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

[RICHARD MILES]

Daniel Majaess wrote:
>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 =)

Dear Daniel,

I have developed some spreadsheets specifically for conveniently measuring 
extinction in V and I bands but have not advertised these as yet.  I can 
send you one or other of them off-line.

For instance for measuring atmospheric extinction coefficients, kv, and 
exo-atmosphere zeropoint Zv, I have two spreadsheets; one using stars where 
(B-V)~0 and a second where (B-V)~0.8.  (The difference between the two is a 
measure of second-order effects/transformation coefficients - especially 
useful when working unfiltered.)  Here's an extract from the former 
spreadsheet:

LIST OF 568 NON-VARIABLE, 'MONOCHROME' 'BLUE' EXTINCTION STARS TAKEN FROM 
HIPPARCOS DATABASE
meeting the following criteria:

6.00 < V < 9.00
0.0004 < delta HpMag < 0.0024 mag
0.010 < (B-V) < 0.040
0.01 < (V-I) < 0.07
No other field star having delta V < 6.0 mag within 60 arcsec
No other bright field star nearby which might confuse identification
All variable stars excluded

The spreadsheet is Excel-based and contains four sheets:
1.  Source data from Hipparcos used as a look-up table by the other sheets
2.  Star selector sheet - you put your latitude, longitude and date/time in. 
You then can specify the airmass range you wish to work at and it highlights 
those Hipparcos stars available together with their azimuth and altitude. 
It even tells you what the approximate exposure time is for each star so 
that the image is say no more than half-saturated.
3.  Data reduction sheet - here you cut and paste from AIP4WIN format and it 
calculates the slope and intercept plus some error calculations.
4.  Plotting sheet - here you have two plots - one is all the points from 
the reduction of individual images, the second is block-averaged points for 
each star.  I should add that I generally take a series of images for each 
star such that the average value is a more accurate figure than that from 
any single image.  The image series can be anywhere from 7 to 21 images 
(always an odd number though).

Hope this gives you a feel for how this works.
Cheers,
Richard Miles
Dorset, UK