VLBA maps of SiO J = 1–0 v = 1 (in blue), v = 2 (in green), and v = 3 (in red) maser emissions from R Leo (upper left, November 13, 2009), TX Cam (upper right, January 31, 2010), U Her (lower left, April 17, 2011), and IK Tau (lower right, November 04, 2011). To ease the comparison between the three maser lines, using the same color code, we plotted the fitting rings obtained with ODRpack for each maser transition (see Table 2).