论文标题
在Cygnus ob2周围的两个辐照球中的星形形成
Star formation in two irradiated globules around Cygnus OB2
论文作者
论文摘要
我们研究了与DR 18和ECX 6-21相关的年轻恒星种群，它们是Cygnus OB2关联的O型恒星照射的两个孤立球。两者都是HII区域，其中包含明显的近期和正在进行的恒星形成的示踪剂。我们还研究周围较小的分子结构。这两个小球都包含自己的嵌入式种群，其中进化较少的类别较高。质量和温度是根据1 MYR的普通年龄的假设估算的，该假设已被发现适当地代表了Cygnus OB2 YSO总体，但对于这两个小球，尤其是ECX 6-21，很可能是高估的。发现导致DR 18侵蚀的早期B恒星被发现是仍嵌入云中的一个中间质量恒星的一部分的一部分，该恒星可能包含近期恒星形成的第二个位置，并带有中间质量恒星。我们确认以前作品中描述的ECX 6-21中嵌入的两个主要星形形成站点，南部地点比北部地点进化得多。我们还讨论了小球6-21-W（$ = G79.8+1.2 $），并提出其非热射频频谱是由于嵌入式喷气机的同步射击引起的，我们的观察结果建议其存在。一些YSO的极端年轻人表明，两个小球的恒星形成在外部受辐照后始于它们。并未发现两个小球的种群特别丰富，但它们包含具有相似质量或高于太阳的恒星的数量，这些恒星在恒星形成过程中暗示了在低质量恒星占主导地位的恒星形成过程中存在的某些差异，而更深入的观察结果可能会证实。
We investigate the young stellar populations associated with DR 18 and ECX 6-21, which are two isolated globules irradiated by the O-type stars of the Cygnus OB2 association. Both are HII regions containing obvious tracers of recent and ongoing star formation. We also study smaller isolated molecular structures in their surroundings. Both globules contain their own embedded populations, with a higher fraction of the less-evolved classes. Masses and temperatures are estimated under the assumption of a common age of 1 Myr, which has been found to appropriately represent the general Cygnus OB2 YSO population but is most probably an overestimate for both globules, especially ECX 6-21. The early-B star responsible for the erosion of DR 18 is found to be part of a small aggregate of intermediate-mass stars still embedded in the cloud, which probably contains a second site of recent star formation, also with intermediate-mass stars. We confirm the two main star forming sites embedded in ECX 6-21 described in previous works, with the southern site being more evolved than the northern site. We also discuss the small globule ECX 6-21-W ($= G79.8+1.2$), and propose that its non thermal radio spectrum is due to synchrotron emission from an embedded jet, whose existence is suggested by our observations. The extreme youth of some of the YSOs suggests that star formation in both globules started after they became externally irradiated. The populations of both globules are not found to be particularly rich, but they contain stars with estimated masses similar or above that of the Sun in numbers that hint at some differences with respect to the star formation process taking place in more quiescent regions where low-mass stars dominate, which deeper observations may confirm.
