Cepheid Variables in M100

A color view of M100

Below is an image of the galaxy called M100, or object 100 in the famed Messier catalog. M100 is a member of the Virgo cluster, the nearest galaxy cluster beyond our Local Group.

Several observing programs within the HST Key Project on the Extragalactic Distance Scale focused on determining the distance to individual galaxies within the Virgo Cluster. Being one of the largest and most spectacular galaxies within the cluster, M100 became one of the target galaxies. The Principle Investigator for the M100 proposal was Dr. Jeremy R. Mould of Caltech, now at Mount Stromlo and Siding Spring Observatories in Sydney, Australia.

You will use the actual HST images obtained by Dr. Mould and his colleagues to estimate the distance to M100. You will do this by discovering Cepheid variable stars in the galaxy.

Caption: An image of the spiral galaxy M100, taken by the Hubble Space Telescope, using the electronic``Wide Field and Planetary Camera 2,'' or WFPC2 (pronouned ``whiff pick two''). When HST was launched in April 1990, it contained the first generation imaging camera WF/PC-1. Astronauts replaced WF/PC-1 with the second generation camera, WFPC2, during the December 1993 HST servicing mission. This image was taken on December 31, 1993, shortly after the servicing mission. Image credit: J. Trauger, JPL, and NASA.

WFPC2 is comprised of 4 electronic detector arrays, or "chips." If you look carefully at the image above, you can see that it appears to be made up of four squares, or "quadrants." The upper right quadrant (quadrant 1) is smaller than the other three, and has higher image resolution. Quadrant 1 is the Planetary Camera, while the other three quadrants comprise the Wide Field Camera. Each detector chip is composed of an 800x800 square array of detectors called "pixels." The chips are identical; the size and resolution of the planetary camera image results from optical elements in the light path.

More pictures and information on Cepheid variables in M100 may be viewed on related STScI Web pages.

On to The HST images of M100 used for the Cepheid hunt

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