Publications by Caroline Terquem

On the eccentricities of the extrasolar planets

Extrasolar Planets: Today and Tomorrow 321 (2004) 379-392

JCB Papaloizou, RP Nelson, C Terquem

Evolution of self-gravitating magnetized disks. II. Interaction between magnetohydrodynamic turbulence and gravitational instabilities

ASTROPHYSICAL JOURNAL 616 (2004) 364-375

S Fromang, SA Balbus, C Terquem, JP De Villiers

Evolution of self-gravitating magnetized disks. II. Interaction between magnetohydrodynamic turbulence and gravitational instabilities

Astrophysical Journal 616 (2004) 364-375

S Fromang, SA Balbus, C Terquem, J-P De Villiers

Stopping inward planetary migration by a toroidal magnetic field

Monthly Notices of the Royal Astronomical Society 341 (2003) 1157-1173

CEJMLJ Terquem

We calculate the linear torque exerted by a planet on a circular orbit on a disc containing a toroidal magnetic field. All fluid perturbations are singular at the so-called magnetic resonances, where the Doppler shifted frequency of the perturbation matches that of a slow MHD wave propagating along the field line. These lie on both sides of the corotation radius. Waves propagate outside the Lindblad resonances, and also in a restricted region around the magnetic resonances. The magnetic resonances contribute to a significant global torque which, like the Lindblad torque, is negative (positive) inside (outside) the planet's orbit. As these resonances are closer to the planet than the Lindblad resonances, the torque they contribute dominates over the Lindblad torque if the magnetic field is large enough. In addition, if β ≡ c2/vA2 increases fast enough with radius, the outer magnetic resonance becomes less important and the total torque is then negative, dominated by the inner magnetic resonance. This leads to outward migration of the planet. Even for β ∼ 100 at corotation, a negative torque may be obtained. A planet migrating inward through a non-magnetized region of a disc would then stall when reaching a magnetized region. It would then be able to grow to become a terrestrial planet or the core of a giant planet. In a turbulent magnetized disc in which the large-scale field structure changes sufficiently slowly, a planet may alternate between inward and outward migration, depending on the gradients of the field encountered. Its migration could then become diffusive, or be limited only to small scales.

The ionization fraction in alpha models of protoplanetary discs


S Fromang, C Terquem, SA Balbus

Dynamical relaxation and the orbits of low-mass extrasolar planets

Monthly Notices of the Royal Astronomical Society 332 (2002)

C Terquem, JCB Papaloizou

We consider the evolution of a system containing a population of massive planets formed rapidly through a fragmentation process occurring on a scale on the order of 100 au and a lower mass planet that assembles in a disc on a much longer time-scale. During the formation phase, the inner planet is kept on a circular orbit owing to tidal interaction with the disc, while the outer planets undergo dynamical relaxation. Interaction with the massive planets left in the system after the inner planet forms may increase the eccentricity of the inner orbit to high values, producing systems similar to those observed.

Linear analysis of the Hall effect in protostellar disks

ASTROPHYSICAL JOURNAL 552 (2001) 235-247

SA Balbus, C Terquem

Dynamical relaxation and massive extrasolar planets

Monthly Notices of the Royal Astronomical Society 325 (2001) 221-230

JCB Papaloizou, C Terquem

Following the suggestion of Black that some massive extrasolar planets may be associated with the tail of the distribution of stellar companions, we investigate a scenario in which 5 ≤ N ≤ 100 planetary mass objects are assumed to form rapidly through a fragmentation process occuring in a disc or protostellar envelope on a scale of 100 au. These are assumed to have formed rapidly enough through gravitational instability or fragmentation that their orbits can undergo dynamical relaxation on a time-scale of ∼100 orbits. Under a wide range of initial conditions and assumptions, the relaxation process ends with either (i) one potential 'hot Jupiter' plus up to two 'external' companions, i.e. planets orbiting near the outer edge of the initial distribution; (ii) one or two 'external' planets or even none at all; (iii) one planet on an orbit with a semi-major axis of 10 to 100 times smaller than the outer boundary radius of the inital distribution together with an 'external' companion. Most of the other objects are ejected and could contribute to a population of free-floating planets. Apart from the potential 'hot Jupiters', all the bound objects are on orbits with high eccentricity, and also with a range of inclination with respect to the stellar equatorial plane. We found that, apart from the close orbiters, the probability of ending up with a planet orbiting at a given distance from the central star increases with the distance. This is because of the tendency of the relaxation process to lead to collisions with the central star. The scenario we envision here does not impose any upper limit on the mass of the planets. We discuss the application of these results to some of the more massive extrasolar planets.

Linear analysis of the hall effect in protostellar disks

Astrophysical Journal 552 (2001) 235-247

SA Balbus, C Terquem

Disk evolution towards planet formation


C Terquem, JCB Papaloizou, RP Nelson

The response of an accretion disc to an inclined dipole with application to AA Tauri

Astronomy and Astrophysics 360 (2000) 1031-1042

C Terquem, JCB Papaloizou

Disks, extrasolar planets and migration

Space Science Reviews 92 (2000) 323-340

C Terquem, JCB Papaloizou, RP Nelson

We review results about protoplanetary disk models, protoplanet migration and formation of giant planets with migrating cores. We first model the protoplanetary nebula as an α-accretion disk and present steady state calculations for different values of α and gas accretion rate through the disk. We then review the current theories of protoplanet migration in the context of these models, focusing on the gaseous disk-protoplanet tidal interaction. According to these theories, the migration timescale may be shorter than the planetary formation timescale. Therefore we investigate planet formation in the context of a migrating core, considering both the growth of the core and the build-up of the envelope in the course of the migration.

Propagating bending waves in accretion discs and the Bardeen-Petterson effect

ASTROPHYSICAL DISCS 160 (1999) 81-90

RP Nelson, JCB Papaloizou, C Terquem

Critical protoplanetary core masses in protoplanetary disks and the formation of short-period giant planets

Astrophysical Journal 521 (1999) 823-838

JCB Papaloizou, C Terquem

Precession of collimated outflows from young stellar objects

Astrophysical Journal 512 (1999)

C Terquem, J Eislöffel, JCB Papaloizou, RP Nelson

We consider several protostellar systems in which either a precessing jet or at least two misaligned jets have been observed. We assume that the precession of jets is caused by tidal interactions in noncoplanar binary systems. For Cep E, V1331 Cyg, and RNO 15-FIR, the inferred orbital separations and disk radii are in the range 4-160 AU and 1-80 AU, respectively, consistent with those expected for pre-main-sequence stars. Furthermore, we assume or use the fact that the source of misaligned outflows is a binary and evaluate the length scale over which the jets should precess as a result of tidal interactions. For T Tau, HH1 VLA 1/2, and HH 24 SVS63, it may be possible to detect a bending of the jets rather than "wiggling." In HH 111 IRS and L1551 IRS5, wiggling may be detected on the current observed scale. Our results are consistent with the existence of noncoplanar binary systems in which tidal interactions induce jets to precess.

The response of accretion disks to bending waves: Angular momentum transport and resonances

Astrophysical Journal 509 (1998) 819-835

CEJMLJ Terquem

On the tidal interaction of a solar-type star with an orbiting companion: Excitation of g-mode oscillation and orbital evolution

The Astrophysical Journal 502 (1998) 788-801

C Terquem, JCB Papaloizou, RP Nelson, DNC Lin

On the Global Warping of a Thin Self-gravitating Near-Keplerian Gaseous Disk with Application to the Disk in NGC 4258

The Astrophysical Journal 497 (1998) 212-226

JCB Papaloizou, C Terquem, DNC Lin

Bending instabilities in magnetized accretion discs

Monthly Notices of the Royal Astronomical Society 292 (1997) 631-645

V Agapitou, JCB Papaloizou, C Terquem

We study the global bending modes of a thin annular disc subject to both an internally generated magnetic field and a magnetic field due to a dipole embedded in the central star with axis aligned with the disc rotation axis. When there is a significant inner region of the disc corotating with the star, we find spectra of unstable bending modes. These may lead to elevation of the disc above the original symmetry plane facilitating accretion along the magnetospheric field lines. The resulting non-axisymmetric disc configuration may result in the creation of hotspots on the stellar surface and the periodic photometric variations observed in many classical T Tauri stars (CTTSs). Time-dependent behaviour may occur including the shadowing of the central source in magnetic accretors even when the dipole and rotation axes are aligned. © 1997 RAS.

On the stability of an accretion disc containing a toroidal magnetic field: The effect of resistivity

Monthly Notices of the Royal Astronomical Society 287 (1997) 771-789

JCB Papaloizou, C Terquem

We extend a previous study of the global stability of a stratified differentially rotating disc containing a toroidal magnetic field to include the effect of a non-zero resistivity η. We consider the situation when the disc is stable to convection in the absence of the magnetic field. The most robust buoyancy driven unstable modes, which occur when the field is strong enough, have low azimuthal mode number m. They grow exponentially, apparently belonging to a discrete spectrum. They exist for the dimensionless ratio η/(H2Ω) smaller than ∼ 10-2, where Ω is the angular velocity and H is the disc semithickness. In contrast the magnetorotational modes develop arbitrarily small radial scale and show transient amplification as expected from a shearing sheet analysis. The most robust modes of this type are local in all directions. Because of their more global character, the buoyancy driven modes may be important for the generation of large-scale fields and outflows. © 1997 RAS.