title: Circumstellar disks and envelopes around young low-mass stars
creator: Quanz, Sascha Patrick
subject: ddc-520
subject: 520 Astronomy and allied sciences
description: In this PhD thesis astronomical observations of the immediate surroundings of young low-mass stars are presented and interpreted. Particular emphasis is put on FU Orionis stars (FUors). These objects are surrounded by an active accretion disk and a circumstellar envelope, both consisting of gas, dust and ice components. During the FUor-phase the envelope is dispersed and partly accreted onto the disk. Using data from the HUBBLE SPACE TELESCOPE, the SPITZER SPACE TELESCOPE, and the VERY LARGE TELESCOPE INTERFEROMETER, accretion disks and envelopes are investigated, and physical parameters, possible dust compositions, and ice properties are derived. Evidence for dust coagulation and grain growth within the disks is found, indicating dust processing in the early phases of accretion disk evolution. Furthermore, evidence for FUors in a young stellar cluster is presented, suggesting that most young, low-mass stars possibly undergo this phase of enhanced accretion, regardless of their immediate stellar environment. Based on spectroscopic diagnostics, an evolutionary sequence for FUors is found, which fits into the general paradigm of low-mass star formation. Finally, a deep near-infrared survey in the Taurus star-forming region reveals numerous new candidates for young low-mass stars and Brown Dwarfs surrounded by circumstellar disks. Based on photometric measurements and theoretical models, the least massive objects discerned by the survey are found to have masses in the range of several Jupiter masses. This makes them excellent candidates for being among the least massive free-floating objects with circum-sub-stellar disks known today.
date: 2007
type: Dissertation
type: info:eu-repo/semantics/doctoralThesis
type: NonPeerReviewed
format: application/pdf
identifier: https://archiv.ub.uni-heidelberg.de/volltextserverhttps://archiv.ub.uni-heidelberg.de/volltextserver/7478/1/Dissertation_SaschaQuanz.pdf
identifier: DOI:10.11588/heidok.00007478
identifier: urn:nbn:de:bsz:16-opus-74785
identifier:   Quanz, Sascha Patrick  (2007) Circumstellar disks and envelopes around young low-mass stars.  [Dissertation]     
relation: https://archiv.ub.uni-heidelberg.de/volltextserver/7478/
rights: info:eu-repo/semantics/openAccess
rights: http://archiv.ub.uni-heidelberg.de/volltextserver/help/license_urhg.html
language: eng