Post on 17-Jan-2018
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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