We study to which extent planetesimal accretion is affected by the perturbing presence of a compagnon star. We concentrate on one crucial parameter: the distribution of encounter velocities within the planetesimal swarm. We numerically explore the evolution of this parameter taking into account the secular perturbations of the binary and friction due to the very likely presence of gas in the disk. $<Δv>$ maps are derived, for planetesimals of different sizes, for a total of 120 binary configurations (eccentricity eb and separation ab). We identify for each case 3 different accreting behaviours. 1) In regions where no significant dV increase is observed, ``classical'' (i.e., single-star) accretion is possible. 2) In regions where $dV>v_{ero}$, the threshold velocity above which all impacts are eroding, no accretion is possible and planet growth is stopped. 3) In between these 2 limiting behaviours, a large fraction of binary configurations leads to significant dV increase, but still below the erosion threshold. In this intermediate case, planetesimal growth can occur, but proceeds slower than in the single-star case, possibly following the so-called type II runaway groth mode.
This paper explains why planets in binary star systems might have a lower frequency. A transient triple state of the binary causes the dispersal of planets.
Hostile tidal forces may inhibit the formation of Jovian planets in binaries with semimajor axes of $\la$$50\au$, binaries that might be called ``close'' in this context. As an alternative to in situ planet formation, a binary can acquire a giant planet when one of its original members is replaced in a dynamical interaction with another star that hosts a planet. Simple scaling relations for the structure and evolution of star clusters, coupled with analytic arguments regarding binary-single and binary-binary scattering, indicate that dynamical processes can deposit Jovian planets in $<$1% of c…
The frequency of planets in binaries is an important issue in the field of extrasolar planet studies, because of its relevance in estimating of the global planet population of our Galaxy and the clues it can give to our understanding of planet formation and evolution. However, only preliminary estimates are available in the literature. We analyze and compare the frequency of planets in multiple systems to the frequency of planets orbiting single stars. We also try to highlight possible connections between the frequency of planets and the orbital parameters of the binaries (such as the periastr…
In this letter we consider the evolution of a planetary system around a star inside a wide binary. We simulate numerically the evolution of the planetary orbits for both co-planar and highly-inclined systems. We find that the Kozai mechanism operates in the latter case. This produces a highly eccentric outer planet whose orbit crosses those of some of the inner planets. Strong planet-planet interactions then follow resulting in the ejection of one or more planets. We note that planetary systems resembling our solar system, formed around single stars in stellar clusters may exchange into binari…
Many recent observational studies have concluded that planetary systems commonly exist in multiple-star systems. At least ~20% of the known extrasolar planetary systems are associated with one or more stellar companions. The orbits of stellar binaries hosting planetary systems are typically wider than 100 AU and often highly inclined with respect to the planetary orbits. The effect of secular perturbations from such an inclined binary orbit on a coupled system of planets, however, is little understood theoretically. In this paper we investigate various dynamical classes of double-planet system…
The statistical properties of planets in binaries were investigated. Any difference to planets orbiting single stars can shed light on the formation and evolution of planetary systems. As planets were found around components of binaries with very different separation and mass ratio, it is particularly important to study the characteristics of planets as a function of the effective gravitational influence of the companion. A compilation of planets in binary systems was made; a search for companions orbiting stars recently shown to host planets was performed, resulting in the addition of two fur…
The orbital eccentricity of a single planet around a component of a stellar binary system with a sufficiently large mutual inclination angle is known to oscillate on a secular timescale through the Kozai mechanism. We have investigated the effects of the Kozai mechanism on double-planet systems in binaries. The evolutionary sequence of a pair of planets under the influence of a binary companion is fairly complex. Various dynamical outcomes are seen in numerical simulations. One interesting outcome is the rigid rotation of the planetary orbits in which the planetary orbital planes secularly pre…
A survey of currently known extrasolar planets indicates that close to 20% of their hosting stars are members of binary systems. While the majority of these binaries are wide (i.e., with separations between 250 and 6500 AU), the detection of Jovian-type planets in the three binaries of Gamma Cephei (separation of 18.5 AU), GL 86 (separation of 21 AU), and HD 41004 (separation of 23 AU) have brought to the forefront questions on the formation of giant planets and the possibility of the existence of smaller bodies in moderately close binary star systems. This paper discusses the late stage of th…
Although it is commonly agreed that the presence of a close stellar companion is likely to affect planet formation and evolution, the precise effects and their actual impact on planet occurrence and properties are still debated. In particular, observational constraints are sparse, a consequence of the discrimination against close binaries in Doppler planet searches. To bring observational constraints on the occurrence and properties of planets in binaries and multiple stars, we have been conducting two dedicated observing programs using both adaptive optics imaging and radial-velocity monitori…
It is already known that about 10% of central stars of PNe are very short-period binaries (hours to days), which are detected through photometric variations. These must have been formed through common-envelope interactions in initially wide binaries, accompanied by ejection of the envelope and its subsequent photoionization as a PN. Radial-velocity observations by ourselves and others are now suggesting that an even larger fraction of planetary nuclei may be spectroscopic binaries, making the total binary fraction very large. However, we have not as yet been able to rule out the possibility th…
Among the extrasolar planetary systems about 30 are located in a stellar binary orbiting one of the stars, preferably the more massive primary. The dynamical influence of the second companion alters firstly the orbital elements of the forming protoplanet directly and secondly the structure of the disk from which the planet formed which in turn will modify the planet's evolution. We present detailed analysis of these effects and present new hydrodynamical simulations of the evolution of protoplanets embedded in circumstellar disks in the presence of a companion star, and compare our results to …
In this chapter of the book "Planets in binaries" we summarize our recent work on the statistical properties of planets in binaries and the differences with respect to planets orbiting single stars. We then present the radial velocity planet search on moderately wide binaries with similar components (twins) ongoing at TNG using the high resolution spectrograph SARG. We discuss the sample selection, the observing and analysis procedures, and the preliminary results of the radial velocity monitoring. We also discuss the second major science goal of the SARG survey, the search for abundance anoma…
We present a population synthesis calculation to derive the total number of planetary nebulae (PN) in the Galaxy that descend from single stars and stars in binary systems. Using the most recent literature results on galactic and stellar formation as well as stellar evolution, we predict the total number of galactic PNe with radii <0.9 pc to be (46,000 +/- 13,000). We do not claim this to be the complete population, since there can be visible PNe with radii larger than this limit. However, by taking this limit, we make our predicted population inherently comparable to the observationally-based…
In a recent work Ciardullo et al. (1999) list 19 planetary nebulae surveyed by the Hubble Space Telescope for the presence of resolved visual binary companions of their central stars. For ten planetary nebulae they argue for probable physical association of the resolved stars with the central stars, while for nine the association is less likely. Such stellar companions, at orbital separations of hundreds to thousands of astronomical units, will cause the structures of these planetary nebulae to possess a non-axisymmetrical signatures. By using images from the literature of these 19 planetary n…
Using a comprehensive binary population synthesis scheme, we investigate the statistical properties of a sample of eclipsing binaries that is detectable by an idealised extrasolar planet transit survey with specifications broadly similar to those of the SuperWASP (Wide Angle Search for Planets) project. In this idealised survey the total number of detectable single stars in the Galactic disc is of the order of 10^6-10^7, while, for a flat initial mass ratio distribution, the total number of detectable eclipsing binaries is of the order of 10^4-10^5. The majority of the population of detectable…
Observations of extrasolar planets reveal that planets can be found in close binary systems, where the semi-major axis of the binary orbit is less than 20 AU. The existence of these planets challenges planet formation theory, because the strong gravitational perturbations due to the companion increase encounter velocities between planetesimals and make it difficult for them to grow through accreting collisions. We study planetesimal encounter velocities in binary systems, where the planetesimals are embedded in a circumprimary gas disc that is allowed to evolve under influence of the gravitati…
We investigate the possible progenitors of the planetary nebulae (PNs) which populate the top 0.5 mag of the [O III] 5007 planetary nebula luminosity function (PNLF). We show that the absolute luminosity of the PNLF cutoff demands that the central stars of these most luminous planetaries be greater than 0.6 Msun, and that such high-mass PN cores must exist in every galaxy. We also use the bolometric-luminosity specific PN number density to show that in early-type galaxies, [O III]-bright planetaries are relatively rare, with only about 10% of stars evolving to these bright magnitudes. We demon…
Coalescing compact binaries are thought to be involved in a wide variety of astrophysical phenomena. In particular, they are important sources of gravitational radiation for both ground-based and space-based laser-interferometer detectors, and they may be sources of supernova explosions or gamma-ray bursts. Mergers of two white dwarfs may produce neutron stars with peculiar properties, including perhaps millisecond radio pulsars sometimes accompanied by planets (as observed in PSR 1257+12). According to a widely held belief, the coalescence of two neutron stars should produce a rapidly rotatin…
Observations suggest that many, if not all, post AGB systems evolve through an aspherical outflow phase. Such outflows require a sufficient engine rotational energy which binaries can provide. Via common envelope evolution, binaries can directly eject equatorial outflows or produce poloidal outflows from magnetized accretion disks around the primary or secondary. We discuss how accretion driven magnetohydrodynamic outflow models all make similar predictions for the outflow power and speed and we distinguish between the launch vs. propagation regimes of such outflows. We suggest that the high v…
Many recent observational studies have concluded that planetary systems commonly exist in multiple-star systems. At least ~20%, and presumably a larger fraction of the known extrasolar planetary systems are associated with one or more stellar companions. These stellar companions normally exist at large distances from the planetary systems (typical projected binary separations are on the orders 100-10000AU) and are often faint (ranging from F to T spectral types). Yet, secular cyclic angular momentum exchange with these distant stellar companions can significantly alter the orbital configuratio…
I propose a method to detect planets around compact binaries that are strong sources of gravitational radiation. This approach is to measure gravitational-wave phase modulations induced by the planets, and its prospect is studied with a Fisher matrix analysis. I find that, using the Laser Interferometer Space Antenna (LISA), planets can be searched for around ~3000 Galactic double white dwarfs with detection limit ~4 M_J (M_J~ 2x10^{30}g: the Jupiter mass). With its follow-on missions, planets with mass ~1 M_J might be detected around double neutron stars even at cosmological distances z~1. In…
The typical product of the star formation process is a binary star. Binaries have provided the first dynamical measures of the masses of pre-main-sequence (PMS) stars, providing support for the calibrations of PMS evolutionary tracks. Surprisingly, in some star-forming regions PMS binary frequencies are higher than among main-sequence solar-type stars. The difference in PMS and main-sequence binary frequencies is apparently not an evolutionary effect; recent attention has focussed on correlations between binary frequency and stellar density or cloud temperatures. Accretion disks are common amo…
The star formation process in molecular clouds usually leads to the formation of multiple stellar systems, mostly binaries. Remaining disks around those stars may be located around individual stars (circumstellar disks) or around the entire binary system (circumbinary disk). We shall briefly review the present observational evidence for both types of disks in binary stars, in particular the properties of circumbinary disks. We then present recent results of the theoretical modeling of the collapse and fragmentation of gravitationally unstable molecular cloud cores and their implications for bi…
This paper reviews the rich corpus of observational evidence for tidal effects in short-period binaries. We review the evidence for ellipsoidal variability and for the observational manifestation of apsidal motion in eclipsing binaries. Among the long-term effects, circularization was studied the most, and a transition period between circular and eccentric orbits has been derived for eight coeval samples of binaries. As binaries are supposed to reach synchronization before circularization, one can expect finding eccentric binaries in pseudo-synchronization state, the evidence for which is revi…
The stars that populate the solar neighbourhood were formed in stellar clusters. Through N-body simulations of these clusters, we measure the rate of close encounters between stars. By monitoring the interaction histories of each star, we investigate the singleton fraction in the solar neighbourhood. A singleton is a star which formed as a single star, has never experienced any close encounters with other stars or binaries, or undergone an exchange encounter with a binary. We find that, of the stars which formed as single stars, a significant fraction are not singletons once the clusters have …
We present new V and R-passband CCD photometry of UU Sge and V477 Lyr, the eclipsing binary nuclei of the planetary nebulae Abell 63 and Abell 46, respectively. We have performed a simultaneous analysis of VR light-curves and estimated the effective temperatures for the primary and secondary stars to be 78 000 $\pm$ 3000 and 6136 $\pm$ 240 K for UU Sge, 49 500 $\pm$ 4500 and 3874 $\pm$ 350 K for V477 Lyr. We have also reanalysed the previously measured radial velocities and combined the results with those obtained from the analysis of the light curves to derive absolute parameters of the compo…
We present an algorithm that can detect blends of bright stars with fainter, un-associated eclipsing binaries. Such systems contaminate searches for transiting planets, in particular in crowded fields where blends are common. Spectroscopic follow-up observations on large aperture telescopes have been used to reject these blends, but the results are not always conclusive. Our approach exploits the fact that a blend with a eclipsing binary changes its shape during eclipse. We analyze original imaging data from the Optical Gravitational Lensing Experiment (OGLE), which were used to discover plane…
The first steps of planet formation are marked by the growth and crystallization of sub-micrometer-sized dust grains accompanied by dust settling toward the disk midplane. In this paper we explore whether the first steps of planet formation are affected by the presence of medium-separation stellar companions. We selected two large samples of disks around single and binary T Tauri stars in Taurus that are thought to have only a modest age spread of a few Myr. The companions of our binary sample are at projected separations between 10 and 450 AU with masses down to about 0.1 solar masses. We use…
Searches for planets in close binary systems explore the degree to which stellar multiplicity inhibits or promotes planet formation. There is a degeneracy between planet formation models when only systems with single stars are studied--several mechanisms appear to be able to produce such a final result. This degeneracy is lifted by searching for planets in binary systems; the resulting detections (or evidence of non-existence) of planets in binaries isolates which models may contribute to how planets form in nature. In this chapter, we consider observational efforts to detect planetary compani…
This paper is devoted to exploring how we can discover and study nearby (< 1-2 kpc) planetary and binary systems by observing their action as gravitational lenses. Lensing can extend the realm of nearby binaries and planets that can be systematically studied to include dark and dim binaries, and face-on systems. As with more traditional studies, which use light from the system, orbital parameters (including the total mass, mass ratio, and orbital separation) can be extracted from lensing data, Also in common with these traditional methods, individual systems can be targeted for study. We discu…
Many planet candidates have been detected by radial velocity variations of the primary star; they are planet candidates, because of the unknown orbit inclination. Detection of the wobble in the two other dimensions, to be measured by astrometry, would yield the inclination and, hence, true mass of the companions. We aim to show that planets can be confirmed or discovered in a close visual stellar binary system by measuring the astrometric wobble of the exoplanet host star as periodic variation of the separation, even from the ground. We test the feasibility with HD 19994, a visual binary with …
we study the long-term evolution of the accretion disk around the neutron star in Be/X-ray binaries. We confirm the earlier result by Hayasaki & Okazaki (2004) that the disk evolves via a two-stage process, which consists of the initial developing stage and the later developed stage. The peak mass-accretion rate is distributed around apastron after the disk is fully developed. This indicates that the modulation of the mass accretion rate is essentially caused by an inward propagation of the one-armed spiral wave. The X-ray luminosity peak around the apastron could provide circumstatial evidenc…
Due to the high efficiency of planet detections, current microlensing planet searches focus on high-magnification events. High-magnification events are sensitive to remote binary companions as well and thus a sample of wide-separation binaries are expected to be collected as a byproduct. In this paper, we show that characterizing binaries for a portion of this sample will be difficult due to the degeneracy of the binary-lensing parameters. This degeneracy arises because the perturbation induced by the binary companion is well approximated by the Chang-Refsdal lensing for binaries with separati…
We present a new catalogue of variable stars compiled from data taken for the University of New South Wales Extrasolar Planet Search. From 2004 October to 2007 May, 25 target fields were each observed for 1-4 months, resulting in ~87000 high precision light curves with 1600-4400 data points. We have extracted a total of 850 variable light curves, 659 of which do not have a counterpart in either the General Catalog of Variable Stars, the New Suspected Variables catalogue or the All Sky Automated Survey southern variable star catalogue. The catalogue is detailed here, and includes 142 Algol-type…
