On the reported death of the MACHO era

Quinn, D. P. and Wilkinson, M. I. and Irwin, Michael J. and Marshall, J. and Koch, Andreas and Belokurov, V. (2009) On the reported death of the MACHO era. Monthly Notices of the Royal Astronomical Society: Letters, 396 (1). L11-L15. ISSN 1745-3925

Abstract

We present radial velocity measurements of four wide halo binary candidates from the sample in Chaname & Gould (CG04) which, to date, is the only sample containing a large number of such candidates. The four candidates that we have observed have projected separations >0.1 pc, and include the two widest binaries from the sample, with separations of 0.45 and 1.1 pc. We confirm that three of the four CG04 candidates are genuine, including the one with the largest separation. The fourth candidate, however, is spurious at the 5σ level. In the light of these measurements, we re-examine the implications for MAssive Compact Halo Object (MACHO) models of the Galactic halo. Our analysis casts doubt on what MACHO constraints can be drawn from the existing sample of wide halo binaries.