The Relative Lens-Source Proper Motion in MACHO 98-SMC-1
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.
Cite
@article{arxiv.astro-ph/9807086,
title = {The Relative Lens-Source Proper Motion in MACHO 98-SMC-1},
author = {The PLANET Collaboration and M. D. Albrow and J. -P. Beaulieu2 and J. A. R. Caldwell and D. L. DePoy and M. Dominik and B. S. Gaudi and A. Gould and J. Greenhill and K. Hill and S. Kane and R. Martin and J. Menzies and R. M. Naber and K. R. Pollard and P. D. Sackett and K. C. Sahu and P. Vermaak and R. Watson and A. Williams and R. W. Pogge},
journal= {arXiv preprint arXiv:astro-ph/9807086},
year = {2016}
}
Comments
Light curve data at http://www.astro.rug.nl/~planet/planetpapers.html ApJ, in press