Jacquelynne Brenda Milingo

ABUNDANCES OF GALACTIC ANTICENTER PLANETARY NEBULAE AND THE OXYGEN ABUNDANCE GRADIENT IN THE GALACTIC DISK

We have obtained spectrophotometric observations of 41 anticenter planetary nebulae (PNe) located in the disk of the Milky Way. Electron temperatures and densities, as well as chemical abundances for He, N, O, Ne, S, Cl, and Ar were determined. Incorporating these results into our existing database of PN abundances yielded a sample of 124 well-observed objects with homogeneously determined abundances extending from 0.9 to 21 kpc in galactocentric distance. We performed a detailed regression analysis which accounted for uncertainties in both oxygen abundances and radial distances in order to establish the metallicity gradient across the disk to be 12 + log(O/H) = (9.09 ± 0.05) – (0.058 ± 0.006) × Rg , with Rg in kpc. While we see some evidence that the gradient steepens at large galactocentric distances, more objects toward the anticenter need to be observed in order to confidently establish the true form of the metallicity gradient. We find no compelling evidence that the gradient differs between Peimbert Types I and II, nor is oxygen abundance related to the vertical distance from the galactic plane. Our gradient agrees well with analogous results for H II regions but is steeper than the one recently published by Stanghellini & Haywood over a similar range in galactocentric distance. A second analysis using PN distances from a different source implied a flatter gradient, and we suggest that we have reached a confusion limit which can only be resolved with greatly improved distance measurements and an understanding of the natural scatter in oxygen abundances.

ALPHA ELEMENT ABUNDANCES IN A LARGE SAMPLE OF GALACTIC PLANETARY NEBULAE

In this paper, we present emission line strengths, abundances, and element ratios (X/O for Ne, S, Cl, and Ar) for a sample of 38 Galactic disk planetary nebulae (PNe) consisting primarily of Peimbert classification Type I. Spectrophotometry for these PNe incorporates an extended optical/near-IR range of λλ3600-9600 A including the [S III] lines at 9069 A and 9532 A, setting this relatively large sample apart from typical spectral coverage. We have utilized Emission Line Spectrum Analyzer, a five-level atom abundance routine, to determine Te , Ne , ionization correction factors, and total element abundances, thereby continuing our work toward a uniformly processed set of data. With a compilation of data from >120 Milky Way PNe, we present results from our most recent analysis of abundance patterns in Galactic disk PNe. With a wide range of metallicities, galactocentric distances, and both Type I and non-Type I objects, we have examined the alpha elements against H II regions and blue compact galaxies (H2BCGs) to discern signatures of depletion or enhancement in PNe progenitor stars, particularly the destruction or production of O and Ne. We present evidence that many PNe have higher Ne/O and lower Ar/Ne ratios compared to H2BCGs within the range of 8.5-9.0 for 12 + log(O/H). This suggests that Ne is being synthesized in the low- and intermediate-mass progenitors. Sulfur abundances in PNe continue to show great scatter and are systematically lower than those found in H2BCG at a given metallicity. Although we find that PNe do show some distinction in alpha elements when compared to H2BCG, within the Peimbert classification types studied, PNe do not show significant differences in alpha elements amongst themselves, at least to an extent that would distinguish in situ nucleosynthesis from the observed dispersion in abundance ratios.

Sulfur, Chlorine, and Argon Abundances in Planetary Nebulae. III. Observations and Results for a Final Sample

This paper is the fourth in a series whose purpose is to study the interstellar abundances of sulfur, chlorine, and argon in the Galaxy using a sample of 86 planetary nebulae. Here we present new high-quality spectrophotometric observations of 20 Galactic planetary nebulae with spectral coverage from 3700 to 9600 A. A major feature of our observations throughout the entire study has been the inclusion of the near-infrared lines of [S iii] λλ9069, 9532, which allows us to calculate accurate S+2 abundances and to either improve upon or convincingly confirm results of earlier sulfur abundance studies. For each of the 20 objects here, we calculate ratios of S/O, Cl/O, and Ar/O and find average values of S/O = (1.1 ± 1.1) × 10-2, Cl/O = (4.2 ± 5.3) × 10-4, and Ar/O = (5.7 ± 4.3) × 10-3. For six objects, we are able to compare abundances of S+3 calculated directly from available [S iv] 10.5 μm measurements with those inferred indirectly from the values of the ionization correction factors for sulfur. In the final paper of the series, we will compile results from all 86 objects, search for and evaluate trends, and use chemical evolution models to interpret our results.

Sulfur, Chlorine, and Argon Abundances in Planetary Nebulae. IIB. Abundances in a Southern Sample

We have undertaken a large spectroscopic survey of over 80 planetary nebulae with the goal of providing a homogeneous spectroscopic database between 3600 and 9600 A, as well as a set of consistently determined abundances, especially for oxygen, sulfur, chlorine, and argon. In the current paper we calculate and report the S/O, Cl/O, and Ar/O abundance ratios for 45 southern planetary nebulae (predominantly type II), using our own recently observed line strengths published in a companion paper. One of the salient features of our work is the use of the near-IR lines of [S III] λλ9069, 9532 coupled with the [S III] temperature, to determine the S+2 ionic abundance. We find the following average abundances for these objects: S/O = 0.011 ± 0.0064, Cl/O = 0.00031 ± 0.00012, and Ar/O = 0.0051 ± 0.0020.

Sulfur, Chlorine, and Argon in Planetary Nebulae. IIA. Observations of a Southern Sample

In this paper we present fully reduced and dereddened emission line strengths for a sample of 45 southern type II planetary nebulae (PNs).The spectrophotometry for these PNs covers an extended optical/near-IR range from 3600 to 9600 A. This PN study and subsequent analysis (presented in a companion paper), together with a similar treatment for a northern PN sample, is aimed at addressing the lack of homogeneous, consistently observed, reduced, and analyzed data sets that include the near-IR [S III] lines at 9069 and 9532 A. The use of type II objects only is intended to select disk nebulae that are uncontaminated by nucleosynthetic products of the progenitor star. Extending spectra redward to include the strong [S III] lines enables us to look for consistency between S+2 abundances inferred from these lines and from the more accessible, albeit weaker, [S III] line at λ6312.

Rotational modulation, shear, and cyclic activity in HII 1883

We present a 30 year compilation of V-band differential photometry for the Pleiades K dwarf HII 1883. HII 1883 has an average rotational period 〈 P rot 〉 of ~0.235 d and displays rotational modulation due to non-uniform surface brightness as large as 0.2 magnitudes in V. Preliminary work yields a cycle period of ~9 yrs and rotational shear δ P rot /〈 P rot 〉 considerably less than solar. With such a long baseline of data available we can explore many aspects of the stars photometric variability. We present studies of the variation of the rotational modulation amplitude, 〈 V 〉, and P rot over the cycle.

Sulfur, Chlorine & Argon Abundances in a Southern Sample of Planetary Nebulae

We present S/O, Cl/O, and Ar/O abundance ratios for 45 predominantly Type II southern PNe. These abundances are based upon line strengths from newly acquired spectrophotometry covering an extended optical range from 3600 - 9600 A. The following average abundance ratios were obtained from this sample: S/O=0.011±0.0064, Cl/O=0.00031±0.00012, and Ar/O=0.0051±0.0020. This study, together with a sample of northern PNe, is aimed at producing a large homogeneous set of observations and abundances. Specifically, we are addressing the lack of homogeneously observed, reduced, and analyzed data sets that include the NIR [S III] lines at 9069 and 9532 A. The data provided by these PNe samples enables us to look for consistency between S +2 abundances inferred from these lines and from the more accessible, albeit weaker, [S III] line at 6312 A. We find reasonable agreement between S +2 determined from the NIR lines and the λ6312 line. This speaks positively for the use and reliability of the NIR lines, despite clearly recognized telluric effects in that portion of the spectrum. The consistent ionic abundance results breathe new life into our treatment of the telluric problem and the use of these strong lines for extrapolating total sulfur abundance. Type II PNe reside close to the Galactic disk and provide S, Cl, Ar, and O abundances free from nucleosynthetic self-contamination. These two qualities allow us to study massive star yields and map the distribution of these elements in radial abundance gradients. Finally, we compare our observed abundance trends with model predictions that are based on several sets of published stellar yields. (A companion paper in this volume by Kwitter & Henry discusses the northern subset observed at KPNO; see also Milingo et al. IIA, 2002, ApJS, 138, 279 and Milingo et al. IIB, 2002, ApJS, 138, 285)