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Light Variations in the Candidate for Protoplanetary Objects HD 179821 = V1427 Aql in 1899-1999
We present photoelectric and photographic observations of the supergiantHD 179821 with a large infrared excess, a candidate for protoplanetaryobjects. Over, ten years of our UBV observations, the star exhibitedsemiregular light variations with amplitudes Delta V = 0.10 mag, B =0.15 mag, and U = 0.25 mag, as well as systematic color and lightvariations. From 1990 until 1996, the yearly mean U-B and B-V colorindices decreased by 0.25 and 0.15, respectively. After 1996, the motionof the star in the two-color (B-V)-(U-B) diagram upward and to the leftslowed down. The color excess that we derived from our observations, byassuming that the star's spectral type was F3I in the 1990s, is E(B-V) =1.0. The photographic observations of HD 179821 from 1899 until 1989show that its brightness mpg generally increased whilesignificantly fluctuating. An analysis of the observational datasuggests that HD 179821 is most likely a post-AGB star of intermediateor low mass.
| The variability of four yellow supergiants - Possible protoplanetary objects
Photoelectric UBV observations of four supergiants with a large IRexcess (IRAS 18095 + 2704, IRAS 19386 + 0155, and SAO 34504), possibleprogenitors of planetary nebulae, are presented. All of them exhibitedbrightness variations with amplitudes from 0.2 to 0.5 m over the period1990-1992.
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