A new infrared view of evolved stars in IZw 18
A new infrared view of evolved stars in IZw 18
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IZw 18 演化恒星的新红外视图
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发表时间：
2004
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通讯作者：
G. O. Mouhcine
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作者：
G. O. Mouhcine
我们报告的结果，从近红外成像IZw 18，最贫金属星系在当地的宇宙，与NICMOS上的哈勃太空望远镜（HST）。在宽F205 W滤波器（F205 W）和中宽带F171 M和F180 M中获得了观测结果，后者覆盖了冷星中强分子吸收的特征。新的数据，加上以前获得的HST/NICMOS图像中的F110 W（E1 J）和F160 W（E1 H）过滤器，提供了这个化学未进化星系中冷恒星人口的普查。我们发现，恒星的年龄为101 Gyr需要解释所观察到的颜色星等图。结合宽波段测光和中波段测光，对观测到的恒星进行了分类。在我们的数据深度范围内，观测到的恒星种群主要是由发光的红超巨星组成的。然而，也存在中年人的成分。我们已经确定了碳星星的候选者，并表明，他们占主导地位的恒星内容的中间质量和年龄。我们表明，低金属丰度的中间年龄的恒星，对于一个给定的颜色，F110 W（BJ-band）相比，本地碳星过剩。在IZw 18中发现的碳星是迄今为止发现的最遥远（超过10 Mpc）的例子。
We report results from near-infrared imaging of IZw 18, the most metal-poor galaxy in the local universe, with NICMOS on board the Hubble Space Telescope (HST). Observations were obtained in the broad F205W filter (∼K) and in the medium-wide bands F171M and F180M, the latter which cover strong molecular absorption features in cool stars. The new data, together with previously obtained HST/NICMOS images in the F110W (∼J )a ndF160W (∼H) filters, provide a census of the cool stellar population in this chemically unevolved galaxy. We find that stars as old as ∼1 Gyr are required to explain the observed colour-magnitude diagrams. Combining broad and medium-wide band photometry, we have classified the observed stars. The observed stellar populations, to the depth of our data, are dominated by luminous red supergiant stars. However, an intermediate-age component is also present. We have identified carbon star candidates, and show that they dominate the stellar content for intermediate mass and age. We show that low metallicity intermediate-age stars have, for a given colour, a F110W (∼J-band) excess compared to local carbon stars. The carbon stars identified in IZw 18 are the most distant (more than 10 Mpc) resolved examples yet discovered.