Yazar "Rhodes, M. D." seçeneğine göre listele

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    An investigation into exoplanet transits and uncertainties
    (Springer, 2017) Ji, Y.; Banks, T.; Budding, E.; Rhodes, M. D.
    A simple transit model is described along with tests of this model against published results for 4 exoplanet systems (Kepler-1, 2, 8, and 77). Data from the Kepler mission are used. The Markov Chain Monte Carlo (MCMC) method is applied to obtain realistic error estimates. Optimisation of limb darkening coefficients is subject to data quality. It is more likely for MCMC to derive an empirical limb darkening coefficient for light curves with S/N (signal to noise) above 15. Finally, the model is applied to Kepler data for 4 Kepler candidate systems (KOI 760.01, 767.01, 802.01, and 824.01) with previously unpublished results. Error estimates for these systems are obtained via the MCMC method.
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    Analysis of Exoplanet Light Curves
    (Astronomical Soc Pacific, 2015) Erdem, A.; Budding, E.; Rhodes, M. D.; Puskullu, Q.; Soydugan, Faruk; Soydugan, Esin; Tuysuz, M.
    We have applied the close binary system analysis package WINFITTER to a variety of exoplanet transiting light curves taken both from the NASA Exoplanet Archive and our own groundbased observations. WINFITTER has parameter options for a realistic physical model, including gravity brightening and structural parameters derived from Kopal's applications of the relevant Radau equation, and it includes appropriate tests for determinacy and adequacy of its best fitting parameter sets. We discuss a number of issues related to empirical checking of models for stellar limb darkening, surface maculation, Doppler beaming, microvariability, and transit time variation (TTV) effects. The Radau coefficients used in the light curve modeling, in principle, allow structural models of the component stars to be tested.
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    Analysis of selected Kepler Mission planetary light curves
    (Springer, 2014) Rhodes, M. D.; Budding, E.
    We have modified the graphical user interfaced close binary system analysis program CurveFit to the form WinKepler and applied it to 16 representative planetary candidate light curves found in the NASA Exoplanet Archive (NEA) at the Caltech website , with an aim to compare different analytical approaches. WinKepler has parameter options for a realistic physical model, including gravity-brightening and structural parameters derived from the relevant Radau equation. We tested our best-fitting parameter-sets for formal determinacy and adequacy. A primary aim is to compare our parameters with those listed in the NEA. Although there are trends of agreement, small differences in the main parameter values are found in some cases, and there may be some relative bias towards a 90(a similar to) value for the NEA inclinations. These are assessed against realistic error estimates. Photometric variability from causes other than planetary transits affects at least 6 of the data-sets studied; with small pulsational behaviour found in 3 of those. For the false positive KOI 4.01, we found that the eclipses could be modelled by a faint background classical Algol as effectively as by a transiting exoplanet. Our empirical checks of limb-darkening, in the cases of KOI 1.01 and 12.01, revealed that the assigned stellar temperatures are probably incorrect. For KOI 13.01, our empirical mass-ratio differs by about 7 % from that of Mislis and Hodgkin (Mon. Not. R. Astron. Soc. 422:1512, 2012), who neglected structural effects and higher order terms in the tidal distortion. Such detailed parameter evaluation, additional to the usual main geometric ones, provides an additional objective for this work.
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    Analysis of the exoplanet containing system Kepler-13
    (Springer, 2018) Budding, E.; Puskullu, C.; Rhodes, M. D.
    We have applied the close binary system analysis program WINFITTER, with its physically detailed fitting function, to an intensive study of the complex multiple system Kepler-13 using photometry data from all 13 short cadence quarters downloaded from the NASA Exoplanet Archive (NEA) (http://exoplanetarchive.ipac.caltech.edu ). The data-point error of our normalized, phase-sequenced and binned (380 points per bin: 0.00025 phase interval) flux values, at 14 ppm, allows the model's specification for the mean reference flux level of the system to a precision better than 1 ppm. Our photometrically derived values for the mass and radius of KOI13.01 are 6.8 +/- 0.6 M-J and 1.44 +/- 0.04 R-J. The star has a radius of 1.67 +/- 0.05 R-circle dot. Our modelling sets the mean of the orbital inclination i at 94.35 +/- 0.14 degrees, with the star's mean precession angle phi(p) -49.1 +/- 5.0 degrees and obliquity theta(o) 67.9 +/- 3.0 degrees, though there are known ambiguities about the sense in which such angles are measured. Our findings did not confirm secular variation in the transit modelling parameters greater than their full correlated errors, as argued by previous authors, when each quarter's data was best-fitted with a determinable parameter set without prejudice. However, if we accept that most of the parameters remain the same for each transit, then we could confirm a small but steady diminution in the cosine of the orbital inclination over the 17 quarter timespan. This is accompanied by a slight increase of the star's precession angle less negative), but with no significant change in the obliquity of its spin axis. There are suggestions of a history of strong dynamical interaction with a highly distorted planet rotating in a 3:2 resonance with its revolution, together with a tidal lag of similar to 30 deg. The mean precessional period is derived to be about 1000 y, but at the present time the motion of the star's rotation axis appears to be supporting the gravitational torque, rather than providing the balance against it that would be expected over long periods of time. The planet has a small but detectable backwarming effect on the star, which helps to explain the difference in brightness just after transit and just before occultation eclipses. In assessing these findings it is recognized that sources of uncertainty remain, notably with possible inherent micropulsational effects, variations from other components of the multiple star, stellar activity, differential rotation and the neglect of higher order terms (than r(1)(5)) in the fitting function, where r(1) is the ratio of the radius of the star to the mean orbital separation of planet and host star.
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    Analysis of the exoplanet containing system Kepler-91
    (Springer, 2016) Budding, E.; Puskullu, C.; Rhodes, M. D.; Demircan, O.; Erdem, A.
    We have applied the graphical user interfaced close binary system analysis program WINFITTER to an intensive study of Kepler-91 using all the available photometry from the NASA Exoplanet Archive (NEA) at the Caltech website: http://exoplanetarchive.ipac.caltech.edu. Our fitting function for the tidal distortion derives from the relevant Radau equation and includes terms up to the fifth power of the fractional radius. This results in a systematic improvement in the mass ratio estimation over that of Lillo-Box et al. (Astron. Astrophys. 562:A109, 2014a) and our derived value for the mass ratio is in close agreement with that inferred from recent high-resolution spectroscopic data. It is clear that the data analysis in terms of simply an eclipsing binary system is compromised by the presence of significant other causes of light variation, in particular non-radial pulsations. We apply a low-frequency filtering procedure to separate out some of this additional light variation. Whilst the derived eccentricity appears then reduced, an eccentric effect remains in the light curve. We consider how this may be maintained in spite of likely frictional effects operating over a long time. There are also indications that could be associated with Trojan or other period-resonant mass concentrations. Suggestions of a possible secular period variation are briefly discussed.
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    Photometric analysis of the system Kepler-1
    (Springer, 2016) Budding, E.; Rhodes, M. D.; Puskullu, C.; Ji, Y.; Erdem, A.; Banks, T.
    We have applied the close binary system analysis program WINFITTER to an intensive study of Kepler-1 (= TrES-2) using all the available photometry (14 quarters; 1570640 measures) from the NASA Exoplanet Archive (NEA) at the Caltech website http://exoplanetarchive.ipac.caltech.edu. The mean individual data-point error of the normalized flux values is 0.00026, leading to the model's specification for the mean reference flux of the system to an accuracy of similar to 0.5 ppm. Completion of the analysis requires a number of prior quantities, relating mainly to the host star, that are adopted from relevant literature. Our new results tend broadly to confirm those of previous authors, though there are a number of significant differences. Specifically, the applied photometric fitting function is more precise than those used before on the full Kepler data-set. The more complete discussion of the interdependent role of errors, using MCMC sampling, allows greater confidence in the obtained parameters themselves as well as understanding or their likely errors. Our photometrically derived values for the mass and radius of Kepler-1b are 1.18 +/- 0.05 M-Jup and 1.21 +/- 0.05 R-Jup. The mass of this Safronov Class I planet is closer to published spectroscopic values than found from previous photometric analysis, which can be attributed to the improved fitting function. The analysis determines a definite photometric Doppler effect from the orbit, but this is not independent of the tidal ('ellipticity') effect, and the two are consistently combined in our fitting function. A corresponding rotation-related Rossiter effect was not detected, allowing an upper limit on the rotation speed of similar to 70 kms(-1). The proportion of light coming from the known companion star is resolved, but turns out rather less than that inferred from the results of direct measurement. The fitting function also predicts a small secondary minimum ('occultation'), when the light reflected by the planet is eclipsed. However, the occultation depth cannot be measured directly from the data to the relevant accuracy, and so models for the planet's atmospheric properties based on this will be compromised by other assumptions and approximations in the light curve's fitting function. Suggestions of secular trends for the variation of parameters are considered, but the evidence of the Kepler data is not yet very persuasive.
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    Transit modelling of selected Kepler systems
    (Springer, 2019) Huang, Q. Y.; Banks, T.; Budding, E.; Puskullu, C.; Rhodes, M. D.
    This paper employs a simple model, considering just geometry and linear or quadratic limb darkening, to fit Kepler transit data via a Markov Chain Monte Carlo (MCMC) methodology for Kepler-1b, 5b, 8b, 12b, 77b, 428b, 491b, 699b, 706b, and 730b. Additional fits were made of the systems using the more sophisticated modeller Winfitter, which gives results in general agreement with the simpler model. Analysis of data with longer integration times showed biasing of the derived parameters, as expected from the literature, leading to larger estimates for radii and reducing estimates of the system inclination.