Centimetre-wave continuum radiation from the rho Ophiuchi molecular cloud
The ρ Oph molecular cloud is undergoing intermediate-mass star formation. Ultraviolet radiation from its hottest young stars heats and dissociates exposed layers, but does not ionize hydrogen. Only faint radiation from the Rayleigh-Jeans tail of ∼10-100 K dust is expected at wavelengths longwards of...
| Main Authors: | , , , , , , , , , , |
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| Format: | Journal article |
| Language: | English |
| Published: |
2008
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| _version_ | 1797081745863999488 |
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| author | Casassus, S Dickinson, C Cleary, K Paladini, R Etxaluze, M Lim, T White, G Burton, M Indermuehle, B Stahl, O Roche, P |
| author_facet | Casassus, S Dickinson, C Cleary, K Paladini, R Etxaluze, M Lim, T White, G Burton, M Indermuehle, B Stahl, O Roche, P |
| author_sort | Casassus, S |
| collection | OXFORD |
| description | The ρ Oph molecular cloud is undergoing intermediate-mass star formation. Ultraviolet radiation from its hottest young stars heats and dissociates exposed layers, but does not ionize hydrogen. Only faint radiation from the Rayleigh-Jeans tail of ∼10-100 K dust is expected at wavelengths longwards of ∼3 mm. Yet cosmic background imager (CBI) observations reveal that the ρ Oph W photodissociation region is surprisingly bright at centimetre wavelengths. We searched for interpretations consistent with the Wilkinson Microwave Anisotropy Probe radio spectrum, new Infrared Space Observatory-Long Wavelength Spectrograph (LWS) parallel mode images and archival Spitzer data. Dust-related emission mechanisms at 1 cm, as proposed by Draine and Lazarian, are a possibility. But a magnetic enhancement of the grain opacity at 1 cm is inconsistent with the morphology of the dust column maps Nd and the lack of detected polarization. Spinning dust, or electric-dipole radiation from spinning very small grains (VSGs), comfortably explains the radio spectrum, although not the conspicuous absence from the CBI data of the infrared circumstellar nebulae around the B-type stars S1 and SR3. Allowing for VSG depletion can marginally reconcile spinning dust with the data. As an alternative interpretation, we consider the continuum from residual charges in ρ Oph W, where most of carbon should be photoionized by the close binary HD 147889 (B2IV, B3IV). Electron densities of ∼102 cm-3, or H-nucleus densities nH > 106 cm-3, are required to interpret ρ Oph W as the C ii Strömgren sphere of HD 147889. However, the observed steep and positive low-frequency spectral index would then imply optically thick emission from an hitherto unobserved ensemble of dense clumps or sheets with a filling factor of ∼10-4 and nH ∼ 107 cm-3. © 2008 Universidad de Chile. Journal compilation © 2008 RAS. |
| first_indexed | 2024-03-07T01:18:20Z |
| format | Journal article |
| id | oxford-uuid:8f79d9c7-b935-4fe6-8c26-a4156fe2f342 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-07T01:18:20Z |
| publishDate | 2008 |
| record_format | dspace |
| spelling | oxford-uuid:8f79d9c7-b935-4fe6-8c26-a4156fe2f3422022-03-26T23:04:34ZCentimetre-wave continuum radiation from the rho Ophiuchi molecular cloudJournal articlehttp://purl.org/coar/resource_type/c_dcae04bcuuid:8f79d9c7-b935-4fe6-8c26-a4156fe2f342EnglishSymplectic Elements at Oxford2008Casassus, SDickinson, CCleary, KPaladini, REtxaluze, MLim, TWhite, GBurton, MIndermuehle, BStahl, ORoche, PThe ρ Oph molecular cloud is undergoing intermediate-mass star formation. Ultraviolet radiation from its hottest young stars heats and dissociates exposed layers, but does not ionize hydrogen. Only faint radiation from the Rayleigh-Jeans tail of ∼10-100 K dust is expected at wavelengths longwards of ∼3 mm. Yet cosmic background imager (CBI) observations reveal that the ρ Oph W photodissociation region is surprisingly bright at centimetre wavelengths. We searched for interpretations consistent with the Wilkinson Microwave Anisotropy Probe radio spectrum, new Infrared Space Observatory-Long Wavelength Spectrograph (LWS) parallel mode images and archival Spitzer data. Dust-related emission mechanisms at 1 cm, as proposed by Draine and Lazarian, are a possibility. But a magnetic enhancement of the grain opacity at 1 cm is inconsistent with the morphology of the dust column maps Nd and the lack of detected polarization. Spinning dust, or electric-dipole radiation from spinning very small grains (VSGs), comfortably explains the radio spectrum, although not the conspicuous absence from the CBI data of the infrared circumstellar nebulae around the B-type stars S1 and SR3. Allowing for VSG depletion can marginally reconcile spinning dust with the data. As an alternative interpretation, we consider the continuum from residual charges in ρ Oph W, where most of carbon should be photoionized by the close binary HD 147889 (B2IV, B3IV). Electron densities of ∼102 cm-3, or H-nucleus densities nH > 106 cm-3, are required to interpret ρ Oph W as the C ii Strömgren sphere of HD 147889. However, the observed steep and positive low-frequency spectral index would then imply optically thick emission from an hitherto unobserved ensemble of dense clumps or sheets with a filling factor of ∼10-4 and nH ∼ 107 cm-3. © 2008 Universidad de Chile. Journal compilation © 2008 RAS. |
| spellingShingle | Casassus, S Dickinson, C Cleary, K Paladini, R Etxaluze, M Lim, T White, G Burton, M Indermuehle, B Stahl, O Roche, P Centimetre-wave continuum radiation from the rho Ophiuchi molecular cloud |
| title | Centimetre-wave continuum radiation from the rho Ophiuchi molecular cloud |
| title_full | Centimetre-wave continuum radiation from the rho Ophiuchi molecular cloud |
| title_fullStr | Centimetre-wave continuum radiation from the rho Ophiuchi molecular cloud |
| title_full_unstemmed | Centimetre-wave continuum radiation from the rho Ophiuchi molecular cloud |
| title_short | Centimetre-wave continuum radiation from the rho Ophiuchi molecular cloud |
| title_sort | centimetre wave continuum radiation from the rho ophiuchi molecular cloud |
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