[Terry B]

Dear All
BL Tel is an interesting binary star. It has a very long period of 778 days. Most eclipsing binary stars have periods between half a day and a few days. At the period increases the chance that binary star happen to allign up so we see an eclipse becomes very small. This makes BL Tel very unusual. The stars are currently undergoing an eclipse. The last eclipse was in May 2011. I took photometry images of the 2011 eclipse and a grapg of the eclipse is below.
For this eclipse I am also taking spectra. The 2 stars are different spectral classes. The brighter star is an F4 star and the eclipsing star is a M star. In the uneclipsed state, the F star spectra dominates but during the eclipse, the M star spectra starts to become visible. The stars will also become more red. I have attached a spectra showing the stars before the eclipse on 29/5 and one from last night. The eclipse is not at maximum yet so should the difference should become more apparent in a few weeks.

The red graph is vert typical of a F3 star with deep Ca II lines called K and H between 3900 and 4000A. Ha, Hb and Hg are also clearly visible.
In the blue graph, the overall colour has shifted to the red. The Ca lines are weaker and there are brouad absorptions visible that are caused by TiO.
I will continue to take spectra weather permititng to hopefully show the further changes in the spectra.

Terry