To date, over 30 multiple exoplanet systems are known, and 28% of stars with planets show significant evidence of a second companion. I briefly review these 30 systems individually, broadly grouping them into five categories: 1) systems with 3 or more giant (M sin i> 0.2 MJup) planets, 2) systems with two giant planets in mean motion resonance (MMR), 3) systems with two giant planets not in MMR but whose dynamical evolution is affected by planet-planet interactions, 4) highly hierarchical systems, having two giant planets with very large period ratios (>30:1), and 5) systems of “Super-Earths”, containing only planets with (M sin i< 20 M⊕). 
It now appears that eccentricities are not markedly higher among planets in known multiple planet systems, and that planets with M sin i< 1 MJup have lower eccentricities than more massive planets. The distribution of semimajor axes for planets in multi-planet systems does not show the 3-day pile-up or the 1 AU “jump” of the apparently-single planet distribution.

Moderately close binaries are a special class of targets for planet searches. From a theoretical standpoint, their hospitality to giant planets is uncertain and debated. From an observational standpoint, many of these systems present technical difficulties for precise radial-velocity measurements and classical Doppler surveys avoid them accordingly. In spite of these adverse factors, present data support the idea that giant planets residing in binary and hierarchical systems provide unique observational constraints on the processes of planet formation and evolution. The interest and the importance of including various types of binary stars in extrasolar planet studies have thus grown over time and significant efforts have recently been put into: (i) searching for stellar companions to the known planet-host stars using direct imaging, and (ii) extending Doppler planet searches to spectroscopic and moderately close visual binaries. In this contribution we review the observational progress made over the past few years in the detection and study of extrasolar planets in binary systems, putting special emphasis on the two developments mentioned above.

Surveys for transiting extrasolar planets, including the space-based missions CoRoT and Kepler, are expected to detect hundreds of Jovian mass planets and tens of terrestrial mass planets. For many of these newly discovered planets, the intervals between successive transits will be measured with an accuracy of a few seconds. These timing measurements allow for the detection of additional planets in the system (not necessarily transiting), via their gravitational interaction with the transiting planet. The transit time variations depend on the mass of the additional planet, and in some cases Earth-mass planets will produce a measurable effect. When two or more planets transit the same star, the densities of the planets can be estimated from the photometry alone. I will review recent developments related to transits in multiple planet systems.

Astrometry as a technique has so far proved of limited utility when employed as either a follow-up tool or to independently search for planetary mass companions orbiting nearby stars. However, this is bound to change during the next decade. In this review, I start by summarizing past and present efforts to detect planets via milli-arcsecond astrometry. Next, I provide an overview of the variety of technical, statistical, and astrophysical challenges that must be met by future ground-based and space-borne efforts in order to achieve the required degree of astrometric measurement precision. Then, I discuss the planet-finding capabilities of future astrometric observatories aiming at micro-arcsecond precision, with a particular focus on their ability to fully describe multiple-component systems. I conclude by putting astrometry in context, illustrating its potential for important contributions to planetary science, as a complement to other indirect and direct methods for the detection and characterization of planetary systems.

The direct detection of very faint companions to bright stars requires the development of effective high-contrast detection techniques, and the past decade has seen remarkable conceptual and instrumental progress in this area. New coronagraphic and interferometric techniques are regularly being deployed for on-sky tests and observations, and extreme adaptive optics (ExAO) systems will soon enable the exploitation of novel coronagraphic approaches. This paper provides an overview of coronagraphic high-contrast techniques, as well as a brief summary of the current state of affairs and future possibilities.

As the SALT High Resolution Spectrograph is nearing completion, we plan to extend the Pennsylvania-Torun Planets Search (PTPS) with HET to the southern hemisphere. Due to overlap of the skies available for both HET and SALT in the declination range (+10, -10) deg, some cooperation and immediate follow-up is possible. Here we present, as an example, a ~1000 star sample of evolved stars for the future SALT Planet Search.

Applications of the theory of the optimal design of radial-velocity planet-search surveys are discussed. Two important practical problems are considered. The first problem is finding the time for future observations to yield the maximum improvement of the accuracy of exoplanetary orbital parameters and masses. In this case, the optimal scheduling rules are designed to maximize the determinant of the Fisher information matrix (the so-called D-optimality criterion). This method is asymptotically equivalent to the maximization of the expected gain of the Shannon information provided by making extra observations. The second problem is finding the most favourable observing time for distinguishing alternative orbital fits (the design of discriminating experiments). In this case, the optimal scheduling rules are designed to maximize the Kullback-Leibler divergence information.
We also consider the potential efficiency of these methods of optimal planning of radial velocity observations for multi-planet systems.

The frequency of planets in binaries is an important issue in the field of extrasolar planet studies, because of its relevance in the estimate of the global planet population of our Galaxy and the clues it can give to our understanding of planet formation and evolution. Here we present an update of the results discussed in Bonavita & Desidera (2007) (hereafter BD07), where we reported the outcomes of our literature search for binaries and multiple systems among the sample with uniform detectability (UD) defined by Fischer & Valenti (2005) (hereafter FV05).

We explore the possibility of detecting Super Earths via transit timing variations with the satellite CoRoT.

We present the radial velocity planet search in moderately wide binaries with similar components (twins) ongoing at Telescopio Nazionale Galileo (TNG) using the Galileo High Resolution Spectrograph (Spettrografo Alta Risoluzione Galileo, SARG). We discuss the sample selection, the observing and analysis procedures, the main results of the radial velocity monitoring and the implications in terms of planet frequency in binary systems. We also briefly discuss the second major science goal of the SARG survey, the search for abundance anomalies caused by the ingestion of planetary material by the central star. Finally, we present some preliminary conclusions regarding the frequency of planets in binary systems.

High-precision radial velocity measurements have suffered from stellar spots effects for more than one decade. With the advent of high-resolution infra-red spectrographs, one is allowed to move into a new spectral domain where the influence of these stellar phenomena on measurements is significantly reduced. 
We present the first results of our CRIRES campaign on TW Hya, around which a periodic optical radial velocity variation was found and attributed to a planet. Our work showed that the signal is not present in the infra-red, pointing to a cold spot instead of to a planet as the explanation for the different data sets. This campaign demonstrates the power of this new approach and shows that CRIRES can deliver high-precision radial velocity measurements.

Extrasolar planet searches blossomed and prospered under the auspices of the radial velocity method. However, efficient as it is, it can misinterpret a periodic signal created by stellar phenomena as being originated from a planet. The most common of these is the presence of a cold spot, frequent in active stars. Here we review the representative cases of HD 166435, GJ 674 and TW Hya and the different methods used to pinpoint the spots' presence. We finish by underlining the importance of infrared measurements, as done in the TW Hya campaign, as a way of reducing the effect of spots on radial velocity measurements to a negligible level.

We present an analysis of how bisectors of spectral lines vary, for a few stars observed during the high-accuracy 
radial-velocity planet survey ongoing at the Telescopio Nazionale Galileo (TNG) using the Galileo High Resolution Spectrograph (Spettrografo Alta Risoluzione Galileo, SARG), and discuss their relation with differential radial velocities. The iodine cell lines employed in the radial velocity measurements were used to improve the wavelength calibration and then removed before bisector analysis. The line bisectors were then computed from average absorption profiles obtained by cross-correlation of the stellar spectra with a mask made from suitable lines of a solar catalog. Bisector velocity spans were determined and the run of bisector velocity span against radial velocity was studied to search for correlations between line asymmetries and radial velocity variations. We present an analysis of spectra of HD 216122B that show a slight contamination likely to be due to a stellar companion, and an analysis of spectra of HD 76036A, a case where the line bisectors are useful for improving the RV measurements. These systems are part of a survey sample being observed with adaptive optics (AdOpt at the TNG since 2006) in an attempt to visually resolve stellar companions.

ALMA will observe extrasolar planetary systems in various stages of formation. From young, planet-forming (protoplanetary), dusty disks, to mature solar-system analogs, ALMA will produce transformational science. We investigate the imaging capabilities of ALMA to infer structure in protoplanetary disks created by a protoplanet, as well as possible direct detection of the protoplanet itself. In addition, ALMA will be able to perform high-accuracy astrometry of main sequence stars, allowing us to search for the astrometric wobble caused by orbiting planets.

We present a method for the analysis of radial velocity (RV) measurements, in the context of searching for planets around chromospherically active stars. We assume that the observed RV signal is induced by the reflex motion of the star as well as by distortions of spectral line profiles, measured by the Bisector Velocity Span (BVS). The RVs are fitted with a Keplerian planetary model complemented by a correction term that is linearly dependent on the BVS. The BVS represents the stellar activity contribution to the observed RV. The coefficient of this linear dependence is an additional free parameter of the model. This approach differs from methods in the literature, which make usage of the BVS measurements before or after fitting the planetary model. We test the method on a simulated data set of a 1-planet configuration. The results are compared with the outcomes of algorithms found in the literature.

The dynamical state of a multiple planet system reflects the underlying processes of planet formation and orbital evolution. Radial velocity planet searches have yielded several systems that appear to be in or near a low-order mean-motion resonance, including several near a 2:1 mean-motion ratio. Still more systems apparently contain one eccentric planet. We demonstrate that many of these systems are indistinguishable from a system with two planets in a 2:1 mean-motion ratio, and outline a framework for determining how often the observed, apparently-single planets are likely to have such a second planet present.

Searches for planets around massive stars are essential for developing general understanding of planet formation and evolution of planetary systems. The main objective of the PSU-TCfA Search for Planets around Evolved Stars is detection of planets around G-K subgiants and giants through highly accurate radial velocity (RV) measurements using an iodine absorption cell on the HET HRS spectrograph. However, the long-period radial velocity variations of red giants may also have other causes than planets (e.g. non-radial pulsations or rotational modulation in the presence of starspots). In this work, for the second red giant with planets found in our survey, HD 102272, we present bisector analysis of cross-correlation functions (CCF) constructed from the spectra used for radial velocity determination but cleaned from the iodine lines.

We investigate biases in the measurement of exoplanet orbital parameters – especially eccentricity – from radial velocity (RV) observations. In this contribution we consider single-planet systems. We create a mock catalog of RV data, choosing planet masses and orbital periods, and observing patterns to mimic those of actual RV surveys. Using Markov chain Monte Carlo (MCMC) simulations, we generate a posterior sample for each mock data set, calculate best-fit orbital parameters for each data set, and compare these to the true values. We find that the precision of our derived eccentricities is most closely related to the effective signal-to-noise ratio, K√N/σ, where K is the velocity amplitude, σ is the effective single-measurement precision, and N is the number of observations. We also find that eccentricities of planets on nearly circular (e<0.05) orbits are preferentially overestimated. While the Butler et al.  (2006) catalog reports e<0.05 for just 20% of its planets, we estimate that the true fraction of e<0.05 orbits is about 50%. We investigate the accuracy, precision, and bias of alternative sets of summary statistics and find that the median values of h = esinω and k = ecosω (where ω is the longitude of periapse) of the posterior sample typically provide more accurate, more precise, and less biased estimates of eccentricity than traditional measures.

We have searched for planetary transits in Carina where the Optical Gravitational Lensing Experiment (OGLE) found many transits. The data that we analyzed were taken with the ESO VLT/VIMOS instrument for 4 continuous nights in 2005. We have detected several new transiting events. We recommend some of them for spectroscopic follow-up. For seven OGLE transits we present light curves. Our search also led us to discover hundreds of new variable stars.