Orion Nebula

February 23, 2007

Orion Nebula - First Light with Physics Department's New CCD Camera

The Physics Department has recently obtained a research-grade CCD camera, which greatlhy enhances the observational astronomy program at Warren Wilson College. The camera is funded with a grant from the American Astronomical Society.

Before obtaining any photographs, we had to balance the telescope with counterweights to compensate the increased weight of the new camera; install filters for Red, Green, and Blue, and an automatic filter holder and rotator; and adjust the focus of the telescope on terrestrial objects. This elaborate procedure enabled us to photograph stars on the first night out. Success was achieved on the evening of Feb. 21, 2007. George Keel helped set-up and take in the telescope and computer. Anesh Prasai helped adjust the color balance while for the first image of a celestial object.

The Orion Nebula (also known as M42) consists of a huge cloud of dust and hydrogen. In the bright center some very young massive stars that have recently formed from the gravitational collapse of the hydrogen and dust in the clouds. These young, large stars are extremly hot (over 30,000 K) and emit most of their energy in the ultraviolet, which is invisible. The ultraviolet light, however, lights up the large hydrogen cloud, mainly through fluorescence. The hydrogen atoms in the cloud absorb the ultraviolet light, then the hydrogen re-radiates the energy as a series of visible wavelengths characteristic of hydrogen. The fluorescence makes the Orion Nebula visible. The location of the Orion Nebula, and an older photograph, is displayed in the PPOW for April 7, 2006 with a description written by Heather Aziz.

The new CCD camera (a special digital camera used for astronomy) is a tremendous improvement over our previous cameras at WWC. The CCD detector is refrigerated to about -30 deg C, thus enabling long exposure times with a minimum of

background noise. The background noise is a major limitation to conventional digital cameras when taking long exposures. The photograph of the Orion Nebula was made with 5 10 sec exposures in each of the primary colors, then the colors were combined with software to give the color photograph. This camera also has a tremendous dynamic range. The top image appears to be overexposed in the brightest regions of the nebula. However, by resetting the contrast on the same digital image, the image reveals the bright stars in the center of the nebula. See the image at right. If you look closely at the image, you can a small cluster of 4 stars very close together in the image center. This small cluster is called the "Trapezium" cluster (the shape forms a trapezoid). These are the ultra hot large stars (about 1500 LY distant) responsible for the fluorescence of the nebula.

The main function of the new CCD camera will be to study cataclysmic variable stars. Cataclysmic variable stars consist of two stars so close together that they are almost in contact. In fact one of the stars in a CV system "sucks" material from the other. These effects make the CV fluctuate drastically in brightness on a fairly rapid time scale. The new camera will enable students to record a long succession of images in one evening to plot the light curves. George Keel has been successfully observing cataclysmic variables with a much more primative camera in the fall of 2006. More later.

The help of the grant from the American Astronomical Society Small Grants Program is much appreciated.