Abstract
Abstract Asymmetrical features in disks provide indirect evidence of embedded objects, such as planets. Observed with the Atacama Large Millimeter/submillimeter Array (ALMA), the circumstellar disk in MWC 758 traced with thermal dust continuum emission at wavelengths of 0.9 mm with an angular resolution up to 01 (15 au) exhibits an asymmetrical dust ring with additional features. In order to analyze the structures azimuthally and radially, we split the dust ring into small segments in azimuth. For each segment, we fit two-Gaussian functions to the radial intensity profile. The obtained best-fit parameters as a function of azimuth are analyzed. Three spiral-like arm structures are identified. When fitting the 0.9 mm features with the spiral density wave theory using the WKB approximation, two sets of disk aspect ratios are found: one solution gives relatively low values (∼0.03) while the other solution is at the upper bound of the free parameter (∼0.2). The planet locations suggested by the upper-bound result are similar to the ones determined by Benisty et al. for the NIR polarized intensity image. Comparing the reported spiral-like structures with the higher angular resolution (004) ALMA image in Dong et al., we identify different structures in the west of the disk due to differences in the adopted analysis methods and the respective resolutions of the images.
Highlights
Several asymmetrical features have recently been found in protoplanetary disks
Observed with the Atacama Large Millimeter/submillimeter Array (ALMA), the circumstellar disk in MWC 758 traced with thermal dust continuum emission at wavelengths of 0.9 mm with an angular resolution up to 0.1 (15 au) exhibits an asymmetrical dust ring with additional features
Around HD135344B, where a ring and an arc are detected at 0.9 mm wavelengths with 0.16 resolution, two planets at different locations are a possible scenario to form the vortices and the features seen in the scattered light image
Summary
Several asymmetrical features have recently been found in protoplanetary disks. In the V1247 Orionis system an asymmetrical ring and a crescent structure are detected in the continuum image obtained by ALMA with a 0.04 resolution at 0.9 mm wavelengths (Kraus et al 2017), and based on hydrodynamics simulations a planet at 100 au is suggested to produce the gap and trigger two vortices, the crescent and the asymmetry in the ring (Kraus et al 2017). We report a detailed analysis on the dust emission at wavelengths of 0.9 mm with an angular resolution up to 0.1 observed with ALMA toward the MWC 758 disk. The brightest emission is 13.6 mJy beam−1 (21.5 K) with an SN of 34, located northwest with a stretched structure extending over a range in azimuth of
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