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

Our love-hate relationship with Polycyclic Aromatic Hydrocarbons… 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 evolution H

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 nebulosity Current sample: 4 of 16 Ae/Be stars in IRS Disks program These four stars have “clean” PAH spectra: no other solid state features in their 5-14 mm spectra

The Spitzer Space Telescope Background-limited sensitivity 3 – 180 m 85 cm f/12 beryllium R-C telescope, T < 5.5K Three scientific instruments provide: Imaging/photometry, 3-180 m Spectroscopy, 5-40 m (R = 90 & 600) Spectrophotometry, 50-100 m 5.5 yr lifetime Launched on 25 August 2003 Birth stone: forsterite

Physical structure of the disks: SEDs (UV-mm) IRS SL LL LL LL LL (Malfait et al. 1998)

Polycyclic Aromatic Hydrocarbons 6.2 mm C-C stretch “skeletal modes” 11.3, 12.0, & 12.7 mm C-H out-of-plane bend Polycyclic Aromatic Hydrocarbons 7.7-7.9 mm C-C stretch 8.6 mm C-H in-plane bend H (coronene) Sloan et al. 2005 (submitted to ApJ)

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

PAH ionization: Ionization correlates with F7.9/F11.3

Lab data showing spectral signature of PAH ionization: C-C stretch C-H bend (From Peeters et al. 2002 & Allamandola et al. 1999)

(adapted from Peeters et al. 2002) ISM (more processed) AeBe, Pne Post AGB (less processed) 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 (Isolated Ae/Be star, PAH Class B) Figure from Sloan et al. 2005 (adapted from Peeters et al. 2002)

F7.9/F11.3 F12.7/F11.3 Foutlier/F11.3 F6.2/F7.9 HD 135344 (F4), 169142 (A5), 34282 (A0), 141569 (A0) 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)