![Location of target PNe and Hertzsprung-Russell diagram (Left) Location of target PNe on an image of the Andromeda galaxy (M31). (Right) Hertzsprung-Russell diagram showing the location of PNe central stars and the theoretical model tracks. The final and corresponding initial masses are indicated on the tracks. Note the remarkable clustering of the brightest PNe central stars (green squares) on the 1.5 Msun track.](/sites/default/files/styles/crop_square_2_2_to_320px/public/images/news/figMampaso.png?h=75a5c044&itok=P8I0wmZw)
Planetary nebulae (PNe) are the ejecta of evolved low-intermediate mass stars present in all stellar systems. Perhaps the easiest thing to do when studying PNe in a galaxy is just counting how many of them appear with a given luminosity, the Planetary Nebula Luminosity Function (PNLF). Not surprisingly, just a few very bright, and many more fainter, PNe populate the PNLF. But, most surprisingly, the bright end bin of the PNLF has a remarkably constant cut-off value in all galaxies and stellar systems studied so far, both young and old, with just a mild, calibrateable dependence on
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