Engineering topics

Wambsganss, J.

Publications and source records attributed to Wambsganss, J..

8 records

NASA NTRS2016

Faint-Source-Star Planetary Microlensing: The Discovery of the Cold Gas-Giant Planet OGLE-2014-BLG-0676Lb

We report the discovery of a planet OGLE-2014-BLG-0676Lb via gravitational microlensing. Observations for the lensing event were made by the following groups: Microlensing Observations in Astrophysics; Optical Gravitational Lensing Experiment; Wise Observatory; RoboNETLas Cumbres Observatory Global Telescope; Microlensing Network for the Detection of Small Terrestrial Exoplanets; and -FUN. All analyses of the light-curve data favoura lens system comprising a planetary mass orbiting a host star. The most-favoured binary lens model has a mass ratio between the two lens masses of (4.78 +/- 0.13) 10(exp -3). Subject to some important assumptions, a Bayesian probability density analysis suggests the lens system comprises a 3.09(+1.02/-1.12) MJ planet orbiting a 0.62(+0.20/-0.22) solar mass host star at a deprojected orbital separation of 4.40(+2.16/-1.46) au. The distance to the lens system is 2.22(+0.96/-0.83) kpc. Planet OGLE-2014-BLG-0676Lb provides additional data to the growing number of cool planets discover redusing gravitational microlensing against which planetary formation theories may be tested. Most of the light in the baseline of this event is expected to come from the lens and thus high-resolution imaging observations could confirm our planetary model interpretation.

OGLE-2014-BLG-0676Lb↗

NASA NTRS2014

A Super-Jupiter Orbiting A Late-Type Star: A Refined Analysis of Microlensing Event OGLE-2012-BLG-0406

We present a detailed analysis of survey and follow-up observations of microlensing event OGLE-2012-BLG-0406 based on data obtained from 10 different observatories. Intensive coverage of the light curve, especially the perturbation part, allowed us to accurately measure the parallax effect and lens orbital motion. Combining our measurement of the lens parallax with the angular Einstein radius determined from finite-source effects, we estimate the physical parameters of the lens system. We find that the event was caused by a 2.73 plus or minus 0.43 M (sub J) planet orbiting a 0.44 plus or minus 0.07 solar mass early M-type star. The distance to the lens is 4.97 plus or minus 0.29 kpc and the projected separation between the host star and its planet at the time of the event is 3.45 plus or minus 0.26 AU. We find that the additional coverage provided by follow-up observations, especially during the planetary perturbation, leads to a more accurate determination of the physical parameters of the lens.

microlensing↗

NASA NTRS1994

Neutron tori around Kerr black holes

Models of stationary, axisymmetric, non-self-gravitating tori around stellar mass Kerr black holes are calculated. Such objects may form as a result of a merger between two neutron stars, a neutron star and a stellar mass black hole, or a 'failed supernova' collapse of a single rapidly rotating star. We explore a large range of parameters: the black hole mass and angular momentum, the torus mass, angular momentum and entropy. Physical conditions within the tori are similar to those in young and hot neutron stars, but their topology is different, and the range of masses and energies is much larger.

Witt, H. J.↗

NASA NTRS1992

Microlensed light curves for thin accretion disks around Schwarzschild and Kerr black holes

Surface brightness maps for thin accretion disks around Schwarzschild and Kerr black holes are presented. These disks are a few times smaller than those used by Rauch and Blandford (1991), and some of the present models are slightly less luminous than theirs. Example of microlensed light curves are calculated by convolving these accretion disk maps with the magnification patterns obtained from microlensing calculations. The light curves exhibit eventlike variations with amplitudes and time scales comparable to those observed in QSO 2237 + 0305. It is concluded that thin thermal accretion disk models are not in contradiction with the observed microlens-induced variations of QSO 2237 + 0305.

Jaroszynski, M.↗

NASA NTRS1992

Gravitational microlensing - Powerful combination of ray-shooting and parametric representation of caustics

We present a combination of two very different methods for numerically calculating the effects of gravitational microlensing: the backward-ray-tracing that results in two-dimensional magnification patterns, and the parametric representation of caustic lines; they are in a way complementary to each other. The combination of these methods is much more powerful than the sum of its parts. It allows to determine the total magnification and the number of microimages as a function of source position. The mean number of microimages is calculated analytically and compared to the numerical results. The peaks in the lightcurves, as obtained from one-dimensional tracks through the magnification pattern, can now be divided into two groups: those which correspond to a source crossing a caustic, and those which are due to sources passing outside cusps. We determine the frequencies of those two types of events as a function of the surface mass density, and the probability distributions of their magnitudes. We find that for low surface mass density as many as 40 percent of all events in a lightcurve are not due to caustic crossings, but rather due to passings outside cusps.

Wambsganss, J.↗

NASA NTRS1991

Expected color variations of the gravitationally microlensed QSO 2237 + 0305

Typical light curves and the corresponding color curves are shown for the present model of QSO 2237 + 0305 A, the image that has been reported to vary. Probabilities are presented for color changes of certain amplitudes as functions of the observed magnitude changes for different intervals between the two observational epochs, different source sizes, and different source size ratios. It may be possible to find the ratio of the continuum source sizes in the two color bands, once a color change correlated with a continuum change is found.

Wambsganss, J.↗

NASA NTRS1990

Interpretation of the microlensing event in QSO 2237 + 0305

A model of microlensing for image A of the gravitationally lensed QSO 2237 + 0305 for which Irwin et al. reported in 1989 an increase of the apparent luminosity by about 0.5 mag on a time scale of a few months is presented. The model, with the Salpeter mass function over the mass range of 0.1-1.0 solar mass and the transverse velocity of the lens (or observer) of 600 km/s, can reproduce the reported luminosity variation if the source of the optical continuum has a radius smaller than about 2 x 10 to the 15th cm. This size is compatible with the accretion disk interpretation of the big ultraviolet bump in quasar spectra. The model demonstrates a very large diversity of light curves while the source crosses individual microcaustics or clusters of microcaustics. It will take more than 100 yr before the full variety of light curves will be sampled by the observations.

Wambsganss, J.↗

NASA NTRS1990

A microlensing model for QSO 2237 + 0305

Models of microlensing are presented for the four images of QSO 2237 + 0305, with the surface mass density and shear for each image based on the macrolensing model developed by Schneider et al. (1988). The computations were done with a new code that makes use of the hierarchical tree method. The high efficiency of this approach makes it possible to include up to 60,000 lensing stars with different masses. Examples are given of amplification maps, light curves, correlation functions, and amplification probabilities. All these are very strongly affected by the shear due to macrolensing. The observed changes in the luminosity of the four images of QSO 2237 + 0305 are most likely induced by microlensing.

Wambsganss, J.↗