Bug Nebula

NGC 6302（也称为臭虫星云或蝴蝶星云）是在天蝎座的一个双极的行星状星云，距离地球约4000光年。它是结构复杂的行星状星云，NGC 6302的光谱显示它的中心恒星是银河系内最热的天体之一，表面的温度高达200,000K，暗示形成它的恒星一定也很大。

这颗中心星被密集的气体和尘埃构成的赤道盘面环绕着，因此并未曾被直接观测到。这个密集的盘面被认为是由恒星流出，形成双极的结构(Gurzadyan 1997)，像是一个沙漏。这个双极性的结构在行星状星云中显示出许多有趣的结构，像是离子墙、节点和瓣状的边缘形状。

观测史

因为他列名在星云和星团新总表，因此至少在1888年之前就已经为人所知。 已知最早的研究是爱德华·爱默生·巴纳德在1907年的描绘和叙述(Meaburn et al. 2005)。

自此之后，它一直是许多工作中的重点，并显示出许多有趣和值得研究的特征。近年来的研究已经从讨论转向至星云是如何被激发 (冲击激波还是光子电离) 出大量尘埃成分的属性。

这是哈伯太空望远镜在2009年9月的最后一次维修任务之后，首度发表的照片。

特性

NGC 6302有着复杂的型态，看起来似乎有着双极性的两个主瓣，有证据显示在上一阶段的质量流失中形成了第二对的瓣。 一道黑色的暗线在外面贯穿丰厚的腰部遮蔽了中央恒星所有光的波长。对NGC 6302的观测建议它有个正交的裙摆(或战轮)，与在蚂蚁星云中找到的相似。(Meaburn et al. 2005)。这个星云与天空平面的夹角是12.8度。

这个行星状星云在西北方有一个突出的瓣，延展到距离中心恒星3.0'的地方，估计在1900年的喷发事件中就已经存在了。它还有一个精确的遵循哈伯型式流出的圆墙部分 (流出的速率和中心源头的距离成比例)，与中心恒星的角距离是1,71’，瓣中气流的速度是263Km/s。在瓣的最边缘，外流的速度高达600km/s。在瓣的西缘显示出的特征，暗示与早先喷发出来的滴状气体发生了碰撞.改变了这个区域(Meaburn et al. 2005)。

尘埃化学

贯穿星云中心，表现突出的暗线，呈现出有着独特的尘埃化学性，证据显示有多种结晶的硅酸盐类，并且被解释为第一批在太阳系外检测出的碳酸盐类。但是因为碳酸盐类在无水的环境中难以形成，这项检测的结果已经有人提出质疑。其他检测到的固体物质包括水冰的结晶和石英。

在NGC 6302的检出物中最有趣的特征是存在于尘埃中的富氧物 (硅酸盐)和富碳物 (多环芳香烃，PAH)等物质。恒星通常不是氧富足或是碳富足，变化在于它们形成和日后生长的过程，因为核心的化学变化会改变恒星的大气层，当恒星或星云被观测到有双重的化学性时，显示它正从富氧性化学转变成富碳性化学。

NGC 6302 (also known as the Bug Nebula, Butterfly Nebula, or Caldwell 69) is a bipolar type planetary nebula in the constellation Scorpius. The structure in this planetary nebula is among the most complex ever seen in any planetary nebulae. The spectrum of Butterfly Nebula shows that its central star is one of the hottest stars known, with a surface temperature in excess of 250,000 degrees Celsius. This implies that the star from which it formed must have been very large in order to become this hot.

The central star, a white dwarf, was identified in 2009, using the upgraded Wide Field Camera 3 on board the Hubble Space Telescope. The star has a current mass of around 0.64 solar masses. The star is surrounded by a dense equatorial disc composed of gas and dust. This dense disc is postulated to have caused the star's outflows to form the bipolar structure seen in the Nebula. similar to an hourglass. This bipolar structure shows features such as ionization walls, knots and sharp edges to the lobes.

Observation history

As it is included in the New General Catalogue, this object has been known since at least 1888. The earliest-known study of NGC 6302 is by Edward Emerson Barnard, who drew and described it in 1907.

The nebula featured in some of the first images released after the final servicing mission of the Hubble Space Telescope in September 2009.

Characteristics

NGC 6302 has a complex structure, which may be approximated as bipolar with two primary lobes, though there is evidence for a second pair of lobes that may have belonged to a previous phase of mass loss. A dark lane runs through the waist of the nebula obscuring the central star at all wavelengths.

The nebula contains a prominent northwest lobe which extends up to 3.0′ away from the central star and is estimated to have formed from an eruptive event around 1,900 years ago. It has a circular part whose walls are expanding such that each part has a speed proportional to its distance from the central star. At an angular distance of 1.71′ from the central star, the flow velocity of this lobe is measured to be 263 km/s. At the extreme periphery of the lobe, the outward velocity exceeds 600 km/s. The western edge of the lobe displays characteristics suggestive of a collision with pre-existing …

Central star

The central star, among the hottest stars known, had escaped detection because of a combination of its high temperature (meaning that it radiates mainly in the ultraviolet), the dusty torus (which absorbs a large fraction of the light from the central regions, especially in the ultraviolet) and the bright background from the star. It was not seen in the first Hubble Space Telescope images; the improved resolution and sensitivity of the new Wide Field Camera 3 of the same telescope later revealed the faint star at the centre. A temperature of 200,000 Kelvin is indicated, and a mass of 0.64 sola…

Dust chemistry

The prominent dark lane that runs through the centre of the nebula has been shown to have an unusual composition, showing evidence for multiple crystalline silicates, crystalline water ice and quartz, with other features which have been interpreted as the first extra-solar detection of carbonates. This detection has been disputed, due to the difficulties in forming carbonates in a non-aqueous environment. The dispute remains unresolved.

One of the characteristics of the dust detected in NGC 6302 is the existence of both oxygen-bearing silicate molecules and carbon-bearing polycyclic aromatic hydrocarbons (PAHs). Stars are usually either oxygen-rich or carbon-rich, the change from the former to the latter occurring late in the evolution of the star due to nuclear and chemical changes in the star's atmosphere. NGC 6302 belongs to a group of objects where hydrocarbon molecules formed in an oxygen-rich environment.