Limits on Stellar and Planetary Companions in Microlensing Event OGLE-1998-BUL-14

Abstract

We present the PLANET photometric data set for \ob14, a high magnification ($A_{\rm max}\sim 16$) event alerted by the OGLE collaboration toward the Galactic bulge in 1998. The PLANET data set consists a total of 461 I-band and 139 $V-$band points, the majority of which was taken over a three month period. The median sampling interval during this period is about 1 hour, and the $1\sigma$ scatter over the peak of the event is 1.5%. The excellent data quality and high maximum magnification of this event make it a prime candidate to search for the short duration, low amplitude perturbations that are signatures of a planetary companion orbiting the primary lens. The observed light curve for \ob14 is consistent with a single lens (no companion) within photometric uncertainties. We calculate the detection efficiency of the light curve to lensing companions as a function of the mass ratio and angular separation of the two components. We find that companions of mass ratio $\ge 0.01$ are ruled out at the 95% confidence level for projected separations between $0.4-2.4 \re$, where $\re$ is the Einstein ring radius of the primary lens. Assuming that the primary is a G-dwarf with $\re\sim3 {\rm AU}$ our detection efficiency for this event is $\sim 60%$ for a companion with the mass and separation of Jupiter and $\sim5%$ for a companion with the mass and separation of Saturn. Our efficiencies for planets like those around Upsilon And and 14 Her are > 75%.