The Zeta-Ophiuchus HII Region

This HII region is particularly prominent because it is, unusually, surrounding a star that is well outside of the plane of the Milky Way galaxy. This star, zeta-Ophiuchi, is about 370 light years from Earth and has a very high velocity. It may have begun its life in a triple or quadruple system and undergone a close encounter with another star in the system, which accelerated it to this speed. Alternately, it may have originally been a binary whose companion exploded as a supernova and been shot out of the galaxy as a result of this violent explosion (Hubrig et al 2011). Zeta-Oph is a very bright, massive star that would be one of the brightest stars in the sky if much of its light weren’t blocked by dust. In the infrared image below, taken with Spitzer, the shock wave created by zeta-Oph’s motion through the surrounding dust is clearly visible.

The shock created by zeta-ophiuchi's rapid motion through the surrounding ISM.
The shock created by zeta-ophiuchi’s rapid motion through the surrounding ISM.

The bubble of ionized gas surrounding this star is clearly visible in hydrogen-alpha emission, as is discussed in the tour. For a more detailed discussion of the hydrogen-alpha observations of this region, check out this webpage.

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