VLT/X-shooter observations of the low-metallicity blue compact dwarf galaxy PHL 293B including a luminous blue variable star
VLT/X-shooter observations of the low-metallicity blue compact dwarf galaxy PHL 293B including a luminous blue variable star
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VLT/X 射手对低金属度蓝色致密矮星系 PHL 293B 的观测，其中包括一颗发光的蓝色变星
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发表时间：
2011
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通讯作者：
Goettingen
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作者：
Y. Izotov;N. Guseva;K. Fricke;C. M. F. Radioastronomie;Bonn;H Germany;M. A. Observatory;Kiev;Ukraine;Luth;O. Paris;Meudon;France.;I. F. Astrophysik;Goettingen Universitat;Goettingen
（节略）我们展示了 VLT/X 射手在波长范围 3000-23000A 内对含有一颗发光蓝变星 (LBV) 恒星的极其缺乏金属的蓝致密矮星 (BCD) 星系 PHL 293B 进行的光谱观测。我们确定了 N、O、Ne、S、Ar 和 Fe 的丰度，并根据宽发射线的通量和宽度研究了 LBV 的特性。我们得出的星际氧丰度为 12+log O/H = 7.71+/-0.02，这与之前的测定结果一致。观察到的窄巴尔默、帕邢和布拉克特氢谱线的通量对应于用单一值 C(Hbeta) = 0.225 进行消光校正后的理论重组值。这意味着在光学范围内观察到的恒星形成区域是唯一的电离源，并且没有在近红外范围内看到但隐藏在光学范围内的其他电离源。对于 PHL 293B 中的 LBV 星，我们在几条 Balmer 氢发射线中发现了具有 P Cygni 轮廓的宽发射，并且首次在几条 Paschen 氢发射线和几条 HeI 发射线中发现了宽幅发射，这意味着 LBV 在 8 年的时间尺度上的时间演化。 LBV星的Hα光度比NGC 2363=Mrk 71中LBV星的Hα光度高一个数量级，NGC 2363=Mrk 71的金属丰度略高12+logO/H = 7.87。 PHL293B 低金属丰度 LBV 中恒星风的终端速度很高，约为 800 km/s，与爆发期间一些河外 LBV 光谱中看到的速度相当。我们发现从 Paschen 和 HeI 发射线得出的平均终端速度比从 Balmer 发射线得出的平均终端速度低约 40-60 km/s。这可能表明存在向外加速的风。
(abridged) We present VLT/X-shooter spectroscopic observations in the wavelength range 3000-23000A of the extremely metal-deficient blue compact dwarf (BCD) galaxy PHL 293B containing a luminous blue variable (LBV) star. We determine abundances of N, O, Ne, S, Ar, and Fe and study the properties of the LBV from the fluxes and widths of broad emission lines. We derive an interstellar oxygen abundance of 12+log O/H = 7.71+/-0.02, which is in agreement with previous determinations. The observed fluxes of narrow Balmer, Paschen and Brackett hydrogen lines correspond to the theoretical recombination values after correction for extinction with a single value C(Hbeta) = 0.225. This implies that the star-forming region observed in the optical range is the only source of ionisation and there is no additional source of ionisation that is seen in the NIR range but is hidden in the optical range. For the LBV star in PHL 293B we find broad emission with P Cygni profiles in several Balmer hydrogen emission lines and for the first time in several Paschen hydrogen lines and in several HeI emission lines, implying temporal evolution of the LBV on a time scale of 8 years. The Halpha luminosity of the LBV star is by one order of magnitude higher than the one obtained for the LBV star in NGC 2363=Mrk 71 which has a slightly higher metallicity 12+logO/H = 7.87. The terminal velocity of the stellar wind in the low-metallicity LBV of PHL293B is high, ~800 km/s, and is comparable to that seen in spectra of some extragalactic LBVs during outbursts. We find that the averaged terminal velocities derived from the Paschen and HeI emission lines are by some ~40-60 km/s lower than those derived from the Balmer emission lines. This probably indicates the presence of the wind accelerating outward.