{
  "id": "0902.1049",
  "version": "v1",
  "published": "2009-02-06T10:17:02.000Z",
  "updated": "2009-02-06T10:17:02.000Z",
  "title": "The mixed chemistry phenomenon in Galactic Bulge PNe",
  "authors": [
    "J. V. Perea-Calderon",
    "D. A. Garcia-Hernandez",
    "P. Garcia-Lario",
    "R. Szczerba",
    "M. Bobrowsky"
  ],
  "comment": "Accepted for Publication in A&A Letters (12 pages, 8 Figures, 3 Tables)",
  "doi": "10.1051/0004-6361:200811457",
  "categories": [
    "astro-ph.SR",
    "astro-ph.GA"
  ],
  "abstract": "We investigate the dual-dust chemistry (DDC) phenomenon in PNe and discuss reasons for its occurrence, by analyzing Spitzer/IRS spectra of a sample of 40 Galactic PNe among which 26 belong to the Galactic Bulge (GB). The mixed chemistry is derived from the simultaneous detection of PAH features in the 6-14 micron range and crystalline silicates (CS) beyond 20 microns in the Spitzer/IRS spectra. Out of the 26 PNe observed in the GB, 21 show signatures of DDC. Our observations reveal that the simultaneous presence of O- and C-rich dust features in the IR spectra of [WC]-type PNe is not restricted to late/cool [WC]-type stars, as previously suggested in the literature, but is a common feature associated with all [WC]-type PNe. Surprisingly, we found that the DDC is seen also in all observed wels, as well as in other PNe with central stars being neither [WC] nor wels. Most sources observed display CS features in their spectra, with only a few PNe exhibiting, in addition, amorphous silicate bands. We appear to detect a recent change of chemistry at the end of the AGB evolution in the low-mass, high-metallicity population of GB PNe observed. The deficit of C-rich AGB stars in this environment suggests that the process of PAH formation in PNe occurs at the very end of the AGB phase. In addition, the population of low-mass, O-rich AGB stars in the GB, do not exhibit CS features in their spectra. Thus, the high detection rate of DDC that we find cannot be explained by long-lived O-rich (primordial or circumbinary) disks. Our most plausible scenario is a final thermal pulse on the AGB (or just after), which could produce enhanced mass loss, capable of removing/mixing (sometimes completely) the remaining H-rich envelope and exposing the internal C-rich layers, and generating shocks responsible for the silicate crystallization.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2009-02-06T10:17:02.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "galactic bulge pne",
      "mixed chemistry phenomenon",
      "spitzer/irs spectra",
      "cs features",
      "final thermal pulse"
    ],
    "tags": [
      "journal article"
    ],
    "publication": {
      "journal": "Astronomy and Astrophysics",
      "year": 2009,
      "month": "Feb",
      "volume": 495,
      "number": 2
    },
    "note": {
      "typesetting": "TeX",
      "pages": 12,
      "language": "en",
      "license": "arXiv",
      "status": "editable",
      "inspire": 812736,
      "adsabs": "2009A&A...495L...5P"
    }
  }
}