Web-page maintained by isima@ucsc.edu. Last updated Oct. 1, 2009.

Web-site hosted by the University of California at Santa Cruz.

UCSC

ISIMA 2011 Conference: Star and Planet Formation

KIAA Beijing, June 27th - July 1st 2011.

The ISIMA conference is hosted in the first week of the ISIMA program, and features invited pedagogical lectures in the morning, with afternoon contributed talks presenting state-of-the-art research on the program topic. Participation to the ISIMA conference is open to everyone who wishes to attend.

The morning lectures are video-recorded, and meant for a broad audience. They will be given by Eugene Chiang (UC Berkeley) for planet formation, and by Lee Hartmann (U. Michigan) and Chris Matzner (U. Toronto) for star formation. The contributed talks are 20 minutes long each, and present the latest developments in the field. All presentations are published online, please click on the link to access them. Each day, open discussion sessions are held to encourage questions and the sharing of ideas.

UPDATE: The movies have now been archived and are no longer available online. Please email isima@ucsc.edu if you would like to request a copy.

Scientific Program

Sunday 6/26:

  • 4 pm - 7 pm: Program Reception

Monday 6/27:

  • 9:00 am - 9:30 am: Welcome words and basic information
  • 9:30 am - 1:00 pm: Lectures.
    • Lee Hartmann: Formation and evolution of star-forming molecular clouds.
    • Coffee Break
    • Eugene Chiang: Observations of Extrasolar Planets
  • 1:00 pm - 2:00pm: Lunch (provided) & basic orientation
  • 2:00 pm - 4:00pm: Visit of campus; Poster installation.
  • 4:00 pm - 4:30 pm: Coffee Break
  • 4:30 pm - 6:00 pm: Project presentations

Tuesday 6/28:

  • 9:00 am - 12:30 am: Lectures
    • Lee Hartmann: Formation and properties of protostars
    • Coffee Break
    • Chris Matzner: Gravitational instability and disk fragmentation in star formation
  • 12:30 pm - 2:00 pm: Lunch break
  • 2:00 pm - 3:00 pm: Poster presentations
  • 3:00 pm - 4:30 pm: Contributed talks
    • Hua-Bai Li: A Bird's-eye View of Magnetic Fields in Molecular Clouds
    • Matthias Gritschneder: The enrichment and triggered formation of our solar system
    • Christoph Federrath: A new Jeans resolution criterion for (M)HD simulations of self-gravitating gas: Application to magnetic field amplification by gravity-driven turbulence.
    • Stephanie Walch: The influence of the turbulent perturbation scale on prestellar core fragmentation and disk formation.
  • 4:30 pm - 5:00 pm: Coffee Break
  • 5:00 pm - 6:00 pm: Open discussion session. Chair: Matthias Gritschneder

Wednesday 6/29:

  • 9:00 am - 12:30 am: Lectures
  • 12:30 pm - 3:00 pm: Lunch break, project discussion time
  • 3:00 pm - 4:30 pm: Contributed talks
    • Christoph Olczak: Dynamics in young star clusters: from planets to massive stars
    • Farzana Meru: SPH simulations of pre-planetesimal collisions: factors affecting the growth of planets
    • Jilin Zhou: Formation of planetary architectures under different environments
    • Xuening Bai: Non-ideal MHD effects in Protoplanetary disks
  • 4:30 pm - 5:00 pm: Coffee Break
  • 5:00 pm - 6:00 pm: Open discussion session. Chair: Christoph Olczak
  • 7:00 pm - late: Conference dinner

Thursday 6/30:

  • 9:00 am - 12:30 am: Lectures
  • 12:30 pm - 3:00 pm: Lunch break, project discussion time
  • 3:00 pm - 4:30 pm: Contributed talks
    • Yoram Lithwick: Origin of Hot Jupiters
    • Fu-Guo Xie: Gas giant formation accelerated through disk accretion processes
    • Adam Showman : Mechanisms for the atmospheric circulation of hot Jupiters.
    • Andrew Cumming: Magnetic interactions between stars and planets
  • 4:30 pm - 5:00 pm: Coffee Break
  • 5:00 pm - 6:00 pm: Open discussion session. Chair: Adam Showman

Friday 7/1:

  • 9:00 am - 12:30 am: Lectures
    • Chris Matzner: Large-scale aspects of massive star formation
    • Coffee Break. Conference photo!
    • Eugene Chiang: Orbital Dynamics (Celestial Mechanics)
  • 12:30 pm - 3:00 pm: Lunch break, project discussion time
  • 2:40 pm - 4:30 pm: Contributed talks
    • Mark Rast : A two-dimensional model of 3D turbulence
    • Alexis Brandeker : Solving the mystery of gas in debris disks
    • Hanno Rein: Stochastic migration in proto-planetary discs and Saturn's rings
    • Takayuki Muto: Dyamical Friction in an Gaseous Slab and its Application to the Interaction between a Protoplanetary Disk and a Planet in an Eccentric Orbit
    • Yanqin Wu: Open problems in the outer planetary systems
  • 4:30pm - 5:00 pm: Coffee Break
  • 5:00 pm - 6:00 pm: Open discussion session. Chair: Alexis Brandeker
  • 6:00 pm: Closing remarks

 

 

 

 

 

 

 

Xuening Bai: Non-ideal MHD effects in Protoplanetary disks

Abstract : The structure and evolution of the protoplanetary disks (PPDs) largely depend on the process of angular momentum transport, for which MHD turbulence driven by the magnetorotational instability (MRI) has been considered as the most promising mechanism. Due to the weak ionization level in PPDs, non-ideal MHD effects such as Ohmic resistivity, Hall effect and ambipolar diffusion (AD) play a significant role. Most MRI calculations for PPDs done so far include only the Ohmic resistivity, and reveal that the MRI operates mainly in the surface layer and the outer regions of the PPDs. However, Hall and AD effects dominate in such regions but remain poorly explored. We perform 3D unstratified shearing-box MRI simulations with AD using a variety of magnetic configurations and AD coefficients. We find that angular momentum transport becomes inefficient when the ion-neutral collision frequency falls below the orbital frequency. Moreover, sustained MRI turbulence requires weak magnetic field in the AD dominated regime. We present a general framework that incorporate these constraints together to predict the MRI-driven accretion rate and the corresponding magnetic field strength in PPDs. Our results indicate that MRI alone have difficulty in accounting for the accretion rate in a large fraction of T-Tauri stars, while angular momentum transport by magnetized wind may be a viable solution.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Alexis Brandeker: Solving the mystery of gas in debris disks

Abstract: A natural consequence of the star formation process is that a new-born star often is surrounded by dust and gas orbiting in a disk-like structure, called a circumstellar disk. Initially the disk is very rich in gas and poor in solids, but as the disk evolves the relative abundance between gas and dust changes. Some of the material falls into the star, some gets dispelled from the system, and then some turn into solid bodies we call planetesimals and planets. After a few million years, remnants from the planet formation process can be observed as a debris disk, rich in dust but poor in gas. Where does the gas go, where does it come from? Thanks to thorough observations of the nearby debris disk system around beta Pictoris, we have been able to study the behaviour of disk gas in detail, and found some surprises. In this talk I will outline what we think the debris gas puzzle looks like, what the pieces already in place are, what important ones are missing, and what pieces we think participants at ISIMA may contribute to finding.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Andrew Cumming: Magnetic interactions between stars and planets

Abstract: A number of models have been put forward for possible magnetic interactions between stars and their orbiting planets. These may be particularly important shortly after planet formation, when the stellar magnetic field is strong. In this talk, I will discuss the different models that have been put forward and how we may be able to test these ideas through observations.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Eugene Chiang, principal lecturer

For the best experience viewing the lectures, please download the .wmv file and use the VLC media player

Christoph Federrath: A new Jeans resolution criterion for (M)HD simulations of self-gravitating gas: Application to magnetic field amplification by gravity-driven turbulence.

Abstract: Cosmic structure formation is characterized by the complex interplay between gravity, turbulence, and magnetic fields. The processes by which gravitational energy is converted into turbulent and magnetic energies, however, remain poorly understood. In this talk, I will present high-resolution, adaptive-mesh simulations with the AMR code FLASH, showing that MHD turbulence is efficiently driven by extracting energy from the gravitational potential during the collapse of a dense gas cloud. If small seeds of the magnetic field are present, they are amplified exponentially fast via the small-scale dynamo process. The magnetic field grows most efficiently on the smallest scales, for which the stretching, twisting, and folding of field lines, and the turbulent vortices are sufficiently resolved. We find that this scale corresponds to about 30 grid cells in the simulations. We thus suggest a new minimum resolution criterion of 30 cells per Jeans length in (magneto)hydrodynamical simulations of self-gravitating gas, in order to resolve turbulence on the Jeans scale, and to capture minimum dynamo amplification of the magnetic field.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Matthias Gritschneder: The enrichment and triggered formation of our solar system

Abstract: We investigate the enrichment of the pre-solar cloud core with short lived radionucleides (SLRs), especially 26Al. The homogeneity and the surprisingly small spread in the ratio 26Al/27Al observed in the overwhelming majority of calcium-aluminium-rich inclusions (CAIs) in a vast variety of primitive chondritic meteorites puts strong constraints on the formation of the the solar system. Freshly synthesized radioactive 26Al has to be included and well mixed within 20 kyr. After discussing various scenarios including X-winds, AGB stars and Wolf-Rayet stars, we come to the conclusion that triggering the collapse of a cold cloud core by a nearby supernova is the most likely scenario. We then narrow down the vast parameter space by considering the pre-explosion survivability of such a clump as well as the cross-section necessary for sufficient enrichment. We employ numerical simulations to address the mixing of the radioactively enriched SN gas with the pre-existing gas and the forced collapse within 20 kyr. We show that a cold clump of 10Msun at a distance of 5 pc can be sufficiently enriched in 26Al and triggered into collapse fast enough - within 18 kyr after encountering the supernova shock - for a range of different metallicities, progenitor masses and dilution of the enriched material. In summary, we envision an environment for the birth place of the solar system 4.567 Gyr ago similar to the situation of the pillars in M16 nowadays, where molecular cloud cores adjacent to an HII region will be hit by a supernova explosion in the future. We show that the triggered collapse and formation as well as the required enrichment with radioactive 26Al of the solar system are possible in this scenario.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Lee Hartmann, principal lecturer

For the best experience viewing the lectures, please download the .wmv file and use the VLC media player

Hua-Bai Li: A Bird's-eye View of Magnetic Fields in Molecular Clouds

Abstract: How the magnetohydrodynamic (MHD) dynamo interplays with spiral density waves to sculpt galactic magnetic fields (B-fields) is still far from clear. The role of B-fields in the formation of molecular clouds, the wombs of stars, is also highly controversial: in some simulations, the B-field only passively follows the gas turbulence/rotation and orients randomly; others suggest that it can be strong enough to channel the gas accretion, brake the rotation, and stays ordered. Until now, all the observations of cloud B-fields are within the Milky Way, which are not helpful for putting constraints on these debates, because much dynamical effects on B-fields (from, e.g., galactic shear and density waves) are hidden from the edge-on view of the disc. State-of-the-art instruments lack sufficient sensitivity to probe extragalactic clouds with the conventional cloud B-field tracer. To obtain the first bird's-eye view of cloud B-fields, a novel observation strategy is needed. We studied the CO (J=2-1) polarization, whose direction should correlate with the local B-fields, from six giant molecular cloud complexes (GMCs) in the nearby face-on galaxy M33. A correlation between the polarization directions and the optical spiral arms is observed, which indicates that the density waves must have compressed and aligned the cloud B-fields with the spiral arms. To maintain this alignment, cloud B-fields must be strong enough to suppress the cloud rotation and dynamically dominate the cloud turbulence.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Yoram Lithwick: Origin of Hot Jupiters

Abstract:In a planetary system with two or more well-spaced, eccentric, inclined planets, secular interactions may lead to chaos. The innermost planet may gradually become very eccentric and/or inclined. Secular chaos is known to be responsible for the eventua destabilization of Mercury in our own Solar System. Here we focus on systems with multiple giant planets. We show that after an extended period of eccentricity diffusion, the inner planet's pericentre can approach the star to within a few stellar radii. Strong tidal interactions with the star pull the planet inward, creating a hot Jupiter. In contrast to other proposed channels for the production of hot Jupiters, such a scenario (which we term "secular migration") explains a range of observations: the pile-up of hot Jupiters at 3-day orbital periods, the fact that hot Jupiters are in general less massive than other RV planets, that they may have misaligned inclinations with respect to stellar spin, and that they have few easily detectable companions (but may have giant companions in distant orbits).

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Farzana Meru: SPH simulations of pre-planetesimal collisions: factors affecting the growth of planets

Abstract: We carry out Smoothed Particle Hydrodynamics simulations to determine the outcome of pre-planetesimal collisions. Previous laboratory results show that bouncing, sticking and fragmentation are the results of dust aggregate collisions (Güttler et al. 2010). However, a detailed parameter study of pre-planetesimal collisions is not possible in the laboratory. We perform a comprehensive study into the outcome of such collisions by considering the collision velocity, the mass ratio of the aggregates, the porosity and the inhomogeneity to determine the conditions that allow dust aggregates to stick and grow into planets. Previous studies suggest that the threshold velocity above which the aggregates will shatter during the collision is approximately 1m/s (Blum & Münch 1993). However, we find that the threshold velocity above which the aggregates fragment varies with the porosity and mass ratio. Furthermore, we determine the properties of the largest and second largest fragments, as well as the fragmented population. Such results can be used in global models that simulate the long-term interactions involving both gas and dust.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Chris Matzner, principal lecturer

For the best experience viewing the lectures, please download the .wmv file and use the VLC media player

Takayuki Muto: Dyamical Friction in an Gaseous Slab and its Application to the Interaction between a Protoplanetary Disk and a Planet in an Eccentric Orbit

Abstract: We present an analytic model for the disk-planet interaction that is especially useful for planets with eccentricity larger than the disk aspect ratio. We first derive a dyncamical friction formula for a particle embedded in a gaseous slab. We then make use of the formula to calculate the force exerted on the planet by the disk. The force is then averaged over the period of the planet. The resulting migration and eccentricity damping timescale agrees very well with the previous works in which the planet eccentricity is moderately larger than the disk aspect ratio. The advantage of this approach is that it is possible to apply this formulation to arbitrary large eccentricity. We have found that the timescale of the orbital evolution depends largely on the adopted disk model in the case of highly eccentric planets. We discuss the possible implication of our results to the theory of planet formation.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Christoph Olczak: Dynamics in young star clusters: from planets to massive stars

Abstract: The young star clusters we observe today are the building blocks of a new generation of stars and planets in our Galaxy and beyond. Despite their fundamental role we still lack knowledge about the initial conditions under which star clusters form and the impact of these often harsh environments on the formation and evolution of their stellar and substellar members. I will demonstrate the vital role numerical simulations play to uncover both key issues. Using dynamical models of different star cluster environments like NGC 2024, the Orion Nebula Cluster (ONC), and NGC 3603, I will show the huge variety of effects stellar interactions potentially have: they can prevent or trigger planet formation, modify the disk structure, affect the stellar multiplicity, and - fortunately - leave characteristic signatures that can be traced observationally. Moreover, I will present a recently developed very efficient measure of mass segregation in stellar systems. Its application to realistic numerical models of young star clusters shows that mass segregation occurs rapidly even for spherical systems without substructure. This finding is a critical step to resolve the controversial debate on mass segregation in young star clusters and provides strong constraints on their initial conditions.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Mark Rast: A two-dimensional model of 3D turbulence

Abstract: A simple two-dimensional point vortex flow, if stochastically stirred, shows statistical properties remarkably similar to those observed in three-dimensional turbulence. These result because the stirring provides a vortex stretching mechanism, and although the orientations of the vortex filaments are artificially confined to be perpendicular to the plane this restriction is only significant to the degree that non-nearest vortex-neighbor interactions are important to the flow statistics. We describe the flow setup, the unusual kinetic energy spectrum which results, and the one and two point Lagrangian statistics observed. We boldly concluded that scalar advection in homogeneous turbulence can be described in terms of a random walk in velocity.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Hanno Rein: Stochastic migration in proto-planetary discs and Saturn's rings

Abstract: Proto-planets that are still embedded in the proto-planetary disc are exposed to stochastic forces, generated by density fluctuations in the disc. This can be described genericly with an analytic model for both single planets and two planets in mean motion resonance. For example, the system GJ876, which is in a deep resonance, is stable for reasonable strengths of the stochastic forces. However, systems with smaller planets such as most systems that have been discovered by Kepler (Super-Earths) can get easily disrupted. Even if these systems are not disrupted completely, stochastic forces create characteristic and observable libration patterns in resonant systems. Interestingly, this system is dynamically very similar to Saturn's rings. The stochastic migration of small bodies in Saturn's rings can be described with the same equations. Analytic predictions of the interactions of a moonlet (also known as a propeller) with ring particles can then be compared to direct collisional N-body simulations. The random walk is fast enough to be directly observable by the Cassini spacecraft, compared to the stochastic migration of proto-plantes which will always be unobservable.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Adam Showman: Mechanisms for the atmospheric circulation of hot Jupiters.

Abstract: The increasing richness of exoplanet observations has motivated a variety of three-dimensional atmospheric circulation models of these planets. Under strongly irradiated conditions, models of tidally locked, short-period planets (both hot Jupiters and terrestrial planets) tend to exhibit a circulation dominated by a fast eastward, or "superrotating," jet stream at the equator. Here, I will discuss a hierarchy of models that illuminate the dynamical mechanisms controlling the atmospheric circulation--including the superrotating equatorial jet--in this regime. Future directions, and short-term projects, relevant to understanding the atmospheric circulation of exoplanets will also be presented.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Stephanie Walch: The influence of the turbulent perturbation scale on prestellar core fragmentation and disk formation.

Abstract: The collapse of weakly turbulent, prestellar cores is a critical stage in the process of star formation. Being highly non-linear and stochastic, the collapse can only be investigated by performing large ensembles of numerical simulations. Standard practice is to quantify the initial turbulent velocity field in a core in terms of the amount of turbulent energy (or some equivalent), and the exponent in the power spectrum (n = -d log P_k/ d log k). Here, I report the results of a parameter study of high-resolution, three-dimensional SPH simulations on the influence of the populated modes in the turbulent velocity field on the collapse of an isolated, weakly turbulent, low-mass prestellar core. We show that, as long as n>=3 (as is usually assumed), a more critical parameter to specify (than n) is the maximum wavelength in the turbulent velocity field, \lambda_MAX, since \lambda_MAX carries most of the turbulent energy, and thereby influences the amount and spatial coherence of the angular momentum in the core. Specifically I will show (i) that the formation of dense filaments during the collapse critically depends on \lambda_MAX and we explain this finding using a force balance analysis; (ii) that the core only has a high probability of fragmenting if \lambda_MAX > R_CORE/2; (iii) that the dominant mode of fragmentation involves the formation and break-up of filaments; (iv) and that, although small protostellar disks (R_DISK < 20 AU) form routinely, more extended disks are rare. In turbulent, low-mass cores of the type we simulated here, the formation of large, fragmenting protostellar disks is suppressed due to early fragmentation in the filaments.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Yanqin Wu: Open problems in the outer planetary systems

Abstract: There are a number of open issues in the outer regions of planetary systems, where formation of planets could not proceed all the way to form terrestrial or larger planets. We have information on these regions via observations of debris disks and our own Kuiper Belt. I will discuss our recent understandings on the connection between the two.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Fu-Guo Xie: Gas giant formation accelerated through disk accretion processes

Abstract: The formation time of gas giants predicted by current theoretical models is usually much longer than the lifetime of the protoplanetary disk, as constrained from recent observations. In order to solve this problem, we propose a disk-accretion model for stage 2 of gas giant formation, during which most of the time is spent. We argue the accreting gases will have sufficient angular momenta due to differential rotation and/or star-planet tide, and they will be disk-like rather than spherical. The formation time of the planet is mainly controled by the energy loss rate. The disk model has its advantage that it seperates the radiative flux (mainly vertically) from the mass-inflow flux (mainly radially). Shorter formation time for gas giants is expected. Recent (preliminary) results will be presented here.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player

Jilin Zhou: Formation of planetary architectures under different environments

Abstract: To date, more than 500 exoplanet has been detected. During the later stage of planet formation, planet migration embedded in gas disk, interplanetary secular perturbations, mean motion resonance and secular resonance, planetary scatterings, tidal interactions between host star and planets, nearby stellar perturbations et al, will contributed the final architecture of the planet system substantially. We will review the mechanisms that will lead to different final planetary architectures, then applied them to the observed system.

Filmed lecture and PDF presentation

For the best experience viewing the presentation, please download the .wmv file and use the VLC media player