Astral Imaging at Dogwood Ridge Observatory

Latitude: 37°48'51.0" N"
Longitude:78°23'41.0"W
Scottsville, Virginia 24590

 

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NGC650 / M76 - The Little Dumbbell Nebula

Image Information

Quoted From SEDS

Dicovered by Pierre Méchain in 1780.

Planetary Nebula M76 was discovered by Pierre Méchain on September 5, 1780, who reported it to Charles Messier, who observed it on October 21, 1780, determined its position and added it to his catalog. While Méchain found it to be a nebula without stars, Messier thought it was composed of small stars with some nebulosity, probably being fooled by foreground or background stars. Lord Rosse erroneously suspected to have detected some spiral structure in this nebula. In 1866, William Huggins, the pioneer of spectroscopy, found its spectrum to be gaseous, showing Nebulium lines. Pioneer astrophotographer Isaac Roberts found that this was not a double, but a single nebula, and first suspected it might be a broad ring seen edgewise. In 1918, Heber D. Curtis correctly classified it as a planetary nebula for the first time.

M76 is among the fainter Messier objects. It is known under the names Little Dumbbell Nebula (the most common), Cork Nebula, Butterfly Nebula, and Barbell Nebula, and it was given two NGC numbers as it was suspected to be a double nebula with two components in contact, a hypothesis brought up by William Herschel, who numbered the "second component" H I.193 on November 12, 1787. NGC 651 is the North following (East) part of the nebula.

The appearance of M76 resembles to some degree that of the Dumbbell Nebula M27. Most probably, the main body (the bar, or cork) is a bright and slightly elliptical ring we see edge-on, from only a few degrees off its equatorial plane. This ring seems to expand at about 42 km/sec. Along the axis perpendicular to this plane, the gas expands significantly more rapidly to form the lower surface brightness "wings" of the butterfly.

While the bright part of the nebula is of about 65 arc seconds in diameter (more accurately, the `cork' is about 42x87", the `wings' 157x87"), this nebula is surrounded by a faint halo covering a region of 290 arc seconds in diameter (Millikan, 1974); 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 mag 16.6 and a high temperature of some 60,000 K, which will probably cool down as a white dwarf over the coming tens of billions of years.

As usual for planetary nebulae, M76's visual magnitude is much brighter (9.6 according to Don Machholz' personal estimate, 10.1 according to Hynes; the present author thinks this is close to his own perception) than photographically (most sources agree on 12.2 mag photographically). This is due to the fact that most visual light is emitted in one spectral line, the green 5007 Angstrom forbidden line of doubly ionized oxygene, [O III] (see our Planetary Nebulae page).

As is not unusual for planetary nebulae, the distance is poorly known, with estimates between 1,700 and 15,000 light years (the latter value is from Kaufmann's Universe; Kenneth Glyn Jones has the value of 8,200). 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. (Our 3400 light years yield 0.68x1.44, 2.6, and 4.8 light years, while with Kenneth Glyn Jones' distance, the cork is 1.7x3.5, the wings 6.2, and the extensions 11.5 light years).

 

 

800 x 522       1600 x 1045

 

This image is compiled from 30 - 10 minute luminance images and 12 - 10 minutes each for the RGB data. A total of 11 hours of data used. All data was acquired using MaxImDl/CCD version 4.56. Images were reduced and saved in MaxIm. The data was then brought into CCDStack where bloom removal, alignment, and sigma reject was performed to produce the individual master channels by summing the luminance and median combining for the color. The RGB data was taken at bin 2x2 while the luminance data was bin 1x1. Back in MaxIm, the RGB was combined using G2V star calculations as a RGB image and double sized to match the luminance. The two resulting images were aligned and saved. Photoshop CS 2 was used for curves and levels on both images. The masters showed a gradient so I used Russell Croman's excellent GradientXTerminator program to remove the gradients before combining the luminance and RGB images. I saturated the color a bit after creating the LRGB image. The image data was collected over September 18-20.

Equipment and Location Information

Date September 18/20, 2006
Location Dogwood Ridge Observatory
Optics OGS10" RC @ f/9
Mount Astro Physics AP1200GTO
Camera SBIG ST10XME w/ AO7
Conditions Temperature middle  40's with very good  seeing. Transparency good to great.

    
  Last Modified :01/23/09 12:40 AM