Search

We develop a new method to measure source proper motions in microlensing events, which can partially overcome problems due to blending. It takes advantage of the fact that the source position is known precisely from the microlensing event itself. We apply this method to the event MOA-2011-BLG-262, which has a short timescale tE = 3.8 day, a companion mass ratio q = 4.7 × 10–3, and a very high or high lens-source relative proper motion μrel = 20 mas yr–1 or 12 mas yr–1 (for two possible models). These three characteristics imply that the lens could be a brown dwarf or a massive planet with a roughly Earth-mass “moon.” The probability of such an interpretation would be greatly increased if it could be shown that the high lens-source relative proper motion was primarily due to the lens rather than the source. Based on the long-term monitoring data of the Galactic bulge from the Optical Gravitational Lensing Experiment, we measure the source proper motion that is small, in a (north, east) Galactic coordinate frame. These values are then important input into a Bayesian analysis of the event presented in a companion paper by Bennett et al. [ABSTRACT FROM AUTHOR]

Super-Jupiter-mass planets should form only beyond the snow line of host stars. However, the core accretion theory of planetary formation does not predict super-Jupiters forming around low-mass hosts. We present a discovery of a 3.9 ± 1.2 MJup mass planet orbiting the 0.59 ± 0.17 M☼ star using the gravitational microlensing method. During the event, the projected separation of the planet and the star is 3.9 ± 1.0 AU, i.e., the planet is significantly further from the host star than the snow line. This is the fourth such planet discovered using the microlensing technique and challenges the core accretion theory. [ABSTRACT FROM AUTHOR]

We combine VI photometry from OGLE-III with VISTA Variables in The Via Lactea survey and Two Micron All Sky Survey measurements of E(J -Ks ) to resolve the longstanding problem of the non-standard optical extinction toward the Galactic bulge. We show that the extinction is well fit by the relation AI= 0.7465×E(V - I) + 1.3700×E(J - Ks ), or, equivalently, AI = 1.217×E(V - I )(1 + 1.126×(E(J - Ks )/E(V - I ) - 0.3433)). The optical and near-IR reddening law toward the inner Galaxy approximately follows an RV ˜ 2.5 extinction curve with a dispersion sRV ˜ 0.2, consistent with extragalactic investigations of the hosts of Type Ia SNe. Differential reddening is shown to be significant on scales as small as our mean field size of 6. The intrinsic luminosity parameters of the Galactic bulge red clump (RC) are derived to be (MI,RC, sI,RC,0, (V - I )RC,0, s(V-I )RC , (J - Ks )RC,0) = (-0.12, 0.09, 1.06, 0.121, 0.66). Our measurements of the RC brightness, brightness dispersion, and number counts allow us to estimate several Galactic bulge structural parameters. We estimate a distance to the Galactic center of 8.20 kpc. We measure an upper bound on the tilt a ˜ 40? between the bulge’s major axis and the Sun–Galactic center line of sight, though our brightness peaks are consistent with predictions of an N-body model oriented at a ˜ 25?. The number of RC stars suggests a total stellar mass for the Galactic bulge of ~2.3 × 1010 M? if one assumes a canonical Salpeter initial mass function (IMF), or ~1.6 × 1010M? if one assumes a bottom-light Zoccali IMF. [ABSTRACT FROM AUTHOR]

We present the gravitational microlensing discovery of a 4 MUranus planet that orbits a 0.7 M☼ star at ≈18 AU. This is the first known analog of Uranus. Similar planets, i.e., cold ice giants, are inaccessible to either radial velocity or transit methods because of the long orbital periods, while low reflected light prevents direct imaging. We discuss how similar planets may contaminate the sample of the very short microlensing events that are interpreted as free-floating planets with an estimated rate of 1.8 per main-sequence star. Moreover, the host star has a nearby stellar (or brown dwarf) companion. The projected separation of the planet is only about three times smaller than that of the companion star, suggesting significant dynamical interactions. [ABSTRACT FROM AUTHOR]