Publications: Dr Andrew Williams

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REFEREED PUBLICATIONS

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Title:		Interpretation of Strong Short-Term Central Perturbations in the Light Curves of Moderate-Magnification Microlensing Events
Authors:		Han, C.; 77 others; Martin, R.; 9 others; Williams, A. and 1 other
Journal:		The Astrophysical Journal, 705, pp. 1116-1121 (2009).
Publication Date:		11/2009
Keywords:		gravitational lensing, planetary systems
DOI:		10.1088/0004-637X/705/2/1116
Abstract
To improve the planet detection efficiency, current planetary microlensing experiments are focused on high-magnification events searching for planetary signals near the peak of lensing light curves. However, it is known that central perturbations can also be produced by binary companions and thus it is important to distinguish planetary signals from those induced by binary companions. In this paper, we analyze the light curves of microlensing events OGLE-2007-BLG-137/MOA-2007-BLG-091, OGLE-2007-BLG-355/MOA-2007-BLG-278, and MOA-2007-BLG-199/OGLE-2007-BLG-419, for all of which exhibit short-term perturbations near the peaks of the light curves. From detailed modeling of the light curves, we find that the perturbations of the events are caused by binary companions rather than planets. From a close examination of the light curves combined with the underlying physical geometry of the lens system obtained from modeling, we find that the short timescale caustic-crossing feature occurring at a low or a moderate base magnification with an additional secondary perturbation is a typical feature of binary-lens events and thus can be used for the discrimination between the binary and planetary interpretations.
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Title:		Extreme Magnification Microlensing Event OGLE-2008-BLG-279: Strong Limits on Planetary Companions to the Lens Star
Authors:		Yee, J. C.; 79 others; Martin, R.; 2 others; Williams, A. and 1 other
Journal:		The Astrophysical Journal, 703, pp. 2082-2090 (2009).
Publication Date:		10/2009
Keywords:		gravitational lensing, planetary systems, planetary systems: formation
DOI:		10.1088/0004-637X/703/2/2082
Abstract
We analyze the extreme high-magnification microlensing event OGLE-2008-BLG-279, which peaked at a maximum magnification of A ~ 1600 on 2008 May 30. The peak of this event exhibits both finite-source effects and terrestrial parallax, from which we determine the mass of the lens, M_l = 0.64 ± 0.10 M_sun, and its distance, D_l = 4.0 ± 0.6 kpc. We rule out Jupiter-mass planetary companions to the lens star for projected separations in the range 0.5-20 AU. More generally, we find that this event was sensitive to planets with masses as small as 0.2 M_Earth ~ 2 M_Mars with projected separations near the Einstein ring (~3 AU).
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Title:		Difference imaging photometry of blended gravitational microlensing events with a numerical kernel
Authors:		Albrow, M. D.; 7 others; Williams, A. and 17 others
Journal:		Monthly Notices of the Royal Astronomical Society, 397, pp. 2099-2105.
Publication Date:		08/2009
Keywords:		methods: statistical , techniques: image processing , techniques: photometric
DOI:		10.1111/j.1365-2966.2009.15098.x
Abstract
The numerical kernel approach to difference imaging has been implemented and applied to gravitational microlensing events observed by the PLANET collaboration. The effect of an error in the source-star coordinates is explored and a new algorithm is presented for determining the precise coordinates of the microlens in blended events, essential for accurate photometry of difference images. It is shown how the photometric reference flux need not be measured directly from the reference image but can be obtained from measurements of the difference images combined with the knowledge of the statistical flux uncertainties. The improved performance of the new algorithm, relative to ISIS2, is demonstrated.
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Title:		The Murchison Widefield Array: Design Overview
Authors:		Lonsdale, C. J.; 44 others; Williams, A. and 1 other
Journal:		Proceedings of the IEEE, 97, pp.1497-1506.
Publication Date:		08/2009
DOI:		10.1109/JPROC.2009.2017564
Abstract
The Murchison Widefield Array (MWA) is a dipole-based aperture array synthesis telescope designed to operate in the 80-300 MHz frequency range. It is capable of a wide range of science investigations, but is initially focused on three key science projects. These are detection and characterization of 3-dimensional brightness temperature fluctuations in the 21cm line of neutral hydrogen during the Epoch of Reionization (EoR) at redshifts from 6 to 10, solar imaging and remote sensing of the inner heliosphere via propagation effects on signals from distant background sources,and high-sensitivity exploration of the variable radio sky. The array design features 8192 dual-polarization broad-band active dipoles, arranged into 512 tiles comprising 16 dipoles each. The tiles are quasi-randomly distributed over an aperture 1.5km in diameter, with a small number of outliers extending to 3km. All tile-tile baselines are correlated in custom FPGA-based hardware, yielding a Nyquist-sampled instantaneous monochromatic uv coverage and unprecedented point spread function (PSF) quality. The correlated data are calibrated in real time using novel position-dependent self-calibration algorithms. The array is located in the Murchison region of outback Western Australia. This region is characterized by extremely low population density and a superbly radio-quiet environment,allowing full exploitation of the instrumental capabilities.
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Title:		The Extreme Microlensing Event OGLE-2007-BLG-224: Terrestrial Parallax Observation of a Thick-Disk Brown Dwarf
Authors:		Gould, A.; 71 others; Martin, R. & Williams, A.
Journal:		The Astrophysical Journal Letters, 698, pp. L147-L151 (2009).
Publication Date:		06/2009
Keywords:		astrometry, gravitational lensing, stars: low-mass, brown dwarfs
DOI:		10.1088/0004-637X/698/2/L147
Abstract
Parallax is the most fundamental technique for measuring distances to astronomical objects. Although terrestrial parallax was pioneered over 2000 years ago by Hipparchus (ca. 140 B.C.E.) to measure the distance to the Moon, the baseline of the Earth is so small that terrestrial parallax can generally only be applied to objects in the Solar System. However, there exists a class of extreme gravitational microlensing events in which the effects of terrestrial parallax can be readily detected and so permit the measurement of the distance, mass, and transverse velocity of the lens. Here we report observations of the first such extreme microlensing event OGLE-2007-BLG-224, from which we infer that the lens is a brown dwarf of mass M = 0.056 ± 0.004 M sun, with a distance of 525 ± 40 pc and a transverse velocity of 113 ± 21 km s-1. The velocity places the lens in the thick disk, making this the lowest-mass thick-disk brown dwarf detected so far. Follow-up observations may allow one to observe the light from the brown dwarf itself, thus serving as an important constraint for evolutionary models of these objects and potentially opening a new window on substellar objects. The low a priori probability of detecting a thick-disk brown dwarf in this event, when combined with additional evidence from other observations, suggests that old substellar objects may be more common than previously assumed.
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Title:		A systematic fitting scheme for caustic-crossing microlensing events
Authors:		Kains, N.; 27 others; Martin, R.; 8 others; Williams, A. and 7 others
Journal:		Monthly Notices of the Royal Astronomical Society, 395, pp. 787-796.
Publication Date:		05/2009
Keywords:		gravitational lensing , methods: miscellaneous , binaries: general , planetary systems , Galaxy: bulge
DOI:		10.1111/j.1365-2966.2009.14615.x
Abstract
We outline a method for fitting binary-lens caustic-crossing microlensing events based on the alternative model parametrization proposed and detailed by Cassan. As an illustration of our methodology, we present an analysis of OGLE-2007-BLG-472, a double-peaked Galactic microlensing event with a source crossing the whole caustic structure in less than three days. In order to identify all possible models we conduct an extensive search of the parameter space, followed by a refinement of the parameters with a Markov Chain Monte Carlo algorithm. We find a number of low-?^2 regions in the parameter space, which lead to several distinct competitive best models. We examine the parameters for each of them, and estimate their physical properties. We find that our fitting strategy locates several minima that are difficult to find with other modelling strategies and is therefore a more appropriate method to fit this type of event.
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Title:		OGLE-2005-BLG-071Lb, the Most Massive M Dwarf Planetary Companion?
Authors:		Dong, Subo; 68 others; Martin, R.; 6 others; Williams, A. and 7 others
Journal:		The Astrophysical Journal, 695, pp. 970-987.
Publication Date:		04/2009
Keywords:		Galaxy: bulge, gravitational lensing, planetary systems
DOI:		10.1088/0004-637X/695/2/970
Abstract
We combine all available information to constrain the nature of OGLE-2005-BLG-071Lb, the second planet discovered by microlensing and the first in a high-magnification event. These include photometric and astrometric measurements from the Hubble Space Telescope, as well as constraints from higher order effects extracted from the ground-based light curve, such as microlens parallax, planetary orbital motion, and finite-source effects. Our primary analysis leads to the conclusion that the host of Jovian planet OGLE-2005-BLG-071Lb is an M dwarf in the foreground disk with mass M = 0.46 ± 0.04 M_sun , distance D_l = 3.2 ± 0.4 kpc, and thick-disk kinematics v_LSR ~ 103 km s^-1 . From the best-fit model, the planet has mass M_p = 3.8 ± 0.4 M_Jupiter , lies at a projected separation r_? = 3.6 ± 0.2AU from its host, and so has an equilibrium temperature of T ~ 55 K, that is, similar to Neptune. A degenerate model gives similar planetary mass M_p = 3.4 ± 0.4 M_Jupiter with a smaller projected separation, r_? = 2.1 ± 0.1AU, and higher equilibrium temperature, T ~ 71 K. These results from the primary analysis suggest that OGLE-2005-BLG-071Lb is likely to be the most massive planet yet discovered that is hosted by an M dwarf. However, the formation of such high-mass planetary companions in the outer regions of M dwarf planetary systems is predicted to be unlikely within the core-accretion scenario. There are a number of caveats to this primary analysis, which assumes (based on real but limited evidence) that the unlensed light coincident with the source is actually due to the lens, that is, the planetary host. However, these caveats could mostly be resolved by a single astrometric measurement a few years after the event.
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Title:		Limits on additional planetary companions to OGLE 2005-BLG-390L
Authors:		Kubas, D.; 27 others; Martin, R.; 8 others; Williams, A. and 2 others
Journal:		Astronomy and Astrophysics, 483, pp.317-324
Publication Date:		05/2008
Keywords:		stars: planetary systems, gravitational lensing
DOI:		10.1051/0004-6361:20077449
Abstract
Aims. We investigate constraints on additional planets orbiting the distant M-dwarf star OGLE 2005-BLG-390L, around which photometric microlensing data has revealed the existence of the sub-Neptune-mass planet OGLE 2005-BLG-390Lb. We specifically aim to study potential Jovian companions and compare our findings with predictions from core-accretion and disc-instability models of planet formation. We also obtain an estimate of the detection probability for sub-Neptune mass planets similar to OGLE 2005-BLG-390Lb using a simplified simulation of a microlensing experiment. Methods: We compute the efficiency of our photometric data for detecting additional planets around OGLE 2005-BLG-390L, as a function of the microlensing model parameters and convert it into a function of the orbital axis and planet mass by means of an adopted model of the Milky Way. Results: We find that more than 50% of potential planets with a mass in excess of 1 M_J between 1.1 and 2.3 AU around OGLE 2005-BLG-390L would have revealed their existence, whereas for gas giants above 3 M_J in orbits between 1.5 and 2.2 AU, the detection efficiency reaches 70%; however, no such companion was observed. Our photometric microlensing data therefore do not contradict the existence of gas giant planets at any separation orbiting OGLE 2005-BLG-390L. Furthermore we find a detection probability for an OGLE 2005-BLG-390Lb-like planet of around 2{-}5%. In agreement with current planet formation theories, this quantitatively supports the prediction that sub-Neptune mass planets are common around low-mass stars.
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Title:	OGLE 2004-BLG-254: a K3 III Galactic bulge giant spatially resolved by a single microlens
Authors:	Cassan, A.; Beaulieu, J.-P.; Fouqué, P.; Brillant, S.; Dominik, M.; Greenhill, J.; Heyrovský, D.; Horne, K.; Jørgensen, U. G.; Kubas, D.; Stempels, H. C.; Vinter, C.; Albrow, M. D.; Bennett, D.; Caldwell, J. A. R.; Calitz, J. J.; Cook, K.; Coutures, C.; Dominis, D.; Donatowicz, J.; Hill, K.; Hoffman, M.; Kane, S.; Marquette, J.-B.; Martin, R.; Meintjes, P.; Menzies, J.; Miller, V. R.; Pollard, K. R.; Sahu, K. C.; Wambsganss, J.; Williams, A.; Udalski, A.; Szymanski, M. K.; Kubiak, M.; Pietrzynski, G.; Soszynski, I.; Zebrun, K.; Szewczyk, O.; Wyrzykowski, L.
Publication:	Astronomy and Astrophysics, Volume 460, Issue 1, December 2006, pp.277-288
Publication Date:	12/2006
Keywords:	gravitational lensing, techniques: high angular resolution, stars: atmospheres, stars:, individual: OGLE 2004-BLG-254
DOI:	10.1051/0004-6361:20054414
Abstract
Aims. We present an analysis of OGLE 2004-BLG-254, a high-magnification (A_o ~ 60) and relatively short duration (t_E ~ 13.2 days) microlensing event in which the source star, a Bulge K-giant, has been spatially resolved by a point-like lens. We seek to determine the lens and source distance, and provide a measurement of the linear limb-darkening coefficients of the source star in the I and R bands. We discuss the derived values of the latter and compare them to the classical theoretical laws, and furthermore examine the cases of already published microlensed GK-giants limb-darkening measurements. Methods: We have obtained dense photometric coverage of the event light curve with OGLE and PLANET telescopes, as well as a high signal-to-noise ratio spectrum taken while the source was still magnified by A ~ 20, using the UVES/VLT spectrograph. We have performed a modelling of the light curve, including finite source and parallax effects, and have combined spectroscopic and photometric analysis to infer the source distance. A Galactic model for the mass and velocity distribution of the stars has been used to estimate the lens distance. Results: From the spectrum analysis and calibrated color-magnitude of the event target, we found that the source was a K3 III Bulge giant, situated at the far end of the Bulge. From modelling the light curve, we have derived an angular size of the Einstein ring theta_E ~ 114 muas, and a relative lens-source proper motion mu = theta_E/t_E ~ 3.1 mas/yr. We could also measure the angular size of the source, theta_* ~ 4.5 muas, whereas given the short duration of the event, no significant constraint could be obtained from parallax effects. A Galactic model based on the modelling of the light curve then provides us with an estimate of the lens distance, mass and velocity as D_L ~ 9.6 kpc, M ~ 0.11 M_sun and v ~ 145~km s^-1 (at the lens distance) respectively. Our dense coverage of this event allows us to measure limb darkening of the source star in the I and R bands. We also compare previous measurements of linear limb-darkening coefficients involving GK-giant stars with predictions from ATLAS atmosphere models. We discuss the case of K-giants and find a disagreement between limb-darkening measurements and model predictions, which may be caused by the inadequacy of the linear limb-darkening law.
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Title:		Discovery of a cool planet of 5.5 Earth masses through gravitational microlensing
Authors:		Beaulieu, J.-P.; Bennett, D. P.; Fouqué, P.; Williams, A.; Dominik, M.; Jorgensen, U. G.; Kubas, D.; Cassan, A.; Coutures, C.; Greenhill, J.; Hill, K.; Menzies, J.; Sackett, P. D.; Albrow, M.; Brillant, S.; Caldwell, J. A. R.; Calitz, J. J.; Cook, K. H.; Corrales, E.; Desort, M.; Dieters, S.; Dominis, D.; Donatowicz, J.; Hoffman, M.; Kane, S.; Marquette, J.-B.; Martin, R.; Meintjes, P.; Pollard, K.; Sahu, K.; Vinter, C.; Wambsganss, J.; Woller, K.; Horne, K.; Steele, I.; Bramich, D. M.; Burgdorf, M.; Snodgrass, C.; Bode, M.; Udalski, A.; Szymanski, M. K.; Kubiak, M.; Wieckowski, T.; Pietrzynski, G.; Soszynski, I.; Szewczyk, O.; Wyrzykowski, L.; Paczynski, B.; Abe, F.; Bond, I. A.; Britton, T. R.; Gilmore, A. C.; Hearnshaw, J. B.; Itow, Y.; Kamiya, K.; Kilmartin, P. M.; Korpela, A. V.; Masuda, K.; Matsubara, Y.; Motomura, M.; Muraki, Y.; Nakamura, S.; Okada, C.; Ohnishi, K.; Rattenbury, N. J.; Sako, T.; Sato, S.; Sasaki, M.; Sekiguchi, T.; Sullivan, D. J.; Tristram, P. J.; Yock, P. C. M.; Yoshioka, T.
Journal:		Nature, Volume 439, Issue 7075, pp. 437-440 (2006).
Publication Date:		01/2006
DOI:		10.1038/nature04441
Abstract
In the favoured core-accretion model of formation of planetary systems, solid planetesimals accumulate to build up planetary cores, which then accrete nebular gas if they are sufficiently massive. Around M-dwarf stars (the most common stars in our Galaxy), this model favours the formation of Earth-mass (M_⊕) to Neptune-mass planets with orbital radii of 1 to 10 astronomical units (AU), which is consistent with the small number of gas giant planets known to orbit M-dwarf host stars. More than 170 extrasolar planets have been discovered with a wide range of masses and orbital periods, but planets of Neptune's mass or less have not hitherto been detected at separations of more than 0.15AU from normal stars. Here we report the discovery of a 5.5^+5.5_-2.7 M_⊕ planetary companion at a separation of 2.6^+1.5_-0.6AU from a 0.22^+0.21_-0.11 M_⊕ M-dwarf star, where M_⊕ refers to a solar mass. (We propose to name it OGLE-2005-BLG-390Lb, indicating a planetary mass companion to the lens star of the microlensing event.) The mass is lower than that of GJ876d (ref. 5), although the error bars overlap. Our detection suggests that such cool, sub-Neptune-mass planets may be more common than gas giant planets, as predicted by the core accretion theory.
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Title:		Full characterization of binary-lens event OGLE-2002-BLG-069 from PLANET observations
Authors:		Kubas, D.; Beaulieu, J., P.; Coutures, C.; Dominik, M.; Albrow, M. D.; Brillant, S.; Caldwell, J. A. R.; Dominis, D.; Donatowicz, J.; Fendt, C.; Fouqué , P.; Jörgensen, U. G.; Greenhill, J.; Hill, K.; Heinmüller, J.; Horne, K.; Kane, S.; Marquette, J. B.; Martin, R.; Menzies, J.; Pollard, K. R.; Sahu, K. C.; Vinter, C.; Wambsganss, J.; Watson, R.; Williams, A.; Thurl, C.
Journal:		Astronomy and Astrophysics, Volume 435, Issue 3, June I 2005, pp.941-948
Publication Date:		06/2005
Keywords:		gravitational lensing, stars: atmospheres, stars: binaries: general
DOI:		10.1051/0004-6361:20042624
Abstract
We analyze the photometric data obtained by PLANET and OGLE on the caustic-crossing binary-lens microlensing event OGLE-2002-BLG-069. Thanks to the excellent photometric and spectroscopic coverage of the event, we are able to constrain the lens model up to the known ambiguity between close and wide binary lenses. The detection of annual parallax in combination with measurements of extended-source effects allows us to determine the mass, distance and velocity of the lens components for the competing models. While the model involving a close binary lens leads to a Bulge-Disc lens scenario with a lens mass of M=(0.51 ± 0.15) M_sun; and distance of D_{L}=(2.9± 0.4) {{kpc}}, the wide binary lens solution requires a rather implausible binary black-hole lens (M › 126 M_sun). Furthermore we compare current state-of-the-art numerical and empirical models for the surface brightness profile of the source, a G5III Bulge giant. We find that a linear limb-darkening model for the atmosphere of the source star is consistent with the data whereas a PHOENIX atmosphere model assuming LTE and with no free parameter does not match our observations.
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Title:		PLANET III: searching for Earth-mass planets via microlensing from Dome C?
Authors:		Beaulieu, J. P.; Cassan, A.; Kubas, D.; Albrow, M.; Bennett, D.; Brillant, S.; Caldwell, J. A. R.; Calitz, H.; Cook, K.; Coutures, C.; Dominik, M.; Dominis, D.; Donatowicz, J.; Fouqué , P.; Greenhill, J.; Hill, K.; Hoffman, M.; Horne, K.; Jörgensen, U. G.; Kane, S.; Martin, R.; Mientjes, P.; Menzies, J. M.; Pollard, K.; Sahu, K.; Vinter, C.; Wambsganss, J.; Williams, A.
Journal:		EAS Publications Series, Volume 14, 2005, pp.297-302
Publication Date:		00/2005
DOI:		10.1051/eas:2005047
Abstract
PLANET, the Probing Lensing Anomaly NETwork, is an international team conducting observations of on-going gravitational microlensing events from five sites in the southern hemisphere. Our primary goal is to detect or to put constraints on sub-stellar companions of M dwarfs from the galactic disk. We report the current status and discuss the future prospects. A 2m robotic telescope at Dome C which would benefit from continuous coverage and dream like seeing (median of 0.27 arcsec) is currently the best option for a ground based aggressive search for Earth-mass planets in the habitable zone.
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Title:		OGLE-2003-BLG-238: Microlensing Mass Estimate of an Isolated Star
Authors:		Jiang, Guangfei; DePoy, D. L.; Gal-Yam, A.; Gaudi, B. S.; Gould, A.; Han, C.; Lipkin, Y.; Maoz, D.; Ofek, E. O.; Park, B.-G.; Pogge, R. W.; Udalski, A.; Kubiak, M.; Szymanski, M. K.; Szewczyk, O.; Zebrun, K.; Wyrzykowski, L.; Soszynski, I.; Pietrzynski, G.; Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; Cassan, A.; Coutures, C.; Dominik, M.; Donatowicz, J.; Fouqué , P.; Greenhill, J.; Hill, K.; Horne, K.; Jörgensen, S. F.; Jörgensen, U. G.; Kane, S.; Kubas, D.; Martin, R.; Menzies, J.; Pollard, K. R.; Sahu, K. C.; Wambsganss, J.; Watson, R.; Williams, A.
Journal:		The Astrophysical Journal, Volume 617, Issue 2, pp. 1307-1315.
Publication Date:		12/2004
Keywords:		Cosmology: Gravitational Lensing, Stars: Fundamental Parameters
DOI:		10.1086/425678
Abstract
Microlensing is the only known direct method to measure the masses of stars that lack visible companions. In terms of microlensing observables, the mass is given by M=(c²/4G)r_Etheta_E and so requires the measurement of both the angular Einstein radius theta_E and the projected Einstein radius r_E. Simultaneous measurement of these two parameters is extremely rare. Here we analyze OGLE-2003-BLG-238, a spectacularly bright (I_min=10.3), high-magnification (A_max=170) microlensing event. Pronounced finite-source effects permit a measurement of theta_E=650muas. Although the timescale of the event is only t_E=38days, one can still obtain weak constraints on the microlens parallax: 4.4AU< r_E< 18AU at the 1 sigma level. Together these two parameter measurements yield a range for the lens mass of 0.36M_solar< M< 1.48M_solar. As was the case for MACHO-LMC-5, the only other single star (apart from the Sun) whose mass has been determined from its gravitational effects, this estimate is rather crude. It does, however, demonstrate the viability of the technique. We also discuss future prospects for single-lens mass measurements.
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Title:		Potential Direct Single-Star Mass Measurement
Authors:		Ghosh, H.; DePoy, D. L.; Gal-Yam, A.; Gaudi, B. S.; Gould, A.; Han, C.; Lipkin, Y.; Maoz, D.; Ofek, E. O.; Park, B.-G.; Pogge, R. W.; Salim, S.; Abe, F.; Bennett, D. P.; Bond, I. A.; Eguchi, S.; Furuta, Y.; Hearnshaw, J. B.; Kamiya, K.; Kilmartin, P. M.; Kurata, Y.; Masuda, K.; Matsubara, Y.; Muraki, Y.; Noda, S.; Okajima, K.; Rattenbury, N. J.; Sako, T.; Sekiguchi, T.; Sullivan, D. J.; Sumi, T.; Tristram, P. J.; Yanagisawa, T.; Yock, P. C. M.; Udalski, A.; Soszynski, I.; Wyrzykowski, L.; Kubiak, M.; Szymanski, M. K.; Pietrzynski, G.; Szewczyk, O.; Zebrun, K.; Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; Cassan, A.; Coutures, C.; Dominik, M.; Donatowicz, J.; Fouqué , P.; Greenhill, J.; Hill, K.; Horne, K.; Jörgensen, U. G.; Kane, S.; Kubas, D.; Martin, R.; Menzies, J.; Pollard, K. R.; Sahu, K. C.; Wambsganss, J.; Watson, R.; Williams, A.
Journal:		The Astrophysical Journal, Volume 615, Issue 1, pp. 450-459.
Publication Date:		11/2004
Keywords:		Astrometry, Cosmology: Gravitational Lensing, Stars: Fundamental Parameters
DOI:		10.1086/423665
Abstract
We analyze the light curve of the microlensing event OGLE-2003-BLG-175/MOA-2003-BLG-45 and show that it has two properties that, when combined with future high-resolution astrometry, could lead to a direct, accurate measurement of the lens mass. First, the light curve shows clear signs of distortion due to the Earth's accelerated motion, which yields a measurement of the projected Einstein radius r_E. Second, from precise astrometric measurements, we show that the blended light in the event is coincident with the microlensed source to within about 15 mas. This argues strongly that this blended light is the lens and hence opens the possibility of directly measuring the lens-source relative proper motion mu_rel and so the mass M=(c²/4G)mu_relt_Er_E, where t_E is the measured Einstein timescale. While the light-curve-based measurement of r_E is, by itself, severely degenerate, we show that this degeneracy can be completely resolved by measuring the direction of proper motion mu_rel.
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Title:		Probing the atmosphere of the bulge G5III star OGLE-2002-BUL-069 by analysis of microlensed Halpha line
Authors:		Cassan, A.; Beaulieu, J. P.; Brillant, S.; Coutures, C.; Dominik, M.; Donatowicz, J.; Jörgensen, U. G.; Kubas, D.; Albrow, M. D.; Caldwell, J. A. R.; Fouqué , P.; Greenhill, J.; Hill, K.; Horne, K.; Kane, S.; Martin, R.; Menzies, J.; Pollard, K. R.; Sahu, K. C.; Vinter, C.; Wambsganss, J.; Watson, R.; Williams, A.; Fendt, C.; Hauschildt, P.; Heinmueller, J.; Marquette, J. B.; Thurl, C.
Journal:		Astronomy and Astrophysics, v.419, p.L1-L4 (2004)
Publication Date:		05/2004
Keywords:		techniques: gravitational microlensing, techniques: high resolution spectra, techniques: high angular resolution, stars: atmosphere models, stars: individual: OGLE 2002-BLG-069
DOI:		10.1051/0004-6361:20040112
Abstract
We discuss high-resolution, time-resolved spectra of the caustic exit of the binary microlensing event OGLE 2002-BLG-069 obtained with UVES on the VLT. The source star is a G5III giant in the Galactic Bulge. During such events, the source star is highly magnified, and a strong differential magnification around the caustic resolves its surface. Using an appropriate model stellar atmosphere generated by the PHOENIX v2.6 code we obtain a model light curve for the caustic exit and compare it with a dense set of photometric observations obtained by the PLANET microlensing follow up network. We further compare predicted variations in the Halpha equivalent width with those measured from our spectra. While the model and observations agree in the gross features, there are discrepancies suggesting shortcomings in the model, particularly for the Halpha line core, where we have detected amplified emission from the stellar chromosphere after the source star's trailing limb exited the caustic. This achievement became possible by the provision of the very efficient OGLE-III Early Warning System, a network of small telescopes capable of nearly-continuous round-the-clock photometric monitoring, on-line data reduction, daily near-real-time modelling in order to predict caustic crossing parameters, and a fast and efficient response of a 8 m class telescope to a 'Target-of-Opportunity' observation request.
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Title:		High-Precision Limb-Darkening Measurement of a K3 Giant Using Microlensing
Authors:		Fields, Dale L.; Albrow, M. D.; An, J.; Beaulieu, J.-P.; Caldwell, J. A. R.; DePoy, D. L.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Jörgensen, U. G.; Kane, S.; Martin, R.; Menzies, J.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.; Glicenstein, J.-F.; Hauschildt, P. H.
Journal:		The Astrophysical Journal, Volume 596, Issue 2, pp. 1305-1319.
Publication Date:		10/2003
Keywords:		Cosmology: Gravitational Lensing, Stars: Atmospheres
Keywords:		gravitational lensing, stars: atmospheres, stars:
DOI:		10.1086/378196
Abstract
We obtain high-precision limb-darkening measurements in five bands (V, V_E, I_E, I, and H) for the K3 III (T_eff=4200 K, [Fe/H]=+0.3, logg=2.3) source of the Galactic bulge microlensing event EROS BLG-2000-5. These measurements are inconsistent with the predictions of atmospheric models at higher than 10 sigma. While the disagreement is present in all bands, it is most apparent in I, I_E, and V_E, in part because the data are better and in part because the intrinsic disagreement is stronger. We find that when limb-darkening profiles are normalized to have unit total flux, the I-band models for a broad range of temperatures all cross each other at a common point. The solar profile also passes through this point. However, the profile as measured by microlensing does not. We hypothesize that the models have incorporated some aspect of solar physics that is not shared by giant atmospheres.
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Title:		Optical Observations and Orbital Parameters of the Close DA plus dMe Binaries BPM 71214, EUVE J0720-31.7, BPM 6502, and EC 13471-1258
Authors:		Kawka, Adela; Vennes, Stéphane; Koch, Rolf; Williams, Andrew
Journal:		The Astronomical Journal, Volume 124, Issue 5, pp. 2853-2867.
Publication Date:		11/2002
Keywords:		Stars: Binaries: Close, stars: individual (BPM 71214), stars: individual (EUVE J0720-31.7), Stars: Individual: Alphanumeric: BPM 6502, stars: individual (EC 13471-1258), Stars: White Dwarfs
DOI:		10.1086/343836
Abstract
We have obtained photometric and spectroscopic observations of the close DA plus dMe binaries BPM 6502 and EC 13471-1258, and spectroscopic observations of the close binaries BPM 71214 and EUVE J0720-31.7. We have updated the ephemerides of BPM 6502 and EUVE J0720-31.7 with the spectroscopic measurements and obtained periods of 0.20162 and 0.15074 days for BPM 71214 and EC 13471-1258, respectively, by measuring the shift in Halpha emission. Photometric variations in R and I due to reprocessing of incoming radiation from the hot white dwarf were observed in BPM 6502. We have also observed eclipses and ellipsoidal variations in B and R for EC 13471-1258, suggesting that the secondary is nearly filling its Roche lobe.
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Title:		A Short, Nonplanetary, Microlensing Anomaly: Observations and Light-Curve Analysis of MACHO 99-BLG-47
Authors:		Albrow, M. D.; An, J.; Beaulieu, J.-P.; Caldwell, J. A. R.; DePoy, D. L.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.
Journal:		The Astrophysical Journal, Volume 572, Issue 2, pp. 1031-1040.
Publication Date:		06/2002
Keywords:		Stars: Binaries: General, Cosmology: Gravitational Lensing, Stars: Planetary Systems
DOI:		10.1086/340310
Abstract
We analyze PLANET and MACHO observations of MACHO 99-BLG-47, the first nearly normal microlensing event for which high signal-to-noise ratio data reveal a well-covered, short-duration anomaly. This anomaly occurs near the peak of the event. Short-duration anomalies near the peak of otherwise normal events are expected to arise both from extreme-separation (either very close or very wide), roughly equal-mass binary lenses and from planetary systems. We show that the lens of MACHO 99-BLG-47 is in fact an extreme-separation binary, not a planetary system, thus demonstrating for the first time that these two important classes of events can be distinguished in practice. However, we find that the wide-binary and close-binary lens solutions fit the data equally well and cannot be distinguished even at Deltachi²=1. This degeneracy is qualitatively much more severe than the one identified for MACHO 98-SMC-1 because the present degeneracy spans two rather than one dimension in the magnification field and does not require significantly different blending fractions. In the Appendix, we explore this result and show that it is related to the symmetry in the lens equation.
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Title:		First Microlens Mass Measurement: PLANET Photometry of EROS BLG-2000-5
Authors:		An, Jin H.; Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; DePoy, D. L.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.
Journal:		The Astrophysical Journal, Volume 572, Issue 1, pp. 521-539.
Publication Date:		06/2002
Keywords:		Stars: Binaries: General, Cosmology: Gravitational Lensing, Stars: Fundamental Parameters
DOI:		10.1086/340191
Abstract
We analyze PLANET photometric observations of the caustic-crossing binary lens microlensing event, EROS BLG-2000-5, and find that modeling the observed light curve requires incorporation of the microlens parallax and the binary orbital motion. The projected Einstein radius (r_E=3.61±0.11 AU) is derived from the measurement of the microlens parallax, and we are also able to infer the angular Einstein radius (theta_E=1.38±0.12 mas) from the finite source effect on the light curve, combined with an estimate of the angular size of the source given by the source position in a color-magnitude diagram. The lens mass, M=0.612±0.057 M_solar, is found by combining these two quantities. This is the first time that parallax effects are detected for a caustic-crossing event and also the first time that the lens mass degeneracy has been completely broken through photometric monitoring alone. The combination of r_E and theta_E also allows us to conclude that the lens lies in the near side of the disk, within 2.6 kpc of the Sun, while the radial velocity measurement indicates that the source is a Galactic bulge giant.
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Title:		Microlensing Constraints on the Frequency of Jupiter-Mass Companions: Analysis of 5 Years of PLANET Photometry
Authors:		Gaudi, B. S.; Albrow, M. D.; An, J.; Beaulieu, J.-P.; Caldwell, J. A. R.; DePoy, D. L.; Dominik, M.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pel, J.-W.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Vreeswijk, P. M.; Watson, R.; Williams, A.
Journal:		The Astrophysical Journal, Volume 566, Issue 1, pp. 463-499.
Publication Date:		02/2002
Keywords:		Cosmology: Gravitational Lensing, Stars: Planetary Systems, Stars: Low-Mass, Brown Dwarfs
DOI:		10.1086/337987
Abstract
We analyze 5 years of PLANET photometry of microlensing events toward the Galactic bulge to search for the short-duration deviations from single-lens light curves that are indicative of the presence of planetary companions to the primary microlenses. Using strict event-selection criteria, we construct a well-defined sample of 43 intensively monitored events. We search for planetary perturbations in these events over a densely sampled region of parameter space spanning two decades in mass ratio and projected separation, but find no viable planetary candidates. By combining the detection efficiencies of the events, we find that, at 95% confidence, less than 25% of our primary lenses have companions with mass ratio q=10^-2 and separations in the lensing zone, [0.6-1.6]theta_E, where theta_E is the Einstein ring radius. Using a model of the mass, velocity, and spatial distribution of bulge lenses, we infer that the majority of our lenses are likely M dwarfs in the Galactic bulge. We conclude that less than 33% of M dwarfs in the Galactic bulge have companions with mass m_p=M_J between 1.5 and 4 AU, and less than 45% have companions with m_p=3M_J between 1 and 7 AU, the first significant limits on planetary companions to M dwarfs. We consider the effects of the finite size of the source stars and changing our detection criterion, but find that these do not alter our conclusions substantially.
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Title:		Limits on the Abundance of Galactic Planets From 5 Years of PLANET Observations
Authors:		Albrow, M. D.; An, J.; Beaulieu, J.-P.; Caldwell, J. A. R.; DePoy, D. L.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pel, J.-W.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Vreeswijk, P. M.; Watson, R; Williams, A.
Journal:		The Astrophysical Journal, Volume 556, Issue 2, pp. L113-L116.
Publication Date:		08/2001
Keywords:		Cosmology: Gravitational Lensing, Stars: Planetary Systems, Stars: Late-Type, Stars: Low-Mass, Brown Dwarfs, Techniques: Photometric
DOI:		10.1086/323141
Abstract
We search for signatures of planets in 43 intensively monitored microlensing events that were observed between 1995 and 1999. Planets would be expected to cause a short-duration (~1 day) deviation on the smooth, symmetric light curve produced by a single lens. We find no such anomalies and infer that less than one-third of the ~0.3 M_solar stars that typically comprise the lens population have Jupiter mass companions with semimajor axes in the range of 1.5 AU< a< 4 AU. Since orbital periods of planets at these radii are 3-15 yr, the outer portion of this region is currently difficult to probe with any other technique.
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Title:		Halpha Equivalent Width Variations across the Face of a Microlensed K Giant in the Galactic Bulge
Authors:		Albrow, M.; An, J.; Beaulieu, J.-P.; Caldwell, J. A. R.; Dominik, M.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Pollard, K.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.; Hauschildt, P. H.
Journal:		The Astrophysical Journal, Volume 550, Issue 2, pp. L173-L177.
Publication Date:		04/2001
Keywords:		Cosmology: Gravitational Lensing, Stars: Atmospheres, Stars: Fundamental Parameters, stars: individual (EROS 2000-BLG-5)
DOI:		10.1086/319635
Abstract
We present Very Large Telescope FORS1 spectroscopy that temporally resolves the second caustic crossing of the Galactic bulge K giant source of microlensing event EROS 2000-BLG-5, the first time this has been accomplished for several phases of a caustic transit. The ~1 Å Halpha equivalent width of the source star increases slightly as the center of the star egresses the caustic and then plummets by 30% during the final limb crossing. These changes are not seen in contemporaneous spectra of control stars in the FORS1 slit but are qualitatively consistent with expectations from stellar atmosphere models as the caustic differentially magnifies different portions of the stellar face of the target. Observations such as these in a variety of stellar lines are equivalent to atmospheric tomography and are expected to provide a direct test of stellar models.
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Title:		PLANET Observations of Microlensing Event OGLE-1999-BUL-23: Limb-darkening Measurement of the Source Star
Authors:		Albrow, M. D.; An, J.; Beaulieu, J.-P.; Caldwell, J. A. R.; DePoy, D. L.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.
Journal:		The Astrophysical Journal, Volume 549, Issue 2, pp. 759-769.
Publication Date:		03/2001
Keywords:		Stars: Binaries: General, Cosmology: Gravitational Lensing, Stars: Atmospheres, Stars: Fundamental Parameters
DOI:		10.1086/319437
Abstract
We present PLANET observations of OGLE-1999-BUL-23, a binary-lens microlensing event toward the Galactic bulge. PLANET observations in the I and V bands cover the event from just before the first caustic crossing until the end of the event. In particular, a densely sampled second caustic crossing enables us to derive the linear limb-darkening coefficients of the source star: c_V=0.786^+0.080_-0.078 and c_I=0.632^+0.047_-0.037. Combined analysis of the light curve and the color-magnitude diagram suggests that the source star is a G/K subgiant in the Galactic bulge (T_eff~=4800 K). The resulting linear limb-darkening coefficient of the source is consistent with theoretical predictions, although it is likely that nonlinearity of the stellar surface brightness profile complicates the interpretation, especially for the I band. The global light curve fit to the data indicates that the event is due to a binary lens of a mass ratio q~=0.39 and a projected separation d~=2.42. The lens/source relative proper motion is (22.8±1.5) km s^-1 kpc^-1, typical of bulge/bulge or bulge/disk events.
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Title:		Discovery of the Optical Counterpart and Early Optical Observations of GRB 990712
Authors:		Sahu, K. C.; Vreeswijk, P.; Bakos, G.; Menzies, J. W.; Bragaglia, A.; Frontera, F.; Piro, L.; Albrow, M. D.; Bond, I. A.; Bower, R.; Caldwell, J. A. R.; Castro-Tirado, A. J.; Courbin, F.; Dominik, M.; Fynbo, J. U.; Galama, T.; Glazebrook, K.; Greenhill, J.; Gorosabel, J.; Hearnshaw, J.; Hill, K.; Hjorth, J.; Kane, S.; Kilmartin, P. M.; Kouveliotou, C.; Martin, R.; Masetti, N.; Maxted, P.; Minniti, D.; Müller, P.; Muraki, Y.; Nakamura, T.; Noda, S.; Ohnishi, K.; Palazzi, E.; van Paradijs, J.; Pian, E.; Pollard, K. R.; Rattenbury, N. J.; Reid, M.; Rol, E.; Saito, T.; Sackett, P. D.; Saizar, P.; Tinney, C.; Vermaak, P.; Watson, R.; Williams, A.; Yock, P.; Dar, A.
Journal:		The Astrophysical Journal, Volume 540, Issue 1, pp. 74-80.
Publication Date:		09/2000
Keywords:		Cosmology: Observations, Gamma Rays: Bursts
DOI:		10.1086/309340
Abstract
We present the discovery observations of the optical counterpart of the gamma-ray burst GRB 990712 taken 4.16 hr after the outburst and discuss its light curve observed in the V, R, and I bands during the first ~35 days after the outburst. The observed light curves were fitted with a power-law decay for the optical transient (OT), plus an additional component that was treated in two different ways. First, the additional component was assumed to be an underlying galaxy of constant brightness. The resulting slope of the decay is 0.97^+0.05_-0.02, and the magnitudes of the underlying galaxy are V=22.3±0.05, R=21.75±0.05, and I=21.35±0.05. Second, the additional component was assumed to be a galaxy plus an underlying supernova with a time-variable brightness identical to that of GRB 980425, appropriately scaled to the redshift of GRB 990712. The resulting slope of the decay is similar, but the goodness of fit is worse, which would imply that either this GRB is not associated with an underlying supernova or the underlying supernova is much fainter than the supernova associated with GRB 980425. The galaxy in this case is fainter: V=22.7±0.05, R=22.25±0.05, and I=22.15±0.05, and the OT plus the underlying supernova at a given time is brighter. Measurements of the brightnesses of the OT and the galaxy by late-time Hubble Space Telescope observation and ground-based observations can thus assess the presence of an underlying supernova. Based on observations collected at SAAO, Sutherland; ESO, Paranal and La Silla (ESO Programs 63.O-0618 and 63-O-0567) and AAT, Australia.
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Title:		Limits on Stellar and Planetary Companions in Microlensing Event OGLE-1998-BUL-14
Authors:		Gaudi, B. S.; Beaulieu, J.-P.; Caldwell, J. A. R.; DePoy, D. L.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.
Journal:		The Astrophysical Journal, Volume 535, Issue 1, pp. 176-189.
Publication Date:		05/2000
Keywords:		Cosmology: Dark Matter, Cosmology: Gravitational Lensing, Stars: Planetary Systems
DOI:		10.1086/308842
Abstract
We present the PLANET photometric data set for OGLE-1998-BUL-14, a high-magnification (A_max~16) event alerted by the OGLE collaboration toward the Galactic bulge in 1998. The PLANET data set consists a total of 461 I-band and 139 V-band points, the majority of which was taken over a 3 month period. The median sampling interval during this period is about 1 hr, and the 1 sigma scatter over the peak of the event is 1.5%. The excellent data quality and high maximum magnification of this event make it a prime candidate to search for the short-duration, low-amplitude perturbations that are signatures of a planetary companion orbiting the primary lens. The observed light curve for OGLE-1998-BUL-14 is consistent with a single lens (no companion) within photometric uncertainties. We calculate the detection efficiency of the light curve to lensing companions as a function of the mass ratio and angular separation of the two components. We find that companions of mass ratio > =0.01 are ruled out at the 95% significance level for projected separations between 0.4 and 2.4r_E, where r_E is the Einstein ring radius of the primary lens. Assuming that the primary is a G dwarf with r_E~3 AU, our detection efficiency for this event is ~60% for a companion with the mass and separation of Jupiter and ~5% for a companion with the mass and separation of Saturn. Our efficiencies for planets like those around upsilo And and 14 Her are > 75%.
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Title:		Detection of Rotation in a Binary Microlens: PLANET Photometry of MACHO 97-BLG-41
Authors:		Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.; Bond, H. E.; van Bemmel, I. M.
Journal:		The Astrophysical Journal, Volume 534, Issue 2, pp. 894-906.
Publication Date:		05/2000
Keywords:		Stars: Binaries: General, Cosmology: Gravitational Lensing, Stars: Planetary Systems
DOI:		10.1086/308798
Abstract
We analyze PLANET collaboration data for MACHO 97-BLG-41, the only microlensing event observed to date in which the source transits two disjoint caustics. The PLANET data, consisting of 46 V-band and 325 I-band observations from five southern observatories, span a period from the initial alert until the end of the event. Our data are incompatible with a static binary lens, but are well fitted by a rotating binary lens of mass ratio q=0.34 and angular separation d~0.5 (in units of the Einstein ring radius), in which the binary separation changes in size by deltad=-0.070±0.009 and in orientation by deltatheta=5.61d±0.36d during the 35.17 days between the separate caustic transits. We use this measurement, combined with other observational constraints, to derive the first kinematic estimate of the mass, distance, and period of a binary microlens. The relative probability distributions for these parameters peak at a total lens mass M~0.3 M_solar (M-dwarf binary system), lens distance D_L~5.5 kpc, and binary period P~1.5 yr. The robustness of our model is demonstrated by its striking agreement with MACHO/GMAN data that cover several sharp features in the light curve not probed by the PLANET observations, and which did not enter our modeling procedure in any way. Available data sets thus indicate that the light curve of MACHO 97-BLG-41 can be modeled as a source crossing two caustics of a physically realistic rotating binary. Thus, contrary to a recent suggestion, the additional effects of a postulated planetary companion to the binary lens are not required. Based on observations at Canopus Observatory, Tasmania, Australia; Perth Observatory, Bickley, Australia; the South African Astronomical Observatory, Sutherland, South Africa; the European Southern Observatory, La Silla, Chile; and the Cerro Tololo Inter-American Observatory, Cerro Tololo, Chile.
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Title:		Combined Analysis of the Binary Lens Caustic-crossing Event MACHO 98-SMC-1
Authors:		fonso, C; ; Alard, C.; Albert, J. N.; Andersen, J.; Ansari, R.; Aubourg, É Bareyre, P.; Bauer, F.; Beaulieu, J. P.; Bouquet, A.; Char, S.; Charlot, X.; Couchot, F.; Coutures, C.; Derue, F.; Ferlet, R.; Glicenstein, J. F.; Goldman, B.; Gould, A.; Graff, D.; Gros, M.; Haissinski, J.; Hamilton, J. C.; Hardin, D.; de Kat, J.; Kim, A.; Lasserre, T.; Lesquoy, É .; Loup, C.; Magneville, C.; Marquette, J. B.; Maurice, É Milsztajn, A.; Moniez, M.; Palanque-Delabrouille, N.; Perdereau, O.; Pré vot, L.; Regnault, N.; Rich, J.; Spiro, M.; Vidal-Madjar, A.; Vigroux, L.; Zylberajch, S.; Alcock, C.; Allsman, R. A.; Alves, D.; Axelrod, T. S.; Becker, A. C.; Cook, K. H.; Drake, A. J.; Freeman, K. C.; Griest, K.; King, L. J.; Lehner, M. J.; Marshall, S. L.; Minniti, D.; Peterson, B. A.; Pratt, M. R.; Quinn, P. J.; Rodgers, A. W.; Stetson, P. B.; Stubbs, C. W.; Sutherland, W.; Tomaney, A.; Vandehei, T.; Rhie, S. H.; Bennett, D. P.; Fragile, P. C.; Johnson, B. R.; Quinn, J.; Udalski, A.; Kubiak, M.; Szymanski, M.; Pietrzynski, G.; Wozniak, P.; Zebrun, K.; Albrow, M. D.; Caldwell, J. A. R.; DePoy, D. L.; Dominik, M.; Gaudi, B. S.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.
Journal:		The Astrophysical Journal, Volume 532, Issue 1, pp. 340-352.
Publication Date:		03/2000
Keywords:		ASTROMETRY, COSMOLOGY: DARK MATTER, COSMOLOGY: GRAVITATIONAL LENSING, GALAXIES: MAGELLANIC CLOUDS
DOI:		10.1086/308561
Abstract
We fit the data for the binary lens microlensing event MACHO 98-SMC-1 from five different microlensing collaborations and find two distinct solutions characterized by binary separation d and mass ratio q: (d,q)=(0.54,0.50) and (d,q)=(3.65,0.36), where d is in units of the Einstein radius. However, the relative proper motion of the lens is very similar in the two solutions, 1.30 km s^-1 kpc^-1 and 1.48 km s^-1 kpc^-1, thus confirming that the lens is in the Small Magellanic Cloud. The close binary can be either rotating or approximately static but the wide binary must be rotating at close to its maximum allowed rate to be consistent with all the data. We measure limb-darkening coefficients for five bands ranging from I to V. As expected, these progressively decrease with rising wavelength. This is the first measurement of limb darkening for a metal-poor A star.
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Title:		A Complete Set of Solutions for Caustic Crossing Binary Microlensing Events
Authors:		Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; Depoy, D. L.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.;
Journal:		The Astrophysical Journal, Volume 522, Issue 2, pp. 1022-1036.
Publication Date:		09/1999
Keywords:		ASTROMETRY, COSMOLOGY: DARK MATTER, COSMOLOGY: GRAVITATIONAL LENSING
DOI:		10.1086/307699
Abstract
We present a method to analyze binary lens microlensing light curves with one well-sampled fold caustic crossing. In general, the surface of chi^2 shows extremely complicated behavior over the nine-parameter space that characterizes binary lenses. This makes it difficult to systematically search the space and verify that a given local minimum is a global minimum. We show that for events with well-monitored caustics, the caustic crossing region can be isolated from the rest of the light curve and easily fitted to a five-parameter function. Four of these caustic crossing parameters can then be used to constrain the search in the larger nine-parameter space. This allows a systematic search for all solutions and thus identification of all local minima. We illustrate this technique using the PLANET data for MACHO 98-SMC-1, an excellent and publicly available caustic crossing data set. We show that a very broad range of parameter combinations are compatible with the PLANET data set, demonstrating that observations of binary lens light curves with a sampling of only one caustic crossing do not yield unique solutions. The corollary to this is that the time of the second caustic crossing cannot be reliably predicted on the basis of early data including the first caustic crossing alone. We investigate the requirements for determination of a unique solution and find that occasional observations of the first caustic crossing may be sufficient to derive a complete solution.
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Title:		Limb Darkening of a K Giant in the Galactic Bulge: PLANET Photometry of MACHO 97-BLG-28
Authors:		Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; Dominik, M.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pel, J.-W.; Pollard, K.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.; Sahu, M. S.
Journal:		The Astrophysical Journal, Volume 522, Issue 2, pp. 1011-1021.
Publication Date:		09/1999
Keywords:		STARS: BINARIES: VISUAL, COSMOLOGY: GRAVITATIONAL LENSING, STARS: FUNDAMENTAL PARAMETERS, STARS: LATE-TYPE
DOI:		10.1086/307681
Abstract
We present the PLANET photometric data set for the binary-lens microlensing event MACHO 97-BLG-28, consisting of 696 I- and V-band measurements, and analyze it to determine the radial surface brightness profile of the Galactic bulge source star. The microlensed source, demonstrated to be a K giant by our independent spectroscopy, crossed an isolated cusp of the central caustic of the lensing binary, generating a sharp peak in the light curve that was well-resolved by dense (3-30 minute) and continuous monitoring from PLANET sites in Chile, South Africa, and Australia. This is the first time that such a cusp crossing has been observed. Analysis of the PLANET data set has produced a measurement of the square-root limb-darkening coefficients of the source star in the I and V bands; the resulting stellar profiles are in excellent agreement with those predicted by stellar atmospheric models for K giants. The limb-darkening coefficients presented here are the first derived from microlensing. They are also among the first found for normal giants by any technique and the first for any star as distant as the Galactic bulge. Modeling of our light curve for MACHO 97-BLG-28 indicates that the lensing binary has a mass ratio q=0.23 and an (instantaneous) separation in units of the angular Einstein ring radius of d=0.69. For a lens in the Galactic bulge, this corresponds to a typical stellar binary with a projected separation between 1 and 2 AU. If the lens lies closer (i.e., in the Galactic disk), the separation is smaller, and one or both of the lens objects is in the brown dwarf regime. Assuming that the source is a bulge K2 giant at 8 kpc, the relative lens-source proper motion is mu=19.4±2.6 km s^-1 kpc^-1, consistent with a disk or bulge lens. If the nonlensed blended light is due to a single star, it is likely to be a young white dwarf in the bulge, consistent with the blended light coming from the lens itself.
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Title:		A Complete Set of Solutions for Caustic Crossing Binary Microlensing Events
Authors:		Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; Depoy, D. L.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.;
Journal:		The Astrophysical Journal, Volume 522, Issue 2, pp. 1022-1036.
Publication Date:		09/1999
Keywords:		ASTROMETRY, COSMOLOGY: DARK MATTER, COSMOLOGY: GRAVITATIONAL LENSING
DOI:		10.1086/307699
Abstract
We present a method to analyze binary lens microlensing light curves with one well-sampled fold caustic crossing. In general, the surface of chi^2 shows extremely complicated behavior over the nine-parameter space that characterizes binary lenses. This makes it difficult to systematically search the space and verify that a given local minimum is a global minimum. We show that for events with well-monitored caustics, the caustic crossing region can be isolated from the rest of the light curve and easily fitted to a five-parameter function. Four of these caustic crossing parameters can then be used to constrain the search in the larger nine-parameter space. This allows a systematic search for all solutions and thus identification of all local minima. We illustrate this technique using the PLANET data for MACHO 98-SMC-1, an excellent and publicly available caustic crossing data set. We show that a very broad range of parameter combinations are compatible with the PLANET data set, demonstrating that observations of binary lens light curves with a sampling of only one caustic crossing do not yield unique solutions. The corollary to this is that the time of the second caustic crossing cannot be reliably predicted on the basis of early data including the first caustic crossing alone. We investigate the requirements for determination of a unique solution and find that occasional observations of the first caustic crossing may be sufficient to derive a complete solution.
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Title:		Limb Darkening of a K Giant in the Galactic Bulge: PLANET Photometry of MACHO 97-BLG-28
Authors:		Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; Dominik, M.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pel, J.-W.; Pollard, K.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.; Sahu, M. S.
Journal:		The Astrophysical Journal, Volume 522, Issue 2, pp. 1011-1021.
Publication Date:		09/1999
Keywords:		STARS: BINARIES: VISUAL, COSMOLOGY: GRAVITATIONAL LENSING, STARS: FUNDAMENTAL PARAMETERS, STARS: LATE-TYPE
DOI:		10.1086/307681
Abstract
We present the PLANET photometric data set for the binary-lens microlensing event MACHO 97-BLG-28, consisting of 696 I- and V-band measurements, and analyze it to determine the radial surface brightness profile of the Galactic bulge source star. The microlensed source, demonstrated to be a K giant by our independent spectroscopy, crossed an isolated cusp of the central caustic of the lensing binary, generating a sharp peak in the light curve that was well-resolved by dense (3-30 minute) and continuous monitoring from PLANET sites in Chile, South Africa, and Australia. This is the first time that such a cusp crossing has been observed. Analysis of the PLANET data set has produced a measurement of the square-root limb-darkening coefficients of the source star in the I and V bands; the resulting stellar profiles are in excellent agreement with those predicted by stellar atmospheric models for K giants. The limb-darkening coefficients presented here are the first derived from microlensing. They are also among the first found for normal giants by any technique and the first for any star as distant as the Galactic bulge. Modeling of our light curve for MACHO 97-BLG-28 indicates that the lensing binary has a mass ratio q=0.23 and an (instantaneous) separation in units of the angular Einstein ring radius of d=0.69. For a lens in the Galactic bulge, this corresponds to a typical stellar binary with a projected separation between 1 and 2 AU. If the lens lies closer (i.e., in the Galactic disk), the separation is smaller, and one or both of the lens objects is in the brown dwarf regime. Assuming that the source is a bulge K2 giant at 8 kpc, the relative lens-source proper motion is mu=19.4±2.6 km s^-1 kpc^-1, consistent with a disk or bulge lens. If the nonlensed blended light is due to a single star, it is likely to be a young white dwarf in the bulge, consistent with the blended light coming from the lens itself.
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Title:		The Relative Lens-Source Proper Motion in MACHO 98-SMC-1
Authors:		Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; Depoy, D. L.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.; Pogge, R. W.
Journal:		The Astrophysical Journal, Volume 512, Issue 2, pp. 672-677.
Publication Date:		02/1999
Keywords:		STARS: BINARIES: VISUAL, GALAXY: HALO, COSMOLOGY: GRAVITATIONAL LENSING, GALAXIES: MAGELLANIC CLOUDS
DOI:		10.1086/306820
Abstract
We present photometric and spectroscopic data for the second microlensing event seen toward the Small Magellanic Cloud (SMC), MACHO 98-SMC-1. The lens is a binary. We resolve the caustic crossing and find that the source took 2Deltat=8.5 hr to transit the caustic. We measure the source temperature T_eff=8000 K both spectroscopically and from the color, (V-I)_0~0.22. We find two acceptable binary-lens models. In the first, the source crosses the caustic at phi=43.2d and the unmagnified source magnitude is I_s=22.15. The angle implies that the lens crosses the source radius in time t_=Deltatsinphi=2.92 hr. The magnitude (together with the temperature) implies that the angular radius of the source is theta_=0.089 muas. Hence, the proper motion is mu=theta_/t_=1.26 km s^-1 kpc^-1. For the second solution, the corresponding parameters are phi=30.6d, I_s=21.81, t_=2.15 hr, theta_=0.104 muas, and mu=theta_/t_=2.00 km s^-1 kpc^-1. Both proper-motion estimates are slower than 99.5% of the proper motions expected for halo lenses. Both are consistent with an ordinary binary lens moving at ~75-120 km s^-1 within the SMC itself. We conclude that the lens is most likely in the SMC proper.
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Title:		The 1995 Pilot Campaign of PLANET: Searching for Microlensing Anomalies through Precise, Rapid, Round-the-Clock Monitoring
Authors:		Albrow, M.; Beaulieu, J.-P.; Birch, P.; Caldwell, J. A. R.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pel, J.-W.; Pollard, K.; Sackett, P. D.; Sahu, K. C.; > Vreeswijk, P.; Williams, A.; Zwaan, M. A.;
Journal:		The Astrophysical Journal, Volume 509, Issue 2, pp. 687-702.
Publication Date:		12/1998
Keywords:		GALAXY: STELLAR CONTENT, COSMOLOGY: GRAVITATIONAL LENSING, STARS: PLANETARY SYSTEMS, STARS: VARIABLES: OTHER, SURVEYS
DOI:		10.1086/306513
Abstract
PLANET (the Probing Lensing Anomalies NETwork) is a worldwide collaboration of astronomers whose primary goal is to monitor microlensing events densely and precisely in order to detect and study anomalies that contain information about Galactic lenses and sources that would otherwise be unobtainable. The results of PLANET's highly successful first year of operation are presented here. Details of the observational setup, observing procedures, and data-reduction procedures used to track the progress in real time at the three participating observing sites in 1995 are discussed. The ability to follow several events simultaneously with a median sampling interval of 1.6 hr and a photometric precision of better than 0.10 mag even at I = 19 has been clearly demonstrated. During PLANET's 1995 pilot campaign, ten microlensing events were monitored, resulting in the most precise and densely-sampled light curves to date; the binary nature of one of these, MACHO 95-BLG-12, was recognized by PLANET on the mountain. Another event, OGLE 95-BLG-04, displayed chromaticity that may betray the presence of blending with unresolved stars projected onto the same resolution element. Although lasting only about a month, the campaign may allow constraints to be placed on the number of planets with mass ratios to the parent star of 0.01 or greater.
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Title:		The 1998 PLANET Gravitational Microlensing Season
Authors:		Depoy, D. L.; Albrow, M. D.; Beaulieu, J. P.; Caldwell, J.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pel, J.-W.; Pogge, R.; Pollard, K.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.
Journal:		American Astronomical Society, 193rd AAS Meeting, #117.01; Bulletin of the American Astronomical Society, Vol. 30, p.1424
Publication Date:		12/1998
Abstract
The Probing Lensing Anomalies NETwork is an international collaboration that makes coordinated observations of on-going graviational microlensing events from four sites in the southern hemisphere. One of our primary goals is to detect planets around other stars from their microlensing effect. During the 1998 bulge observing season we intensely monitored numerous microlensing events; one event was observed more than 500 times at I and 200 times at V. The frequency and general quality of our photometry gives us excellent sensitivity to second order gravitational microlensing effects (such as those due to the presence of a planet).
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Title:		Limits on Planetary Companions in Microlensing Event OGLE-BUL-98-14
Authors:		Gaudi, B. S.; Albrow, M. D.; Beaulieu, J. P.; Caldwell, J. A. R.; Depoy, D. L.; Dominik, M.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pogge, R. W.; Pollard, K.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.
Journal:		American Astronomical Society, 193rd AAS Meeting, #108.07; Bulletin of the American Astronomical Society, Vol. 30, p.1416
Publication Date:		12/1998
Abstract
As part of an ongoing effort to detect second order effects in gravitational microlensing events, the Probing Lensing Anomalies NETwork (PLANET) collaboration has obtained nearly continuous photometry of the microlensing event OGLE-BUL-98-14 with four telescopes located in Tasmania, Perth, South Africa and Chile. The complete data set consists of over 500 points in I and 200 in V taken over a period of ~ 120 days, making this one of the most well sampled microlensing events to date. The scatter in I is ~ 2% (1 sigma). OGLE-BUL-98-14 was a high magnification event (maximum magnification > 10) with a timescale of ~ 40 days. These facts, combined with the high sampling rate and good photometry, make this an extremely promising event for detection of second order effects. We find that the observed lightcurve is completely consistent with a point-source point-lens model. We can rule out the presence of a companion with mass ratio > 10(-3) over a substantial range of projected separations. Furthermore, the lack of detected finite-source or parallax effects allows us to put a lower limit on the mass of the lens, M_lens > 0.1 M_sun.
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Title:		Light curves of SN 1998A and comparison with similar unusual SNe
Authors:		Woodings, Simon J.; Williams, Andrew J.; Martin, Ralph; Burman, Ronald R.; Blair, David G.
Journal:		Monthly Notices of the Royal Astronomical Society, Volume 301, Issue 1, pp. L5-L9.
Publication Date:		11/1998
Keywords:		SUPERNOVAE: GENERAL, SUPERNOVAE: INDIVIDUAL: SN 1998A, SUPERNOVAE: INDIVIDUAL: SN 1987A, SUPERNOVAE: INDIVIDUAL: SN 1909A, SUPERNOVAE: INDIVIDUAL: SN 1993J
Abstract
Preliminary photometric data for SN 1998A are presented, showing that it increased in brightness by 1.0±0.1 mag in RI over the 80-d period following discovery. Maximum brightness occurred approximately 70 d after discovery, centred within a broad plateau-like peak lasting about 30 d. The shapes of the light curves during the entire 170-d period are similar to those of SNe 1987A and 1909A, suggesting that SNe 1998A and 1909A may also have had blue supergiant progenitors. Spectroscopic and further photometric study of SN 1998A will allow more detailed comparisons between this and other unusual Type II supernovae.
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Title:		Initial statistics from the Perth Automated Supernova Search
Authors:		Williams, A. J.
Journal:		Publications Astronomical Society of Australia, vol. 14, no. 2, p. 208-13
Publication Date:		08/1997
Keywords:		SUPERNOVAE, STARS, STATISTICS
Abstract
The Perth Automated Supernova Search uses the 61-cm PLAT (Perth Lowell Automated Telescope) at Perth Observatory, Western Australia. Since 1993 January 1, five confirmed supernovae have been found by the search. The analysis of the first three years of data is discussed, and preliminary results presented. We find a Type Ib/c rate of 0.43 ± 0.43 SNu, and a Type IIP rate of 0.86 ± 0.49 SNu, where SNu are 'supernova units'. These values are for a Hubble constant of 75 km per sec per Mpc.
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Title:		Southern Hemisphere automated supernova search.
Authors:		Williams, A. J.; Martin, R.; Verveer, A.; Blair, D. G.; Koch, R.; Lynch, M. J. & Burman, R.
Journal:		Review of Scientific Instruments, Volume 66, Issue 4, April 1995, pp.2777-2784.
Publication Date:		04/1995
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Title:		Supernova 1993k - First Photometric Results
Authors:		Wiliams, A. J.; Martin, R.; Koch, R.; Blair, D. G.; Lynch, M.
Journal:		Experimental Astronomy, v. 5, p. 151.
Publication Date:		00/1994
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Title:		A narrow-band search for extraterrestrial intelligence (SETI) using the interstellar contact channel hypothesis
Authors:		Blair, D. G.; Norris, R. P.; Troup, E. R.; Twardy, R.; Wellington, K. J.; Williams, A. J.; Wright, A. E.; Zadnik, M. G.
Journal:		Royal Astronomical Society, Monthly Notices (ISSN 0035-8711), vol. 257, no. 1, July 1, 1992, p. 105-109.
Publication Date:		07/1992
Keywords:		ASTRONOMICAL SPECTROSCOPY, NARROWBAND, PROJECT SETI, EMISSION SPECTRA, GLOBULAR CLUSTERS, RADIO TELESCOPES
Abstract
A search is reported for narrow spectral line emission from 176 targets (including 166 stars and seven globular clusers) at the hypothesized 'interstellar communications channel' frequency of 4.462336275 GHz (= pi times the neutral hydrogen line at 1.42 GHz) using the Parkes Radio telescope. The frequency was Doppler corrected for the solar barycenter, target barycenter, and cosmic microwave background (CMB) reference frames. If a 'Galactic club' of extraterrestrial civilizations exists, then the null results, down to a 3 sigma limit of 2 Jy (6 Jy in CMB frame), set an upper limit of 10 exp 8 yr on the lifetime of such civilizations.
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NON-REFEREED PUBLICATIONS - Dr Andrew Williams

Shortcut to refereed publications

Title:		Hunting for Frozen Super-Earths via Microlensing
Authors:		Beaulieu, J-P.; Albrow, M.; Bennett, D.; Brillang, S.; Caldwell, J. A. R.; Calitz, J. J.; Cassan, A.; Cook, K. H.; Coutures, C.; Dieters, S.; Dominik, M.; Dominis-Prester, D.; Donatowicz, J.; Fouqué, P.; Greenhill, J.; Hill, K.; Hoffman, M.; Jørgensen, U. G.; Kane, S.; Kubas, D.; Marquette, J-B.; Martin, R.; Meintjes, P.; Menzies, J.; Pollard, K.; Sahu, K.; Vinter, C.; Wambsganss, J.; Williams, A.; Woller, K.; Zub, M.; Horne, K.; Allan, A.; Bode, M.; Bramich, D. M.; Burgdorf, M.; Fraser, S.; Mottram, C.; Rattenbury, N.; Snodgrass, C.; Steele, I. and Tsapras, Y.
Journal:		The Messenger, 128 , page 33.
Publication Date:		06/2007
Abstract
In order to obtain a census of planets with masses in the range of Earth to Jupiter, eight telescopes are being used by the combined microlensing campaign of the PLANET and RoboNet collaborations for high-cadence photometric round-the-clock follow-up of ongoing events, alerted by the OGLE and MOA surveys. In 2005 we detected a planet of 5.5 Earth masses at 2.6 AU from its parent 0.22 MA M star. This object is the first member of a new class of cold telluric planets. Its detection confirms the power of this method and, given our detection efficiency, suggests that these recently-detected planets may be quite common around M stars, as confirmed by subsequent detection of a ~ 13 Earth-mass planet. Using a network of dedicated 1 2-m-class telescopes, we have entered a new phase of planet discovery, and will be able to provide constraints on the abundance of frozen Super-Earths in the near future.
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Title:		The PLANET Microlensing Campaign: Implications for Planets around Galactic Disk and Bulge Stars
Authors:		Dominik, M., Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; Cassan, A.; Coutures, C.; Greenhill, J.; Hill, K.; Fouqué , P.; Horne, K.; Jorgensen, U. G.; Kane, S.; Kubas, D.; Martin, R.; Menzies, J.; Pollard, K. R.; Sahu, K.; Wambsganss, J.; Watson, R.; Williams, A.
Journal:		Extrasolar Planets: Today and Tomorrow, ASP Conference Proceedings, Vol. 321, held 30 June - 4 July 2003, Institut D'Astrophysique de Paris, France. Edited by Jean-Philippe Beaulieu, Alain Lecavelier des Etangs and Caroline Terquem. ISBN: 1-58381-183-4, 2004, p.121
Publication Date:		12/2004
Abstract
With round-the-clock monitoring of galactic bulge microlensing events, the PLANET experiment constrains the abundance and can yield the discovery of planets down to the mass of earth around galactic disk and bulge stars. Data taken until 1999 imply that less than 1/3 of bulge M-dwarfs are surrounded by jupiter-mass companions at orbital radii between 1 and 4 AU. The current rate of microlensing alerts allows 15--25 jupiters and 1--3 earths to be probed per year.
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Title:		PLANET II: A Microlensing and Transit Search for Extrasolar Planets
Authors:		Sackett, Penny D.; Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; Coutures, C.; Dominik, M.; Greenhill, J.; Hill, K.; Horne, K.; Jorgensen, U.-G.; Kane, S.; Kubas, D.; Martin, R.; Menzies, J. W.; Pollard, K. R.; Sahu, K. C.; Wambsganss, J.; Watson, R.; Williams, A.
Journal:		Bioastronomy 2002: Life Among the Stars, Proceedings of IAU Symposium #213. Edited by R. Norris, and F. Stootman. San Francisco: Astronomical Society of the Pacific, 2003., p.35
Publication Date:		06/2004
Abstract
Due to their extremely small luminosity compared to the stars they orbit, planets outside our own Solar System are extraordinarily difficult to detect directly in optical light. Careful photometric monitoring of distant stars, however, can reveal the presence of exoplanets via the microlensing or eclipsing effects they induce. The international PLANET collaboration is performing such monitoring using a cadre of semi-dedicated telescopes around the world. Their results constrain the number of gas giants orbiting 1--7 AU from the most typical stars in the Galaxy. Upgrades in the program are opening regions of ``exoplanet discovery space'' -- toward smaller masses and larger orbital radii -- that are inaccessible to the Doppler velocity technique.
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Title:		The PLANET microlensing follow-up network: results and prospects for the detection of extra-solar planets
Authors:		Dominik, M.; Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; DePoy, D. L.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pel, J.-W.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.
Journal:		Planetary and Space Science, Volume 50, Issue 3, p. 299-307.
Publication Date:		03/2002
Abstract
Among various techniques to search for extra-solar planets, microlensing has some unique characteristics. Contrary to all other methods which favour nearby objects, microlensing is sensitive to planets around stars at distances of several kpc. These stars act as gravitational lenses leading to a brightening of observed luminous source stars. The lens stars that are tested for the presence of planets are not generally seen themselves. The largest sensitivity is obtained for planets at orbital separations of 1-10AU offering the view on an extremely interesting range with regard to our own solar system and in particular to the position of Jupiter. The microlensing signal of a jupiter-mass planet lasts typically a few days. This means that a planet reveals its existence by producing a short signal at its quasi-instantaneous position, so that planets can be detected without the need to observe a significant fraction of the orbital period. Relying on the microlensing alerts issued by several survey groups that observe ~10⁷ stars in the Galactic bulge. PLANET (Probing Lensing Anomalies NETwork) performs precise and frequent measurements on ongoing microlensing events in order to detect deviations from a light curve produced by a single point-like object. These measurements allow constraints to be put on the abundance of planets. From 42 well-sampled events between 1995 and 1999, we infer that less than /1/3 of M-dwarfs in the Galactic bulge have jupiter-mass companions at separations between 1 and 4AU from their parent star, and that /< 45% have 3-jupiter-mass companions between 1 and 7AU.
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Title:		Microlensing Constraints on the Frequency of Jupiter-Mass Planets
Authors:		Gaudi, B. S.; Albrow, M. D.; An, J. H.; Beaulieu, J.-P.; Caldwell, J. A. R.; Depoy, D. L.; Dominik, M.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Pogge, R. W.; Pollard, K.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.
Journal:		Microlensing 2000: A New Era of Microlensing Astrophysics, ASP Conference Proceedings, Vol. 239. Edited by J. W. Menzies and Penny D. Sackett. San Francisco: Astronomical Society of the Pacific, ISBN: 1-58381-076-5, 2001, p.135
Publication Date:		00/2001
Abstract
Microlensing is the only technique likely, within the next 5 years, to constrain the frequency of Jupiter-analogs. The PLANET collaboration has monitored nearly 100 microlensing events of which more than 20 have sensitivity to the perturbations that would be caused by a Jovian-mass companion to the primary lens. No clear signatures of such planets have been detected. These null results indicate that Jupiter mass planets with separations of 1.5-3 AU occur in less than 1/3 of systems. A similar limit applies to planets of 3 Jupiter masses between 1-4 AU.
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Title:		PLANET Observations of Anomalous Microlensing Events
Authors:		Menzies, J.; Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; Depoy, D. L.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Dominik, M.; Naber, R. M.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.
Journal:		Microlensing 2000: A New Era of Microlensing Astrophysics, ASP Conference Proceedings, Vol. 239. Edited by J. W. Menzies and Penny D. Sackett. San Francisco: Astronomical Society of the Pacific, ISBN: 1-58381-076-5, 2001, p.109
Publication Date:		00/2001
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Title:		The PLANET Microlensing Collaboration Search for Extrasolar Planets: Status Report (Contributed Talk)
Authors:		Beaulieu, J. P.; Albrow, M.; An, J.; Caldwell, J. A. R.; Depoy, D. L.; Dominik, M.; Gaudi, B. S.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R.; Pogge, R.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.;
Journal:		Disks, Planetesimals, and Planets, ASP Conference Proceedings, Vol. 219, edited by F. Garzó n, C. Eiroa, D. de Winter, and T. J. Mahoney. Astronomical Society of the Pacific, ISBN 1-58381-051-X, 2000, p.550
Publication Date:		00/2000
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Title:		Variable Star Research by the PLANET Collaboration
Authors:		Albrow, M. D.; Pollard, K. R.; Beaulieu, J.-P.; Caldwell, J. A. R.; Menzies, J.; Vermaak, P.; Depoy, D. L.; Gaudi, B. S.; Gould, A.; Pogge, R. W.; Dominik, M.; Naber, R. M.; Sackett, P. D.; Greenhill, J.; Hill, K.; Kane, S.; Watson, R.; Martin, R.; Williams, A.; Sahu, K. C.;
Journal:		The Impact of Large-Scale Surveys on Pulsating Star Research, ASP Conference Series, Vol. 203; also IAU Colloquium #176. Edited by L. Szabados and D. Kurtz. ISBN: 1-58381-030-7 (2000), p.25-30
Publication Date:		00/2000
Abstract
We review the current status and future prospects of the PLANET collaboration, an international team of astronomers performing high-precision photometric monitoring of microlensing events. Our photometric precision and sampling is characterised and the suitability of the database for variable star studies is discussed. Preliminary results on K-giant stability are presented.
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Title:		Microlensing Constraints on the Frequency of Jupiter Mass Planets
Authors:		Gaudi, B. S.; Albrow, M. D.; Beaulieu, J.-P.; Caldwell, J. A. R.; DePoy, D. L.; Dominik, M.; Gould, A.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pogge, R. W.; Pollard, K. R.; Sackett, P. D.; Sahu, K. C.; Vermaak, P.; Watson, R.; Williams, A.
Journal:		American Astronomical Society, 195th AAS Meeting, #24.04; Bulletin of the American Astronomical Society, Vol. 31, p.1408
Publication Date:		12/1999
Abstract
Microlensing is the only technique likely, within the next 5 years, to constrain the frequency of Jupiter-analogs. The PLANET collaboration has monitored nearly 100 microlensing events of which more than 20 have sensitivity to the perturbations that would be caused by a Jovian-mass companion to the primary lens. No clear signatures of such planets have been detected. These null results indicate that Jupiter mass planets with separations of 1.5-3 AU occur in less than 1/3 of systems. A similar limit applies to planets of 3 Jupiter masses for separations of 1-4 AU. These are the best limits for extrasolar planets at these separations by any technique.
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Title:		Supernova 1999ga in NGC 2442
Authors:		Woodings, S.; Martin, R.; Williams, A.; Biggs, J.; Verveer, A.
Journal:		IAU Circ., 7316, 1 (1999). Edited by Green, D. W. E.
Publication Date:		11/1999
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Title:		Supernova 1999ex in IC 5179
Authors:		Martin, R.; Williams, A.; Woodings, S.; Biggs, J.; Verveer, A.
Journal:		IAU Circ., 7310, 1 (1999). Edited by Green, D. W. E.
Publication Date:		11/1999
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Title:		Supernova 1999ee in IC 5179
Authors:		Williams, A.; Biggs, J.; Verveer, A.
Journal:		IAU Circ., 7284, 2 (1999). Edited by Green, D. W. E.
Publication Date:		10/1999
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Title:		Supernova 1999cz in NGC 5078
Authors:		Williams, A.; Martin, R.; Woodings, S.; Livingston, C.; Biggs, J.; Verveer, A.
Journal:		IAU Circ., 7214, 1 (1999). Edited by Green, D. W. E.
Publication Date:		07/1999
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Title:		Supernova 1999ca in NGC 3120
Authors:		Woodings, S.; Martin, R.; Williams, A.; Verveer, A.; Biggs, J.
Journal:		IAU Circ., 7158, 1 (1999). Edited by Green, D. W. E.
Publication Date:		05/1999
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Title:		Supernova 1998ce in MCG -4-24-19
Authors:		Woodings, S.; Martin, R.; Williams, A.; Biggs, J.; Verveer, A.
Journal:		IAU Circ., 6912, 1 (1998). Edited by Green, D. W. E.
Publication Date:		05/1998
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Title:		Supernova 1998A in IC 2627
Authors:		Williams, A.; .Woodings, S.; Martin, R.; Verveer, A.; Biggs, J.
Journal:		IAU Circ., 6805, 2 (1998). Edited by Green, D. W. E.
Publication Date:		01/1998
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Title:		Supernova 1998X in NGC 6754
Authors:		Woodings, S.; Martin, R.; Williams, A.; Patat, F.; della Valle, M.
Journal:		IAU Circ., 6847, 1 (1998). Edited by Green, D. W. E.
Publication Date:		03/1998
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Title:		Supernova 1998E in NGC 5161
Authors:		Woodings, S.; Martin, R.; Williams, A.; Suntzeff, N.; Ruiz, M.-T.
Journal:		IAU Circ., 6817, 1 (1998). Edited by Green, D. W. E.
Publication Date:		01/1998
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Title:		Supernova 1998A in IC 2627
Authors:		Williams, A.; Woodings, S.; Martin, R.; Verveer, A.; Biggs, J.
Journal:		IAU Circ., 6805, 2 (1998). Edited by Green, D. W. E.
Publication Date:		01/1998
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Title:		The Perth Automated Supernova Search
Authors:		Williams, A. J.
Journal:		PhD Thesis - University of Western Australia
Publication Date:		12/1997
Keywords:		SUPERNOVAE, STATISTICS
Abstract
An automated search for supernovae in late spiral galaxies has been established at Perth Observatory, Western Australia. This automated search uses three low-cost PC-clone computers, a liquid nitrogen cooled CCD camera built locally, and a 61-cm telescope automated for the search. The images are all analysed automatically in real-time by routines in Perth Vista, the image processing system ported to the PC architecture for the search system. The telescope control software written for the project, Teljoy, maintains open-loop position accuracy better than 30" of arc after hundreds of jumps over an entire night. Total capital cost to establish and run this supernova search over the seven years of development and operation was around US$30,000. To date, the system has discovered a total of 6 confirmed supernovae, made an independent detection of a seventh, and detected one unconfirmed event assumed to be a supernova. The various software and hardware components of the search system are described in detail, the analysis of the first three years of data is discussed, and results presented. We find a Type Ib/c rate of 0.43 ± 0.43 SNu, and a Type IIP rate of 0.86 ± 0.49 SNu, where SNu are 'supernova units', expressed in supernovae per 10¹⁰ solar blue luminosity galaxy per century. These values are for a Hubble constant of 75 km/s per Mpc, and scale as (H0/75)². The small number of discoveries has left large statistical uncertainties, but our strategy of frequent observations has reduced systematic errors - altering detection threshold or peak supernova luminosity by ± 0.5 mag changes estimated rates by only around 20%. Similarly, adoption of different light curve templates for Type Ia and Type IIP supernovae has a minimal effect on the final statistics (2% and 4% change, respectively).
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Title:		Supernova 1997Z in NGC 3261
Authors:		Martin, R.; Williams, A.; Woodings, S.; Benetti, S.; Turatto, M.; Cappellaro, E.
Journal:		IAU Circ., 6558, 1 (1997). Edited by Green, D. W. E.
Publication Date:		02/1997
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Title:		Interstellar communication channel search of 49 stars closer than 11.5 PC
Authors:		Zadnik, Marjan G.; Winterflood, John; Williams, Andrew J.; Wellington, Kelvin J.; Vaile, Roberta; Blair, David G.; Tarter, Jill C.; Backus, Peter R.; Norris, Ray P.; Heiligman, Gary
Journal:		Conference Paper, Astronomical and Biochemical Origins and the Search for Life in the Universe, IAU Colloquium 161, Publisher: Bologna, Italy, p. 657.
Publication Date:		01/1997
Keywords:		INTERSTELLAR COMMUNICATION, STELLAR SPECTRA, EARTH (PLANET), EMISSION SPECTRA, SIGNAL DETECTION, RADIO TELESCOPES, NARROWBAND, LINE SPECTRA, PROJECT SETI
Abstract
We report on a search for narrowband emissions from the vicinity of 36 solar type (F6 to K4) target stars and 13 other nonsolar-type stars within 11.5 parsec at five possible interstellar beacon frequencies of pif(H), 2pif(H), ef(OH), e(f(OH)+f(H)), and He-3 (4.462, 8.925, 4.532, 8.393, and 8.666 GHz respectively). The frequencies were selected by scaling important naturally occurring lines by fundamental constants. The stars were selected for a distance of less than 11.5 parsec to give sufficient time for a nearby civilization to have detected early Earth radio leakage signals and to have replied. The search was carried using the 64-m Parkes telescope with the Phoenix instrumentation and the 22-m Mopra telescope for candidate verification. The instrument combination allowed a low interference, high resolution, high sensitivity search. We did not detect any signals from any of the target stars. If a civilization at a distance of 10 pc had beamed 10 kW signals at us using a 100-m dish, we would have detected the transmission at the 10 sigma level. Thus we can exclude signals above this level.
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Title:		The Planet Collaboration: Probing Lensing Anomalies.
Authors:		Albrow, M.; Beaulieu, J.-P.; Birch, P.; Caldwell, J. A. R.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pel, J.-W.; Pollard, K.; Sackett, P. D.; Sahu, K. C.; Vreeswiji, P.; Watson, R.; Williams, A.; Zwaan, M.
Journal:		Variables Stars and the Astrophysical Returns of the Microlensing Surveys. Edited by Roger Ferlet, Jean-Pierre Maillard and Brigitte Raban. Cedex, France : Editions Frontieres, 1997., p.135
Publication Date:		00/1997
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Title:		The PLANET Collaboration: Current Status and Future Prospects
Authors:		Albrow, M.; Beaulieu, J.-P.; van Bemmel, I.; Birch, P.; Caldwell, J. A. R.; Greenhill, J.; Hill, K.; Kane, S.; Martin, R.; Menzies, J.; Naber, R. M.; Pel, J.-W.; Pollard, K.; Sackett, P. D.; Sahu, K. C.; Vreeswijk, P.; Watson, R.; Williams, A.; Zwaan, M.
Journal:		Planets Beyond the Solar System and the Next Generation of Space Missions. Proceedings of a workshop held at Space Telescope Science Institute, Baltimore, MD, October 16-18, 1996. ASP Conference Series, Vol. 119, 1997, ed. David Soderblom (1997), p.91-94
Publication Date:		00/1997
Abstract
Follow-up observations of gravitational microlensing events is a method by which planetary systems may be detected. This report gives a brief description of the PLANET collaboration and its current research and progress.
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Title:		Supernova 1996N in NGC 1398
Authors:		Williams, A.; Martin, R.; Germany, L.; Schmidt, B.; Stathakis, R.; Johnston, H.
Journal:		IAU Circ., 6351, 1 (1996). Edited by Green, D. W. E.
Publication Date:		03/1996
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Title:		The PLANET Collaboration
Authors:		Albrow. M.; Birch. P.; Caldwell, J.; Martin, R.; Menzies. J.; Pel. J.; Pollard. K.; Sackett. P.; Sahu. K.; Vreeswijk. P.; Williams. A.; Zwaan. M.
Journal:		Astrophysical applications of gravitational lensing: proceedings of the 173rd Symposium of the International Astronomical Union; held in Melbourne; Australia; 9-14 July; 1995. Edited by C. S. Kochanek and Jacqueline N. Hewitt. International Astronomical Union. Symposium no. 173; Kluwer Academic Publishers; Dordrecht, p.227
Publication Date:		00/1996
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Title:		PLANET (Probing Lensing Anomalies NETwork)
Authors:		Albrow, Michael; Birch, Peter; Caldwell, John A. R.; Martin, Ralph; Menzies, John; Pel, Jan-Willem; Pollard, Karen; Sackett, Penny D.; Sahu, Kailash C.; Vreeswijk, Paul; Williams, Andrew; Zwaan, Martin
Journal:		American Astronomical Society, 187th AAS Meeting, #117.04; Bulletin of the American Astronomical Society, Vol. 27, p.1449
Publication Date:		12/1995
Abstract
The PLANET (Probing Lensing Anomalies NETwork) collaboration has carried out frequent monitoring of about 7 microlensing events during the 1995 bulge season. The events were monitored in V and I bands, with a typical time interval of about 1.5 to 3 hrs between successive observations of each event. One of the prime objectives of the PLANET collaboration is to look for planets around the lensing objects the signature of which would be sharp extra peaks on the point-source/point-lens microlensing light curve. The data can also be used to look for anomalies caused by other factors such as binary sources/lenses, extended source characteristics, etc. Three 60cm to 1-m class telescopes, situated at La Silla (Chile), Sutherland (South Africa) and Perth (Australia) were used to achieve an almost continuous coverage of the events. The first PLANET campaign lasted about 45 days, starting from 12th July 1995. In principle, such observations are sensitive to the presence of earth-size planets. The data analysis is now in progress.
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Title:		Supernova 1995W in NGC 7650
Authors:		Williams, A.; Martin, R.; Greenhill, J.; Hill, K. M.; Benetti, S.; Augusteijn, T.; Sarajedini, A.
Journal:		IAU Circ., 6206, 2 (1995). Edited by Marsden, B. G.
Publication Date:		08/1995
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Title:		Supernova 1993K in NGC 2223
Authors:		Williams, A.; Martin, R.; Schmidtke, P. C.; Phillips, M. M.; Maza, J.; Wischnjewsky, M.
Journal:		IAU Circ., 5733, 1 (1993). Edited by Marsden, B. G.
Publication Date:		03/1993
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Title:		Automatic Direct Imaging and Photometric Telescopes in Australia
Authors:		Carter, B. D.; Bernbrick, C.; Moore, K. G.; Zealey, W.; Blair, D. G.; Burman, T.; Williams, A.; Tsang, C. P.; Evans, M.; Lynch, M. J.; Zadnik, M.; Forster, D.; Dai, X.; Koch, R.; Candy, M.; Birch, P.; Martin, R.; Verveer, A.; Coates, D. W.; Thompson, K.; Stewart, R. T.; Jones, K. L.; O'Mara, B. J.; Page, A. A.; Ross, J. E.; Avery, H. P.; Mottram, K.
Journal:		Automated Telescopes for Photometry and Imaging, ASP Conference Series, Vol. 28, 1992, S.J. Adelman, R.J. Dukes, Jr.; and C.J. Adelman, Eds., p. 135.
Publication Date:		00/1992
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Title:		A Test for the Interstellar Contact Channel Hypothesis in SETI
Authors:		Blair, D. G.; Norris, R.; Wellington, K. J.; Williams, A.; Wright, A.
Journal:		Bioastronomy The Exploration Broadens, Proceedings of the Third International Symposium on Bio- astronomy Held at Val Cenis, Savoie, France, 18-23 June 1990, edited by J. Heidmann and M.J. Klein. Springer-Verlag Berlin Heidelberg New York. Also Lecture Notes in Physics, volume 390, p.271
Publication Date:		00/1991

Title:		Automated Image Acquisition and Analysis with a Small Teleswcope
Authors:		Koch, R.; Dai, X.; Lynch, M. J.; Rye, P. J.; Zadnik, M.; Martin, R.; Verveer, A.; Candy, M.; Birch, P.; Blair, D. G.; Burman, R. R. and Williams, A.
Journal:		Proceedings: Image Processing and the Impact of New Technologies, Canberra, ACT, December 18-20, 1989. IREE Australia, p. 287.
Publication Date:		00/1990
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