The kinematics of circumstellar disks around T Tauri stars

• Main Author: Koerner, David
• Format: Others
• Language: en
• Published: 1995
• Online Access: https://thesis.library.caltech.edu/4347/1/Koerner_dw_1995.pdf; Koerner, David (1995) The kinematics of circumstellar disks around T Tauri stars. Dissertation (Ph.D.), California Institute of Technology. doi:10.7907/css3-2v20. https://resolver.caltech.edu/CaltechETD:etd-10312007-162008 <https://resolver.caltech.edu/CaltechETD:etd-10312007-162008>

NOTE: Text or symbols not renderable in plain ASCII are indicated by [...]. Abstract is included in .pdf document. Aperture synthesis images of molecular gas around the T Tauri stars, GM Aurigae, RY Tauri, DL Tauri, DO Tauri, and AS 209 are interpreted with the aid of a kinematic model of a circumstellar disk. The velocity structure and morphology of the gas strongly suggest that circumstellar disks with radii of a few hundred AU are present around all five stars. Explicit identification of kinematic patterns in the spectral line maps is achieved for the two largest disks, GM Aur and DO Tau. Maps of the relatively old T Tauri star, GM Aur, in the [...] line at 4" resolution reveal compact gas associated with the stellar position and at the core of a larger rotating gaseous disk, 950 x 530 AU in extent. The mean velocity gradient across the disk, which is oriented along [...], is consistent with rotation about an axis at [...]. The structure observed in [...] aperture synthesis maps agrees well with synthetic maps of the gas emission generated from a model. For a disk that is inclined [...] from face on, in Keplerian rotation, a 0.80 [...] central mass (star + disk), a systemic velocity, [...], of 15.38 km [...] and a mass, 0.1 [...] is derived. A survey of T Tauri stars for circumstellar molecular gas also yields evidence for rotating disks. RY Tau, DL Tau, DO Tau, and AS 209 are detected in CO[...] emission elongated along [...], respectively, with deconvolved half-maximum radii of 110, 250, 350, and 290 AU in aperture synthesis images at [...] resolution. Three of these, RY Tau, DL Tau, and AS 209, exhibit velocity gradients parallel to this direction in first moment velocity maps, suggesting rotation of the circumstellar gas. Spectra of RY Tau and AS 209 exhibit a characteristic double-peaked shape, but that of DO Tau is dominated by the presence of high-velocity blue-shifted gas. DL Tau's spectrum has a linewidth that is too narrow [...] to be resolved into double peaks. Position-Velocity Diagrams (PVDs) constructed parallel and perpendicular to the axis of elongation imply rotation and infall or outflow, respectively. Those for RY Tau, DL Tau, and AS 209 show predominantly rotation, but some evidence of an orthogonal gradient (infall or outflow) is seen for RY Tau and AS 209. In contrast, the PVDs for DO tau suggest that its molecular emission originates predominantly from outflow or infall. Recent evidence of infall in circumstellar gas around T Tauri stars has motivated construction of a kinematic model of molecular emission from a disk of rotating and infalling gas. The velocity structure of the model disk assumes that infalling gas obeys angular momentum conservation on ballistic trajectories until it reaches the radial value, [...], where the magnitude of the rotational velocity component reaches the Keplerian value. For [...], gas is assumed to be in circular Keplerian orbits. Synthetic spectral line maps are generated by the model and cross-correlated with aperture synthesis maps for a range of the free parameters, including [...]. The best-fit value of [...] for RY Tau, DL Tau, and AS 209, approximately matches that of the outer radius of their emission, indicating these disks are predominantly in Keplerian rotation. However, emission from these stars is marginally resolved and uncertainties in the best-fit parameters are correspondingly high. In contrast, kinematic patterns are well-resolved in emission from DO Tau found in maps within a narrow, near-systemic velocity range. These are best matched by simulations from a model disk with [...] = 350 AU and an outer radius of 500 AU. This result strongly suggests that, in this case, infall from the molecular cloud onto a rotating disk is still in progress.