Stability of planets in triple star systems

Context: Numerous theoretical studies of the stellar dynamics of triple systems have been carried out, but fewer purely empirical studies that have addressed planetary orbits within these systems. Most of these empirical studies have been for coplanar orbits and with a limited number of orbital parameters. Aims: Our objective is to provide a more generalized empirical mapping of the regions of planetary stability in triples by considering both prograde and retrograde motion of planets and the outer star; investigating highly inclined orbits of the outer star; extending the parameters used to all relevant orbital elements of the triple's stars and expanding these elements and mass ratios to wider ranges that will accommodate recent and possibly future observational discoveries. Methods: Using N-body simulations, we integrated numerically the various four-body configurations over the parameter space, using a symplectic integrator designed specifically for the integration of hierarchical multiple stellar systems. The triples were then reduced to binaries and the integrations repeated to highlight the differences between these two types of system. Results: This established the regions of secular stability and resulted in 24 semi-empirical models describing the stability bounds for planets in each type of triple orbital configuration. The results were then compared with the observational extremes discovered to date to identify regions that may contain undiscovered planets.Comment: 12 pages, 8 figures, 14 tables. Accepted for publication in Astronomy & Astrophysic

New constrains on Gliese 86 B

We present the results of multi epochs imaging observations of the companion to the planetary host Gliese 86. Associated to radial velocity measurements, this study aimed at characterizing dynamically the orbital properties and the mass of this companion (here after Gliese 86 B), but also at investigating the possible history of this particular system. We used the adaptive optics instrument NACO at the ESO Very Large Telescope to obtain deep coronographic imaging in order to determine new photometric and astrometric measurements of Gliese 86 B. Part of the orbit is resolved. The photometry of Gliese B indicates colors compatible with a ~70 Jupiter mass brown dwarf or a white dwarf. Both types of objects allow to fit the available, still limited astrometric data. Besides, if we attribute the long term radial velocity residual drift observed for Gliese A to B, then the mass of the latter object is ~0.5 Msun. We analyse both astrometric and radial velocity data to propose first orbital parameters for Gliese B. Assuming Gliese B is a ~0.5 Msun white dwarf, we explore the constraints induced by this hypothesis and refine the parameters of the system.Comment: 10 pages, 18 figures, accepted in A&

High-Resolution Imaging of the Dust Disk around 49 Ceti

Sub-arcsecond scale Keck images of the young A1V star, 49 Ceti, resolve emission at lambda = 12.5 and 17.9 microns from a disk with long axis at PA 125 pm 10 degrees and inclination phi = 60 pm 15 degrees . At 17.9 microns, the emission is brighter and more extended toward the NW than the SE. Modeling of the mid-infrared images combined with flux densities from the literature indicate that the bulk of the mid-infrared emission comes from very small grains (a ~ 0.1 microns) confined between 30 and 60 AU from the star. This population of dust grains contributes negligibly to the significant excess observed in the spectral energy distribution. Most of the non- photospheric energy is radiated at longer wavelengths by an outer disk of larger grains (a ~ 15 microns), inner radius ~ 60 AU, and outer radius ~ 900 AU. Global properties of the 49 Cet disk show more affinity with the Beta Pic and HR 4796A disks than with other debris disks. This may be because they are all very young (t < 20 Myr), adding strength to the argument that they are transitional objects between Herbig Ae and "Vega-like" A stars with more tenuous circumstellar disks.Comment: 19 pages, 6 figures. Accepted for publicaion in Ap

Optical SETI: A Spectroscopic Search for Laser Emission from Nearby Stars

We have searched for nonastrophysical emission lines in the optical spectra of 577 nearby F, G, K, and M main-sequence stars. Emission lines of astrophysical origin would also have been detected, such as from a time--variable chromosphere or infalling comets. We examined ~20 spectra per star obtained during four years with the Keck/HIRES spectrometer at a resolution of 5 km/s, with a detection threshold 3% of the continuum flux level. We searched each spectrum from 4000-5000 angstroms for emission lines having widths too narrow to be natural from the host star, as well as for lines broadened by astrophysical mechanisms. We would have detected lasers that emit a power, P>60 kW, for a typical beam width of ~0.01 arcsec (diffraction-limit from a 10-m aperture) if directed toward Earth from the star. No lines consisstent with laser emission were found.Comment: 27 pages, 11 figures, uses aastex.st

Investigating the flyby scenario for the HD 141569 system

HD 141569, a triple star system, has been intensively observed and studied for its massive debris disk. It was rather regarded as a gravitationally bound triple system but recent measurements of the HD 141569A radial velocity seem to invalidate this hypothesis. The flyby scenario has therefore to be investigated to test its compatibility with the observations. We present a study of the flyby scenario for the HD141569 system, by considering 3 variants: a sole flyby, a flyby associated with one planet and a flyby with two planets. We use analytical calculations and perform N-body numerical simulations of the flyby encounter. The binary orbit is found to be almost fixed by the observational constraint on a edge-on plane with respect to the observers. If the binary has had an influence on the disk structure, it should have a passing time at the periapsis between 5000 and 8000 years ago and a distance at periapsis between 600 and 900 AU. The best scenario for reproducing the disk morphology is a flyby with only 1 planet. For a 2 Mj (resp. 8 Mj) planet, its eccentricity must be around 0.2 (resp. below 0.1). In the two cases, its apoapsis is about 130 AU. Although the global disk shape is reasonably well reproduced, some features cannot be explain by the present model and the likehood of the flyby event remains an issue. Dynamically speaking, HD 141569 is still a puzzling system

On the observability of resonant structures in planetesimal disks due to planetary migration

We present a thorough study of the impact of a migrating planet on a planetesimal disk, by exploring a broad range of masses and eccentricities for the planet. We discuss the sensitivity of the structures generated in debris disks to the basic planet parameters. We perform many N-body numerical simulations, using the symplectic integrator SWIFT, taking into account the gravitational influence of the star and the planet on massless test particles. A constant migration rate is assumed for the planet. The effect of planetary migration on the trapping of particles in mean motion resonances is found to be very sensitive to the initial eccentricity of the planet and of the planetesimals. A planetary eccentricity as low as 0.05 is enough to smear out all the resonant structures, except for the most massive planets. The planetesimals also initially have to be on orbits with a mean eccentricity of less than than 0.1 in order to keep the resonant clumps visible. This numerical work extends previous analytical studies and provides a collection of disk images that may help in interpreting the observations of structures in debris disks. Overall, it shows that stringent conditions must be fulfilled to obtain observable resonant structures in debris disks. Theoretical models of the origin of planetary migration will therefore have to explain how planetary systems remain in a suitable configuration to reproduce the observed structures.Comment: 16 pages, 13 figures. Accepted for publication in A&

Dust Production from collisions in extrasolar planetary systems The inner Beta-Pictoris disc

Dust particles observed in extrasolar planetary discs originate from undetectable km-sized bodies but this valuable information remains uninteresting if the theoretical link between grains and planetesimals is not properly known. We outline in this paper a numerical approach we developed in order to address this issue for the case of dust producing collisional cascades. The model is based on a particle-in-a-box method. We follow the size distribution of particles over eight orders of magnitude in radius taking into account fragmentation and cratering according to different prescriptions. A very particular attention is paid to the smallest particles, close to the radiation pressure induced cut-off size $R_{pr}$, which are placed on highly eccentric orbits by the stellar radiation pressure....(abstract continued in the uploaded paper)Comment: A&A accepted (in press

Mixing and Accretion in lambda Bootis Stars

Strong evidence for deep mixing has been uncovered for slowly rotating F, and A stars of the main sequence. As the accretion/diffusion model for the formation of lboo stars is heavily dependent on mixing in superficial regions, such deep mixing may have important repercussions on our understanding of these stars. It is shown that deep mixing at a level similar to that of FmAm stars increases the amount of matter that needs to be accreted by the stars with respect with the standard models by some three orders of magnitude. It is also shown that significantly larger accretion rates have to be maintained, as high as $10^{-11}$~M_\sun yr^{-1}, to prevent meridional circulation from canceling the effect of accretion. The existence of old ($\approx 1$~Gyr) is not a likely outcome of the present models for accretion/diffusion with or without deep mixing. It is argued that lboo stars are potentially very good diagnostics of mixing mechanisms in moderately fast rotators.Comment: To appear in Astrophysical Journal Letters. 4 pages, 2 fgure

High latitude gas in the Beta Pictoris system. A possible origin related to Falling Evaporating Bodies

The presence of off-plane Ca II ions in the Beta Pictoris disk, and the non-detection of off-plane Na I atoms, can be explained as a consequence of the evaporation process of Falling Evaporating Bodies (FEBs). In the star-grazing regime, the FEBs are subject to inclination oscillations up to 30 - 40 degrees that causes most metallic species released by sublimation to move off plane The ions are be stopped at about 100 AU from the star. We show that collisions with a neutral medium can stop the ions. The required H I column density is reduced to 10^17 cm^-2, one order of magnitude below present detection limits. We also investigate the possibility that the ions are slowed down magnetically. While the sole action of a magnetic field of the order of 1 microGauss is not effective, the combined effect of magnetic and collisional deceleration processes lead to an additional lowering of the required H I column density.Comment: 17 page