Establishing new diffuse interstellar band correlations to identify common carriers

ABSTRACT Observations from the Apache Point Observatory Catalog of Optical Diffuse Interstellar Bands (DIBs) were analysed to establish highly correlated pairs in terms of their equivalent widths (EWs) (r > 0.95), which importantly facilitate the identification of common carriers. A total of 154 846 possible DIB pairs were originally examined, yet only those with a sufficient number of sightlines (n > 9) that included EW uncertainties were subsequently investigated. The highest correlations for the resulting 56 893 DIB pairs are 6284.05–6203.58 Å (r = 0.990 ± 0.001), 6203.58–5780.64 Å (r = 0.986 ± 0.001), 6993.12–6269.89 Å (r = 0.984 ± 0.001), 6843.76–6792.51 Å (r = 0.984 ± 0.005), 6203.58–5487.64 Å (r = 0.983 ± 0.002), and 5061.50–4969.12 Å (r = 0.983 ± 0.009). The bands 5363.77, 5780.64, 6203.58, and 6284.05 Å appear most frequently. Novel relations linked to those DIBs and others warrant further research, in particular those pairs that involve one or both DIBs with low EWs (e.g. 5609.82, 6269.89, 6993.12, and 7224.16 Å). Numerous DIBs correlated with the prominent 4429.33 Å band were also discovered. The intriguing proposal of anionic hydrogen clusters as possible DIB carriers is also discussed.

Displacement cascade evolution in tungsten with pre-existing helium and hydrogen clusters: a molecular dynamics study

The effects of radiation damage on bcc tungsten with preexisting helium and hydrogen clusters have been investigated in a high-energy environment via a comprehensive molecular dynamics simulation study. This research determines the interactions of displacement cascades with helium and hydrogen clusters integrated into a tungsten crystal generating point defect statistics. Helium or hydrogen clusters of atoms~0.1% of the total number of atoms have been randomly distributed within the simulation model and primary knock-on-atom (PKA) energies of 2.5, 5, 7.5 and 10 keV have been used to generate displacement cascades. The simulations quantify the extent of radiation damage during a simulated irradiation cycle using the Wigner-Seitz point defect identification technique. The generated point defects in crystals with and without pre-existing helium/hydrogen defects exhibit a power relationship with applied PKA energy. The point defects are classified by their atom type, defect type, and distribution within the irradiated model. The presence of pre-existing helium and hydrogen clusters significantly increases the defects (5 - 15 times versus pure tungsten models). The vacancy composition is primarily tungsten (e. g., ~70% at 2.5 keV) in models with pre-existing helium, but the interstitials are primarily He (e. g., ~89% at 10 keV). On the other hand, models with pre-existing hydrogen have a vacancy composition that is primarily tungsten (more than 90% irrespective of PKA energy), and the interstitial composition is more balanced between tungsten (average 46%) and hydrogen (average 54%) interstitials across the PKA range. The distribution of the atoms reveals that the tungsten point defects prefer to reside close to the position of cascade initiation, but helium or hydrogen defects reside close to the positions where clusters are built.