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We present Atacama Large Millimeter/submillimeter Array (ALMA) Band 6observations of dust continuum emission of the disk around WW Cha. The dustcontinuum image shows a smooth disk structure with a faint (low-contrast) dustring, extending from $\sim 40$ au to $\sim 70$ au, not accompanied by any gap.We constructed the simple model to fit the visibility of the observed data byusing MCMC method and found that the bump (we call the ring without the gap thebump) has two peaks at $40$ au and $70$ au. The residual map between the modeland observation indicates asymmetric structures at the center and the outerregion of the disk. These asymmetric structures are also confirmed bymodel-independent analysis of the imaginary part of the visibility. Theasymmetric structure at the outer region is consistent with a spiral observedby SPHERE. To constrain physical quantities of the disk (dust density andtemperature), we carried out radiative transfer simulations. We found that themidplane temperature around the outer peak is close to the freezeouttemperature of CO on water ice ($\sim 30$ K). The temperature around the innerpeak is about $50$ K, which is close to the freezeout temperature of H$_2$S andalso close to the sintering temperature of several species. We also discuss thesize distribution of the dust grains using the spectral index map obtainedwithin the Band 6 data.

ALMA observation of the protoplanetary disk around WW Cha: faint double-peaked ring and asymmetric structure