Cassiopeia A - Astronomy News

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Date: Oct 30 12:54 2006

RE: Cassiopeia A	Permalink

Title: Spitzer IRAC Images and Sample Spectra of Cassiopeia A's Explosion Authors: J. A. Ennis (1), L. Rudnick (1), W. T. Reach (2), J. D. Smith (3), J. Rho (2), T. DeLaney (4), H. Gomez (5), T. Kozasa (6) ((1) University of Minnesota, (2) California Institute of Technology, (3) Steward Observatory, (4) Harvard-Smithsonian Center for Astrophysics, (5) University of Wales, (6) Hokkaido University) We present Spitzer IRAC images, along with representative 5.27 to 38.5 micron IRS spectra of the Cassiopeia A supernova remnant. We find that various IRAC channels are each most sensitive to a different spectral and physical component. Channel 1 (3.6 micron) matches radio synchrotron images. Where Channel 1 is strong with respect to the other channels, the longer-wavelength spectra show a broad continuum gently peaking around 26 micron, with weak or no lines. We suggest that this is due to un-enriched progenitor circumstellar dust behind the outer shock, processed by shock photons and electrons. Where Channel 4 (8 micron) is bright relative to the other IRAC channels, the long-wavelength spectra show a strong, 2-3 micron-wide peak at 21 micron, likely due to silicates and proto-silicates, as well as strong ionic lines of (Ar II), (Ar III), (S IV) and (Ne II). In these locations, the dust and ionic emission originate from the explosion's O-burning layers. The regions where Channels 2 (4.5 micron) and 3 (5.6 micron) are strongest relative to Channel 4 show a spectrum that rises gradually to 21 micron, and then flattens or rises more slowly to longer wavelengths, along with higher ratios of (Ne II) to (Ar II). Dust and ionic emission in these locations arise primarily from the C- and Ne- burning layers. These findings are consistent with asymmetries in the explosion producing variations in the velocity structure in different directions, but preserving the nucleosynthetic layers. At each location, the dust and ionic lines in the mid-infrared, and the hotter and more highly ionised optical and X-ray emission are then dominated by the layer currently encountering the reverse shock in that direction. Read more (1334kb, PDF) __________________

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Date: Oct 26 22:58 2006

NASA's Spitzer Peels Back Layers of Star's Explosion	Permalink

Astronomers using NASA's infrared Spitzer Space Telescope have discovered that an exploded star, named Cassiopeia A, blew up in a somewhat orderly fashion, retaining much of its original onion-like layering. "Spitzer has essentially found key missing pieces of the Cassiopeia A puzzle" - Jessica Ennis of the University of Minnesota, Minneapolis, lead author of a paper to appear in the Nov. 20 issue of the Astrophysical Journal. Read more -- Edited by Blobrana at 00:00, 2006-10-27 __________________

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Date: Aug 29 18:25 2006

RE: Cassiopeia A	Permalink

A new image taken with NASA's Hubble Space Telescope provides a detailed look at the tattered remains of a supernova explosion known as Cassiopeia A (Cas A) that is about 10,000 light-years away in the constellation Cassiopeia. It is the youngest known remnant from a supernova explosion in the Milky Way. The new Hubble image shows the complex and intricate structure of the star's shattered fragments. The image is a composite made from 18 separate images taken in December 2004 using Hubble's Advanced Camera for Surveys (ACS). Expand (1.2mb, 1280 x 921) Position (2000): R.A. 23h 23m 24s Dec. +58° 48' 54" Cerdit NASA Source __________________

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Date: Sep 22 20:00 2005

Tycho's supernova	Permalink

Tycho's Remnant Provides Shocking Evidence for Cosmic Rays In 1572, the Danish astronomer Tycho Brahe observed and studied the explosion of a star that became known as Tycho's supernova in the constellation Cassiopeia . More than four centuries later, a Chandra x-ray telescopic image of the supernova remnant shows an expanding bubble of multimillion degree debris (green and red) inside a more rapidly moving shell of extremely high energy electrons (filamentary blue). Expand Position(2000): RA 00h 25m 17s , Dec +64 ° 08' 37" The supersonic expansion (about nine million kilometres per hour) of the stellar debris has created two X-ray emitting shock waves - one moving outward into the interstellar gas, and another moving back into the debris. These shock waves produce sudden, large changes in pressure and temperature, like an extreme version of sonic booms produced by the supersonic motion of airplanes. According to the standard theory, the outward-moving shock wave should be about 2 light years ahead of the stellar debris. What Chandra found instead is that the stellar debris has kept pace with the outer shock and is only about half a light year behind. The Chandra result for Tycho's remnant significantly changes astronomers' view of the evolution of supernova remnants. A large component of cosmic ray nuclei alters the dynamics of the shock wave, and may require changing the way that astronomers estimate the explosive energy of a supernova from the properties of its remnant. "The most likely explanation for this behaviour is that a large fraction of the energy of the outward-moving shock wave is going into the acceleration of atomic nuclei to speeds approaching the speed of light" - Jessica Warren, Rutgers University. The Chandra observations provide the strongest evidence yet that nuclei are indeed accelerated and that the energy contained in the high-speed nuclei in Tycho's remnant is about 100 times that observed in high-speed electrons. "With only a single object involved we can't state with confidence that supernova shock waves are the primary source of cosmic rays. What we have done is present solid evidence that the shock wave in at least one supernova remnant has accelerated nuclei to cosmic ray energies" - John P. Hughes of Rutgers University in Piscataway, New Jersey, and coauthor of a report to be published in an upcoming issue of The Astrophysical Journal. This finding is important for understanding the origin of cosmic rays, the high-energy nuclei which pervade the Galaxy and constantly bombard the Earth. Since their discovery in the early years of the 20th century, many sources of cosmic rays have been proposed, including flares on the sun and similar events on other stars, pulsars, black hole accretion disks, and the prime suspect - supernova shock waves. Chandra's observations of Tycho's supernova remnant strengthen the case for this explanation. __________________

Blobrana

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Posts: 131433

Date: Jun 16 17:44 2005

RE: Cassiopeia A	Permalink

On November 11, 1572, Tycho Brahe noticed a star in the constellation Cassiopeia that was as bright as the planet Jupiter (which was in the night sky in Pisces). No such star had ever been observed at this location before. It soon equalled Venus in brightness (-4.5 magnitude in the predawn sky). For about two weeks the star could be seen in daylight. By the end of November it began to fade , and was lost... Expand Until now... The Hubble Space Telescope Wide Field Planetary Camera-2 captured an image of a small section of sky containing a candidate star, the progenitor companion to Tycho's Supernova. The star, 9,800 light-years away, is like our Sun except several billion years older, and moving through space at three times the speed of the other stars in its neighbourhood. This discovery provides the first direct evidence supporting the long-held belief that Type Ia supernovae come from binary star systems containing a normal star and a burned-out white dwarf star. The normal star spills material onto the dwarf, which eventually triggers an explosion. Expand Position (J2000): R.A. 00h 25m 08s.07 Dec. +64ï¿½ 09' 55".7 __________________

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Date: Jun 10 15:21 2005

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Title: Infrared Echoes near the Supernova Remnant Cassiopeia A
Authors: O. Krause, G. H. Rieke, S. M. Birkmann, E. Le Floc'h, K. D. Gordon, E. Egami, J. Bieging, J. P. Hughes, E. T. Young, J. L. Hinz, S. P. Quanz, D. C. Hines

Two images of Cassiopeia A obtained at 24 micrometer with the Spitzer Space Telescope over a one year time interval show moving structures outside the shell of the supernova remnant to a distance of more than 20 arcmin.
Individual features exhibit apparent motions of 10 to 20 arcsec per year, independently confirmed by near-infrared observations. The observed tangential velocities are at roughly the speed of light. It is likely that the moving structures are infrared echoes, in which interstellar dust is heated by the explosion and by flares from the compact object near the center of the remnant.

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Blobrana

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Date: Jun 9 21:59 2005

RE: 3 Cassipeiae	Permalink

Expand This composite picture shows the progression of the light echo in the course of a year. Features that haven't changed show up in white and grey. Emissions from Nov. 30, 2003, are marked in blue. New emissions from Dec. 2, 2004, are marked in orange. This gaseous shell is about 10 light years in diameter, and has a temperature of about 50 million degrees. Cassiopeia A is the youngest known supernova remnant in our Milky Way Galaxy, and the strongest extrasolar radio source in the sky. Tracing its expansion, astronomers have found that the supernova must have blown up around the year 1667. Strangely, it was not widely noticed by astronomers of the time. However, it was perhaps observed by John Flamsteed on August 16, 1680, who catalogued a star near its position as "3 Cassiopeiae". However, he did not recognize it as a supernova, or "New Star", and simply catalogued it as ordinary star. As this star was not noticed elsewhere, it cannot have been much brighter than 6th magnitude. Later astronomers didn't find any sufficiently bright star near Flamsteed's position, and classified his catalogue entry as erroneous. As the supernova was rather close, its observed maximum brightness was extremely faint for a supernova, only about 250,000 solar luminosities, fainter than the brighter "normal" stars. This indicates that it was heavily obscured by interstellar matter. The supernova remnant was found among the earliest discrete radio sources, in 1947 by radio astronomers from Cambridge, England, and is the strongest radio source in the sky beyond the solar system. This radio source was first named Cassiopeia A and later catalogued 3C 461. Its optical counterpart couldn’t be found until a more precise position was obtained, by radio interferometry in 1950. Consequently, David Dewhirst of Cambridge obtained first deep optical photos of this region in the sky and discovered a strange faint nebula, which was then investigated by Walter Baade and Rudolph Minkowski with the then-new Palomar 5-meter telescope. Spectroscopic observations soon confirmed the rapidly expanding shell of a supernova remnant, and it was also catalogued as G111.7-2.1. Within two years, American astronomers were able to determine its angular expansion rate, and calculating back confirmed that the expansion must have started around the year AD 1667. But it is a mystery as to the position of "3 Cassipeiae" which does not exactly coincide with that of Cassiopeia A, and some historians think Flamsteed may simply have catalogued an erroneous position of another star. -- Edited by Blobrana at 23:03, 2005-06-09 __________________

Blobrana

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Date: Jun 9 21:32 2005

Cassiopeia A	Permalink

An enormous light echo etched in the sky by a fitful dead star was spotted by the infrared eyes of NASA's Spitzer Space Telescope. An echo has been detected around a star that died 325 years ago in the constellation Cassiopeia. The reverberation implies that the stellar remnant let out a burst of energy 50 years ago. The dead star in question is Cassiopeia A, whose explosion or supernova was witnessed by Tycho Brahe in 1572. Situated 10,000 light years away, astronomers believe a dense neutron star is all that is left of the original star. "We had thought the stellar remains inside Cassiopeia A were just fading away. Spitzer came along and showed us this exploded star, one of the most intensively studied objects in the sky, is still undergoing death throes before heading to its final grave " - Dr. Oliver Krause, University of Arizona, Tucson. Expand Position (J2000): RA: 23:23:24 Dec: +58:48.9 This stunning false-colour picture shows off the many sides of the supernova remnant Cassiopeia A. It is made up of images taken by three of NASA's Great Observatories, using three different wavebands of light. Infrared data from the Spitzer Space Telescope are coloured red; visible data from the Hubble Space Telescope are yellow; and X-ray data from the Chandra X-ray Observatory are green and blue. Spitzer reveals warm dust in the outer shell about a few hundred degrees Kelvin (80 degrees Fahrenheit) in temperature, Hubble sees the delicate filamentary structures of hot gases about 10,000 degrees Kelvin (18,000 degrees Fahrenheit). Chandra probes unimaginably hot gases, up to about 10 million degrees Kelvin (18 million degrees Fahrenheit). These extremely hot gases were created when ejected material from Cassiopeia A smashed into surrounding gas and dust. Chandra can also see Cassiopeia A's neutron star (turquoise dot at centre of shell). Blue Chandra data were acquired using broadband X-rays (low to high energies); green Chandra data correspond to intermediate energy X-rays; yellow Hubble data were taken using a 900 nanometer-wavelength filter, and red Spitzer data are from the telescope's 24-micron detector. Infrared echoes trace the dusty journeys of light waves blasted away from supernova or erupting stars. As the light waves move outward, they heat up clumps of surrounding dust, causing them to glow in infrared light. The echo from Cassiopeia A is the first witnessed around a long-dead star and the largest ever seen. It was discovered by accident during a Spitzer instrument test. "We had no idea that Spitzer would ever see light echoes. Sometimes you just trip over the biggest discoveries " - Dr. George Rieke of the University of Arizona. A supernova remnant like Cassiopeia A typically consists of an outer, shimmering shell of expelled material and a core skeleton of a once-massive star, called a neutron star. Neutron stars come in several varieties, ranging from intensely active to silent. Typically, a star that has recently died will continue to act up. Consequently, astronomers were puzzled that the star responsible for Cassiopeia A appeared to be silent so soon after its death. The new infrared echo indicates the Cassiopeia A neutron star is active and may even be an exotic, spastic type of object called a magnetar. Magnetars are like screaming dead stars, with eruptive surfaces that rupture and quake, pouring out tremendous amounts of high-energy gamma rays. Spitzer may have captured the "shriek" of such a star in the form of light zipping away through space and heating up its surroundings. "Magnetars are very rare and hard to study, especially if they are no longer associated with their place of origin. If we have indeed uncovered one, then it will be just about the only one for which we know what kind of star it came from and when," -Dr. George Rieke. Astronomers first saw hints of the infrared echo in strange, tangled dust features that showed up in the Spitzer test image. When they looked at the same dust features again a few months later using ground-based telescopes, the dust appeared to be moving outward at the speed of light. Follow-up Spitzer observations taken one year later revealed the dust was not moving, but was being lit up by passing light. A close inspection of the Spitzer pictures revealed a blend of at least two light echoes around Cassiopeia A, one from its supernova explosion, and one from the hiccup of activity that occurred around 1953. Additional Spitzer observations of these light echoes may help pin down their enigmatic source. Krause was lead author with Rieke of a study about the discovery appearing this week in the journal Science. -- Edited by Blobrana at 22:35, 2005-06-09 __________________

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