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Guzman-Ramirez, L,Lagadec, E,Wesson, R,Zijlstra, AA,Muller, A,Jones, D,Boffin, HMJ,Sloan, GC,Redman, MP,Smette, A,Karakas, AI,Nyman, LA
Monthly Notices Of The Royal Astronomical Society
Witnessing the emergence of a carbon star
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circumstellar matter ISM: abundances planetary nebulae: individual: (BD+30 36 39) infrared: stars PLANETARY-NEBULA BD+30-DEGREES-3639 POST-AGB STARS GALACTIC BULGE MASS-LOSS DUST EVOLUTION MOCASSIN PHOTOIONIZATION CHEMISTRY EMISSION
During the late stages of their evolution, Sun-like stars bring the products of nuclear burning to the surface. Most of the carbon in the Universe is believed to originate from stars with masses up to a few solar masses. Although there is a chemical dichotomy between oxygen-rich and carbon-rich evolved stars, the dredge-up itself has never been directly observed. In the last three decades, however, a few stars have been shown to display both carbon-and oxygen-rich material in their circumstellar envelopes. Two models have been proposed to explain this dual chemistry: one postulates that a recent dredge-up of carbon produced by nucleosynthesis inside the star during the Asymptotic Giant Branch changed the surface chemistry of the star. The other model postulates that oxygen-rich material exists in stable keplerian rotation around the central star. The two models make contradictory, testable, predictions on the location of the oxygen-rich material, either located further from the star than the carbon-rich gas, or very close to the star in a stable disc. Using the FaintObject InfraRed CAmera (FORCAST) instrument on board the Stratospheric Observatory for Infrared Astronomy (SOFIA) Telescope, we obtained images of the carbon-rich planetary nebula BD + 30 degrees 3639 which trace both carbon-rich polycyclic aromatic hydrocarbons and oxygen-rich silicate dust. With the superior spectral coverage of SOFIA, and using a 3D photoionization and dust radiative transfer model we prove that the O-rich material is distributed in a shell in the outer parts of the nebula, while the C-rich material is located in the inner parts of the nebula. These observations combined with the model, suggest a recent change in stellar surface composition for the double chemistry in this object. This is evidence for dredge-up occurring similar to 10(3) yr ago.
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