[Aavso-photometry] Need High-dec (B-V)~0 stars & Secondary Extinction Pairs (3 new additions for your lists);

[Daniel Majaess]

Hi, my bad, let me explain further, the A0 stars listed in your book are 
too bright for our situation especially since I need a plate solution 
solve via pinpoint so photometry can be automatically extracted via Dave 
Lane's pipeline.  It has been my experience that stars in the Hipparcos 
catalog between the 8.5-9.5 mag limit have larger photometric errors 
sometimes of order 0.1 magnitudes, and since the protocol depends on 
knowing the standard V-band measurement, I wanted photometry aside from 
the Tycho/Hip.  I guess if I can reduce the error at every spot in the 
line, I'll feel better.
Regarding the list, yesterday it came to me that I could exploit the 
wonderful functionality of Vizier to help me in my quest.  I went to the 
catalog section and called up Neckel's and Mermillod's UBV database, set 
the appropriate conditions in the B-V cell ("=0") and in the 
corresponding V-cell ("8.5..9.5") and bango, out comes the data =)  What 
a wonderful online interface the French have made available to us =)  
Once I reduce the data further and plan an observing script I'll foward 
the info to the list.

Many thanks,
Daniel.

arne wrote:
> Daniel Majaess wrote:
>   
>> Hi, I've derived the local parameters for Halifax Nova Scotia by 
>> following an extinction pair across various values of airmass and the 
>> secondary coefficients appear to be essentially zero---especially in the 
>> visual band.  So I am now thinking of shifting gears and adopting the 
>> protocol outlined in Henden's book whereby a bunch of different stars 
>> (at varying airmass) with (B-V)~0 are imaged.  I was wondering if anyone 
>> had a list of high-dec, bright (7.5-9.5 mag) stars with a color (B-V)~0, 
>> and also they need to have well-defined visual and blue magnitudes so 
>> Hipparcos data will not cut it.   Any suggestions would be lovely =)
>>
>> Also, here are some nice secondary extinction pairs that I am using and 
>> you may want to add to your respective lists.  I *believe* I got them 
>> from scanning through Dave Lane's ECU but I was sent a number of 
>> suggestions from wonderful AAVSO members =)  Anyways, here they are: 
>> HD96730 ( 11:06:52.69 +36:42:29.2 ), HD 97184 ( 11:16:01.55 +42:24:01.0 
>> ), HD92454 ( 10:42:31.14 +68:34:22.2 ).
>>
>>     
>
> Certainly there is a list in Henden's book of bright zero-color (A0) stars.
> As for Hipparcos stars (such as Richard Miles' nice red-blue pair list),
> I wonder why you feel that "Hipparcos data will not cut it."  For
> the all-sky extinction method, you only need stars with approximate
> zero color, as transformation is a second-order effect.  For example,
> say that you have one star with zero color and another with
> (B-V) = 0.2  (Hipparcos colors are *much* better than this!).  If
> your V-band transformation coefficient is 0.05, pretty typical, then
> the error made by not transforming the instrumental magnitude of
> the second star is 0.2*0.05 = 0.01mags, which will usually be about
> your limit for handling all-sky measures.
> Arne
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