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Actually all this has been done in a paper that was in the last (final)
SAAO Circular (not on-line as far as I know) by Caldwell et al. It shows
graphical and analytical relations among all the UBVRIJHK and uvby colors.
The full citation cribbed from SIMBAD is:
1993SAAOC..15....1C
CALDWELL J.A.R., COUSINS A.W.J., AHLERS C.C., VAN WAMELEN P., MARITZ E.J.
South African Astron. Obs. Circ., 15, 1-29 (1993)
Statistical relations between photometric colours of common types of stars in
the UBV (RI)c, JHK and uvby systems.
A lot of the relations don't make much astrophysical sense, since there
are multiple effects (temperature, reddening, metallicity, luminosity)
involved. I find it unnecessary to know much more about JHK colors than
what I show on my simple list that Yoshida-san cited earlier. To first
order, J-K color scales quite closely to V-R or Stromgren b-y: unreddened
A0 stars are 0.0 of course, the Sun is at about 0.4, K0III is at ~0.6,
M0III is at ~1.0, and cooler than that gives larger numbers. Beyond such
rough values, you'll run into trouble real fast if you try to estimate
spectral types (say) more accurately than that. In most instances nowadays
you have additional information beyond star colors (like sky location and
proper-motion) to help decide on generic star types. For cases where there
are circumstellar shells or clouds, emission lines, etc., all these colors
become very problematic, and one is wise to avoid interpreting things
too far.
For JHK stuff based on models (and in some notional standard system,
_not_ the de facto standard 2MASS system), see the work by Bessell & Brett:
1988PASP..100.1134B
BESSELL M.S., BRETT J.M.
Publ. Astron. Soc. Pac., 100, 1134-1151 (1988)
JHKLM photometry: standard systems, passbands and intrinsic colors.
...which is available via ADS.
\Brian
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