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We present new Doppler images of both components of the double-lined binary $sigma^{2}$ CrB, based on the high-resolution spectroscopic data collected during 11 nights in 2015 March--April. The observed spectra form two independent data sets with sufficient phase coverage. We apply the least-squares deconvolution to all observed spectra to obtain high signal-to-noise mean profiles, from which we derive the Doppler images of both components of $sigma^{2}$ CrB simultaneously. The surfaces of both F9 and G0 components are dominated by pronounced polar spots. The F9 component exhibits a weak spot at latitude 30$^{circ}$ and its mid-to-low latitudes are relatively featureless. The G0 star shows an extended spot structure at latitude 30$^{circ}$, and its surface spot coverage is larger than that of the F9 star, which suggests a higher level of magnetic activity. With the cross-correlation method, we derive a solar-like surface differential rotation on the G0 star of $sigma^{2}$ CrB for the first time, and the surface shear rate is $Delta Omega = 0.180 pm 0.004$ rad d$^{-1}$ and $alpha = Delta Omega / Omega_{eq} = 0.032 pm 0.001$. We do not obtain a clear surface shear law for the F9 star due to the lack of mid-to-low latitude features, but detect a systematic longitude shift of high-latitude spots, which indicates a slower rotation with respect to the co-rotating frame.
We present recent polarimetric images of the highly variable star R CrB using ExPo and archival WFPC2 images from the HST. We observed R CrB during its current dramatic minimum where it decreased more than 9 mag due to the formation of an obscuring d
Mid-infrared photometry of R Coronae Borealis stars obtained from various satellites from IRAS to WISE has been utilized in studying the variations of the circumstellar dusts contributions to the spectral energy distribution of these stars. The varia
Surface abundances of 14 (11 majority class and 3 minority class) R Coronae Borealis stars (RCBs) along with the final flash object, V4334 Sgr (Sakurais object) are revised based on their carbon abundances measured from the observed C2 bands; note th
The R Coronae Borealis (RCB) stars are rare hydrogen-deficient, carbon-rich, supergiants, best known for their spectacular declines in brightness at irregular intervals. Efforts to discover more RCB stars have more than doubled the number known in th
The R Coronae Borealis (RCB) stars are rare hydrogen--deficient, carbon--rich supergiants. They undergo extreme, irregular declines in brightness of many magnitudes due to the formation of thick clouds of carbon dust. It is thought that RCB stars res