Infrared photometry for three RV Tau variable stars

We have analyzed our long-term (1995-2008) JHKLM photometry for three variable RV Tau supergiants. It follows from this analysis that: the amplitude of the JHK brightness variations is approximately the same, 0 (m) . 9-1 (m) , for the three stars; a negative linear trend is noticeable in the variations of the mean J brightness for AC Her; and the mean J brightness of R Sct and V Vul remained constant. The observed J brightness fluctuations in the supergiants are shown to be consistent either only with the temperature pulsations (AC Her and V Vul) or with the temperature and radial pulsations (R Sct). We have detected long-term pulsations in the J brightness and J-H color variations of the supergiants with the following characteristic time scales: similar to 1500 days (AC Her), similar to 3500 days (R Sct), and similar to 800 and similar to 1500 days (V Vul). Our search for a periodic component in the infrared brightness variations of the three stars has revealed periods that differ from those obtained from optical observations. We show that relatively hot dust shells (T (d) similar to 700-800 K) exist around the supergiants under study; the densest and most massive shell was observed for V Vul. The ranges of optical-depth variations for the dust shells were tau(1.25 A mu m) a parts per thousand 0.04-0.10 (AC Her), a parts per thousand 0.02-0.12 (R Sct), and a parts per thousand 0.18-0.32 (V Vul). The spectral types in the infrared varied over narrower ranges than those that followed from optical observations of these stars.