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Physics & Astronomy Department

Astr110 Photography Projects, Fall 2006

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Little Dumbbell Nebula (M76), Phil DeBoer

M76

Planetary Nebula M76 was first discovered by Pierre Mechain on September 5, 1780. It is located in the constellation Perseus. It is also recognized by the title “Little Dumbbell Nebula.” Mechain found it to be a nebula without stars. A nebula is a diffuse mass of interstellar dust or gas or both, visible as luminous patches or areas of darkness depending on the way the mass absorbs or reflects incident radiation. In 1866, William Huggins, found its spectrum to be gaseous, showing Nebulium lines. Pioneer astrophotographer Isaac Roberts found that it was a single nebula, as opposed to a double nebula. It wasn’t until 1918, when Heber D. Curtis correctly classified it as a planetary nebula for the first time.

The main body (the bar, or cork) is commonly believed to be a bright and slightly elliptical ring we see edge-on. This ring seems to expand at about 42 km/sec. The lower surface brightness “wings” of the butterfly are formed by rapidly expanding gas. While the bright part of the nebula (the ‘cork’ and ‘wings’) is of about 65 arc seconds in diameter, this nebula is surrounded by a faint halo covering a region of 290 arc seconds in diameter; this material was probably ejected in the form of stellar winds from the central star when it was still in the Red Giant phase of evolution. Today the central star is of magnitude 16.6 and a high temperature of some 60,000 K, as is noted by its blue color. At this temperature level, it also produces ultraviolet light which is why the object appears to glow. The red and green tints inform us that the nebula is made of Hydrogen and Oxygen gases. The distance to M76 is poorly known, with estimates between 1,700 and 15,000 light years. Accordingly, the true dimensions of the cork is between 0.34x0.72 and 3.1x6.4 light years, while the wings extend up to between 1.3 and 11.3 light years, and the faint halo reaches out to between 2.4 and 21 light years. I estimate the linear size of M76 to be 7.28 light years.

References:
Frommert, Hartmut. "Messier 76." 16 Nov. 2006 http://seds.lpl.arizona.edu/messier/m/m076.html

"Little Dumbbell Nebula." Wikipedia. 16 Nov. 2006 <http://en.wikipedia.org/wiki/Little_Dumbbell_Nebula>.

Right Ascension (J2000) 1:42:45
Declination (J2000) +51:36:11
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 300 seconds for each (B,V,R,C)
Date observed October 19, 2006 for each (B,V,R,C)