  We present ten years of new photometric monitoring of the light variability
of five evolved stars with strong mid-infrared emission from surrounding dust.
Three are known carbon-rich proto-planetary nebulae (PPNe) with F$-$G spectral
types; the nature of the other two was previously unknown. For the three PPNe,
we determine or refine the pulsation periods of IRAS 04296+3429 (71 days),
06530$-$0213 (80 days), and 23304+6147 (84 days). A secondary period was found
for each, with a period ratio P$_2$/P$_1$ of 0.9. The light variations are
small, 0.1-0.2 mag. These are similar to values found in other PPNe. The other
two are found to be giant stars. IRAS 09296+1159 pulsates with a period of only
47 days but reaches pulsational light variations of 0.5 mag. Supplemental
spectroscopy reveals the spectrum of a CH carbon star. IRAS 08359$-$1644 is a
G1III star that does not display pulsational variability; rather, it shows
non-periodic decreases of brightness of up to 0.5 mag over this ten-year
interval. These drops in brightness are reminiscent of the light curves of R
Corona Borealis variables, but with much smaller decreases in brightness, and
are likely due to transient dust obscuration. Its SED is very similar to that
of the unusual oxygen-rich giant star HDE 233517, which possesses mid-infrared
hydrocarbon emission features. These two non-PPNe turn out to members of the
rare group of giant stars with large mid-infrared excesses due to dust, objects
which presumably have interesting evolutionary histories.

Solar and Stellar Astrophysics