Fig. 3: The radius and radial velocity of the stellar surface of R Doradus.
From: One month convection timescale on the surface of a giant evolved star
a, The half-power radius R as a function of the position angle (PA) with respect to the north celestial pole. Positive angles point in the direction of the right ascension. The curves indicate R measured for three epochs of ALMA band 7 (338 GHz) observations. The horizontal lines indicate the average radius for each epoch. The lower figure boundary on the radius is the estimated photospheric radius of 25.6 mas, measured at 2.3 µm (ref. 28). The red vertical bar indicates the granule size measured from the spatial PSD, with the linear size translated to an angular size at R. The 1σ s.d. on the radius (similar for each epoch) is plotted in the bottom right corner (magenta error bar) and is at most 0.17 mas. b, The radial velocity V at the surface of R Doradus. The velocity is determined from the difference of the half-power radius between the third and fourth epochs (18 and 27 July 2023; solid line) and that between the fourth and fifth epochs (27 July and 2 August 2023; dashed line). The horizontal lines denote the average velocity. The velocity determined in this way corresponds to the movement of the τ338GHz = 1 optical depth surface and is an average between the respective epochs. This indicates the movement of the shocks induced by the convective motions. The 1σ s.d. in the radius determination translates to an uncertainty on the velocity of ≲2.6 km s−1 and is indicated in the top right of the panel (magenta error bar).
