We determine the radial abundance gradient of helium in the disc of the Galaxy from published spectra of 19 $\text{H}\thinspace \text{II}$ regions and ring nebulae surrounding massive O stars. We revise the Galactocentric distances of the objects considering {\it Gaia} DR2 parallaxes and determine the physical conditions and the ionic abundance of He$^{+}$ in a homogeneous way, using between 3 and 10 $\text{He}\thinspace \text{I}$ recombination lines in each object. We estimate the total He abundance of the nebulae and its radial abundance gradient using four different ICF(He) schemes. The slope of the gradient is always negative and weakly dependent on the ICF(He) scheme, especially when only the objects with log($\eta$) $<$ 0.9 are considered. The slope values go from $-$0.0078 to $-$0.0044 dex kpc$^{-1}$, consistent with the predictions of chemical evolution models of the Milky Way and chemodynamical simulations of disc galaxies. Finally, we estimate the abundance deviations of He, O and N in a sample of ring nebulae around Galactic WR stars, finding a quite similar He overabundance of about +0.24 $\pm$ 0.11 dex in three stellar ejecta ring nebulae.

中文翻译：

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来自银河系 H ii 区域和环形星云光谱的氦丰度及其径向梯度

我们根据已发表的 19 个 $\text{H}\thinspace \text{II}$ 区域和围绕大质量 O 星的环形星云的光谱确定了银河系圆盘中氦的径向丰度梯度。我们考虑到 {\it Gaia} DR2 视差修改了物体的半乳中心距离，并以均匀的方式确定了 He$^{+}$ 的物理条件和离子丰度，使用 3 到 10 $\text{He}\每个对象中的thinspace \text{I}$ 重组线。我们使用四种不同的 ICF(He) 方案估计星云的总 He 丰度及其径向丰度梯度。梯度的斜率总是负的并且弱依赖于 ICF(He) 方案，特别是当只考虑 log($\eta$) $<$ 0.9 的对象时。斜率值从 $-$0.0078 到 $-$0.0044 dex kpc$^{-1}$，与银河系化学演化模型和盘状星系化学动力学模拟的预测一致。最后，我们估计了银河系 WR 恒星周围环形星云样本中 He、O 和 N 的丰度偏差，发现在三个恒星喷出物环形星云中，He 过剩量非常相似，约为 +0.24 $\pm$ 0.11 dex。