Date: Tue, 14 Mar 2006 04:06:24 -0500
From: Bob Wing <wing

Date:    Monday night, March 13-14, 2006

Dear Rick, Erwin, et al.,
 
The real problem is that if Z Tau gets much fainter than the companion,
as it probably does, then only one star is visible, at approximately
the right place, and the companion is likely to be misidentified as the 
companion on the chart, if the scale permits.  Then if the observer 
sees only one star, he/she will have to think consciously about which 

This is of some importance because Z Tauri is an interesting star.
its mean light curve with an extraordinarily long period of 495 days
The GCVS (I'm looking at the 4th edition, 1987) gives its period as
as S7.5,1e, which presumably refers to a phase near maximum light.  
present in the spectrum in addition to the dominant TiO bands).  
Interestingly, this is very similar to the description of Chi Cygni, 
amplitude of any Mira on record (10 magnitudes!).  In fact, there are 

V = 17 or even 18.  It would be nice to know.  Observing it at minimum
will be challenging, but doable with a CCD with sufficient scale to
separate the two stars (I don't know the separation). 

Mira near minimum light provides an opportunity to observe an extremely
cool (by stellar standards) gas, which is bright enough to be observed
spectroscopically (at least in the infrared).  At low temperatures one
sees molecules that are not present at warmer phases.  And with the
molecules that have never been seen in any star.  It was in just such
that bands of zirconium sulfide (ZrS) were first identified.  

So let's get after Z Tau and see how faint it actually gets.  I just 
downloaded Bulletin 69 (Predictions for 2006) and see that Z Tau 
(0546+15A) is listed as "urgently in need of observation."  It had a 
predicted min last January 19, so it won't have another one until April 
of 2007.  But it's still faint now, and there should still be a chance
this year, before it goes behind the sun, to observe it while it's 
significantly fainter than its companion.

    Ohio State

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