Re: Target zone selection

[Doug Welch <welch@physics.mcmaster.ca>]

> And so it goes. What will you do with a Mark IV?

Hi Tom et al,

Thanks for the very informative responses! I have both
general and specific goals for a Mark IV. A general
goal is to do an effective survey for lower amplitude,
shortish period variables - the ones which are missed
by essentially all other surveys. For every mode you
can detect in a star, you are able to nail down one
more physical characteristic. Radial pulsators have
large amplitudes and beautiful lightcurves, but compared
to multimode pulsators, their lightcurves contain
less information.

My specific interest is to locate the galactic counterparts
of the first-overtone/second-overtone "Cepheids" which have
been found in both the LMC and SMC. These stars were almost
unknown before the MACHO work - CO Aur being the one exception.
Briefly, they have (first-overtone) periods between 0.4 and 
about 1.0 day, typically have luminosities which are on the
short-period extension of the first-overtone sequence of the
Cepheid P-L relation, and are *all* double-mode pulsators.
Their smaller photometric amplitudes and double periods
kept them from being discovered until recently. It seems that
these stars cannot be very young, but they are too faint to
study spectroscopically in the LMC and SMC, so efforts to
determine metallicity must be confined to galactic counterparts.
Too bad there aren't any (or just one or two)! I would use a
Mark IV to survey low and intermediate galactic latitudes for
these stars and to define a sample which could be studied
spectroscopically and dynamically to determine the precursor
population. It wold also be interesting to look for
amplitude modulation and period change.

TASS imagers would be ideal for this program (and others like
it) because of the need for long time baseline, frequent
imaging of relatively large areas of sky. Basically, one
could not get enough observing time to do this type of work
any other way!

Cheers,
Doug