MessageToEagle.com – Thousands of planetary nebulae are continuously observed and studied, but astronomers have long struggled to measure one of their key properties – their distance.
Now, astronomers, based at the University of Hong Kong: Dr David Frew, Prof Quentin Parker and Dr Ivan Bojicic, have come up with a simple and elegant method that help to estimate more accurate distances to planetary nebulae.
“For many decades, measuring distances to Galactic planetary nebulae has been a serious, almost intractable problem because of the extremely diverse nature of the nebulae themselves and their central stars. But finding those distances is crucial if we want to understand their true nature and physical properties,” Dr Frew, lead author on the paper, said.
Their method requires only an estimate of the dimming toward the object, caused by intervening interstellar gas and dust, the projected size of the object on the sky, taken from the latest high resolution surveys) and a measurement of how bright the object is (as obtained from the best modern imaging).
The result is so-called ‘surface-brightness relation’ has been robustly calibrated using more than 300 planetary nebulae whose accurate distances have been determined via independent and reliable means.
“The basic technique is not new but what marks out this work from what has gone before is the use of the most up-to-date and reliable measurements of all three of those crucial properties,” Prof Parker explained.
This is combined with the use of the authors’ own robust techniques to effectively remove “doppelgangers” and mimics that have seriously contaminated previous planetary nebulae catalogues and added considerable errors to other distance measurements.
The new approach works over a factor of several hundred thousand in surface brightness, and allows astronomers to measure the distances to planetary nebulae up to 5 times more accurately than previous methods.
“Our new scale is the first to accurately determine distances for the very faintest planetaries” said Dr Frew. “Since the largest nebulae are the most common, getting their distances right is a crucial step”.
Despite their name, planetary nebulae have nothing to do with planets. They were described as such by early astronomers whose telescopes showed them as glowing disc-like objects.
We now know that planetary nebulae are actually the final stage of activity of stars like our Sun. When they reach the end of their lives, these stars eject most of their atmosphere into space, leaving behind a hot dense core. Light from this core causes the expanding cloud of gas to glow in different colors as it slowly grows, fading away over tens of thousands of years.
There are thousands of planetary nebulae in the Milky Way alone, and they provide targets for professional and amateur astronomers alike, with the latter often taking spectacular images of these beautiful objects.
The new method will give astronomers a far better insight into how these objects form and develop, and how stars as a whole evolve and die.
The scientists publish their results in Monthly Notices of the Royal Astronomical Society.
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source: Royal Astronomical Society