We investigate directly imaging exoplanets around eclipsing binaries, using the eclipse as a natural tool for dimming the binary and thus increasing the planet to star brightness contrast. At eclipse, the binary becomes point-like, making coronagraphy possible. We select binaries where the planet-star contrast would be boosted by $>10\times$ during eclipse, making it possible to detect a planet that is $\gtrsim10\times$ fainter or in a star system that is $\sim2$-$3\times$ more massive than otherwise. Our approach will yield insights into planet occurrence rates around binaries versus individual stars. We consider both self-luminous (SL) and reflected light (RL) planets. In the SL case, we select binaries whose age is young enough so that an orbiting SL planet would remain luminous; in U Cep and AC Sct, respectively, our method is sensitive to SL planets of $\sim$4.5$M_J$ and $\sim$9$M_J$ with current ground- or near-future space-based instruments, and $\sim$1.5$M_J$ and $\sim$6$M_J$ with future ground-based observatories. In the RL case, there are three nearby ($\lesssim50$ pc) systems -- V1412 Aql, RR Cae, RT Pic -- around which a Jupiter-like planet at a planet-star separation of $\gtrsim20$ mas might be imaged with future ground- and space-based coronagraphs. A Venus-like planet at the same distance might be detectable around RR Cae and RT Pic. A habitable Earth-like planet represents a challenge; while the planet-star contrast at eclipse and planet flux are accessible with a 6-8m space telescope, the planet-star separation is 1/3 - 1/4 of the angular separation limit of modern coronagraphy.
Exoplanet imaging missions utilizing an external occulter (starshade) for starlight suppression require precise alignment between the telescope and starshade, necessitating maintenance of the starshade orbit during observations. Differential lateral acceleration between the two spacecraft serves as a proxy for fuel use and number of required interruptions to the observation. Comparison against results from high fidelity simulations of stationkeeping validates the use of this easy-to-compute proxy. Among starshade positions constrained to the surface of a sphere centered about the telescope, mi…
Starshade in formation flight with a space telescope is a rapidly maturing technology that would enable imaging and spectral characterization of small planets orbiting nearby stars in the not-too-distant future. While performance models of the starshade-assisted exoplanet imaging have been developed and used to design future missions, their results have not been verified from the analyses of synthetic images. Following a rich history of using community data challenges to evaluate image-processing capabilities in astronomy and exoplanet fields, the Starshade Technology Development to TRL5 (S5),…
High-contrast imaging enabled by a starshade in formation flight with a space telescope can provide a near-term pathway to search for and characterize temperate and small planets of nearby stars. NASA's Starshade Technology Development Activity to TRL5 (S5) is rapidly maturing the required technologies to the point at which starshades could be integrated into potential future missions. Here we reappraise the noise budget of starshade-enabled exoplanet imaging to incorporate the experimentally demonstrated optical performance of the starshade and its optical edge. Our analyses of stray light so…
Operating in an unprecedented contrast regime ($10^{-7}$ to $10^{-9}$), the Roman Coronagraph Instrument (CGI) will serve as a pathfinder for key technologies needed for future Earth-finding missions. The Roman Exoplanet Imaging Data Challenge (Roman EIDC) was a community engagement effort that tasked participants with extracting exoplanets and their orbits for a 47 UMa-like target star, given: (1) 15 years of simulated precursor radial velocity (RV) data, and (2) six epochs of simulated imaging taken over the course of the Roman mission. The Roman EIDC simulated images include 4 epochs with C…
The addition of an external starshade to the {\it Nancy Grace Roman Space Telescope} will enable the direct imaging of Earth-radius planets orbiting at $\sim$1 AU. Classification of any detected planets as Earth-like requires both spectroscopy to characterize their atmospheres and multi-epoch imaging to trace their orbits. We consider here the ability of the Starshade Rendezvous Probe to constrain the orbits of directly imaged Earth-like planets. The target list for this proposed mission consists of the 16 nearby stars best suited for direct imaging. The field of regard for a starshade mission…
Launching a starshade to rendezvous with the Nancy Grace Roman Space Telescope would provide the first opportunity to directly image the habitable zones of nearby sunlike stars in the coming decade. A report on the science and feasibility of such a mission was recently submitted to NASA as a probe study concept. The driving objective of the concept is to determine whether Earth-like exoplanets exist in the habitable zones of the nearest sunlike stars and have biosignature gases in their atmospheres. With the sensitivity provided by this telescope, it is possible to measure the brightness of zo…
All water-covered rocky planets in the inner habitable zones of solar-type stars will inevitably experience a catastrophic runaway climate due to increasing stellar luminosity and limits to outgoing infrared radiation from wet greenhouse atmospheres. Reflectors or scatterers placed near Earth's inner Lagrange point (L1) have been proposed as a 'geo-engineering" solution to anthropogenic climate change and an advanced version of this could modulate incident irradiation over many Gyr or "rescue" a planet from the interior of the habitable zone. The distance of the starshade from the planet that …
Very high quality light curves are now available for thousands of detached eclipsing binary stars and transiting exoplanet systems as a result of surveys for transiting exoplanets and other large-scale photometric surveys. I have developed a binary star model (ELLC) that can be used to analyse the light curves of detached eclipsing binary stars and transiting exoplanet systems that is fast and accurate, and that can include the effects of star spots, Doppler boosting and light-travel time within binaries with eccentric orbits. The model represents the stars as triaxial ellipsoids. The apparent…
Future direct imaging missions will primarily observe planets that have been previously detected, mostly via the radial velocity (RV) technique, to characterize planetary atmospheres. In the meantime, direct imaging may discover new planets within existing planetary systems that have bright enough reflected flux, yet with insufficient signals for other methods to detect. Here, we investigate the parameter space within which planets are unlikely to be detected by RV in the near future due to precision limitations, but could be discovered through reflected light with future direct imaging missio…
Three transiting exoplanet candidate stars were discovered in a ground-based photometric survey prior to the launch of NASA's {\it Kepler} mission. {\it Kepler} observations of them were obtained during Quarter 1 of the {\it Kepler} mission. All three stars are faint by radial velocity follow-up standards, so we have examined these candidates with regard to eliminating false positives and providing high confidence exoplanet selection. We present a first attempt to exclude false positives for this set of faint stars without high resolution radial velocity analysis. This method of exoplanet conf…
We report new methods for evaluating realistic observing programs that search stars for planets by direct imaging, where observations are selected from an optimized star list, and where stars can be observed multiple times. We show how these methods bring critical insight into the design of the mission & its instruments. These methods provide an estimate of the outcome of the observing program: the probability distribution of discoveries (detection and/or characterization), & an estimate of the occurrence rate of planets (eta). We show that these parameters can be accurately estimated from a s…
The original {\it Kepler} mission observed and characterized over 2400 eclipsing binaries in addition to its prolific exoplanet detections. Despite the mechanical malfunction and subsequent non-recovery of two reaction wheels used to stabilize the instrument, the {\it Kepler} satellite continues collecting data in its repurposed {\it K2} mission surveying a series of fields along the ecliptic plane. Here we present an analysis of the first full baseline {\it K2} data release: the Campaign 0 data-set. In the 7761 light curves, we have identified a total of 207 eclipsing binaries. Of these, 97 a…
We investigate in this paper the astrophysical false-positive configuration in exoplanet-transit surveys that involves eclipsing binaries and giant planets which present only a secondary eclipse, as seen from the Earth. To test how an eclipsing binary configuration can mimic a planetary transit, we generate synthetic light curve of three examples of secondary-only eclipsing binary systems that we fit with a circular planetary model. Then, to evaluate its occurrence we model a population of binaries in double and triple system based on binary statistics and occurrence. We find that 0.061% +/- 0…
Mass, radius, and age are three of the most fundamental parameters for celestial objects, enabling studies of the evolution and internal physics of stars, brown dwarfs, and planets. Brown dwarfs are hydrogen-rich objects that are unable to sustain core fusion reactions but are supported from collapse by electron degeneracy pressure. As they age, brown dwarfs cool, reducing their radius and luminosity. Young exoplanets follow a similar behaviour. Brown dwarf evolutionary models are relied upon to infer the masses, radii and ages of these objects. Similar models are used to infer the mass and ra…
We present here the first release of the open-source python package ExoTETHyS, which aims to provide a stand-alone set of tools for modeling spectro-photometric observations of the transiting exoplanets. In particular, we describe: (1) a new calculator of stellar limb-darkening coefficients that outperforms the existing software by one order of magnitude in terms of light-curve model accuracy, i.e., down to <10 parts per million (ppm); (2) an exact transit light-curve generator based on the entire stellar intensity profile rather than limb-darkening coefficients. New tools will be added in lat…
We present high-precision light curves of several M- and K-type, active detached eclipsing binaries (DEBs), recorded with 2-minute cadence by the Transiting Exoplanet Survey Satellite (TESS). Analysis of these curves, combined with new and literature radial velocity (RV) data, allows to vastly improve the accuracy and precision of stellar parameters with respect to previous studies of these systems. Results for one previously unpublished DEB are also presented.
For much of human history we have wondered how our solar system formed, and whether there are any other planets like ours around other stars. Only in the last 20 years have we had direct evidence for the existence of exoplanets, with the number of known exoplanets dramatically increasing in recent years, especially with the success of the Kepler mission. Observations of these systems are becoming increasingly more precise and numerous, thus allowing for detailed studies of their masses, radii, densities, temperatures, and atmospheric compositions. However, one cannot accurately study exoplanet…
WFIRST will conduct a coronagraphic program of characterizing the atmospheres of planets around bright nearby stars. When observed with the WFIRST Wide Field Camera, these stars will saturate the detector and produce very strong diffraction spikes. In this paper, we forecast the astrometric precision that WFIRST can achieve by centering on the diffraction spikes of highly saturated stars. This measurement principle is strongly facilitated by the WFIRST H4RG detectors, which confine excess charges within the potential well of saturated pixels. By adopting a simplified analytical model of the di…
The prime Kepler mission detected 34,032 transit-like signals, out of which 8,054 were identified as likely due to astrophysical planet transits or eclipsing binaries. We manually examined 306 of the remaining 25,978 detections, and found six plausible transiting or eclipsing objects, five of which are plausible planet candidates (PCs), and one stellar companion. One of our new PCs is a possible new second planet in the KOI 4302 system. Another new PC is a possible new planet around the KOI 4246, and when combined with a different possible planet rescued by the False Positive Working Group, we…
Although white dwarfs are believed to be the end point of most stellar evolution, unlike main sequence stars, they have not yet been the subject of dedicated time-domain surveys for exoplanets. We discuss how their size and distinctive colour make them excellent targets for wide-field searches for exoplanets. In particular, we note that planets of Earth-size can give rise to multi-magnitude eclipses of massive white dwarfs. Such a large signal is almost unmistakable and would be detectable even with very low-precision photometry. For objects of smaller size, the high accuracy photometry curren…
A 2014 study of the eclipsing binary star 1SWASPJ011351.29+314909.7 (J0113+31) reported an unexpectedly high effective temperature for the M-dwarf companion to the 0.95-M$_{\odot}$ primary star. The effective temperature inferred from the secondary eclipse depth was $\sim$600 K higher than the value predicted from stellar models. Such an anomalous result questions our understanding of low-mass stars and might indicate a significant uncertainty when inferring properties of exoplanets orbiting them. We seek to measure the effective temperature of the M-dwarf companion using the light curve of J0…
Identifying long-period eclipsing binaries with space-based photometry is still a challenge even in the century of space telescopes due to the relatively short observation sequences and short lifetime of these missions. The Transiting Exoplanet Survey Satellite (TESS) space telescope is an appropriate tool to supplement previous space-based observations. In this paper we report the first results of the eclipse timing variation (ETV) analyses of eclipsing binaries (EBs) measured by CoRoT and TESS space telescopes. Among the 1428 EB candidates we found 4 new potential triple candidates, for whic…
In this study we identify 11 Kepler systems (KIC 5255552, 5653126, 5731312, 7670617, 7821010, 8023317, 10268809, 10296163, 11519226, 11558882 and 12356914) with a "flip-flop" effect in the eclipse timing variations O-C diagrams of the systems, report on what these systems have in common and whether these systems are dynamically stable. These systems have previously reported high eccentric binary stars with highly eccentric third bodies/outer companions. We find that all of the additional bodies in the system are dynamically stable for the configurations previously reported and are therefore li…
Context: Few exoplanets around hot stars with radiative envelopes have been discovered, although new observations from the TESS mission are improving this. Stars with radiative envelopes have little mixing at their surface, and thus their surface abundances provide a sensitive test case for a variety of processes including potentially star-planet interactions. Atomic diffusion is particularly important in these envelopes, producing chemically peculiar objects such as Am and HgMn stars. Aims: An exoplanet candidate around the B6 star HD 235349 was identified by TESS. Here we determine the natur…
Evidence from the analysis of eclipsing binary systems revealed that late-type stars are larger and cooler than predicted by models, and that this is probably caused by stellar magnetic activity. In this work, we revisit this problem taking into account the advancements in the last decade. We provide and updated a list of 32 eclipsing binary or multiple systems, including at least one star with a mass $\lesssim 0.7$ M$_{\odot}$ and with mass and radius measured to an accuracy better than 3%. The~comparison with stellar structure and evolution theoretical models reveals an overall discrepancy o…
Circumbinary Planets (CBPs) can be misaligned with their host binary stars. Orbital dynamics, simulations, and recent observations of proto-planetary disks all suggest that the planet can stably orbit in a plane perpendicular to that of an eccentric host binary star (i.e., a polar orbit). No solid claim of detection of such a configuration has been made; the nine systems detected by the transit technique are nearly coplanar, but their discovery is also biased towards that configuration. Here, we develop Eclipse Timing Variations (ETVs) as a method to detect misaligned CBPs. We find that since …
We are using precise radial velocities from CORALIE together with precision photometry from the Next Generation Transit Survey (NGTS) to follow up stars with single-transit events detected with the Transiting Exoplanet Survey Satellite (TESS). As part of this survey we identified a single transit on the star TIC-320687387, a bright (T=11.6) G-dwarf observed by TESS in Sector 13 and 27. From subsequent monitoring of TIC-320687387 with CORALIE, NGTS, and Lesedi we determined that the companion, TIC-320687387 B,is a very low-mass star with a mass of $96.2 \pm _{2.0}^{1.9} M_J$ and radius of $1.14…
In our solar system, the densely cloud-covered atmosphere of Venus stands out as an example of how polarimetry can be used to gain information on cloud composition and particle mean radius. With current interest running high on discovering and characterizing extrasolar planets in the habitable zone where water exists in the liquid state, making use of spectropolarimetric measurements of directly-imaged exoplanets could provide key information unobtainable through other means. In principle, spectropolarimetric measurements can determine if acidity causes water activities in the clouds to be too…
The EBLM project - XX. Absolute dynamical masses of five low-mass eclipsing binaries, and an evaluation of mass estimation methods
University of Birmingham（伯明翰大学）；Thüringer Landessternwarte Tautenburg（图林根州陶滕堡天文台）；Keele University（基尔大学）；Shanghai Jiao Tong University（上海交通大学）；Institut d’astrophysique de Paris（巴黎天体物理研究所）；Université Pierre & Marie Curie（皮埃尔和玛丽·居里大学）；Tufts University（塔夫茨大学）；Uppsala University（乌普萨拉大学）
The TESS Ten Thousand Catalog: 10,001 uniformly-vetted and -validated Eclipsing Binary Stars detected in Full-Frame Image data by machine learning and analyzed by citizen scientists
NASA Goddard Space Flight Center（美国国家航空航天局戈达德空间飞行中心）；SETI Institute（搜寻地外文明计划研究所）；Department of Astronomy, University of Virginia（弗吉尼亚大学天文系）；Department of Astronomy, San Diego State University（圣地亚哥州立大学天文系）；Department of Physics, Kavli Institute for Astrophysics and Space Research, M.I.T.（麻省理工学院物理系、Kavli天体物理与空间研究所）；Department of Computer Science, Princeton University（普林斯顿大学计算机科学系）；Institute of Plant Physiology and Genetics, Bulgaria（保加利亚植物生理与遗传学研究所）
The Transiting Exoplanet Survey Satellite (TESS) is currently concluding its 2-year primary science mission searching 85% of the sky for transiting exoplanets. TESS has already discovered well over one thousand TESS objects of interest (TOIs), but these candidate exoplanets must be distinguished from astrophysical false positives using other instruments or techniques. The 3-band Multi-color Simultaneous Camera for Studying Atmospheres of Transiting Planets (MuSCAT), as well as the 4-band MuSCAT2, can be used to validate TESS discoveries. Transits of exoplanets are achromatic when observed in m…
Tidal forces are important for understanding how close binary stars and compact exoplanetary systems form and evolve. However, tides are difficult to model and significant uncertainties exist about the strength of tides. Here, we investigate tidal circularization in close binaries using a large sample of well-characterised eclipsing systems. We searched TESS photometry from the southern hemisphere for eclipsing binaries. We derive best-fit orbital and stellar parameters by jointly modelling light curves and spectral energy distributions. To determine the eccentricity distribution of eclipsing …
We report results of the first five observing campaigns for the open stellar cluster NGC 7243 in the frame of project Young Exoplanet Transit Initiative (YETI). The project focuses on the monitoring of young and nearby stellar clusters, with the aim to detect young transiting exoplanets, and to study other variability phenomena on time-scales from minutes to years. After five observing campaigns and additional observations during 2013 and 2014, a clear and repeating transit-like signal was detected in the light curve of J221550.6+495611. Furthermore, we detected and analysed 37 new eclipsing b…
We present a new method to assess the properties of transiting planet candidates by multicolor photometry. By analyzing multicolor transit/eclipse light curves and apparent magnitudes of the target in parallel, this method attempts to identify the nature of the system and provide a quantitative constraint on the properties of unresolved companion(s). We demonstrate our method by observing the six systems hosting candidate transiting planets, identified by the K2 mission (EPIC 206036749, EPIC 206500801, EPIC 210513446, EPIC 211800191, EPIC 220621087, and EPIC 220696233). Applying our analysis c…
In this work we keep pushing K2 data to a high photometric precision, close to that of the Kepler main mission, using a PSF-based, neighbour-subtraction technique, which also overcome the dilution effects in crowded environments. We analyse the open cluster M 44 (NGC 2632), observed during the K2 Campaign 5, and extract light curves of stars imaged on module 14, where most of the cluster lies. We present two candidate exoplanets hosted by cluster members and five by field stars. As a by-product of our investigation, we find 1680 eclipsing binaries and variable stars, 1071 of which are new disc…
We apply the ${\tt weirddetector}$, a nonparametric signal detection algorithm based on phase dispersion minimization, in a search for low duty-cycle periodic signals in the Transiting Exoplanet Survey Satellite (${\it TESS}$) photometry. Our approach, in contrast to commonly used model-based approaches specifically for flagging transits, eclipsing binaries, or other similarly periodic events, makes minimal assumptions about the shape of a periodic signal, with the goal of finding "weird" signals of unexpected or arbitrary shape. In total, 248,301 ${\it TESS}$ sources from the first-year South…
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, $I_λ(μ) = 1 - c\left(1-μ^α\right)$, has recently been proposed as a good compromise between complexity and precision in the treatment of limb-darkening. 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 false-positive probability (FPP) of Kepler transiting candidates is a key value for statistical studies of candidate properties. A previous investigation of the stellar population in the Kepler field has provided an estimate for the FPP of less than 5% for most of the candidates. We report here the results of our radial velocity observations on a sample of 46 Kepler candidates with a transit depth greater than 0.4%, orbital period less than 25 days and host star brighter than Kepler magnitude 14.7. We used the SOPHIE spectrograph mounted on the 1.93-m telescope at the Observatoire de Haute…
Dept. of Physics, University of Warwick（华威大学物理系）；Centre for Exoplanets and Habitability, University of Warwick（华威大学系外行星与宜居性中心）
Young exoplanets and their corresponding host stars are fascinating laboratories for constraining the timescale of planetary evolution and planet-star interactions. However, because young stars are typically much more active than the older population, in order to discover more young exoplanets, greater knowledge of the wide array of young star variability is needed. Here Kohonen Self Organising Maps (SOMs) are used to explore young star variability present in the first year of observations from the Transiting Exoplanet Survey Satellite (TESS), with such knowledge valuable to perform targeted d…
We present a solution for the light curve of two bodies mutually transiting a star with polynomial limb darkening. The term "mutual transit" in this work refers to a transit of the star during which overlap occurs between the two transiting bodies. These could be an exoplanet with an exomoon companion, two exoplanets, an eclipsing binary and a planet, or two stars eclipsing a third in a triple star system. We include analytic derivatives of the light curve with respect to the positions and radii of both bodies. We provide code that implements a photodynamical model for a mutual transit. We inc…
We exploit high quality photometry from the EVEREST pipeline to evaluate false-positive exoplanet candidates from the K2 mission. We compare the practical capabilities of EVEREST's pixel-level decorrelation scheme to the data analysis pipelines widely used at the time of these planet candidates' discovery. Removing stellar variability from the EVEREST-corrected light curves, we search for potential secondary eclipses. For each object exhibiting a secondary eclipse, we compare the implied brightness temperature of the planet candidate to its calculated equilibrium temperature. We thereby identi…
The analysis of the wavelength-dependent albedo of exoplanets represents a direct way to provide insight of their atmospheric composition and to constrain theoretical planetary atmosphere modelling. Wavelength-dependent albedo can be inferred from the exoplanet's reflected light of the host star, but this is not a trivial task. In fact, the planetary signal may be several orders of magnitude lower ($10^{-4}$ or below) than the flux of the host star, thus making its extraction very challenging. Successful detection of the planetary signature of 51~Peg\,b has been recently obtained by using cros…
The Transiting Exoplanet Survey Satellite (TESS) has produced a large number of single transit event candidates which are being monitored by the Next Generation Transit Survey (NGTS). We observed a second epoch for the TIC-231005575 system (Tmag = 12.06, Teff = 5500 +- 85 K) with NGTS and a third epoch with Las Cumbres Observatory's (LCO) telescope in South Africa to constrain the orbital period (P = 61.777 d). Subsequent radial velocity measurements with CORALIE revealed the transiting object has a mass of M2 = 0.128 +- 0.003 M$_\odot$, indicating the system is a G-M binary. The radius of the…
