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NGC 6888 – the crescent nebula
first light image of TAO
Seeing conditions during HA-data acquisition below average, transparency very good. Seeing conditions for R, G average. Seeing conditions for B and L fine. Transparency in RGB very good. Moon present while imaging L and B.The Crescent Nebula, aka NGC 6888, is a very well renown and most intriguing object located in the constellation “swan” in the northern hemisphere. At an apparent size of about 18 by 13 arc-minutes it is a very pale nebula. Even in a moderate amateur telescope you cannot see this nebula. One would need absolute dark skies (or narrow band filters) and a decent “light buckett” to glimpse the nebula visually. It’s absolute diameter is some 25 by 18 light years. Gazing at NGC 6888 means we are looking 4700 Years into the past.NGC 6888 renders a nebula coming from the blueish star at the center. And this is known to once have been a super-giant star. That means the star has had a giant mass! Small stars like our sun dwell some Billions of years with their fule. Super Giant stars are kind of play-boys, as they deplete their fule at “full speed”. And in this particular case the central star qualifies for being summed upon the socalled “Wolf Rayet” stars. After only a coule of Million years the fule is almost used up and the star is standing right before a significant change: it is gonna go supernova quite soon,…spoken in cosmmological terms, though. So, at present we are looking at a star that vents its outer layers into space at terrific speed and therefor the star sustains severe loss of mass. The gas is holding lots of oxygen and hydrogen,…just before the individual big “bang” of the WR-star.Read an intruiging story about the Crescent-nebula written by Tammy Plottner from UT.
NGC 7008 – The Fetus-Nebula – 9″ TMB f/9
Located in the constellation Cygnus, some 1200 lightyears away, this planetary nebula, aka PK93+5.2, H I-192, h 2099, GC 4627 is a most spectacular object for a powerful telescope (say larger than 16″ aperture). It appears rather bright in a 20″ dobsonian, as its visual magnitude is 10m7. In blue, however, it is only 13m3 bright. It holds 1.4 arc minutes in diamter which is considerably large for a PN.
Discovered by William Herschel in 1787 the distinctive shape of the nebula donates the name, reminding the observer of an embryo. The dark hole which can be seen very well in the image near the center, origins back a long time ago, when a seperate nova blew this part of the nebula up.
M 76 – 9″ TMB Apo f/8
M76 can be found in the constellation of Perseus quite close to Andromeda. It’s central star appears to be a binary system with a yellowish (southern) component. But this is only an optical binary system at a distance of 1.4 arc”. Hubble Space Telescope revealed the southern component to be located some thousands of lightyears in the background and therefore the central star is solitude. (you can see this optical binary system in the enlarged crop-image.)
This PN (the faintets of all Messier objects) was long time believed to be a galaxy until precise spectroscopic investigations from the early 19th century revealed its true nature?
the PN is said to be seen from an edge on view – the “barr” or “cork” like brighter part is said to be a kind of ring-like structure – consisting of the material the very hot CS blows out. this brigther part holds approx. 1 arc min in longitud. axis. however the fainter outer parts – the wings of the “butterfly” measure approx. double size.
and further out there are remnants from the periode when the CS dwelled in its “super-giant” phase, commencing to evaporate outer star-mass. it has some diameter of approx. 4-5 arc minutes.
M 27 – 9″ TMB Apo f/6.8
August to October 09: 16″ RC + Astrodon LRGB
14x lum @ 1×1, 600s
11x red @ 2×2, 600s
25x green @ 2×2, 600s
35x blue @ 2×2, 600s
Software: AstroArt4 image acquisition, CCD Soft, preprocessing in CCD Stack, Maxim Dl, CCD Sharp; postprocessing in PS CS4.
M 1 – 9″ TMB Apo f/9
The socalled Crab-nebula is one of the best reknown celestial objects of the northern hemisphere. More so as it’s appearance on earth has been monitored by chinese astronomers from 4th of April 1054 till the following moths. This object renders a supernova-remnant. This is was remains after a giant explosion of a star (SN type 2).
In a distance of 6300 Lightyears M1 can be found in the constellation Taurus and it is relatively bright, shining at 8m4 and holding some 6 by 4 arc minutes (equaling about 11 by 7 lightyears), which makes it an easy object for a moderate telescope, dark skies granted of course, as the contrast is rather low in visual light.
The SN was visible for several days (weeks) during daylight and many months at night, until it drifted out of focus of the former astronomers, as they had no telescopes available. In the year 1731 John Bevid, and a little later 1785 Charles Messier “re-discovered” the nebula. Actually the discovery of this very nebula yield to the decision of Mr. Messier to create the very well known catalogue, named after him.
Usually massive stars are capable of creating heavier elements than just Helium, the normal product of stellar hydrogen-fusion. This fusion-process yields in the production of elemts like oxygen, nitrogen, and sulfur, up to iron in the core of such star. As a consequence the star becomes unstable (when running out of fuel to power its nuclear fusion reactions) and then the consecutive supernova explosion (type 2) can possibly lead to formation of far heavier elements, which will then be spread in space by means of the explosion and enrich the space with material needed to form new stars and planets. (Literally such an explosion could be regarded as a sacrifice of these stars, promoting the creation of further stars and planets, and life per se.)
What we see in the image are the socalled filament structures (redish coralle-like entities) of parts of the athmosphere of the progenitor star. In these structures elements like carbon, oxygen, neon, nitrogen and sulfur can be found. This nebula-shaped mantle, which is very hot at some 11.000 Kelvin, grows and expands centripedically at a velocity of 1500 km/s. What remained in the center of the stars original phenotypical location is a socalled pulsar, a fast rotating neutronstar, holding a phenomenal strong magnetic field of 8 potences Tesla but being only some 25 km in diamter! This magenitic field interacts with the nebula around and the electrons, which are forced by such magentic field to move at near lighspeed, emitting synchrotron-radiation, leading to the typical blueish light in the core of the nebula.
This very pulsar is also a serious source of radiowaves, x-ray and gamma-radiation. Though this object is very well investigated and much is known about the processes having gone through in the past and phenomena going on at present, some puzzling questions are still open: theory suggests, that the entire mass of the nebula and the pulsar added up is considerably less than the predicted mass of the progenitor star! Where has all the mass gone which is missing? In many cases, stars immediately prior to a supernova explosion expell serious amount of mass in a socalled stellar wind (typical example would be the crescent nebula, as a pre-supernova status of a bunch of stars, called Wolf Rayet stars, forming nebulosity around them). Such nebulosity however, cannot be found around M1. May further investigations reveal the reasons for this.
M 57 – The Ring Nebula – 9″ TMB Apo f/9
The socalled “Ring-nebula” aka as NGC 6720 is probably one of the most popular planetary nebulas, located in the constellation “Lyra” in a distance of 2300 light years. When Antoine Darquier and observed a comet in 1779 he just by chance came across this very bright PN that shines at 9m7. Ever since it is a very spectacular object for both, visual and photografic observation. Even in a standard telescope the ring-shape which donates the name can easily be seen. The very well visible central star was discovered by Friedrich Hahn 21 years later.
The apparent size in such telescopic view measures some 1.2 arc minutes in its longitudinal axis. However, very deep astroimages like this one above reveal its true size, which is more than twice that, currently 3.4 arc minutes. This so called outer shell is expanding hydrogen gas, that is expelling from the central hot star (~100.000K) at a velocity of approximately 19 km per second, which equals the beginning of this expulsion some 20.000 years ago when a gian red star commenced its dying-process. Ever since the nebula keeps on spreading into outer space and nowadays the absolute diameter of the entire objects is said to hold 1.3 light years.
The greenish interior of the ring mostly comes from ionized oxygen and nitrogen gas, that is heated by the radiation of the central star, which – like in almost all planetary nebulae – happens to be a white dwarf, not bigger than earth. In the enlarged crop one can also see some dark spots within the inner ring-structure which represent huge amounts of dust and dirt, standing out as remnants of the dying central star.
NGC 1514 – 9″ TMB Apo f/18 + f/9
This 10m0 bright PN aka the ‘crystal-ball-nebula’ located in the constellation of Taurus measures some 1.9 arc minutes in a circular shape, which is rather large for a PN. The central star is very bright at 9m5, therefore it can easily be seen in a standard amateur telescope. William Herschel described this object in 1790 forcing him to reconsider and reformulate his own theory which assumed the nebulosity around some particular stars might origin in minute stars, too tiny to be resolved. (Remeber, the telescopes of that era were significantly inferior to modern scopes in terms of resolution power and intensity). Most recent investigations reveal the central star to be a very close binary system with a rotation periode of 9hours and 50minutes. Following Vorontsov-Velyaminov classification of PNs NGC 1514 is part of the category multiple type 3+2; that indicates the existence of two expanding gas-shells. This very gas near its center is expanding outward at about 25 km/sec, while the whole objects moves away from earth at 60 km/sec. Since the object is located some 2000 light years away, the effect of both dynamical phenomena will hardly be detectable within a life span of a human. (source courtesy part: Ice In Space).
NGC 2392 LRGB – 9″ TMB Apo f/18 + f/9
This rather samll PN (42 arc seconds) is located some 3000 LY away from earth and can be found in the constellation of Gemini. It measures a couple of billion km in diameter and holds a hot white dwarf star at its center, that can easily be observed in a small telescope. When Herschel discovered this PN in 1787 he noticed some halo like formation around the very bright star; but his telescope was not precise enough to disclose its real nature; to discover the structure of the nebulosity one must referr to a serious telescope. In my 9″ TMB you can gather the idea why this PN is called the “Eskimo”. Its bright central star is very hot at this time at 40000 Kelvin. HST revealed there are 2 gas shells, that expand at different velocities. The inner one is rather fast with about 90 km/s, being expelled some 1060 years ago; and the outer one, that makes the “hair” of the Eskimo seems to originate in the periode of the central star when it dwelled in its red giantz phase, commencing to evaporate gas. This shell displays a way lower speed at some 20 km/s. The initial explosion that lead to its phase as a PN is said to have happened some 5000 years ago.