Molecules around ae aurigae patrick boiss iap
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Collaborators Andersson BG. Galazutdinov G. Federman S. Gerin M. Gry C. Hilly-Blant P. Krelowski J. Le Petit F. Pagani L. Pineau des Forêts G. Rollinde E. Roueff E. Sheffer Y. Molecules around AE Aurigae Patrick Boissé, IAP. Purpose of the initial project. Study of

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Molecules around ae aurigae patrick boiss iap

Collaborators

Andersson BG.

Galazutdinov G.

Federman S.

Gerin M.

Gry C.

Hilly-Blant P.

Krelowski J.

Le Petit F.

Pagani L.

Pineau des Forêts G.

Rollinde E.

Roueff E.

Sheffer Y.

Molecules around AE AurigaePatrick Boissé, IAP


Purpose of the initial project
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 34078

    type : O 9V,

    d = 500 pc,

    proper motion: m ≈ 0.4 arcsec/yr--> Vt = 100 km/s


Probing the structure: method

IS cloud

observer

HD 34078

I(l)

l


Purpose of the initial project1
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 (Dt) --> spatial structure (Dl)

    • optical spectra (OHP/Elodie) --> CH, CH+, DIBs

      (cf Rollinde et al. 2003)

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

Dt = 1 yr -->Dl ≈ 20 AU


H 2 absorption in fuse spectra
H2 absorption in FUSE spectra


Implications of FUSE spectra

  • Cold H2

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

    • T01 = 77 K

  • Large amount of highly excited H2 up to

    • (v, J ) = (0, 11) (E = 10200 K) and

    • (v, J ) = (2, 1) (E = 11800 K)

  • Same velocity for cold and hot H2(DV < 2 km/s)

  • Excitation diagram, to be compared to

    • standard IS material (cf Gry et al. 2002)

    • the HD37903 line of sight (Meyer et al. 2001)



First scenario

Bow shock:

IS cloud

Hot excited gas

observer

HD 34078

cold molecular gas


Modelling of the absorbing gas
Modelling of the absorbing gas

  • PDR code of Le Bourlot et al. (1993)

  • (n ,c) = (700 cm-3, 1) and (104cm-3, 104)


H 2 line variations method 1
H2 line variations - method - 1

J = 0, 1, 2 damped lines : DN > 0 --> broadening


H 2 line variations method 2
H2 line variations - method - 2


H 2 line variations observations
H2 line variations: observations

Jan 2000 - oct 2002

  • jan 2000 - oct 2002: dN(H2) / N(H2) < 5 %

  • jan 2000 - nov 2004: analysis in progress, "probable" variations


Ch line profiles
CH line profiles

CH and CH+ lines (4300, 4232 and 3957Å):t ≈ 1

--->DW ≈ a DN

Jan 1993 - feb 2002

R ≈ 200 000


Ch variations over 13 years
CH variations over 13 years

-->dN(CH) / N(CH) ≈ 20 % (12 - 38%)


Ch variations
CH+ variations

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


Specific features of hd 34078
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)


Cloud star association iram observations
Cloud/star association ? --> IRAM Observations

  • Map of the CO(2-1) emission in the star field

    • Morphology correlated with the star position ?

      • No no star/cloud association

      • Yes star <--> cloud interaction

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


Iram co 2 1 iram 30m map 2004
IRAM CO(2-1) IRAM 30m map - 2004

Unambiguous star cloud association !


Iram co 2 1 map central part
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 !!


Revised scenario

observer

cold molecular gas

hot excited gas


  • Consistency with observations

  • Presence of CO, CH, CH+, CN, C2, C3 … molecules

    • small 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 temperature

    • delayed dust -> gas heating

  • HighCH/H2 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


Conclusions
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
Prospects

Needed : modelling of

  • the star - cloud interactionand

  • 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 ?

    • comparison to "standard" lines of sight

    • comparison to HD 37903


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