Date: Tue, 14 Mar 2006 08:21:32 -0500
From: arne <arne
To: Bob Wing <wing
References: <200603140906.k2E96OU5030689

the oddball cases, especially those with close companions.  So
as you might have expected, I have looked at this close pair.

I have a BV image set from 2001 December 19, at the time when Z Tau
was about the same brightness as its neighbor to the NE (fading
to minimum); and another from December 29, 2003, again about the same
brightness (but on the rise to maximum).  A 3x3arcmin section of the
http://www.aavso.org/tmp2/ztaub.jpg
The separation is about 5.3 arcsec, and it is unquestionable that
the flat bottom is caused by mistaken observations of this companion.
However, to resolve the pair with amateur equipment will require
good pixelization and excellent skies, along with large aperture if
the range really is 7 or 8 magnitudes as Bob suggests.  On the
other hand, I do have good calibration of the companion, so you
can measure both stars as a blend and we can subtract out the
contribution from the companion using Lew Cook's Nemisis spreadsheet.

I'll see if I can get new data at SRO and NOFS during the current
minimum.  CCD observers should give it a try, at least until Z Tau
brightens above the magnitude of the companion.
Arne

Bob Wing wrote:
> 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.
> 
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