Wide Dust Gaps in Protoplanetary Disks Induced by Eccentric Planets: A Mass-eccentricity Degeneracy

The tidal perturbation of embedded protoplanets on their natal disks has been widely attributed to be the cause of gap-ring structures in submillimeter images of protoplanetary disks around T Tauri stars. Numerical simulations of this process have been used to propose scaling of characteristic dust-gap width/gap-ring distance with respect to planet mass. Applying such scaling to analyze observed gap samples yields a continuous mass distribution for a rich population of hypothetical planets in the range of several Earth to Jupiter masses. In contrast, the conventional core-accretion scenario of planet formation predicts a bimodal mass function due to (1) the onset of runaway gas accretion above ∼20 Earth masses and (2) suppression of accretion induced by gap opening. Here, we examine the dust disk response to the tidal perturbation of eccentric planets as a possible resolution of this paradox. Based on simulated gas and dust distributions, we show the gap-ring separation of Neptune-mass planets with small eccentricities might become comparable to that induced by Saturn-mass planets on circular orbits. This degeneracy may obliterate the discrepancy between the theoretical bimodal mass distribution and the observed continuous gap width distribution. Despite damping due to planet–disk interaction, modest eccentricity may be sustained either in the outer regions of relatively thick disks or through resonant excitation among multiple super Earths. Moreover, the ring-like dust distribution induced by planets with small eccentricities is axisymmetric even in low viscosity environments, consistent with the paucity of vortices in Atacama Large Millimeter/submillimeter Array images.

Star formation in CALIFA survey perturbed galaxies – I. Effects of tidal interactions

ABSTRACT We explore the effects of tidal interactions on star formation (SF) by analysing a sample of CALIFA survey galaxies. The sample consists of tidally and non-tidally perturbed galaxies whose star-forming regions are paired at the closest stellar mass surface densities, even between the same galaxy types. The regions are then compared, both on the resolved star-formation main sequence (SFMS) plane and in annular property profiles. Star-forming regions in tidally perturbed galaxies exhibit flatter SFMS slopes compared to star-forming regions in non-tidally perturbed galaxies. Despite the fact that the annular profiles show star-forming regions in tidally perturbed galaxies as being mostly older, their SF properties are never reduced against those of non-tidally perturbed galaxies. Star-forming regions in non-tidally perturbed galaxies are better candidates for SF suppression (quenching). The lowered SF with increasing stellar mass density in tidally perturbed galaxies may suggest a lower dependence of SF on stellar mass. Though the SFMS slopes, either flatter or steeper, are found independent of stellar mass density, the effect of global stellar mass cannot be ignored when distinguishing between galaxy types. Since a phenomenon or property other than local/global stellar mass may be taking part in the modulation of SF, the integrated SF properties are related to the tidal perturbation parameter. We find weak, but detectable, positive correlations for perturbed galaxies suggesting that tidal perturbations induced by close companions increase the gas accretion rates of these objects.

Analytical Study of Earth Tides on Low Orbits Satellites

The main objective of this paper is to calculate the perturbations of tide effect on LEO's satellites . In order to achieve this goal, the changes in the orbital elements which include the semi major axis (a) eccentricity (e) inclination , right ascension of ascending nodes ( ), and fifth element argument of perigee ( ) must be employed. In the absence of perturbations, these element remain constant. The results show that the effect of tidal perturbation on the orbital elements depends on the inclination of the satellite orbit. The variation in the ratio decreases with increasing the inclination of satellite, while it increases with increasing the time.

Atmospheric tides in Earth-like planets

Context. Atmospheric tides can strongly affect the rotational dynamics of planets. In the family of Earth-like planets, which includes Venus, this physical mechanism coupled with solid tides makes the angular velocity evolve over long timescales and determines the equilibrium configurations of their spin. Aims. Unlike the solid core, the atmosphere of a planet is subject to both tidal gravitational potential and insolation flux coming from the star. The complex response of the gas is intrinsically linked to its physical properties. This dependence has to be characterized and quantified for application to the wide variety of extrasolar planetary systems. Methods. We develop a theoretical global model where radiative losses, which are predominant in slowly rotating atmospheres, are taken into account. We analytically compute the perturbation of pressure, density, temperature, and velocity field caused by a thermogravitational tidal perturbation. From these quantities, we deduce the expressions of atmospheric Love numbers and tidal torque exerted on the fluid shell by the star. The equations are written for the general case of a thick envelope and the simplified one of a thin isothermal atmosphere. Results. The dynamics of atmospheric tides depends on the frequency regime of the tidal perturbation: the thermal regime near synchronization and the dynamical regime characterizing fast-rotating planets. Gravitational and thermal perturbations imply different responses of the fluid, i.e. gravitational tides and thermal tides, which are clearly identified. The dependence of the torque on the tidal frequency is quantified using the analytic expressions of the model for Earth-like and Venus-like exoplanets and is in good agreement with the results given by global climate models (GCM) simulations.Introducing dissipative processes such as radiation regularizes the tidal response of the atmosphere, otherwise it is singular at synchronization. Conclusions. We demonstrate the important role played by the physical and dynamical properties of a super-Earth atmosphere (e.g. Coriolis, stratification, basic pressure, density, temperature, radiative emission) in its response to a tidal perturbation. We point out the key parameters defining tidal regimes (e.g. inertia, Brunt-Väisälä, radiative frequencies, tidal frequency) and characterize the behaviour of the fluid shell in the dissipative regime, which cannot be studied without considering the radiative losses.

Probing the mass assembly of massive nearby galaxies with deep imaging

According to a popular scenario supported by numerical models, the mass assembly and growth of massive galaxies, in particular the Early-Type Galaxies (ETGs), is, below a redshift of 1, mainly due to the accretion of multiple gas–poor satellites. In order to get observational evidence of the role played by minor dry mergers, we are obtaining extremely deep optical images of a complete volume limited sample of nearby ETGs. These observations, done with the CFHT as part of the ATLAS3D, NGVS and MATLAS projects, reach a stunning 28.5 – 29 mag.arcsec−2 surface brightness limit in the g' band. They allow us to detect the relics of past collisions such as faint stellar tidal tails as well as the very extended stellar halos which keep the memory of the last episodes of galactic accretion. Images and preliminary results from this on-going survey are presented, in particular a possible correlation between the fine structure index (which parametrizes the amount of tidal perturbation) of the ETGs, their stellar mass, effective radius and gas content.

Tidal Perturbation and Active Galaxy Nuclei

Theories of nuclear activity mechanisms in disk galaxies (such as Seyfert galaxies) range from intrinsic (e.g. bars) to external (tidal perturbation by passing companions). The Byrd et al. (1986, 1987) simulation survey determined the tidal perturbation necessary to induce nuclear activity. Observational surveys have raised doubt as to the tidal explanation of Seyfert-type activity in galaxies with some suggesting a weak or nonexistent correlation between tidal perturbation and Seyfert activity compared to a normal sample. The simulations show a several hundred million year delay in the appearance of activity after perturbation and a similar duration which can explain these null results. For double galaxies, we derive from the tidal hypothesis that: (1) There should be an excess of pairs where both are active over pairs with one active. (2) Nuclear activity will be preferentially excluded from pairs which are unequal and favorably distributed to pairs where the members are equal. (3) The size of pair members to create activity can be smaller if the pair members are equal in size than if they are unequal. (4) Pairs where one or both members are active should have a smaller velocity difference times separation than if both are normal. All the predictions are seen in observations of activity in Karachentsev’s (1983) list of double galaxies. Optimally, statistical studies of nuclear activity and companions should include their sizes, separations, and radial velocities relative to the primary. The study by Dultzin-Hacyan et al. (1999) which finds an excess of large companions around Seyfert 2 galaxies is a step in the right direction.