{"id":{"repo_id":"uiuc","oai_identifier":"oai:www.ideals.illinois.edu:2142/19307"},"canonical_url":"https://search.dev.ndltd.org/etd/uiuc/oai:www.ideals.illinois.edu:2142/19307","repository":{"repo_id":"uiuc","name":"University of Illinois - Urbana-Champaign","base_url":"https://www.ideals.illinois.edu/oai-pmh"},"display":{"title":"A millimeter-wave interferometric study of gas-phase silicon dicarbide in the circumstellar envelope surrounding IRC+10216","abstract":"We have used the Berkeley-Illinois-Maryland Association (BIMA) Array to map emission from the 4$\\sb{22}$-$3\\sb{21}$ and 4$\\sb{04}$-$3\\sb{03}$ transitions of SiC$\\sb2$ in the circumstellar envelope (CSE) surrounding IRC+10216. The NRAO 12-m telescope was used to fill in missing flux from large scale structure not detected by the interferometer. The interferometry and 12-m single-element data were combined to make full synthesis maps of emission from SiC$\\sb2$ toward IRC+10216.","abstract_html":"We have used the Berkeley-Illinois-Maryland Association (BIMA) Array to map emission from the 4$\\sb{22}$-$3\\sb{21}$ and 4$\\sb{04}$-$3\\sb{03}$ transitions of SiC$\\sb2$ in the circumstellar envelope (CSE) surrounding IRC+10216. The NRAO 12-m telescope was used to fill in missing flux from large scale structure not detected by the interferometer. The interferometry and 12-m single-element data were combined to make full synthesis maps of emission from SiC$\\sb2$ toward IRC+10216.","abstract_has_math":true,"creators":["Gensheimer, Paul David"],"institution":"University of Illinois at Urbana-Champaign","degree_name":"Ph.D.","degree_level":"Dissertation","degree_discipline":"Astronomy","degree_department":null,"school":null,"contributors":["Snyder, Lewis E."],"advisors":[],"committee_chairs":[],"committee_members":[],"year":2011,"date_issued":"2011-05-07T12:03:24Z","date_published":"2011-05-07T12:03:24Z","updated_at":"2026-07-22T22:25:12Z","subjects":["Physics, Astronomy and Astrophysics"],"languages":["eng"],"rights":["Copyright 1994 Gensheimer, Paul David"],"rights_urls":[],"identifier_entries":[{"key":"dc:identifier","label":"Identifier","values":["AAI9512370","(UMI)AAI9512370"],"render_values":[{"text":"AAI9512370","href":null,"code":true},{"text":"(UMI)AAI9512370","href":null,"code":true}]}]},"links":{"outbound_url":"http://hdl.handle.net/2142/19307","outbound_label":"Handle","outbound_source":"dc:identifier"},"metadata_groups":[{"id":"people","label":"People","entries":[{"key":"dc:contributor","label":"Contributor","values":["Snyder, Lewis E."]},{"key":"dc:creator","label":"Author","values":["Gensheimer, Paul David"]}]},{"id":"academic_context","label":"Academic Context","entries":[{"key":"dc:date","label":"Dc Date","values":["2011-05-07T12:03:24Z","10000-01-01","1994"]},{"key":"dc:type","label":"Dc Type","values":["text"]},{"key":"thesis:degree_discipline","label":"Discipline","values":["Astronomy"]},{"key":"thesis:degree_level","label":"Degree Level","values":["Dissertation"]},{"key":"thesis:degree_name","label":"Degree Name","values":["Ph.D."]},{"key":"thesis:institution_name","label":"Thesis Institution Name","values":["University of Illinois at Urbana-Champaign"]}]},{"id":"subjects_keywords","label":"Subjects and Keywords","entries":[{"key":"dc:subject","label":"Dc Subject","values":["Physics, Astronomy and Astrophysics"]}]},{"id":"language_rights","label":"Language and Rights","entries":[{"key":"dc:language","label":"Dc Language","values":["eng"]},{"key":"dc:rights","label":"Dc Rights","values":["Copyright 1994 Gensheimer, Paul David"]}]},{"id":"identifiers","label":"Identifiers","entries":[{"key":"dc:identifier","label":"Identifier","values":["AAI9512370","(UMI)AAI9512370","http://hdl.handle.net/2142/19307"]}]},{"id":"additional","label":"Additional Metadata","entries":[{"key":"dc:description","label":"Description","values":["We have used the Berkeley-Illinois-Maryland Association (BIMA) Array to map emission from the 4$\\sb{22}$-$3\\sb{21}$ and 4$\\sb{04}$-$3\\sb{03}$ transitions of SiC$\\sb2$ in the circumstellar envelope (CSE) surrounding IRC+10216. The NRAO 12-m telescope was used to fill in missing flux from large scale structure not detected by the interferometer. The interferometry and 12-m single-element data were combined to make full synthesis maps of emission from SiC$\\sb2$ toward IRC+10216.","We find that full synthesis maps of the 4$\\sb{22}$-$3\\sb{21}$ and 4$\\sb{04}$-$3\\sb{03}$ transitions of SiC$\\sb2$ show a distinctly shell-like structure. The emission is not uniformly distributed. Instead, it shows a clumpy appearance on the plane of the sky. The maps of the 4$\\sb{22}$-$3\\sb{21}$ transition show a distinct bipolar structure with lobes oriented along a roughly north-south axis. The maps of the 4$\\sb{04}$-$3\\sb{03}$ transition show an asymmetric appearance in which the east side of the CSE is $\\sim$2-3 brighter than the west side. Radiative transfer models of the data suggest that most of the observed SiC$\\sb2$ is confined to a shell with inner radius $\\sim$2 $\\times$ 10$\\sp{16}$ cm and outer radius $\\sim$6 $\\times$ 10$\\sp{16}$ cm. The abundance of SiC$\\sb2$ ( (SiC$\\sb2$) / (H$\\sb2$)) within the shell is $\\sim$10$\\sp{-6}$. We cannot rule out the possibility that some SiC$\\sb2$ originates in the inner envelope near the photosphere but we can put an upper limit on the abundance of SiC$\\sb2$ in the inner envelope. Our data constrains the fractional abundance of SiC$\\sb2$ in the inner envelope (r $\\sbsp{\\sim}{<}$ 2 $\\times$ 10$\\sp{16}$ cm) to be no more than $\\sim$3 $\\times$ 10$\\sp{-8}$. The distribution and abundance of SiC$\\sb2$ suggest that ion-molecule reactions involving C$\\sb2$H$\\sb2$ may be responsible for producing much of the SiC$\\sb2$.","Our data also places important constraints on the excitation mechanisms for SiC$\\sb2$. Kinetic temperatures in the outer CSE ($\\sbsp{\\sim}{<}$60 K) where much of the SiC$\\sb2$ resides are not high enough to excite the high excitation temperatures across K-ladders observed by Thaddeus et al. (1984) and Avery et al. (1992). This suggests that radiative excitation through the lowest-lying vibrationally-excited state, the $\\nu\\sb3$ = 1 antisymmetric mode, may be responsible for the high excitation temperatures across K-ladders. To test this hypothesis we made a sensitive search for rotational transitions of vibrationally excited SiC$\\sb2$ with the NRAO 12-m. Our data suggests that the column density of vibrationally excited SiC$\\sb2$ is at least two orders of magnitude lower than the column density of the ground vibrational state. The upper limit on the column density of vibrationally excited SiC$\\sb2$ is consistent with radiative excitation through the $\\nu\\sb3$ = 1 antisymmetric mode.","Made available in DSpace on 2011-05-07T12:03:24Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9512370.pdf: 8774793 bytes, checksum: 2b3a9f9f6a90139904475d413cca4b88 (MD5) Previous issue date: 1994","Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:36:04Z Item is restricted indefinitely.","Restriction data tranferred 2014-07-01T11:14:27-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission","ETDs are only available to UIUC Users without author permission","U of I Only"]},{"key":"dc:title","label":"Title","values":["A millimeter-wave interferometric study of gas-phase silicon dicarbide in the circumstellar envelope surrounding IRC+10216"]}]}],"canonical_facts":{"dc:contributor":["Snyder, Lewis E."],"dc:creator":["Gensheimer, Paul David"],"dc:date":["2011-05-07T12:03:24Z","10000-01-01","1994"],"dc:description":["We have used the Berkeley-Illinois-Maryland Association (BIMA) Array to map emission from the 4$\\sb{22}$-$3\\sb{21}$ and 4$\\sb{04}$-$3\\sb{03}$ transitions of SiC$\\sb2$ in the circumstellar envelope (CSE) surrounding IRC+10216. The NRAO 12-m telescope was used to fill in missing flux from large scale structure not detected by the interferometer. The interferometry and 12-m single-element data were combined to make full synthesis maps of emission from SiC$\\sb2$ toward IRC+10216.","We find that full synthesis maps of the 4$\\sb{22}$-$3\\sb{21}$ and 4$\\sb{04}$-$3\\sb{03}$ transitions of SiC$\\sb2$ show a distinctly shell-like structure. The emission is not uniformly distributed. Instead, it shows a clumpy appearance on the plane of the sky. The maps of the 4$\\sb{22}$-$3\\sb{21}$ transition show a distinct bipolar structure with lobes oriented along a roughly north-south axis. The maps of the 4$\\sb{04}$-$3\\sb{03}$ transition show an asymmetric appearance in which the east side of the CSE is $\\sim$2-3 brighter than the west side. Radiative transfer models of the data suggest that most of the observed SiC$\\sb2$ is confined to a shell with inner radius $\\sim$2 $\\times$ 10$\\sp{16}$ cm and outer radius $\\sim$6 $\\times$ 10$\\sp{16}$ cm. The abundance of SiC$\\sb2$ ( (SiC$\\sb2$) / (H$\\sb2$)) within the shell is $\\sim$10$\\sp{-6}$. We cannot rule out the possibility that some SiC$\\sb2$ originates in the inner envelope near the photosphere but we can put an upper limit on the abundance of SiC$\\sb2$ in the inner envelope. Our data constrains the fractional abundance of SiC$\\sb2$ in the inner envelope (r $\\sbsp{\\sim}{<}$ 2 $\\times$ 10$\\sp{16}$ cm) to be no more than $\\sim$3 $\\times$ 10$\\sp{-8}$. The distribution and abundance of SiC$\\sb2$ suggest that ion-molecule reactions involving C$\\sb2$H$\\sb2$ may be responsible for producing much of the SiC$\\sb2$.","Our data also places important constraints on the excitation mechanisms for SiC$\\sb2$. Kinetic temperatures in the outer CSE ($\\sbsp{\\sim}{<}$60 K) where much of the SiC$\\sb2$ resides are not high enough to excite the high excitation temperatures across K-ladders observed by Thaddeus et al. (1984) and Avery et al. (1992). This suggests that radiative excitation through the lowest-lying vibrationally-excited state, the $\\nu\\sb3$ = 1 antisymmetric mode, may be responsible for the high excitation temperatures across K-ladders. To test this hypothesis we made a sensitive search for rotational transitions of vibrationally excited SiC$\\sb2$ with the NRAO 12-m. Our data suggests that the column density of vibrationally excited SiC$\\sb2$ is at least two orders of magnitude lower than the column density of the ground vibrational state. The upper limit on the column density of vibrationally excited SiC$\\sb2$ is consistent with radiative excitation through the $\\nu\\sb3$ = 1 antisymmetric mode.","Made available in DSpace on 2011-05-07T12:03:24Z (GMT). No. of bitstreams: 2 license.txt: 4922 bytes, checksum: 910b249b4beec47e7ab768910c8f966f (MD5) 9512370.pdf: 8774793 bytes, checksum: 2b3a9f9f6a90139904475d413cca4b88 (MD5) Previous issue date: 1994","Item marked as restricted to the 'UIUC Users [automated]' Group (id=2) by Howard Ding (hding2@illinois.edu) on 2011-05-07T14:36:04Z Item is restricted indefinitely.","Restriction data tranferred 2014-07-01T11:14:27-05:00 Original Data Group with Access UIUC Users [automated] Release Date: none Reason: ETDs are only available to UIUC Users without author permission","ETDs are only available to UIUC Users without author permission","U of I Only"],"dc:identifier":["AAI9512370","(UMI)AAI9512370","http://hdl.handle.net/2142/19307"],"dc:language":["eng"],"dc:rights":["Copyright 1994 Gensheimer, Paul David"],"dc:subject":["Physics, Astronomy and Astrophysics"],"dc:title":["A millimeter-wave interferometric study of gas-phase silicon dicarbide in the circumstellar envelope surrounding IRC+10216"],"dc:type":["text"],"thesis:degree_discipline":["Astronomy"],"thesis:degree_level":["Dissertation"],"thesis:degree_name":["Ph.D."],"thesis:institution_name":["University of Illinois at Urbana-Champaign"]},"updated_at":"2026-07-22T22:25:12Z"}