Messier 27 – the Dumbbell Nebula

Space is full of interesting objects. We often think of stars and galaxies, but there are other kinds of distant objects that have been discovered over the past 250 years. In 1764 the French astronomer Charles Messier found a whole new class of objects. He was hunting for comets, and had started to create a list of things in the sky that might look a little like a comet, but which didn’t move. The list, now known as the Messier Objects, was originally intended to help him and others find comets by confirming which things viewed though telescopes weren’t actually comets.

Nearly 250 years ago, he turned his telescope to the sky and found something he catalogued as the 27th object in his list. For some time the telescopes available showed objects like M27 as looking a bit like the distant, outer planets in our own solar system, and they picked up the general name “Planetary Nebulae.” Just what they were wasn’t explained for another century, when William Huggins was able to look at the light from one of these fuzzy, roundish objects. Through spectroscopy he realized that he wasn’t looking at light being reflected from an object like a planet, or light from a hot luminous object like a star, but light being generated by excited gasses.

Planetary nebulae are now known to be the spectacular remnants of a star that is throwing off vast quantities of gas late in its life. Some of them appear to be shedding multiple shells of gas. In the case of Messier 27, also called the Dumbbell Nebula, researchers have estimated that the bright gas we can see with telescopes likely was emitted from a star in the centre of the object about 10,000 years ago.

In early May 2013 I decided to try using the University of Iowa’s Rigel telescope at the Winer Observatory, southeast of Tucson, Arizona (http://www.winer.org/) to image M27. This telescope can be used by anyone over the Internet on the Sierra Stars Observatory Network (http://www.sierrastars.com), and I’ve been experimenting with it for the past few weeks.

To take an image of Messier 27 I first programmed the telescope to take a single shot of the nebula for 150 seconds, to get a feeling for exposures, which the telescope captured early on the morning of 7 May 2013. M27 is quite a bright object, and many people have fun finding it with a small telescope. It has a magnitude of 7.5, meaning that it’s just below the limit of objects you can expect to see on a dark sky with your eyes, but it’s well within the expected range of objects to see with a modest amateur telescope or binoculars.  It’s in the Vulpecula constellation (“the little fox”) just south of Cygnus, the swan. The 150 second exposure wasn’t overexposed for the nebula, and in fact looked a bit faint, so I decided to take a series of 300 second images. I set the telescope to take two 300 second exposures with no filter, and two more 300 second exposures with each of the red, green, and blue filters on the system. The images were captured early on the morning of Thursday 9 May 2013. Here’s the result, after combining the “black and white” frames first (“Luminance”) and then preparing the colour information (“RGB”), using free software called Fitswork4:

M27 imaged with Rigel

Messier 27, the Dumbbell Nebular, imaged with the 37 cm Rigel telescope owned by the University of Iowa, located in Arizona (the “Iowa Robotic Telescope Facility” or IRTF). The image was prepared from a series of monochrome pictures taken through colour filters (the “LRGB” process). combined with Fitswork4 and adjusted a bit with Adobe Photoshop Elements.

The Dumbbell Nebula sits about 1,360 light years away from earth, and is about one light-year across. It’s also notable because of the star that remains at its centre: it’s the largest-known white dwarf star.

This first try at M27 is encouraging, but I wasn’t able to get good registration, or alignment, of the red, green, and blue frames. As a result the colours I was able to produce in the combined image are a bit off. If I can improve the registration process the image should be a bit better. I need to do some more work on my “workflow” to process image files once I have them.

For more information on M27, check out Wikipedia: http://en.wikipedia.org/wiki/Messier_27

Copyright © 2013 David Allan Galbraith
Advertisements