Resolving the gas distribution and kinematics in the inner regions of protoplanetary disks

Star formation can be characterised by the presence of accretion disks and outflows that originate from the inner regions of these disks. Despite playing a crucial role in the star formation process, the mechanism by which jets are formed is unknown. The jets appear to originate from the very inner regions of protoplanetary disks, making it difficult to observe thejet-launchingregionbyconventionalmeans. Inordertoachievethehigh-angularresolutionrequiredtoobservetheinnerdiskitisnecessarytoobservewithopticalinterferometry. In this thesis I aim to answer the question of how astrophysical jets and winds are launched from the inner regions of circumstellar disks by observing with spectrally dispersed interferometry in the near-infrared wavelength regime. In this thesis I present near-infrared, K-band VLTI/AMBER and VLT/CRIRES observations of the Herbig B[e] star MWC297. I interpret velocity-resolved images across the Brγ line, aswellas thederivedtwo-dimensionalphotocentredisplacementvectors, andfitkinematic models to our visibility and phase data in order to constrain the gas velocity field on sub-AUscales. Thevelocity-resolvedchannelmapsandmomentmapsrevealthemotionof the Brγ-emitting gas in six velocity channels, marking the first time that kinematic effects in the sub-AU inner regions of a protoplanetary disk could be directly imaged. The Brγ photocentre shifts trace a rotation-dominated velocity field, where the blue- and red-shifted emissions are displaced along a position angle of 24◦±3◦ and the approaching part of the disk is offset west of the star. The visibility drop in the line as well as the strong non-zero phase signals are modeled using a disk-wind model with a poloidal velocity of∼20kms−1. Simulations show that adding a poloidal velocity component causes the perceived system axis to shift, offeringapowerful newdiagnostic for thedetectionof non-Keplerianvelocity fields. In addition to the K-band data, I present analysis of AMBER spectro-interferometric data for MWC297 in the H-band, spectrally and spatially resolving multiple different Brackett series lines. I use the differential phase data to construct photocentre displacement vectors for each of the Brackett series lines, which show that all the lines in the H-band trace a similar velocity field. I construct a global kinematic model for the whole H-band, with the results showing that the H-band Brackett series lines originate from a compact disk wind region, with a poloidal velocity of∼220kms−1. I also present AMBER and CHARA interferometry data along with CRIRES spectroscopy data (R = 100000) of the Herbig Be star MWC147. The continuum emission is fitted with aninclinedGaussianandaringwitharadiusof0.60mas(0.39au),whichiswellwithinthe expected dust sublimation radius of 1.52 au. No significant change is detected in the measured visibilities across the Brγ line, indicating that the line-emitting gas is located in the same region as the continuum-emitting disk. The differential phase data is used to construct photocentre displacement vectors across the Brγ line, revealing a velocity profile consistent with a rotating disk. The AMBER spectro-interferometry data is fitted with a kinematic model of a disk in Keplerian rotation, where both the line-emitting and continuum-emitting components of the disk originate from the same compact region close to the central star. The presence of line-emitting gas in the same region as the K-band continuum supports the interpretation that the K-band continuum traces an optically thick gas disk. I present spectro-interferometric observations of the Brγ emission from the the T Tauri star CW Tau. I construct photocentre shifts from the GRAVITY differential phase data, which indicate motion along a PA of 120.5◦ which is close to the previously observed jet axis for this object. This suggests that the velocity field traced by the Brγ emission of CW Tau traces a high-velocity outflow close to the radius where the disk is truncated by the stellar magnetic field. Each of the individual studies in this work introduces a new insight into the jet-launching region of young stellar objects. I use observations with high-spatial and high-spectral resolution to place strong physical constraints on the morphology and velocity fields of the jet-launching regions in young stars. The technical achievements presented in this thesis demonstrate the effectiveness of spectro-interferometry as a tool for studying the dynamic physical processes associated with star formation

Thermal Conductivity of Single Wall Carbon Nanotubes: Diameter and Annealing Dependence

The thermal conductivity, k(T), of bulk single-wall carbon nanotubes (SWNT's) displays a linear temperature dependence at low T that has been attributed to 1D quantization of phonons. To explore this issue further, we have measured the k(T) of samples with varying average tube diameters. We observe linear k(T) up to higher temperatures in samples with smaller diameters, in agreement with a quantization picture. In addition, we have examined the effect of annealing on k(T). We observe an enhancement in k(T) for annealed samples which we attribute to healing of defects and removal of impurities. These measurements demonstrate how the thermal properties of an SWNT material can be controlled by manipulating its intrinsic nanoscale properties.Comment: Proc. of the XV. Int. Winterschool on Electronic Properties of Novel Materials, Kirchberg/Tirol, Austria, 200

Backlund transformations and Hamiltonian flows

In this work we show that, under certain conditions, parametric Backlund transformations (BTs) for a finite dimensional integrable system can be interpreted as solutions to the equations of motion defined by an associated non-autonomous Hamiltonian. The two systems share the same constants of motion. This observation lead to the identification of the Hamiltonian interpolating the iteration of the discrete map defined by the transformations, that indeed will be a linear combination of the integrals appearing in the spectral curve of the Lax matrix. An application to the Toda periodic lattice is given.Comment: 19 pages, 2 figures. to appear in J. Phys.

Chemical doping of individual semiconducting carbon-nanotube ropes

We report the effects of potassium doping on the conductance of individual semiconducting single-walled carbon nanotube ropes. We are able to control the level of doping by reversibly intercalating and de-intercalating potassium. Potassium doping changes the carriers in the ropes from holes to electrons. Typical values for the carrier density are found to be ∼100–1000 electrons/μm. The effective mobility for the electrons is μeff∼20–60 cm2 V-1 s-1, a value similar to that reported for the hole effective mobility in nanotubes [R. Martel et al., Appl. Phys. Lett. 73, 2447 (1998)]

Discrete Hirota reductions associated with the lattice KdV equation

We study the integrability of a family of birational maps obtained as reductions of the discrete Hirota equation, which are related to travelling wave solutions of the lattice KdV equation. In particular, for reductions corresponding to waves moving with rational speed N/M on the lattice, where N,M are coprime integers, we prove the Liouville integrability of the maps when N + M is odd, and prove various properties of the general case. There are two main ingredients to our construction: the cluster algebra associated with each of the Hirota bilinear equations, which provides invariant (pre)symplectic and Poisson structures; and the connection of the monodromy matrices of the dressing chain with those of the KdV travelling wave reductions

Thermal transport measurements of individual multiwalled nanotubes

The thermal conductivity and thermoelectric power of a single carbon nanotube were measured using a microfabricated suspended device. The observed thermal conductivity is more than 3000 W/K m at room temperature, which is two orders of magnitude higher than the estimation from previous experiments that used macroscopic mat samples. The temperature dependence of the thermal conductivity of nanotubes exhibits a peak at 320 K due to the onset of Umklapp phonon scattering. The measured thermoelectric power shows linear temperature dependence with a value of 80 $\mu$V/K at room temperature.Comment: 4 pages, figures include