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The 12C/13C Ratio in the Planetary Nebula NGC 3242 from Hubble Space Telescope STIS Observations*

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Francesco Palla1, Daniele Galli1, Alessandro Marconi1, Letizia Stanghellini2,4 and Monica Tosi3

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We present high-resolution Hubble Space Telescope ultraviolet spectroscopy of NGC 3242, the only planetary nebula with a measured abundance of 3He. The Space Telescope Imaging Spectrograph has been used to observe the C III multiplet near 1908 Å. The presence of 12C and 13C lines at these wavelengths allows a direct estimate of the carbon isotopic ratio in the ionized gas of the nebula. We have detected the 12C doublet and obtained an upper limit on the 13C 1909.6 Å line, resulting in a carbon isotopic ratio of 12C/13C > 38, in agreement with standard stellar models. The lack of the 13C line and the presence of the 3He line in the spectrum indicate that the progenitor star did not undergo a phase of deep mixing during the last stages of its evolution. The significance of this result for studies of stellar nucleosynthesis and Galactic chemical evolution is discussed.


Footnote
*  Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555.
Subject headings

Galaxy: evolution; ISM: abundances; planetary nebulae: individual (NGC 3242); stars: evolution


Dates

Issue 1 (2002 March 20)

Received 2001 December 12, accepted for publication 2002 February 14

Published 2002 February 27



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