Article

# The planetary nebula population of M33 and its metallicity gradient: A look into the galaxy's distant past

01/2009; DOI:10.1088/0004-637X/696/1/729
Source: arXiv

ABSTRACT The Planetary Nebula (PN) population of M33 is studied via multi-fiber
spectroscopy with Hectospec at the MMT. In this paper we present the spectra of
102 PNe, whereas plasma diagnostic and chemical abundances were performed on
the 93 PNe where the necessary diagnostic lines were measured. About 20% of the
PNe are compatible with being Type I; the rest of the sample is the progeny of
an old disk stellar population, with main sequence masses M<3M${_\odot}$ and
ages t$>$0.3 Gyr.
By studying the elemental abundances of the PNe in the M33 disk we were able
to infer that: (1) there is a tight correlation between O/H and Ne/H, broadly
excluding the evolution of oxygen; (2) the average abundances of the
$\alpha$-elements are consistent with those of \hii regions, indicating a
negligible global enrichment in the disk of M33 from the epoch of the formation
of the PN progenitors to the present time; (3) the radial oxygen gradient
across the M33 disk has a slope of -0.031$\pm$0.013 dex kpc$^{-1}$, in
agreement, within the errors, with the corresponding gradient derived from HII
regions. Our observations do not seem to imply that the metallicity gradient
across the M33 disk has flattened considerably with time. We report also the
discovery of a PN with Wolf-Rayet features, PN039, belonging the class of late
[WC] stars

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5 Feb 2013

### Keywords

$\alpha$-elements

[WC] stars

chemical abundances

epoch

main sequence masses M<3M${_\odot}$

necessary diagnostic lines

negligible global enrichment

observations

old disk stellar population

plasma diagnostic

PN

PN progenitors

PNe

present time

spectra

Wolf-Rayet features