本帖最后由 gohomeman1 于 2009-11-25 01:24 编辑
http://hubblesite.org/newscenter/archive/releases/2008/2008/21/full/results/20/
The full news release story:
报告全文：
Call it the case of the missing dwarf.
这是一个白矮星失踪案例。
A team of stellar astronomers is engaged in an interstellar CSI (crimescene investigation). They have two suspects, traces of assault andbattery, but no corpse.
一个恒星天文学家团队正在进行星际犯罪现场调查（CSI）。他们找到了两个嫌疑分子，也发现了攻击后的痕迹，但没找到尸体。
The southern planetary nebula SuWt 2 is the scene of the crime, some6,500 light-years from Earth in the direction of the constellationCentaurus.
位于南天半人马座南部的行星状星云SuWt2就是这个犯罪现场，它离我们约6500光年。
SuWt 2 consists of a bright, nearly edge-on glowing ring of gas. Faintlobes extend perpendicularly to the ring, giving the faintest parts ofthe nebula an hourglass shape.
SuWt2有一个明亮的近环形发光气体环，暗弱的两瓣从环边垂直延伸出去，这些最暗淡的部分像一个沙漏状。
These glowing ejecta are suspected to have been energized by a starthat has now burned out and collapsed to a white dwarf. But the whitedwarf is nowhere to be found.
这些发光喷射物怀疑是由一颗已经爆发为白矮星的恒星所激发，但科学家找不到白矮星。
The mystery deepened when researchers obtained ultraviolet observations in the early 1990's with NASA's International Ultraviolet Explorer satellite, expecting to see signs of a faint but very hot star. But no ultraviolet radiation was detected.
当NASA的国际紫外线探测卫星（IUE）在上世纪90年代上天，研究人员拥有了紫外观测能力后，迷雾更重了。研究者希望发现单个黯淡但非常热的恒星的紫外辐射，但并没有探测到。
Instead, at the center of the nebular ring are two suspicious characters: a pair of tightly bound stars that whirl around each other every five days, neither one of which is a white dwarf. These stars are hotter than our Sun (their spectral class is A) but they are still not hot enough to make the nebula glow.Only a flood of ultraviolet radiation, such as that from the missingwhite dwarf, could do that.
取而代之的是，星云环中心是两个可疑的对象：一对密近双星，互相绕转时间仅5天，两者都不是白矮星。它们的光谱是A型，比我们的太阳热，但还不足以激发星云发光。只有足量的紫外辐射（比如由失踪的白矮星发出），才能激发星云发光。
The study is being conducted by Katrina Exter and Howard Bond of the Space Telescope Science Institute in Baltimore, Md. and a team of British and American colleagues. Their extensive photometry and spectroscopy of the binary show that both stars are larger than main-sequence stars of their masses. This may imply that they have started to evolve toward becoming red giants. Both stars also appear to be rotating more slowly than expected; they would be expected to always be facing the same sides toward each other, but they do not.
研究团队由马里兰州巴尔的摩市太空望远镜科研所的卡特里娜.Exter 和 霍华德.邦德牵头，包括美国、英国的同事们组成。他们对双星进行了广泛的照相和光谱研究，显示两个子星都大于同光谱型主序星的质量。这意味着它们应该演化为红巨星。同时，两个子星的自转比预期慢很多，如此意味着它们应该互相面对面（潮汐锁定），但事实上又不是。
The astronomers suggest a simple explanation for the facts at the scene: the stars at the center of SuWt 2 were born as a family of three, with the A stars circling each other tightly and a more massive star orbiting further out. This allowed room for the massive star to evolve to become a red giant, which only then engulfed the pair of A stars. Trapped inside the red giant in what astronomers call a "common envelope," the pair spiraled down toward the core, causing the envelope to spin faster. Eventually, the outer layers of the red giant were ejected in the plane of the orbit, producing the ring-shaped nebula seen today. The unusually slow spins of the two A stars may have been another consequence of their victimization by their massive sibling.
对此现场事实，天文学家做了以下简单推测：SuWt2系统诞生时是由3颗恒星组成的家，两颗A型主序星互相绕转，另一颗大质量恒星在远方与其互相绕转（图1）。这样的组合就允许大质量恒星首先演化为红巨星（图2），然后其外层大气将包住整对双星（图3）。天文学家称这种被困在红巨星中的现象为“共同演化”，双星将逐渐螺旋线移向中心，并使壳层旋转加速（图4）。最终，红巨星的外层将脱落在轨道平面上，形成今天看见的环状星云（图5）。这两个异常缓慢旋转的A型双星可能是它们大质量伙伴的另一对替罪羊而已。
The ground-based observations were obtained with telescopes at the Cerro Tololo Inter-American Observatory, Chile; the New Technology Telescope at the European Southern Observatory, Chile; the Anglo-Australian Telescope, Australia; and the South African Astronomical Observatory.
参加观测的地面望远镜有：智利托洛洛山美洲天文台（CTIO），智利欧洲南方天文台（ESO）的新技术望远镜（NTT）， 澳大利亚英澳天文台望远镜（AAO）以及南非天文台（SAAO）等。
Ultraviolet radiation from the exposed hot core of the red giant would have caused the nebula to glow. If the giant's core were of high enough mass, it would then shrink and cool off rapidly to a faint white dwarf, which might explain its current invisibility.
来自红巨星暴露核心的紫外辐射能够激发星云发光。如果红巨星的核心质量够大，它就会收缩得很小并迅速冷却为黯淡的白矮星，这也许是现在它已经看不见的原因所在。
Their results are being presented today at the 212th meeting of the American Astronomical Society in St. Louis, Mo. Other members of the team are Keivan Stassun (Vanderbilt University, Tenn.), Pierre Maxted and Barry Smalley (Keele University, UK), and Don Pollacco (Queen's University, UK).
本研究报告公布于今天在密苏里州圣路易斯市举行的第212届美国天文学会上。团队其他成员包括： 田纳西州范德堡大学的 Keivan Stassun，英国基尔大学的Pierre Maxted 和 Barry Smalley 以及英国女王大学的 Don Pollacco。
CONTACT
本文联系人
Ray Villard
Space Telescope Science Institute, Baltimore, Md.
马里兰州巴尔的摩市，太空望远镜科研所
410-338-4514
villard@stsci.edu
Howard Bond/Katrina Exter
Space Telescope Science Institute, Baltimore, Md.
马里兰州巴尔的摩市，太空望远镜科研所
410-338-4718/4993
bond@stsci.edu/kexter@stsci.edu |
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