arXiv subjects

K. B. Kwitter

Publications and source records attributed to K. B. Kwitter.

25 records · Page 2Linked to original sources

arXiv2001

Sulfur, Chlorine, & 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 3600-9600 Angstroms, 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 an earlier paper. One of the salient features of our work is the use of the NIR lines of [S III] 9069,9532 coupled with the [S III] temperature, to determine the S++ 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).

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arXiv2001

Observational Tests Of Intermediate Mass Star Yields Using Planetary Nebulae

This paper summarizes a project designed to study abundances in a sample of planetary nebulae representing a broad range in progenitor mass and metallicity. We collect abundances of C, N, and O determined for the entire sample and compare them with theoretical predictions of planetary nebula abundances from a grid of intermediate-mass star models. We find very good agreement between observations and theory, lending strong support to our current understanding of nucleosynthesis in stars with progenitor masses below 8 solar masses. This agreement between observation and theory also supports the validity of published stellar yields of C and N in the study of the abundance evolution of these two elements.

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arXiv1999

A New Look At Carbon Abundances In Planetary Nebulae. IV. Implications For Stellar Nucleosynthesis

This paper is the fourth and final report on a project designed to study carbon abundances in a sample of planetary nebulae representing a broad range in progenitor mass and metallicity. We present newly acquired optical spectrophotometric data for three Galactic planetary nebulae IC 418, NGC 2392, and NGC 3242 and combine them with UV data from the IUE Final Archive for identical positions in each nebula to determine accurate abundances of He, C, N, O, and Ne at one or more locations in each object. We then collect abundances of these elements for the entire sample and compare them with theoretical predictions of planetary nebula abundances from a grid of intermediate mass star models. We find some consistency between observations and theory, lending modest support to our current understanding of nucleosynthesis in stars below 8 M_o in birth mass. Overall, we believe that observed abundances agree with theoretical predictions to well within an order of magnitude but probably not better than within a factor of 2 or 3. But even this level of consistency between observation and theory enhances the validity of published intermediate-mass stellar yields of carbon and nitrogen in the study of the abundance evolution of these elements.

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arXiv1999

Morphology and Composition of the Helix Nebula

We present new narrow-band filter imagery in H-alpha and [N II] 6584 along with UV and optical spectrophotometry measurements from 1200 to 9600 Angstroms of NGC 7293, the Helix Nebula, a nearby, photogenic planetary nebula of large diameter and low surface brightness. Detailed models of the observable ionized nebula support the recent claim that the Helix is actually a flattened disk whose thickness is roughly one-third its diameter with an inner region containing hot, highly ionized gas which is generally invisible in narrow-band images. The outer visible ring structure is of lower ionization and temperature and is brighter because of a thickening in the disk. We also confirm a central star effective temperature and luminosity of 120,000K and 100L_sun, and we estimate a lower limit to the nebular mass to be 0.30M_sun. Abundance measurements indicate the following values: He/H=0.12 (+/-0.017), O/H=4.60x10^-4 (+/-0.18), C/O=0.87 (+/-0.12), N/O=0.54 (+/-0.14), Ne/O=0.33 (+/-0.04), S/O=3.22x10^-3 (+/-0.26), and Ar/O=6.74x10^-3 (+/-0.76). Our carbon abundance measurements represent the first of their kind for the Helix Nebula. The S/O ratio which we derive is anomalously low; such values are found in only a few other planetary nebulae. The central star properties, the super-solar values of He/H and N/O, and a solar level of C/O are consistent with a 6.5M_sun progenitor which underwent three phases of dredge-up and hot bottom burning before forming the planetary nebula.

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arXiv1997

A New Look At Carbon Abundances In Planetary Nebulae. III. DDDM1, IC 3568, IC4593, NGC 6210, NGC 6720, NGC 6826, & NGC 7009

This paper is the third in a series reporting on a study of carbon abundances in a carefully chosen sample of planetary nebulae representing a large range in progenitor mass and metallicity. We make use of the IUE Final Archive database containing consistently-reduced spectra to measure line strengths of C III] 1909 along with numerous other UV lines for the planetary nebulae DDDM1, IC 3568, IC 4593, NGC 6210, NGC 6720, NGC 6826, & NGC 7009. We combine the IUE data with line strengths from optical spectra obtained specifically to match the IUE slit positions as closely as possible, to determine values for the abundance ratios He/H, O/H, C/O, N/O, and Ne/O. The ratio of C III] 1909/C II 4267 is found to be effective for merging UV and optical spectra when He II 1640/4686 is unavailable. Our abundance determination method includes a 5-level program whose results are fine-tuned by corrections derived from detailed photoionization models constrained by the same set of emission lines. All objects appear to have subsolar levels of O/H, and all but one show N/O levels above solar. In addition, the seven planetary nebulae span a broad range in C/O values. We infer that many of our objects are matter bounded, and thus the standard ionization correction factor for N/O may be inappropriate for these PNe. Finally, we estimate C/O using both collisionally-excited and recombination lines associated with C+2 and find the well established result that abundances from recombination lines usually exceed those from collisionally-excited lines by several times.

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arXiv1997

On the Origin of Planetary Nebula K648 in Globular Cluster M15

We examine two scenarios for formation of the planetary nebula K648: a prompt scenario where the planetary nebula is ejected and formed immediately after a helium shell flash and a delayed scenario where a third dredge up occurs and the envelope is ejected during the following interpulse phase. We present models of both scenarios and find that each can produce K648-like systems. We suggest that the prompt scenario is more favorable but cannot rule out the delayed scenario.

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arXiv1997

Planetary Nebula Abundances, Stellar Yields, And The Galactic Evolution of C-12 and N-14

A project which aims to understand the abundance patterns of He, C, N, O, Ne, S, and Ar for a small sample of planetary nebulae is described. Abundance ratios of O/H, C/O, and N/O especially show a broad range relative to their solar values, and AGB stellar evolution models used to interpret the patterns indicate that reasonable ranges in progenitor mass and metallicity are adequate to explain the observed abundance spread. Chemical yields of intermediate-mass stars inferred from these same models are used to calculate chemical evolution models of the solar neighborhood. These models indicate that intermediate-mass stars account for roughly half of the C-12 and nearly all of the N-14 in that region.

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