Why do most CMDs cite (B - V), (V - I), etc. indexes?

[Weltevreden SA]

Most professional papers cite photometric CMD colour relationships using the Johnson UBVRI notation instead of the Strömgren uvby system. Why? As I understand it, the Strömgren system was devised specifically for photometric precision, while the Johnson system originated in early colour TV experiments and the broad bandwidths used at the time. The relatively few papers that cite the Strömgren system in their data reduction sections are usually devoted to narrow-band spectroscopy of some sort, usually ugrix. The bandwidth spreads can be very different, e.g. V=100nm versus b=20nm, or I=150nm versus BetaN=3nm. I'm curious how the seemingly clunky UBVRI system managed to hold on. =Dana in SA

[pdalek]

See Michael Bessell's review on the subject
http://www.mso.anu.edu.au/~bessell/araapaper.pdf

[gregbradley]

What's CMD mean?
Greg.

[pdalek]

Colour Magnitude Diagram

A Hertzsprung–Russell diagram is a particular CMD specific to stars.

[madbadgalaxyman]

There is a very strong bandwagon heading in the direction of the (Sloan Digital Sky Survey) ugriz system, in the literature. However, this is still a very broadband system with limited resolution. In fact, ugriz it is not that much different from UBVRI , except that it has a broader wavelength coverage.
(see:
http://www.sdss2.org/dr5/algorithms/sdssUBVRITransform.html
Galaxies papers are now very often on the ugriz system.

Perhaps the Johnson-Cousins UBVRI system has been maintained for convenience and for the easy ability to to intercompare new stellar data with the older photoelectric photometer observations that were the basis of our study of stars.

We do carry a lot of historical baggage in astronomy; many have said that the magnitude system would never have been kept on, if astronomers were rational people;
indeed, mid-infrared and submillimeter and radio astronomers have never adopted it.