OGLE-2017-BLG-1038: A Possible Brown-dwarf Binary Revealed by Spitzer Microlensing Parallax

We report the analysis of microlensing event OGLE-2017-BLG-1038, observed by the Optical Gravitational Lensing Experiment, Korean Microlensing Telescope Network, and Spitzer telescopes. The event is caused by a giant source star in the Galactic Bulge passing over a large resonant binary lens caustic. The availability of space-based data allows the full set of physical parameters to be calculated. However, there exists an eightfold degeneracy in the parallax measurement. The four best solutions correspond to very-low-mass binaries near ($M_1 = 170^{+40}_{-50} M_J$ and $M_2 = 110^{+20}_{-30} M_J$), or well below ($M_1 = 22.5^{+0.7}_{-0.4} M_J$ and $M_2 = 13.3^{+0.4}_{-0.3} M_J$) the boundary between stars and brown dwarfs. A conventional analysis, with scaled uncertainties for Spitzer data, implies a very-low-mass brown dwarf binary lens at a distance of 2 kpc. Compensating for systematic Spitzer errors using a Gaussian process model suggests that a higher mass M-dwarf binary at 6 kpc is equally likely. A Bayesian comparison based on a galactic model favors the larger-mass solutions. We demonstrate how this degeneracy can be resolved within the next ten years through infrared adaptive-optics imaging with a 40 m class telescope.Comment: 20 pages, 11 figures, 4 table

OGLE-2017-BLG-1038 : a possible Brown-dwarf binary revealed by spitzer microlensing parallax

We report the analysis of microlensing event OGLE-2017-BLG-1038, observed by the Optical Gravitational Lensing Experiment, Korean Microlensing Telescope Network, and Spitzer telescopes. The event is caused by a giant source star in the Galactic Bulge passing over a large resonant binary-lens caustic. The availability of space-based data allows the full set of physical parameters to be calculated. However, there exists an eightfold degeneracy in the parallax measurement. The four best solutions correspond to very-low-mass binaries near ( M1=170−50+40MJ and M2=110−30+20MJ ), or well below ( M1=22.5−0.4+0.7MJ and M2=13.3−0.3+0.4MJ ) the boundary between stars and brown dwarfs. A conventional analysis, with scaled uncertainties for Spitzer data, implies a very-low-mass brown-dwarf binary lens at a distance of 2 kpc. Compensating for systematic Spitzer errors using a Gaussian process model suggests that a higher mass M-dwarf binary at 6 kpc is equally likely. A Bayesian comparison based on a galactic model favors the larger-mass solutions. We demonstrate how this degeneracy can be resolved within the next 10 years through infrared adaptive-optics imaging with a 40 m class telescope

Photometry and spectroscopy of transiting extrasolar planets.

The search for exoplanets is often most captivating when concerning the discovery of Earth-like planets that could possibly sustain life, according to our current understanding of the environmental requirements. However, current estimates suggest that habitable planets are a minority. In order to fully understand the trends, structure and formation of planetary systems, more information about exoplanets and their systems is needed. No exoplanets offer up as much information as transiting exoplanets. The data collected for this thesis was as part of a follow-up effort for the KELT-South (Kilo-degree Extremely Little Telescope in the southern hemisphere) project, which uses the wide-field surveying photometric telescope to search for transiting exoplanets, usually of the hot Jupiter variety. Follow-up lightcurves have been produced for many different candidate stars. Of those presented four suggest spurious survey data, and five suggest false-positives due to blended or grazing eclipsing binaries; these have been ruled out as exoplanet candidates. Eight of the lightcurves produced still appear to be likely transiting exoplanets, but require further photometry or high precision spectroscopy in order to be confirmed. Radial velocity (RV) follow-up was performed on two KELT-South transiting exoplanet candidates (HD 113204 and HD 9468). More data is needed for both targets though an upper projected mass limit of 0:24MX was placed on the companion of HD 9468. A meaningful estimate for the projected mass of the planetary companion of HD 113204 could not be made as there was too little data

KELT-22Ab: A Massive, Short-Period Hot Jupiter Transiting a Near-solar Twin

We present the discovery of KELT-22Ab, a hot Jupiter from the KELT-South survey. KELT-22Ab transits the moderately bright (V similar to 11.1) Sun-like G2V star TYC 7518-468-1. The planet has an orbital period of P = 1.3866529 +/- 0.0000027 days, a radius of R-P = 1.285(-0.071)(+0.12) R-J, and a relatively large mass of M-P = 3.47(-0.14)(+0.15), M-J. The star has R-star = 1.099(-0.046)(0.079) R-circle dot, M-star = 1.092(-0.041)(+0.045) M-circle dot, T-eff = 5767(-49)(+50) K, log g(star) = 4.393(-0.060)(+0.039) (cgs), and [m/H] = +0.259(-0.083)(+0.085); thus other than its slightly super-solar metallicity, it appears to be a near-solar twin. Surprisingly, KELT-22A exhibits kinematics and a Galactic orbit that are somewhat atypical for thin-disk stars. Nevertheless, the star is rotating rapidly for its estimated age, and shows evidence of chromospheric activity. Imaging reveals a slightly fainter companion to KELT-22A that is likely bound, with a projected separation of 6 '' (similar to 1400 au). In addition to the orbital motion caused by the transiting planet, we detect a possible linear trend in the radial velocity of KELT-22A, suggesting the presence of another relatively nearby body that is perhaps non-stellar. KELT-22Ab is highly irradiated (as a consequence of the small semimajor axis of a/R-star, and is mildly inflated. At such small separations, tidal forces become significant. The configuration of this system is optimal for measuring the rate of tidal dissipation within the host star. Our models predict that, due to tidal forces, the semimajor axis is decreasing rapidly, and KELT-22Ab is predicted to spiral into the star within the next Gyr