Occultation and Microlensing

Agol, Eric

doi:10.1086/342880

Cited by 59 publications

(57 citation statements)

References 14 publications

(30 reference statements)

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“…In this paper, I consider a system consisting of a finite-size lens and a point source. The microlens magnification of a finite-size lensing object has been studied by several authors (Bromley 1996;Bozza et al 2002;Agol 2002). Agol (2002) presents an exact analytic solution for the light curve of a uniform source.…”

Section: Introductionmentioning

confidence: 99%

Astrometric Microlensing by Finite‐Size Lenses

Takahashi

2003

ApJ

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Thanks to the revolutionary progress in the technique of astrometrical observation, a realistic possibility has emerged of elucidating the nature of baryonic dark matter (massive compact halo objects, small cold clouds) from the centroidal image trajectory of the microlens phenomena. To check if the size of lens objects can be determined by astrometrical observation, I have calculated astrometrical trajectories of microlensing phenomena caused by a spherical finite-size lens consisting of opaque material and found that these trajectories can be classified into three types according to occultation of the plus and minus images. All three types of trajectories have distinct features that reflect the effects of a finite-size lens. From these trajectories, the angular radius of the lens can be determined for two types of trajectories, and from the third type of trajectory, the upper and the lower limits of the angular radius can be determined if these features can be measured. I have investigated finite-lens effects in nearby high proper motion stars identified by Salim & Gould that could cause observable astrometric microlensing events during the Space Interferometry Mission's lifetime. None of them shows finite-lens effects with 10 las positional accuracy, one event shows finite-lens effects with 1 las positional accuracy, and six events show finite-lens effects with 0.1 las positional accuracy.

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Section: Introductionmentioning

confidence: 99%

Astrometric Microlensing by Finite‐Size Lenses

Takahashi

2003

ApJ

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“…One application has yet to be realized: in 1973, André Maeder predicted that binary star systems in which one star is a degenerate, compact object -a white dwarf, neutron star, or black hole -could cause repeated magnification of its companion star (instead of the standard eclipses) if the orbit happened to be viewed edge-on (5). The magnification of these self-lensing binary systems is small, typically a part in one thousand or less if the companion is Sun-like, and so it was not until high-precision stellar photometry was made possible with the Corot and Kepler spacecrafts that this could be detected (6,7). Stellar evolution models predict that about a dozen self-lensing binaries could be found by the Kepler spacecraft (8), but none have been discovered to date.…”

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confidence: 99%

KOI-3278: A Self-Lensing Binary Star System

Kruse

Agol

2014

Science

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Over 40% of Sun-like stars are bound in binary or multistar systems. Stellar remnants in edge-on binary systems can gravitationally magnify their companions, as predicted 40 years ago. By using data from the Kepler spacecraft, we report the detection of such a "self-lensing" system, in which a 5-hour pulse of 0.1% amplitude occurs every orbital period. The white dwarf stellar remnant and its Sun-like companion orbit one another every 88.18 days, a long period for a white dwarf-eclipsing binary. By modeling the pulse as gravitational magnification (microlensing) along with Kepler's laws and stellar models, we constrain the mass of the white dwarf to be ∼63% of the mass of our Sun. Further study of this system, and any others discovered like it, will help to constrain the physics of white dwarfs and binary star evolution.Einstein's general theory of relativity predicts that gravity can bend light and, consequently, that massive objects can distort and magnify more distant sources (1). This lensing effect provided one of the first confirmations of general relativity during a solar eclipse (2). Gravitational lensing has since become a widely used tool in astronomy to study galactic dark matter, exoplanets, clusters, quasars, cosmology, and more (3,4). One application has yet to be realized: in 1973, André Maeder predicted that binary star systems in which one star is a degenerate, compact object -a white dwarf, neutron star, or black hole -could cause repeated magnification of its companion star (instead of the standard eclipses) if the orbit happened to be viewed edge-on (5). The magnification of these self-lensing binary systems is small, typically a part in one thousand or less if the companion is Sun-like, and so it was not until high-precision stellar photometry was made possible with the Corot and Kepler spacecrafts that this could be detected (6,7). Stellar evolution models predict that about a dozen self-lensing binaries could be found by the Kepler spacecraft (8), but none have been discovered to date. A self-lensing binary system allows the measurement of the mass of the compact object, which is not true for most galaxy-scale microlensing events in which there is a degeneracy between the velocity, distance, and mass of the lensing object (9). Microlensing does affect several known white dwarfs The rows are separated by the orbital period, P = 88.18 days. White represents brighter flux and black dimmer, whereas gray represents missing data or outliers that have been removed. ppm, parts per million.in binaries in which the depth of eclipse is made slightly shallower (10-14) but does not result in brightening because occultation dominates over magnification at the short orbital periods of those systems. Here, we report that Kepler Object of Interest 3278 (KOI-3278) (15,16), a term intended for planetary candidates, is instead a self-lensing binary composed of a white dwarf star orbiting a Sun-like star. The candidate planetary transit signal is actually the repeated occultation of the white dwarf as it passes...

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“…Lensing effects in compact binaries were discussed in e.g. Maeder (1973), Gould (1995), Marsh (2001) and Agol (2002Agol ( , 2003. Sahu & Gilliland (2003) explored the expected influence of microlensing effects on light curves of compact binaries and planetary systems observed by Kepler.…”

Section: Light Curve Modelmentioning

confidence: 99%

Kepler Observations of the Beaming Binary KPD 1946+4340

Bloemen

2014

High-Precision Studies of Compact Variable Stars

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The Kepler Mission has acquired 33.5 d of continuous one-minute photometry of KPD 1946+4340, a short-period binary system that consists of a subdwarf B star (sdB) and a white dwarf. In the light curve, eclipses are clearly seen, with the deepest occurring when the compact white dwarf crosses the disc of the sdB (0.4 per cent) and the more shallow ones (0.1 per cent) when the sdB eclipses the white dwarf. As expected, the sdB is deformed by the gravitational field of the white dwarf, which produces an ellipsoidal modulation of the light curve. Spectacularly, a very strong Doppler beaming (also known as Doppler boosting) effect is also clearly evident at the 0.1 per cent level. This originates from the sdB's orbital velocity, which we measure to be 164.0 ± 1.9 km s −1 from supporting spectroscopy. We present light curve models that account for all these effects, as well as gravitational lensing, which decreases the apparent radius of the white dwarf by about 6 per cent when it eclipses the sdB. We derive system parameters and uncertainties from the light curve using Markov Chain Monte Carlo simulations. Adopting a theoretical white dwarf mass-radius relation, the mass of the subdwarf is found to be 0.47 ± 0.03 M ⊙ and the mass of the white dwarf 0.59 ± 0.02 M ⊙ . The effective temperature of the white dwarf is 15 900 ± 300 K. With a spectroscopic effective temperature of T eff = 34 730 ± 250 K and a surface gravity of log g = 5.43 ± 0.04, the subdwarf has most likely exhausted its core helium, and is in a shell He burning stage.The detection of Doppler beaming in Kepler light curves potentially allows one to measure radial velocities without the need of spectroscopic data. For the first time, a photometrically observed Doppler beaming amplitude is compared to a spectroscopically established value. The sdB's radial velocity amplitude derived from the photometry (168 ± 4 km s −1 ) is in perfect agreement with the spectroscopic value. After subtracting our best model for the orbital effects, we searched the residuals for stellar oscillations but did not find any significant pulsation frequencies.

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Occultation and Microlensing

Cited by 59 publications

References 14 publications

Astrometric Microlensing by Finite‐Size Lenses

Astrometric Microlensing by Finite‐Size Lenses

KOI-3278: A Self-Lensing Binary Star System

Kepler Observations of the Beaming Binary KPD 1946+4340

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