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

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

Feb 1999

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1999apj...512..672a&link_type=abstract

The Astrophysical Journal, Volume 512, Issue 2, pp. 672-677.

Astronomy and Astrophysics

Astronomy

59

Stars: Binaries: Visual, Galaxy: Halo, Cosmology: Gravitational Lensing, Galaxies: Magellanic Clouds

Scientific paper

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 2Deltat=8.5 hr 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=43.2d and the unmagnified source magnitude is I_s=22.15. The angle implies that the lens crosses the source radius in time t_*=Deltatsinphi=2.92 hr. The magnitude (together with the temperature) implies that the angular radius of the source is theta_*=0.089 muas. Hence, the proper motion is mu=theta_*/t_*=1.26 km s^-1 kpc^-1. For the second solution, the corresponding parameters are phi=30.6d, I_s=21.81, t_*=2.15 hr, theta_*=0.104 muas, and mu=theta_*/t_*=2.00 km s^-1 kpc^-1. 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^-1 within the SMC itself. We conclude that the lens is most likely in the SMC proper.

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