显微镜座AU

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显微镜座AU
AU Microscopii debris disk.jpg
显微镜座AU的岩屑盘。
观测资料
历元 J2000
星座 显微镜座
星官
赤经 20h 45m 09.53147s[1]
赤纬 –31° 20′ 27.2425″[1]
视星等(V) 8.73[2]
特性
光谱分类M1 Ve
U−B 色指数1.01
B−V 色指数1.45
变星类型[闪]焰星
天体测定
径向速度 (Rv)–6.0[2] km/s
自行 (μ) 赤经:+279.96[1] mas/yr
赤纬:-360.61[1] mas/yr
视差 (π)100.91 ± 1.06[1] mas
距离32.3 ± 0.3 ly
(9.9 ± 0.1 pc)
绝对星等 (MV)8.61
详细资料
质量0.31[3] M
半径0.84[3] R
亮度0.09[3] L
温度3,500 ± 100[3] K
自转速度 (v sin i)9.3[2] km/s
年龄12 ± 2[3] Myr
其他命名
CD -31°17815, GCTP 4939.00, GJ 803, HD 197481, HIP 102409, LTT 8214, SAO 212402, Vys 824, LDS 720 A.
参考数据库
SIMBADdata
ARICNSdata

显微镜座AU(AU Mic)是距离我们32.3光年(9.9秒差距)远,大约是离太阳最近距离恒星8倍远的一颗红矮星[4]。它的视星等为8.73 [2],这是太黯淡了,因此裸眼看不见它。因为它是在南天显微镜座的一颗变星,所以用变星命名法命名。如同老人增四(绘架座β)一样,它有一个岩屑盘的尘埃拱星盘环绕着。

恒星的性质[编辑]

显微镜座AU是一颗年轻的恒星,只有1,200万年的历史;还不到太阳年龄的1%[5]恒星光谱类型为M1Ve[2],是一颗红矮星[6]。它的半径为太阳的60%,尽管质量超过太阳的一半[7][8],它的辐射量只有太阳的9%[3],比太阳少了许多。这些能量从表面释出,温度只有3,700K[9],使它发出凉爽的橙红色光[10]。显微镜座AU是绘架座β移动星群的成员之一[11][12],它可能受到显微镜座AT重力约束,两者构成联星 [13]

无线电X射线,在所有的电磁频谱上都观察得到显微镜座AU,并且在所有的这些波段都观测到闪焰的活动[14][15][16][17]。这些闪焰在1973年首度被发现[18][19],在这些随机的爆发之后,其亮度几乎是正弦式变化,周期为4.865天,而振幅随时间的变化很缓慢。在1971年测量V波段的变化只有0.3星等;到1980年,更只有0.1星等[20]

岩屑盘[编辑]

哈伯太空望远镜的显微镜座AU岩屑盘影像。
这段短片显示碎屑盘的图像。

在2003年,保罗·卡拉斯和他的研究伙伴首度使用夏威夷毛纳基山天文台2.2米口径的望远镜,在可见光的波段解析出显微镜座AU有尘埃的星周盘[4]这些大的岩屑盘以侧面朝向着地球疔潇。苽擭[21],测量到其半径至少有200天文单位距离恒星有如此大的距离疔潇。苽擭,盘中尘埃的寿命足以超过显微镜 AU现在的年龄[4]盘中气体和尘埃粒子的质量比率大约是疔潇。苽擭6:1,远低于通常假设的100:1的初始值[22],因此被归类为"缺乏气体"的岩屑盘估计在可见的盘中气体总量大约相当于月球的质量疔潇。苽擭,而当尘埃产生成更大的星子时,估计质量至少是月球的6倍[23]

显微镜座AU的光谱能量分布次微米波长上显示岩屑盘内有一个扩展到17天文单位的洞孔[24],而散射光的影像估计洞孔的半径是12天文单位[25]结合光谱能量分布和表面的亮度疔潇。苽擭,估计洞孔的半径更小,只有1-10天文单位[26]。 在40天文单位之内,盘的内部结构显示出是非对称[27],内部的结构已经与受到较大天体影响或最近有行星形成的比较,期望能看见更大的身影[27]

出现在内部的洞孔和不对称引导了很多的天文学家在此搜寻行星循着显微镜疔潇。苽擭 AU的轨道,迄2007年尚无任何可以导致行星的发现[26][28]

盘面上的表面亮度(单位面积的亮度)是从恒星的投影距离和形状特性的函数在盘面内侧疔潇。苽擭15天文单位距离内的密度似乎是一个定值[25],大约密度开始降低;开始减缓的较慢,大约是 此处;再往外,光度下降得更陡峭,大约是 ,此处[25]这种疔潇。苽擭"破裂幂律"形状与绘架座β的盘面轮廓非常相似。

观测的方法[编辑]

显微镜座AU的盘面已经被各种不同波段的波长观测过,给了我们这个系统不同型态的资讯在疔潇。苽擭光学波长下观测到的光线是恒星的光,它们被尘埃粒子反射(散射)进入我们的视线内观察这些波长时疔潇。苽擭,利用日冕仪遮版阻挡直接来自恒星的光,这样可以提供高分辨率的盘面影像因为波长比尘埃粒子直径大的光波不易被散射疔潇。苽擭,在不同的波长上比较(例如,可见光和红外线)就可以得知盘面上尘埃粒子尺寸大小的讯息[29]

艺术家对显微镜座AU的观点。创建者: NASA/ESA/G. Bacon (STScI)

哈伯太空望远镜凯克望远镜都曾用来进行光学的观测,也曾经使用红外线和次微米波观测过这个系统由尘埃粒子直接发射出的光线呈现出内热的结果疔潇。苽擭(修正黑体辐射),但在这种波长下无法解析出盘面,所以这样的观测只能测量来自系统整体的光观测的波长越长疔潇。苽擭,就能提供越大尘埃粒子的讯息,也观察到距离恒星越远的范围,这样的观测已经由詹姆士·克拉克·玛克斯威尔望远镜史匹哲太空望远镜完成。

参考资料[编辑]

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外部链接[编辑]