Tag Archives: Wolf-Rayet

Intriguing Wolf-Rayet star discovered

A new, very intriguing Wolf-Rayet star has been discovered in the Milky Way. Actually it is a massive triple star system. It has been nicknamed Apep after an ancient Egyptian deity, this may be the first ever gamma-ray burst progenitor found.

The research has been mainly conducted at the University of Sydney using data from the Anglo-Australian Telescope (AAT) and ESO’s Very Large Telescope. The announcement was made public yesterday in several media releases by the European Southern Observatory and the University of Sydney, following the publication of the research paper in Nature Astronomy.


Image of Apep captured in the thermal infrared with the VISIR camera on the European Southern Observatory’s VLT telescope in Chile. Credit: Professor Peter Tuthill/ESO.

Earlier this week I was contacted from a journalist from The Age, Liam Mannix, who wanted to talk to me as “expert of Wolf-Rayet stars who has not participated in this research”. He called me and I spent 20 minutes to half an hour explaining what Wolf-Rayet stars are, the few of these stars known in our Galaxy (~600s) as they are the descendant of the most massive stars (and these are quite rare), and more. Of course, this conversation was latter summarized in a line in the article that he prepared:

Systems like this are very, very rare,” says Angel Lopez-Sanchez, an astrophysicist at Macquarie University who studies Wolf-Rayets and was not involved in the research. “It is a very exciting finding.”

But in any case I’m very happy I had this conversation with Liam and that I could contribute at least to the dissemination of this nice work.

Planetary nebula NGC 5189 around WR-like star with the AAT for #StargazingABC

This is the object we observed at the Anglo-Australian Telescope as part of the “Stargazing Live” events at Siding Spring Observatory (NSW, Australia).

We used the APOGEE camera at the AAT Cassegrain focus and took some short exposures in several broad-band filters (B, V, R and I).

The planetary nebular NGC 5189 is located in the constellation of Musca (“The Fly”), near the South Celestial Pole.

The distance to NGC 5189 is around 1780 light-years from Earth, as measured in 2008.

It shows one of the more remarkable complex morphologies among all the known planetary nebulae, with many structures at different scales, indicating that the progenitor star experienced multiple outbursts.

Each outburst had different velocities, inducing shock-waves in the surrounding gas.

The central star is classified as Wolf-Rayet-type [WR] because it is very hot, it shows intense features of helium, carbon and oxygen, and it has very high stellar winds.

The most massive stars undergo the Wolf-Rayet (WR) phase before exploding as supernova, but the central stars of ~10% of planetary nebula also show Wolf-Rayet-type features.

The Wolf-Rayet-type stars in planetary nebulae are much older objects than the “standard” WR stars, as they descend from evolved low-mass stars and not from high-mass stars.

That is why Wolf-Rayet-type stars in planetary nebula are named [WR].

Wolf-Rayet-type stars are closely related to white dwarf stars.

The central Wolf-Rayet-type star in NGC 5189 is a very rare, low-mass (about the mass of the Sun) WO (oxygen-rich) star. Its temperature is 165 000 K and its stellar wind moves at 2500 km/s.

The Wolf-Rayet-type star in NGC 5189 has a companion star of around 0.8 times the mass of our Sun. It needs 4 days to complete an orbit around the [WR] star, as discovered in 2015.

The complex morphology in NGC 5189 seems to be consequence of the interaction between the progenitor of the Wolf-Rayet-type star and its companion star.

In the AAT image, the green color is coming from glowing nitrogen and hydrogen, the blue color from glowing oxygen. The red color is coming from the stellar emission