NGC 6164-65 in Norma and NGC 6188, NGC 6193 in Ara

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NGC 6164 and NGC 6165 are the two brightest bulge of the remarkable bipolar nebula associated with HD 148937 (Mahy et al. 2017). Up to now, HD148937 is the only magnetic O-type star known to be surrounded by a nebula. The nebula is particularly complex and is composed of a close bipolar ejecta nebula, an ellipsoidal wind-blown shell. The amazing blue central star, known as HD 148937, was classified as a member of the peculiar Of?p spectral class by Walborn (1972, 1973). HD 148937 has exotic emission lines (carbon emission lines (CII) equal in strength to Nitrogen (NIII)) and other peculiar spectra indicative of significant mass loss. Based on spectroscopic monitoring, was concluded that an important component of the change in the spectrum of HD148937 is associated with variable distortion by a companion comparable in mass and luminosity to the magnetic star, in an eccentric, long-period (26 year) orbit (Wade et al. 2019). The exact formation process of this nebula raises many questions. The latest investigations reveal two possible scenarios that can be considered to explain the ejection of such a nebula: a giant eruption triggered by the stellar wind and the magnetic field, or a merger event between two massive stars in a binary configuration (Mahy et al. 2021). The true age of the star is not known although estimates of its age vary from a pre-main sequence age of 350 000 years to a more evolved age of one to two million years. The latest data from Gaia EDR3 (Bailer-Jones+, 2021) yields a distance of 1.154 kpc (3 764 ly).

Interesting shape of NGC 6188 (Rim Nebula) is seen on the right side of the frame. The nebula is clouds of glowing hydrogen gas, about 4 000 light-years away in the southern constellation Ara. The nebula complex is a large cavity expanded by the Ara OB1 stellar association, very massive, young stars powering the nebula glow with stellar winds and intense ultraviolet radiation. The cluster NGC 6193 (partly seen) is embedded in the NGC 6188.

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