Hundreds of extrasolar planets have been discovered around various types of stars by various techniques during the past decade. Among them precise radial velocity measurements for stars are fundamental technique to detect and confirm exoplanets. In this paper activities in East-Asian region in this research field are introduced: East-Asian Planet Search Network, which is a network searching for planets around evolved intermediate-mass stars, and Subaru/IRD project, which will search for habitable planets around M-type dwarfs using infrared radial-velocity method.

Gravitational microlensing has a unique sensitivity to exoplanets at outside of the snow-line with masses down to the Earth-mass. Because of the rarity and short timescale of the planetary signal, the survey groups, MOA-II in New Zealand and OGLE-IV in Chile carry out the wide field survey observation towards the galactic bulge to issue alerts in real time. Then telescopes of the follow-up groups conduct high cadence follow-up observation to get dense sampling of the short planetary signal. Recent high cadence survey observations by MOA-II and OGLE-IV have started to find exoplanets without follow-up observation systematically. This is a transition to the next generation 24-hour high cadence survey network which can reveal the mass function of exoplanets down to Earth-mass outside of the snow-line. The Wide Field Infrared Survey Telescope (WFIRST) is the highest ranked recommendation for a large space mission in the recent New Worlds, New Horizons (NWNH) in Astronomy and Astrophysics 2010 Decadal Survey. Exoplanet microlensing program is one of the primary science of WFIRST. WFIRST will find about 2,000 bound planets and 1,000 unbound planets by the high precision continuous survey with 15 min. cadence. WFIRST can complete the statistical census of planetary systems in the Galaxy, from the outer habitable zone to gravitationally unbound planets – a discovery space inaccessible to other exoplanet detection techniques.

We present our effort to detect and characterize transiting systems with small exoplanets. First we present our on-going project to detect transiting exoplanets around late-type stars. As many authors point out, late-type stars can host potentially habitable rocky planets, whose transits are detectable with 2-meter class telescopes. We aim at detecting (small-sized) transiting exoplanets around M-type stars and are conducting a survey using the Okayama 1.88m telescope. We introduce our campaign at Okayama. Next we discuss the characterization of small-sized exoplanets. We focus on the measurement of the spin-orbit angle, the angle between the stellar spin axis and planetary orbital axis. The spin-orbit relations are of great importance in discussing planetary formations, evolutions, and migrations. To this point, the Rossiter-McLaughlin (RM) effect, an apparent radial velocity anomaly during a planetary transit, has been mainly investigated to measure the projected spin-orbit angles. However, as the size of the transiting planet becomes smaller, the detection of the RM effect becomes challenging because of the small RM signal. We have newly developed a technique to investigate spin-orbit relations for smaller planets by combining Kepler's ultra-precise photometry and spectroscopic measurements. We show that, contrary to planetary systems with close-in giant planets, most of the systems with small-sized planets (including Earth-sized ones) have smaller spin-orbit angles, which implies a different evolutional history of the planetary systems. We also discuss future prospects on the detection and characterization of smaller transiting exoplanets.

Galactic gravitational microlensing is a powerful technique to detect extrasolar planets at large orbital distances from their stars, from giant down to Earth-mass planets. We report a statistical analysis (Cassan et al. 2012) that combines six years of microlensing observations gathered between 2002 to 2007 by the PLANET and OGLE collaborations. From these data, we estimate the frequency of cool extrasolar planets, with masses ranging from 5 Earths to 10 Jupiters and orbits between 0.5 to 10 Astronomical Units. We find that in average, one in six stars has a Jupiter-like gas giant as companion planet, that about half the stars are orbited by a Neptune-like giant, and two-thirds are associated to super-Earths. Our study also suggests that planets should be ubiquitous throughout the Galaxy. Current deployment of wide-field imagers and possible space-based observations onboard ESA spacecraft EUCLID will soon allow a large increase of the number of monitored microlensing events. These new observatories should provide in a near future a more detailed view on planet abundance as a function of mass.

By using the 1-m reflecting telescope at Weihai Observatory of Shandong University, the transit observations of seven stars are carried out to accurately estimate the physical parameters of extrasolar planets. Besides, a new high-resolution spectrograph (WES) was installed on this telescope for radial velocity measurements on exoplanets, we will show some preliminary results.

There are different methods for finding exoplanets such as radial spectral shifts, astrometrical measurements, transits, timing, etc. Gravitational microlensing (including pixel-lensing) is among the most promising techniques with the potential of detecting Earth-like planets at distances about a few astronomical units from their host stars. Here we emphasize the importance of polarization measurements which can help to resolve degeneracies in theoretical models. In particular, the polarization angle could give additional information about the relative position of the lens with respect to the source.

High atmospheric abundances of oxygen has been widely considered to be a reliable biosignature for life on exoplanets in the habitable zones of all types of stars. Recently it was proposed that the unique UV spectra of observed planet-hosting M dwarfs could lead to the buildup of molecular oxygen in the atmospheres of habitable but lifeless planets around these stars (Tian et al. 2014). However, the detectability of the accumulated O2 was not modeled. In this work we developed a new line by line radiative transfer model based on HITRAN database and used the model to simulate the reflectivity in the visible and near IR range. We show that abiotically produced and maintained O2 in the 0.2% level is observable at 13105 cm−1 (0.76 μm) with the spectra resolution of 70.

The formation of terrestrial and gas giant planets has likely imprinted signatures on the chemical composition of their parent stars, as shown for example by the higher occurrence of giant planets for higher stellar metallicities. There are two new signatures that have been recently proposed by Meléndez et al. (2009, 2012) and Ramírez et al. (2009, 2010) for the formation of rocky planets, and by Ramírez et al. (2011) for gas giant planets. We review here our on-going work on the planet-star connection using solar twins, for which chemical abundances are being obtained at unprecedented precision (0.01 dex).

Since the discovery of its transiting nature, the super-Earth 55 Cnc e has become one of the most enthusiastically studied exoplanets, having been observed spectroscopically and photometrically, in the ultraviolet, optical and infrared regimes. To this rapidly growing data set, we contribute 42 days of new, nearly continuous MOST photometry of the 55 Cnc system. Our analysis of these observations together with the discovery photometry obtained in 2011 allows us to determine the planetary radius (1.990+0.084−0.080) and orbital period (0.7365417+0.0000025−0.0000028) of 55 Cnc e with unprecedented precision. We also followed up on the out-of-transit phase variation first observed in the 2011 photometry, and set an upper limit on the depth of the planet's secondary eclipse, leading to an upper limit on its geometric albedo of 0.6.

We review the possible formation and orbital stability of Earth-mass or super Earth-mass planets around either of the stars Alpha Centauri A or B and describe a program at Mt John University Observatory using the Doppler method that aims to detect such planets. From New Zealand, we are able to observe the Alpha Centauri system year-round. This is critical in order to acquire data of sufficient quantity and phase coverage to detect the orbit of a terrestrial-mass planet in the habitable zone. Our observations are being made at high resolution (R = 70,000) and high signal-to-noise with the Hercules vacuum echelle spectrograph attached to the 1-m McLellan telescope by a 25-m long optical fibre and using an iodine cell. We discuss the velocity precision and instrumental stability required for success and outline the progress of the observations so far. At present we are collecting about 10,000 observations of each star, A and B, per year with a typical precision of 2.5 m/s per observation.

In the context of life detection on terrestrial exoplanets, new methods of search for spectral signatures of chlorophyll and other biomarkers in the Earthshine have been developed in the last few decades. Astronomical observations made at OHP and ESO (NTT) showed a significant signal when continents are facing the Moon. This signal, called the Vegetation Red Edge (VRE), is undoubtedly due to chlorophyll absorption properties. In order to strengthen these results, the LUCAS (LUmière Cendrée en Antarctique par Spectroscopie) project dedicated to the measurement of the Earthshine from the Concordia Research Station (C Dome, Antarctica) has been set up. One of the objectives of LUCAS was to observe prolonged variations of the VRE corresponding to various parts of the Earth facing the Moon. An extension of this project, called LUCAS II, would allow long-term observations to detect seasonal variations of the vegetation signal. These data, together with accurate measurements of the Earth's albedo, will help validate a model of global and spectral albedo of our planet.

Detecting the small velocity amplitudes (≤ 10 m/s) produced by habitable zone rocky planets around M Dwarfs requires radial velocity precisions of a few m s−1. However, an iodine absorption cell, commonly used as a high precision wavelength reference on non-stabilised spectrographs, is not efficient for very red and faint objects like M Dwarfs. Instead, arc lamps have to be used. With the exception of the ultra-stabilised HARPS spectrograph, achieving ~m s−1 calibration with arc lamps has not been possible because typical spectrographs experience drifts of several hundred m s−1 due to local atmospheric changes in pressure and temperature. We outline and present results from an innovative differential wavelength calibration method that enables ~m s−1 precision from non-stabilised, high-resolution spectrographs. This technique allows the detection of rocky planets with radial velocity amplitudes of a few m s−1.

Surface environment of habitable exoplanets will be important for astrobiologists on exoplanets in near future. Diverse surface environments on the Earth including continents, ocean, and meteorological condition (clouds and rains) serve as the backbone of biodiversity. One of the promising approaches to know the landscape of the terrestrial exoplanets is to use scattered light of the planet through direct imaging.

Since spin rotation and orbital revolution change illuminating area on planetary surface and cause time variation to disk-integrated brightness, light curves carry spatial information on the planetary surface. We propose an inversion technique of annual reflected light curves to sketch a two-dimensional albedo map of exoplanets, named the spin-orbit tomography (SOT). Applying the SOT to realistic simulations of the reflected light of an Earth-twin, we demonstrate how the SOT works. The mean cloud and continental distributions can be roughly obtained with single band photometry and difference of two-bands photometry, respectively. The SOT retrieves the planetary image without actually resolving the planet, which can be used to know the habitat of the exoplanets in near future.

GM Cephei is an active T Tauri star in the young open cluster Trumpler 37, showing abrupt UX Orionis type of photometric variability. Its light curves exhibit frequent, sporadic brightening events, each of <0.5 mag and lasting for days, which must have been originated from unsteady circumstellar accretion. In addition, the star undergoes a brightness drop up to ~1 mag lasting for about a month, during which the star became bluer when fainter. Moreover, the brightness drops seem to have a recurrence timescale of about 300 days. It is proposed that the brightness drop arises from obscuration of the central star by an orbiting dust concentration, exemplifying disk inhomogeneity in transition between grain coagulation and planetesimal formation in a young circumstellar disk. GM Cep was found to show a few percent polarization in the optical wavelengths, and an enhanced level of polarization during the occultation phase.

Studying the amazingly diverse planet zoo provides us with unprecedented opportunities for understanding planet Earth and ultimately ourselves. An assessment of a planet's “habitability” reflects our Earth-centric prejudice and can serve to prioritise targets to actually search for signatures of life similar to ours. The probability for life beyond Earth to exist however remains unknown, and studies on habitability or statistics of planetary systems do not change this. But we can leave speculation behind, and embark on a journey of exploration. A sample of detected cosmic habitats would provide us with insight on the conditions for life to emerge, develop, and sustain, but disentangling the biota fraction from the duration of the biotic era would depend particularly on our knowledge about the dynamics of planetary systems. Apart from the fact that planets usually do not come alone, we also must not forget that the minor bodies in the Solar system vastly outnumber the planets. A focus on just what we might consider “habitable” planets is too narrow to understand their formation and evolution. While uniqueness prevents understanding, we need to investigate the context and embrace diversity. A comprehensive picture of planet populations can only arise by exploiting a variety of different detection techniques, where not only Kepler but also gravitational microlensing can now enter hitherto uncharted territory below the mass or size of the Earth. There is actually no shortage of planets, the Milky Way alone may host hundreds of billions, and so far we have found only about 1000.

The Kepler mission observed exoplanet transits for 4 full years (greater than its expected lifetime of 3.5 years) until it became inoperable for its original purpose, as a result of a reaction wheel failure. Kepler was spectacularly successful in its goal of observing exoplanet transits of host star disks for the purpose of measuring the statistics of such transits in its target star sample. The Kepler data, when fully analyzed, will determine the statistics of planets in the underlying population, and in particular the expected number of terrestrial planets in habitable zone orbits per solar-type star, the quantity known as eta-sub-Earth. This report is an initial examination of Kepler's third catalog (Feb. 2012) of planets and candidate planets. I find that the apparent projected value of eta-sub-Earth is several times smaller than I had found from the second catalog, but that the data are now approaching the point where intrinsic biases can be uncovered. When all bias factors are eventually found, it is likely that the true value of eta-sub-Earth will be substantially greater than its current apparent value.

The Kepler Mission was designed to measure the frequency of Earth-like planets in the habitable zone of Sun-like stars. A requirement for determining the underlying planet population from a sample of detected planets is understanding the completeness of that sample—what fraction of the planets that could have been discovered in a given data set were actually detected. Here we describe an experiment designed to address a specific aspect of that question, which is the issue of signal throughput efficiency. We investigate the extent to which the Kepler pipeline preserves transit signals by injecting simulated transit signals into the pixel-level data, processing the modified pixels through the pipeline, and measuring their detection statistics. For the single channel that we examine initially, we inject simulated transit signal trains into the pixel time series of each of the 1801 targets for the 89 days that constitute Quarter 3. For the 1680 that behave as expected in the pipeline, on average we find the strength of the injected signal is recovered at 99.6% of the strength of the original signal. Finally we outline the further work required to characterise the completeness of the Kepler pipeline.

The Kepler Mission simultaneously measures the brightness of more than 150,000 stars every 29.4 minutes primarily for the purpose of transit photometry. Over the course of its 3.5-year primary mission Kepler has observed over 190,000 distinct stars, announcing 2,321 planet candidates, 2,165 eclipsing binaries, and 105 confirmed planets. As Kepler moves into its 4-year extended mission, the total number of transit-like features identified in the light curves has increased to as many as ~18,000. This number of signals has become intractable for human beings to inspect by eye in a thorough and timely fashion. To mitigate this problem we are developing machine learning approaches to perform the task of reviewing the diagnostics for each transit signal candidate to establish a preliminary list of planetary candidates ranked from most credible to least credible. Our preliminary results indicate that random forests can classify potential transiting planet signatures with an accuracy of more than 98.6% as measured by the area under a receiver-operating curve.

The multiple-planet systems discovered by the Kepler mission show an excess of planet pairs with period ratios just wide of exact commensurability for first-order resonances like 2:1 and 3:2. In principle, these planet pairs could be in resonance if their orbital eccentricities are sufficiently small, because the width of first-order resonances diverges in the limit of vanishingly small eccentricity. We consider a widely-held scenario in which pairs of planets were captured into first-order resonances by migration due to planet-disk interactions, and subsequently became detached from the resonances, due to tidal dissipation in the planets. In the context of this scenario, we find a constraint on the ratio of the planet's tidal dissipation function and Love number that implies that some of the Kepler planets are likely solid. However, tides are not strong enough to move many of the planet pairs to the observed separations, suggesting that additional processes are at play.

The Kepler mission has found many planetary systems, among them more than 80 systems host three planet candidates which reveal a configuration of near 4:2:1 mean motion resonance. In this paper, we focus on the configuration formation of resonant systems. As shown from our model and N-body simulations, we find that 3:2 mean motion resonance always forms at the early stage of star evolution and planets undergo high rate of migration, while 2:1 mean motion resonance happens at the late stage of the star formation, more often.