NGC 6210, Turtle- Nebula
The Turtle Nebula NGC 6210 is located at a distance of about 6,500 light years in the constellation Hercules. Through the satellite mission "GAIA", the distance
could be determined to 6,350 light years with an uncertainty of about 350 light years. It also appears to be about 3,000 light-years above the galactic plane, which
has the advantage that it is not dimmed by some dust in front of it.
The apparent magnitude is given as 8.8mag, and the apparent size in the sky is 30x30 arcseconds, so it can be easily seen in small telescopes.
NGC 6210 has a diameter of 0,5 lightyears and shines in an intense blue/turquoise. The colour is due to single or double ionised oxygen. Two regions can be
distinguished: a brighter, inner region, which is responsible for 99% of the emissions and in which many filaments and gas arcs can be found. It expands into the
surrounding space at 19...24 kilometres per second. The outer region, on the other hand, is much fainter and forms the halo of the PN.
The central star belongs to the group of hydrogen-rich white dwarfs and has the spectral class O(H). With a temperature of 75,000 Kelvin it is quite hot, which
leads to a high luminosity of 7,400 Suns. The progenitor star appears to have had a mass of 1.25 suns, but has lost about 0.7 solar masses, so that the white dwarf
now appears to have a final mass of 0.56 solar masses. A special feature is that the central star ejects four jets of hot gas that bore into the cold outer shell, forming
the four "feet" of the turtle.
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The planetary nebula NGC 6210 appears very bright in a 20" telescope and glows an intense green colour. At high magnification, the inner ring shows interesting
structures such as brighter areas and a broken patch. A small knot at the western end can also be seen. Of the four little feet, only two are faintly indicated, but you
can still easily imagine the shape of a turtle.
The central star, on the other hand, is very bright and quite conspicuous even at low magnification. All in all, a rather interesting object.
