Detalles de publicación
PP 09011
The mixed chemistry phenomenon in Galactic Bulge Planetary Nebulae
(1): European Space Astronomy Centre, INSA S.A. P.O. Box 78, E-28080 Madrid, Spain ; (2): Instituto de Astrofisica de Canarias, C/ Via Lactea s/n, 38200 La Laguna, Spain; (3): Herschel Science Centre. European Space Astronomy Centre, Research and Scientific Support Department of ESA, Villafranca del Castillo, P.O. Box 78, E-28080 Madrid, Spain; (4): N. Copernicus Astronomical Center, Rabianska 8, 87-100 Torun, Poland; (5) Department of Physics. University of Maryland, College Park, MD 20742-4111, USA
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 micron range
and crystalline silicates beyond 20 microns 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.
(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 micron range
and crystalline silicates beyond 20 microns 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.