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TOPIC: White dwarf planets


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Posts: 131433
Date:
SDSSJ104341.53+085558.2
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Title: SDSSJ104341.53+085558.2: A second white dwarf with a gaseous debris disc
Authors: B.T. Gaensicke, T.R. Marsh, J. Southworth
(Version v2)

Intermediate resolution spectroscopy of the white dwarf SDSSJ104341.53+085558.2 contains double-peaked emission lines of CaII8498,8542,8662 and identifies this object to be the second single white dwarf to be surrounded by a gaseous disc of metal-rich material, similar to the recently discovered SDSSJ1228+1040. A photospheric Magnesium abundance of 0.3 times the solar value, determined from the observed MgII4481 absorption line, implies that the white dwarf is accreting from the circumstellar material. The absence of Balmer emission lines and of photospheric HeI4471 absorption indicates that the accreted material is depleted in volatile elements and, by analogy with SDSS1228+1040, may be the result of the tidal disruption of an asteroid. Additional spectroscopy of the DAZ white dwarfs WD1337+705 and GD362 does not reveal CaII emission lines. GD362 is one of the few cool DAZ that display strong infrared flux excess, thought to be originating in a circumstellar dust disc, and its temperature is likely too low to sublimate sufficient amounts of disc material to generate detectable CaII emission. WD1337+705 is, as SDSS1228+1040 and SDSS1043+0855, moderately hot, but has the lowest Mg abundance of those three stars, suggesting a possible correlation between the photospheric Mg abundance and the equivalent width of the CaII emission triplet. Our inspection of 7360 white dwarfs from SDSS DR4 fails to unveil additional strong "metal gas disc" candidates, and implies that these objects are rather rare.

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Posts: 131433
Date:
SDSS1228+1040
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Metal Ring Round White Dwarf Solves Missing Planets Puzzle
Astrophysicists at the University of Warwick have found an unusual ring of metal-rich gas orbiting very close around a white dwarf star. The presence of the ring helps solve a problem for astronomers who, up till now, have been puzzled by the apparent absence of planets around white dwarf stars. Their research is published today in the Friday December 22nd edition of the journal Science. Click on the picture above for a print quality high resolution artist's impression of the White Dwarf and its ring.
The research team led by Dr Boris Gänsicke and Professor Tom Marsh from the University of Warwick's Department of Physics found this unusual gas disc around a relatively young white dwarf star called SDSS1228+1040. It is located in the constellation Virgo and it is around 463 light years distant from our solar system. The star became a white dwarf around 100 million years ago, and is still fairly hot with a surface temperature around 22000 degrees.

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Posts: 131433
Date:
SDSS 1228+1040
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An asteroid has been ripped to shreds and vaporized after straying too close to a hot white dwarf star, observations suggest. The asteroid was probably flung towards the white dwarf by the gravity of one or more unseen planets, astronomers say.
Stars like the Sun become bloated red giants when they age, then gradually blow off their outer layers until only a dense, inactive core called a white dwarf is left.
Scientists are interested in signs of planets and asteroids around these stellar embers because they offer a preview of what will eventually happen to solar systems like our own.
Astronomers have previously seen other white dwarfs orbited by dusty debris discs and with unusually large amounts of metal on their surfaces, suggesting they are absorbing asteroids that have wandered too close to them and been torn apart.
Now, researchers led by Boris Gaensicke of the University of Warwick, UK, have found the best evidence yet of an asteroid being consumed by a white dwarf. The evidence comes in the form of a hot ring of metallic vapour around a white dwarf called SDSS 1228+1040.

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Posts: 131433
Date:
4U 0142+61 8
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Title: A Debris Disk Around An Isolated Young Neutron Star
Authors: Zhongxiang Wang, Deepto Chakrabarty, David L. Kaplan (MIT)

Pulsars are rotating, magnetized neutron stars that are born in supernova explosions following the collapse of the cores of massive stars. If some of the explosion ejecta fails to escape, it may fall back onto the neutron star or it may possess sufficient angular momentum to form a disk.
Such 'fallback' is both a general prediction of current supernova models and, if the material pushes the neutron star over its stability limit, a possible mode of black hole formation. Fallback disks could dramatically affect the early evolution of pulsars, yet there are few observational constraints on whether significant fallback occurs or even the actual existence of such disks. Here we report the discovery of mid-infrared emission from a cool disk around an isolated young X-ray pulsar.
The disk does not power the pulsar's X-ray emission but is passively illuminated by these X-rays.
The estimated mass of the disk is of order 10 Earth masses, and its lifetime (at least a million years) significantly exceeds the spin-down age of the pulsar, supporting a supernova fallback origin. The disk resembles protoplanetary disks seen around ordinary young stars, suggesting the possibility of planet formation around young neutron stars.


Infrared images of the 4U 0142+61 field.
Spitzer/IRAC mid-IR images taken on 17 January 2005 in the 8.0 µm band (a; 75 min exposure) and the 4.5 µm band (b; 77 min exposure).


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Posts: 131433
Date:
Pulsar 4U 0142+61
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The Spitzer Space Telescope has uncovered new evidence that planets might rise up out of a dead star's ashes.

The infrared telescope surveyed the scene around a pulsar, the remnant of an exploded star, and found a surrounding disk made up of debris shot out during the star's death throes. The dusty rubble in this disk might ultimately stick together to form planets.
This is the first time scientists have detected planet-building materials around a star that died in a fiery blast.

"We're amazed that the planet-formation process seems to be so universal. Pulsars emit a tremendous amount of high energy radiation, yet within this harsh environment we have a disk that looks a lot like those around young stars where planets are formed" - Dr. Deepto Chakrabarty of the Massachusetts Institute of Technology in Cambridge, principal investigator of the new research.

A paper on the Spitzer finding appears in the April 6 issue of Nature. Other authors of the paper are lead author Zhongxiang Wang and co-author David Kaplan, both of the Massachusetts Institute of Technology.

The finding also represents the missing piece in a puzzle that arose in 1992, when Dr. Aleksander Wolszczan of Pennsylvania State University found three planets circling a pulsar called PSR B1257+12. Those pulsar planets, two the size of Earth, were the first planets of any type ever discovered outside our solar system. Astronomers have since found indirect evidence the pulsar planets were born out of a dusty debris disk, but nobody had directly detected this kind of disk until now.



The pulsar observed by Spitzer, named 4U 0142+61, is 13,000 light-years away in the Cassiopeia constellation. It was once a large, bright star with a mass between 10 and 20 times that of our sun. The star probably survived for about 10 million years, until it collapsed under its own weight about 100,000 years ago and blasted apart in a supernova explosion.

Some of the debris, or "fallback," from that explosion eventually settled into a disk orbiting the shrunken remains of the star, or pulsar. Spitzer was able to spot the warm glow of the dusty disk with its heat-seeking infrared eyes. The disk orbits at a distance of about 1 million miles and probably contains about 10 Earth-masses of material.
Pulsars are a class of supernova remnants, called neutron stars, which are incredibly dense. They have masses about 1.4 times that of the sun squeezed into bodies only 10 miles wide. One teaspoon of a neutron star would weigh about 2 billion tons. Pulsar 4U 0142+61 is an X-ray pulsar, meaning that it spins and pulses with X-ray radiation.
Any planets around the stars that gave rise to pulsars would have been incinerated when the stars blew up. The pulsar disk discovered by Spitzer might represent the first step in the formation of a new, more exotic type of planetary system, similar to the one found by Wolszczan in 1992.

"I find it very exciting to see direct evidence that the debris around a pulsar is capable of forming itself into a disk. This might be the beginning of a second generation of planets" - Dr. Aleksander Wolszczan.

Pulsar planets would be bathed in intense radiation and would be quite different from those in our solar system.

"These planets must be among the least hospitable places in the galaxy for the formation of life" - Dr. Charles Beichman, astronomer at NASA's Jet Propulsion Laboratory and the California Institute of Technology, both in Pasadena, California.

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Posts: 131433
Date:
PSR B1257+12
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"At the time those planets were discovered, it was a puzzle how they could have formed, although the one way that astronomers know to form planets is out of some sort of disk of debris. No one had ever seen a disk around a pulsar, around an old dead star." - Deepto Chakrabarty of the Massachusetts Institute of Technology.

Using the Spitzer Space Telescope observatory a team of astronomers spied the disk around a pulsar about 13,000 light-years from Earth, in the constellation Cassiopeia.

The 3 planet system circling a pulsar called PSR B1257+12 was discovered by Aleksander Wolszczan in 1992 using the Arecibo radio telescope in Puerto Rico.

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Posts: 131433
Date:
White dwarf planets
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Astronomers using NASA's Spitzer Space Telescope will hold a media teleconference at 1 p.m. EDT Wednesday, April 5 to announce the discovery of a strange place where planets might be forming.

Astronomers have found five stellar corpses that appear to be swallowing asteroids that once orbited them. The discoveries suggest terrestrial planets are common in the universe and that future missions should be able to image planets around the faint, dead stars.

About 10% of all white dwarfs show signs of metals in the spectra– and thus probable planetary systems.

Read more (April 5th)

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