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Molecules around AE Aurigae Patrick Boissé, IAP

Collaborators Andersson BG. Galazutdinov G. Federman S. Gerin M. Gry C. Hilly-Blant P. Krelowski J. Le Petit F. Pagani L. Pineau des Forêts G. Rollinde E. Roueff E. Sheffer Y. Molecules around AE Aurigae Patrick Boissé, IAP. Purpose of the initial project. Study of

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Molecules around AE Aurigae Patrick Boissé, IAP

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  1. Collaborators Andersson BG. Galazutdinov G. Federman S. Gerin M. Gry C. Hilly-Blant P. Krelowski J. Le Petit F. Pagani L. Pineau des Forêts G. Rollinde E. Roueff E. Sheffer Y. Molecules around AE AurigaePatrick Boissé, IAP

  2. Purpose of the initial project Study of • the small scale structure in diffuse molecular gas (H2, CH, CH+, etc) • using a large transverse velocity O star AE Aur = HD 34078 type : O 9V, d = 500 pc, proper motion: m ≈ 0.4 arcsec/yr--> Vt = 100 km/s

  3. Probing the structure: method IS cloud observer HD 34078 I(l) l

  4. Purpose of the initial project Study of • the small scale structure in diffuse molecular gas (H2, CH, CH+, etc) • using a large transverse velocity O star Repeated observations (Dt) --> spatial structure (Dl) • optical spectra (OHP/Elodie) --> CH, CH+, DIBs (cf Rollinde et al. 2003) • FUV spectra (FUSE) --> H2(cf Boissé et al. 2005) Dt = 1 yr -->Dl ≈ 20 AU

  5. H2 absorption in FUSE spectra

  6. Implications of FUSE spectra • Cold H2 • N(H2) = 6.4 10 20 cm -2 (J = 0, 1, 2) • T01 = 77 K • Large amount of highly excited H2 up to • (v, J ) = (0, 11) (E = 10200 K) and • (v, J ) = (2, 1) (E = 11800 K) • Same velocity for cold and hot H2(DV < 2 km/s) • Excitation diagram, to be compared to • standard IS material (cf Gry et al. 2002) • the HD37903 line of sight (Meyer et al. 2001)

  7. Excitation diagram

  8. First scenario Bow shock: IS cloud Hot excited gas observer HD 34078 cold molecular gas

  9. Modelling of the absorbing gas • PDR code of Le Bourlot et al. (1993) • (n ,c) = (700 cm-3, 1) and (104cm-3, 104)

  10. H2 line variations - method - 1 J = 0, 1, 2 damped lines : DN > 0 --> broadening

  11. H2 line variations - method - 2

  12. H2 line variations: observations Jan 2000 - oct 2002 • jan 2000 - oct 2002: dN(H2) / N(H2) < 5 % • jan 2000 - nov 2004: analysis in progress, "probable" variations

  13. CH line profiles CH and CH+ lines (4300, 4232 and 3957Å):t ≈ 1 --->DW ≈ a DN Jan 1993 - feb 2002 R ≈ 200 000

  14. CH variations over 13 years -->dN(CH) / N(CH) ≈ 20 % (12 - 38%)

  15. CH+ variations --> - 1.5 < dN(CH+) / N(CH+) < 0. 3 %/yr

  16. Specific features of HD 34078 • Excited H2 • Large CH/H2 ratio (about x 2) • CH variation • unidentified absorption lines present Any cloud-star association ? cf Herbig (1958)

  17. Cloud/star association ? --> IRAM Observations • Map of the CO(2-1) emission in the star field • Morphology correlated with the star position ? • No no star/cloud association • Yes star <--> cloud interaction • CO(2-1)/CO(1-0): "anomalous" excitation ratio ?

  18. IRAM CO(2-1) IRAM 30m map - 2004 Unambiguous star cloud association !

  19. IRAM CO(2-1) map - central part • ≈ E - W symmetry about the star position • high CO (2-1)/CO(1-0) excitation ratio Apparent paradox: CO emission reinforced close to this O9 star close = 10 " at 500pc or 0.025 pc !!

  20. Revised scenario observer cold molecular gas hot excited gas

  21. Consistency with observations • Presence of CO, CH, CH+, CN, C2, C3 … molecules • small fraction of the cloud photoionised-dissociated • CO emission compressed gas, not yet photodissociated • Increase of N(CH) (+ N(H2) ?) • consistent with the star penetrating into the cloud • Low H2 temperature • delayed dust -> gas heating • HighCH/H2 abundance ratio • time dependent effects --> enhanced CH production ? (destruction of small grains ? photodesorption ?) • Unidentified lines • transient (unstable) species not commonly seen on other lines of sight

  22. Conclusions AE Aurigae is associated to a translucent cloud due to a chance encounter : • unique case to study the response of a cloud to a "flash of UV light" --> time dependence of physical - chemical processes • AE Aur can (probably) be used nevertheless to probe the cloud structure

  23. Prospects Needed : modelling of • the star - cloud interactionand • time-dependent processes in the cloud • Difficult problem ! • … but many observational constraints available • interpretation of the CO kinematical structure ? • which other species/transitions do we expect ? • comparison to "standard" lines of sight • comparison to HD 37903

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