Broad Balmer Wings in BA Hyper/Supergiants Distorted by Diffuse
  Interstellar Bands: Five Examples in the 30 Doradus Region from the
  VLT-FLAMES Tarantula Survey
  Extremely broad emission wings at H$\beta$ and H$\alpha$ have been found in
VFTS data for five very luminous BA supergiants in or near 30 Doradus in the
Large Magellanic Cloud. The profiles of both lines are extremely asymmetrical,
which we have found to be caused by very broad diffuse interstellar bands
(DIBs) in the longward wing of H$\beta$ and the shortward wing of H$\alpha$.
These DIBs are well known to interstellar but not to many stellar specialists,
so that the asymmetries may be mistaken for intrinsic features. The broad
emission wings are generally ascribed to electron scattering, although we note
difficulties for that interpretation in some objects. Such profiles are known
in some Galactic hyper/supergiants and are also seen in both active and
quiescent Luminous Blue Variables. No prior or current LBV activity is known in
these 30 Dor stars, although a generic relationship to LBVs is not excluded;
subject to further observational and theoretical investigation, it is possible
that these very luminous supergiants are approaching the LBV stage for the
first time. Their locations in the HRD and presumed evolutionary tracks are
consistent with that possibility. The available evidence for spectroscopic
variations of these objects is reviewed, while recent photometric monitoring
does not reveal variability. A search for circumstellar nebulae has been
conducted, with an indeterminate result for one of them.
