Molecules around AE Aurigae Patrick Boiss, IAP

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Molecules around AE AurigaePatrick Boissé, 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.

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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 --gt Vt 100
  km/s

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Probing the structure method
IS cloud
observer
HD 34078
I(l)
l
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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) --gt spatial structure
  (Dl)
• optical spectra (OHP/Elodie) --gt CH, CH, DIBs
• (cf Rollinde et al. 2003)
• FUV spectra (FUSE) --gt H2 (cf Boissé et al.
  2005)

Dt 1 yr --gt Dl 20 AU
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H2 absorption in FUSE spectra
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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 lt 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)

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Excitation diagram
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First scenario
Bow shock
IS cloud
Hot excited gas
observer
HD 34078
cold molecular gas
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Modelling of the absorbing gas

• PDR code of Le Bourlot et al. (1993)
• (n ,c) (700 cm-3, 1) and (104 cm-3, 104)

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H2 line variations - method - 1
J 0, 1, 2 damped lines DN gt 0 --gt
broadening
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H2 line variations - method - 2
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H2 line variations observations
Jan 2000 - oct 2002

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

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CH line profiles
CH and CH lines (4300, 4232 and 3957Å) t 1
---gt DW a DN
Jan 1993 - feb 2002 R 200 000
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CH variations over 13 years
--gt dN(CH) / N(CH) 20 (12 - 38)
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CH variations
--gt - 1.5 lt dN(CH) / N(CH) lt 0. 3 /yr
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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)
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Cloud/star association ? --gt 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 lt--gt cloud interaction
• CO(2-1)/CO(1-0) "anomalous" excitation ratio ?

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IRAM CO(2-1) IRAM 30m map - 2004
Unambiguous star cloud association !
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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 !!

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Revised scenario
observer
cold molecular gas
hot excited gas
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• Consistency with observations
• Presence of CO, CH, CH, CN, C2, C3 molecules
• small fraction of the cloud photoionised-dissociat
  ed
• 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 -gt gas heating
• High CH/H2 abundance ratio
• time dependent effects --gt enhanced CH production
  ? (destruction of small grains ? photodesorption
  ?)
• Unidentified lines
• transient (unstable) species not commonly seen on
  other lines of sight

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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"
• --gt time dependence of physical - chemical
  processes
• AE Aur can (probably) be used nevertheless
• to probe the cloud structure

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Prospects

• Needed modelling of
• the star - cloud interaction and
• 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