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A spectroscopic and photometric study of gravitational microlensing events

Kane, Stephen Robert 2000 , 'A spectroscopic and photometric study of gravitational microlensing events', PhD thesis, University of Tasmania.

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Gravitational microlensing has generated a great deal of scientific interest over
recent years. This has been largely due to the realization of its wide-reaching
applications, such as the search for dark matter, the detection of planets, and
the study of Galactic structure. A significant observational advance has been
that most microlensing events can be identified in real-time while the source is
still being lensed. More than 400 microlensing events have now been detected
towards the Galactic bulge and Magellanic Clouds by the microlensing survey
teams EROS, MACHO, OGLE, DUO, and MOA. The real-time detection of
these events allows detailed follow-up observations with much denser sampling,
both photometrically and spectroscopically.
The research undertaken in this project on photometric studies of gravitational
microlensing events has been performed as a member of the PLANET
(Probing Lensing Anomalies NETwork) collaboration. This is a worldwide collaboration
formed in the early part of 1995 to study microlensing anomalies -
departures from an achromatic point source, point lens light curve - through
rapidly-sampled, multi-band, photometry. PLANET has demonstrated that it
can achieve 1% photometry under ideal circumstances, making PLANET observations
sensitive to detection of Earth-mass planets which require characterization
of 1%-2% deviations from a standard microlensing light curve.
The photometric work in this project involved over 5 months using the 1.0 m
telescope at Canopus Observatory in Australia, and 3 separate observing runs
using the 0.9 m telescope at the Cerro Tololo Inter-American Observatory (CTIO)
in Chile. Methods were developed to reduce the vast amount of photometric data
using the image analysis software MIDAS and the photometry package DoPHOT.
Modelling routines were then written to analyse a selection of the resulting light
curves in order to detect any deviation from an achromatic point source - point
lens light curve.
The photometric results presented in this thesis are from observations of 34
microlensing events over three consecutive bulge seasons. These results are presented
along with a discussion of the observations and the data reduction procedures.
The colour-magnitude diagrams indicate that the microlensed sources
are main sequence and red clump giant stars. Most of the events appear to exhibit
standard Paczyriski point source - point lens curves whilst a few deviate significantly from the standard model. Various microlensing models that include
anomalous structure are fitted to a selection of the observed events resulting in
the discovery of a possible binary source event. These fitted events are used to
estimate the sensitivity to extra-solar planets and it is found that the sampling
rate for these events was insufficient by about a factor of 7.5 for detecting a
Jupiter-mass planet. This result assumes that deviations of 5% can be reliably
If microlensing is caused predominantly by bulge stars, as has been suggested
by Kiraga and Paczyliski [54], the lensed stars should have larger extinction than
other observed stars since they would preferentially be located at the far side of
the Galactic bulge. Hence, spectroscopy of Galactic microlensing events may be
used as a tool for studying the kinematics and extinction effects in the Galactic
The spectroscopic work in this project involved using Kurucz model spectra
to create theoretical extinction effects for various spectral classes towards the
Galactic centre. These extinction effects are then used to interpret spectroscopic
data taken with the 3.6 m ESO telescope. These data consist of a sample of
microlensed stars towards the Galactic bulge and are used to derive the extinction
offsets of the lensed source with respect to the average population and a
measurement of the fraction of bulge-bulge lensing is made. Hence, it is shown
statistically that the microlensed sources are generally located on the far side of
the Galactic bulge. Measurements of the radial velocities of these sources are
used to determine the kinematic properties of the far side of the Galactic bulge.

Item Type: Thesis - PhD
Authors/Creators:Kane, Stephen Robert
Keywords: Microlensing (Astrophysics), Microlensing (Astrophysics), Astronomical photometry
Copyright Holders: The Author
Copyright Information:

Copyright 2000 the Author - The University is continuing to endeavour to trace the copyright owner(s) and in the meantime this item has been reproduced here in good faith. We would be pleased to hear from the copyright owner(s).

Additional Information:

Thesis (Ph.D.)--University of Tasmania, 2000. Includes bibliographical references

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