M27 Dumbbell Nebula

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2012/05/28 - Collimation was a bit off, I really should spend some time on that. Another narrowband image, I enjoy using these in my light polluted backyard. Seeing was not so good, still got some nice data.

The Dumbbell Nebula is a planetary nebula in the constellation Vulpecula, at a distance of about 1,360 light years. This object was the first planetary nebula to be discovered; by Charles Messier in 1764. At its brightness of visual magnitude 7.5 and its diameter of about 8 arcminutes, it is easily visible in binoculars, and a popular observing target in amateur telescopes.

This PN appears to be shaped like an prolate spheroid and is viewed from our perspective along the plane of its equator. In 1992, Moreno-Corral et al. computed that the rate of expansion in the plane of the sky of this PN was no more than 2″.3 per century. From this, an upper limit to the age of 14,600 yr may be determined. In 1970, Bohuski, Smith, and Weedman found an expansion velocity of 31 km/s. Given its semi-minor axis radius of 1.01 ly, this implies that the kinematic age of the nebula is some 9,800 years.

Like many nearby planetary nebulae, the Dumbbell contains knots. Its central region is marked by a pattern of dark and bright cusped knots and their associated dark tails (see picture). The knots vary in appearance from symmetric objects with tails to rather irregular tail-less objects. Similarly to the Helix Nebula and the Eskimo Nebula, the heads of the knots have bright cusps which are local photoionization fronts.

The central star, a white dwarf, is estimated to have a radius which is 0.055 ± 0.02 R which gives it a size larger than any other known white dwarf. The central star mass was estimated in 1999 by Napiwotzki to be 0.56 ± 0.01 M.


Object information
Name : M27 Dumbbell Nebula
Type : Planetary nebula
Constellation : Vulpecula
Distance : 1.360 light-year
Apparent dimensions : 8'.0 x 5'.6
Apparent magnitude : 7.50

Image information
Image date : 2012/05/28
Right ascension : 19:59:36.340
Declination : 22°43' 16.09"
Focal length : 0.00 mm
Focal ratio : 
Image resolution : 0.000 arcsec/pixel
Field of view : 
Sky quality : 19.46 magnitude/square arcsecond
Sensor temperature : 0°C
Light frames : 3 hours, 45 minutes total exposure time
5x 900 sec. hydrogen-alpha unbinned
5x 900 sec. oxygen-III unbinned
5x 900 sec. sulfur-II unbinned
Image acquisition scripted with Nebulosity v3
Auto-guiding with PHD (medium dither, settle < 0.3)
Bias frames : 100x unbinned
Dark frames : Bap pixel map
Flat frames : No flats
Processing : PixInsight for calibration (bias frames, bad pixel map and flat frames), alignment and integration.
Adobe Photoshop CS6 for final touch.

Equipment information
Telescope : Sky-Watcher BKP250 10" 1200mm f/4.8 Newtonian
Corrector : Guan Sheng Optical 2" coma corrector and field flattener
Focuser : Moonlite CR newtonian focuser with DC motor and USBnFocus adapter
Mount : Sky-Watcher NEQ6-Pro german equatorial mount controlled with EQMOD via HiTec Astro EQDir
Camera : QSI 683wsg-8 cooled CCD camera with Kodak KAF-8300 sensor and Off Axis Guide (OAG) port
Guidecamera : Starlight Xpress Lodestar autoguider
Filters : Astrodon Tru-Balance E-Series LRGB & Astrodon 3nm H-α, 3nm O-III, 3nm S-II and 3nm N-II
Observatory site : Etten-Leur, The Netherlands