SAAO - South African Astronomical Observatory
09.11.2012 00:00 Age: 4 yrs
Category: SAAO Press Releases
By: Dr Nicola Loaring

Dying stellar pair responsible for the majestic shape of the planetary nebula Fleming 1


This new ESO Very Large Telescope image shows the planetary nebula Fleming 1 in the constellation of Centaurus (The Centaur). This striking object is a glowing cloud of gas around a rare pair of dying stars. The two stars are in orbit around each other and their motions can fully explain the remarkably symmetric structures of the jets (red wisps in the image) in this and similar objects. Credit: H. Boffin (ESO). [Click to enlarge]

Astronomers using ESO’s Very Large Telescope (VLT) have discovered a pair of dying stars orbiting each other at the centre of one of the most stunning examples of a planetary nebula, Fleming 1. The new result confirms a longdebated theory about what controls the spectacular and symmetric appearance of the gas flung out from the nebula into space. The results are published in the 9th November 2012 issue of the journal Science.

A planetary nebula is a cloud of very hot gas that is seen to glow around Sun-like stars in the final stages of their lives. For the majority of their lifetimes, stars like the Sun are busily burning hydrogen gas to helium gas in their centres or "cores". When the star runs out of fuel to burn, the central core of the star contracts and the outer layers of the star expand and are blown off into space forming a gas cloud around the central star. The central star is now somewhat hotter and smaller than it was previously and is therefore referred to as a White Dwarf.

Over time, the outer layers expand further and further away from the star and may form intricate shapes, like rings or bubbles, which we see beautifully lit up by the central star. Many of these planetary nebulae are strikingly complex, with bright knots and intense jets — outflows of very fast-moving gas that are ejected from the central regions of planetary nebulae.

Fleming 1 is a planetary nebula located in the southern constellation of Centaurus (The Centaur). It was discovered just over a century ago by Williamina Fleming, a former maid who was hired by Harvard College Observatory in the US after showing an aptitude for astronomy. It is an example of a planetary nebula that has two strikingly symmetric jets emanating from its centre flowing in opposite directions into space. Astronomers have long debated how these symmetric jets could be created, but no consensus has been reached. Now, a research team led by Henri Boffin (ESO, Chile) has combined new observations of Fleming 1 with existing computer modelling to explain in detail for the first time how these bizarre shapes are formed.

The team used ESO’s Very Large Telescope (VLT) located in Chile to study the light coming from the central star. They found that Fleming 1 is likely to have not one but two white dwarfs at its centre. Such a stellar system is referred to a binary star system and in the case of Fleming 1 the two stars orbit around each other every 1.2 days.
Simulations have long predicted that the beautiful shape of Fleming 1 was produced by a pair of stars. Similar to a garden sprinkler, one star ejects gas in two opposite streams that slightly change direction each time it goes around its companion star. This study now confirms this scenario is the cause of such shapes.

“This is the most comprehensive case yet of a binary central star for which simulations have correctly predicted how it shaped the surrounding nebula — and in a truly spectacular fashion,” explains co-author Brent Miszalski, from SAAO and SALT (South Africa).

The two stars at the centre of Fleming 1 were found to have masses of approximately 0.68 and 0.85 times the mass of the Sun, respectively. With some help from the SAAO 1.9m telescope in Sutherland, the team found there to be very little change in the brightness of the two stars, ruling out the possibility of there being a “normal” star like our Sun in the binary star system. A normal star would produce a larger variation in brightness. The centre of the planetary nebula therefore very likely contains a pair of white dwarfs — a rare and exotic find.

More information
This research was presented in a paper “An Interacting Binary System Powers Precessing Outflows of an Evolved Star”, H. M. J. Boffin et al., to appear in the journal Science on 9 November 2012.

Further images (including the one at the top of the page) and animations can be found at http://www.eso.org/public/news/eso1244/

The team is composed of H. M. J. Boffin (European Southern Observatory, Chile), B. Miszalski (South African Astronomical Observatory; Southern African Large Telescope Foundation, South Africa), T. Rauch (Institute for Astronomy and Astrophysics, University of Tübingen, Germany), D. Jones (European Southern Observatory, Chile), R. L. M. Corradi (Instituto de Astrofísica de Canarias; Departamento de Astrofísica, Universidad de La Laguna, Spain), R. Napiwotzki (University of Hertfordshire, United Kingdom), A. C. Day-Jones (Universidad de Chile, Chile), and J. Köppen (Observatoire de Strasbourg, France).

ESO, the European Southern Observatory, builds and operates a suite of the world's most advanced ground-based astronomical telescopes. ESO operates three unique world-class observing sites in the Atacama Desert region of Chile. It is supported by 15 countries: Austria, Belgium, Brazil, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. http://www.eso.org/public/

Press release PDF

Contact Information
Dr Brent Miszalski
South African Astronomical Observatory
021 447 0025
brent(at)saao.ac.za