论文标题
超紧张的HII区域W49N的扩展环：A2
An expanding ring of the hypercompact HII region W49N:A2
论文作者
论文摘要
我们将250〜GHz连续体和H29Alpha线数据介绍W49N：A2，A2，一个由O9恒星电离的超稳定性HII区域。 The data obtained with ALMA at a resolution of ~0"05 (600 au) confirmed the presence of an ionized ring with a radius of~700 au inclined by ~50degree (0degree for pole-on). It has a width of ~1000 au and is relatively flat with a scale height of less than several hundred au. The tilted ring, or the apparent ellipse, has a prominent velocity difference between its NW and SE沿着较小的轴脊表明，它以13.2 km/s的速度在赤道平面上膨胀，表现出2.7 km/s的旋转迹象，该旋转率显着（2.5 sigma），比在20 m $ _ $ _ $ _ $ _ $ _ $ _ $ _ $ _ $ _ $ _ $ _ $ _ $ _ $ _的速度上小的速度小。 〜170 Au通过保存其原始的特定角动量，使其具有电离环的遗迹。将绩效型HII区域转变为超跨性HII区域。
We present 250~GHz continuum and H29alpha line data toward W49N:A2, a hypercompact HII region ionized by an O9 star. The data obtained with ALMA at a resolution of ~0"05 (600 au) confirmed the presence of an ionized ring with a radius of~700 au inclined by ~50degree (0degree for pole-on). It has a width of ~1000 au and is relatively flat with a scale height of less than several hundred au. The tilted ring, or the apparent ellipse, has a prominent velocity difference between its NW and SE ridges along the minor axis, suggesting that it is expanding in the equatorial plane at a velocity of 13.2 km/s. The ring also shows a hint of rotation at 2.7 km/s, which is significantly (2.5sigma) smaller than the Kepler velocity of 5.2 km/s at its radius around the 20 M$_sun star. This can be interpreted that the ring gas has been transported from the radius of ~170 au by conserving its original specific angular momentum that it had there. The ionized ring may thus be a remnant of the accretion disk that fed the O9 star, whose radiation or magnetic activities became so strong that the disk accretion was reversed due to the intense thermal or magneto-hydrodynamic pressure around the star. The data has revealed a rare example of how a massive star terminates its accretion at the end of its formation, transforming a hypercompact HII region into an ultracompact HII region.
