A Study of H2 Emission in Three Bipolar Proto-Planetary Nebulae: IRAS 16594-4656, Hen 3-401, and Rob 22

TL;DR

This study uses high-resolution imaging and spectroscopy to analyze H2 emission in three bipolar proto-planetary nebulae, revealing their structures, kinematics, and estimated ages, advancing understanding of their morphology and evolution.

Contribution

It provides detailed spatial-kinematical analysis of H2 emission in three proto-planetary nebulae, offering new insights into their structures and dynamics.

Findings

IRAS 16594-4656 has a peanut-shaped bipolar structure with H2 emission from walls and faint blobs.

Hen 3-401 shows elongated lobes with H2 emission and possible small disk, with Hubble-like flow.

Rob 22 exhibits an S-shaped H2 pattern with lobes nearly in the plane of the sky.

Abstract

We have carried out a spatial-kinematical study of three proto-planetary nebulae, IRAS 16594-4656, Hen 3-401, and Rob 22. High-resolution H2 images were obtained with NICMOS on the HST and high-resolution spectra were obtained with the Phoenix spectrograph on Gemini-South. IRAS 16594-4656 shows a "peanut-shaped" bipolar structure with H2 emission from the walls and from two pairs of more distant, point-symmetric faint blobs. The velocity structure shows the polar axis to be in the plane of the sky, contrary to the impression given by the more complex visual image and the visibility of the central star, with an ellipsoidal velocity structure. Hen 3-401 shows the H2 emission coming from the walls of the very elongated, open-ended lobes seen in visible light, along with a possible small disk around the star. The bipolar lobes appear to be tilted 10-15 deg with respect to the plane of the sky and their kinematics display a Hubble-like flow. In Rob 22, the H2 appears in the form of an "S" shape, approximately tracing out the similar pattern seen in the visible. H2 is especially seen at the ends of the lobes and at two opposite regions close to the unseen central star. The axis of the lobes is nearly in the plane of the sky. Expansion ages of the lobes are calculated to be approximately 1600 yr (IRAS 16594-4656), 1100 yr (Hen 3-401), and 640 yr (Rob 22), based upon approximate distances.