279 research outputs found
Microlensing search for extra solar planets
No full textGravitational microlensing may be used to probe distant stars for planetary companions.
The presence of a planet in the vicinity of a star acting as the lens may cause a short lived
anomaly in the observed lightcurve of the lensing event. By quantifying these anomalies we
may place limits on the mass of the companion relative to the lens as well as the position of
the planet relative to the primary lens. The detection probability is proportional to mp,
where mp is the planet mass. All current follow-up teams use dedicated observations on a
preselected sample of mainly high-amplification events. Microlensing has yet to yield an
undisputed planetary detection.
In chapter 1 we give an introduction to the field of extra-solar planets and proceed
to present the theory employed in microlensing studies in chapter 2. Chapter 3 deals
with the principles of data aquisition and data reduction techniques that provide the high
precision photometry needed for these studies.
In the data analysis presented in chapters 4 and 5 of this thesis, we use a different
observing approach. We spread our observing time between many targets obtaining 1 to
2 frames per night on each event. Our aim is not to characterize, but only detect the
first exoplanetary signal in a microlensing campaign. The pilot run presented in chapter
4 showed it is possible to place significant limits on the presence of planets even from
observations performed from a Northern site. In Chapter 5 we analyse data obtained
from the JKT at La Palma together with publicly available OGLE data to place useful
constraints on the presence of planets orbiting the lens stars. We detect no undisputed
planetary signals but calculate high detection probabilities for two events.
In chapter 6 we present our analysis of three years (1998-2000) of OGLE data (146
events). We compute the detection probability for each event individually and the total
detection probability for the whole sample. Our selection criteria return 6 candidate
events, 5 of which could possibly be attributed to planets. However, the OGLE data is
insufficient to draw definite conclusions. If we assume that the observed deviations are
not due to planetary companions, we conclude that less than 18% of the lens stars have
planets with mp = m5., orbiting them at an orbital radius of 1.1 <a<3 AU.
We conclude with a summary of this thesis in chapter 7
MOA-2010-BLG-311: A planetary candidate below the threshold of reliable detection
No full textpeer reviewedWe analyze MOA-2010-BLG-311, a high magnification (A_max>600) microlensing event with complete data coverage over the peak, making it very sensitive to planetary signals. We fit this event with both a point lens and a 2-body lens model and find that the 2-body lens model is a better fit but with only Delta chi^2~140. The preferred mass ratio between the lens star and its companion is $q=10^(-3.7+/-0.1), placing the candidate companion in the planetary regime. Despite the formal significance of the planet, we show that because of systematics in the data the evidence for a planetary companion to the lens is too tenuous to claim a secure detection. When combined with analyses of other high-magnification events, this event helps empirically define the threshold for reliable planet detection in high-magnification events, which remains an open question
Constraints on Jupiters from observations of Galactic bulge microlensing events during 2000
No full textY. Tsapras et al.We present observations of eight Galactic bulge microlensing events taken with the 1.0-m Jacobus Kapteyn Telescope (JKT) on La Palma during 2000 June and July. The JKT observing schedule was optimized using a prioritizing algorithm to automatically update the target list. For most of these events we have sampled the light curves at times where no information was available from the OGLE alert team. We assume a point-source point-lens (PSPL) model and perform a maximum likelihood fit to both our data and the OGLE data to constrain the event parameters of the fit. We then refit the data assuming a binary lens and proceed to calculate the probability of detecting planets with mass ratio q = 10−3. We have seen no clear signatures of planetary deviations on any of the eight events and we quantify constraints on the presence of planetary companions to the lensing stars. For two well-observed events, 2000BUL31 and 2000BUL33, our detection probabilities peak at ∼30 and ∼20 per cent respectively for q = 10−3 and a∼RE for a Δχ2 threshold value of 60.Peer reviewe
A Super-Jupiter orbiting a late-type star: A refined analysis of microlensing event OGLE-2012-BLG-0406
No full textpeer reviewedWe present a detailed analysis of survey and follow-up observations of microlensing event OGLE-2012-BLG-0406 based on data obtained from 10 different observatories. Intensive coverage of the lightcurve, especially the perturbation part, allowed us to accurately measure the parallax effect and lens orbital motion. Combining our measurement of the lens parallax with the angular Einstein radius determined from finite-source effects, we estimate the physical parameters of the lens system. We find that the event was caused by a planet orbiting a early M-type star. The distance to the lens is \ kpc and the projected separation between the host star and its planet at the time of the event is AU. We find that the additional coverage provided by follow-up observations, especially during the planetary perturbation, leads to a more accurate determination of the physical parameters of the lens
RedDots: Limits on habitable and undetected planets orbiting nearby stars GJ 832, GJ 674, and Ross 128
No full textContext . The nearby ( d < 5 pc) M dwarfs GJ 832, GJ 674, and Ross 128 each host a single exoplanet, with Ross 128 b located within the optimistic habitable zone. Due to their low mass and close proximity, these three systems are prime candidates for further characterization studies. Aims . Using HARPS spectroscopic data obtained by the RedDots campaign, as well as archival data from HARPS and CARMENES, supplemented with ASH2 and T90 photometry, we aim to search for additional planets in the three systems. We also aim to determine limits on possible undetected, habitable planets. We investigate (i) the reliability of the recovered orbital eccentricities and (ii) the reliability of Bayesian evidence as a diagnostic for selecting the best model. Methods . We employed Markov-chain Monte Carlo, nested sampling, and Gaussian process (GP) analyses to fit a total of 20 different models comprising 0–2 Keplerian signals and three different GP kernels for stellar activity. We used the residuals to create grids for injection-recovery simulations to obtain detection limits on potentially undiscovered planets. Results . Our refined orbital elements for GJ 832 b, GJ 674 b, and Ross 128 b confirm (GJ 832, GJ 674) or increase (Ross 128) prior eccentricity determinations. No additional planets were found in any of the systems. The detection limits obtained for all three systems are between 30 and 50 cm s −1 for orbital periods in the range of 1–10 000 days. This corresponds to habitable planet masses of <1.5 M ⊕ for GJ 832 and < 1 M ⊕ for GJ 674 and Ross 128. Using N-body simulations, we find that undiscovered secondary planets are unlikely (Ross 128) or incapable (GJ 674) of having caused the observed eccentricities of the known planets. We find that the eccentricity of GJ 832b is not significantly different from zero. Conclusions . GJ 832 b, GJ 674 b, and Ross 128 b retain their status as hosting lonely and (for the latter two) eccentric planets ( e = 0.04, 0.24, 0.21; respectively). This is unexpected in classical planet formation scenarios, which favor circular orbits and multiplanet configurations, demonstrating that planet formation in these cases is more complicated than traditionally thought. Additionally, the eccentricity of Ross 128 indicates that it spends some of its orbit outside of the optimistic habitable zone. Finally, our results show that Bayesian evidence, when used in conjunction with GP, is not a robust diagnostic for selecting the best model in cases of low- activity stars. In such cases, we advise an inspection of the shapes of the posterior distributions and to ensure that relevant simulations are performed to assess the validity of the perceived best model
Candidate gravitational microlensing events for future direct lens imaging
No full textThis material is based upon work supported by the National Science Foundation (NSF) Graduate Research Fellowship Program under grant No. DGE-0822215, awarded to C.B.H., and an international travel allowance through the Graduate Research Opportunities Worldwide, also awarded to C.B.H. and taken to Cheongju, Korea. T.S. is supported by the grant JSPS23340044 and JSPS24253004. The OGLE project has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement No. 246678 to A.U. Work by C.H. was supported by the Creative Research Initiative Program (2009-0081561) of the National Research Foundation of Korea. A.G. and B.S.G. acknowledge support from NSF AST-1103471 and from NASA grant NNX12AB99G. S.D. is supported by "The Strategic Priority Research Program—The Emergence of Cosmological Structures" of the Chinese Academy of Sciences (Grant No. XDB09000000). Work by J.C.Y. was performed in part under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program. M.D., K.H., M.H., C.S., R.A.S., and Y.T. acknowledge grant NPRP-09-476-1-78 from the Qatar National Research Fund (a member of the Qatar Foundation). This publication was made possible by NPRP grant #X-019-1-006 from the Qatar National Research Fund (a member of the Qatar Foundation).The mass of the lenses giving rise to Galactic microlensing events can be constrained by measuring the relative lens-source proper motion and lens flux. The flux of the lens can be separated from that of the source, companions to the source, and unrelated nearby stars with high-resolution images taken when the lens and source are spatially resolved. For typical ground-based adaptive optics (AO) or space-based observations, this requires either inordinately long time baselines or high relative proper motions. We provide a list of microlensing events toward the Galactic bulge with high relative lens-source proper motion that are therefore good candidates for constraining the lens mass with future high-resolution imaging. We investigate all events from 2004 to 2013 that display detectable finite-source effects, a feature that allows us to measure the proper motion. In total, we present 20 events with μ ≥ 8 mas yr–1. Of these, 14 were culled from previous analyses while 6 are new, including OGLE-2004-BLG-368, MOA-2005-BLG-36, OGLE-2012-BLG-0211, OGLE-2012-BLG-0456, MOA-2012-BLG-532, and MOA-2013-BLG-029. In ≤12 yr from the time of each event the lens and source of each event will be sufficiently separated for ground-based telescopes with AO systems or space telescopes to resolve each component and further characterize the lens system. Furthermore, for the most recent events, comparison of the lens flux estimates from images taken immediately to those estimated from images taken when the lens and source are resolved can be used to empirically check the robustness of the single-epoch method currently being used to estimate lens masses for many events.Peer reviewe
MOA-2013-BLG-220Lb : massive planetary companion to galactic-disk host
No full textWork by J. C. Yee was supported in part by a Distinguished University Fellowship from The Ohio State University and in part under contract with the California Institute of Technology (Caltech) funded by NASA through the Sagan Fellowship Program. Work by CH was supported by the Creative Research Initiative Program (2009-0081561) of the National Research Foundation of Korea. Work by A.G. and B.S.G. was supported by NSF grant AST 1103471. Work by A.G., B.S.G., and R.W.P. was supported by NASA grant NNX12AB99G. T.S. acknowledges the support from the grant JSPS23340044 and JSPS24253004. The OGLE project has received funding from the European Research Council under the European Community's Seventh Framework Programme (FP7/2007-2013)/ERC grant agreement no. 246678 to AU. This publication was made possible by NPRP grant X-019-1-006 from the Qatar National Research Fund (a member of Qatar Foundation).We report the discovery of MOA-2013-BLG-220Lb, which has a super-Jupiter mass ratio q = 3.01 ± 0.02 × 10-3 relative to its host. The proper motion, μ = 12.5 ± 1 mas yr-1, is one of the highest for microlensing planets yet discovered, implying that it will be possible to separately resolve the host within ∼7 yr. Two separate lines of evidence imply that the planet and host are in the Galactic disk. The planet could have been detected and characterized purely with follow-up data, which has important implications for microlensing surveys, both current and into the Large Synoptic Survey Telescope (LSST) era.Peer reviewe
An analysis of binary microlensing event OGLE-2015-BLG-0060
No full textWe present the analysis of stellar binary microlensing event OGLE-2015-BLG-0060 based on observations obtained from 13 different telescopes. Intensive coverage of the anomalous parts of the light curve was achieved by automated follow-up observations from the robotic telescopes of the Las Cumbres Observatory. We show that, for the first time, all main features of an anomalous microlensing event are well covered by follow-up data, allowing us to estimate the physical parameters of the lens. The strong detection of second-order effects in the event light curve necessitates the inclusion of longer-baseline survey data in order to constrain the parallax vector. We find that the event was most likely caused by a stellar binary-lens with masses M⋆1 = 0.87±0.12M⊙ and M⋆2 = 0.77±0.11M⊙. The distance to the lensing system is 6.41 ± 0.14 kpc and the projected separation between the two components is 13.85 ± 0.16 au. Alternative interpretations are also considered
Results from the wide angle search for planets prototype (WASP0) - II. Stellar variability in the Pegasus field
No full textThis article was published in Monthly Notices of the Royal Astronomical Society ©: 2005 Kane, SR et al. Published by Oxford University Press on behalf of The Royal Astronomical Society. All rights reserved.
http://mnras.oxfordjournals.org/content/362/1/11
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