Atomic masses of strontium and ytterbium

The atomic masses of the three most abundant isotopes of strontium, ${}^{86,87,88}$Sr, and of the six most abundant isotopes of ytterbium, ${}^{170,171,172,173,174,176}$Yb, have been obtained from measurements of cyclotron frequency ratios of pairs of ions simultaneously trapped in a Penning trap. Our results, with one standard deviation uncertainty, are $M$(${}^{86}$Sr) $=$ 85.909 260 730 9 (91) u, $M$(${}^{87}$Sr) $=$ 86.908 877 497 0 (91) u, $M$(${}^{88}$Sr) $=$ 87.905 612 257 1 (97) u, and $M$(${}^{170}$Yb) $=$ 169.934 767 241 (18) u, $M$(${}^{171}$Yb) $=$ 170.936 331 514 (19) u, $M$(${}^{172}$Yb) $=$ 171.936 386 655 (18) u, $M$(${}^{173}$Yb) $=$ 172.938 216 213 (18) u, $M$(${}^{174}$Yb) $=$ 173.938 867 539 (18) u, $M$(${}^{176}$Yb) $=$ 175.942 574 702 (22) u. These results have application to photon-recoil determinations of the fine-structure constant.