Showing papers on "Planetary system published in 2003"

Evolutionary models for cool brown dwarfs and extrasolar giant planets. The case of HD 209458

Abstract: We present evolutionary models for cool brown dwarfs and extra-solar giant planets. The models reproduce the main trends of observed methane dwarfs in near-IR color-magnitude diagrams. We also present evolutionary models for irradiated planets, coupling for the first time irradiated atmosphere profiles and inner structures. We focus on HD 209458-like systems and show that irradiation effects can substantially affect the radius of sub-jovian mass giant planets. Irradiation effects, however, cannot alone explain the large observed radius of HD 209458b. Adopting assumptions which optimise irradiation effects and taking into account the extension of the outer atmospheric layers, we still find $\\sim$ 20% discrepancy between observed and theoretical radii. An extra source of energy seems to be required to explain the observed value of the first transit planet.

A Unique Solution of Planet and Star Parameters from an Extrasolar Planet Transit Light Curve

Abstract: There is a unique solution of the planet and star parameters from a planet transit light curve with two or more transits if the planet has a circular orbit and the light curve is observed in a bandpass where limb darkening is negligible. The existence of this unique solution is very useful for current planet transit surveys for several reasons. First, there is an analytic solution that allows a quick parameter estimate, in particular of Rp. Second, the stellar density can be uniquely derived from the transit light curve alone. The stellar density can then be used to immediately rule out a giant star (and hence a much larger than planetary companion) and can also be used to put an upper limit on the stellar and planet radius even considering slightly evolved stars. Third, the presence of an additional fully blended star that contaminates an eclipsing system to mimic a planet transit can be largely ruled out from the transit light curve given a spectral type for the central star. Fourth, the period can be estimated from a single-transit light curve and a measured spectral type. All of these applications can be used to select the best planet transit candidates for mass determination by radial velocity follow-up. To use these applications in practice, the photometric precision and time sampling of the light curve must be high (better than 0.005 mag precision and 5 minute time sampling for a two-transit light curve).

Towards a Deterministic Model of Planetary Formation I: a Desert in the Mass and Semi Major Axis Distributions of Extra Solar Planets

Abstract: We examine the accretion of cores of giant planets from planetesimals, gas accretion onto the cores, and their orbital migration. We adopt a working model for nascent protostellar disks with a wide variety of surface density distributions in order to explore the range of diversity among extra solar planetary systems. If some cores can acquire more mass than a critical value of several Earth masses during the persistence of the disk gas, they would be able to rapidly accrete gas and evolve into gas giant planets. The gas accretion process is initially regulated by the Kelvin-Helmholtz contraction of the planets' gas envelope. Based on the assumption that the exponential decay of the disk-gas mass occurs on the time scales $\sim 10^{6}-10^{7}$ years and that the disk mass distribution is comparable to those inferred from the observations of circumstellar disks of T Tauri stars, we carry out simulations to predict the distributions of masses and semi major axes of extra solar planets. Since planets' masses grow rapidly from $10 M_{\oplus}$ to $100 M_{\oplus}$, the gas giant planets rarely form with asymptotic masses in this intermediate range. Our model predicts a paucity of extra solar planets with mass in the range 10-$100 M_{\oplus}$ and semi major axis less than 3AU. We refer to this deficit as a ``planet desert''. The effect of migration is to sharpen the boundaries and to enhance the contrast of the planet desert. The mass and semi major axis distributions generated in our simulations for the gas giants are consistent with those of the known extra solar planets.

The formation of a star cluster: predicting the properties of stars and brown dwarfs

Abstract: We present results from the largest numerical simulation of star formation to resolve the fragmentation process down to the opacity limit. The simulation follows the collapse and fragmentation of a large-scale turbulent molecular cloud to form a stellar cluster and, simultaneously, the formation of circumstellar discs and binary stars. This large range of scales enables us to predict a wide variety of stellar properties for comparison with observations. The calculation clearly demonstrates that star formation is a highly-dynamic and chaotic process. Star formation occurs in localized bursts within the cloud via the fragmentation both of dense molecular cloud cores and of massive circumstellar discs. Star-disc encounters form binaries and truncate discs. Stellar encounters disrupt bound multiple systems. We find that the observed statistical properties of stars are a natural consequence of star formation in such a dynamical environment. The cloud produces roughly equal numbers of stars and brown dwarfs, with masses down to the opacity limit for fragmentation (5 Jupiter masses). The initial mass function is consistent with a Salpeter slope (Γ = -1.35) above 0.5 M O ., a roughly flat distribution (r = 0) in the range 0.006-0.5 M O ., and a sharp cut-off below 0.005 M O .. This is consistent with recent observational surveys. The brown dwarfs form by the dynamical ejection of low-mass fragments from dynamically unstable multiple systems before the fragments have been able to accrete to stellar masses. Close binary systems (with separations ≤10 au) are not formed by fragmentation in situ. Rather, they are produced by hardening of initially wider multiple systems through a combination of dynamical encounters, gas accretion, and/or the interaction with circumbinary and circumtriple discs. Finally, we find that the majority of circumstellar discs have radii less than 20 au due to truncation in dynamical encounters. This is consistent with observations of the Orion Trapezium cluster and implies that most stars and brown dwarfs do not form large planetary systems.

From molecular cores to planet-forming disks: An SIRTF legacy program

Abstract: Crucial steps in the formation of stars and planets can be studied only at mid‐ to far‐infrared wavelengths, where the Space Infrared Telescope (SIRTF) provides an unprecedented improvement in sensitivity. We will use all three SIRTF instruments (Infrared Array Camera [IRAC], Multiband Imaging Photometer for SIRTF [MIPS], and Infrared Spectrograph [IRS]) to observe sources that span the evolutionary sequence from molecular cores to protoplanetary disks, encompassing a wide range of cloud masses, stellar masses, and star‐forming environments. In addition to targeting about 150 known compact cores, we will survey with IRAC and MIPS (3.6–70 μm) the entire areas of five of the nearest large molecular clouds for new candidate protostars and substellar objects as faint as 0.001 solar luminosities. We will also observe with IRAC and MIPS about 190 systems likely to be in the early stages of planetary system formation (ages up to about 10 Myr), probing the evolution of the circumstellar dust, the raw material for planetary cores. Candidate planet‐forming disks as small as 0.1 lunar masses will be detectable. Spectroscopy with IRS of new objects found in the surveys and of a select group of known objects will add vital information on the changing chemical and physical conditions in the disks and envelopes. The resulting data products will include catalogs of thousands of previously unknown sources, multiwavelength maps of about 20 deg^2 of molecular clouds, photometry of about 190 known young stars, spectra of at least 170 sources, ancillary data from ground‐based telescopes, and new tools for analysis and modeling. These products will constitute the foundations for many follow‐up studies with ground‐based telescopes, as well as with SIRTF itself and other space missions such as SIM, JWST, Herschel, and TPF/Darwin.

From Molecular Cores to Planet-forming Disks: A SIRTF Legacy Program

Abstract: Crucial steps in the formation of stars and planets can be studied only at mid-infrared to far-infrared wavelengths, where SIRTF provides an unprecedented improvement in sensitivity. We will use all three SIRTF instruments (IRAC, MIPS, and IRS) to observe sources that span the evolutionary sequence from molecular cores to protoplanetary disks, encompassing a wide range of cloud masses, stellar masses, and star-forming environments. In addition to targeting about 150 known compact cores, we will survey with IRAC and MIPS (3.6 to 70 micron) the entire areas of five of the nearest large molecular clouds for new candidate protostars and substellar objects as faint as 0.001 solar luminosities. We will also observe with IRAC and MIPS about 190 systems likely to be in the early stages of planetary system formation(ages up to about 10 Myr), probing the evolution of the circumstellar dust, the raw material for planetary cores. Candidate planet-forming disks as small as 0.1 lunar masses will be detectable. Spectroscopy with IRS of new objects found in the surveys and of a select group of known objects will add vital information on the changing chemical and physical conditions in the disks and envelopes. The resulting data products will include catalogs of thousands of previously unknown sources, multiwavelength maps of about 20 square degrees of molecular clouds, photometry of about 190 known young stars, spectra of at least 170 sources, ancillary data from ground-based telescopes, and new tools for analysis and modeling. These products will constitute the foundations for many follow-up studies with ground-based telescopes, as well as with SIRTF itself and other space missions such as SIM, JWST, Herschel, and TPF.

A Possible Bifurcation in Atmospheres of Strongly Irradiated Stars and Planets

Abstract: We show that under certain circumstances the differences between the absorption mean and Planck mean opacities can lead to multiple solutions for an LTE atmospheric structure. Since the absorption and Planck mean opacities are not expected to differ significantly in the usual case of radiative equilibrium, nonirradiated atmospheres, the most interesting situations in which the effect may play a role are strongly irradiated stars and planets, and also possibly structures in which there is a significant deposition of mechanical energy, such as stellar chromospheres and accretion disks. We have presented an illustrative example of a strongly irradiated giant planet in which the bifurcation effect is predicted to occur for a certain range of distances from the star.

Theoretical Spectra and Atmospheres of Extrasolar Giant Planets

Abstract: We present a comprehensive theory of the spectra and atmospheres of irradiated extrasolar giant planets. We explore the dependences on stellar type, orbital distance, cloud characteristics, planet mass, and surface gravity. Phase-averaged spectra for specific known extrasolar giant planets that span a wide range of the relevant parameters are calculated, plotted, and discussed. The connection between atmospheric composition and emergent spectrum is explored in detail. Furthermore, we calculate the effect of stellar insolation on brown dwarfs. We review a variety of representative observational techniques and programs for their potential for direct detection, in light of our theoretical expectations, and we calculate planet-to-star flux ratios as a function of wavelength. Our results suggest which spectral features are most diagnostic of giant planet atmospheres and reveal the best bands in which to image planets of whatever physical and orbital characteristics.

Runaway Migration and the Formation of Hot Jupiters

Abstract: We evaluate the coorbital corotation torque on a migrating protoplanet. The coorbital torque is assumed to come from orbit crossing fluid elements that exchange angular momentum with the planet when they execute a U-turn at the end of horseshoe streamlines. When the planet migrates inward, the fluid elements of the inner disk undergo one such exchange as they pass to the outer disk. The angular momentum they gain is removed from the planet, and this corresponds to a negative contribution to the corotation torque, which scales with the drift rate. In addition, the material trapped in the coorbital region drifts radially with the planet, giving a positive contribution to the corotation torque, which also scales with the drift rate. These two contributions do not cancel out if the coorbital region is depleted, in which case there is a net corotation torque that scales with the drift rate and the mass deficit in the coorbital region and has the same sign as the drift rate. This leads to a positive feedback on the migrating planet. In particular, if the coorbital mass deficit is larger than the planet mass, the migration rate undergoes a runaway that can vary the protoplanet semimajor axis by 50% over a few tens of orbits. This can happen only if the planet mass is sufficient to create a dip or gap in its surrounding region and if the surrounding disk mass is larger than the planet mass. This typically corresponds to planet masses in the sub-Saturnian to Jovian mass range embedded in massive protoplanetary disks. Runaway migration is a good candidate to account for the orbital characteristics of close orbiting giant planets, most of which have sub-Jovian masses. These are known to cluster at short periods, whereas planets of greater than two Jovian masses are rare at short periods, indicating a different type of migration process operated for the two classes of object. Further, we show that in the runaway regime, migration can be directed outward, which makes this regime potentially rich in a variety of important effects in shaping a planetary system during the last stages of its formation.

A Planetary Companion to γ Cephei A

Abstract: We report on the detection of a planetary companion in orbit around the primary star of the binary system γ Cephei. High-precision radial velocity measurements using four independent data sets spanning the time interval 1981-2002 reveal long-lived residual radial velocity variations superposed on the binary orbit that are coherent in phase and amplitude with a period or 2.48 yr (906 days) and a semiamplitude of 27.5 m s-1. We performed a careful analysis of our Ca II H and K S-index measurements, spectral line bisectors, and Hipparcos photometry. We found no significant variations in these quantities with the 906 day period. We also reanalyzed the Ca II λ8662 measurements of Walker et al., which showed possible periodic variations with the "planet" period when first published. This analysis shows that periodic Ca II equivalent width variations were only present during 1986.5-1992 and absent during 1981-1986.5. Furthermore, a refined period for the Ca II λ8662 variations is 2.14 yr, significantly less than the residual radial velocity period. The most likely explanation of the residual radial velocity variations is a planetary-mass companion with M sin i = 1.7MJ and an orbital semimajor axis of a2 = 2.13 AU. This supports the planet hypothesis for the residual radial velocity variations for γ Cep first suggested by Walker et al. With an estimated binary orbital period of 57 yr, γ Cep is the shortest period binary system in which an extrasolar planet has been found. This system may provide insights into the relationship between planetary and binary star formation.

Determining the Inclination of the Rotation Axis of a Sun-like Star

Abstract: Asteroseismology provides us with the possibility of determining the angle, i, between the direction of the rotation axis of a pulsating Sun-like star and the line of sight. A knowledge of i is important not just for obtaining improved stellar parameters, but also in order to determine the true masses of extrasolar planets detected from the radial velocity shifts of their central stars. By means of Monte Carlo simulations, we estimate the precision of the measurement of i and other stellar parameters. We find that the inclination angle can be retrieved accurately when ie30 � for stars that rotate at least twice as fast as the Sun. Subject headings: planetary systems — stars: fundamental parameters — stars: oscillations — stars: rotation

On the Radii of Extrasolar Giant Planets

Abstract: We have computed evolutionary models for extrasolar planets that range in mass from 0.1MJ to 3.0MJ and that range in equilibrium temperature from 113 to 2000 K. We present four sequences of models, designed to show the structural effects of a solid (20 M⊕) core and of internal heating due to the conversion of kinetic to thermal energy at pressures of tens of bars. The model radii at ages of 4-5 Gyr are intended for future comparisons with radii derived from observations of transiting extrasolar planets. To provide such comparisons, we expect that of order 10 transiting planets with orbital periods less than 200 days can be detected around bright (V < 10-11) main-sequence stars, for which accurate well-sampled radial velocity (RV) measurements can also be readily accumulated. Through these observations, structural properties of the planets will be derivable, particularly for low-mass, high-temperature planets. Implications regarding the transiting companion to OGLE-TR-56 recently announced by Konacki et al. are discussed. With regard to the transiting planet HD 209458b, we find, in accordance with other recent calculations, that models without internal heating predict a radius that is ~0.3RJ smaller than the observed radius. Two resolutions have been proposed for this discrepancy. Guillot & Showman hypothesize that deposition of kinetic wind energy at pressures of tens of bars is responsible for heating the planet and maintaining its large size. Our models confirm that dissipation of the type proposed by Guillot & Showman can indeed produce a large radius for HD 209458b. Bodenheimer, Lin, & Mardling suggest that HD 209458b owes its large size to dissipation of energy arising from ongoing tidal circularization of the planetary orbit. This mechanism requires the presence of an additional planetary companion to continuously force the eccentricity. We show that residual scatter in the current RV data set for HD 209458b is consistent with the presence of an as-of-yet undetected second companion and that further RV monitoring of HD 209458 is indicated. Tidal circularization theory also can provide constraints on planetary radii. Extrasolar giant planets with periods of order 7 days should be actively circularizing. We find that the observed eccentricities of e ~ 0.14 for both HD 217107b (P = 6.276 days; M sin i = 1.80MJ) and HD 68988b (P = 7.125 days, M sin i = 1.29MJ) likely indicate either relatively small planetary radii for these objects (R ~ 1.1RJ) or tidal quality factors in the neighborhood of QP ~ 107. For these two planets, it will be difficult to differentiate the contribution from tidal and kinetic heating. But the radius of HD 168746b (P = 6.403 days, M sin i = 0.23MJ) is sensitive to whether the planet's interior is heated by tidal dissipation or kinetic heating. The tidal circularization timescale of this planet is shorter than the age of its host star, but we show that within the observational uncertainties, the published RV data can also be fitted with a circular orbit for this planet. As more RV planets with periods of order 1 week are discovered, QP(Teq,MP) and RP(Teq,MP) will become better determined.

Statistical properties of exoplanets. II. Metallicity, orbital parameters, and space velocities

Abstract: In this article we present a detailed spectroscopic analysis of more than 50 extra-solar planet host stars. Stellar atmospheric parameters and metallicities are derived using high resolution and high S/N spectra. The spectroscopy results, added to the previous studies, imply that we have access to a large and uniform sample of metallicities for about 80 planet hosts stars. We make use of this sample to confirm the metal-rich nature of stars with planets, and to show that the planetary frequency is rising as a function of the (Fe/H). Furthermore, the source of this high metallicity is shown to have most probably a "primordial" source, confirming previous results. The comparison of the orbital properties (period and eccentricity) and minimum masses of the planets with the stellar properties also reveal some emerging but still not significant trends. These are discussed and some explanations are proposed. Finally, we show that the planet host stars included in the CORALIE survey have similar kinematical properties as the whole CORALIE volume-limited planet search sample. Planet hosts simply seem to occupy the metal-rich envelope of this latter population.

Multiplicity among solar–type stars. III. Statistical properties of the F7-K binaries with periods up to 10 years

Abstract: Two CORAVEL radial velocity surveys - one among stars in the solar neighbourhood, the other in the Pleiades and in Praesepe - are merged to derive the statistical properties of main-sequence binaries with spectral types F7 to K and with periods up to 10 years. A sample of 89 spectroscopic orbits was finally obtained. Among them, 52 relate to a free-of-bias selection of 405 stars (240 field stars and 165 cluster stars). The statistics corrected for selection eects yield the following results: (1) No discrepancy is found between the binaries among field stars and the binaries in open cluster. The distributions of mass ratios, of periods, the period-eccentricity diagram and the binary frequencies are all within the same error intervals. (2) The distribution of mass ratios presents two maxima: a broad peak from q 0: 2t oq 0:7, and a sharp peak for q> 0:8 (twins). Both are present among the early-type as well as among the late-type part of the sample, indicating a scale-free formation process. The peak for q> 0:8 gradually decreases when long-period binaries are considered. Whatever their periods, the twins have eccentricities significantly lower than the other binaries, confirming a dierence in the formation processes. Twins could be generated by in situ formation followed by accretion from a gaseous envelope, whereas binaries with intermediate mass ratios could be formed at wide separations, but they are made closer by migration led by interactions with a circumbinary disk. (3) The frequency of binaries with P< 10 years is about 14%. (4) About 0.3% of binaries are expected to appear as false positives in a planet search. Therefore, the frequency of planetary systems among stars is presently 7 +4%. The extension of the distribution of mass ratios in

Periodic Flux Variability of Stars due to the Reflex Doppler Effect Induced by Planetary Companions

Abstract: Upcoming space-based photometric satellites offer the possibility of detecting continuum flux variability at the micromagnitude (μmag) level. We show that the Doppler flux variability induced by the reflex motion of stars due to planetary companions has an amplitude of (3 - α)K/c, where K is the reflex radial velocity amplitude and α ≈ is the logarithmic slope of the source spectral flux in the observed frequency band. For many of the known close-in planetary systems with periods P 0.2 yr, the periodic Doppler variability, (μmag), is significant relative to the variability caused by reflected light from the planetary companion. For companions with P 0.2 yr, the Doppler signal is larger than the reflected light signal. We show that the future photometric satellites should reach the sensitivity to detect this Doppler variability. In particular, the Kepler satellite should have the photon noise sensitivity to detect at a signal-to-noise ratio 5 all planets with minimum mass Mp sin i 5MJ and P 0.1 yr around the ~104 main-sequence stars with spectral types A-K and apparent magnitude V < 12 in its field of view.

Resonant trapping of planetesimals by planet migration: debris disk clumps and vega's similarity to the solar system

Abstract: This paper describes a model that can explain the observed clumpy structures of debris disks. Clumps arise because after a planetary system forms, its planets migrate because of angular momentum exchange with the remaining planetesimals. Outward migration of the outermost planet traps planetesimals outside its orbit into its resonances, and resonant forces cause azimuthal structure in their distribution. The model is based on numerical simulations of planets of different masses, Mpl, migrating at different rates, pl, through a dynamically cold (e < 0.01) planetesimal disk initially at a semimajor axis a. Trapping probabilities and the resulting azimuthal structures are presented for a planet's 2 : 1, 5 : 3, 3 : 2, and 4 : 3 resonances. Seven possible dynamical structures are identified from migrations defined by μ = Mpl/M* and θ = pl (a/*)1/2. Application of this model to the 850 μm image of Vega's disk shows that its two clumps of unequal brightness can be explained by the migration of a Neptune-mass planet from 40 to 65 AU over 56 Myr; tight constraints are set on possible ranges of these parameters. The clumps are caused by planetesimals in the 3 : 2 and 2 : 1 resonances; the asymmetry arises because of the overabundance of planetesimals in the 2 : 1(u) over the 2 : 1(l) resonance. The similarity of this migration to that proposed for our own Neptune hints that Vega's planetary system may be much more akin to the solar system than previously thought. Predictions are made that would substantiate this model, such as the orbital motion of the clumpy pattern, the location of the planet, and the presence of lower level clumps.

Embedded Clusters in Molecular Clouds

Abstract: Stellar clusters are born embedded within giant molecular clouds (GMCs) and during their formation and early evolution are often only visible at infrared wavelengths, being heavily obscured by dust. Over the last 15 years advances in infrared detection capabilities have enabled the first systematic studies of embedded clusters in galactic molecular clouds. In this article we review the current state of empirical knowledge concerning these extremely young protocluster systems. From a survey of the literature we compile the first extensive catalog of galactic embedded cluster properties. We use the catalog to construct the mass function and estimate the birthrate for embedded clusters within roughly 2 Kpc of the Sun. We find that the embedded cluster birthrate exceeds that of visible open clusters by an order of magnitude or more indicating a high infant mortality rate for protocluster systems. Less than 4-7% of embedded clusters survive emergence from molecular clouds to become bound clusters of Pleiades age. The vast majority (90%) of stars that form in embedded clusters form in rich clusters of 100 or more members with masses in excess of 50 solar masses. We review the role of embedded clusters in investigating the nature of the IMF which, in one nearby example, has been measured over the entire range of stellar and substellar mass, from OB stars to subsellar objects near the deuterium burning limit. We also review the role embedded clusters play in the investigation of circumstellar disk evolution and the important constraints they provide for understanding the origin of planetary systems. Finally, we discuss current ideas concerning the origin and dynamical evolution of embedded clusters and the implications for the formation of bound open clusters.

Expected Detection and False Alarm Rates for Transiting Jovian Planets

Abstract: Ground-based searches for transiting Jupiter-sized planets have so far produced few detections of planets but many of stellar systems with eclipse depths, durations, and orbital periods that resemble those expected from planets. The detection rates prove to be consistent with our present knowledge of binary and multiple-star systems and of Jovian-mass extrasolar planets. Space-based searches for transiting Earth-sized planets will be largely unaffected by the false alarm sources that afflict ground-based searches, except for distant eclipsing binaries whose light is strongly diluted by that of a foreground star. A by-product of the rate estimation is evidence that the period distribution of extrasolar planets is depressed for periods between 5 and 200 days.

Extrasolar Planets in Mean‐Motion Resonance: Apses Alignment and Asymmetric Stationary Solutions

Abstract: In recent years several pairs of extrasolar planets have been discovered in the vicinity of mean-motion commensurabilities. In some cases, such as the GJ 876 system, the planets seem to be trapped in a stationary solution, the system exhibiting a simultaneous libration of the resonant angle θ1 = 2λ2 - λ1 - 1 and of the relative position of the pericenters. In this paper we analyze the existence and location of these stable solutions, for the 2 : 1 and 3 : 1 resonances, as functions of the masses and orbital elements of both planets. This is undertaken via an analytical model for the resonant Hamiltonian function. The results are compared with those of numerical simulations of the exact equations. In the 2 : 1 commensurability, we show the existence of three principal families of stationary solutions: (1) aligned orbits, in which θ1 and 1 - 2 both librate around zero, (2) antialigned orbits, in which θ1 = 0 and the difference in pericenter is 180°, and (3) asymmetric stationary solutions, in which both the resonant angle and 1 - 2 are constants with values different from 0° or 180°. Each family exists in a different domain of values of the mass ratio and eccentricities of both planets. Similar results are also found in the 3 : 1 resonance. We discuss the application of these results to the extrasolar planetary systems and develop a chart of possible planetary orbits with apsidal corotation. We estimate, also, the maximum planetary masses in order for the stationary solutions to be dynamically stable.

Evidence for a T Tauri Phase in Young Brown Dwarfs

Abstract: As part of a multifaceted program to investigate the origin and early evolution of substellar objects, we present high-resolution Keck optical spectra of 14 very low mass sources in the IC 348 young cluster and the Taurus star-forming cloud. All of our targets, which span a range of spectral types from M5 to M8, exhibit moderate to very strong Hα emission. In half of the IC 348 objects, the Hα profiles are broad and asymmetric, indicative of ongoing accretion. Of these, IC 348-355 (M8) is the lowest mass object to date to show accretion-like Hα. Three of our ~M6 IC 348 targets with broad Hα also harbor broad O I (8446 A) and Ca II (8662 A) emission, and one shows broad He I (6678 A) emission; these features are usually seen in strongly accreting classical T Tauri stars. We find that in very low mass accretors, the Hα profile may be somewhat narrower than that in higher mass stars. We propose that low accretion rates combined with small infall velocities at very low masses can conspire to produce this effect. In the nonaccretors in our sample, Hα emission is commensurate with, or higher than, saturated levels in field M dwarfs of similar spectral type. Our results constitute the most compelling evidence to date that young brown dwarfs undergo a T Tauri-like accretion phase similar to that in stars. This is consistent with a common origin for most low-mass stars, brown dwarfs, and isolated planetary mass objects.

Secular evolution of hierarchical planetary systems

Abstract: We investigate the dynamical evolution of coplanar, hierarchical, two-planet systems where the ratio of the orbital semimajor axes α = a1/a2 is small Hierarchical two-planet systems are likely to be ubiquitous among extrasolar planetary systems We show that the orbital parameters obtained from a multiple-Kepler fit to the radial velocity variations of a host star are best interpreted as Jacobi coordinates and that Jacobi coordinates should be used in any analyses of hierarchical planetary systems An approximate theory that can be applied to coplanar, hierarchical, two-planet systems with a wide range of masses and orbital eccentricities is the octopole-level secular perturbation theory, which is based on an expansion to order α3 and orbit averaging It reduces the coplanar problem to 1 degree of freedom, with e1 (or e2) and 1 - 2 as the relevant phase-space variables (where e1,2 are the orbital eccentricities of the inner and outer orbits, respectively, and 1,2 are the longitudes of periapse) The octopole equations show that if the ratio of the maximum orbital angular momenta, λ = L1/L2 ≈ (m1/m2)α1/2, for given semimajor axes is approximately equal to a critical value λcrit, then libration of 1 - 2 about either 0° or 180° is almost certain, with possibly large amplitude variations of both eccentricities From a study of the HD 168443 and HD 12661 systems and their variants using both the octopole theory and direct numerical orbit integrations, we establish that the octopole theory is highly accurate for systems with α 01 and reasonably accurate even for systems with α as large as , provided that α is not too close to a significant mean-motion commensurability or above the stability boundary The HD 168443 system is not in a secular resonance, and its 1 - 2 circulates The HD 12661 system is the first extrasolar planetary system found to have 1 - 2 librating about 180° The secular resonance means that the lines of apsides of the two orbits are on average antialigned, although the amplitude of libration of 1 - 2 is large The libration of 1 - 2 and the large amplitude variations of both eccentricities in the HD 12661 system are consistent with the analytic results on systems with λ ≈ λcrit The evolution of the HD 12661 system with the best-fit orbital parameters and sin i = 1 (i is the inclination of the orbital plane from the plane of the sky) is affected by the close proximity to the 11 : 2 mean-motion commensurability, but small changes in the orbital period of the outer planet within the uncertainty can result in configurations that are not affected by mean-motion commensurabilities The stability of the HD 12661 system requires sin i > 03

Statistical properties of exoplanets - I. The period distribution: Constraints for the migration scenario

Abstract: Interesting emerging observational properties of the period-mass distribution of extra-solar planets are discussed. New recent detections confirm the already emphasized lack of massive planets ($m_2\sin{i}\ge 2\,M_{\rm Jup}$) on short-period orbits ($P\le 100$ days). Furthermore, we point out i) a shortage of planets in the 10–100 day period range as well as ii) a lack of light planets ($m_2\sin{i}\le 0.75\,M_{\rm Jup}$) on orbits with periods larger than ~100 days. The latter feature is shown not to be due to small-number statistics with Monte-Carlo simulations. These observational period-related characteristics are discussed in the context of the migration process of exoplanets. They are found to be in agreement with recent simulations of planet interactions with viscous disks. The observed valley at a few tens of days in the period distribution is interpreted as a transition region between two categories of planets that suffered different migration scenarios. The lack of light planets on longer-period orbits and the corresponding intriguing sharp limit in mass is tentatively explained by the runaway migration process recently studied by Masset & Papaloizou (2003). The observed properties also have implications for the observation strategies of the on-going surveys and of future higher-precision searches.

The geometry of resonant signatures in debris disks with planets

Abstract: Using simple geometrical arguments, we paint an overview of the variety of resonant structures a single planet with moderate eccentricity (e

Physics of the Solar System: Dynamics and Evolution, Space Physics, and Spacetime Structure

Abstract: 1. Dynamical Principles.- 2. The Gravitational Field of an Isolated Body.- 3. Planetary Rotation.- 4. Gravitational Torques and Tides.- 5. The Interior of the Earth.- 6. Planetary Magnetism.- 7. Atmospheres.- 8. Upper Atmospheres.- 9. The Sun and the Solar Wind.- 10. Magnetospheres.- 11. The Two-Body Problem.- 12. Perturbation Theory.- 13. The Three-Body Problem.- 14. The Planetary System.- 15. Dynamical Evolution of the Solar System.- 16. Origin of the Solar System.- 17. Relativistic Effects in the Solar System.- 18. Artificial Satellites.- 19. Telecommunications.- 20. Precise Measurements in Space.

Parent Stars of Extrasolar Planets. VII. New Abundance Analyses of 30 Systems

Abstract: The results of new spectroscopic analyses of 30 stars with giant planet and/or brown dwarf companions are presented. Values for Teff and [Fe/H] are used in conjunction with Hipparcos data and Padua isochrones to derive masses, ages, and theoretical surface gravities. These new data are combined with spectroscopic and photometric metallicity estimates of other stars harboring planets and published samples of F, G, and K dwarfs to compare several subsets of planet bearing stars with similarly well-constrained control groups. The distribution of [Fe/H] values continues the trend uncovered in previous studies in that stars hosting planetary companions have a higher mean value than otherwise similar nearby stars. We also investigate the relationship between stellar mass and the presence of giant planets, and we find statistically marginal but suggestive evidence of a decrease in the incidence of radial velocity companions orbiting relatively less massive stars. If confirmed with larger samples, this would represent a critical constraint to both planetary formation models, as well as to estimates of the distribution of planetary systems in our Galaxy.

Measuring the oblateness and rotation of transiting extrasolar giant planets

Abstract: We investigate the prospects for characterizing extrasolar giant planets by measuring planetary oblateness from transit photometry and inferring planetary rotational periods. The rotation rates of planets in the solar system vary widely, reflecting the planets' diverse formational and evolutionary histories. A measured oblateness, assumed composition, and equation of state yields a rotation rate from the Darwin-Radau relation. The light curve of a transiting oblate planet should differ significantly from that of a spherical one with the same cross-sectional area under identical stellar and orbital conditions. However, if the stellar and orbital parameters are not known a priori, fitting for them allows changes in the stellar radius, planetary radius, impact parameter, and stellar limb-darkening parameters to mimic the transit signature of an oblate planet, diminishing the oblateness signature. Thus, even if HD 209458b had an oblateness of 0.1 instead of our predicted 0.003, it would introduce a detectable departure from a model spherical light curve at the level of only one part in 105. Planets with nonzero obliquity break this degeneracy because their ingress light curve is asymmetric relative to that from egress and their best-case detectability is of order 10-4. However, the measured rotation rate for these objects is nonunique due to degeneracy between obliquity and oblateness and the unknown component of obliquity along the line of sight. Detectability of oblateness is maximized for planets transiting near an impact parameter of 0.7, regardless of obliquity. Future measurements of oblateness will be challenging because the signal is near the photometric limits of current hardware and inherent stellar noise levels.

Seven New Keck Planets Orbiting G and K Dwarfs

Abstract: Planetary mass companions orbiting seven nearby G and K dwarfs have been found from the Keck Precision Doppler Survey. A "51 Peg-like" planet orbiting HD 49674 has the smallest mass yet found, M sin i = 0.12 MJ. This system does not transit. A double-planet system orbits HD 37124, with periods of 153 days and 6 yr and minimum masses of 0.91 and 1.70 MJ. Single companions with moderate eccentricity have been found orbiting HD 108874, HD 72659, HD 114729, and HD 145675 with orbital periods ranging from 1.09 to 5.98 yr, yielding minimum masses ranging from 0.90 to 4.87 MJ. Periodic Doppler velocity variations, consistent with a mildly eccentric planet in a 1 AU orbit, are reported for the chromospherically active K0 dwarf HD 128311. It remains plausible that these velocity variations are due to stellar photospheric "jitter."

A Planetary Companion to the G-Type Giant Star HD 104985

Abstract: We report the detection of a planetary-mass companion to the G9 III giant star HD 104985 from precise Doppler velocity measurements made using the High Dispersion Echelle Spectrograph (HIDES) at Okayama Astrophysical Observatory. The radial velocity variability of this star is best explained by an orbital motion with a period of 198.2 ± 0.3 days, a velocity semiamplitude of 161 ± 2 m s-1, and an eccentricity of 0.03 ± 0.02. Assuming a stellar mass of 1.6 M☉, we obtained a minimum mass and a semimajor axis of 6.3MJ and 0.78 AU, respectively, for the companion. A probable upper limit to the stellar mass of 3 M☉ yielded m2 sin i = 9.6MJ, which falls in the planetary-mass regime. This is the first discovery of a planetary companion orbiting a G-type giant star.