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
