TY  - JOUR
A1  - Beaulieu, Jean-Philippe
A1  - Bennett, David P.
A1  - Fouqué, Pascal
A1  - Williams, Andrew
A1  - Dominik, Martin
A1  - Jorgensen, Uffe Grae
A1  - Kubas, Daniel
A1  - Cassan, Arnaud
A1  - Coutures, Christian
A1  - Greenhill, John
A1  - Hill, Kym
A1  - Menzies, John
A1  - Sackett, Penny D.
A1  - Albrow, Michael D.
A1  - Brillant, Stephane
A1  - Caldwell, John A. R.
A1  - Calitz, Johannes Jacobus
A1  - Cook, Kem H.
A1  - Corrales Cosmeli, Esperanza de Santa Cecilia
A1  - Desort, Morgan
A1  - Dieters, Stefan
A1  - Dominis, Dijana
A1  - Donatowicz, Jadzia
A1  - Hoffman, Martie
A1  - Kane, Stephen R.
A1  - Marquette, Jean-Baptiste
A1  - Martin, Ralph
A1  - Meintjes, Pieter
A1  - Pollard, Karen R.
A1  - Sahu, Kailash C.
A1  - Vinter, Christian
A1  - Wambsganss, Joachim
A1  - Woller, Kristian
A1  - Horne, Keith
A1  - Steele, Iain
A1  - Bramich, Daniel M.
A1  - Burgdorf, Martin
A1  - Snodgrass, Colin
A1  - Bode, Mike
A1  - Udalski, Andr
T1  - Discovery of a cool planet of 5.5 Earth masses through gravitational microlensing
N2  - 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(1-4). 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 0.15 AU from normal stars. Here we report the discovery of a 5.5(-2.7)(+5.5)M(+) planetary companion at a separation of 2.6(- 0.6)(+1.5) AU from a 0.22(-0.11)(+0.21)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.
Y1  - 2006
UR  - http://www.nature.com/nature/
U6  - https://doi.org/10.1038/Nature04441
SN  - 0028-0836
ER  - 
TY  - JOUR
A1  - Kubas, Daniel
A1  - Cassan, A.
A1  - Beaulieu, Jean-Philippe
A1  - Coutures, C.
A1  - Dominik, M.
A1  - Albrow, Michael D.
A1  - Brillant, Stephane
A1  - Caldwell, John A. R.
A1  - Dominis, Dijana
A1  - Donatowicz, J.
A1  - Fendt, Christian
A1  - Fouque, P.
A1  - Jorgensen, Uffe Grae
A1  - Greenhill, John
A1  - Hill, K.
A1  - Heinmüller, Janine
A1  - Horne, Keith
A1  - Kane, Stephen R.
A1  - Marquette, Jean-Baptiste
A1  - Martin, Ralph
A1  - Menzies, J. W.
A1  - Pollard, K. R.
A1  - Sahu, K. C.
A1  - Vinter, C.
A1  - Wambsganss, Joachim
A1  - Watson, R.
A1  - Williams, A.
A1  - Thurl, C.
T1  - Full characterization of binary-lens event OGLE-2002-BLG-069 from PLANET observations
N2  - 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-⊙ 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-⊙). 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
Y1  - 2005
SN  - 0004-6361
ER  - 
TY  - JOUR
A1  - Cassan, A.
A1  - Beaulieu, Jean-Philippe
A1  - Brillant, Stephane
A1  - Coutures, C.
A1  - Dominik, M.
A1  - Donatowicz, J.
A1  - Jorgensen, Uffe Grae
A1  - Kubas, Daniel
A1  - Albrow, Michael D.
A1  - Caldwell, John A. R.
A1  - Fouque, P.
A1  - Greenhill, John
A1  - Hill, K.
A1  - Horne, Keith
A1  - Kane, Stephen R.
A1  - Martin, Ralph
A1  - Menzies, J. W.
A1  - Pollard, K. R.
A1  - Sahu, K. C.
A1  - Vinter, C.
A1  - Wambsganss, Joachim
A1  - Watson, R.
A1  - Williams, A.
A1  - Fendt, Christian
A1  - Hauschildt, P.
A1  - Heinmueller, Janine
A1  - Marquette, Jean-Baptiste
A1  - Thurl, C.
T1  - Probing the atmosphere of the bulge G5III star OGLE-2002-BUL-069 by analysis of microlensed H alpha line
N2  - 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
Y1  - 2004
ER  - 
TY  - JOUR
A1  - Jiang, G. F.
A1  - DePoy, D. L.
A1  - Gal-Yam, A.
A1  - Gaudi, B. S.
A1  - Gould, A.
A1  - Han, C.
A1  - Lipkin, Y.
A1  - Maoz, D.
A1  - Ofek, E. O.
A1  - Park, B. G.
A1  - Pogge, R. W.
A1  - Udalski, A.
A1  - Kubiak, Marcin
A1  - Szymanski, M. K.
A1  - Szewczyk, O.
A1  - Zerbrun, K.
A1  - Wyrzykowski, L.
A1  - Soszynski, I.
A1  - Pietrzynski, G.
A1  - Albrow, Michael D.
A1  - Beaulieu, Jean-Philippe
A1  - Caldwell, John A. R.
A1  - Cassan, A.
A1  - Coutures, C.
A1  - Dominik, M.
A1  - Donatowicz, J.
A1  - Fouque, P.
A1  - Greenhill, John
A1  - Hill, K.
A1  - Horne, Keith
A1  - Jorgensen, S. F.
A1  - Jorgensen, Uffe Grae
A1  - Kane, Stephen R.
A1  - Kubas, Daniel
A1  - Martin, Ralph
A1  - Menzies, J. W.
A1  - Pollard, R.
A1  - Sahu, K. C.
A1  - Wambsganss, Joachim
A1  - Watson, R.
A1  - Williams, A.
T1  - OGLE-2003-BLG-238 : Microlensing mass estimate of an isolated star
N2  - 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 (c(2)/4G)(r) over tilde (E)theta(E) and so requires the measurement of both the angular Einstein radius theta(E) and the projected Einstein radius (r) over tilde (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) = 650 muas. Although the timescale of the event is only t(E) 38 days, one can still obtain weak constraints on the microlens parallax: 4.4 AU < <(r)over tilde>(E) < 18 AU at the 1 &sigma; level. Together these two parameter measurements yield a range for the lens mass of 0.36 M-&ODOT; < M < 1.48 M-&ODOT;. 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
Y1  - 2004
SN  - 0004-637X
ER  - 
TY  - JOUR
A1  - Sackett, Penny D.
A1  - Albrow, Michael D.
A1  - Beaulieu, Jean-Philippe
A1  - Caldwell, John A. R.
A1  - Coutures, C.
A1  - Dominik, M.
A1  - Greenhill, John
A1  - Hill, K.
A1  - Horne, Keith
A1  - Jorgensen, Uffe Grae
A1  - Kane, Stephen R.
A1  - Kubas, Daniel
A1  - Martin, Ralph
A1  - Menzies, J. W.
A1  - Pollard, K. R.
A1  - Sahu, K. C.
A1  - Wambsganß, Joachim
A1  - Watson, R.
A1  - Williams, A.
T1  - PLANET II : a microlensing and transit search for extrasolar planets
N2  - 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.
Y1  - 2003
UR  - http://arxiv.org/pdf/astro-ph/0211098
ER  - 
TY  - THES
A1  - Kubas, Daniel
T1  - Applications of Galactic Microlensing
T1  - Anwendungen des Galaktischen Mikrolinseneffektes
N2  - Subject of this work is the study of applications of the Galactic Microlensing effect, where the light of a distant star (source) is bend according to Einstein's theory of gravity by the gravitational field of intervening compact mass objects (lenses), creating multiple (however not resolvable) images of the source. Relative motion of source, observer and lens leads to a variation of deflection/magnification and thus to a time dependant observable brightness change (lightcurve), a so-called microlensing event, lasting weeks to months.  The focus lies on the modeling of binary-lens events, which provide a unique tool to fully characterize the lens-source system and to detect extra-solar planets around the lens star. Making use of the ability of genetic algorithms to efficiently explore large and intricate parameter spaces in the quest for the global best solution, a modeling software (Tango) for binary lenses is developed, presented and applied to data sets from the PLANET microlensing campaign. For the event OGLE-2002-BLG-069 the 2nd ever lens mass measurement has been achieved, leading to a scenario, where a G5III Bulge giant at 9.4 kpc is lensed by an M-dwarf binary with total mass of M=0.51 solar masses at distance 2.9 kpc. Furthermore a method is presented to use the absence of planetary lightcurve signatures to constrain the abundance of extra-solar planets.
N2  - Thema der Arbeit ist das Studium von Anwendungen des Galaktischen Mikrolinseneffektes bei dem das Licht eines entfernten Sternes (Quelle) nach Einstein's Theorie der Gravitation im Schwerefeld eines sich hinreichend nahe der Sichlinie zur Quelle befindlichen massereichen kompakten Objektes (Linse) abgelenkt wird und Mehrfachbilder der Quelle erzeugt werden (welche jedoch nicht aufgelöst werden können). Die Relativbewegung von Quelle, Beobachter und Linse führt zur einer Änderung der Ablenk-und Verstärkungswirkung und somit zu einer beobachtbaren Helligkeitsänderung der Quelle (Lichtkurve), einem sogenannten Mikrolinsenereignis, welches Wochen bis Monate andauert.  Der Schwerpunkt liegt in der Modelierung von Doppellinsen-Ereignissen, welche die einzigartige Möglichkeit bieten das Linsen-Quelle System vollständig zu charakterisieren und extra-solare Planeten um den Linsenstern zu detektieren. Unter Verwendung der Eigenschaft genetischer Algorithmen hoch-dimensionale und komplizierte Parameterräume effizient nach dem besten globalen Model zu durchsuchen, wird eine Modelier-Software (Tango) entwickelt, präsentiert und auf Daten der PLANET Mikrolinsen Beobachtungskampagne angewandt. Dabei konnte für das Ereignis OGLE-2002-BLG-069 zum zweitenmal überhaupt die Linsenmasse bestimmt werden, in einem Szenario bei dem ein G5III Bulge Riese, 9.4 kpc entfernt, von einem M-Zwerg Binärsystem mit einer Gesamtmasse von M=0.51 Sonnenmassen in einer Entfernung von 2.9 kpc gelinst wird. Darüberhinaus wird ein Verfahren vorgestellt mit dem man die Abwesenheit planetarer Lichtkurvensignaturen nutzen kann, um Aussagen über die Häufigkeit extrasolarer Planeten zu treffen.
KW  - Planeten
KW  - Gravitation
KW  - Milchstrasse
KW  - Genetik
KW  - Gravitationslinsen
KW  - Mikrolinsen
KW  - OGLE
KW  - PLANET
KW  - Optimierung
KW  - microlensing
KW  - planet
KW  - OGLE
KW  - gravity
KW  - genetics
Y1  - 2005
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:517-opus-5179
ER  -