Infrared photometry for two RV Tau stars and V1027 Cyg

We present and discuss the results of our long-term JHKLM photometry for two RV Tau stars (R Sge and RV Tau) and the yellow supergiant V1027 Cyg, a candidate for protoplanetary nebulae. The amplitude of the infrared brightness variations in R Sge and RV Tau over fourteen years of observations was 0{_./ ^m }9-1 ^m ; the infrared brightness variations in V1027 Cyg over eighteen years did not exceed 0{_./ ^m }25. The infrared brightness and color of R Sge fluctuated about their gradually changing mean values; the infrared brightness variations agree with a period of 70.77 days. The periodic J brightness and J-H color variations in R Sge can be explained by temperature pulsations with Δ T ≤ 200 K and radial pulsations with [Δ R/R] ≤ 0.2. From 1995 to 2008, the mean J brightness of RV Tau increased, while its mean J-H color index decreased; the variations in the mean J brightness can be associated mainly with stellar temperature variations; a periodic component with P = 78.73 days is observed in the infrared brightness and color fluctuations. The variations in the mean J brightness and J-H color index of the supergiant V1027 Cyg over eighteen years of observations did not exceed a few hundredths of a magnitude; both temperature and radial pulsations may be present in the observed J brightness variations. The most probable period of the infrared brightness fluctuations in V1027 Cyg is 237 ± 2 days. The dust shell of R Sge may consist of two layers with grain temperatures of ∼1000 and ∼700 K; the optical depth at 1.25 µm is ∼0.02 and ∼0.24, respectively. The grain temperatures in the circumstellar dust shells of the supergiants RV Tau and V1027 Cyg are ∼600 K (RV Tau) and ∼700 K (V1027 Cyg). Their optical depths at 1.25 µm are ∼0.24 (RV Tau) and ∼0.008 (V1027 Cyg).