Molecules around AE AurigaePatrick Boissé, IAP

Collaboratorso Andersson BG.o Galazutdinov G.o Federman S.o Gerin M.o Gry C.o Hilly-Blant P.o Krelowski J.

o Le Petit F.o Pagani L.o Pineau des Forêts G.o Rollinde E.o Roueff E.o Sheffer Y.

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 starAE Aur = HD 34078

type : O 9V, d = 500 pc,proper motion: ≈ 0.4 arcsec/yr --> Vt = 100 km/s

I(

observer

IS cloud

HD 34078

Probing the structure: method

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 t) - spatial structure l)

o optical spectra (OHP/Elodie) --> CH, CH+, DIBs (cf Rollinde et al. 2003)

o FUV spectra (FUSE) --> H2 (cf Boissé et al. 2005)

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l =Vtrans Δ t t = 1 yr --> l ≈ 20 AU

H2 absorption in FUSE spectra

• Cold H2

o N(H2) = 6.4 10 20 cm -2 (J = 0, 1, 2)

o T01 = 77 K

• Large amount of highly excited H2 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 H2 (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

Excitation diagram

observer

IS cloud

HD 34078

Bow shock:

cold molecular gas

Hot excited gas

First scenario

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

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

H2 line variations - method - 2

H2 line variations: observations

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

Jan 2000 - oct 2002

CH line profilesCH and CH+ lines (4300, 4232 and 3957Å): ≈

---> W ≈ N

Jan 1993 - feb 2002R ≈ 200 000

CH variations over 13 years

--> N(CH) / N(CH) ≈ 20 % (12 - 38%)

CH+ variations

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

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)

o Map of the CO(2-1) emission in the star field Morphology correlated with the star position ?

o No no star/cloud associationo Yes star <--> cloud interaction

o CO(2-1)/CO(1-0): "anomalous" excitation ratio ?

Cloud/star association ? --> IRAM Observations

IRAM CO(2-1) IRAM 30m map - 2004

Unambiguous star cloud association !

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 !!

observer

cold molecular gas

Revised scenario

hot excited gas

Consistency with observations

• Presence of CO, CH, CH+, CN, C2, C3 … moleculessmall 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 temperaturedelayed dust -> gas heating

• High CH/H2 abundance ratiotime dependent effects --> enhanced CH production ? (destruction of small grains ? photodesorption ?)

• Unidentified lines transient (unstable) species not commonly seen on other lines of sight

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

Prospects

Needed : modelling of o the star - cloud interaction ando 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 sighto comparison to HD 37903