Evidence for Prolonged Main Sequence Stellar Evolution of F Stars in close binaries

Binary F stars exhibit large brightness anomaly, which is defined here as the difference between the absolute magnitude from the uvby photometry and the actual absolute magnitude of the star. We have found that the anomaly inversely correlates with the binary components separation. There is evidence that the correlation reflects actual population differences between close and wide binary pairs, in which case it indicates that the anomaly is somehow associated with the interaction of binary's components. The anomaly has also been found to correlate with both kinematics and metallicity. The sense of the correlations implies that the anomaly increases as the star evolves, suggesting a peculiar evolution of a primary F star in a tight binary pair. This conclusion has further been supported by the study of the age-velocity relation (AVR) of F stars that are cataloged in the HIPPARCOS as single. Among these stars, those with brightness anomaly were previously shown to be most likely unidentified close binaries. We have found that the AVR of these binary candidates is different from that of the ``truly single'' F stars. The discrepancy between the two AVRs indicates that the putative binaries are, on average, older than similar normal single F stars at the same effective temperature and luminosity, which is consistent with the inferred peculiar evolution in close binaries. It appears that this peculiarity is caused by the impact of the components interaction in a tight pair on stellar evolution, which results in the prolonged main sequence lifetime of the primary F star.Comment: 8 pages, 7 figures, accepted by Astronomy and Astrophysic

Effect of core--mantle and tidal torques on Mercury's spin axis orientation

The rotational evolution of Mercury's mantle and its core under conservative and dissipative torques is important for understanding the planet's spin state. Dissipation results from tides and viscous, magnetic and topographic core--mantle interactions. The dissipative core--mantle torques take the system to an equilibrium state wherein both spins are fixed in the frame precessing with the orbit, and in which the mantle and core are differentially rotating. This equilibrium exhibits a mantle spin axis that is offset from the Cassini state by larger amounts for weaker core--mantle coupling for all three dissipative core--mantle coupling mechanisms, and the spin axis of the core is separated farther from that of the mantle, leading to larger differential rotation. The relatively strong core--mantle coupling necessary to bring the mantle spin axis to its observed position close to the Cassini state is not obtained by any of the three dissipative core--mantle coupling mechanisms. For a hydrostatic ellipsoidal core--mantle boundary, pressure coupling dominates the dissipative effects on the mantle and core positions, and dissipation together with pressure coupling brings the mantle spin solidly to the Cassini state. The core spin goes to a position displaced from that of the mantle by about 3.55 arcmin nearly in the plane containing the Cassini state. With the maximum viscosity considered of $\nu\sim 15.0\,{\rm cm^2/s}$ if the coupling is by the circulation through an Ekman boundary layer or $\nu\sim 8.75\times 10^5\,{\rm cm^2/s}$ for purely viscous coupling, the core spin lags the precessing Cassini plane by 23 arcsec, whereas the mantle spin lags by only 0.055 arcsec. Larger, non hydrostatic values of the CMB ellipticity also result in the mantle spin at the Cassini state, but the core spin is moved closer to the mantle spin.Comment: 35 pages, 7 figure

Une sonde photométrique pour l'analyse in situ : Principe, méthode, premiers essais

Certains composés dissous ne sont pas stables une fois prélevés hors de leur milieu. Pour éviter que l'information ne se perde entre le prélèvement et l'analyse, il est nécessaire d'effectuer cette dernière in situ. La solution que nous présentons, consiste à développer une réaction colorimétrique en profondeur; la cellule photométrique est immergée et reliée à un spectrophotomètre en surface, par 2 fibres optiques (fig. 1a, b, c). Cependant, lors d'un essai préliminaire, nous avons observé que, dans le circuit de mélange de la sonde, les proportions entre réactif et échantillon ne sont pas constantes. Ces variations de débits sont corrigées par des mesures à deux longueurs d'onde (λ1 et λ2)* et par l'adjonction d'un colorant auxiliaire ne perturbant pas la réaction calorimétrique. L'étalonnage se fait directement sur la cellule photométrique : dans un diagramme Absorbance à λ1 = f (Absorbance à λ2) (fig. 2), on place une droite d'étalonnage et des points particuliers. Les règles de mélange sont vérifiées indépendamment de toute réaction chimique avec différentes solutions d'hélianthine dans un tampon à pH 7 et du rouge de chlorophénol à la place du réactif (fig. 4 et 5). En outre nous utilisons le rouge de chlorophénol, jaune sous forme acide, comme colorant auxiliaire pour le dosage du fer total dans un premier essai in situ (lac d'Aydat, Puy de Dôme, France). Les résultats sont comparés à ceux obtenus par prélèvements et analyses au laboratoire (fig. 6). L'accord est satisfaisant. L'incorporation au système présenté, d'une pompe osmotique devrait permettre, avec cet appareillage simple, des mesures pendant plusieurs mois sans intervention.Various dissolved compounds are mot stables in surface conditions. We realized a prototype to collect chemical data related to redox sensitive species without any contact with the atmospheric oxygen.The principle of this probe for in situ measurements is to produce colorimetric reaction in depth. A photometric cell and a horizontal coiled glass tube for fluid mixing are immersed and connected with two optic fibers to a spectrophotometer on boat (fig. la, b, c). Reagent is injected continuously from surface and sample is sucked up with a peristaltic pump through a tubular filter.Every species which can be analysed by colorimetric method should be determined, in deep river or in lake, with this simple equipment.Nevertheless, during preliminary trial, we detected a lack of reproducibility in the mixing ratio of the sample with the complexing agent. The problem is solved by adding an auxiliary dye with reagent and measuring optical densities at two different wavelengths (λ1 and λ2). In the system, with a the sample proportion, absorbance A at λ is expressed as :A=ɛe∙l∙Ce∙α+ɛr∙l∙Cr∙(1-α)We suggest to calibrate directly the cell of the probe and work in a calibration graph. It is built with first, marking on an A1λ1=f(A2λ2)graph (fig. 2), the « pivot » point (P) (when α= 0), second, plotting the « calibration curve »A2=A1 (ɛe2/ɛe1)(when α= 1), third, plotting the different S1 (A1i, A2i) measured from standards. Therefore, if sample signal Re at two wavelengths is plotted in this graph, by joining P and Re, the straight line intersects with calibration curve at C. On this curve, interpolation of C between two standards determine the concentration of the analyte.Experimental verification of the mixing rule has been clone independently of chemical reaction, with different heliantine solutions in pH 7 buffer as samples and chlorophenol red as reagent, bath in laboratory and at 15 meters depth (Beffes lake, France) (fig. 4 and 5).Furthermore, chlorophenol red, previously tested, is used as auxiliary dye for total iron measurement, in Aydat lake (Puy de Dôme, France) for a first in situ trial.Results are compared to those got from oceanographic bottle sampling and laboratory analysis (fig. 6). Data from the probe are in good agreement with data from the laboratory method.Next development of this chemical sensor will consist in adding to the system an osmotic pump which should allow measurements without intervention during several months

Tidal decay and circularization of the orbits of short-period planets

We analyze the long-term tidal evolution of a single-planet system through the use of numerical simulations and averaged equations giving the variations of semi-major axis and eccentricity of the relative orbit. For different types of planets, we compute the variations due to the planetary and stellar tides. Then, we calculate the critical value of the eccentricity for which the stellar tide becomes dominant over the planetary tide. The timescales for orbital decay and circularization are also discussed and compared.Comment: 8 pages, 3 figures, corrected typo

On the equilibrium rotation of Earth-like extra-solar planets

The equilibrium rotation of tidally evolved "Earth-like" extra-solar planets is often assumed to be synchronous with their orbital mean motion. The same assumption persisted for Mercury and Venus until radar observations revealed their true spin rates. As many of these planets follow eccentric orbits and are believed to host dense atmospheres, we expect the equilibrium rotation to differ from the synchronous motion. Here we provide a general description of the allowed final equilibrium rotation states of these planets, and apply this to already discovered cases in which the mass is lower than twelve Earth-masses. At low obliquity and moderate eccentricity, it is shown that there are at most four distinct equilibrium possibilities, one of which can be retrograde. Because most presently known "Earth-like" planets present eccentric orbits, their equilibrium rotation is unlikely to be synchronous.Comment: 4 pages, 2 figures. accepted for publication in Astronomy and Astrophysics. to be published in Astronomy and Astrophysic

On planetary mass determination in the case of super-Earths orbiting active stars. The case of the CoRoT-7 system

This investigation uses the excellent HARPS radial velocity measurements of CoRoT-7 to re-determine the planet masses and to explore techniques able to determine mass and elements of planets discovered around active stars when the relative variation of the radial velocity due to the star activity cannot be considered as just noise and can exceed the variation due to the planets. The main technique used here is a self-consistent version of the high-pass filter used by Queloz et al. (2009) in the first mass determination of CoRoT-7b and CoRoT-7c. The results are compared to those given by two alternative techniques: (1) The approach proposed by Hatzes et al. (2010) using only those nights in which 2 or 3 observations were done; (2) A pure Fourier analysis. In all cases, the eccentricities are taken equal to zero as indicated by the study of the tidal evolution of the system; the periods are also kept fixed at the values given by Queloz et al. Only the observations done in the time interval BJD 2,454,847 - 873 are used because they include many nights with multiple observations; otherwise it is not possible to separate the effects of the rotation fourth harmonic (5.91d = Prot/4) from the alias of the orbital period of CoRoT-7b (0.853585 d). The results of the various approaches are combined to give for the planet masses the values 8.0 \pm 1.2 MEarth for CoRoT-7b and 13.6 \pm 1.4 MEarth for CoRoT 7c. An estimation of the variation of the radial velocity of the star due to its activity is also given.The results obtained with 3 different approaches agree to give masses larger than those in previous determinations. From the existing internal structure models they indicate that CoRoT-7b is a much denser super-Earth. The bulk density is 11 \pm 3.5 g.cm-3 . CoRoT-7b may be rocky with a large iron core.Comment: 12 pages, 11 figure

Detectability of Weakly Interacting Massive Particles in the Sagittarius Dwarf Tidal Stream

Tidal streams of the Sagittarius dwarf spheroidal galaxy (Sgr) may be showering dark matter onto the solar system and contributing approx (0.3--23)% of the local density of our Galactic Halo. If the Sagittarius galaxy contains WIMP dark matter, the extra contribution from the stream gives rise to a step-like feature in the energy recoil spectrum in direct dark matter detection. For our best estimate of stream velocity (300 km/sec) and direction (the plane containing the Sgr dwarf and its debris), the count rate is maximum on June 28 and minimum on December 27 (for most recoil energies), and the location of the step oscillates yearly with a phase opposite to that of the count rate. In the CDMS experiment, for 60 GeV WIMPs, the location of the step oscillates between 35 and 42 keV, and for the most favorable stream density, the stream should be detectable at the 11 sigma level in four years of data with 10 keV energy bins. Planned large detectors like XENON, CryoArray and the directional detector DRIFT may also be able to identify the Sgr stream.Comment: 26 pages, 4 figure

Gaia Data Processing Architecture

Gaia is ESA's ambitious space astrometry mission the main objective of which is to astrometrically and spectro-photometrically map 1000 Million celestial objects (mostly in our galaxy) with unprecedented accuracy. The announcement of opportunity for the data processing will be issued by ESA late in 2006. The Gaia Data Processing and Analysis Consortium (DPAC) has been formed recently and is preparing an answer. The satellite will downlink close to 100 TB of raw telemetry data over 5 years. To achieve its required accuracy of a few 10s of Microarcsecond astrometry, a highly involved processing of this data is required. In addition to the main astrometric instrument Gaia will host a Radial Velocity instrument, two low-resolution dispersers for multi-color photometry and two Star Mappers. Gaia is a flying Giga Pixel camera. The various instruments each require relatively complex processing while at the same time being interdependent. We describe the overall composition of the DPAC and the envisaged overall architecture of the Gaia data processing system. We shall delve further into the core processing - one of the nine, so-called, coordination units comprising the Gaia processing system.Comment: 10 Pages, 2 figures. To appear in ADASS XVI Proceeding

Tidal friction in close-in satellites and exoplanets. The Darwin theory re-visited

This report is a review of Darwin's classical theory of bodily tides in which we present the analytical expressions for the orbital and rotational evolution of the bodies and for the energy dissipation rates due to their tidal interaction. General formulas are given which do not depend on any assumption linking the tidal lags to the frequencies of the corresponding tidal waves (except that equal frequency harmonics are assumed to span equal lags). Emphasis is given to the cases of companions having reached one of the two possible final states: (1) the super-synchronous stationary rotation resulting from the vanishing of the average tidal torque; (2) the capture into a 1:1 spin-orbit resonance (true synchronization). In these cases, the energy dissipation is controlled by the tidal harmonic with period equal to the orbital period (instead of the semi-diurnal tide) and the singularity due to the vanishing of the geometric phase lag does not exist. It is also shown that the true synchronization with non-zero eccentricity is only possible if an extra torque exists opposite to the tidal torque. The theory is developed assuming that this additional torque is produced by an equatorial permanent asymmetry in the companion. The results are model-dependent and the theory is developed only to the second degree in eccentricity and inclination (obliquity). It can easily be extended to higher orders, but formal accuracy will not be a real improvement as long as the physics of the processes leading to tidal lags is not better known.Comment: 30 pages, 7 figures, corrected typo

Tidal torques. A critical review of some techniques

We point out that the MacDonald formula for body-tide torques is valid only in the zeroth order of e/Q, while its time-average is valid in the first order. So the formula cannot be used for analysis in higher orders of e/Q. This necessitates corrections in the theory of tidal despinning and libration damping. We prove that when the inclination is low and phase lags are linear in frequency, the Kaula series is equivalent to a corrected version of the MacDonald method. The correction to MacDonald's approach would be to set the phase lag of the integral bulge proportional to the instantaneous frequency. The equivalence of descriptions gets violated by a nonlinear frequency-dependence of the lag. We explain that both the MacDonald- and Darwin-torque-based derivations of the popular formula for the tidal despinning rate are limited to low inclinations and to the phase lags being linear in frequency. The Darwin-torque-based derivation, though, is general enough to accommodate both a finite inclination and the actual rheology. Although rheologies with Q scaling as the frequency to a positive power make the torque diverge at a zero frequency, this reveals not the impossible nature of the rheology, but a flaw in mathematics, i.e., a common misassumption that damping merely provides lags to the terms of the Fourier series for the tidal potential. A hydrodynamical treatment (Darwin 1879) had demonstrated that the magnitudes of the terms, too, get changed. Reinstating of this detail tames the infinities and rehabilitates the "impossible" scaling law (which happens to be the actual law the terrestrial planets obey at low frequencies).Comment: arXiv admin note: sections 4 and 9 of this paper contain substantial text overlap with arXiv:0712.105