Full Citation: Meadows V. S., Arney G. N., Des Marais D. J., and Schmidt B. E. (2020). Preface. In Planetary…
In the near future, extremely large ground-based telescopes may conduct some of the first searches for life beyond the solar system. High spectral resolution observations of reflected light from nearby exoplanetary atmospheres could be used to search for the biosignature oxygen. However, while Earth’s abundant O2 is photosynthetic, early ocean loss may also produce high atmospheric O2 via water vapor photolysis and subsequent hydrogen escape. To explore how to use spectra to discriminate between these two oxygen sources, we generate high-resolution line-by-line synthetic spectra of both a habitable Earth-like and post-ocean-loss Proxima Centauri b.
Context. GJ 1148 is an M-dwarf star hosting a planetary system composed of two Saturn-mass planets in eccentric orbits with periods of 41.38 and 532.02 days.
Aims. We reanalyze the orbital configuration and dynamics of the GJ 1148 multi-planetary system based on new precise radial velocity measurements taken with CARMENES.
Methods. We combined new and archival precise Doppler measurements from CARMENES with those available from HIRES for GJ 1148 and modeled these data with a self-consistent dynamical model. We studied the orbital dynamics of the system using the secular theory and direct N-body integrations. The prospects of potentially habitable moons around GJ 1148 b were examined.
Results. The refined dynamical analyses show that the GJ 1148 system is long-term stable in a large phase-space of orbital parameters with an orbital configuration suggesting apsidal alignment, but not in any particular high-order mean-motion resonant commensurability. GJ 1148 b orbits inside the optimistic habitable zone (HZ). We find only a narrow stability region around the planet where exomoons can exist. However, in this stable region exomoons exhibit quick orbital decay due to tidal interaction with the planet.
Conclusions. The GJ 1148 planetary system is a very rare M-dwarf planetary system consisting of a pair of gas giants, the inner of which resides in the HZ. We conclude that habitable exomoons around GJ 1148 b are very unlikely to exist.
High-contrast direct imaging of exoplanets can provide many important observables, including measurements of the orbit, spectra that probe the lower layers of the atmosphere, and phase variations of the planet, but cannot directly measure planet radius or mass. Our future understanding of directly imaged exoplanets will therefore rely on extrapolated models of planetary atmospheres and bulk composition, which need robust calibration. We estimate the population of extrasolar planets that could serve as calibrators for these models. Critically, this population of “standard planets” must be accessible to both direct imaging and the transit method, allowing for radius measurement.
Spatially resolving exoplanet features from single-point observations is essential for evaluating the potential habitability of exoplanets. The ultimate goal of this protocol is to determine whether these planetary worlds harbor geological features and/or climate systems. We present a method of extracting information from multi-wavelength single-point light curves and retrieving surface maps. It uses singular value decomposition (SVD) to separate sources that contribute to light curve variations and infer the existence of partially cloudy climate systems. Through analysis of the time series obtained from SVD, physical attributions of principal components (PCs) could be inferred without assumptions of any spectral properties. Combining with viewing geometry, it is feasible to reconstruct surface maps if one of the PCs are found to contain surface information. Degeneracy originated from convolution of the pixel geometry and spectrum information determines the quality of reconstructed surface maps, which requires the introduction of regularization. For the purpose of demonstrating the protocol, multi-wavelength light curves of Earth, which serves as a proxy exoplanet, are analyzed. Comparison between the results and the ground truth is presented to show the performance and limitation of the protocol. This work provides a benchmark for future generalization of exoplanet applications
The search for spectroscopic biosignatures with the next generation of space telescopes could provide observational constraints on the abundance of exoplanets with signs of life. An extension of this spectroscopic characterization of exoplanets is the search for observational evidence of technology, known as technosignatures. Current mission concepts that would observe biosignatures from ultraviolet to near-infrared wavelengths could place upper limits on the fraction of planets in the Galaxy that host life, although such missions tend to have relatively limited capabilities of constraining the prevalence of technosignatures at mid-infrared wavelengths. Yet searching for technosignatures alongside biosignatures would provide important knowledge about the future of our civilization. If planets with technosignatures are abundant, then we can increase our confidence that the hardest step in planetary evolutionthe Great Filteris probably in our past. But if we find that life is commonplace while technosignatures are absent, then this would increase the likelihood that the Great Filter awaits to challenge us in the future.
Robust atmospheric and radiative transfer modeling will be required to properly interpret reflected-light and thermal emission spectra of terrestrial exoplanets. This will help break observational degeneracies between the numerous atmospheric, planetary, and stellar factors that drive planetary climate. Here, we simulate the climates of earthlike worlds around the Sun with increasingly slow rotation periods, from earthlike to fully Sun-synchronous, using the ROCKE-3D general circulation model. We then provide these results as input to the Spectral Planet Model, which employs the Spectral Mapping Atmospheric Radiative Transfer model to simulate the spectra of a planet as it would be observed from a future space-based telescope. We find that the primary observable effects of slowing planetary rotation rate are the altered cloud distributions, altitudes, and opacities that subsequently drive many changes to the spectra by altering the absorption band depths of biologically relevant gas species (e.g., ${{rm{H}}}_{2}{rm{O}}$, ${{rm{O}}}_{2}$, and ${{rm{O}}}_{3}$). We also identify a potentially diagnostic feature of synchronously rotating worlds in mid-infrared ${{rm{H}}}_{2}{rm{O}}$ absorption/emission lines.
One of the main science motivations for the ESA PLAnetary Transit and Oscillations (PLATO) mission is to measure exoplanet transit radii with 3 per cent precision. In addition to flares and starspots, stellar oscillations and granulation will enforce fundamental noise floors for transiting exoplanet radius measurements. We simulate light curves of Earth-sized exoplanets transiting continuum intensity images of the Sun taken by the Helioseismic and Magnetic Imager (HMI) instrument aboard the Solar Dynamics Observatory (SDO) to investigate the uncertainties introduced on the exoplanet radius measurements by stellar granulation and oscillations. After modelling the solar variability with a Gaussian process, we find that the amplitude of solar oscillations and granulation is of order 100 ppm similar to the depth of an Earth transit and introduces a fractional uncertainty on the depth of transit of 0.73 per cent assuming four transits are observed over the mission duration. However, when we translate the depth measurement into a radius measurement of the planet, we find a much larger radius uncertainty of 3.6 per cent. This is due to a degeneracy between the transit radius ratio, the limb darkening, and the impact parameter caused by the inability to constrain the transit impact parameter in the presence of stellar variability. We find that surface brightness inhomogeneity due to photospheric granulation contributes a lower limit of only 2 ppm to the photometry in-transit. The radius uncertainty due to granulation and oscillations, combined with the degeneracy with the transit impact parameter, accounts for a significant fraction of the error budget of the PLATO mission, before detector or observational noise is introduced to the light curve. If it is possible to constrain the impact parameter or to obtain follow-up observations at longer wavelengths where limb darkening is less significant, this may enable higher precision radius measurements.
The search for water-rich Earth-sized exoplanets around low-mass stars is rapidly gaining attention because they represent the best opportunity to characterize habitable planets in the near future. Understanding the atmospheres of these planets and determining the optimal strategy for characterizing them through transmission spectroscopy with our upcoming instrumentation is essential in order to constrain their environments. For this study, we present simulated transmission spectra of tidally locked Earth-sized ocean-covered planets around late-M to mid-K stellar spectral types, utilizing the results of general circulation models previously published by Kopparapu et al. as inputs for our radiative transfer calculations performed using NASA’s Planetary Spectrum Generator (psg.gsfc.nasa.gov). We identify trends in the depth of H2O spectral features as a function of planet surface temperature and rotation rate. These trends allow us to calculate the exposure times necessary to detect water vapor in the atmospheres of aquaplanets through transmission spectroscopy with the upcoming James Webb Space Telescope as well as several future flagship space telescope concepts under consideration (the Large UV Optical Infrared Surveyor and the Origins Space Telescope) for a target list constructed from the Transiting Exoplanet Survey Satellite (TESS) Input Catalog (TIC). Our calculations reveal that transmission spectra for water-rich Earth-sized planets around low-mass stars will be dominated by clouds, with spectral features <20 ppm, and only a small subset of TIC stars would allow for the characterization of an ocean planet in the habitable zone. We thus present a careful prioritization of targets that are most amenable to follow-up characterizations with next-generation instrumentation, in order to assist the community in efficiently utilizing precious telescope time.
Hyperspectral observations have become one of the most popular and powerful methods for atmospheric remote sensing, and are widely used for temperature, gas, aerosol, and cloud retrievals. However, accurate forward radiative transfer simulations are computationally expensive since typical line-by-line approaches involve a large number of monochromatic radiative transfer calculations. This study explores the feasibility of machine learning techniques (using neural network (NN) as an example) for fast hyperspectral radiative transfer simulations, by performing calculations at a small fraction of hyperspectral wavelengths and extending them across the entire spectral range. Results from the NN model are compared with those from a principal component analysis (PCA) model, which uses a similar principle of dimensionality reduction. We consider hyperspectral radiances from both actual satellite observations and accurate line-by-line simulations. The NN model can alleviate the computational burden by two to three orders of magnitude, and generate radiances with small relative errors (generally less than 0.5% compared to exact calculations); the performance of the NN model is better than that of the PCA model. The model can be further improved by optimizing the training procedure and parameters, the representative wavelengths, and the machine learning technique itself.
VPL graduate student at the University of Washington, Andrew Lincowski, successfully defended his dissertation on Thursday February 27th! Andrew was…
We derive analytic, closed-form solutions for the light curve of a planet transiting a star with a limb-darkening profile that is a polynomial function of the stellar elevation, up to an arbitrary integer order. We provide improved analytic expressions for the uniform, linear, and quadratic limb-darkened cases, as well as novel expressions for higher-order integer powers of limb darkening. The formulae are crafted to be numerically stable over the expected range of usage. We additionally present analytic formulae for the partial derivatives of instantaneous flux with respect to the radius ratio, impact parameter, and limb-darkening coefficients. These expressions are rapid to evaluate and compare quite favorably in speed and accuracy to existing transit light-curve codes. We also use these expressions to numerically compute the first partial derivatives of exposure-time-averaged transit light curves with respect to all model parameters. An additional application is modeling eclipsing binary or eclipsing multiple star systems in cases where the stars may be treated as spherically symmetric. We provide code which implements these formulae in C++, Python, IDL, and Julia, with tests and examples of usage (https://github.com/rodluger/Limbdark.jl).
The upcoming launch of the James Webb Space Telescope (JWST) combined with the unique features of the TRAPPIST-1 planetary system should enable the young field of exoplanetology to enter into the realm of temperate Earth-sized worlds. Indeed, the proximity of the system (12pc) and the small size (0.12 Rsun) and luminosity (0.05 Lsun) of its host star should make the comparative atmospheric characterization of its seven transiting planets within reach of an ambitious JWST program. Given the limited lifetime of JWST, the ecliptic location of the star that limits its visibility to 100d per year, the large number of observational time required by this study, and the numerous observational and theoretical challenges awaiting it, its full success will critically depend on a large level of coordination between the involved teams and on the support of a large community. In this context, we present here a community initiative aiming to develop a well-defined sequential structure for the study of the system with JWST and to coordinate on every aspect of its preparation and implementation, both on the observational (e.g. study of the instrumental limitations, data analysis techniques, complementary space-based and ground-based observations) and theoretical levels (e.g. model developments and comparison, retrieval techniques, inferences). Depending on the outcome of the first phase of JWST observations of the planets, this initiative could become the seed of a major JWST Legacy Program devoted to the study of TRAPPIST-1.
We are on the verge of characterizing the atmospheres of terrestrial exoplanets in the habitable zones of M dwarf stars. Due to their large planet-to-star radius ratios and higher frequency of transits, terrestrial exoplanets orbiting M dwarf stars are favorable for transmission spectroscopy. In this work, we quantify the effect that water clouds have on the amplitude of water vapor transmission spectral features of terrestrial exoplanets orbiting M dwarf stars. To do so, we make synthetic transmission spectra from general circulation model (GCM) experiments of tidally locked planets. We improve upon previous work by considering how varying a broad range of planetary parameters affects transmission spectra. We find that clouds lead to a 10100 times increase in the number of transits required to detect water features with the James Webb Space Telescope (JWST) with varying rotation period, incident stellar flux, surface pressure, planetary radius, and surface gravity. We also find that there is a strong increase in the dayside cloud coverage in our GCM simulations with rotation periods gsim12 days for planets with Earth’s radius. This increase in cloud coverage leads to even stronger muting of spectral features for slowly rotating exoplanets orbiting M dwarf stars. We predict that it will be extremely challenging to detect water transmission features in the atmospheres of terrestrial exoplanets in the habitable zone of M dwarf stars with JWST. However, species that are well-mixed above the cloud deck (e.g., CO2 and CH4) may still be detectable on these planets with JWST.
The characterization of rocky, Earth-like planets is an important goal for future large ground- and space-based telescopes. In support of developing an efficient observational strategy, we have applied Bayesian statistical inference to interpret the albedo spectrum of cloudy true-Earth analogs that include a diverse spread in their atmospheric water vapor mixing ratios. We focus on detecting water-bearing worlds by characterizing their atmospheric water vapor content via the strong 0.94 ?m H2O absorption feature, with several observational configurations. Water vapor is an essential signpost when assessing planetary habitability, and determining its presence is important in vetting whether planets are suitable for hosting life. We find that R = 140 spectroscopy of the absorption feature combined with a same-phase green-optical photometric point at 0.5250.575 ?m is capable of distinguishing worlds with less than 0.1× Earth-like water vapor levels from worlds with 1× Earth-like levels or greater at a signal-to-noise ratio of 5 or better with 2? confidence. This configuration can differentiate between 0.01× and 0.1× Earth-like levels when the signal-to-noise ratio is 10 or better at the same confidence. However, strong constraints on the water vapor mixing ratio remained elusive with this configuration even at a signal-to-noise of 15. We find that adding the same-phase optical photometric point does not significantly help characterize the H2O mixing ratio, but does enable an upper limit on atmospheric ozone levels. Finally, we find that a 0.94 ?m photometric point, instead of spectroscopy, combined with the green-optical point, fails to produce meaningful information about atmospheric water content.
Graduate Student Jacob Lustig-Yaeger (University of Washington) presented an invited talk on “The Era of Terrestrial Exoplanet Characterization” at the…
The TRAPPIST-1 system, consisting of an ultracool host star having seven known Earth-sized planets, will be a prime target for atmospheric characterization with the James Webb Space Telescope (JWST). However, the detectability of atmospheric molecular species may be severely impacted by the presence of clouds and/or hazes. In this work, we perform 3D general circulation model (GCM) simulations with the LMD-G model supplemented by 1D photochemistry simulations at the terminator with the Atmos model to simulate several possible atmospheres for TRAPPIST-1e, 1f, and 1g: (1) modern Earth, (2) Archean Earth, and (3) CO2-rich atmospheres. The JWST synthetic transit spectra were computed using the GSFC Planetary Spectrum Generator. We find that the TRAPPIST-1e, 1f, and 1g atmospheres, with clouds and/or hazes, could be detected using JWST’s NIRSpec Prism from the CO2 absorption line at 4.3 ?m in less than 15 transits at 3? or less than 35 transits at 5?. However, our analysis suggests that other gases would require hundreds (or thousands) of transits to be detectable. We also find that H2O, mostly confined in the lower atmosphere, is very challenging to detect for these planets or similar systems if the planets’ atmospheres are not in a moist greenhouse state. This result demonstrates that the use of GCMs, self-consistently taking into account the effect of clouds and subsaturation, is crucial to evaluate the detectability of atmospheric molecules of interest, as well as for interpreting future detections in a more global (and thus robust and relevant) approach.
? Centauri A is the closest solar-type star to the Sun and offers an excellent opportunity to detect the thermal emission of a mature planet heated by its host star. The MIRI coronagraph on the James Webb Space Telescope can search the 13 au (1”2”) region around ? Cen A which is predicted to be stable within the ? Cen AB system. We demonstrate that with reasonable performance of the telescope and instrument, a 20 hr program combining on-target and reference star observations at 15.5 ?m could detect thermal emission from planets as small as ~5 R?. Multiple visits every 36 months would increase the geometrical completeness, provide astrometric confirmation of detected sources, and push the radius limit down to ~3 R?. An exozodiacal cloud only a few times brighter than our own should also be detectable, although a sufficiently bright cloud might obscure any planet present in the system. While current precision radial velocity (PRV) observations set a limit of 50100 M? at 13 au for planets orbiting ? Cen A, there is a broad range of exoplanet radii up to 10 R? consistent with these mass limits. A carefully planned observing sequence along with state-of-the-art post-processing analysis could reject the light from ? Cen A at the level of ~10?5 at 1”2” and minimize the influence of ? Cen B located 7”8” away in the 20222023 timeframe. These space-based observations would complement on-going imaging experiments at shorter wavelengths as well as PRV and astrometric experiments to detect planets dynamically. Planetary demographics suggest that the likelihood of directly imaging a planet whose mass and orbit are consistent with present PRV limits is small, ~5%, and possibly lower if the presence of a binary companion further reduces occurrence rates. However, at a distance of just 1.34 pc, ? Cen A is our closest sibling star and certainly merits close scrutiny.
The Large UV/Optical/Infrared Surveyor (LUVOIR) mission is one of four Decadal Survey Mission Concepts studied by NASA in preparation for the US National Academies’ Astro2020 Decadal Survey. This observatory has the major goal of characterizing a wide range of exoplanets, including those that might be habitable — or even inhabited. It would simultaneously enable a great leap forward in a broad range of astrophysics — from the epoch of reionization, through galaxy formation and evolution, to star and planet formation. Powerful remote sensing observations of Solar System bodies will also be possible. This Final Report on the LUVOIR study presents the scientific motivations and goals of the mission concept, the engineering design, and technology development information. Please refer to the LUVOIR Final Report Appendices (separate document) for additional information.
Near-term studies of Venus-like atmospheres with James Webb Space Telescope (JWST) promise to advance our knowledge of terrestrial planet evolution. However, the remote study of Venus in the solar system and the ongoing efforts to characterize gaseous exoplanets both suggest that high altitude aerosols can limit observational studies of lower atmospheres, and potentially make it challenging to recognize exoplanets as “Venus-like.” To support practical approaches for exo-Venus characterization with JWST, we use Venus-like atmospheric models with self-consistent cloud formation of the seven TRAPPIST-1 exoplanets to investigate the atmospheric depth that can be probed using both transmission and emission spectroscopy. We find that JWST/Mid-IR Instrument Low Resolution Spectrometer secondary eclipse emission spectroscopy in the 6 ?m opacity window could probe at least an order of magnitude deeper pressures than transmission spectroscopy, potentially allowing access to the subcloud atmosphere for the two hot innermost TRAPPIST-1 planets. In addition, we identify two confounding effects of sulfuric acid aerosols that may carry strong implications for the characterization of terrestrial exoplanets with transmission spectroscopy: (1) there exists an ambiguity between cloud-top and solid surface in producing the observed spectral continuum; and (2) the cloud-forming region drops in altitude with semimajor axis, causing an increase in the observable cloud-top pressure with decreasing stellar insolation. Taken together, these effects could produce a trend of thicker atmospheres observed at lower stellar insolationa convincing false positive for atmospheric escape and an empirical “cosmic shoreline.” However, developing observational and theoretical techniques to identify Venus-like exoplanets and discriminate them from stellar windswept worlds will enable advances in the emerging field of terrestrial comparative planetology.
To investigate water vapor detection for exoplanets, we generated reflectance spectra over a grid of water vapor column masses (given by the integral of a species’ mass density over the atmospheric column, yielding the mass of that species per unit area). As the depth of a gas spectral feature is, to a large degree, controlled by the absorption optical depth across the feature, varying the column mass is akin to varying feature strength. Our column mass grid spans 10?5101?g?cm?2, where the total gas and water vapor column masses for Earth are 1.0 × 103 g?cm?2 and 3?g?cm?2, respectively. We adopt 1 bar of total atmospheric pressure, assume molecular nitrogen is the background atmospheric gas, use an Earth-like surface gravity of 10?m?s?2, and assume a gray surface albedo of 0.3. Our calculations generally apply to scenarios where the water vapor column is measured above some opaque “surface” (e.g., a solid surface or planet-wide cloud deck). Quadrature-phase spectra were modeled with the widely used Spectral Mapping Atmospheric Radiative Transfer (SMART) model (developed by D.?Crisp; Meadows & Crisp 1996), which is a line-by-line, multiple-scattering radiative transfer tool.
Planets residing in circumstellar habitable zones offer us the best opportunities to test hypotheses of life’s potential pervasiveness and complexity. Constraining the precise boundaries of habitability and its observational discriminants is critical to maximizing our chances at remote life detection with future instruments. Conventionally, calculations of the inner edge of the habitable zone (IHZ) have been performed using both 1D radiative-convective and 3D general circulation models. However, these models lack interactive 3D chemistry and do not resolve the mesosphere and lower thermosphere region of the upper atmosphere. Here, we employ a 3D high-top chemistry-climate model (CCM) to simulate the atmospheres of synchronously rotating planets orbiting at the inner edge of habitable zones of K- and M-dwarf stars (between T eff = 2600 and 4000 K). While our IHZ climate predictions are in good agreement with general circulation model studies, we find noteworthy departures in simulated ozone and HOx photochemistry. For instance, climates around inactive stars do not typically enter the classical moist greenhouse regime even with high (gsim10?3 mol mol?1) stratospheric water vapor mixing ratios, which suggests that planets around inactive M-stars may only experience minor water-loss over geologically significant timescales. In addition, we find much thinner ozone layers on potentially habitable moist greenhouse atmospheres, as ozone experiences rapid destruction via reaction with hydrogen oxide radicals. Using our CCM results as inputs, our simulated transmission spectra show that both water vapor and ozone features could be detectable by instruments NIRSpec and MIRI LRS on board the James Webb Space Telescope.
Habitability is a measure of an environment’s potential to support life, and a habitable exoplanet supports liquid water on its surface. However, a planet’s success in maintaining liquid water on its surface is the end result of a complex set of interactions between planetary, stellar, planetary system and even Galactic characteristics and processes, operating over the planet’s lifetime. In this chapter, we describe how we can now determine which exoplanets are most likely to be terrestrial, and the research needed to help define the habitable zone under different assumptions and planetary conditions. We then move beyond the habitable zone concept to explore a new framework that looks at far more characteristics and processes, and provide a comprehensive survey of their impacts on a planet’s ability to acquire and maintain habitability over time. We are now entering an exciting era of terrestiral exoplanet atmospheric characterization, where initial observations to characterize planetary composition and constrain atmospheres is already underway, with more powerful observing capabilities planned for the near and far future. Understanding the processes that affect the habitability of a planet will guide us in discovering habitable, and potentially inhabited, planets.
To date a dozen transiting Tatooines or circumbinary planets (CBPs) have been discovered, by eye, in the data from the Kepler mission; by contrast, thousands of confirmed circumstellar planets orbiting around single stars have been detected using automated algorithms. Automated detection of CBPs is challenging because their transits are strongly aperiodic with irregular profiles. Here, we describe an efficient and automated technique for detecting circumbinary planets that transit their binary hosts in Kepler light curves. Our method accounts for large transit timing variations (TTVs) and transit duration variations (TDVs), induced by binary reflex motion, in two ways: (1) We directly correct for large-scale TTVs and TDVs in the light curves by using Keplerian models to approximate binary and CBP orbits; and (2) We allow additional aperiodicities on the corrected light curves by employing the Quasi-periodic Automated Transit Search algorithm. We demonstrate that our method dramatically improves detection significance using simulated data and two previously identified CBP systems, Kepler-35 and Kepler-64.
We implement a search for exoplanets in campaigns zero through eight (C08) of the K2 extension of the Kepler spacecraft. We apply a modified version of the QATS planet search algorithm to K2 light curves produced by the EVEREST pipeline, carrying out the C08 search on 1.5 × 105 target stars with magnitudes in the range of Kp = 9?15. We detect 818 transiting planet candidates, of which 374 were undiscovered by prior searches, with {64, 15, 5, 2, 1} in {2, 3, 4, 5, 6}-planet multiplanet candidate systems, respectively. Of the new planets detected, 100 orbit M dwarfs, including one that is potentially rocky and in the habitable zone. A total of 154 of our candidates reciprocally transit with our solar system: they are geometrically aligned to see at least one solar system planet transit. We find candidates that display transit timing variations and dozens of candidates on both period extremes with single transits or ultrashort periods. We point to evidence that our candidates display similar patterns in frequency and sizeperiod relation to confirmed planets, such as tentative evidence for the radius gap. Confirmation of these planet candidates with follow-up studies will increase the number of K2 planets by up to 50%, and characterization of their host stars will improve statistical studies of planet properties. Our sample includes many planets orbiting bright stars amenable for radial velocity follow-up and future characterization with JWST. We also list the 579 eclipsing binary systems detected as part of this search.