NOVAE
Novae are the result of the interaction of stars in close
binary systems, where a white dwarf (WD) accretes H rich
material from a companion, typically a giant or subgiant
low-mass star (Bode & Evans 2008). When the
accreted material reaches a critical mass, a thermonuclear
runaway (TNR) occurs.
Highly processed material is ejected at velocities ∼1000
km/s (Bode 2010) in a classical nova (CN) event. With
time, the nova remnants will expand and mix into the
interstellar medium (ISM).
The morphology and expansion of a nova remnant
depend on the details of the nova event, but also on
the interactions of the ejecta with the stellar companion
and the pre-existing circumstellar material, which may
consists of an accretion disk and a common envelope.
DYNAMICS
The expansion and dispersal of nova shells reveal details of the nova ejection and give insights into the plasma physics and shock phenomena associated with the blast produced by the interaction of H-poor, metal-rich ejecta with the circumstellar environment. Moreover, the fast expansion of novae allows the study of their full dynamical evolution on timescales comparable with human lifetimes.
Multi-epoch images and high-dispersion spectroscopic observations of some classical nova shell
around nova-like systems can be used to derive expansion rates and expansion velocities.
More info
- Novae here
- Animations here
WOLF-RAYET
WOLF-RAYET NEBULAE
Massive stars are the main actors shaping and stirring the ISM. They destroy their natal molecular clouds by a combination of their powerful UV fluxes and stellar winds creating the largest cavities in the ISM. In particular, very massive stars (M > 30 M๏) will evolve through a phase of strong mass-loss rate and slow wind, a red supergiant (RSG) or luminous blue variable (LBV) phase. After expelling most of their outer hydrogen-rich envelopes, the core is exposed becoming a Wolf-Rayet (WR) star. WR stars exhibit the strongest stellar winds of all stars, which interacts with the material previously ejected compressing it whilst the central star ionizes it. This creates the so-called WR nebulae. The wind-wind interaction produces an adiabatically-shocked region that reaches temperatures of millions of degrees. This hot bubble is surrounded by an optical nebula that is rich in dust and complex molecules formed in the previous evolutionary phase (RSG or LBV). Thus, multi wavelength studies of WR nebulae are most needed in order to unveil the variety of complexes processes acting in the vicinity of the most powerful sources of kinetic energy in the ISM.
WOLF-RAYET STARS
The Wolf-Rayet phenomenon occurs in massive and low-mass stars. Those stars classified as the Wolf-Rayet-type exhibit the strongest and fastest stellar winds in the universe reaching velocities as high as 4000 km/s. This fast wind interacts with the circumstellar material compressing it producing nebulae. Understanding the stellar
feedback requires detailed treatment of state-of-the-art stellar atmosphere's code in
combination with multi-wavelength spectroscopic analysis.
More info
-Wolf-Rayet nebulae here
-Wolf-Rayet stars here