Eclipse Mapping Method Research Articles

JWST-TST DREAMS: Nonuniform Dayside Emission for WASP-17b from MIRI/LRS

We present the first spectroscopic characterization of the dayside atmosphere of WASP-17b in the mid-infrared using a single JWST MIRI/LRS eclipse observation. From forward-model fits to the 5–12 μm emission spectrum, we tightly constrain the heat redistribution factor of WASP-17b to be 0.92 ± 0.02 at the pressures probed by this data, indicative of inefficient global heat redistribution. We also marginally detect a supersolar abundance of water, consistent with previous findings for WASP-17b, but note our weak constraints on this parameter. These results reflect the thermodynamically rich but chemically poor information content of MIRI/LRS emission data for high-temperature hot Jupiters. Using the eclipse mapping method, which utilizes the signals that the spatial emission profile of an exoplanet imprints on the eclipse light curve during ingress/egress due to its partial occultation by the host star, we also construct the first eclipse map of WASP-17b, allowing us to diagnose its multidimensional atmospheric dynamics for the first time. We find a day–night temperature contrast of order 1000 K at the pressures probed by this data, consistent with our derived heat redistribution factor, along with an eastward longitudinal hotspot offset of 18.7−3.8+11.1◦ , indicative of the presence of an equatorial jet induced by day–night thermal forcing being the dominant redistributor of heat from the substellar point. These dynamics are consistent with general circulation model predictions for WASP-17b. This work is part of a series of studies by the JWST Telescope Scientist Team, in which we use Guaranteed Time Observations to perform Deep Reconnaissance of Exoplanet Atmospheres through Multi-instrument Spectroscopy.

Optimizing Photometric Light Curve Analysis: Evaluating Scipy's Minimize Function for Eclipse Mapping of Cataclysmic Variables

With a particular focus on Scipy's minimize function—the eclipse mapping method is thoroughly researched and implemented utilizing Python and essential libraries. Many optimization techniques are used, including Sequential Least Squares Programming (SLSQP), Nelder-Mead, and Conjugate Gradient (CG). However, for the purpose of examining photometric light curves—these methods seek to solve the maximum entropy equation under a chi-squared constraint. Therefore, these techniques are first evaluated on two-dimensional Gaussian data without a chi-squared restriction, and then they are used to map the accretion disc and uncover the Gaussian structure of the Cataclysmic Variable KIC 201325107. Critical analysis is performed on the code structure to find possible faults and design problems. Additionally, the analysis shows how several factors impacting computing time and image quality are included—including the variance in Gaussian weighting, disc image resolution, number of data points in the light curve, and degree of constraint.

The impact of faculae on the radius determination of exoplanets: the case of the M-star GJ 1214

ABSTRACT Precise measurements of exoplanets radii are of key importance for our understanding of the origin and nature of these objects. Measurement of the planet radii using the transit method has reached a precision that the effects of stellar surface features have to be taken into account. While the effects from spots have already been studied in detail, our knowledge of the effects caused by faculae is still limited. This is particularly the case for M-stars. Faculae can pose a problem if they are inhomogeneously distributed on the stellar surface. Using the eclipse mapping method, we study the distribution of the faculae on the surface of GJ 1214 using the Ca ii H&K lines as tracers. In order to assess the homogeneity of the distribution in a quantitative way, we introduce the inhomogeneity factor (IHF). IHF is 0 per cent if the distribution is homogeneous, positive, if the plage regions are preferentially located along the path of the planet, and negative, if they are preferentially located outside the path of the planet. For GJ 1214, we derive a rather small value of $\rm IHF=7.7_{-7.7}^{+12.0}{{\ \rm per\ cent}}$. We discuss the relevance of this result in the context of the PLATO and ARIEL missions.

Eclipse mapping of Algol-type systems with oscillating δ Scuti type components

The oscillating Algol-type (oEA) stars are the former secondaries of evolved, semi-detached eclipsing binaries which are (still) undergoing mass transfer and form a newly detected class of pulsators close to the main sequence. Their unique feature consists of mass accretion onto the atmosphere of the pulsating star. Mass accretion affects the mass, radius, density as well as the star’s evolution. Such stars are therefore very attractive targets for asteroseismic studies. A new tool for mode identification of pulsating components in eclipsing binaries consists in using the event of primary eclipse as a spatial filter to resolve the pulsations across the stellar surface of the pulsator. During an eclipse, depending on the spatial structure of modes represented by the wave numbers (l,m), different shapes of the pulsation amplitude and phase variations can be observed. A comparison between the modelled and the observed amplitudes and phases then provides the correct mode identification. The method needs a geometrical model, the pulsation frequencies and the light curves as input. The geometrical model can be obtained from a simultaneous modelling of the light and radial velocity curves. The pulsation frequencies are obtained from subtracting a binary model from the original light curves followed by a frequency analysis of the residuals. We will identify and illustrate systems where observations with a fast CCD camera equipping the 3.6-m DOT telescope could deliver the data needed for the application of the eclipse mapping method.

The Dynamic Eclipse Mapping method in pulsating binaries

A short description of Dynamic Eclipse Mapping methodology is given. These tools are designed for mapping the surface patterns of non-radial oscillations on eclipsing binary components, using the effective surface sampling of the eclipses. I present two approaches to the problem, an image reconstruction (EM) and a direct model fitting (DF) method, review their capabilities and limitations, then report about the status of their application on real data, with emphasis on the encountered difficulties and caveats.

Photometric mode identification methods of non-radial pulsations in eclipsing binaries - I. Dynamic eclipse mapping

We present the Dynamic Eclipse Mapping (DEM) method designed specifically to reconstruct the surface intensity patterns of non-radial stellar oscillations in eclipsing binaries. The method needs a geometric model of the binary, accepts the light curve and the detected pulsation frequencies on input, and on output yields estimates of the pulsation patterns, in form of images -- thus allowing a direct identification of the surface mode numbers$(\ell,m)$. Since it has minimal modelling requirements and can operate on photometric observations in arbitrary wavelength bands, DEM is well suited to analyze the wide-band time series collected by space observatories. The method was extensively tested on simulated data, in which almost all photometrically detectable modes with a latitudinal complexity $\ell-|m|\le 4$ were properly restored. Multimode pulsations can be also reconstructed in a natural manner, as well as pulsations on components with tilted rotation axis of known direction. It can also be used in principle to isolate the contribution of hidden modes from the light curve. Sensitivity tests show that moderate errors in the geometric parameters and the assumed limb darkening can be partially tolerated by the inversion, in the sense that the lower degree modes are still recoverable. Tidally induced or mutually resonant pulsations, however, are an obstacle that neither the eclipse mapping, nor any other inversion technique can ever surpass. We conclude that, with reasonable assumptions, Dynamic Eclipse Mapping could be a powerful tool for mode identification, especially in moderately close eclipsing binary systems, where the pulsating component is not seriously affected by tidal interactions so that the pulsations are intrinsic to them, and not a consequence of the binarity.

Mapping pulsations on rapidly rotating components of eclipsing binaries

We report on the progress in the development of an eclipse mapping method for reconstruction of non-radial pulsation patterns on components of eclipsing binaries. In this paper we present our attempts to use the method on distorted modes caused by rapid rotation, and we estimate that it can properly detect this phenomenon.

Indirect imaging of an accretion disk rim in the long-period interacting binary W Crucis

Light curves of the long-period Algols are known for their complex shape (asymmetry in the eclipse, light variations outside eclipse, changes from cycle-to-cycle), and their interpretation is not possible in the standard model of binary stars. Complex structures present in these active Algol systems could be studied with the eclipse-mapping method which was successfully applied to the new 7-color photometric observations in the Geneva system of W Cru, belonging to the isolated group of these active Algols. Several cycles of this long-period (198.5 days) eclipsing binary have been covered by observations. We have used a modified Rutten's approach to the eclipse-mapping. The optimization of the system's parameters and the recovery of the disk intensity distribution are performed using a genetic algorithm (GA). It is found that a hot component is hidden in the thick accretion disk which confirms previous findings. The mass of the component, M1 = 8.2 Ms indicates that it is a mid-B type star. The mass-losing component is filling its critical lobe which means it is a G-type supergiant with a mass M2 = 1.6 Ms. The disk is geometrically very extended and its outer radius is about 80% of the primary's critical lobe. A reconstructed image reveals a rather clumpy and nonuniform brightness distribution of an accretion disk rim in this almost edge-on seen system. This clumpyness accounts for light curve distortions and asymmetries, as well as for secular changes.

Indirect Imaging of the Accretion Disk Rim in W Crucis

The eclipsing binary W Crucis belongs to the rare group of strongly interacting binaries, which are believed to be shortly after the first and rapid mass transfer between components, prior to the Algol phase. New 7-colour photometric measurements in the Geneva system are presented for this long period binary. Several consecutive cycles were covered, which revealed rather complex light curves with pronounced bumps and asymmetries in the eclipse shoulders, as well in out-of-eclipse brightness. We modelled light curves with a variant of Rutten’s 3D eclipse-mapping method, which makes it possible to indirectly image the accretion disk rim. A patchy structure has emerged, which explains the rather erratic and complex light curve and its cycle-to-cycle variations.

Flickering Mapping of the Cataclysmic Variables

We report results of simulation to evaluate the ability of the eclipse mapping method to reproduce the spatial distribution of flickering in cataclysmic variables stars.Flickering is a fast intrinsic brightness scintilation occurring on time scales from seconds to minutes with amplitudes of 0.01 - 1 mag. Flickering is observed in all sources believed to be powered by accretion is considered a fundamental signature of accretion. Nevertheless, it is one of the least undestood aspects of the accretion process.

What can we learn from accretion disc eclipse mapping experiments?

AbstractThe accretion disc eclipse mapping method is an astrotomographic inversion technique that makes use of the information contained in eclipse light curves to probe the structure, the spectrum and the time evolution of accretion discs in cataclysmic variables. This paper presents examples of eclipse mapping results that have been key to improve our understanding of accretion physics. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Physical parameter eclipse mapping of the quiescent disc in V2051 Ophiuchi

We analyse simultaneous UBVR quiescent light curves of the cataclysmic variable V2051 Oph using the Physical Parameter Eclipse Mapping (PPEM) method in order to map the gas temperature and surface density of the disc for the first time. The disc appears optically thick in the central regions, and gradually becomes optically thin towards the disc edge or shows a more and more dominating temperature inversion in the disc chromosphere. The gas temperatures in the disc range from about 13 500 K near the white dwarf to about 6000 K at the disc edge. The intermediate part of the disc has temperatures of 9000 to 6500 K. The quiescent disc (chromosphere) shows a prominent bright region with temperatures of 10 500 K around the impact region of the stream from the secondary with an extension towards smaller azimuths. The disc has a size of 0.53±0.03Rℒ1 and a mass accretion rate ℳ˙=1015 to 1017 g s−1. The light curves must include an uneclipsed component, a hot chromosphere and/or a disc wind. The PPEM method allows us to determine a new distance of 146±20 pc, compatible with previous rough estimates. For the white dwarf we then reconstruct a temperature of 19 600 K, if the lower hemisphere of the white dwarf is occulted by the disc. We suggest that the accretion disc is a sandwich of a cool, optically thick central disc with hot chromospheric layers on both sides, as was suggested for HT Cas. This chromosphere is the origin of the emission lines. We find that although V2051 Oph is very similar to the SU UMa-type dwarf novae HT Cas, OY Car and Z Cha, there must be a substantial difference in order to explain its unique light curve. The reason for the difference could be a higher mass transfer rate caused by the more massive secondary, and/or a small but significant magnetic field of the white dwarf, just strong enough to disrupt the innermost disc.

Physical Parameter Mapping of Accretion Disks

AbstractWe present a further development of the classical eclipse mapping method, which reconstructs the spatial distribution of physical parameters in the accretion disks of cataclysmic variables.

Accretion disc mapping

We review two techniques of indirect imaging of accretion discs in cataclysmic variable stars. The light curves of eclipsing systems depend on the distribution of surface brightness over the disc and the eclipse mapping method uses this information to find the continuum surface brightness image of the disc. The shapes of the emission lines from the disc are a function of both orbital phase and velocity. Doppler tomography combines the profiles of an emission line at many orbital phases to image the disc in the light of the line. The two methods are being used to solve problems concerning the physical conditions and the effect of the gas stream upon the disc.

Images of accretion discs - I. The eclipse mapping method

A method of mapping the surface brightness distributions of accretion discs in eclipsing cataclysmic binaries is described and tested with synthetic eclipse data. Accurate synthetic light curves are computed by numerical simulation of the accretion disc eclipse, and images of the disc are reconstructed by maximum entropy methods. The conventional definition of entropy leads to a distorted image of the disc, from which only the locations of compact bright spots are reliably determined. A modified form of entropy, sensitive to the azimuthal structure of the image but not to its radial profile, suppresses azimuthal structure but correctly recovers the radial structure of the accretion disc. This eclipse mapping method permits powerful tests of accretion disc theory by deriving the spatial structure of discs from observational data with a minimum of model-dependent assumptions. Mass transfer rates for eclipsing cataclysmic variables can be measured by this method with an uncertainty of about a factor of two.