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A portion of the open cluster M67, located in Cancer

Best Observing Season: Spring Level: Introductory Learning Goals: The student will study the properties of some objects in the constellation Cancer. Terminology: barred spiral, extragalactic, irregular galaxy, planetary nebula Software: MaxIm, Megastar Archive Image Directory: sprcon Archive Image List: *.fts, cancer.gif References: Eicher. The Universe From Your Backyard; Levy, David. 1989, Observing Variable Stars (University Press, Cambridge)

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Background and Theory

The seemingly sparse region in the spring sky between Leo and Gemini contains Cancer the Crab.  (If you use your imagination, you can just make out the crab’s claws marked by the two bright stars, and its body comprised of the four central stars).  Viewing this piece of the universe with the unaided eye may seem uninspiring, with merely a few faint stars and the Beehive open star cluster interrupting the black void.  Within this void, however, exists a cache of deep sky objects.  The region contains several bright open clusters, such as the Beehive (which spans an area of 95 arcminutes, or three times the moon’s diameter!).  You will also find an assortment of galaxies, from spirals to irregulars, a planetary nebula and two irregular variable stars, SY Cnc and YZ Cnc.

Procedure

Observing

1.      Make an observing file which contains the objects in Table 1 below.  See the Appendix (Guide for Remote Observers) for details.

2.      Observe the objects in the table with the filters and approximate exposure times listed.  The list consists of three open clusters, several barred spiral, spiral, irregular galaxies, a planetary nebula, and two irregular variable stars.  Photometry of the variable stars also requires observations of at least one star with a known magnitude.  (For a finding chart, complete with calibrator star, see cnc-ref.jpg in varstars.)

Image Analysis

1.      Retrieve the finding chart from disk or construct your own using MegaStar. 

2.      Examine your images and identify the open clusters, galaxy types, and the nebula.  How many stars do you think are in these open clusters?  Make a guess based on your images, then check with your textbook.  What could be causing this stellar association?

3.      Galaxies are so far away that it takes many years for the light we see today to reach us.  For example, NGC2713 lies 75 Megaparsecs (75 million parsecs) away.  To convert to light years, multiply the distance in parsecs by 3.26 light years per parsec.  How long did it take for the light from the galaxies in Table 2 to reach us?

4.      Using your images of the planetary nebula NGC2610, do one of the following:

5.      Compare your B and V images of the planetary nebula NGC2610.  What changes do you notice between the two filters?  What could be causing this?

6.      Make a tri-color image of NGC2610 (with B, V, and R filters) using MaxIm. Remember, the three images must be aligned first. Consult your instructor for directions.  What does this composite image tell you about the light coming from the nebula?