Off-campus UMass Amherst users: To download dissertations, please use the following link to log into our proxy server with your UMass Amherst user name and password.
Non-UMass Amherst users, please click the view more button below to purchase a copy of this dissertation from Proquest.
(Some titles may also be available free of charge in our Open Access Dissertation Collection, so please check there first.)
High-spatial resolution observations of circumstellar disks
Abstract
We review current indirect evidence that supports the hypothesis that disks of gas and dust surround young stars in their formation stages. Current theoretical models explain this evidence, in particular the observed spectral energy distributions $\lambda$F$\sb{\lambda}\propto\lambda\sp{-\eta}$ and luminosities. We argue that a consequence of these models is a flared disk structure H(r) $\propto$ r$\sp{\rm z}$ that should be observable, yielding a relation between the flaring constant z and the spectral index $\eta$ that can be used to propose an evolutionary sequence for the geometry of such disks. We performed high resolution observations in the infrared, aimed imaging scattered radiation from dust embedded in circumstellar disks in solar type pre-main sequence stars. We used an infrared array recently developed by the Kitt Peak National Observatory, in combination with the 4 meter telescope. These observations were analyzed using different super-resolution techniques such as image motion suppression, speckle shift-and-add, contrast-ratio analysis, maximum entropy restorations, and speckle interferometry. We present the results of these studies for the star SCrA, as a case study. However, we discovered that the response function of the telescope has three peaks, with typical separations of half to one arc second, and variations in intensity and position of 30% in times as short as one minute. This unstable response sets a limit of only 2 mag/$\prime\prime\sp2$ fainter than the central star for any extended structure that can be resolved, which is brighter than the 3.75 mag/$\prime\prime\sp2$ expected for a flared disk, and thus hampers the possibility of recovering disks structures. In addition, we find that the noise in long exposure images in the infrared is proportional to the signal, possibly due to the low number of speckles at these wavelengths. On the other hand, the noise in the speckles themselves appears to be of Poisson type, but the events that make those statistics are not individual photons, but bunches of many, such that the number of photons in each event is proportional to the intensity of the source.
Subject Area
Astrophysics
Recommended Citation
Salas-Casales, Luis, "High-spatial resolution observations of circumstellar disks" (1990). Doctoral Dissertations Available from Proquest. AAI9110210.
https://scholarworks.umass.edu/dissertations/AAI9110210