Bengaluru researchers study special planetary nebula

Bengaluru: Researchers from the Indian Institute of Astrophysics (IIA), Bengaluru, have studied the dust and gas around a special kind of planetary nebula— stars which have ejected its outer shell at the end of their lives.  

They made use of the Vainu Bappu Observatory in Kavalur, Tamil Nadu, to make the observations. 

Planetary nebulae are gas and dust shells ejected by stars like the sun after they exhaust hydrogen and helium fuel in their cores — something that sun is expected to do five billion years from now. 

As the radiation emitted by these objects resembled planets when astronomers viewed these objects with small telescopes more than a century ago, they were called planetary nebulas, even though they are not planets. 

While most stars in this older phase of their lives produce cores (the central stars) with tiny residual hydrogen envelopes, around 25 per cent of them show a deficiency of hydrogen but are rich in helium at their surfaces instead. A subset of them can also have ionised helium, carbon and oxygen called Wolf-Rayet (WR) characteristics. Planetary Nebula PN IC 2003 is one of those rare planetary nebulae which has a hydrogen-deficient central remnant star. 

“The processes governing the formation and evolution of such objects are imprinted in the planetary nebular gas surrounding them, and hence their physical and chemical structures are required to be studied in detail,” the researchers said in a statement. 

The supervisor and co-author of the study Prof C Muthumariapan said that previous studies did not take into account the dust that is present in these shells but only the gas. 

“If you include gas and dust, then some of the radiation which is supposed to be absorbed with the gas is absorbed by dust and it emits radiation in a different way,” he added. 

“We could even reproduce the large temperature gradient usually seen in the nebula with WR stars. Our determination of abundances of elements like helium, nitrogen, oxygen are significantly different from the values obtained empirically,” said co-author of the study K Khushbu.