Astronomy and Astrophysics – Astronomy
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994aas...185.4705j&link_type=abstract
American Astronomical Society, 185th AAS Meeting, #47.05; Bulletin of the American Astronomical Society, Vol. 26, p.1384
Astronomy and Astrophysics
Astronomy
2
Scientific paper
All 158 Galactic globular clusters (GC) are being surveyed for planetary nebulae (PN). Presently, only 2 PN are known: K648 in M15, and IRAS 18333-2357 in M22, yet ~ 12 PN are expected in the GC system, according to the production rates seen by extragalactic surveys. Finding PN allows us to measure abundances of key elements (He, C, N, O, Ne, Ar, S) which, when compared with the stellar populations in the clusters, defines the enrichment rates for low metallicity stars, and provides clues about primordial abundances and Galactic chemical evolution. Finding PN in GCs also serves to fix the distances and reddening to PN, allowing determination of their masses and luminosities. Previous surveys are incomplete, unpublished, and inadequately faint. We have used the on-band/off-band imaging technique at [OIII] lambda5007 at the KPNO 2.1m to survey 32 northern GCs. While no new PN have been found yet, the M15 and M22 PN are trivially easy to recover. Thus, the survey is sensitive to PN at the faintest detectable limits. We hope to observe the southern GCs with the CTIO 1.5m during the next season. A failure to find any new PN presents a puzzle which can be explained by: (1) a failure of the stellar flux model of Renzini and Buzzoni for old, metal-poor stars, (2) the existence of an alternative to the AGB for GC stars, or (3) the production of undetectable nebulae. We favor the latter possibility, which can occur if the central stars produced have evolutionary times for heating longer than the kinematic times for the nebulae to disperse. Failing to find any new PN means that the central stars have M < 0.55 M_sun.
Fullton Laura Kellar
Jacoby George H.
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