DIGIT survey of far-infrared lines from protoplanetary disks I. [O I], [CII], OH, H<subscript>2</subscript>O, and CH<superscript>+</superscript>.
In: Astronomy & Astrophysics / Astronomie et Astrophysique, Jg. 559 (2013-12-01), S. 1-22
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Zugriff:
We present far-infrared (50-200 μm) spectroscopic observations of young pre-main-sequence stars taken with Herschel/PACS as part of the DIGIT key project. The sample includes 16 Herbig AeBe and 4 T Tauri sources observed in SED mode covering the entire spectral range. An additional 6 Herbig AeBe and 4 T Tauri systems have been observed in SED mode with a limited spectral coverage. Multiple atomic fine structure and molecular lines are detected at the source position: [O I], [C II], CO, OH, H 2 O, CH + . The most common feature is the [O I] 63 μm line detected in almost all of the sources, followed by OH. In contrast with CO, OH is detected toward both Herbig AeBe groups (flared and non-flared sources). An isothermal LTE slab model fit to the OH lines indicates column densities of 1013 < NOH < 10 16 cm -2 , emitting radii 15 < r < 100AU and excitation temperatures 100 < T ex < 400 K. We used the non-LTE code RADEX to verify the LTE assumption. High gas densities (n ⩾ 10 10 cm -3 ) are needed to reproduce the observations. The OH emission thus comes from a warm layer in the disk at intermediate stellar distances. Warm H 2 O emission is detected through multiple lines toward the T Tauri systems AS 205, DG Tau, S CrA and RNO 90 and three Herbig AeBe systems HD 104237, HD 142527, HD 163296 (through line stacking). Overall, Herbig AeBe sources have higher OH/H 2 O abundance ratios across the disk than do T Tauri disks, from near- to far-infrared wavelengths. Far-infrared CH + emission is detected toward HD 100546 and HD 97048. The slab model suggests moderate excitation (Tex ~ 100K) and compact (r ~ 60AU) emission in the case of HD 100546. Off-source [O I] emission is detected toward DG Tau, whose origin is likely the outflow associated with this source. The [CII] emission is spatially extended in all sources where the line is detected. This suggests that not all [CII] emission is associated with the disk and that there is a substantial contribution from diffuse material around the young stars. The flux ratios of the atomic fine structure lines ([O I] 63 μm, [O I] 145 μm, [CII]) are analyzed with PDR models and require high gas density (n ⩾ 10 5 cm -3 ) and high UV fluxes (Go ~ 10 3 -10 7 ), consistent with a disk origin for the oxygen lines for most of the sources. [ABSTRACT FROM AUTHOR]
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Titel: |
DIGIT survey of far-infrared lines from protoplanetary disks I. [O I], [CII], OH, H<subscript>2</subscript>O, and CH<superscript>+</superscript>.
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Autor/in / Beteiligte Person: | Fedele, D. ; Bruderer, S. ; van Dishoeck, E. F. ; Carr, J. ; Herczeg, G. J. ; Salyk, C. ; Evans II, N. J. ; Bouwman, J. ; Meeus, G. ; Henning, Th. ; Green, J. ; Najita, J. R. ; Güdel, M. |
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Zeitschrift: | Astronomy & Astrophysics / Astronomie et Astrophysique, Jg. 559 (2013-12-01), S. 1-22 |
Veröffentlichung: | 2013 |
Medientyp: | academicJournal |
ISSN: | 0004-6361 (print) |
DOI: | 10.1051/0004-6361/201321118 |
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