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The Relative Lens-Source Proper Motion in MACHO 98-SMC-1

The PLANET Collaboration·M. D. Albrow·J. -P. Beaulieu2·J. A. R. Caldwell·D. L. DePoy·M. Dominik·B. S. Gaudi·A. Gould·J. Greenhill·K. Hill·S. Kane·R. Martin·J. Menzies·R. M. Naber·K. R. Pollard·P. D. Sackett·K. C. Sahu·P. Vermaak·R. Watson·A. Williams·R. W. Pogge
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Abstract

We present photometric and spectroscopic data for the second microlensing event seen toward the Small Magellanic Cloud (SMC), MACHO-98-SMC-1. The lens is a binary. We resolve the caustic crossing and find that the source took 2 Delta t = 8.5 hours to transit the caustic. We measure the source temperature T_eff=8000 K both spectroscopically and from the color (V-I)_0~0.22. We find two acceptable binary-lens models. In the first, the source crosses the caustic at phi=43.2 deg and the unmagnified source magnitude is I_s=22.15. The angle implies that the lens crosses the source radius in time t_* = Delta t sin phi = 2.92 hours. The magnitude (together with the temperature) implies that the angular radius of the source is theta_* = 0.089 micro-arsec. Hence, the proper motion is mu=theta_*/t_*=1.26 km/s/kpc. For the second solution, the corresponding parameters are phi=30.6 deg, I_s=21.81, t_*=2.15 hours, theta_* = 0.104 micro-asrsec, mu=2.00 km/s/kpc. Both proper-motion estimates are slower than 99.5% of the proper motions expected for halo lenses. Both are consistent with an ordinary binary lens moving at ~ 75-120 km/s within the SMC itself. We conclude that the lens is most likely in the SMC proper.

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The PLANET Collaboration, M. D. Albrow, J. -P. Beaulieu2, J. A. R. Caldwell, D. L. DePoy, M. Dominik, B. S. Gaudi, A. Gould, J. Greenhill, K. Hill, S. Kane, R. Martin, J. Menzies, R. M. Naber, K. R. Pollard, P. D. Sackett, K. C. Sahu, P. Vermaak, R. Watson, A. Williams, R. W. Pogge. 1998-09-27. The Relative Lens-Source Proper Motion in MACHO 98-SMC-1. https://arxiv.org/abs/astro-ph/9807086

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