Diffuse interstellar bands and the structure of the ISM
This may be interpreted as evidence that the profile of sub-structure of the lambda 6614 DIB is skewed towards the red in these three sightlines (Sk -68°135, Sk -69°223 and Sk -69°243) to a greater degree than that found in the Galactic ISM. Compared to Galactic trends, the LMC DIBs are found to be weak with respect to the reddening and neutral potassium column density towards Sk -67°2 and Sk -68°135. This may be attributable to a combination of the high UV flux and reduced shielding of interstellar clouds due to the low metallicity of the interstellar gas of the LMC, and results in the destruction of DIB carriers by photodissociation and/or photoionisation. Relative to N(H I) the lambda 6284 DIB observed in four LMC sightlines is shown to be approximately 1/5 to 1/2 of its average strength in the Milky Way. This supports the idea that the metallicity and/or dust-to-gas ratio of the ISM is closely linked with the chemistry that governs the abundance of DIB carriers relative to N(H I). Variations in the N(Ca II)/N(Ti II) ratio are found over at least an order of magnitude in the LMC ISM, and are taken as evidence for significant variation in the Ca n/Ca m ionisation balance. Derived logarithmic titanium depletions are found to be relatively low in the six LMC sightlines studied, with values between approximately -0.8 and -1.9, which are similar to the levels of depletion generally seen in the warm, shocked interstellar medium of the Galaxy.