molecules around ae aurigae patrick boissé, iap

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 star

AE Aur = HD 34078type : 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)

€

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 too 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 profiles

CH 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 association

o 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