Bibcode
Perea-Calderón, J. V.; García-Hernández, D. A.; García-Lario, P.; Szczerba, R.; Bobrowsky, M.
Referencia bibliográfica
Astronomy and Astrophysics, Volume 495, Issue 2, 2009, pp.L5-L8
Advertised on:
2
2009
Revista
Número de citas
70
Número de citas referidas
53
Descripción
Aims: We investigate the dual-dust chemistry phenomenon in planetary
nebulae (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). Methods: The mixed chemistry is
derived from the simultaneous detection of Polycyclic Aromatic
Hydrocarbon (PAH) features in the 6-14 μm range and crystalline
silicates beyond 20 μm in the Spitzer/IRS spectra. Results:
Out of the 26 planetary nebulae observed in the Galactic Bulge, 21 show
signatures of dual-dust chemistry. Our observations reveal that the
simultaneous presence of oxygen and carbon-rich dust features in the
infrared spectra of [WC]-type planetary nebulae 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 planetary nebulae.
Surprisingly, we found that the dual-dust chemistry is seen also in all
observed weak emission-line stars (wels), as well as in other planetary
nebulae with central stars being neither [WC] nor wels. Most sources
observed display crystalline silicate features in their spectra, with
only a few PNe exhibiting, in addition, amorphous silicate bands. Conclusions: We appear to detect a recent change of chemistry at the
end of the Asymptotic Giant Branch (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 Galactic Bulge, do not
exhibit crystalline silicate features in their spectra. Thus, the high
detection rate of dual-dust chemistry 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.
Based on observations made with the Spitzer Space Telescope, which is
operated by the Jet Propulsion Laboratory, California Institute of
Technology, under NASA contract 1407.
Tables A1, A2 and Figs. B1 to B6 are only available in electronic form
at http://www.aanda.org
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