THE ORBIT OF THE STAR S2 AROUND SGR A* FROM VERY LARGE TELESCOPE AND KECK DATA

Abstract

Two recent papers (Ghez et al. 2008, Gillessen et al. 2009) have estimated\nthe mass of and the distance to the massive black hole in the center of the\nMilky Way using stellar orbits. The two astrometric data sets are independent\nand yielded consistent results, even though the measured positions do not match\nwhen simply overplotting the two sets. In this letter we show that the two sets\ncan be brought to excellent agreement with each other when allowing for a small\noffset in the definition of the reference frame of the two data sets. The\nrequired offsets in the coordinates and velocities of the origin of the\nreference frames are consistent with the uncertainties given in Ghez et al.\n(2008). The so combined data set allows for a moderate improvement of the\nstatistical errors of mass of and distance to Sgr A*, but the overall\naccuracies of these numbers are dominated by systematic errors and the\nlong-term calibration of the reference frame. We obtain R0 = 8.28 +- 0.15(stat)\n+- 0.29(sys) kpc and M(MBH) = 4.30 +- 0.20(stat) +- 0.30(sys) x 10^6 Msun as\nbest estimates from a multi-star fit.\n