Grain Survival in Supernova Remnants and Herbig-Haro Objects

Area of Science:

• Astrophysics
• Cosmic Dust Studies
• Supernova Remnant Research

Background:

• Interstellar dust grains are crucial for star formation and chemical evolution.
• Previous studies suggested supernova remnant (SNR) and Herbig-Haro (HH) object shocks efficiently destroy dust grains.
• The prevailing view posits near-complete metal depletion into the gas phase within these shock environments.

Purpose of the Study:

• To investigate the survival rate of interstellar dust grains in shock waves associated with SNRs and HH objects.
• To challenge the established understanding of dust destruction mechanisms in astrophysical shocks.
• To determine the gas-phase abundance of iron (Fe) and oxygen (O) based on observed spectral line ratios.

Main Methods:

• Utilizing the flux ratio of the [Fe ii] lambda8617 and [O i] lambda6300 emission lines as a diagnostic tool.
• Calculating the [Fe ii]/[O i] flux ratio in various shock models.
• Comparing model predictions with observational data from SNRs and HH objects.

Main Results:

• The [Fe ii]/[O i] flux ratio is sensitive to the gas-phase Fe/O abundance but robust against variations in gas ionization, temperature, and density.
• Observational data are best reproduced when models assume only 20% of iron remains in the gas phase, implying significant dust survival.
• This contradicts the consensus that shocks destroy nearly all dust grains and metals are fully in the gas phase.

Conclusions:

• A substantial fraction of interstellar dust grains survive passage through astrophysical shocks.
• The observed spectral line ratios indicate that metals, particularly iron, are significantly incorporated into dust grains rather than being fully ionized.
• Further research is needed to refine models of dust processing and destruction in energetic astrophysical environments.