53 research outputs found
Microlensing Searches for Exoplanets
Gravitational microlensing finds planets through their gravitational
influence on the light coming from a more distant background star. The presence
of the planet is then inferred from the tell-tale brightness variations of the
background star during the lensing event, even if no light is detectable from
the planet or the host foreground star. This review covers fundamental
theoretical concepts in microlensing, addresses how observations are performed
in practice, the~challenges of obtaining accurate measurements, and explains
how planets reveal themselves in the data. It~concludes with a presentation of
the most important findings to-date, a description of the method's strengths
and weaknesses, and a discussion of the future prospects of microlensing.Comment: 35 pages,9 figures, invited review for Geosciences Special Issue
"Detection and Characterization of Extrasolar Planets
Microlensing limits on numbers and orbits of extra-solar planets from the 1998-2000 OGLE events
We analyze three years (1998-2000) of OGLE observations of microlensing
events to place limits on the abundance of planets with a planet-to-star mass
ratio at distances AU from their host stars, i.e. `cool
Jupiters'. We fit a total of 145 events using a maximum likelihood fit that
adjusts 6 parameters. Each data point on the lightcurve allows us to exclude
planets close to the two images of the source appearing on opposite sides of
the Einstein ring of the lens star. We proceed to compute detection probability
maps for each event, using threshold values of 25, 60, 100 and
combine the results from all events to place global constraints. Our selection
criteria returned 5 candidate events for a planet with mass ratio .
Only two of these remained as plausible candidates after three were rejected
due to poor data quality at the time of the anomalies. Our results suggest that
less than 21 ()% of the lens stars have Jupiter-mass planets orbiting them
at an orbital radius of AU. is the number of planet
anomaly candidates that are actually due to planets. The datasets presented
here were obtained from the DoPhot analysis of the events available at the OGLE
website. The main conclusion of this work is that observing time is more
efficiently allocated by observing many events with sampling intervals that
produce non-overlapping detection zones than using intensive sampling on a
small number of events
The abundance of galactic planets from OGLE-III 2002 microlensing data
From the 389 2002 OGLE-III observations of Galactic Bulge microlensing events
we select 321 that are well described by a point-source point-lens lightcurve
model. From this sample we identify n=1 event, 2002-BLG-055, which we regard as
a strong planetary lensing candidate, and another, 2002-BLG-140, which is a
possible candidate. If each of the 321 lens stars has 1 planet with a mass
ratio q=m/M=10^{-3} and orbit radius a=R_E, the Einstein ring radius, analysis
of detection efficiencies indicates that 14 planets should have been detectable
with \Delta\chi^2 > 25. Assuming our candidate is due to planetary lensing,
then the abundance of planets with q=10^{-3} and a=R_E is n_p \approx n/14 =
7%. Conversion to physical units (M_Jup, and AU) gives the abundance of `cool
Jupiters' (m \approx M_Jup, a \approx 4 AU) per lens star as n_p \approx n/5.5
= 18%. The detection probability scales roughly with q and
(\Delta\chi^2)^{-1/2}, and drops off from a peak at a \approx 4 AU like a
Gaussian with a dispersion of 0.4 dex.Comment: 10 pages, 10 figures. Accepted for publication in MNRA
The LCOGT Network
Motivated by the increasing need for observational resources for the study of
time varying astronomy, the Las Cumbres Observatory Global Telescope (LCOGT) is
a private foundation, whose goal is to build a global network of robotic
telescopes for scientific research and education. Once completed, the network
will become a unique tool, capable of continuous monitoring from both the
Northern and Southern Hemispheres. The network currently includes 2 x 2.0 m
telescopes, already making an impact in the field of exoplanet research. In the
next few years they will be joined by at least 12 x 1.0 m and 20 x 0.4 m
telescopes. The increasing amount of LCOGT observational resources in the
coming years will be of great service to the astronomical community in general,
and the exoplanet community in particular.Comment: 2 pages, 1 figure, to appear in the proceedings of IAU Symposium 276
"The Astrophysics of Planetary Systems: Formation, Structure, and Dynamical
Evolution
Simulator for Microlens Planet Surveys
We summarize the status of a computer simulator for microlens planet surveys.
The simulator generates synthetic light curves of microlensing events observed
with specified networks of telescopes over specified periods of time.
Particular attention is paid to models for sky brightness and seeing,
calibrated by fitting to data from the OGLE survey and RoboNet observations in
2011. Time intervals during which events are observable are identified by
accounting for positions of the Sun and the Moon, and other restrictions on
telescope pointing. Simulated observations are then generated for an algorithm
that adjusts target priorities in real time with the aim of maximizing planet
detection zone area summed over all the available events. The exoplanet
detection capability of observations was compared for several telescopes.Comment: Proc. IAU Symp. No. 293 "Formation, detection, and characterization
of extrasolar habitable planets", ed. by N. Haghighipour. 4 pages, in pres
ROME/REA : a gravitational microlensing search for exoplanets beyond the snow line on a global network of robotic telescopes
Funding: KH acknowledges support from STFC grant ST/R000824/1.Planet population synthesis models predict an abundance of planets with semimajor axes between 1 and 10 au, yet they lie at the edge of the detection limits of most planet finding techniques. Discovering these planets and studying their distribution is critical to understanding the physical processes that drive planet formation. ROME/REA is a gravitational microlensing project whose main science driver is to discover exoplanets in the cold outer regions of planetary systems. To achieve this, it uses a novel approach combining a multiband survey with reactive follow-up observations, exploiting the unique capabilities of the Las Cumbres Observatory global network of robotic telescopes combined with a Target and Observation Manager system. We present the main science objectives and a technical overview of the project, including initial results.PostprintPeer reviewe
Results from the Wide Angle Search for Planets Prototype (WASP0) I: Analysis of the Pegasus Field
WASP0 is a prototype for what is intended to become a collection of
wide-angle survey instruments whose primary aim is to detect extra-solar
planets transiting across the face of their parent star. The WASP0 instrument
is a wide-field (9-degree) 6.3cm aperture F/2.8 Apogee 10 CCD camera (2Kx2K
chip, 16-arcsec pixels) mounted piggy-back on a commercial telescope. We
present results from analysis of a field in Pegasus using the WASP0 camera,
including observations of the known transiting planet around HD 209458. We also
present details on solving problems which restrict the ability to achieve
photon limited precision with a wide-field commercial CCD. The results
presented herein demonstrate that millimag photometry can be obtained with this
instrument and that it is sensitive enough to detect transit due to extra-solar
planets.Comment: 9 pages, 10 figures, Accepted for publication in MNRA
Microlensing mass measurement from images of rotating gravitational arcs
Gravitational microlensing[SUP]1[/SUP] is a powerful technique for measuring the mass of isolated and faint or non-luminous objects in the Milky Way[SUP]2,3[/SUP]. In most cases, however, additional observations to the photometric light curve are required to measure accurately the mass of the microlens. Long-baseline optical/infrared interferometry provides a new and efficient way to deliver such independent constraints[SUP]4-7[/SUP], as demonstrated recently by first interferometric observations in microlensing event TCP J05074264+2447555 (`Kojima-1')[SUP]8[/SUP]. Here we report real-time observations of gravitationally lensed arcs in rotation around a microlens, Gaia19bld[SUP]9[/SUP], made with the PIONIER instrument[SUP]10[/SUP] at the Very Large Telescope Interferometer. Our data allowed us to determine the angular separation and length of the arcs, as well as their rotation rate. Combining these measurements with ground-based photometric data enabled the determination of the microlens mass, M = 1.147 ± 0.029 M[SUB]â[/SUB], to a very high accuracy. We anticipate interferometric microlensing to play an important future role in the mass and distance determination of isolated stellar-mass black holes[SUP]11-13[/SUP] in the Galaxy, which cannot be addressed by any other technique
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