1. Molecules around AE Aurigae Patrick Boissé, IAP Collaborators oAndersson BG. oGalazutdinov G. oFederman S. oGerin M. oGry C. oHilly-Blant P. oKrelowski J. oLe Petit F. oPagani L. oPineau des Forêts G. oRollinde E. oRoueff E. oSheffer Y.

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

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

4. Purpose of the initial project Study of the small scale structure in diffuse molecular gas (H 2, CH, CH +, etc) using a large transverse velocity O star Repeated observations  t) -  spatial structure  l) ooptical spectra (OHP/Elodie) --> CH, CH +, DIBs (cf Rollinde et al. 2003) oFUV spectra (FUSE) --> H 2 (cf Boissé et al. 2005)  t = 1 yr -->  l ≈ 20 AU

5. H 2 absorption in FUSE spectra

6. Cold H 2 o N(H 2 ) = 6.4 10 20 cm -2 (J = 0, 1, 2) o T 01 = 77 K Large amount of highly excited H 2 up to o (v, J ) = (0, 11) (E = 10200 K) and o (v, J ) = (2, 1) (E = 11800 K) Same velocity for cold and hot H 2 (  V < 2 km/s ) Excitation diagram, to be compared to o standard IS material (cf Gry et al. 2002) o the HD37903 line of sight (Meyer et al. 2001) Implications of FUSE spectra

7. Excitation diagram

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

9. Modelling of the absorbing gas PDR code of Le Bourlot et al. (1993) (n,  = (700 cm -3, 1) and (10 4  cm -3  10 4 )

10. H 2 line variations - method - 1 J = 0, 1, 2 damped lines :  N > 0 --> broadening

11. H 2 line variations - method - 2

12. H 2 line variations: observations jan 2000 - oct 2002:  N(H 2 ) / N(H 2 ) < 5 % jan 2000 - nov 2004: analysis in progress, "probable" variations Jan 2000 - oct 2002

13. CH line profiles CH and CH + lines (4300, 4232 and 3957Å):  ≈  --->  W ≈   N Jan 1993 - feb 2002 R ≈ 200 000

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

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

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

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

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. observer cold molecular gas Revised scenario hot excited gas

21. Consistency with observations Presence of CO, CH, CH +, CN, C 2, C 3 … molecules small fraction of the cloud photoionised-dissociated CO emission compressed gas, not yet photodissociated Increase of N(CH) (+ N(H 2 ) ?) consistent with the star penetrating into the cloud Low H 2 temperature delayed dust -> gas heating High CH/H 2 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 o the star - cloud interaction and o 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 ? o comparison to "standard" lines of sight o comparison to HD 37903