The HST images of M100 for the Cepheid variable hunt
Although beautiful, the color image of M100 above is not what will be
used for our Cepheid hunt. That image was taken simply to test the
newly-corrected optics of the Hubble Space Telescope. To hunt for
Cepheids, several exposures of the same region must be taken over the
course of months to look for the brightness variations characteristic
of Cepheid variables.
Although the color image of M100 was centered on the galactic nucleus
at least partially for artistic reasons, that is not the best
alignment for Cepheid hunting. The nucleus is so crowded and bright
it would be difficult to detect Cepheids in that region. Including
the bright nucleus would also increase the contrast in the images,
making it more difficult to do the long exposures needed to examine
faint regions. It is much wiser to minimize the amount of nucleus in
the images. Dr. Mould and his colleagues chose to position WFPC2 as
Orientation of WFPC2 displayed on a ground-based image of M100
taken by Dr. R. Peletier at the prime focus of the INT telescope in La
Palma (adapted from Figure 1 in Ferrarese et al., 1996). The
four chips are labeled PC1 (the planetary camera), WF2, WF3 and WF4
(the three wide-field cameras). Note that the HST observers chose to
place the high-resolution planetary camera on the faint outskirts of
the galaxy, and that very little of the galactic nucleus is imaged.
Click on PC1, WF2, WF3 or WF4 to view a large-format Hubble Space
telescope image taken by that chip.
We'll have to zoom in to a scale where stars are easily distinguished
in order to look for Cepheids. In this lab, we will only look for
Cepheids in WF4.
On to Looking for variable phenomena
Back to A color view of M100
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