Planetary Nebula Of The Week - 2

**   NGC 2440  **

CONSTELLATION OF PUPPIS

Like a butterfly, a white dwarf star begins its life by casting off a cocoon that enclosed its former self. In this analogy, however, the Sun would be a caterpillar and the ejected shell of gas would become the prettiest of all! The above cocoon, the planetary nebula designated NGC 2440, contains one of the hottest white dwarf stars known. The white dwarf can be seen as the bright dot near the photo's center. Our Sun will eventually become a "white dwarf butterfly", but not for another 5 billion years. The above false color image and was post-processed by F. Hamilton.(Credit: H. Bond (STSci), R. Ciardullo (PSU), HST, NASA )) ASTRONOMY PICTURE OF THE DAY - APRIL 26, 1998

NGC 2440 - HST Image

  Here is a wonderful Hubble Space Telescope image of a planetary nebulae - NGC2440 ("New General Catalogue entry number 2440"). Planetary nebulae are important because they allow astronomers to study the very last stages of a stars life (or perhaps the first stages of its death!?). Very large stars (which are rare) die in enormous explosions called Supernova. However, MOST stars end their lives by swelling their outer layers and then suddenly collapsing the innermost part and expelling the outer atmosphere as a gaseous shell. This shell is the planetary nebula, which was so named because they appear to resolve into a disk reminiscent of planets when seen with the early telescopes. Planetary nebulae offer clues about the now-dead stars that made them and how these stars lived and died. In a way, this is Astro-Paleontology -- digging through the "fossils" of dead stars, looking for clues about how they lived!
(Courtesy of Barry Kellett, Rutherford Appleton Laboratory)  

Location Chart From 'MegaStar'

Additional Factinos:

• Distance: Estimated to be 4,800 light years from our solar system.
• Radial Velocity: 63 km/sec, moving away from our solar system.
• Expansion Velocity: Estimated to be 24 km/sec
• Discovered by William Herschel in 1790
• Uranometria 2000.0 Chart No. 319

   

SKY VIEW IMAGE  (8.5' Field)	Kitt Peak National  Observatory Image

  OBSERVATION NOTES

Steve Gottlieb:
N2440 = PK 234+2.1 = E560-PN9
07 41.9 -18 13
13": very bright and small with a very high surface brightness.  This
planetary has a double shell structure with an elongated box-shape oriented
NW-SE and a fainter shell oriented SW-NE.  One or two condensations are
visible in the central part.  Located 3.0' W of mag 9 SAO 153271.

---

Schematic Evolution of a Planetary Nebula  1.A star like the Sun, with hydrogen burning at the centre. (core)    2.As the hydrogen is exhausted, only a thin layer burns around a growing core of helium.   3.The helium core contracts under the imense presure, and the outer envelope continues to expand. The star is now a red giant.  4.When the envelope gets too large the gravity of the star is to weak to hold it and it escapes into space, while the inner part collapses to form the hot central star.   5.A new planetary nebula forms, with dense ionized hydrogen (yellow) surrounding a (very) hot central star (white).   6.The disk of ionized hydrogen is now large enough to see in a telescope.   7.All the hydrogen and most of the other elements have now become ionized. The brightness of the nebula starts to fade.   8.The nebula is now barely visible against the sky, and about to fade from view. This is the stage that NGC2440 has reached in this excellent Hubble Space Telescope picture.

http://ast.star.rl.ac.uk/

Courtesy Barry Kellett, Rutherford Appleton Laboratory

NGC 2440 Image Taken With OIII Filter

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01/25/98