Post AGB stars

(Gledhill)

Planetary Nebula formation by jets and outflows

Planetary Nebulae (PN) are thought to form when a fast wind begins to blow from a post-AGB star as it evolves to hotter temperatures. However there is little observational information on how the PN formation process occurs, resulting in a huge parameter space for models to explore. The ro-vibrational transitions of H2 in the infrared K-band are an important tracer of excited molecular gas in post-AGB outflows and by using Integral Field Spectroscopy (IFS) we can obtain both the spatial and spectral distribution of the emission simultaneously. The continuum subtracted spectrum of the post-AGB object IRAS 18276-1431 (Gledhill et al. 2011 MNRAS 411 1453) shows a number of H2 emission lines, allowing discrimination between radiative and shock excitation.

The outflows from post-AGB stars can be remarkably similar to the molecular outflows and jets from pre-main sequence sources powering Herbig-Haro objects. For example we detect a fast (150 km/s) collimated H2 outflow from the post-AGB object IRAS 16342-3814 with a similar luminosity in H2 to the Herbig-Haro object HH211 and other Class 0 sources (Gledhill & Forde 2012 MNRAS 421 346). The jet-hosting evolved objects often show the infrared CO bandheads in emission, which are thought to indicate the presence of an active accretion disc.

Near-infrared Imaging Polarimetry of Post-AGB Stars

In the NIR, the dusty circumstellar envelopes (CSEs) around post-AGB stars are seen by scattered light and are therefore polarized, whereas the point-spread function (PSF) of the bright central star is unpolarized. Imaging polarimetry allows us to separate the two components and to image the extended CSE in compact AGB and post-AGB sources. This technique was first used by Gledhill et al. (2001 MNRAS 322 321) and subsequently Gledhill (2005 MNRAS 356 883) and Gledhill et al. (2009 MNRAS 392 1217).