谁还知道 Abell 39？

浩瀚

这是我从百渡上搜到的，谁还有他的更多资料？

Abell 39
Abell 39是 一个美丽的行星状星云，它有着惊人对称的球形。直径约5光年。位于武仙座方向，距离地球约7000光年。这颗银河系中最大的球体，正提供着有关恒星化学组成的有利线索。具有六光年直径的行星状星云 Abell 39 是由一颗与太阳类似的恒星，在数千年前抛出它的大气所造成的。Abell 39 近乎完美的球形，使得天文学家得以精确地估计出有多少相关的物质是真正地在吸收或辐射出光线。观测的结果显示Abell 39的氧含量大约只有太阳的一半。这个一点都不意外的有趣结果，证实了星球间的化学组成都是不一样的。目前天文学家还不知道，为什么中央星会偏离这个行星状星云的球心约0.1光年呢？在照片中，我们可以在Abell39周围与后方，看到实际上是距离地球有数百万光年的星系 。





[ 本帖最后由 夜猫子 于 2007-2-4 22:24 编辑 ]

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http://baike.baidu.com/view/307597.htm 这是地址

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Spherical Planetary Nebula Abell 39


One of the largest spheres in our Galaxy is giving valuable clues about the chemical composition of stars by its very shape. Planetary nebula Abell 39, now six light-years across, was once a sun-like star's outer atmosphere expelled thousands of years ago. The nearly perfect spherical nature of Abell 39 allows astronomers to accurately estimate how much relative material is actually absorbing and emitting light. Observations indicate that Abell 39 contains only about half of the oxygen found in the Sun, an intriguing but not surprising confirmation of the chemical differences between stars. The reason why the central star is slightly off center by 0.1 light-years is currently unknown. Abell 39 lies about 7000 light years away, although several galaxies millions of light years away can be seen through and aroun

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This nebula has the rare property of being extremely round and limb-brightened, exactly as the perfect, simple, theoretical planetary nebula ought to. A high resolution version of this nebula was taken at the WIYN 3.5-m telescope.

Shape: spherical shell, like a bubble

Distance: approx. 7,000 light years

Location: Hercules constellation

RA: 00 28 20.00 DEC: -11 23 24.0

Size: 6 light years across

Abundances/Description: It contains about half the amount of oxygen as the Sun. The central star is slightly off center but the cause of this shift is unknown. Note that you can see small distant galaxies through the image of the nebula.

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The large planetary nebula, Abell 39, appears on the sky as a beautiful, nearly perfect spherical shell, and photometric measurements support that interpretation (see: ). Its very simple geometry offers a special opportunity to test nebular photoionization models with one of the usual uncertainties removed.

Based on imaging in 0.7" seeing at [OIII] 5007 with the WIYN 3.5-m telescope, it has a diameter of 155", as defined by the peak intensity point on the rim, and is circular to within 0.5". The shell thickness that matches the observations best, when modeled with a thin spherical shell projected onto the sky, is 10". A faint, high excitation halo exists outside the main shell, extending the diameter to 190".

Optical spectra obtained at the KPNO Mayall 4-m telescope, combined with UV spectra from the Hubble Space Telescope and STIS, were used to constrain photoionization models (CLOUDY 94.01) to derive the parameters of the nebula and its central star. The star has Teff = 150,000K and a mass ~.6 solar masses. From the photoionization models, the nebula is found to be a factor of 3-4 lower than Solar in metallicity. This result is not unusual by itself, but it does serve as a caution for abundance determinations using the ``ionization correction factor'' (ICF) method, which erroneously predicts a nearly normal abundance. The discrepancy arises from the uniformly high ionization state of helium t

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The simple spherical geometry of planetary nebula Abell 39 will help astronomers identify the source of very serious errors in measuring the chemical composition of dying stars.

"The truly spherical nature of this beautiful nebula helps us eliminate a common confusion concerning the actual three-dimensional geometry of most nebulae," says George Jacoby, director of the Wisconsin-Indiana-Yale-NOAO (WIYN) Observatory and co-author of a study with Gary Ferland of University of Kentucky and Kirk Korista of Western Michigan University.

The butterfly-like shape of many nebulae, and filaments or clumps of dense gas within them, cause starlight to penetrate the nebulae unevenly, depending on the density and thickness of the clumps, as well as the distance of the gas from the star. Only in rare cases can the nebula's geometry be deduced from indirect measurements in order to model the interactions.

As reported today in San Diego at the 197th meeting of the American Astronomical Society, researchers found that the star that produced Abell 39 had only half the amount of oxygen found in the Sun. This result is not especially unusual, because the Sun has a relatively enriched composition of heavy elements. But for some stars, the same sorts of analyses have yielded compositions that can disagree with each other by a factor of three or more.

"Such discrepancies are totally unsatisfactory for developing a detailed picture of how chemical elements were built up over time in our

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看不懂

巴刹拿

翻译来翻译下


上一次那个谁谁不是发过一张英文的帖子吗，后来有个厉害的家伙居然把它翻译了，这次也麻烦了~！