The dust envelope of R CrB in June 2001: Detection of a compact IR source

Abstract

We present the results of a joint analysis of JHK interferometric and UBVJHKLM photometric observations of RCrB acquired in June 2001. The baseline for the IOTA interferometer was 21.18 m. During the observations, the star was in its bright state in the V band and near its maximum brightness in the L band. Our analysis reveals an IR source that is considerably smaller than the extended dust envelope discovered earlier. We identify this compact IR source with the emission from a group of dust clouds. The linear scale (diameter) of the IR source was d in,c ≈ 13.5D* (its angular diameter is θin,c≈6.4 mas). About 7% of the star’s radiation was obscured by this group of clouds, which contributed ∼14% of the total IR excess of R CrB and ∼22% of the K-band flux. The color temperature of the compact source was only ∼300 K higher than the color temperature of the extended dust envelope. The inner boundary of the extended dust envelope had a diameter of d in,e ≈ 90D* (θin,e≈43 mas).