We set out a simulation to explore the follow-up of exoplanet candidates. We look at comparing photometric (transit method) and spectroscopic (Doppler shift method) techniques using three instruments: NGTS, HARPS and CORALIE. We take into account precision of follow-up and required observing time in attempt to rank each method for a given set of planetary system parameters. The methods are assessed on two criteria, SNR of the detection and follow-up time before characterisation. We find that different follow-up techniques are preferred for different regions of parameter space. For SNR we find that the ratio of spectroscopic to photometric SNR for a given system goes like $R_p/P^{\frac{1}{3}}$. For follow-up time we find that photometry is favoured for the shortest period systems ($<10$ d) as well as systems with small planet radii. Spectroscopy is then preferred for systems with larger radius, and thus more massive, planets (given our assumed mass-radius relationship). Finally, we attempt to account for availability of telescopes and weight the two methods accordingly.
Photometric stability is a key requirement for time-resolved spectroscopic observations of transiting extrasolar planets. In the context of the Exoplanet Characterisation Observatory (EChO) mission design, we here present and investigate means of translating spacecraft pointing instabilities as well as temperature fluctuation of its optical chain into an overall error budget of the exoplanetary spectrum to be retrieved. Given the instrument specifications as of date, we investigate the magnitudes of these photometric instabilities in the context of simulated observations of the exoplanet HD189…
The Characterising Exoplanet Satellite (CHEOPS) is a space mission designed to perform photometric observations of bright stars to obtain precise radii measurements of transiting planets. The high-precision photometry of CHEOPS relies on careful on-ground calibration of its payload. For that purpose, intensive pre-launch campaigns of measurements were carried out to calibrate the instrument and characterise its photometric performances. We report on main results of these campaigns, provide a complete analysis of data sets and estimate in-flight photometric performance by mean of end-to-end sim…
In anticipation of future flagship missions focused on the goal of achieving direct imaging of rocky exoplanets, we have developed a database of models to help the community examine the potential spectral characteristics of a broad range of rocky planet atmospheres. Using the publicly available Planetary Spectrum Generator (PSG), we have computed a grid of 141,600 rocky exoplanet geometric albedo spectra across a 7-dimensional parameter space. Using this grid, we have performed a color-color analysis seeking to identify the most useful near-ultraviolet and red or near-infrared photometric foll…
We demonstrate the newly developed resource for exoplanet researchers - The Exoplanet Transit Database. This database is designed to be a web application and it is open for any exoplanet observer. It came on-line in September 2008. The ETD consists of three individual sections. One serves for predictions of the transits, the second one for processing and uploading new data from the observers. We use a simple analytical model of the transit to calculate the central time of transit, its duration and the depth of the transit. These values are then plotted into the observed - computed diagrams (O-…
The direct detection of exoplanets has been the subject of intensive research in the recent years. Data obtained with future high-contrast imaging instruments optimized for giant planets direct detection are strongly limited by the speckle noise. Specific observing strategies and data analysis methods, such as angular and spectral differential imaging, are required to attenuate the noise level and possibly detect the faint planet flux. Even though these methods are very efficient at suppressing the speckles, the photometry of the faint planets is dominated by the speckle residuals. The determi…
Scientific Validation of the SPARC4 Pipeline: Multi-band Imaging, Polarimetry, and Photometric Time Series for Improved Characterization of Transiting Exoplanets
Laboratório Nacional de Astrofísica（国家天体物理实验室）；Instituto Nacional de Pesquisas Espaciais（国家空间研究所）；Centro Federal de Educação Tecnológica Celso Suckow da Fonseca（塞尔索·苏科瓦·达丰塞卡联邦技术教育中心）
Spectrophotometric stability, which is crucial in the spectral characterization of transiting exoplanets, is affected by photometric variations arising from field-stop loss in space telescopes with pointing jitter or primary mirror deformation. This paper focuses on a new method for removing slit-loss or field-stop-loss photometric variation through the use of a pupil mask. Two types of pupil function are introduced: the first uses conventional (e.g., Gaussian or hyper-Gaussian) apodizing patterns; whereas the second, which we call a block-shaped mask, employs a new type of pupil mask designed…
Context: The space telescope Gaia is dedicated mainly to performing high-precision astrometry, but also spectroscopy and epoch photometry which can be used to study various types of photometric variability. One such variability type is exoplanetary transits. The photometric data accumulated so far have finally matured enough to allow the detection of some exoplanets. Aims: In order to fully exploit the scientific potential of Gaia, we search its photometric data for the signatures of exoplanetary transits. Methods: The search relies on a version of the Box-Least-Square (BLS) method, applied to…
The status of laboratory spectroscopic data for exoplanet characterisation missions such as EChO is reviewed. For many molecules (eg H2O, CO, CO2, H3+, O2, O3) the data are already available. For the other species work is actively in progress constructing this data. Much of the is work is being undertaken by ExoMol project (www.exomol.com). This information will be used to construct and EChO-specific spectroscopic database.
We propose the application of coronagraphic techniques to the spectroscopic direct detection of exoplanets via the Doppler shift of planetary molecular lines. Even for an unresolved close-in planetary system, we show that the combination of a visible nuller and an extreme adaptive optics system can reduce the photon noise of a main star and increase the total signal-to-noise ratio (S/N) of the molecular absorption of the exoplanetary atmosphere: it works as a spectroscopic coronagraph. Assuming a 30 m telescope, we demonstrate the benefit of these high-contrast instruments for nearby close-in …
We present an analysis of high-resolution imaging of an exoplanet by a meter-class telescope positioned at a real image of the exoplanet created by the solar gravity lens. We assume an exoplanet viewed in full phase and a simple deconvolution method to correct for the intrinsic blur caused by aberrations in the solar gravity lens, and account for the foreground light of the solar corona. We derive equations for the measurement times required for the telescope to produce such a high-resolution image, and find that due to shot noise considerations these times are large compared to human lifespan…
We propose a novel approach to utilize low-cadence photometric surveys for exoplanetary transit search. Even if transits are undetectable in the survey database alone, it can still be useful for finding preferred times for directed follow-up observations that will maximize the chances to detect transits. We demonstrate the approach through a few simulated cases. These simulations are based on the Hipparcos Epoch Photometry data base, and the transiting planets whose transits were already detected there. In principle, the approach we propose will be suitable for the directed follow-up of the ph…
Prioritizing High-Precision Photometric Monitoring of Exoplanet and Brown Dwarf Companions with JWST -- Strategic Exoplanet Initiatives with HST and JWST White Paper
The fine precision of photometric data available from missions like Kepler provide researchers with the ability to measure changes in light on the order of tens of parts per million (ppm). This level of precision allows researchers to measure the loss of light due to exoplanet transits as well as the light emitted by an exoplanet, or planetary photometric emissions. The planetary photometric emissions are due to the thermal emissions of the exoplanet, and reflected stellar light. In many cases it is assumed that the incident stellar light may be modeled as plane parallel rays. For extremely cl…
Determining wavelength-dependent exoplanet radii measurements is an excellent way to probe the composition of exoplanet atmospheres. In light of this, Borsa et al. (2016) sought to develop a technique to obtain such measurements by comparing ground-based transmission spectra to the expected brightness variations during an exoplanet transit. However, we demonstrate herein that this is not possible due to the transit light curve normalisation necessary to remove the effects of the Earth's atmosphere on the ground-based observations. This is because the recoverable exoplanet radius is set by the …
To ensure robust constraints are placed on exoplanet atmospheric transmission spectra, future observations need to obtain high signal-to-noise ratio (SNR) measurements assuming smaller amplitude molecular signatures than those of clear solar metallicity atmospheres. Analyzing 37 exoplanet transmission spectra we find clear solar molecular features are measured in <7% of cases.
EXONEST is an algorithm dedicated to detecting and characterizing the photometric signatures of exoplanets, which include reflection and thermal emission, Doppler boosting, and ellipsoidal variations. Using Bayesian Inference, we can test between competing models that describe the data as well as estimate model parameters. We demonstrate this approach by testing circular versus eccentric planetary orbital models, as well as testing for the presence or absence of four photometric effects. In addition to using Bayesian Model Selection, a unique aspect of EXONEST is the capability to distinguish …
We present improved physical parameters for four hot Jupiters: KELT-7 b, HAT-P-14 b, WASP-29 b, WASP-95 b, and a hot Neptune: WASP-156 b, by performing critical and rigorous analysis of the time-series observations from the Transiting Exoplanet Survey Satellite (TESS). Being a space-based telescope, the transit photometric data obtained by TESS are free from any noise component due to the interference of Earth's atmosphere. In our analysis of the observed data, we have used critical noise reduction techniques, e.g., the wavelet denoising and Gaussian process regression, in order to effectively…
The fields of astronomy and astrophysics are currently engaged in an unprecedented era of discovery as recent missions have revealed thousands of exoplanets orbiting other stars. While the Kepler Space Telescope mission has enabled most of these exoplanets to be detected by identifying transiting events, exoplanets often exhibit additional photometric effects that can be used to improve the characterization of exoplanets. The EXONEST Exoplanetary Explorer is a Bayesian exoplanet inference engine based on nested sampling and originally designed to analyze archived Kepler Space Telescope and CoR…
Optical-NIR Multi-band Photometric Analysis and Characterization of Giant Exoplanets with CPI-C
Nanjing Institute of Astronomical Optics \& Technology, Chinese Academy of Sciences, \ 210042, China；CAS Key Laboratory of Astronomical Optics \& Technology, Nanjing Institute of Astronomical Optics \& Technology, \ 210042, China
Although there exists a large sample of known exoplanets, little spectroscopic data exists that can be used to study their global atmospheric properties. This deficiency can be addressed by performing phase-resolved spectroscopy -- continuous spectroscopic observations of a planet's entire orbit about its host star -- of transiting exoplanets. Planets with characteristics suitable for atmospheric characterization have orbits of several days, thus phase curve observations are highly resource intensive, especially for shared use facilities. In this work, we show that an infrared spectrograph ope…
The EXoplanet Climate Infrared TElescope (EXCITE): A balloon-borne mission to measure spectroscopic phase curves of transiting hot Jupiters
NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Brown University（布朗大学）；Arizona State University（亚利桑那州立大学）；La Sapienza Università di Roma（罗马第一大学）；Cornell University（康奈尔大学）；StarSpec Technologies Inc.（StarSpec科技有限公司）；Center for Space Sciences and Technology, University of Maryland, Baltimore County（马里兰大学巴尔的摩县分校空间科学与技术中心）
New photometric follow-up observations of exoplanet transits of 'hot Jupiters' TrES-3b and Qatar-1b are presented. Weighted mean values of the solutions of light curves in R-fiter for both planetary systems are reported and compared with the previous results. The transit light curves were analysed using the WINFITTER code. The physical properties of the planets were estimated. The planet radii are found to be $R_p = 1.381 \pm 0.033 R_J$ for TrES-3b and $R_p = 1.142 \pm 0.025 R_J$ for Qatar-1b. Transit times and their uncertainties were also determined and a new linear ephemeris was computed fo…
We introduce BASE (Bayesian astrometric and spectroscopic exoplanet detection and characterisation tool), a novel program for the combined or separate Bayesian analysis of astrometric and radial-velocity measurements of potential exoplanet hosts and binary stars. The capabilities of BASE are demonstrated using all publicly available data of the binary Mizar A.
In a previous paper we presented the Directed Follow-Up (DFU) approach, which we suggested can be used to efficiently augment low-cadence photometric surveys in a way that will optimize the chances to detect transiting exoplanets. In this paper we present preliminary tests of applying the DFU approach to the future ESA space mission Gaia. We demonstrate the strategy application to Gaia photometry through a few simulated cases of known transiting planets, using Gaia expected performance and current design. We show that despite the low cadence observations DFU, when tailored for Gaia's scanning …
Located within 10 degrees of the North Pole, northern Ellesmere Island offers continuous darkness in the winter months. This capability can greatly enhance the detection efficiency of planetary transit surveys and other time domain astronomy programs. We deployed two wide-field cameras at 80 degrees North, near Eureka, Nunavut, for a 152-hour observing campaign in February 2012. The 16-megapixel-camera systems were based on commercial f/1.2 lenses with 70mm and 42mm apertures, and they continuously imaged 504 and 1,295 square degrees respectively. In total, the cameras took over 44,000 images …
The statistical validation of transiting exoplanets proved to be an efficient technique to secure the nature of small exoplanet signals which cannot be established by purely spectroscopic means. However, the spectroscopic diagnoses are providing us with useful constraints on the presence of blended stellar contaminants. In this paper, we present how a contaminating star affects the measurements of the various spectroscopic diagnoses as function of the parameters of the target and contaminating stars using the model implemented into the PASTIS planet-validation software. We find particular case…
We present a radiative-convective equilibrium model for young giant exoplanets. Model predictions are compared with the existing photometric measurements of planet beta Pictoris b in the J, H, Ks, L', NB 4.05, M' bands . This model will be used to interpret future photometric and spectroscopic observations of exoplanets with SPHERE, mounted at the VLT with a first light expected mid-2014.
The XO project aims at detecting transiting exoplanets around bright stars from the ground using small telescopes. The original configuration of XO (McCullough et al. 2005) has been changed and extended as described here. The instrumental setup consists of three identical units located at different sites, each composed of two lenses equipped with CCD cameras mounted on the same mount. We observed two strips of the sky covering an area of 520 deg$^2$ for twice nine months. We build lightcurves for ~20,000 stars up to magnitude R~12.5 using a custom-made photometric data reduction pipeline. The …
Since 2008 we have run an observational program to accurately measure the characteristics of known exoplanet systems hosting close-in transiting giant planets, i.e. hot Jupiters. Our study is based on high-quality photometric follow-up observations of transit events with an array of medium-class telescopes, which are located in both the northern and the southern hemispheres. A high photometric precision is achieved through the telescope-defocussing technique. The data are then reduced and analysed in a homogeneous way for estimating the orbital and physical parameters of both the planets and t…
The next generation of ground and space-based telescopes will image habitable planets around nearby stars. A growing literature describes how to characterize such planets with spectroscopy, but less consideration has been given to the usefulness of planet colors. Here, we investigate whether potentially Earth-like exoplanets could be identified using UV-visible-to-NIR wavelength broadband photometry (350-1000 nm). Specifically, we calculate optimal photometric bins for identifying an exo-Earth and distinguishing it from uninhabitable planets including both Solar System objects and model exopla…
We developed a simple, physical and self-consistent cloud model for brown dwarfs and young giant exoplanets. We compared different parametrisations for the cloud particle size, by either fixing particle radii, or fixing the mixing efficiency (parameter fsed) or estimating particle radii from simple microphysics. The cloud scheme with simple microphysics appears as the best parametrisation by successfully reproducing the observed photometry and spectra of brown dwarfs and young giant exoplanets. In particular, it reproduces the L-T transition, due to the condensation of silicate and iron clouds…
Rings around exoplanets (exorings) are one of the most expected discoveries in exoplanetary research. There is an increasing number of theoretical and observational efforts for detecting exorings, but none of them have succeeded yet. Most of those methods focus on the photometric signatures of exorings during transits, whereas less attention has been paid to light diffusely reflected: what we denote here as the bright side of the light curve. This is particularly important when we cannot detect the typical stellar flux drop produced by transiting exoplanets. Here, we endeavour to develop a gen…
A reasonable basis for future astronomical investigations of exoplanets lies in our best knowledge of the planets and satellites in the Solar System. Solar System bodies exhibit a wide variety of surface environments, even including potential habitable conditions beyond Earth, and it is essential to know how they can be characterized from outside the Solar System. In this study, we provide an overview of geological features of major Solar System solid bodies with minor atmospheres (i.e., the Terrestrial Moon, Mercury, the Galilean moons, and Mars) that affect surface albedo at local to global …
The field of exoplanetary science has diversified rapidly over recent years as the field has progressed from exoplanet detection to exoplanet characterization. For those planets known to transit, the primary transit and secondary eclipse observations have a high yield of information regarding planetary structure and atmospheres. The current restriction of these information sources to short-period planets may be abated in part through refinement of orbital parameters. This allows precision targeting of transit windows and phase variations which constrain the dynamics of the orbit and the geomet…
Studies on Near Earth Asteroids (NEAs) throw light on discoveries, identification, orbit prediction and civil alert capabilities, including potential asteroid impact hazards. Due to various new observational programs, the discovery rate of NEAs has drastically increased over the last few years. In this paper we present the statistical survey and analysis of fundamental parameters (derived from Photometric and Spectroscopic observations) of a large sample of NEAs from various databases like IAU Minor Planet Center, European Asteroid Research Node (E.A.R.N.), Near Earth Objects - Dynamic Site (N…
We present optimal survey strategies for the upcoming NIX imager, part of the ERIS instrument to be installed on the Very Large Telescope (VLT). We will use a custom 2.2 micron K-peak filter to optimise the efficiency of a future large-scale direct imaging survey, aiming to detect brown dwarfs and giant planets around nearby stars. We use the results of previous large scale imaging surveys (primarily SPHERE SHINE and Gemini GPIES) to inform our choice of targets, as well as improved planet population distributions. We present four possible approaches to optimise survey target lists for the hig…
Photometric follow-ups of transiting exoplanets may lead to discoveries of additional, less massive bodies in extrasolar systems. This is possible by detecting and then analysing variations in transit timing of transiting exoplanets. We present photometric observations gathered in 2009 and 2010 for exoplanet WASP-3b during the dedicated transit-timing-variation campaign. The observed transit timing cannot be explained by a constant period but by a periodic variation in the observations minus calculations diagram. Simplified models assuming the existence of a perturbing planet in the system and…
We report the results of the high precision photometric follow-up observations of five transiting hot jupiters - WASP-33b, WASP-50b, WASP-12b, HATS-18b and HAT-P-36b. The observations are made from the 2m Himalayan Chandra Telescope at Indian Astronomical Observatory, Hanle and the 1.3m J. C. Bhattacharyya Telescope at Vainu Bappu Observatory, Kavalur. This exercise is a part of the capability testing of the two telescopes and their back-end instruments. Leveraging the large aperture of both the telescopes used, the images taken during several nights were used to produce the transit light curv…
Colour-magnitude diagrams form a traditional way of presenting luminous objects in the Universe and compare them to each others. Here, we estimate the photometric distance of 44 transiting exoplanetary systems. Parallaxes for seven systems confirm our methodology. Combining those measurements with fluxes obtained while planets were occulted by their host stars, we compose colour-magnitude diagrams in the near and mid-infrared. When possible, planets are plotted alongside very low-mass stars and field brown dwarfs, who often share similar sizes and equilibrium temperatures. They offer a natural…
Using a 3D GCM, we create dynamical model atmospheres of a representative transiting giant exoplanet, HD 209458b. We post-process these atmospheres with an opacity code to obtain transit radius spectra during the primary transit. Using a spectral atmosphere code, we integrate over the face of the planet seen by an observer at various orbital phases and calculate light curves as a function of wavelength and for different photometric bands. The products of this study are generic predictions for the phase variations of a zero-eccentricity giant planet's transit spectrum and of its light curves. W…
As a test-bed for future investigations of directly imaged terrestrial exoplanets, we present the recovery of the surface components of the Earth from multi-band diurnal light curves obtained with the EPOXI spacecraft. We find that the presence and longitudinal distribution of ocean, soil and vegetation are reasonably well reproduced by fitting the observed color variations with a simplified model composed of a priori known albedo spectra of ocean, soil, vegetation, snow and clouds. The effect of atmosphere, including clouds, on light scattered from surface components is modeled using a radiat…
The Young Exoplanet Transit Initiative (YETI) is a project focused on the photometric monitoring of stellar open clusters in order to find new young transiting exoplanets, eclipsing binaries and study other variability phenomena. Here, we present the status of the initiative and plans for future photometric campaigns of three open clusters younger than 50 Myr: NGC 869, NGC 884 and IC 4665, by using the world-wide one meter-class telescope network. Based on the experience gained by several astronomical observatories included in this network, dedicated numerical algorithms and recent results obt…
Young brown dwarfs are analogs to giant exoplanets, as they share effective temperatures, near-infrared colors, and surface gravities. Thus, the detailed characterization of young brown dwarfs might shed light on the study of giant exoplanets, that we are currently unable to observe with sufficient signal-to-noise to allow precise characterization of their atmospheres. 2MASS J22081363+2921215 is a young L3 brown dwarf, member of the beta-Pictoris young moving group (23 +/-3 Myr), that shares its effective temperature and mass with the beta Pictoris b giant exoplanet. We performed a ~2.5 hr spe…
CONTEXT. It is theoretically possible for rings to have formed around extrasolar planets in a similar way to that in which they formed around the giant planets in our solar system. However, no such rings have been detected to date. AIMS: We aim to test the possibility of detecting rings around exoplanets by investigating the photometric and spectroscopic ring signatures in high-precision transit signals. METHODS: The photometric and spectroscopic transit signals of a ringed planet is expected to show deviations from that of a spherical planet. We used these deviations to quantify the detectabi…
Refraction deflects photons that pass through atmospheres, which affects transit light curves. Refraction thus provides an avenue to probe physical properties of exoplanet atmospheres and to constrain the presence of clouds and hazes. In addition, an effective surface can be imposed by refraction, thereby limiting the pressure levels probed by transmission spectroscopy. The main objective of the paper is to model the effects of refraction on photometric light curves for realistic planets and to explore the dependencies on atmospheric physical parameters. We also explore under which circumstanc…
The current and upcoming high precision photometric surveys such as TESS, CHEOPS, and PLATO will provide the community with thousands of new exoplanet candidates. As a consequence, the presence of such a correlation is crucial in selecting the targets with the lowest RV jitter for efficient RV follow-up of exoplanetary candidates. Studies of this type are also crucial to design optimized observational strategies to mitigate RV jitter when searching for Earth-mass exoplanets. Our goal is to assess the correlation between high-precision photometric variability measurements and high-precision RV …
The stellar rotation periods of ten exoplanet host stars have been determined using newly analysed Ca II H & K flux records from Mount Wilson Observatory and Stromgren b, y photometric measurements from Tennessee State University's automatic photometric telescopes (APTs) at Fairborn Observatory. Five of the rotation periods have not previously been reported, with that of HD 130322 very strongly detected at Prot = 26.1 \pm 3.5 d. The rotation periods of five other stars have been updated using new data. We use the rotation periods to derive the line-of-sight inclinations of the stellar rotation…
Blind source separation techniques are used to reanalyse two exoplanetary transit lightcurves of the exoplanet HD189733b recorded with the IR camera IRAC on board the Spitzer Space Telescope at 3.6$μ$m during the "cold" era. These observations, together with observations at other IR wavelengths, are crucial to characterise the atmosphere of the planet HD189733b. Previous analyses of the same datasets reported discrepant results, hence the necessity of the reanalyses. The method we used here is based on the Independent Component Analysis (ICA) statistical technique, which ensures a high degree …
Context. The launch of the exoplanet space missions obtaining exquisite photometry from space has resulted in the discovery of thousands of planetary systems with very different physical properties and architectures. Among them, the exoplanet CoRoT-29b was identified in the light curves the mission obtained in summer 2011, and presented an asymmetric transit light curve, which was tentatively explained via the effects of gravity darkening. Aims. Transits of CoRoT-29b are measured with precision photometry, to characterize the reported asymmetry in their transit shape. Methods. Using the OSIRIS…
