We present new optical emission-line images of the young supernova remnant ( SNR ) 1E 0102–7219 ( hereafter E0102 ) in the Small Magellanic Cloud obtained with the Hubble Space Telescope ( HST ) Advanced Camera for Surveys ( ACS ) .
E0102 is a member of the oxygen-rich class of SNRs showing strong oxygen , neon , and other metal-line emissions in its optical and X-ray spectra , and an absence of hydrogen and helium .
The progenitor of E0102 may have been a Wolf-Rayet star that underwent considerable mass loss prior to exploding as a Type Ib/c or IIL/b supernova .
The ejecta in this SNR are generally fast-moving ( V > 1000 km s ^ { -1 } ) and emit as they are compressed and heated in the reverse shock .
In 2003 , we obtained optical [ O III ] , H \alpha , and continuum images with the ACS Wide Field Camera .
The [ O III ] image through the F475W filter captures the full velocity range of the ejecta , and shows considerable high-velocity emission projected in the middle of the SNR that was Doppler-shifted out of the narrow F502N bandpass of a previous Wide Field and Planetary Camera 2 image from 1995 .
Using these two epochs separated by \sim 8.5 years , we measure the transverse expansion of the ejecta around the outer rim in this SNR for the first time at visible wavelengths .
From proper-motion measurements of 12 ejecta filaments , we estimate a mean expansion velocity for the bright ejecta of \sim 2000 km s ^ { -1 } and an inferred kinematic age for the SNR of \sim 2050 \pm 600 years .
The age we derive from HST data is about twice that inferred by Hughes et al .
( 2000 , ApJ , 543 , L61 ) from X-ray data , though our 1- \sigma error bars overlap .
Our proper-motion age is consistent with an independent optical kinematic age derived by Eriksen et al .
( 2003 , AIPC , 565 , 419 ) using spatially resolved [ O III ] radial-velocity data .
We derive an expansion center that lies very close to conspicuous X-ray and radio hotspots , which could indicate the presence of a compact remnant ( neutron star or black hole ) .