scholarly journals High-precision calculation of the light curve and its interpretation

2020 ◽  
Vol 633 ◽  
pp. A96 ◽  
Author(s):  
M. K. Abubekerov ◽  
N. Yu. Gostev
Keyword(s):  
Light Curve ◽  
High Precision ◽  
Binary Star ◽  
Practical Importance ◽  
Light Curves ◽  
Elliptical Orbit ◽  
Nonlinear Fitting ◽  
Precise Calculation ◽  
Adopted Model ◽  
Limb Darkening

We present a highly precise calculation of the theoretical light curve and its derivatives for a binary star-planet system in an elliptical orbit. We also describe an analytical fitting by limb-darkening coefficients to reduce the number of parameters for nonlinear fitting. We demonstrate the practical importance of the precision computation of theoretical light curves through the example of the interpretation of the light curve of HD 209458 and the synthetic light curve. We also compare the results obtained using our algorithm to those provided by a lower-precision algorithm to demonstrate the benefits of computing with a higher precision. We discuss the capability of making more accurate conclusions concerning the agreement of the observed light curve with the adopted model.

scholarly journals Comparison of the power-2 limb-darkening law from the STAGGER-grid to Kepler light curves of transiting exoplanets

2018 ◽  
Vol 616 ◽  
pp. A39 ◽  
Author(s):  
P. F. L. Maxted
Keyword(s):  
Light Curve ◽  
Probability Distributions ◽  
Binary Star ◽  
Magnetic Activity ◽  
Light Curves ◽  
Practical Implementation ◽  
Light Curve Analysis ◽  
Stagger Grid ◽  
Least Squares Fit ◽  
Limb Darkening

Context. Inaccurate limb-darkening models can be a significant source of error in the analysis of the light curves for transiting exoplanet and eclipsing binary star systems, particularly for high-precision light curves at optical wavelengths. The power-2 limb-darkening law, Iλ(µ) = 1 − c(1−µα), has recently been proposed as a good compromise between complexity and precision in the treatment of limb-darkening. Aims. My aim is to develop a practical implementation of the power-2 limb-darkening law and to quantify the accuracy of this implementation. Methods. I have used synthetic spectra based on the 3D stellar atmosphere models from the STAGGER-grid to compute the limb-darkening for several passbands (UBVRI, CHEOPS, TESS, Kepler, etc.). The parameters of the power-2 limb-darkening laws are optimized using a least-squares fit to a simulated light curve computed directly from the tabulated Iλ(μ) values. I use the transformed parameters h1 = 1 − c(1 − 2−α) and h2 = c2−α to directly compare these optimized limb-darkening parameters to the limb darkening measured from Kepler light curves of 16 transiting exoplanet systems. Results. The posterior probability distributions (PPDs) of the transformed parameters h1 and h2 resulting from the light curve analysis are found to be much less strongly correlated than the PPDs for c and α. The agreement between the computed and observed values of (h1, h2) is generally very good but there are significant differences between the observed and computed values for Kepler-17, the only star in the sample that shows significant variability between the eclipses due to magnetic activity (star spots). Conclusions. The tabulation of h1 and h2 provided here can be used to accurately model the light curves of transiting exoplanets. I also provide estimates of the priors that should be applied to transformed parameters h1 and h2 based on my analysis of the Kepler light curves of 16 stars with transiting exoplanets.

scholarly journals First systematic high-precision survey of bright supernovae

2020 ◽  
Vol 643 ◽  
pp. A35
Author(s):  
E. Paraskeva ◽  
A. Z. Bonanos ◽  
A. Liakos ◽  
Z. T. Spetsieri ◽  
J. R. Maund
Keyword(s):  
Light Curve ◽  
High Precision ◽  
Early Stage ◽  
Binary Star ◽  
Light Curves ◽  
Host Galaxies ◽  
Rapid Variability ◽  
Type Ia ◽  
Ia Supernovae ◽  
High Cadence

Rapid variability before and near the maximum brightness of supernovae has the potential to provide a better understanding of nearly every aspect of supernovae, from the physics of the explosion up to their progenitors and the circumstellar environment. Thanks to modern time-domain optical surveys, which are discovering supernovae in the early stage of their evolution, we have the unique opportunity to capture their intraday behavior before maximum. We present high-cadence photometric monitoring (on the order of seconds-minutes) of the optical light curves of three Type Ia and two Type II SNe over several nights before and near maximum light, using the fast imagers available on the 2.3 m Aristarchos telescope at Helmos Observatory and the 1.2 m telescope at Kryoneri Observatory in Greece. We applied differential aperture photometry techniques using optimal apertures and we present reconstructed light curves after implementing a seeing correction and the Trend Filtering Algorithm (TFA, Kovács et al. 2005, MNRAS, 356, 557). TFA yielded the best results, achieving a typical precision between 0.01 and 0.04 mag. We did not detect significant bumps with amplitudes greater than 0.05 mag in any of the SNe targets in the VR-, R-, and I-bands light curves obtained. We measured the intraday slope for each light curve, which ranges between −0.37−0.36 mag day−1 in broadband VR, −0.19−0.31 mag day−1 in R band, and −0.13−0.10 mag day−1 in I band. We used SNe light curve fitting templates for SN 2018gv, SN 2018hgc and SN 2018hhn to photometrically classify the light curves and to calculate the time of maximum. We provide values for the maximum of SN 2018zd after applying a low-order polynomial fit and SN 2018hhn for the first time. We conclude that optimal aperture photometry in combination with TFA provides the highest-precision light curves for SNe that are relatively well separated from the centers of their host galaxies. This work aims to inspire the use of ground-based, high-cadence and high-precision photometry to study SNe with the purpose of revealing clues and properties of the explosion environment of both core-collapse and Type Ia supernovae, the explosion mechanisms, binary star interaction and progenitor channels. We suggest monitoring early supernovae light curves in hotter (bluer) bands with a cadence of hours as a promising way of investigating the post-explosion photometric behavior of the progenitor stars.

scholarly journals The Eclipses of the Close Binary Star BE UMa

1996 ◽  
Vol 158 ◽  
pp. 471-472
Author(s):  
Janet H. Wood ◽  
E. L. Robinson ◽  
E.-H. Zhang
Keyword(s):  
Light Curve ◽  
High Speed ◽  
Binary Star ◽  
Light Curves ◽  
Close Binary ◽  
Primary Star ◽  
Secondary Star ◽  
Different Depths ◽  
The Mean ◽  
Close Binary Star

BE UMa is a close binary star, not transferring mass, with an extremely hot primary star irradiating the inner face of the cool secondary star. The light curve shows a large-amplitude, sinusoidal variation with a period of 2.29 d, and an eclipse that is centered on the minimum of the variation [1], [3]. According to [1], the eclipse is partial, not total. However, it has been argued [2] that the eclipse was really flat bottomed and thus total. This has important repercussions for the deduced model of the system. To resolve this issue we obtained simultaneous UBVR photometry of BE UMa using the Stiening 4-channel, high-speed photometer on the 82-inch telescope at McDonald Observatory. The mean light curves are shown in Fig. 1. The eclipse in all colours is round bottomed and partial. The different depths are caused by the different contribution from the red secondary star in each bandpass.

scholarly journals A Comparison Between Binary Star Light Curves and Those of Possible Binary Asteroids

1984 ◽  
Vol 80 ◽  
pp. 387-392
Author(s):  
H. J. Schober
Keyword(s):  
Light Curve ◽  
Binary Star ◽  
Variable Stars ◽  
Eclipsing Binaries ◽  
Light Curves ◽  
Binary Asteroids ◽  
Binary Nature ◽  
Rotation Rates ◽  
Photoelectric Observations

AbstractSince about ten years coordinated programs of photoelectric observations of asteroids are carried out to derive rotation rates and light curves. Quite a number of those asteroids exhibit features in their light curves, with similar characteristics as variable stars and especially eclipsing binaries. This would allow also an interpretation that there might be an evidence for the binary nature of some asteroids, based on observational hints. A few examples are given and a list of indications for the possible binary nature of asteroids, based on their light curve features, is presented.

scholarly journals Model-free inverse method for transit imaging of stellar surfaces

2019 ◽  
Vol 630 ◽  
pp. A122 ◽  
Author(s):  
Erik Aronson ◽  
Nikolai Piskunov
Keyword(s):  
Light Curve ◽  
Synthetic Data ◽  
Brightness Distribution ◽  
Stellar Atmosphere ◽  
Light Curves ◽  
Stellar Surface ◽  
Model Free ◽  
Very Large Telescope ◽  
Limb Darkening ◽  
Low Dispersion

Context. We present a model-free method for mapping surface brightness variations. Aims. We aim to develop a method that is not dependent on either stellar atmosphere models or limb-darkening equation. This method is optimized for exoplanet transit surveys such that a large database of stellar spot coverage can be created. Methods. The method uses light curves from several transit events of the same system. These light curves are phase-folded and median-combined to for a high-quality light curve without temporal local brightness variations. Stellar specific intensities are extracted from this light curve using a model-free method. We search individual light curves for departures from the median-combined light curve. Such departures are interpreted as brightness variations on the stellar surface. A map of brightness variations on the stellar surface is produced by finding the brightness distribution that can produce a synthetic light curve that fits observations well. No assumptions about the size, shape, or contrast of brightness variations are made. Results. We successfully reproduce maps of stellar disks from both synthetic data and archive observations from FORS2, the visual and near UV FOcal Reducer and low dispersion Spectrograph for the Very Large Telescope (VLT).

scholarly journals Detectability of shape deformation in short-period exoplanets

2019 ◽  
Vol 621 ◽  
pp. A117 ◽  
Author(s):  
B. Akinsanmi ◽  
S. C. C. Barros ◽  
N. C. Santos ◽  
A. C. M. Correia ◽  
P. F. L. Maxted ◽  
...  
Keyword(s):  
Light Curve ◽  
Accurate Determination ◽  
Light Curves ◽  
Shape Deformation ◽  
Love Number ◽  
Tidal Forces ◽  
Tidal Deformation ◽  
Short Period ◽  
Limb Darkening ◽  
Instrumental Precision

Context. Short-period planets are influenced by the extreme tidal forces of their parent stars. These forces deform the planets causing them to attain nonspherical shapes. The nonspherical shapes, modeled here as triaxial ellipsoids, can have an impact on the observed transit light-curves and the parameters derived for these planets. Aims. We investigate the detectability of tidal deformation in short-period planets from their transit light curves and the instrumental precision needed. We also aim to show how detecting planet deformation allows us to obtain an observational estimate of the second fluid Love number from the light curve, which provides valuable information about the internal structure of the planet. Methods. We adopted a model to calculate the shape of a planet due to the external potentials acting on it and used this model to modify the ellc transit tool. We used the modified ellc to generate the transit light curve for a deformed planet. Our model is parameterized by the Love number; therefore, for a given light curve we can derive the value of the Love number that best matches the observations. Results. We simulated the known cases of WASP-103b and WASP-121b which are expected to be highly deformed. Our analyses show that instrumental precision ≤50 ppm min−1 is required to reliably estimate the Love number and detect tidal deformation. This precision can be achieved for WASP-103b in ∼40 transits using the Hubble Space Telescope and in ∼300 transits using the forthcoming CHEOPS instrument. However, fewer transits will be required for short-period planets that may be found around bright stars in the TESS and PLATO survey missions. The unprecedented precisions expected from PLATO and JWST will permit the detection of shape deformation with a single transit observation. However, the effects of instrumental and astrophysical noise must be considered as they can increase the number of transits required to reach the 50 ppm min−1 detection limit. We also show that improper modeling of limb darkening can act to bury signals related to the shape of the planet, thereby leading us to infer sphericity for a deformed planet. Accurate determination of the limb darkening coefficients is therefore required to confirm planet deformation.

scholarly journals Fast and precise light-curve model for transiting exoplanets with rings

2019 ◽  
Vol 490 (1) ◽  
pp. 1111-1119 ◽  
Author(s):  
Edan Rein ◽  
Aviv Ofir
Keyword(s):  
Solar System ◽  
Light Curve ◽  
Source Code ◽  
Light Curves ◽  
Small Range ◽  
Silicate Material ◽  
Computationally Efficient ◽  
Curve Model ◽  
In Transit ◽  
Limb Darkening

ABSTRACT The presence of silicate material in known rings in the Solar system raises the possibility of ring systems existing even within the snow line – where most transiting exoplanets are found. Previous studies have shown that the detection of exoplanetary rings in transit light curves is possible, albeit challenging. To aid such future detection of exoplanetary rings, we present the Polygon + Segments model for modelling the light curve of an exoplanet with rings. This high-precision model includes full ring geometry as well as possible ring transparency and the host star’s limb darkening. It is also computationally efficient, requiring just a 1D integration over a small range, making it faster than existing techniques. The algorithm at its core is further generalized to compute the light curve of any set of convex primitive shapes in transit (e.g. multiple planets, oblate planets, moons, rings, combination thereof, etc.) while accounting for their overlaps. The python source code is made available.

scholarly journals A New Method of Light Curve Analysis: Application to V444 Cygni

1980 ◽  
Vol 88 ◽  
pp. 73-78
Author(s):  
S.A.H. Smith ◽  
A. C. Theokas
Keyword(s):  
Light Curve ◽  
Narrow Band ◽  
Curve Analysis ◽  
Light Curves ◽  
New Method ◽  
Light Curve Analysis ◽  
Arbitrary Degree ◽  
Analysis Application ◽  
Limb Darkening

A new method of light curve analysis is introduced for systems involving an atmospheric eclipse. Occultation or partial eclipses may be treated, with or without the presence of transparency effects. Besides admitting an arbitrary degree of transparency to the eclipsing component, an arbitrary law of limb darkening may also be given the eclipsed star.The method has successfully been applied to the study of narrow band continuum light curves of V444 Cygni obtained by Cherepashchuk and Khaliullin. Primary and secondary minima are examined separately.

The Eclipsing Binary WX Eridani

1979 ◽  
Vol 46 ◽  
pp. 385
Author(s):  
M.B.K. Sarma ◽  
K.D. Abhankar
Keyword(s):  
Light Curve ◽  
Spectral Type ◽  
Orbital Period ◽  
Primary Component ◽  
Light Curves ◽  
Absorption Feature ◽  
Primary Star ◽  
Eclipsing Binary ◽  
The Times ◽  
Phase Angles

AbstractThe Algol-type eclipsing binary WX Eridani was observed on 21 nights on the 48-inch telescope of the Japal-Rangapur Observatory during 1973-75 in B and V colours. An improved period of P = 0.82327038 days was obtained from the analysis of the times of five primary minima. An absorption feature between phase angles 50-80, 100-130, 230-260 and 280-310 was present in the light curves. The analysis of the light curves indicated the eclipses to be grazing with primary to be transit and secondary, an occultation. Elements derived from the solution of the light curve using Russel-Merrill method are given. From comparison of the fractional radii with Roche lobes, it is concluded that none of the components have filled their respective lobes but the primary star seems to be evolving. The spectral type of the primary component was estimated to be F3 and is found to be pulsating with two periods equal to one-fifth and one-sixth of the orbital period.

Sign in / Sign up

Export Citation Format

Share Document