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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

Back: List of Special Stars

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

Back: List of Special Stars

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

Back: List of Special Stars

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

Back: List of Special Stars

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

Back: List of Special Stars

03/07/2006

Photo: Starfire Optical Range Mission

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