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Estrellas Especiales III

Z Camelopardalis

This binary of a yellow post main sequence star and a white dwarf was one of the first dwarf novae to be discovered. It erupts every few weeks, increasing the star's luminosity about 40 times. In March 2007 has been found that this star can produce real novae, too. This is shown by the shreds of gas around it. These many thousand times brighter eruptions occur only about every 10 000 years.

Constellation: Camelopardalis

Distance: 530 light-years

Spectral class: G1

Visual magnitude: 10.2

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03/09/2007

Photo: NASA/JPL-Caltech

Geminga

Geminga is a very weak neutron star and the pulsar next to us, which almost only emits extremely hard gamma-rays, but no radio waves. Why this is so is unknown. It has a period of 4.2 revolutions per second.

The supernova explosion 300 000 years ago, which left behind Geminga, could be responsible for the existence of the Local Bubble. Some thousand years ago our Sun entered this several hundred light-years big area, which is nearly dust-free.

Constellation: Gemini

Age: 300 000 years

Distance: 552 light-years

Visual magnitude: 25.5

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06/27/2006

The arrow points to the direction in which Geminga moves.

Photo: Image courtesy of P.A. Caraveo (INAF/IASF), Milan and ESA.

L1014

A very young star, the smallest of this age discovered so far. It is hidden within a dark cosmic cloud in which no stars have been suspected. If it won't grow much more it will become a brown dwarf.

Constellation: Cygnus

Age: 10 000 - 100 000 years

Distance: 600 light-years

Luminosity: 0.2 * Sun

Mass: 0.024 * Sun (25 * Jupiter)

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Photo: Tyler Bourke & Tracy Huard (CfA)

CW Leonis

The pulsating red giant once was surrounded by billions of comets. Due to its expansion these now melt to water, which we can measure quite good from earth. The star's temperature is yet just 2300 kelvin. It will die in maybe 10 000 - 30 000 years and then be a planetary nebula and a white dwarf.

The spectral class C refers to its extremely high content of carbon. Otherwise it would be an M star.

Constellation: Leo

Distance: 650 light-years

Spectral class: C9.5

Visual magnitude: 10.96 - 14.8

Luminosity: 20 000 * Sun

Mass: 1.5 - 4 * Sun

Diameter: 500 * Sun

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Graphic: Smithsonian Astrophysical Observatory

R Aquarii

R Aquarii is a symbiotic star, a double whose partners exchange matter. The A star, a Mira-type red giant, is orbited by a very hot white dwarf or the progenitor of a white dwarf in a very excentric orbit.

Doing so, the partners cast out jets and could possibly generate novae. Maybe they are responsible for a nova in 1073.

Constellation: Aquarius

Distance: 650 light-years

Space between R Aquarii A and B: 5 - 30 AU

Orbit period of R Aquarii A and B: 18 years

R Aquarii A

Spectral class: M5 - M8.5

Visual magnitude: 5.8 - 11.5

Luminosity: 5000 * Sun

Mass: 1.75 * Sun

Diameter: 355 * Sun

R Aquarii B

Mass: 1 * Sun

Diameter: circa 0.03 * Sun (3 * Earth)

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Photo: Anglo-Australian Observatory/Royal Obs. Edinburgh

Helix Nebula

The Helix Nebula or NGC 7293 is one of the nearest planetary nebulae. When it still was an ordinary star, it probably was orbited by planets, asteroids and comets. These were scorched into a dust disk which now trickles down on the 110 000 Kelvin hot white dwarf. Thereby X-rays are generated.

Constellation: Aquarius

Distance: 680 light-years

Helix Nebula

Age: 10 600 years

Visual magnitude: 7,3

Diameter: 2.5 light-years

The white dwarf

Visual magnitude: 13

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02/04/2007

Photo: NASA/JPL-Caltech/K. Su (University of Arizona)

Phi Persei

The close double system one million years ago consisted of two stars with 6 times (star B) and 5 times (star A) the mass of the Sun. Then the bigger one started to expand and got swallowed up by its partner nearly completely. Left behind is the hot core of star B, in which still fusion processes take place. It is a visible progenitor star of a white dwarf. Normally this stadium is hidden underneath the surface of a red giant.

On the other hand star A, which without its partner would be nearing its end as well, received a huge amount of fresh hydrogen. Its rotational speed enormously was raised by that and the star got flattened. It is surrounded by a gas disk which is eight times wider than the star itself.

When finally in the far distant future star A will expand, then the tables will turn and star B will consume its hull.

Constellation: Perseus

Age: 10 million years

Distance: 720 light-years

Space between Phi Persei A and B: 1 AU

Orbit period of Phi Persei A and B: 127 days

Phi Persei A

Spectral class: B2Vpe

Visual magnitude: 4.09

Luminosity: 2000 * Sun

Mass: 9 * Sun

Phi Persei B

Visual magnitude: 6

Luminosity: 200 * Sun

Mass: 1 * Sun

Graphic: Bill Pounds

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FK Comae Berenices

The yellow giant attracts attention by the enormous activity of its surface. This is marked by numerous sunspots, many more as we know from our Sun.

The star rotates with 180 km/sec and changes, due to the spots, every 2.40 days its luminosity for 0.1 visual magnitudes.

Constellation: Coma Berenices

Distance: 760 light-years

Spectral class: G5 - G8

Visual magnitude: 8.17

Luminosity: 30 * Sun

Diameter: 8 * Sun

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The temperature distribution for different points in time.

Graphic: Heidi Korhonen

L1157

This young star hasn't started the nuclear fusion yet and obtains its energy still from the collapse of its birth cloud. It emits two opponent jets, each three quarters of a light-year long. Those have just recently broke through the surrounding cloud. L1157 is orbited by a disk of matter, which once could form a planetary system. It is the first star to be discovered in this state of stellar evolution.

Constellation: Cepheus

Age: 10 000 years

Distance: 800 light-years

Mass: circa 1 * Sun

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11/30/2007

Photo: NASA/JPL-Caltech/UIUC

HD 12545

On our Sun we can often see sunspots. But those are nothing compared to what this red giant has to offer. One spot, 10 000 times bigger than the largest sunspot, is 1300 kelvin cooler than the rest of its surface with its 4800 kelvin.

The star makes a full rotation every 24 days.

Constellation: Triangulum

Distance: 1076 light-years

Spectral class: K0

Visual magnitude: 8.41

Mass: 2 * Sun

Diameter: 10 * Sun

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Graphic: NOAO/AURA/NSF

32 Cygni (Omicron-2 Cygni)

This is an eclipsing binary of the Algol type. A red giant or supergiant is orbited by a blue star. But the dimming amounts to only 0.06 magnitudes, because the blue star can shine through the thin atmosphere of the red from behind.

At the giant protuberances (eruptions) with a length of 30 solar diameters have been observed.

Constellation: Cygnus

Age: < 20 million years

Distance: 1100 light-years

Visual magnitude A and B: 3.98

Orbit period of 32 Cygni A and B: 3.143 years

32 Cygni A

Spectral class: K2

Luminosity: 11 100 * Sun

Mass: 9.7 * Sun

Diameter: 230 * Sun

32 Cygni B

Spectral class: B3

Mass: 5 * Sun

Diameter: 3.5 * Sun

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The long nebula near the star has nothing to do with it.

Photo: ESO Online Digitized Sky Survey

Brown Dwarfs 2MASS J05352184-0546085

The pair of young brown dwarfs lies in the Orion Nebula. It is an eclipsing binary. Due to that the mass and size of the two could be measured very exactly.

The dwarfs do still shrink and therefore are very large and hot for their mass. Their temperatures are 2700 and 2800 Kelvin. Interestingly the bigger one is the cooler. Probably this is because it is younger, about 500 000 years old. The double then formed later from the individual brown dwarfs.

Constellation: Orion

Age: 1 million years

Distance: 1420 light-years

Orbit period of 2MASS J05352184-0546085 A and B: 9.78 days

2MASS J05352184-0546085 A

Spectral class: M6.5

Luminosity: 0.020 * Sun

Mass: 55 * Jupiter (0.0541 * Sun)

Diameter: 0.7 * Sun

2MASS J05352184-0546085 B

Spectral class: M6.5

Luminosity: 0.014 * Sun

Mass: 35 * Jupiter (0.0340 * Sun)

Diameter: 0.5 * Sun

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03/16/2006

Graphic: N

HH 34

The Protostar HH 34 near Orion Nebula has got two gaseous jets. These throw out gas with a speed of 250 km/sec. They are produced by material falling on the star and heating up.

The Protostar hasn't reached the T Tauri stadium yet.

Constellation: Orion

Distance: 1500 light-years

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The Protostar is at the bottom in the middle.

Photo: Eso

V380 Orionis

A very young white mean sequence star near the Orion Nebula. It is still surrounded by the cloud (NGC 1999) from which it was formed. The black cloud in the foreground is a Bok globule where a new star develops.

Constellation: Orion

Distance: 1500 light-years

Spectral class: A0

Visual magnitude: 10.7

Mass: 3.5 * Sun

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Photo: Nasa, Hubble Telescope

Rosette HH1

Stars arise from gaseous nebulae and grow during the formation phase by attracting additional gas. But thisprotostar in the Rosetta Nebula is one of the last stars to form there, so for it isn't much gas left. It even blows an 8000 AU long jet into space. And so it will become a red or brown dwarf , if it doesn't disintegrate completely before.

Constellation: Monoceros

Distance: 1500 light-years

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Photo: T. Rector/University of Alaska Anchorage, WIYN and NOAO/AURA/NSF

Nova Persei 1901 (GK Persei)

In 1901 this impressing nova occured, which for a short while could keep up with the brightest stars in the sky. In less than two days the star increased its brightness 10 000 times.

The double star GK Persei is an unusual nova star. Both partners are relative far away from each other, which makes a flowing of matter from the bigger partner to the white dwarf (B) difficult. Admittedly the bigger star (A) is about to leave the main sequence and therefore increases its diameter.

Today there are still every 3-4 years mini-novae at which the star increases its brightness by only ten times. The so called Firework Nebula, a remnant from 1901, has an expansion speed of 1200 km/s.

Constellation: Perseus

Distance: 1533 light-years

Orbit period of GK Persei A and B: 1.996803 days

Spectral class von GK Persei A: K2

Visual magnitude: 13.1 normal - 0.2 as nova

Mass des Nebels: 0.0001 * Sun

Diameter des Nebels: 0.7 light-years

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The Firework Nebula and GK Persei A in the center.

Photo: NOAO/AURA/NSF

Nova Herculis 1934 (DQ Herculis)

DQ Herculis is a very close system of a white dwarf (A) and a red dwarf (B). Here in 1934 a slow novaexploded. Due to this pair in 1956 the phenomenon of the novae was understood.

Constellation: Hercules

Distance: 1600 light-years

Orbit period of DQ Herculis A and B: 4.65 hours

Spectral class von DQ Herculis B: M

Visual magnitude: 14.4 normal - 1.5 as nova

Luminosity as nova: 100 000 * Sun

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The nova remnant in the year 1993.

Photo: William Herschel Telescope

The NGC 2440-Star

NGC 2440 is a name for a planetary nebula, the Insect Nebula. In its center is a white dwarf, which emitted the nebula not long ago.

This white dwarf is the hottest star known so far. Its surface temperature is more than 200 000 kelvin (ourSun has only 6000).

Constellation: Puppis

Distance: 1600 light-years

Visual magnitude: 17.7

Luminosity: 250 * Sun

Mass: 1 * Sun

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Photo: Nasa

RX J0806

The pair of white dwarfs is the narrowest known double star and one of the strongest sources for gravitational waves in our Milky Way. Each year the orbit period decreases for 1.2 milliseconds and the distance gets half a meter less. So the stars will crash together in several hundred thousand years.

Constellation: Cancer

Distance: 1600 light-years

Mass A and B: each 0.5 * Sun

Space between RX J0806 A and B: 0.0005 AU

Orbit period of RX J0806 A and B: 321 seconds

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Graphic: GSFC/D. Berry

FU Orionis

The big young star hasn't reached the main sequence yet. It will continue to shrink and meanwhile heat up.

In the year 1936 it suddenly appeared in the sky, before it was an undiscovered tiny star of 16. magnitude. But it wasn't a nova, the star kept its new magnitude. What happened was the following: the dust disk around the star came closer to it, heated up, ionized and to a part fell down on it. The disk began to glow and let pass the light better than before.

Constellation: Orion

Distance: 1600 light-years

Spectral class: G0

Visual magnitude: 9.5

Luminosity: 80 * Sun

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Photo: ESO Online Digitized Sky Survey

MACHO-LMC-5

MACHO-LMC-5 is a very small red dwarf in our galaxy, STAR-0516-7029 however is a blue star in the Large Magellanic Cloud. In the years 1993 - 1994 the smaller passed in front of the visual equally bright, but much more luminous blue one - a microlensing event. By that the brightness of the blue one was multiplied. And as a result in 2004 for the first time the mass of a single star (the red one) beyond the Sun could be measured directly with the help of the Hubble Telescope.

Constellation: Dorado

Distance: 1800 light-years

Spectral class: M4-5

Mass: 0.097 * Sun

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02/08/2007

MACHO-LMC-5 (red) and STAR-0516-7029 (blue)

Photo: NASA, ESA and D. Bennett (University of Notre Dame)

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