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CfA Press Release
 

HIGH RESOLUTION DIGITAL IMAGE OF THE ENTIRE ANDROMEDA GALAXY PRODUCED

CAMBRIDGE, MA -- The Andromeda Galaxy, the nearest major galaxy to theMilky Way, has been digitially imaged in its entirety using advancedelectronic detectors to produce a large mosaic of unprecedentedresolution and clarity by Somak Raychaudhury of theHarvard-Smithsonian Center for Astrophysics, Puragra Guhathakurta ofSpace Telescope Science Institute and Andreas Berlind of PrincetonUniversity Observatory.

The giant image, measuring more that 4 feet by 6 feet, was unveiledfor the first time at the American Astronomical Society meeting todayin Minneapolis, Minnesota. Imaged at near-infrared wavelengths, thephotomosaic has a resolution of 2 arcseconds and has beenelectronically processed to remove obscuring foreground stars in ourown galaxy. The resulting image allows a detailed study of thedistribution of stars in Andromeda.

At a distance of two million light years from Earth, Andromeda gives astronomers a unique opportunity to study a system similar to our own --in size, shape, and morphology--at very close quarters. In fact, Andromeda, the Milky Way, and their respective satellite dwarf galaxies form a small cluster known as the "Local Group."

However, Andromeda's close proximity also means it has a very large angular size on the sky. Its major axis is over three degrees long, or six times the size of the full Moon. This makes it difficult to image the Andromeda galaxy at full resolution with digital CCD cameras, since most CCD cameras on "meter-class" telescopes have a field of view of about 1/10th of a degree, or about 1/30 the size of the galaxy's longest axis. Moreover, the full field of Andromeda is contaminated by hundreds of bright foreground stars in our own galaxy. Eliminating these stars digitally requires arcsecond resolution.

To image the entire galaxy at this high resolution, the three astronomers used a Tektronix Charge-Coupled Device (CCD) Camera with 2048x2048 picture elements, on the Burrell Schmidt Telescope of Case Western Reserve University's Warner and Swasey Observatory at Kitt Peak National Observatory, Arizona. This telescope has a 0.9-meter primary mirror with a 0.6-m corrector.

The resulting composite digital image of the Andromeda galaxy isreally a computer-generated mosaic of 41 individual overlappingsnapshots, each with a field of view of about a degree, at aresolution of 2 arcseconds, taken with a near-infrared (I) filter,over three nights of observation in November 1992.

Because each image has a generous overlap with its neighboring images, they could be matched with each other to a high level of accuracy. The final composite covers 3 by 4 degrees, which is more than the visible region of the Andromeda galaxy, and has a resolution that allows both detailed photometric studies and the identification and removal of contaminating foreground stars.

 
 
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