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arXiv 0903.2496astro-ph.GA
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一个大质量红超巨星团的发现及其GLIMPSE

The Discovery of a Massive Cluster of Red Supergiants with GLIMPSE

Michael J. Alexander, Henry A. Kobulnicky, Dan P. Clemens, Katherine Jameson, April Pinnick, Michael Pavel

摘要:

我们报告发现了一个以前未知的大质量星系星团,l=29.22,b=-0.20。在斯皮策GLIMPSE巡天的中红外图像中,根据后续的近红外光谱,该星团至少包含8颗晚型超巨星,另外还有3-6颗候选超巨星余烬,其红外光度与类似的距离和红化一致。团簇位于13-CO柱密度和8微米发射的局部最小值。我们将这一特征解释为进化中的大质量恒星的高能风所雕刻的洞。在分子图中看到的VLSR ~95 km/s处的13-CO空穴对应于6.1/8.7+/-1 kpc的近/远运动学距离。我们计算出的平均分光光度距离为7.0^+3.7_-2.4 kpc,与推断的运动学距离基本一致。这个位置使它接近银河酒吧的北端。对于平均消光星等A_V=12.6+/-0.5mag(A_K=1.5+/-0.1mag),星系团可能成员的色星等图与1800 - 2400万年的等时线拟合得很好。估计星团质量约为20,000 Msun。由于最大质量的原始星团恒星可能已经死亡,在这附近没有发现强烈的无线电辐射。因此,这个RSG星团是隐藏在许多尘埃遮蔽之后的青春期大质量星系团的代表。这个星团加入了两个类似的红超巨星星团,作为我们银河系酒吧末端与盾牌座旋臂底部相连的不稳定区域的居民,这表明那里最近发生了广泛的大质量恒星形成。

英文摘要:

We report the discovery of a previously unknown massive Galactic star cluster at l=29.22, b=-0.20. Identified visually in mid-IR images from the Spitzer GLIMPSE survey, the cluster contains at least 8 late-type supergiants, based on followup near-IR spectroscopy, and an additional 3-6 candidate supergiant embers having IR photometry consistent with a similar distance and reddening. The cluster lies at a local minimum in the 13-CO column density and 8 micron emission. We interpret this feature as a hole carved by the energetic winds of the evolving massive stars. The 13-CO hole seen in molecular maps at V_LSR ~95 km/s corresponds to near/far kinematic distances of 6.1/8.7+/-1 kpc. We calculate a mean spectrophotometric distance of 7.0^+3.7_-2.4 kpc, broadly consistent with the kinematic distances inferred. This location places it near the northern end of the Galactic bar. For the mean extinction of A_V=12.6+/-0.5 mag (A_K=1.5+/-0.1 mag), the color-magnitude diagram of probable cluster members is well fit by isochrones in the age range 18-24 Myr. The estimated cluster mass is ~20,000 Msun. With the most massive original cluster stars likely deceased, no strong radio emission is detected in this vicinity. As such, this RSG cluster is representative of adolescent massive Galactic clusters that lie hidden behind many magnitudes of dust obscuration. This cluster joins two similar red supergiant clusters as residents of the volatile region where the end of our Galaxy's bar joins the base of the Scutum-Crux piral arm, suggesting a recent episode of widespread massive star formation there.

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