The Importance of Var Cas 06 if it is NOT due to microlensing

Doug Welch
Dec 12, 2006

I am skeptical that the outburst of Var Cas 06 is due to microlensing. (If it is, I know who I will ask to buy lottery tickets for me from now on!) High-amplification microlensing events are exceedingly unlikely, especially in the near-field. To me, the importance of the outburst is far greater if it is NOT due to microlensing since it appears to mimic a point mass microlensing lightcurve sufficiently well that it would trigger a detection in a microlensing survey. Said slightly differently, such contaminant events might be producing part (or most) of the microlensing signal thought to be due to MACHOs, resulting in incorrect estimates of the galaxy mass in such objects.

The next steps are harder but also more important. What is the lightcurve history of this star from archival images? Has an outburst ever been recorded before? (Obviously, the low-hanging digital archive fruit has already been picked.) Does a high-dispersion spectrum reveal anything unusual about this apparent main-sequence A star? Do high S/N spectra taken now change with time? Is the star a single-lined spectroscopic binary?

My money is on this outburst not being due to microlensing. If additional evidence is consistent with this viewpoint then we will have learned something much more valuable than the opportunity to have observed YAME ("yet another microlensing event").