NGC 6543

Planetary nebula	Lists of nebulae
The Cat's Eye Nebula. Composite image using optical images from the HST and X-ray data from the Chandra X-ray Observatory NGC 6543, the Cats Eye Nebula A planetary nebula is an astronomical object consisting of a glowing shell of gas and plasma formed by certain types of stars at the end of their lives. ... Download high resolution version (800x874, 64 KB)X-ray/optical composite image of NGC 6543, the Cats Eye Nebula (X-ray: NASA/UIUC/Y.Chu et al. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble for his discovery of galaxies outside the Milky Way. ... For other uses, see Chandra (disambiguation). ...
Observation data (Epoch J2000.0)
Right ascension	17h 58m 33.4s [1]
Declination	+66° 37′ 59″ [1]
Distance	3,300±900 ly [2]
Apparent magnitude (V)	+8.9 [1]
Apparent dimensions (V)	Core: 20″ [2] Halo: 5′.8 arcmins
Constellation	Draco
Physical characteristics
Radius	Core: 0.2 ly[3]
Absolute magnitude (V)	-
Notable features	complex structure
Other designations	NGC 6543

The Cat's Eye Nebula (NGC 6543) is a planetary nebula in the constellation of Draco. Structurally, it is one of the most complex nebulae known, with high-resolution Hubble Space Telescope observations revealing remarkable structures such as knots, jets and sinewy arc-like features. In astronomy, an epoch is a moment in time for which celestial coordinates or orbital elements are specified. ... Right ascension (RA; symbol α: Greek letter alpha) is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. ... In astronomy, declination (dec) is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. ... To help compare different orders of magnitude, this page lists distances between 1019 m (1,100 light years) and 1020 m (11,000 light years). ... A light year, abbreviated ly, is the distance light travels in one year: roughly 9. ... // Headline text HEY!! HOW ARE YOU ALL?? Its nice of you to come read this page. ... It has been suggested that milliarcsecond be merged into this article or section. ... This article or section does not cite its references or sources. ... Draco (Latin for Dragon) is a far northern constellation that is circumpolar for many northern hemisphere observers. ... In classical geometry, a radius of a circle or sphere is any line segment from its center to its boundary. ... A light year, abbreviated ly, is the distance light travels in one year: roughly 9. ... In astronomy, absolute magnitude is the apparent magnitude, m, an object would have if it were at a standard luminosity distance away from us (in the absence of interstellar extinction!). It allows the overall brightnesses of objects to be compared without regard to distance. ... The New General Catalogue (NGC) is the most well-known catalogue of deep sky objects in amateur astronomy. ... NGC 6543, the Cats Eye Nebula A planetary nebula is an astronomical object consisting of a glowing shell of gas and plasma formed by certain types of stars at the end of their lives. ... Draco (Latin for Dragon) is a far northern constellation that is circumpolar for many northern hemisphere observers. ... The Hubble Space Telescope (HST) is a telescope in orbit around the Earth, named after astronomer Edwin Hubble for his discovery of galaxies outside the Milky Way. ...

It was discovered by William Herschel on February 15, 1786, and was the first planetary nebula whose spectrum was investigated, by the English amateur astronomer William Huggins in 1864. Sir Wilhelm Friedrich Herschel, FRS KH (November 15, 1738 – August 25, 1822) was a German-born British astronomer and composer who became famous for discovering the planet Uranus. ... February 15 is the 46th day of the year in the Gregorian Calendar. ... 1786 was a common year starting on Sunday (see link for calendar). ... Extremely high resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines) Spectroscopy is the study of spectra, that is, the dependence of physical quantities on frequency. ... It has been suggested that this article or section be merged with Skygazing. ... William Huggins Sir William Huggins, OM , FRS (February 7, 1824 – May 12, 1910) was a British astronomer. ... 1864 (MDCCCLXIV) was a leap year starting on Friday (see link for calendar) of the Gregorian calendar or a leap year starting on Sunday of the 12-day-slower Julian calendar. ...

Modern studies reveal several mysteries. The intricacy of the structure may be caused in part by material ejected from a binary central star, but as yet, there is no direct evidence that the central star has a companion. Also, measurements of chemical abundances reveal a large discrepancy between measurements done by two different methods, the cause of which is uncertain. A binary system is an astronomy term referring to two objects in space, usually stars, which are so close that their gravitational forces attract one another into a mutual orbit. ...

General information

NGC 6543 is a very well-studied planetary nebula. It is relatively bright at magnitude 8.1, and also has a high surface brightness. It is situated at right ascension 17h 58.6m and declination +66°38'. Its high declination means it is easily observable from the northern hemisphere, where historically most large telescopes have been situated. NGC 6543 is situated almost exactly in the direction of the North Ecliptic Pole. // Headline text HEY!! HOW ARE YOU ALL?? Its nice of you to come read this page. ... Surface brightness is a concept used in astronomy when describing extended astronomical objects such as galaxies and nebulae. ... Right ascension (RA; symbol α: Greek letter alpha) is the astronomical term for one of the two coordinates of a point on the celestial sphere when using the equatorial coordinate system. ... In astronomy, declination (dec) is one of the two coordinates of the equatorial coordinate system, the other being either right ascension or hour angle. ... Insert non-formatted text here The Northern Hemisphere is the half of a planets surface (or celestial sphere) that is north of the equator (the word hemisphere literally means half ball). On the Earth, the Northern Hemisphere contains most of the land and population. ... 50 cm refracting telescope at Nice Observatory. ... The ecliptic coordinate system is a celestial coordinate system that uses the ecliptic for its fundamental plane. ...

While the bright inner nebula is rather small at 20 arcseconds in diameter ^[2], it has an extended halo of matter that the progenitor star ejected during its red giant phase. This halo extends over a diameter of about 386 arcseconds (6.4 arcminutes). A second of arc or arcsecond is a unit of angular measurement which comprises one-sixtieth of an arcminute, or 1/3600 of a degree of arc or 1/1296000 ≈ 7. ... Halo around the sun at the South Pole (NOAA) Icebow over the Kluane Range viewed from the Alaska Highway (J. Hall) Ice-bow around the sun at temperate latitude. ... Artists conception of the remains of artificial structures on the Earth after the Sun enters its red giant phase and swells to roughly 100 times its current size. ... A minute of arc, arcminute, or MOA is a unit of angular measurement, equal to one sixtieth (1/60) of one degree. ...

Observations show that the main body of the nebula has a density of about 5,000 particles/cm³ and a temperature of about 8,000 K.¹ The outer halo has a somewhat higher temperature of about 15,000 K and a much lower density. The kelvin (symbol: K) is the SI unit of temperature, and is one of the seven SI base units. ...

The central star of NGC 6543 is an O-type star, with a temperature of approximately 80,000 K. It is approximately 10,000 times as luminous as the sun, and its radius is about 0.65 times the solar value. Spectroscopic analysis shows that the star is currently losing mass in a fast stellar wind at a rate of about 3.2×10⁻⁷ solar masses per year - about 20 trillion tons per second. The velocity of this wind is about 1900 km/s. Calculations indicate that the central star currently weighs just over one solar mass, but theoretical evolutionary calculations imply that it had an initial mass of about 5 solar masses.² In astronomy, stellar classification is a classification of stars based initially on photospheric temperature and its associated spectral characteristics, and subsequently refined in terms of other characteristics. ... The Sun is the star of our solar system. ... Extremely high resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines) Spectroscopy is the study of spectra, that is, the dependence of physical quantities on frequency. ... A solar wind is a stream of particles (mostly high-energy protons ~ 500 keV) which are ejected from the upper atmosphere of a star (in the case of a star other than the Earths Sun, it may be called a stellar wind instead). ... The word ton or tonne is derived from the Old English tunne, and ultimately from the Old French tonne, and referred originally to a large cask with a capacity of 252 wine gallons, which holds approximately 2100 pounds of water. ... In astronomy, the solar mass is a unit of mass used to express the mass of stars and larger objects such as galaxies. ...

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Observations

The nebula was discovered by William Herschel on February 15, 1786, and was the first planetary nebula to be observed with a spectroscope, by William Huggins in 1864. Huggins' observations were the first indication that planetary nebulae consist of extremely rarefied gases. Since those early observations, NGC 6543 has been observed right across the electromagnetic spectrum. Sir Wilhelm Friedrich Herschel, FRS KH (November 15, 1738 – August 25, 1822) was a German-born British astronomer and composer who became famous for discovering the planet Uranus. ... February 15 is the 46th day of the year in the Gregorian Calendar. ... 1786 was a common year starting on Sunday (see link for calendar). ... A spectroscope is a device which measures the spectrum of light. ... William Huggins Sir William Huggins, OM , FRS (February 7, 1824 – May 12, 1910) was a British astronomer. ... Density (symbol: ρ - Greek: rho) is a measure of mass per unit of volume. ... Legend: γ = Gamma rays HX = Hard X-rays SX = Soft X-Rays EUV = Extreme ultraviolet NUV = Near ultraviolet Visible light NIR = Near infrared MIR = Moderate infrared FIR = Far infrared Radio waves: EHF = Extremely high frequency (Microwaves) SHF = Super high frequency (Microwaves) UHF = Ultrahigh frequency VHF = Very high frequency HF = High frequency...

Infrared observations

The Cat's Eye Nebula in infrared light, as seen by the Infrared Space Observatory.

Observations of NGC 6543 at infrared wavelengths reveal the presence of stellar dust at low temperatures. The dust is believed to have formed during the last phases of the progenitor star's life. It absorbs light from the central star and re-radiates it at infrared wavelengths. The spectrum of the infrared dust emission implies that the dust temperature is about 70 K. Infrared image of planetary nebula NGC 6543, from the Infrared Space Observatory. ... Infrared image of planetary nebula NGC 6543, from the Infrared Space Observatory. ... The Infrared Space Observatory (ISO)is a space telescope for infrared light designed and operated by the European Space Agency (ESA). ... Image of a small dog taken in mid-infrared (thermal) light (false color) Infrared (IR) radiation is electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves. ... Interstellar cloud is the generic name given to accumulations of gas and dust in our galaxy. ...

Infrared emission also reveals the presence of un-ionised material such as molecular hydrogen (H₂). In many planetary nebulae, molecular emission is greatest at larger distances from the star, where more material is un-ionised, but molecular hydrogen emission in NGC 6543 seems to be bright at the inner edge of its outer halo. This may be due to shock waves exciting the H₂ as ejecta moving at different speeds collide.³ ion (disambiguation) An ion is an atom or group of atoms with a net electric charge. ... Molecular hydrogen, H2, is a molecule formed from two atoms of hydrogen. ... Shock Waves is a horror movie from 1977 directed by Ken Wiederhorn. ...

Optical and ultraviolet observations

False colour image of NGC 6543 taken with the Hubble Space Telescope's Wide Field and Planetary Camera 2.

NGC 6543 has been extensively observed at ultraviolet and optical wavelengths. Spectroscopic observations at these wavelengths are used in abundance determinations, while images at these wavelengths have been used to reveal the intricate structure of the nebula. Optical Hubble Space Telescope image of NGC 6543. ... Optical Hubble Space Telescope image of NGC 6543. ... A Hubble Space Telescope image of the Hubble Deep Field showing the characteristic stairstep composition of WFPC2 images The Wide Field and Planetary Camera 2 (WFPC2) is a camera installed on the Hubble Space Telescope. ... Ultraviolet (UV) light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than soft X-rays. ... The visible spectrum is the portion of the optical spectrum (light or electromagnetic spectrum) that is visible to the human eye. ... The wavelength is the distance between repeating units of a wave pattern. ...

The Hubble Space Telescope image produced here is in false colour, designed to highlight regions of high and low ionisation. Three images were taken, in filters isolating the light emitting by singly ionised hydrogen at 656.3 nm, singly ionised nitrogen at 658.4 nm and doubly ionised oxygen at 500.7 nm. The images were combined as red, green and blue channels respectively, although their true colours are red, red and green. The image reveals two 'caps' of less ionised material at the edge of the nebula. ion (disambiguation) An ion is an atom or group of atoms with a net electric charge. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... A nanometre (American spelling: nanometer) is 1. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ...

X-ray observations

Recent observations at X-ray wavelengths by the Chandra X-ray Observatory have revealed the presence of extremely hot gas within NGC 6543. The image at the top of this article is a combination of optical images from the Hubble Space Telescope with the Chandra X-ray images. It is thought that the very hot gas results from the violent interaction of a fast stellar wind with material previously ejected. This interaction has hollowed out the inner bubble of the nebula. In the NATO phonetic alphabet, X-ray represents the letter X. An X-ray picture (radiograph) taken by Röntgen An X-ray is a form of electromagnetic radiation with a wavelength approximately in the range of 5 pm to 10 nanometers (corresponding to frequencies in the range 30 PHz... For other uses, see Chandra (disambiguation). ...

Chandra observations have also revealed a point source at the position of the central star. The star would not be expected to emit strongly in X-rays, and so their presence is something of a mystery. It may suggest the presence of a high temperature accretion disk within a binary star system.⁴ An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... Artists impression of a binary star system consisting of a black hole, with an accretion disc around it, and a main sequence star. ...

Distance

The outward expansion of NGC 6543 over several years can be used to calculate its distance

A long standing problem in the study of planetary nebulae is that their distances are generally not well known. Many methods for estimating distances to planetary nebulae rely on making general assumptions, which may be very inaccurate for the object concerned. Expansion of NGC 6543 over a period of three years. ... Expansion of NGC 6543 over a period of three years. ...

In recent years, however, observations made using the Hubble Space Telescope have allowed a new method of determining distances. All planetary nebulae are expanding, and observations several years apart and with high enough angular resolution will reveal the growth of the nebula in the plane of the sky. This is typically very small—only a few milliarcseconds a year or less. Spectroscopic observations can reveal the velocity of expansion of the nebula along the line of sight using the Doppler effect. Then, comparing the angular expansion with the known expansion velocity, the distance to the nebula can be calculated. Angular resolution describes the resolving power of a telescope. ... High resolution spectrum of the Sun showing thousands of elemental absorption lines (fraunhofer lines). ... A source of waves moving to the left. ...

Hubble Space Telescope observations of NGC 6543 several years apart have been used to calculate its distance. Its angular expansion rate is approximately 10 milliarcseconds per year, while its expansion velocity along the line of sight has been found to be 16.4 km/s. Combining these two results implies that NGC 6543 is about 1000 parsecs (3×10¹⁹ m) away from Earth. ^[2] Stellar parallax motion The parsec (symbol pc) is a unit of length used in astronomy. ...

Age

The angular expansion of the nebula can also be used to estimate its age. If it has been expanding at a constant rate, then to have reached a diameter of 20 arcseconds at 10 milliarcseconds a year would have taken 1000 years.^[2] This may be an upper limit to the age, as ejected material will be slowed as it encounters material ejected from the star at earlier stages of its evolution, as well as the interstellar medium. The distribution of ionized hydrogen (known by astronomers as H II (aitch two) from old spectroscopic terminology) in the parts of the Galactic interstellar medium visible from the Earths northern hemisphere (from the Wisconsin H-Alpha Mapper Survey) In astronomy, the interstellar medium (or ISM) is the matter (interstellar...

Composition

Image of NGC 6543 processed to reveal the concentric rings surrounding the inner core. Also visible are the linear structures, possibly caused by precessing jets from a binary central star system.

Like most astronomical objects, NGC 6543 consists mostly of hydrogen and helium, with heavier elements present in small quantities. The exact composition may be determined by spectroscopic studies. Abundances are generally expressed relative to hydrogen, the most abundant element. Image File history File links Download high resolution version (1200x1200, 107 KB)Concentric rings in the planetary nebula NGC 6543. ... Image File history File links Download high resolution version (1200x1200, 107 KB)Concentric rings in the planetary nebula NGC 6543. ... General Name, Symbol, Number hydrogen, H, 1 Chemical series nonmetals Group, Period, Block 1, 1, s Appearance colorless Atomic mass 1. ... General Name, Symbol, Number helium, He, 2 Chemical series noble gases Group, Period, Block 18, 1, s Appearance colorless Atomic mass 4. ...

Different studies generally find varying values for elemental abundances. This is often because spectrographs attached to telescopes do not collect all the light from objects being observed, instead gathering light from a slit or small aperture. Therefore, different observations may sample different parts of the nebula. For Acoustic uses in spectrographs of sound waves, see below. ... Definitions of Aperture in the 1707 Glossographia Anglicana Nova For other uses, see Aperture (disambiguation). ...

However, results for NGC 6543 broadly agree that, relative to hydrogen, the helium abundance is about 0.12, carbon and nitrogen abundances are both about 3×10⁻⁴, and the oxygen abundance is about 7×10⁻⁴. These are fairly typical abundances for planetary nebulae, with the carbon, nitrogen and oxygen abundances all larger than the values found for the sun, due to the effects of nucleosynthesis enriching the star's atmosphere in heavy elements before it is ejected as a planetary nebula.^1,6 General Name, Symbol, Number carbon, C, 6 Chemical series nonmetals Group, Period, Block 14, 2, p Appearance black (graphite) colorless (diamond) Atomic mass 12. ... General Name, Symbol, Number nitrogen, N, 7 Chemical series nonmetals Group, Period, Block 15, 2, p Appearance colorless Atomic mass 14. ... General Name, Symbol, Number oxygen, O, 8 Chemical series Nonmetals, chalcogens Group, Period, Block 16, 2, p Appearance colorless (gas) very pale blue (liquid) Atomic mass 15. ... The Sun is the star of our solar system. ... Nucleosynthesis is the process of creating new atomic nuclei from preexisting nucleons (protons and neutrons). ...

Deep spectroscopic analysis of NGC 6543 may indicate that the nebula contains a small amount of material which is highly enriched in heavy elements; this is discussed further below.

Kinematics and morphology

A composite image showing the giant outer halo of NGC 6543 surrounding the inner core.

The Cat's Eye Nebula is structurally a very complex nebula, and the mechanism or mechanisms which have given rise to its complicated morphology are not well understood. Download high resolution version (1019x932, 318 KB)Outer halo of NGC 6543. ... Download high resolution version (1019x932, 318 KB)Outer halo of NGC 6543. ...

The structure of the bright portion of the nebula is primarily caused by the interaction of a fast stellar wind being emitted by the central star with material ejected during the formation of the nebula. This interaction causes the emission of X-rays discussed above. The stellar wind has 'hollowed out' the inner bubble of the nebula, and appears to have burst the bubble at both ends.⁷ A solar wind is a stream of particles (mostly high-energy protons ~ 500 keV) which are ejected from the upper atmosphere of a star (in the case of a star other than the Earths Sun, it may be called a stellar wind instead). ...

It is also suspected that the central star of the nebula may be a binary star. The existence of an accretion disk caused by mass transfer between the two components of the system may give rise to polar jets, which would interact with previously ejected material. Over time, the direction of the polar jets would vary due to precession.⁸ Artists impression of a binary star system consisting of a black hole, with an accretion disc around it, and a main sequence star. ... An accretion disc (or accretion disk) is a structure formed by material falling into a gravitational source. ... A polar jet is a phenomenon often seen in astronomy. ... Precession refers to a change in the direction of the axis of a rotating object. ...

Outside the bright inner portion of the nebula, there are a series of concentric rings, thought to have been ejected before the formation of the planetary nebula, while the star was on the asymptotic giant branch of the Hertzsprung-Russell Diagram. These rings are very evenly spaced, suggesting that the mechanism responsible for their formation ejected them at very regular intervals and at very similar speeds.⁹ The Asymptotic Giant Branch is the name given to a region of the Hertzsprung-Russell Diagram populated by evolving low to medium-mass stars. ... The Hertzsprung-Russell diagram (usually referred to by the abbreviation H-R diagram or HRD, also known as a Colour-Magnitude (CM) diagram) shows the relationship between absolute magnitude, luminosity, classification, and surface temperature of stars. ...

Further out, a large faint halo extends to large distances from the star. The halo again predates the formation of the main nebula.

Open questions

Despite intensive study, the Cat's Eye Nebula still holds many mysteries. The concentric rings surrounding the inner nebula seem to have been ejected at intervals of a few hundred years, a timescale which is rather difficult to explain. Thermal pulsations which cause planetary nebulae to be formed in the first place are believed to take place at intervals of tens of thousands of years, while smaller surface pulsations are thought to occur at intervals of years to decades. A mechanism which would eject material over the timescales required to form the concentric rings in the Cat's Eye Nebula is not yet known.

The spectra of planetary nebulae consist of emission lines superimposed on a continuum. The emission lines may be formed either by collisional excitation of ions in the nebula, or by recombination of electrons with ions. Collisionally excited lines are generally much stronger than recombination lines, and so have historically been used to determine abundances. However, recent studies have found that abundances derived from recombination lines seen in the spectrum of NGC 6543 are some three times higher than those derived from collisionally excited lines.¹ The cause of this discrepancy is disputed—suggestions include the presence of some material highly enriched in heavy elements, or sizable temperature fluctuations within the nebula. A spectral line is a dark or bright line in an otherwise uniform and continuous spectrum, resulting from an excess or deficiency of photons in a narrow frequency range, compared with the nearby frequencies. ... Look up continuum in Wiktionary, the free dictionary. ... Collisional excitation is a process which gives rise to spectral lines in the spectra of astronomical objects such as planetary nebulae and H II regions. ... ion (disambiguation) An ion is an atom or group of atoms with a net electric charge. ... Recombination usually denotes a genetic event that occurs during the formation of sperm and egg cells (especially in areas of study of biology topics). ... Properties The electron is a lightweight fundamental subatomic particle that carries a negative electric charge. ...

External links

Wikimedia Commons has media related to:

Cat's Eye Nebula

• Chandra X-Ray Observatory Photo Album: NGC 6543 (Cat's Eye Nebula)
• NASA APOD - October 31, 1999: The Cat's Eye Nebula
• Hubble Probes the Complex History of a Dying Star - HubbleSite article about the Cat's Eye Nebula.
• Hubble's Color Toolbox: Cat's Eye Nebula - article showing the image composite process used by scientists to produce an image of the Cat's Eye Nebula.

Image File history File links Commons-logo. ... Wikimedia Commons logo by Reid Beels The Wikimedia Commons (also called Commons or Wikicommons) is a repository of free content images, sound and other multimedia files. ...

References

   

2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 31 is the 243rd day of the year in the Gregorian calendar (244th in leap years), with 122 days remaining. ... 2006 (MMVI) is a common year starting on Sunday of the Gregorian calendar. ... August 31 is the 243rd day of the year in the Gregorian calendar (244th in leap years), with 122 days remaining. ... Image File history File links LinkFA-star. ...