The projected mass method of Bahcall and Tremaine has been used to derive the mass of the core of M31. From the observed radial velocities of 43 globular clusters, the mass interior to ̃ 30' is found to be M I = (9 ± 2) × 10 10 M sun . For six clusters with ̃ 100' M I = (2.4 ± 1.2) × 10 11 M sun . From the observed radial velocities of M32, M33, NGC 147, NGC 185, NGC 205, and LGS 3, the total mass of the Andromeda Subgroup of the Local Group is calculated to be M I = (7.5 ± 3.9) × 10 11 9) M sun .
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S. van den Bergh (1981) studied this question.