Simulating the Role of Stellar Rotation in the Spectroscopic Effects of Differential Limb Magnification

Finite-source effects of gravitationally microlensed stars have been well discussed in the literature, but the role that stellar rotation plays has been neglected. A differential magnification map applied to a differentially Doppler-shifted surface alters the profiles of absorption lines, compromising their ordinarily symmetric nature. Herein, we assess the degree to which this finite-source effect of differential limb magnification (DLM), in combination with stellar rotation, alters spectroscopically derived stellar properties. To achieve this, we simulated a grid of high-magnification microlensing events using synthetic spectra. Our analysis shows that rotation of the source generates differences in the measured equivalent widths of absorption lines supplementary to DLM alone, but only of the order of a few percent. Using the wings of H alpha from the same simulated data, we confirmed the result of Johnson et al. (2010) that DLM alters measurements of effective temperature by < 100 K for dwarf stars, while showing rotation to bear no additional effect.Comment: Accepted for publication in PASA, 7 pages, 5 figures, 1 tabl

Early Estimation of Microlensing Event Magnifications

Gravitational microlensing events with high peak magnifications provide a much enhanced sensitivity to the detection of planets around the lens star. However, estimates of peak magnification during the early stages of an event by means of chi^2 minimization frequently involve an overprediction, making observing campaigns with strategies that rely on these predictions inefficient. I show that a rudimentary Bayesian formulation, incorporating the known statistical characteristics of a detection system, produces much more accurate predictions of peak magnification than chi^2 minimisation. Implementation of this system will allow efficient follow-up observing programs that focus solely on events that contribute to planetary abundance statistics.Comment: Accepted by ApJ. 19 pages, incl 7 figures and 2 table

The Frequency of Binary Stars in the Core of 47 Tucanae

Differential time series photometry has been derived for 46422 main-sequence stars in the core of 47 Tucanae. The observations consisted of near-continuous 160-s exposures alternating between the F555W and F814W filters for 8.3 days in 1999 July with WFPC2 on the Hubble Space Telescope. Using Fourier and other search methods, eleven detached eclipsing binaries and fifteen W UMa stars have been discovered, plus an additional ten contact or near-contact non-eclipsing systems. After correction for non-uniform area coverage of the survey, the observed frequencies of detached eclipsing binaries and W UMa's within 90 arcseconds of the cluster center are 0.022% and 0.031% respectively. The observed detached eclipsing binary frequency, the assumptions of a flat binary distribution with log period and that the eclipsing binaries with periods longer than about 4 days have essentially their primordial periods, imply an overall binary frequency of 13 +/- 6 %. The observed W UMa frequency and the additional assumptions that W UMa's have been brought to contact according to tidal circularization and angular momentum loss theory and that the contact binary lifetime is 10^{9} years, imply an overall binary frequency of 14 +/- 4 %. An additional 71 variables with periods from 0.4 - 10 days have been found which are likely to be BY Draconis stars in binary systems. The radial distribution of these stars is the same as that of the eclipsing binaries and W UMa stars and is more centrally concentrated than average stars, but less so than the blue straggler stars. A distinct subset of six of these stars fall in an unexpected domain of the CMD, comprising what we propose to call red stragglers.Comment: Accepted for publication in the Astrophysical Journal, 65 pages including 26 figure

KMT-2018-BLG-1292: A Super-Jovian Microlens Planet in the Galactic Plane

We report the discovery of KMT-2018-BLG-1292Lb, a super-Jovian $M_{\rm planet} = 4.5\pm 1.3\,M_J$ planet orbiting an F or G dwarf $M_{\rm host} = 1.5\pm 0.4\,M_\odot$, which lies physically within {\cal O}(10\,\pc) of the Galactic plane. The source star is a heavily extincted $A_I\sim 5.2$ luminous giant that has the lowest Galactic latitude, $b=-0.28^\circ$, of any planetary microlensing event. The relatively blue blended light is almost certainly either the host or its binary companion, with the first explanation being substantially more likely. This blend dominates the light at $I$ band and completely dominates at $R$ and $V$ bands. Hence, the lens system can be probed by follow-up observations immediately, i.e., long before the lens system and the source separate due to their relative proper motion. The system is well characterized despite the low cadence $\Gamma=0.15$--$0.20\,{\rm hr^{-1}}$ of observations and short viewing windows near the end of the bulge season. This suggests that optical microlensing planet searches can be extended to the Galactic plane at relatively modest cost.Comment: 35 pages, 3 Tables, 8 figure

The Frequency and Mass-Ratio Distribution of Binaries in Clusters I: Description of the method and application to M67

We present a new method for probabilistic generative modelling of stellar colour-magnitude diagrams (CMDs) to infer the frequency of binary stars and their mass-ratio distribution. The method invokes a mixture model to account for overlapping populations of single stars, binaries and outliers in the CMD. We apply the model to Gaia observations of the old open cluster, M67, and find a frequency $f_B(q > 0.5) = 0.258 \pm 0.019$ for binary stars with mass ratio greater than 0.5. The form of the mass-ratio distribution function rises towards higher mass ratios for $q > 0.3$.Comment: 9 pages, 6 figures, accepted by MNRA

Physics at a Fermilab Proton Driver

This report documents the physics case for building a 2 MW, 8 GeV superconducting linac proton driver at Fermilab.Comment: 52 pages, 15 figure