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8-13um Dust Emission Features in Galactic Bulge Planetary Nebulae | | S. Casassus
; P.F. Roche
; D.K. Aitken
; C.H. Smith
; | | Date: |
7 May 2001 | | Journal: | Mon.Not.Roy.Astron.Soc. 327 (2001) 744 | | Subject: | astro-ph | | Affiliation: | 1,2), P.F. Roche , D.K. Aitken , C.H. Smith ( Oxford University; Universidad de Chile; University of Hertfordshire; UNSW | | Abstract: | A sample of 25 IR-bright planetary nebulae (PNe) towards the Galactic bulge is analysed through 8-13um spectroscopy. The classification of the warm-dust emission features provides a measure of the C/O chemical balance, and represents the first C/O estimates for bulge PNe. Out of 13 PNe with identified dust types, 4 PNe have emission features associated with C-based grains, while the remaining 9 have O-rich dust signatures. The low fraction of C-rich PNe, <30%, contrasts with that for local PNe, around 80%, although it follows the trend for a decreasing frequency of C-rich PNe with galactocentric radius (paper~I). We investigate whether the PNe discussed here are linked to the bulge stellar population (similar to type~IV, or halo, PNe) or the inner Galactic disk (a young and super-metal-rich population). Although 60% of the PNe with warm dust are convincing bulge members, none of the C-rich PNe satisfy our criteria, and they are probably linked to the inner Galactic disk. In the framework of single star evolution, the available information on bulge PNe points towards a progenitor population similar in age to that of local PNe (type I PNe are found in similar proportions), but super-metal-rich (to account for the scarcity of C-rich objects). Yet the metallicities of bulge PNe, as inferred from [O/H], fail to reach the required values - except for the C-rich objects. It is likely that the sample discussed here is derived from a mixed disk/bulge progenitor population and dominated by type IV PNe, as suggested by Peimbert (1992). The much higher fraction of O-rich PNe in this sample than in the solar neighbourhood should result in a proportionally greater injection of silicate grains into the inner Galactic medium. | | Source: | arXiv, astro-ph/0105101 | | Services: | Forum | Review | PDF | Favorites | |
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