spitzer irs spectra of pah emission from herbig ae/be stars

Spitzer IRS spectra of PAH emission from Herbig Ae/Be stars

Eric 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 evolution

Our love-hate relationship with Polycyclic Aromatic Hydrocarbons…

HH

H

H

H

H HH

H

H

HH

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 m 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)

IRSSL

IRSSL

IRSSL

IRSSLLL

LL

LL

LL

(Malfait et al. 1998)

6.2 m C-C stretch“skeletal modes”

7.7-7.9 m C-C stretch 8.6 m C-H in-plane bend

11.3, 12.0, & 12.7 m C-H out-of-plane bend

PolycyclicAromaticHydrocarbons

HH

H

H

H

H HH

H

H

HH

Sloan et al. 2005 (submitted to ApJ)

(coronene)

Measuring PAH feature strengths and their ratios

• Simple line segment achors• Model independent• Error bars: of mean of two

telescope nods

HD 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:

C-Cstretch

C-Hbend

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…

F7.9/F11.3

F12

.7/F

11.3

Fo

utl

ier/F

11.3

F6.

2/F

7.9

HD 135344 (F4), 169142 (A5), 34282 (A0), 141569 (A0)

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)