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Published byThomas Ramsey Modified over 9 years ago
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Molecules around AE Aurigae Patrick Boissé, IAP Collaborators oAndersson BG. oGalazutdinov G. oFederman S. oGerin M. oGry C. oHilly-Blant P. oKrelowski J. oLe Petit F. oPagani L. oPineau des Forêts G. oRollinde E. oRoueff E. oSheffer Y.
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Purpose of the initial project Study of the small scale structure in diffuse molecular gas (H 2, CH, CH +, etc) using a large transverse velocity O star AE Aur = HD 34078 type : O 9V, d = 500 pc, proper motion: ≈ 0.4 arcsec/yr --> V t = 100 km/s
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I( observer IS cloud HD 34078 Probing the structure: method
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Purpose of the initial project Study of the small scale structure in diffuse molecular gas (H 2, CH, CH +, etc) using a large transverse velocity O star Repeated observations t) - spatial structure l) ooptical spectra (OHP/Elodie) --> CH, CH +, DIBs (cf Rollinde et al. 2003) oFUV spectra (FUSE) --> H 2 (cf Boissé et al. 2005) t = 1 yr --> l ≈ 20 AU
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H 2 absorption in FUSE spectra
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Cold H 2 o N(H 2 ) = 6.4 10 20 cm -2 (J = 0, 1, 2) o T 01 = 77 K Large amount of highly excited H 2 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 H 2 ( 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
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Excitation diagram
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observer IS cloud HD 34078 Bow shock: cold molecular gas Hot excited gas First scenario
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Modelling of the absorbing gas PDR code of Le Bourlot et al. (1993) (n, = (700 cm -3, 1) and (10 4 cm -3 10 4 )
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H 2 line variations - method - 1 J = 0, 1, 2 damped lines : N > 0 --> broadening
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H 2 line variations - method - 2
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H 2 line variations: observations jan 2000 - oct 2002: N(H 2 ) / N(H 2 ) < 5 % jan 2000 - nov 2004: analysis in progress, "probable" variations Jan 2000 - oct 2002
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CH line profiles CH and CH + lines (4300, 4232 and 3957Å): ≈ ---> W ≈ N Jan 1993 - feb 2002 R ≈ 200 000
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CH variations over 13 years --> N(CH) / N(CH) ≈ 20 % (12 - 38%)
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CH + variations --> - 1.5 < N(CH + ) / N(CH + ) < 0. 3 %/yr
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Specific features of HD 34078 Excited H 2 Large CH/H 2 ratio (about x 2) CH variation unidentified absorption lines present Any cloud-star association ? cf Herbig (1958)
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oMap 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
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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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observer cold molecular gas Revised scenario hot excited gas
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Consistency with observations Presence of CO, CH, CH +, CN, C 2, C 3 … molecules small fraction of the cloud photoionised-dissociated CO emission compressed gas, not yet photodissociated Increase of N(CH) (+ N(H 2 ) ?) consistent with the star penetrating into the cloud Low H 2 temperature delayed dust -> gas heating High CH/H 2 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
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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" --> 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 o the star - cloud interaction and o 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 sight o comparison to HD 37903
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