Late Stages of Stellar Evolution

Abstract

A large fraction of ISO observing time was used to study the late stages of stellar evolution. Many molecular and solid state features, including crystalline silicates and the rotational lines of water vapour, were detected for the first time in the spectra of (post-)Asymptotic Giant Branch (AGB) stars. Their analysis has greatly improved our knowledge of stellar atmospheres and circumstellar environments. A surprising number of objects, particularly young planetary nebulae with Wolf-Rayet (WR) central stars, were found to exhibit emission features in their ISO spectra that are characteristic of both oxygen-rich and carbon-rich dust species, while far-IR observations of the PDR around NGC 7027 led to the first detections of the rotational line spectra of CH and CH + .

MIDCOURSE SPACE EXPERIMENTVERSUSIRASTWO-COLOR DIAGRAMS AND THE CIRCUMSTELLAR ENVELOPE-SEQUENCE OF OXYGEN-RICH LATE-TYPE STARS

“…As an interesting side note, these are colors involving the MSX D filter, whereas in the previous section (3.1) we mentioned that the "carbon feature", the SiC line, appears in the MSX C filter. Plausible components with carbonbearing molecules which could affect the flux density in the D filter are those of HCN and C 2 H 2 at ∼ 14 µm (see e.g.,Blommaert et al 2005).…”

Infrared spectroscopy of asymptotic giant branch stars in the Galactic bulge

“…The most commonly detected molecules in the near-IR to mid-IR range are H 2 O, OH, CO, CO 2 , SiO and SO 2 (see e.g. Cami et al 1997;Justtanont et al 1998;Ryde et al 1998;Duari, Cherchneff & Willacy 1999;Yamamura et al 1999a;Yamamura, de Jong & Cami 1999b;Jørgensen et al 2001;Matsuura et al 2002;Blommaert et al 2005), and most of those are also prominently present in our Spitzer spectra (see Fig. 4).…”

“…The vertical dot-dashed line represents a track of increasing luminosity without mass-loss. Note that the six OH/IR stars in our sample that were selected from IRAS have no corresponding 2MASS and ISOGAL fluxes and are therefore not shown in this CMD [figures taken from Blommaert et al (2006), with permission] (Skrutskie, Cutri & Stiening 2006). at wavelengths longer than 30 µm (an overview can be found in Blommaert et al 2005). Typically, oxide dust dominates the spectra of stars with low mass-loss rates, while high mass-loss rate objects exhibit strong silicate emission (SE).…”

“…Previous space-based studies (IRAS and ISO) have revealed a large variety of dust materials in these types of objects, including aluminium oxides (Miyata et al 2000;Cami 2002), magnesium-iron oxides (Cami 2002;Posch et al 2002), and various crystalline and amorphous silicates (for a review on ISO results, see Blommaert et al 2005). However, while there is some observational evidence that these compositional variations are related to the mass-loss rate, the origin of these variations and the physical and chemical processes driving this complexity are not well understood.…”

Concluding remarks

“…I have only mentioned PN and post-AGB stars [133,134] in passing as they were not discussed in detail at LIAC 40. Difficulties and uncertainties have been identified with modelling evolution from the MS to white dwarf stages.…”