Re: RR Lyrae stars

[Stupendous Man <richmond@a188-l009.rit.edu>]

> 1. In terms of deriving the mean magnitude of the star, among other 
> methods, they mention "Most recent investigations have defined the mean 
> magnitude by integrating the lightcurves in intensity units to derive 
> the intensity mean magnitude." Anyone care to shed any light on this? 

  I would interpret this to mean:

       a) convert magnitude to intensity (using an arbitrary zero point)
       b) integrate intensity over time, then divide by the period,
               to find the mean intensity level
       c) convert the mean intensity level back to a magnitude

If you like to think graphically, you could

       a) convert magnitude to intensity
       b) plot intensity vs. time
       c) find the horizontal line which divides the areas above and below
               the curves equally; this is the mean intensity

> 2. Is there anyway to determine Fe/H by photometry?

  Without narrow-band filters, I think not.

> 3. What do they mean by the term "statistical parallax"?

  This is a technique developed to estimate roughly the distance to
a class of (presumably) identical stars.  The idea is something like this:

        a) define a group of stars which you think SHOULD have the
                    same intrinsic luminosity
        b) pick out a subset of these stars which have the same
                    apparent magnitude - and, presumably, the same distance
        c) very carefully measure the radial velocities of this subset
        d) very carefully measure the proper motions of this subset
        e) guess the Sun's peculiar motion relative to this set of stars
        f) use the (guessed) motion of the Sun relative to the stars
                    and their 3-D motions to figure out their distances

  There are, as you can see, many assumptions; but, for stars which
are too distant to measure a real parallax, it's better than nothing.

                      Michael Richmond