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SN 1006 * HST * ACS * WFC

ACS - F658 N (H-alpha+[N II])
WFPC2 - F439W (B)
WFPC2 - F555W (V)
WFPC2 - F814W (I)

Mind the Gap

A small section of the image was inserted manually, replaced or "cloned" from nearby regions. This was done to fill in and complete the part of the supernova remnant filament seen in the image. This small section of the original ACS image is blank because there is a narrow (about 1.5 arcseconds or 30 pixels) gap between the two CCD detector chips comprising the ACS WFC instrument. Because the filament appears quite smooth and predictable in this region, and the nearby background is blank, it was justifiable to do this instead of cropping the image and losing much of the interesting, beautiful structure of the SNR.

Although the WFPC2 images do not include a gap, the nebula does not appear in those images since the exposures are much shorter in order to image the stars in three colors. However, the stars that are missing from the ACS image do appear in the WFPC2 images, so no stars were inserted into the ACS gap.

Above is a small section of the original ACS H-alpha image showing the SNR filament and the ACS/WFC chip gap, at center is the filled version of the image, and at bottom is the color image combined from the ACS and WFPC2 data.

Graphic courtesy of Z. Levay (STScI)