Re: USNO A2.0 "R"

[Michael Koppelman <lolife@bitstream.net>]

Well, I found part of the answer to this. The USNO A2.0 catalog 
has an * by HD 189797 which means the magnitudes are probably 
wrong. Since the spectral type of HD 189797 is A2, V-R should be 
somewhere around 0.08. Since V is 9.37 R should be around 9.29. 
That's a long ways away from USNO's 10.2.

GSC 1071-1970 is of type A0 so V-R should be around 0.02 making 
R about 10.48, which is still pretty far off of USNO's 10.9 but 
much closer. Since GSC 1071-1970 is not flagged as "wrong", one 
could assume that V-R could be as high as 0.4, but it seems odd 
for an A0 star. B-V is 0.11 (according to SIMBAD), which is much 
closer to an A type star than V-R=0.4.

It brings me back to my question, which I haven't found an 
answer for, which is what does USNO mean by R?

If we are to be successful with this star, I'm going to need to 
get some good color photometry of the comp stars. Also of note, 
GSC 1071-1970 is listed as having "suspected intrinsic 
variability" in Tycho, so that might not be a good choice. I 
wonder if TASS has proven any variability in it? It should be in 
the September data set.

Cheers,
Michael


On Tuesday, September 17, 2002, at 12:14  AM, Michael Koppelman wrote:

> I'm sure I could find this somewhere, but I'm wondering how the 
> USNO A2.0 "R" compares to the Cousins R. The reason I ask is 
> when I use the R magnitudes on the comp stars of the star I am 
> working on, they don't really match up. Using the USNO A2.0 R 
> magnitudes the difference between my two comp stars should be 
> 0.7. With my data, using an average of over 200 measurements, 
> the difference is 1.2. When you split the difference I get 9.95 
> vs. USNO's 10.2 and 11.15 vs. USNO's 10.9.
>
> The stars in question are HD 189797 and GSC 1071-1970.
>
> The other weird part is, using these comp stars I got an 
> average of 10.23 on my variable star. TASS gets I~9.2 and V~9.7 
> at this part of the phase. I would have thought that my R would 
> be in between the V and I values. I'm wondering if my R comes 
> out so dim because I'm using dim USNO magnitudes or something? 
> Are there any other good sources for R magnitudes?
>
> Thanks!
> Michael
>
>