“Blue Bumper” Stars

Question

I was recently overviewing various massive compact halo object studies (the Anglo-Australian MACHO collaboration and the French I/II EROS collaboration), and they frequently reference "blue bumper stars," irregular variable stars which produce light curves very similar to gravitational microlensing event. Further searches for more information about them was mostly fruitless, producing a few conference proceedings:

• The MACHO Project LMC variable star inventory: Aperiodic blue variables (code 1995llnl.reptR....P)
• The MACHO Project LMC Variable Star Inventory: Aperiodic Blue Variables (code 1995AAS...18710202P),

but little else.

Is there any more information on this type of variable star, especially a more rigorous and targeted study of them? Also, how is it possible to get the full text for either of those articles?

Answer 1

I did some hunting and followed the paper trail to Cook et al. (1995). In Section 4, they identify a class of stars that brighten aperiodically. They reckon that these "blue bumpers" are Be stars: B-type stars that show strong emission lines. Then again, this is off one paper and I'm really not sure if this is a widely accepted view, but I imagine there would've been more fanfare if this was an exciting new class of object?

I'm not massively learned on the subject of Be stars, but the current consensus seems to be that they are rotating very rapidly, to the extent that there is a substantial circumstellar disk of material around the equator. Be stars are themselves a type of shell star, all of which are known to show aperiodic variations, presumably because of the unstable nature of the system. In fact, the whole class seems to form an observational problem because of their variable nature and light from the star getting mixed up with the disk.