1. 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)

2. 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

3. 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

4. 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, m
Spectroscopy, 5-40 m (R = 90 & 600)
Spectrophotometry, m
5.5 yr lifetime
Launched on 25 August 2003
Birth stone: forsterite

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

6. 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
mm C-C stretch
8.6 mm C-H in-plane bend H
(coronene)
Sloan et al (submitted to ApJ)

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

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

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

10. (adapted from Peeters et al. 2002)
ISM (more processed) AeBe, Pne Post AGB (less processed)
IRAS
(YSO in MC, PAH Class A)
HD (Post AGB star “Red Rectangle” PAH Class B)
AFGL 2688 (Post AGB star “Cygnus Egg” PAH Class C)
HD (Isolated
Ae/Be star, PAH Class B)
Figure from Sloan et al. 2005
(adapted from Peeters et al. 2002)

11. F7.9/F11.3
F12.7/F11.3
Foutlier/F11.3
F6.2/F7.9
HD (F4), (A5), (A0), (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…

12. 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

13. Thanks!
If you would like more information on this or any other IRS Disks Projects, Dr. Keller or myself