Astronomers using the SPHERE-ZIMPOL instrument on ESO’s Very Large Telescope (VLT) have confirmed the presence of the circumstellar dust disk around an ageing red giant star called L2 Puppis.
This image from ESO’s Very Large Telescope shows a butterfly-like nebula around the red giant star L2 Puppis. Image credit: ESO / Pierre Kervella.
L2 Puppis, also known as HD 56096, lies in the constellation Puppis at a distance of about 200 light-years. It’s one of the closest red giants to Earth known to be entering its final stages of life.
With a mass in a range from 1 to 3 solar masses, this red giant shines at a luminosity that is somewhere between 1,500 and 2,400 times that of our Sun, radiated from a surface with a temperature of 5,660 degrees Fahrenheit (3,127 degrees Celsius).
The new observations with VLT’s SPHERE-ZIMPOL show the dust that surrounds L2 Puppis in exquisite detail. They confirm earlier findings of the dust being arranged in a disc, which from Earth is seen almost completely edge-on.
The astronomers – Dr Pierre Kervella of the Universidad de Chile in Santiago and his colleagues from France and the United States – found the dust disc to begin about 900 million km from the star (slightly farther than the distance from the Sun to Jupiter) and discovered that it flares outwards, creating a symmetrical, funnel-like shape surrounding the star.
Dr Kervella and co-authors also observed a companion star about 300 million km from L2 Puppis. This companion is likely to be another red giant of slightly lower mass, but less evolved.
The combination of a large amount of dust surrounding a slowly dying star, along with the presence of a companion star, mean that this is exactly the type of system expected to create a bipolar planetary nebula.
“The origin of bipolar planetary nebulae is one of the great classic problems of modern astrophysics, especially the question of how, exactly, stars return their valuable payload of metals back into space — an important process, because it is this material that will be used to produce later generations of planetary systems,” explained Dr Kervella, lead author of the paper reporting the results in the journal Astronomy & Astrophysics.
In addition to L2 Puppis’s dust disc, the astronomers found two cones of material, which rise out perpendicularly to the disc.
Importantly, within these cones, they found two long, slowly curving plumes of material. From the origin points of these plumes, the scientists deduce that one is likely to be the product of the interaction between the material from L2 Puppis and the companion star’s wind and radiation pressure, while the other is likely to have arisen from a collision between the stellar winds from the two stars, or be the result of an accretion disc around the companion star.
The astronomers said there are two leading theories of bipolar planetary nebulae, both relying on the existence of a binary star system.
The new observations suggest that both of these processes are in action around L2 Puppis, making it appear very probable that the pair of stars will, in time, give birth to a butterfly.
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P. Kervella et al. 2015. The dust disk and companion of the nearby AGB star L2 Puppis. SPHERE/ZIMPOL polarimetric imaging at visible wavelengths. A&A, vol. 578, A77; doi: 10.1051/0004-6361/201526194
