HaTr 10, a Planetary Nebula with Extremely Strong Nitrogen Lines

Abstract

Optical spectra and direct images reveal that a very faint, scarcely studied object (HaTr 10) which appears as an incomplete elliptical ring of 04 × 0 2 is a heavily obscured planetary nebula with exceptionally strong nitrogen lines ([N ii] λ6583/Hα ≈ 6). In the Hα/[N ii] versus Hα/[S ii] diagnostic diagram, the object does not resemble H ii regions or supernova remnants. It is quite far from the locus of the bulk of (bipolar) planetary nebulae. Photoionization models can well reproduce the observed emission lines, by using a gas of density 500 cm−3 and with abundances of N = 8.6, O = 8.2, and all other elements with solar abundances. On our deepest CCD frames the nebula is considerably larger (15 × 1 0), showing butterfly‐like faint extensions. These symmetrical lobes, the ring around its waist, and the very high nitrogen abundance support the classification of HaTr 10 as an extreme bipolar planetary nebula. We suggest that very deep frames of nebulae that appear morphologically akin to HaTr 10 should be obtained to enable or support a reliable classification.