by neufer » Mon Sep 03, 2012 2:22 pm
Tszabeau wrote:
Perhaps it should be called the Seven Dwarves since, there are actual brown dwarfs among the non-existent sisters.
- There are more than seven known Pleiades sisters and less than seven known Pleiades dwarfs.
http://en.wikipedia.org/wiki/Teide_1 wrote:
<<Teide 1 was the first brown dwarf to be verified, in 1995. It is located in the Pleiades open star cluster, approximately 400 light years from Earth. The apparent magnitude of this faint object is 17.76, which is so faint that it can only seen in large amateur or bigger telescopes.
This object is more massive than a planet (55 ± 15 MJ), but less massive than a star (0.052 MSun). The radius of the brown dwarf is about that of Jupiter (or one-tenth that of the Sun). Its surface temperature is 2600 ± 150 K, which is about half that of the Sun. Its luminosity is 0.1% that of the Sun, meaning it takes six months for Teide 1 to emit the amount of radiation emitted by the Sun in four hours. Its age is only 120 million years compared to the Sun's age of 4.6 billion years. This brown dwarf is hot enough to fuse lithium in its core, but not hot enough to fuse hydrogen like the Sun.>>
Tszabeau wrote:
Speaking of brown dwarfs, does anyone know if they only form in orbit around fully developed stars or can they form on their own?
Most
known brown dwarfs are in planetary like orbits around other stars.
It is not unreasonable to speculate that most of those that don't orbit stars (including Teide 1 above) escaped from larger shorter lived stars that have lost/ejected over half their mass (thereby making orbital velocity > escape velocity).
http://en.wikipedia.org/wiki/Gliese_229 wrote:
<<Gliese 229 (also written as Gl 229 or GJ 229) is a red dwarf star about 19 light years away in the constellation Lepus. It has 58% of the mass of the Sun, 69% of the Sun's radius, and a very low projected rotation velocity of 1 km/s (vs. ~2 km/s for the Sun) at the stellar equator. The star is known to be a low activity flare star, which means it undergoes random increases in luminosity because of magnetic activity at the surface. The spectrum shows emission lines of calcium in the H and K bands. The emission of X-rays has been detected from the corona of this star. These may be caused by magnetic loops interacting with the gas of the star's outer atmosphere. No large-scale star spot activity has been detected.
In 1994 a substellar companion was imaged and it was confirmed in 1995. Gliese 229B is a brown dwarf orbiting the star; although it is too small to sustain hydrogen-burning nuclear fusion, with a mass of 20 to 50 times that of Jupiter (0.02 to 0.05 solar masses) it is still too massive to be a planet. Gliese 229B was the first confirmed substellar-mass object. This object has a surface temperature of 950 K.>>
Tszabeau wrote:
Do they, in-turn have orbiting planets?
http://en.wikipedia.org/wiki/2M1207 wrote:
<<2M1207, 2M1207A or 2MASS J12073346-3932539 is a brown dwarf located in the constellation Centaurus; a companion object, 2M1207b, may be the first extrasolar planetary mass companion to be directly imaged, and is the first discovered orbiting a brown dwarf.
2M1207 was discovered during the course of the 2MASS infrared sky survey: hence the "2M" in its name, followed by its celestial coordinates. With a fairly early (for a brown dwarf) spectral type of M8, it is very young, and probably a member of the TW Hydrae association. Its estimated mass is around 25 Jupiter masses. The companion, 2M1207b, is estimated to have a mass of 3–10 Jupiter masses. Still glowing red hot, it will shrink to a size slightly smaller than Jupiter as it cools over the next few billion years.
An initial photometric estimate for the distance to 2M1207 was 70 parsecs. In December 2005, American astronomer Eric Mamajek reported a more accurate distance (53 ± 6 parsecs) to 2M1207 using the moving cluster method. The new distance gives a fainter luminosity for 2M1207. Recent trigonometric parallax results have confirmed this moving cluster distance, leading to a distance estimate of 53 ± 1 parsec or 172 ± 3 light years.
Like classical T Tauri stars, many brown dwarfs are surrounded by disks of gas and dust which accrete onto the brown dwarf. 2M1207 was first suspected to have such a disk because of its broad Hα line. This was later confirmed by ultraviolet spectroscopy. The existence of a dust disk has also been confirmed by infrared observations. In general, accretion from disks is known to produce fast-moving jets, perpendicular to the disk, of ejected material. This has also been observed for 2M1207; an April 2007 paper in the Astrophysical Journal reports that this brown dwarf is spouting jets of material from its poles. The jets, which extend around 109 kilometers into space, were discovered using the Very Large Telescope (VLT) at the European Southern Observatory. Material in the jets streams into space at a few kilometers per second.>>
[quote="Tszabeau"]
Perhaps it should be called the Seven Dwarves since, there are actual brown dwarfs among the non-existent sisters.[/quote]
[list]There are more than seven known Pleiades sisters and less than seven known Pleiades dwarfs.[/list]
[quote=" http://en.wikipedia.org/wiki/Teide_1"]
[float=right][img3=""]http://upload.wikimedia.org/wikipedia/commons/thumb/f/f7/Relative_star_sizes.svg/500px-Relative_star_sizes.svg.png[/img3][/float]
<<Teide 1 was the first brown dwarf to be verified, in 1995. It is located in the Pleiades open star cluster, approximately 400 light years from Earth. The apparent magnitude of this faint object is 17.76, which is so faint that it can only seen in large amateur or bigger telescopes.
This object is more massive than a planet (55 ± 15 MJ), but less massive than a star (0.052 MSun). The radius of the brown dwarf is about that of Jupiter (or one-tenth that of the Sun). Its surface temperature is 2600 ± 150 K, which is about half that of the Sun. Its luminosity is 0.1% that of the Sun, meaning it takes six months for Teide 1 to emit the amount of radiation emitted by the Sun in four hours. Its age is only 120 million years compared to the Sun's age of 4.6 billion years. This brown dwarf is hot enough to fuse lithium in its core, but not hot enough to fuse hydrogen like the Sun.>>[/quote][quote="Tszabeau"]
Speaking of brown dwarfs, does anyone know if they only form in orbit around fully developed stars or can they form on their own?[/quote]
Most [url=http://en.wikipedia.org/wiki/List_of_brown_dwarfs]known brown dwarfs[/url] are in planetary like orbits around other stars.
It is not unreasonable to speculate that most of those that don't orbit stars (including Teide 1 above) escaped from larger shorter lived stars that have lost/ejected over half their mass (thereby making orbital velocity > escape velocity).
[quote=" http://en.wikipedia.org/wiki/Gliese_229"]
[float=right][img3=""]http://upload.wikimedia.org/wikipedia/commons/7/78/Brown_Dwarf_Gliese_229B.jpg[/img3][/float]
<<Gliese 229 (also written as Gl 229 or GJ 229) is a red dwarf star about 19 light years away in the constellation Lepus. It has 58% of the mass of the Sun, 69% of the Sun's radius, and a very low projected rotation velocity of 1 km/s (vs. ~2 km/s for the Sun) at the stellar equator. The star is known to be a low activity flare star, which means it undergoes random increases in luminosity because of magnetic activity at the surface. The spectrum shows emission lines of calcium in the H and K bands. The emission of X-rays has been detected from the corona of this star. These may be caused by magnetic loops interacting with the gas of the star's outer atmosphere. No large-scale star spot activity has been detected.
[b][color=#0000FF]In 1994 a substellar companion was imaged and it was confirmed in 1995. Gliese 229B is a brown dwarf orbiting the star; although it is too small to sustain hydrogen-burning nuclear fusion, with a mass of 20 to 50 times that of Jupiter (0.02 to 0.05 solar masses) it is still too massive to be a planet. Gliese 229B was the first confirmed substellar-mass object. This object has a surface temperature of 950 K.[/color][/b]>>[/quote]
[quote="Tszabeau"]
Do they, in-turn have orbiting planets?[/quote][quote=" http://en.wikipedia.org/wiki/2M1207"]
[float=right][img3="[b]European Southern Observatory infrared image of [color=#0000FF]brown dwarf 2M1207A (bluish)[/color] and [color=#FF0000]companion planet 2M1207b (reddish)[/color], taken in 2004.[/b]"]http://upload.wikimedia.org/wikipedia/commons/thumb/0/05/2M1207b_-_First_image_of_an_exoplanet.jpg/512px-2M1207b_-_First_image_of_an_exoplanet.jpg[/img3][/float]
<<2M1207, 2M1207A or 2MASS J12073346-3932539 is a brown dwarf located in the constellation Centaurus; a companion object, 2M1207b, may be the first extrasolar planetary mass companion to be directly imaged, and is the first discovered orbiting a brown dwarf.
2M1207 was discovered during the course of the 2MASS infrared sky survey: hence the "2M" in its name, followed by its celestial coordinates. With a fairly early (for a brown dwarf) spectral type of M8, it is very young, and probably a member of the TW Hydrae association. Its estimated mass is around 25 Jupiter masses. The companion, 2M1207b, is estimated to have a mass of 3–10 Jupiter masses. Still glowing red hot, it will shrink to a size slightly smaller than Jupiter as it cools over the next few billion years.
An initial photometric estimate for the distance to 2M1207 was 70 parsecs. In December 2005, American astronomer Eric Mamajek reported a more accurate distance (53 ± 6 parsecs) to 2M1207 using the moving cluster method. The new distance gives a fainter luminosity for 2M1207. Recent trigonometric parallax results have confirmed this moving cluster distance, leading to a distance estimate of 53 ± 1 parsec or 172 ± 3 light years.
Like classical T Tauri stars, many brown dwarfs are surrounded by disks of gas and dust which accrete onto the brown dwarf. 2M1207 was first suspected to have such a disk because of its broad Hα line. This was later confirmed by ultraviolet spectroscopy. The existence of a dust disk has also been confirmed by infrared observations. In general, accretion from disks is known to produce fast-moving jets, perpendicular to the disk, of ejected material. This has also been observed for 2M1207; an April 2007 paper in the Astrophysical Journal reports that this brown dwarf is spouting jets of material from its poles. The jets, which extend around 109 kilometers into space, were discovered using the Very Large Telescope (VLT) at the European Southern Observatory. Material in the jets streams into space at a few kilometers per second.>>[/quote]