A Multiwavelength Analysis of the Halo Planetary Nebula DdDm-1

TL;DR

This study provides a detailed multiwavelength analysis of the halo planetary nebula DdDm-1, revealing its morphology, chemical composition, and central star properties using new optical, UV, and IR data.

Contribution

First resolved imaging of DdDm-1 showing its elliptical components and halo, combined with comprehensive abundance analysis using new and existing spectral data.

Findings

Morphology consists of two orthogonal elliptical components with an extended halo.

Nebular abundances indicate sub-solar metallicity and dust depletion of Si and Fe.

Central star has an effective temperature of 55,000 K and luminosity of 1000 L_sun.

Abstract

We present new HST optical imagery as well as new UV and IR spectroscopic data obtained with the Hubble and Spitzer Space Telescopes, respectively, of the halo planetary nebula DdDm-1. For the first time we present a resolved image of this object which indicates that the morphology of DdDm-1 can be described as two orthogonal elliptical components in the central part surrounded by an extended halo. The extent of the emission is somewhat larger than was previously reported in the literature. We combine the spectral data with our own previously published optical measurements to derive nebular abundances of He, C, N, O, Ne, Si, S, Cl, Ar, and Fe. Our abundance determinations include the use of the newly developed program ELSA for obtaining abundances directly from emission line strengths along with detailed photoionization models to render a robust set of abundances for this object. The metallicity, as gauged by oxygen, is found to be 0.46 dex below the solar value, confirming DdDm-1's status as a halo PN. In addition, we find that Si and Fe are markedly underabundant, suggesting their depletion onto dust. The very low (but uncertain) C/O ratio suggests that the chemistry of the nebula should be consistent with an oxygen-rich environment. We find that the sulfur abundance of DdDm-1 is only slightly below the value expected based upon the normal lockstep behavior between S and O observed in H II regions and blue compact galaxies. The central star effective temperature and luminosity are estimated to be 55,000 K and 1000 solar luminosities, respectively, implying an initial progenitor mass of <1 solar masses. Finally, we report on a new radial velocity determination from echelle observations.