Estrellas Especiales I
Altair
A blue-white star, which is quite good visible in summer on the northern hemisphere. Altair is one of the fastest rotating stars we know of. In 6.5 hours it rotates once. The smaller Sun needs 600 hours for this. Due to its fast rotation Altair ist strongly oblate on its poles.
Constellation: Aquila
Age: < 1 billion years
Distance: 16.77 light-years
Spectral class: A7
Visual magnitude: 0.77
Luminosity: 11.39 * Sun
Mass: 2 * Sun
Diameter: 1.631 * Sun
Radial velocity: -26.1 km/sec
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Graphic: Zina Deretsky, National Science Foundation
Gliese 229
A pair of a red dwarf which is a flare star and a brown dwarf.
Constellation: Lepus
Age: 3 billion years
Distance: 18.8 light-years
Radial velocity: 5.2 km/sec
Space between Gliese 229 A and B: 44 AU
Gliese 229 A
Spectral class: M1
Visual magnitude: 8.15
Luminosity: 0.016 * Sun
Mass: 0.46 * Sun
Diameter: 0.527 * Sun
Gliese 229 B
Luminosity: 0.000006 * Sun
Mass: 0.05 * Sun (45 * Jupiter)
Diameter: 0.1027 * Sun (1 * Jupiter)
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The red dwarf and right to it the tiny brown dwarf.
Photo: Nasa, Hubble Telescope
Delta Pavonis
The yellow star is older as our Sun, but besides very similar to it. It is one of the main targets for the search of Earth-like planets and life.
Constellation: Pavo
Distance: 19.92 light-years
Spectral class: G8
Visual magnitude: 3.55
Luminosity: 1.231 * Sun
Mass: 0.98 * Sun
Diameter: 1.188 * Sun
Radial velocity: -21.7 km/sec
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Photo: ESO Online Digitized Sky Survey
Gliese 105
A small triple system. The C star, a red dwarf, is with 2600 kelvin surface temperature the coolest known main sequence star. Its mass is just enough to start the hydrogen fusion.
The B star is a bigger red dwarf, A is a yellow-orange star.
Constellation: Cetus
Distance: 23.5 light-years
Space between Gliese 105 A and B: 1200 AU
Space between Gliese 105 A and C: 24 AU
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Gliese 105 A and C
Graphic: Nasa, Hubble Telescope
Kappa Ceti
A yellow star of sunlike measures, but with much more raving attributes. It is a superflare star with eruptions a million times heavier than those of our Sun. They are caused by disturbances of the magnetic field from a still undiscovered near companion.
Constellation: Cetus
Age: 800 million years
Distance: 29.87 light-years
Spectral class: G5
Visual magnitude: 4.83
Luminosity: 0.851 * Sun
Mass: 1 * Sun
Diameter: 0.984 * Sun
Radial velocity: 18.9 km/sec
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Photo: ESO Online Digitized Sky Survey
Methane Dwarf
This one belongs to a special kind of brown dwarfs. Those should be quite common, but are difficult to discover. Its name the star got because of its high concentration of methane which shows in its spectra. The star is extremely red and cool with a surface temperature of only 1000 kelvin.
Constellation: Ophiuchus
Distance: 30 light-years
Mass: circa 50 * Jupiter (0.05 * Sun)
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The dwarf is to the right between the white lines.
Photo: SDSS
TVLM513-46546
This is an ultracool red dwarf, at the lower end of the mass limit for stars. Such small stars for a long time have been assumed to be quiet and simple. However, TVLM513-46546 is a very active flare star with a complex magnetic field and a hot spot, which covers half of its surface. The star spins every two days, like a cosmic lighthouse with a brighter and a darker side.
Constellation: Boötes
Age: > 1 billion years
Distance: 35 light-years
Spectral class: M8.5
Visual magnitude: 11
Luminosity: 0.0002 * Sun
Mass: 0.09 * Sun
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12/09/2007
GJ 3685A
The star with its magnetic field lines.
Graphic: Gemini Observatory/ Dana Berry, SkyWorks Digital Animation
This very old red dwarf suffered on April 24th 2004 a heavy eruption, when caused by a flare its luminosity increased 10 000 times. This 20 minute lasting flare was a million times stronger than the strongest flares of the Sun. Even for flare stars this is unusual fierce.
Constellation: Leo
Distance: 45 light-years
Spectral class: M4
Visual magnitude: 13.25
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Photos: NASA, JPL, Caltech
18 Scorpii
The yellow main sequence star is of all known stars the one most similar to our Sun. Even its rotation period is nearly identical. The sunspot cycle is seven years long (that of the Sun is eleven years). Unfortunately there haven't been any planets discovered yet.
Constellation: Scorpius
Age: 4.2 billion years
Distance: 45.7 light-years
Spectral class: G2
Visual magnitude: 5.50
Luminosity: 1.05 * Sun
Mass: 1.012 * Sun
Diameter: 1.02 * Sun
Radial velocity: 12 km/sec
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Photo: ESO Online Digitized Sky Survey
G29-38
The white dwarf is surrounded by a dust disk, which in its composition reminds of the comets in our solar system. Maybe the dead star still is orbited by many ancient comets. Possible near planets would have been swallowed by the star long ago during its red-giant-phase.
Constellation: Pisces
Age as white dwarf: 500 million years
Distance: 46 light-years
Spectral class: DA
Visual magnitude: 13.03
Mass: 0.69 * Sun
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Graphic: NASA/JPL
AB Doradus
AB Doradus is a multiple system made of 3 stars at least. The largest of those, the orange star A, spins about 50 times faster than the Sun and therefore has a much stronger magnetic field. B and C are red dwarfs, whereas star B could be double. Star C is the star with the lowest known mass, only slightly above the border to a brown dwarf.
Constellation: Dorado
Age: 50 million years
Distance: 48.59 light-years
Space between AB Doradus A and B: 135 AU
Space between AB Doradus A and C: 2.3 AU
Orbit period of AB Doradus A and C: 11.75 years
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12/11/2007
Orbit of AB Doradus C around A
Image: Dr. Laird M. Close/Steward Observatory
Castor
Castor or Alpha Geminorum, with Pollux one of the two twin stars, is a sextuple system of three quite self-similar pairs. A1/2 and B1/2 are white stars, C1/2 or YY Geminorum in contrast are red dwarfs and flare stars which are a strong X-ray source.
Constellation: Gemini
Distance: 51.6 light-years
Radial velocity: 6 km/sec
Orbit period of Castor A1 and A2: 9.2127 days
Orbit period of Castor B1 and B2: 2.92828 days
Orbit period of Castor C1 and C2: 19.539414 hours
Orbit period of Castor A and B: 467 years
Orbit period of Castor A/B and C: 10 000 years
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Castor in X-ray.
Photo: ESA/XMM-Newton/EPIC
BPM 37093 (Diamond Star)
The interior of this probably very old white dwarf is a diamond with a diameter of more than 4000 kilometers.
The inside of white dwarfs often is pure carbon. The pressure in this star has agglomerated it to form a diamond.
Constellation: Centaurus
Distance: 54 light-years
Spectral class: DA6
Visual magnitude: 13.96
Luminosity: 0.0006 * Sun
Diameter: 0.0029 * Sun
Radial velocity: -12 km/sec
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Source: Harvard-Smithsonian Center for
Astrophysics /
Travis Metcalfe, Ruth Bazinet
Delta Equulei
The double of two sunlike yellow stars was until sometime in the 20th century the closest known double star which could be separated optically.
Star A itself is in turn a very close double. For its two components there are no separated dates available yet.
Constellation: Equuleus
Age: 1.6 - 2.8 billion years
Distance: 60.3 light-years
Space between Delta Equulei A and B: 4.81 AU
Orbit period of Delta Equulei A and B: 5.7 years
Delta Equulei Aa and Ab combined
Spectral class: F5
Visual magnitude: 5.11
Luminosity: 2.23 * Sun
Mass: 1.22 * Sun
Diameter: 2.38 * Sun
Delta Equulei B
Spectral class: G0
Visual magnitude: 5.40
Luminosity: 2.17 * Sun
Mass: 1.17 * Sun
Diameter: 1.05 * Sun
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03/03/2006
Photo: ESO Online Digitized Sky Survey
Gliese 710
The variable red dwarf is heading nearly directly for us and in about 1.5 million years will have only 1 light-year distance. Then it will shine as bright as Antares and throw some comets from the Oort Cloud to the direction of the Sun.
Constellation: Ophiuchus
Distance: 63 light-years
Spectral class: K5-M1
Visual magnitude: 9
Luminosity: 0.042 * Sun
Mass: 0.4 - 0.6 * Sun
Diameter: 0.67 * Sun
Radial velocity: 14 km/sec
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Photo: Palomar Digitized Sky Survey
DENIS-P J020529.0-115925
This is an old triple system made of brown dwarfs. The existence of the third (C) isn't proofed without doubt yet, but very likely.
The would-be stars can't produce any more energy and now slowly glow out. The warmest (A) of them has a temperature of just 1800 kelvin.
Constellation: Cetus
Age: 1 - 10 billion years
Distance: 65 light-years
Radial velocity: 22 km/sek
Space between A and B: 10 AU
Space between B and C: 1.9 AU
Orbit period of B and C: 8 years
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Somewhere ia a stellar-poor area of the Milky Way lies the dark triplet.
Photo: ESO Online Digitized Sky Survey
Alpha Caeli
Although the double star is the brightest in its constellation, it gains as good as none scientific attention. The exact separation of the two components is a minimum value, modern measurings aren't available.
Star A is a yellowish main sequence star or maybe a weak Delta Scuti variable, whereas star B is a red dwarf and flare star.
Constellation: Caelum
Distance: 65.7 light-years
Space between Alpha Caeli A and B: at least 1000 AU
Orbit period of Alpha Caeli A and B: at least 130 years
Alpha Caeli A
Spectral class: F2
Visual magnitude: 4.46
Luminosity: 5.2 * Sun
Mass: 1.5 * Sun
Diameter: 1.5 * Sun
Alpha Caeli B
Spectral class: M0.5
Visual magnitude: 12.5
Luminosity: 0.01 * Sun
Mass: 0.3 * Sun
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05/16/2006
The B star isn't visible because it is outshined by Alpha Caeli
A. Near the star a probably far distant giant elliptic galaxy can be seen (at the upper left).
Photo: ESO Online Digitized Sky Survey
Mizar and Alcor
Mizar and Alcor is the most famous double star in the sky. Both partners form the middle of the handle of theBig Dipper. At good conditions the double can be seen without problems. However it is not sure if Mizar and Alcor really orbit each other or only are neighbors.
Mizar itself is a quadruple system. All 5 stars are white to blue main sequence stars.
Constellation: Ursa Major
Distance of Mizar: 78.2 light-years
Distance of Alcor: 81.2 light-years
Space between Mizar Aa and Mizar Ab: 0.29 AU
Orbit period of Mizar Aa and Mizar Ab: 20.454 days
Space between Mizar Ba and Mizar Bb: 3.12 AU
Orbit period of Mizar Ba and Mizar Bb: 57 years
Space between Mizar A and Mizar B: 345 AU
Space between Mizar and Alcor: 200 000 AU
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Photo: ESO Online Digitized Sky Survey
Phecda
The white star has a very high rotation speed and therefore casts part of its hull out into space. Most other stars of this kind like Tsih are much biggerblue stars.
Constellation: Ursa Major
Age: 300 million years
Distance: 84 light-years
Spectral class: Ae0
Visual magnitude: 2.44
Luminosity: 64 * Sun
Mass: 2.7 * Sun
Diameter: 3 * Sun
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The Big Dipper, a part of the constellation Ursa Major.
Phecda, one of the seven stars of the Dipper is on the right
just slightly above the middle. The bright star at the top is
Dubhe, the second bright star from left is the double Mizar and Alcor.
Photo: Akira Fuji, ESA
Diphda
The orange-red Beta Ceti, also known as Deneb Kaitos, shines very bright in X-rays. It already finished its red giant stadium, when it fusioned in its outer areas hydrogen to helium. Now the star has shrinked again, fusioning helium to carbon in its core.
Constellation: Cetus
Age: 1 billion years
Distance: 95.8 light-years
Spectral class: K1
Visual magnitude: 2.04
Luminosity: 115 * Sun
Mass: 3 * Sun
Diameter: 23.4 * Sun
Radial velocity: 13.3 km/sec
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Diphda in X-rays.
Photo: Nasa
Rotanev
Rotanev, the brightest star in Delphinus, although called Beta Delphini, is a double star of two similar yellowsubgiants, which have left the main sequence not a long time ago. The slightly bigger A star is in its evolutionary state further as the B star and has catched up with this in spectral class on its way to become ared giant.
Constellation: Delphinus
Distance: 97 light-years
Space between Rotanev A and B: 8 - 18 AU
Orbit period of Rotanev A and B: 26.7 years
Rotanev A
Spectral class: F5
Visual magnitude: 4.0
Luminosity: 18 * Sun
Mass: circa 2 * Sun
Rotanev B
Spectral class: F5
Visual magnitude: 4.9
Luminosity: 8 * Sun
Mass: < 2 * Sun
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03/07/2006
Photo: Starfire Optical Range Mission