Westbrook Nebula

It is being formed by a star that has passed through the red giant phase and has ceased nuclear fusion at its core.

The outer part of the nebula is the result of interaction between rapid bipolar outflow and the gas that was ejected when the star was passing through its asymptotic giant branch phase.

[6] The dynamics of the molecular gas envelope can be studied by examining microwave emission-line spectra from carbon monoxide rotational transitions.

The narrow cores of the spectral lines show the familiar parabolic profile of a slow (20 km/sec), high optical depth stellar wind from an Asymptotic Giant Branch (AGB) star.

[6] The photosphere of this star is now hot enough to have begun ionizing the nebula, and the ionization region is expanding rapidly.

Two spectra of carbon monoxide in the Westbrook Nebula are shown. The component shown in yellow arises from the slow wind from the star's AGB phase. The component shown in red is from the faster wind expelled after the star left the AGB. Adapted from Gammie et al. . [ 5 ]