We monitored the chromospheric activity in the Ca ii H and K lines of 13 solar-type stars (including the Sun): 8 of them over 3 years at the Canada-France-Hawaii Telescope (CFHT) and 5 in a single run at the Very Large Telescope (VLT). A total of 10 of the 13 targets have close planetary companions. All of the stars observed at the CFHT show long-term (months to years) changes in H and K intensity levels. Four stars display short-term (days) cyclical activity. For two, HD 73256 and 1 Cet, the activity is likely associated with an active region rotating with the star; however, the flaring in excess of the rotational modulation may be associated with a hot Jupiter. A planetary companion remains a possibility for 1 Cet. For the other two, HD 179949 and And, the cyclic variation is synchronized to the hot Jupiter's orbit. For both stars this synchronicity with the orbit is clearly seen in two out of three epochs. The effect is only marginal in the third epoch at which the seasonal level of chromospheric activity had changed for both stars. Short-term chromospheric activity appears weakly dependent on the mean K line reversal intensities for the sample of 13 stars. In addition, a suggestive correlation exists between this activity and the M p sin i of the star's hot Jupiter. Because of their small separation ( 0.1 AU ), many of the hot Jupiters lie within the Alfvén radius of their host stars, which allows a direct magnetic interaction with the stellar surface. We discuss the conditions under which a planet's magnetic field might induce activity on the stellar surface and why no such effect was seen for the prime candidate, Boo. This work opens up the possibility of characterizing planet-star interactions, with implications for extrasolar planet magnetic fields and the energy contribution to stellar atmospheres.

We investigate the possibility of substantial inflation of short-period Jupiter-mass planets, as a result of their internal tidal dissipation associated with the synchronization and circularization of their orbits. We employ the simplest prescription based on an equilibrium model with a constant lag angle for all components of the tide. We show that 1) in the low-eccentricity limit, the synchronization of the planets' spin with their mean motion is established before tidal dissipation can significantly modify their internal structure. 2) But, above a critical eccentricity, which is a function of the planets' semimajor axis, tidal dissipation of energy during the circularization process can induce planets to inflate in size before their eccentricity is damped. 3) For moderate eccentricities, the planets adjust to stable thermal equilibria in which the rate of their internal tidal dissipation is balanced by the enhanced radiative flux associated with their enlarged radii. 4) For sufficiently large eccentricities, the planets swell beyond two Jupiter radii and their internal degeneracy is partially lifted. Thereafter, their thermal equilibria become unstable and they undergo runaway inflation until their radii exceed the Roche radius. 5) We determine the necessary and sufficient condition for this tidal inflation instability. 6) These results are applied to study short-period planets. We show that for young Jupiter-mass planets, with a period less than 3 days, an initial radius about 2 Jupiter radii, and an orbital eccentricity greater than 0.2, the energy dissipated during the circularization of their orbits is sufficiently intense and protracted to inflate their sizes up to their Roche radii. 7) We estimate the mass loss rate, the asymptotic planetary masses, and the semi-major axes for various planetary initial orbital parameters. The possibility of gas overflow through both inner (L1) and outer (L2) Lagrangian points for the planets with short periods or large eccentricities is discussed. 8) Planets with more modest eccentricity (< 0.3) and semi-major axis (> 0.03 − 0.04 AU) lose mass via Roche-lobe overflow mostly through the inner Lagrangian (L1) point. Due to the conservation of total angular momentum, these mass-losing planets migrate outwards, such that their semi-major

Three-dimensional equatorial trapped waves excited by stellar isolation and the resulting equatorial superrotating jet in a vertical stratified atmosphere of a tidally-locked hot Jupiter are investigated. Taking the hot Jupiter HD 189733b as a fiducial example, we analytically solve linear equations subject to stationary stellar heating with a uniform zonal-mean flow included. We also extract wave information in the final equilibrium state of the atmosphere from our radiative hydrodynamical simulation for HD 189733b. Our analytic wave solutions are able to qualitatively explain the three-dimensional simulation results. Apart from previous wave studies, investigating the vertical structure of waves allows us to explore new wave features such as the wavefronts tilts related to the Rossbywave resonance as well as dispersive equatorial waves. We also attempt to apply our linear wave analysis to explain some numerical features associated with the equatorial jet development seen in the general circulation model by Showman and Polvani. During the spin-up phase of the equatorial jet, the acceleration of the jet can be in principle boosted by the Rossby-wave resonance. However, we also find that as the jet speed increases, the Rossby-wave structure shifts eastward, while the Kelvin-wave structure remains approximately stationary, leading to the decline of the acceleration rate. Our analytic model of jet evolution implies that there exists only one stable equilibrium state of the atmosphere, possibly implying that the final state of the atmosphere is independent of initial conditions in the linear regime. Limitations of our linear model and future improvements are also discussed.

We present our observational results of the 1.1 mm continuum and the HCO + (3-2) line in HL Tau at angular resolutions of 0. 1 obtained with ALMA and our data analysis of the 2.9 mm and 1.1 mm continuum and the HCO + (3-2) and (1-0) lines of the HL Tau disk. The Keplerian rotation of the HL Tau disk is well resolved in the HCO + (3-2) emission, and the stellar mass is estimated to be 2.1±0.2 M with a disk inclination angle of 47 • . The radial profiles of the HCO + column density and excitation temperature are measured with the LTE analysis of the two transitions of the HCO + emission. An HCO + gas gap at a radius of 30 au, where the column density drops by a factor of 4-8, is found in the HCO + column density profile, coincident with the dust gap traced by the continuum emission. No other clear HCO + gas gap is seen. This HCO + gas gap can be opened by a planet with mass of 0.5-0.8 M J , which is comparable to the planet mass adopted in numerical simulations to form the dust gap at the same radius in the HL Tau disk. In addition to the disk component, a one-arm spiral with a length of ∼3 (520 au) stretching out from the inner disk is observed in the HCO + (3-2) emission. The observed velocity structures along the spiral suggest an infalling and rotating gas stream toward the inner disk.

Several short-period Jupiter-mass planets have been discovered around nearby solar-type stars. During the circularization of their orbits, the dissipation of tidal disturbance by their host stars heats the interior and inflates the sizes of these planets. Based on a series of internal structure calculations for giant planets, we examine the physical processes that determine their luminosity-radius relation. In the gaseous envelope of these planets, efficient convection enforces a nearly adiabatic stratification. During their gravitational contraction, the planets' radii are determined, through the condition of a quasi-hydrostatic equilibrium, by their central pressure. In interiors of mature, compact, distant planets, such as Jupiter, degeneracy pressure and the nonideal equation of state determine their structure. However, in order for young or intensely heated gas giant planets to attain quasihydrostatic equilibria, with sizes comparable to or larger than 2R J , their interiors must have sufficiently high temperature and low density such that degeneracy effects are relatively weak. Consequently, the effective polytropic index monotonically increases, whereas the central temperature increases and then decreases with the planets' size. These effects, along with a temperature-sensitive opacity for the radiative surface layers of giant planets, cause the power index of the luminosity's dependence on radius to decrease with increasing radius. For planets larger than twice Jupiter's radius, this index is sufficiently small that they become unstable to tidal inflation. We make comparisons between cases of uniform heating and cases in which the heating is concentrated in various locations within the giant planet. Based on these results, we suggest that accurate measurement of the sizes of close-in young Jupiters can be used to probe their internal structure under the influence of tidal heating. Subject headings: planetary systems -planets and satellites: general On-line material: color figure

Aims. The protoplanetary disk around HL Tau is so far the youngest candidate of planet formation, and it is still embedded in a protostellar envelope with a size of thousands of au. In this work, we study the gas kinematics in the envelope and its possible influence on the embedded disk. Methods. We present our new ALMA cycle 3 observational results of HL Tau in the 13 CO (2-1) and C 18 O (2-1) emission at resolutions of 0 ′′. 8 (110 au), and we compare the observed velocity pattern with models of different kinds of gas motions. Results. Both the 13 CO and C 18 O emission lines show a central compact component with a size of 2 ′′ (280 au), which traces the protoplanetary disk. The disk is clearly resolved and shows a Keplerian motion, from which the protostellar mass of HL Tau is estimated to be 1.8±0.3 M ⊙ , assuming the inclination angle of the disk to be 47 • from the plane of the sky. The 13 CO emission shows two arc structures with sizes of 1000-2000 au and masses of 3 × 10 −3 M ⊙ connected to the central disk. One is blueshifted and stretches from the northeast to the northwest, and the other is redshifted and stretches from the southwest to the southeast. We find that simple kinematical models of infalling and (counter-)rotating flattened envelopes cannot fully explain the observed velocity patterns in the arc structures. The gas kinematics of the arc structures can be better explained with three-dimensional infalling or outflowing motions. Nevertheless, the observed velocity in the northwestern part of the blueshifted arc structure is ∼60-70% higher than the expected free-fall velocity. We discuss two possible origins of the arc structures: (1) infalling flows externally compressed by an expanding shell driven by XZ Tau and (2) outflowing gas clumps caused by gravitational instabilities in the protoplanetary disk around HL Tau.

We present a simplified model to study the orbital evolution of a young hot Jupiter inside the magnetospheric cavity of a proto-planetary disk. The model takes into account the disk locking of stellar spin as well as the tidal and magnetic interactions between the star and the planet. We focus on the orbital evolution starting from the orbit in the 2:1 resonance with the inner edge of the disk, followed by the inward and then outward orbital migration driven by the tidal and magnetic torques as well as the Roche-lobe overflow of the tidally inflated planet. The goal in this paper is to study how the orbital evolution inside the magnetospheric cavity depends on the cavity size, planet mass, and orbital eccentricity. In the present work, we only target the mass range from 0.7 to 2 Jupiter masses. In the case of the large cavity corresponding to the rotational period ≈ 7 days, the planet of mass > 1 Jupiter mass with moderate initial eccentricities ( 0.3) can move to the region < 0.03 AU from its central star in 10 7 years, while the planet of mass < 1 Jupiter mass cannot. We estimate the critical eccentricity beyond which the planet of a given mass will overflow its Roche radius and finally lose all of its gas onto the star due to runaway mass loss. In the case of the small cavity corresponding to the rotational period ≈ 3 days, all of the simulated planets lose all of their gas even in circular orbits. Our results for the orbital evolution of young hot Jupiters may have the potential to explain the absence of low-mass giant planets inside ∼ 0.03 AU from their dwarf stars revealed by transit surveys.

We perform a linear analysis to investigate the dynamical response of a non‐synchronized hot Jupiter to stellar irradiation. In this work, we consider the diurnal Fourier harmonic of the stellar irradiation acting at the top of a radiative layer of a hot Jupiter with no clouds and winds. In the absence of the Coriolis force, the diurnal thermal forcing can excite internal waves propagating into the planet's interior when the thermal forcing period is longer than the sound crossing time of the planet's surface. When the Coriolis effect is taken into consideration, the latitude‐dependent stellar heating can excite weak internal waves (g modes) and/or strong baroclinic Rossby waves (buoyant r modes) depending on the asynchrony of the planet. When the planet spins faster than its orbital motion (i.e. retrograde thermal forcing), these waves carry negative angular momentum and are damped by radiative loss as they propagate downwards from the upper layer of the radiative zone. As a result, angular momentum is transferred from the lower layer of the radiative zone to the upper layer and generates a vertical shear. We estimate the resulting internal torques for different rotation periods based on the parameters of HD 209458b.