump and the western filamentary emission. The spectroscopic observations determine the expansion velocity of the central clump to be ∼ 56 km s −1 . This is far smaller than the expansion velocity of 3C 396 obtained from X-ray observations, implying the inhomogeneity of the ambient medium. The electron number density of the [Fe II] emission gas is ≤ 2,000 cm −3 . The H 2 line emission, on the other hand, lies slightly outside the filamentary [Fe II] emission in the western boundary, and forms a rather straight filament. We suggest that the [Fe II] emission represents dense clumps in the wind material from the red supergiant phase of a Type IIL/b progenitor of 3C 396 which have been swept up by the 1 Here we only consider [Fe II] emission from the radiative SNR shocks, excluding [Fe II] emission from the supernova ejecta (e.g., Moon at al. 2008)