Based on a culmination of ten years of research work, the new method to estimate more accurate distances between planetary nebulae and the Earth developed by HKU astronomers promises a new era in scientists’ ability to study and understand the fascinating if brief period in the final stages of the lives of low- and mid-mass stars. Credit: The University of Hong Kong
A way of estimating more accurate distances to the thousands of “planetary nebulae” has just been announced by 3 astronomers at Uni of Hong Kong (HKU): Dr David Frew, Professor Quentin Parker and Dr Ivan Bojicic, based on 10 yrs of research work. With this technique, “planetary nebulae” finally get a more meaningful physical presence.
Ghostly and beautiful planetary nebulae” have nothing to do with planets but acquired this name because these glowing spheres of ionized gas resembled planets to early observers. They are the colourful, ejected shrouds of dying stars, which offer a brief window into the history of many stars’ lives, including the Sun.
More accurate distances be can be estimated simply with 3 sets of data: 1. Size of the object on the sky taken from the latest high resolution surveys. 2. an accurate measurement of how bright the object is in the red hydrogen-alpha emission line. 3.An estimate of the dimming toward the nebula caused by interstellar-reddening. The resulting “surface brightness – radius relation’ has been robustly calibrated using >300 planetary nebulae whose accurate distances have been determined via independent and reliable means (eg. trigonometric parallax measurements of their central stars).
Dr David Frew said: ‘measuring distances to Galactic “planetary nebulae” has been an intractable problem for many decades, because of the extremely diverse nature of both the nebulae themselves and their central stars. However, understanding their true nature and physical characteristics depends crucially on knowing their distance.’
Incredibly, the new distance scale works over a factor of more than 6 powers of 10 in surface brightness. The technique can provide distances accurate to 20%, a major advance on previous estimators that can have errors of a factor of 2 or more. “In the past, the old distance scales worked fairly well for small planetary nebulae but got systematically worse for the larger nebulae. Ours is the first scale to be able to estimate distances for all planetary nebulae. As big planetary nebulae are the most common, we will use our new scale in making an unbiased census of planetary nebulae in the Milky Way, which will then help answer some important research questions.” Dr Frew added. This latest research promises a new era in ability to understand the final stages of the lives of low- and mid-mass stars. http://www.hku.hk/press/news_detail_13660.html
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