Person:

Rosenfeld, Katherine

We report the first detection of c-C3H2 in a circumstellar disk. The c-C3H2 J = 6-5 line (217.882 GHz) is detected and imaged through Atacama Large Millimeter Array (ALMA) Science Verification observations toward the disk around the Herbig Ae star HD 163296 at 0.''8 resolution. The emission is consistent with that arising from a Keplerian rotating disk. Two additional c-C3H2 transitions are also tentatively detected, bolstering the identification of this species, but with insufficient signal-to-noise ratio to constrain the spatial distribution. Using a previously developed model for the physical structure of this disk, we fit a radial power-law distribution model to the c-C3H2 6-5 emission and find that c-C3H2 is present in a ring structure from an inner radius of about 30 AU to an outer radius of about 165 AU. The column density is estimated to be 1012-1013 cm–2. The clear detection and intriguing ring structure suggest that c-C3H2 has the potential to become a useful probe of radiation penetration in disks.

Near a black hole, differential rotation of a magnetized accretion disk is thought to produce an instability that amplifies weak magnetic fields, driving accretion and outflow. These magnetic fields would naturally give rise to the observed synchrotron emission in galaxy cores and to the formation of relativistic jets, but no observations to date have been able to resolve the expected horizonscale magnetic-field structure. We report interferometric observations at 1.3- millimeter wavelength that spatially resolve the linearly polarized emission from the Galactic Center supermassive black hole, Sagittarius A*. We have found evidence for partially ordered fields near the event horizon, on scales of ∼6 Schwarzschild radii, and we have detected and localized the intra-hour variability associated with these fields.

nterferometric observations at millimeter wavelengths provide a precious, detailed view of certain astrophysical objects. This thesis is composed of studies that both rely on and enable this technique to study the structure of planet-forming disks and soon image the closest regions around super-massive black holes. Young stars form out of a cloud of gas and dust that, before its eventual dissipation, flattens to a disk. However the disk population is diverse and recent high-resolution images have revealed a wide variety of interesting features. To understand these observations we use detailed radiative transfer models to motivate various physical scenarios. First we identify a set of traits in the disk around V4046 Sgr that marks the coupled progression of the gas and dust distributions in the presence of at least one embedded companion. Next, we investigate how the vertical temperature structure of a disk can be spatially resolved and apply our framework to observations of the disk around HD163296. Lastly, we show how large-scale radial flows of gas may be observable and question how this phenomenon might be distinguished from other scenarios such as warps or outflows. The last chapter summarizes the APHIDS project which changes the sampling rate of data taken at the SMA so that it may be used for VLBI campaigns.