Spitzer IRS spectra of PAH emission from Herbig Ae/Be stars Eric Leibensperger (Ithaca College, Ithaca, NY) And Luke Keller (Advisor) In collaboration

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  • Spitzer IRS spectra of PAH emission from Herbig Ae/Be starsEric Leibensperger(Ithaca College, Ithaca, NY)AndLuke Keller (Advisor)

    In collaboration with the Spitzer IRS Disks Team:G.C. Sloan (Cornell University), W.J. Forrest (University of Rochester), A. Li (University of Missouri-Columbia), J. Najita (NOAO), D.M. Watson (University of Rochester), C.H. Chen (NOAO), J.D. Green (University of Rochester), F. Kemper (University of Virginia), L. Hartmann (CfA), T.L. Herter (Cornell University), P. D'Alessio (UNAM), B. Sargent (University of Rochester), P. W. Morris (IPAC/CalTech), D.J. Barry (Cornell University), P. Hall (Cornell University), B.R. Brandl (Sterrewacht Leiden), P.C. Myers (CfA), and J.R. Houck (Cornell University)

  • What can the PAHs tell us about AeBe stars and their disks?

    Physical structure of the disks: e.g. PAH primarily from far out (~100 AU) in a flared disk

    Physical properties of the emission regions

    ionization fraction (radiation field and e- density), gas temperature, not to mention chemical properties

    Dust grain processing and evolutionOur love-hate relationship with Polycyclic Aromatic Hydrocarbons

  • Herbig Ae/Be stars Intermediate mass (2-8 M) Main sequence stars of spectral type B, A, F Broad line emission in optical-IR IR excess due to thermal emission from dust No requirement for association with nebulosityCurrent sample: 4 of 16 Ae/Be stars in IRS Disks programThese four stars have clean PAH spectra: no other solid state features in their 5-14 mm spectra

  • The Spitzer Space TelescopeBackground-limited sensitivity 3 180 m85 cm f/12 beryllium R-C telescope, T < 5.5KThree scientific instruments provide:Imaging/photometry, 3-180 mSpectroscopy, 5-40 m (R = 90 & 600)Spectrophotometry, 50-100 m5.5 yr lifetime Launched on 25 August 2003Birth stone: forsterite

  • Physical structure of the disks: SEDs (UV-mm)LLLLLLLL(Malfait et al. 1998)

  • 6.2 mm C-C stretchskeletal modes7.7-7.9 mm C-C stretch 8.6 mm C-H in-plane bend11.3, 12.0, & 12.7 mm C-H out-of-plane bendPolycyclicAromaticHydrocarbonsSloan et al. 2005 (submitted to ApJ)(coronene)

  • Measuring PAH feature strengths and their ratios Simple line segment achors Model independent Error bars: s of mean of two telescope nodsHD 141569

  • PAH ionization:

    Ionization correlates withF7.9/F11.3

  • (From Peeters et al. 2002 & Allamandola et al. 1999)Lab data showing spectral signature of PAH ionization:

  • Figure from Sloan et al. 2005(adapted from Peeters et al. 2002)IRAS 03260+3111(YSO in MC, PAH Class A)HD 44179 (Post AGB star Red Rectangle PAH Class B)AFGL 2688 (Post AGB star Cygnus Egg PAH Class C)HD 100546 (IsolatedAe/Be star, PAH Class B)ISM (more processed) AeBe, Pne Post AGB (less processed)

  • Conclusions:

    Ae/Be stars seem to have distinctive PAH spectra among strong PAH emitters

    As ionization increases, PAH size decreases (this is consistent with their star spectral types)

    All based on a VERY small sample

  • The next steps:

    Larger sample (WANTED: more blue outliers) Isolate PAH from solid state features Model PAH & dust emission

    Li & Lunine (2004): porous cometary-type dust, PAHs ionized

  • Thanks!If you would like more information on this or any other IRS Disks Projects, e-mail Dr. Keller (lkeller@ithaca.edu) or myself (eleiben1@ithaca.edu)