Physical parameters and wind properties of galactic early B supergiants
Physical parameters and wind properties of galactic early B supergiants
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DOI：
10.1051/0004-6361:20053685
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发表时间：
2005-09
影响因子：
6.5
通讯作者：
P. Crowther;D. Lennon;N. Walborn
中科院分区：
文献类型：
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作者：
P. Crowther;D. Lennon;N. Walborn
我们目前的光学研究的物理和风属性，加上CNO化学丰度，25 O9.5-B3银河系超巨星。我们采用非LTE，线覆盖，扩展模型大气，这提供了一个适度的向下修订，在早期的B超巨星的有效温标高达1-2千K相对于以前的非覆盖的结果。所谓的B1处的“双稳态跳跃”（$T_{\rm eff} \sim 21$ kK）是一种更为渐进的趋势（具有大的散射）从24 kK以上的B 0 -0.5超巨星的$v_{\infty}/v_{\rm esc}\sim 3.4 $到20 kK ≤ T eff ≤ 24 kK的B0.7-1超巨星的$v_{\infty}/v_{\rm esc}\sim 2.5$，20 kK以下的B 1.5 -3超巨星的v_{\infty}/v_{\rm esc}\sim为1.9。这在一定程度上解释了在观测到的紫外光谱特性之间的突破B0.5和B0.7亚型讨论的沃尔伯恩等人。我们比较推导（均匀）风密度与麦哲伦云B超巨星最近的结果，一般确认理论预期的更强的风之间的银河系超巨星。然而，风的强度远低于当前辐射驱动风理论的预测，特别是在B型中亚型，如果风已经聚集在H α线形成区域，这个问题就会加剧。总的来说，CNO元素丰度揭示了银河系B超巨星表面的强烈加工物质，平均N/C和N/O丰度分别比太阳值高10倍和5倍，HD 2905（BC 0.7 Ia）表示我们样品中加工程度最低，HD 152236（B1.5 Ia +）最高。
We present optical studies of the physical and wind properties, plus CNO chemical abundances, of 25 O9.5–B3 Galactic supergiants. We employ non-LTE, line blanketed, extended model atmospheres, which provide a modest downward revision in the effective temperature scale of early B supergiants of up to 1-2 kK relative to previous non-blanketed results. The so-called “bistability jump” at B1 ($T_{\rm eff} \sim 21$ kK) from Lamers et al. is rather a more gradual trend (with large scatter) from $v_{\infty}/v_{\rm esc}\sim3.4$ for B0–0.5 supergiants above 24 kK to $v_{\infty}/v_{\rm esc}\sim 2.5$ for B0.7–1 supergiants with 20 kK ≤ T eff ≤ 24 kK, and $v_{\infty}/v_{\rm esc}\sim 1.9$ for B1.5–3 supergiants below 20 kK. This, in part, explains the break in observed UV spectral characteristics between B0.5 and B0.7 subtypes as discussed by Walborn et al. We compare derived (homogeneous) wind densities with recent results for Magellanic Cloud B supergiants and generally confirm theoretical expectations for stronger winds amongst Galactic supergiants. However, winds are substantially weaker than predictions from current radiatively driven wind theory, especially at mid-B subtypes, a problem which is exacerbated if winds are already clumped in the H α line forming region. In general, CNO elemental abundances reveal strongly processed material at the surface of Galactic B supergiants, with mean N/C and N/O abundances 10 and 5 times higher than the Solar value, respectively, with HD 2905 (BC0.7 Ia) indicating the lowest degree of processing in our sample, and HD 152236 (B1.5 Ia + ) the highest.