识别两组在$l\sim38^{\circ}$银河系方向排列的大质量恒星
Identifying two groups of massive stars aligned in the $l\sim38^{\circ}$ Galactic direction
摘要：
内容：最近的近红外数据有助于揭示我们银河系中新的和以前已知的星团中大规模和模糊的恒星星族。这些发现使我们将银河系视为一个活跃的恒星形成机器。目的：我们寻找年轻的大质量星团候选者作为过密度的OB型恒星。第一次搜索，集中在银河系方向$l=38^{\circ}$，导致检测到两个对象与一个显着的人口OB-type恒星候选人。研究方法：使用修改后的朋友的朋友算法AUTOPOP，并使用2 MASS和UKIDSS-GPS近红外（$J$，$H$和$K$）测光为我们的一个星团候选者（命名为Masgomas-6），我们选择了30颗恒星进行多目标和长缝$H$ -和$K$ -光谱。利用光谱分类和近红外测光数据，我们得到了个体的距离、消光和径向速度。结果如下：在30颗光谱观测到的恒星中，20颗被归类为大质量恒星，包括OB型（矮星、巨星和超巨星）、两颗红超巨星、两颗沃尔夫-拉叶星（WR 122 -11和新WR 122 -16）和一颗过渡天体（LBV候选者IRAS 18576+0341）。单个星团的距离和径向速度并不一致，这表明我们在同一条视线上观察到两个大质量恒星群：Masgomas-6a和Masgomas-6 b。第一组大质量恒星位于3.9 $^{+0.4}_{-0.3}$ kpc，包含沃尔夫-雷耶特和大部分的OB-矮星，而马斯戈马-6 b位于$9.6\pm0.4$ kpc，拥有LBV候选者和进化的超巨星。我们能够在两个银河臂上识别大质量恒星，但我们不能清楚地识别这些大质量恒星是否形成星团或协会。
英文摘要：
Context: Recent near-infrared data have contributed to unveil massive and obscured stellar populations in both new and previously known clusters in our Galaxy. These discoveries lead us to view the Milky Way as an active star-forming machine. Aims: We look for young massive cluster candidates as over-densities of OB-type stars. The first search, focused on the Galactic direction $l=38^{\circ}$, resulted in the detection of two objects with a remarkable population of OB-type star candidates. Methods: With a modified version of the friends-of-friends algorithm AUTOPOP and using 2MASS and UKIDSS-GPS near-infrared ($J$, $H$, and $K$) photometry for one of our cluster candidates (named Masgomas-6) we selected 30 stars for multi-object and long-slit $H$- and $K$-spectroscopy. With the spectral classification and the near-infrared photometric data, we derive individual distance, extinction and radial velocity. Results: Of the 30 spectroscopically observed stars, 20 are classified as massive stars, including OB-types (dwarfs, giants and supergiants), two red supergiants, two Wolf-Rayet (WR122-11 and the new WR122-16), and one transitional object (the LBV candidate IRAS 18576+0341). The individual distances and radial velocities do not agree with a single cluster, indicating that we are observing two populations of massive stars in the same line-of-sight: Masgomas-6a and Masgomas-6b. The first group of massive stars, located at 3.9$^{+0.4}_{-0.3}$ kpc, contains both Wolf-Rayets and most of the OB-dwarfs, and Masgomas-6b, at $9.6\pm0.4$ kpc, hosts the LBV candidate and an evolved population of supergiants. We are able to identify massive stars at two Galactic arms, but we can not clearly identify whether these massive stars form clusters or associations.
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