Study of Planet forming Systems Orbiting Intermediate-mass Stars

Sweta ShahIthaca College

Advisor: Dr. Luke KellerIn collaboration with the NASA Spitzer Space Telescope

InfraRed Spectrograph Disk’s Team

Image credit: Caltech

Theory of Planet formationAdapted from Hogerheide 1998

Why intermediate mass (Herbig Ae Be) stars ?

• Hot and massive 12,000 - 18,000 K

• 2-10 solar mass

• Excess thermal (IR) radiation

• ‘e’ Emission line spectra

Circumstellar disks in Orion Nebula (Hubble Space Telescope Image: McCaughrean & O’Dell 1995)

Spectral characteristics of the Accretion Disk

• Thermal IR excess

• PAH

• Dust -silicates

Spectral Energy Distribution (Malfait et al. 1998)

UV mm

Correlation of SED and disk geometry

(Malfait et al. 1998)

Physical structure of the disks: SEDs (UV-mm)

IRSSL

IRSSL

IRSSL

IRSSLLL

LL

LL

LL

(Malfait et al. 1998)

Spectral features - PAH?

• Polycyclic Aromatic Hydrocarbon

• Excited by UV radiation

HH

H

H

HH H

H

H

H

HH

Sloan, Keller, Leibensperger et al. 2005

very stable

What is the shape of the disk?

How do we test this hypothesis?

Measuring the strength of “bumps” in Infrared continuum

6

13

25

Star with no disk

Flared disks

Flat disks

Dust grain growth and settling

Keller, Shah et al. 2006, paper in preparation

Increasing 6-13 m SED slope

Incr

easi

ng 1

3-25

m

SE

D s

lope

Ultimate Goal

Disk evolution in time

IPAH ?!

Thanks!(Any ?)

Spitzer InfraRed Telescope Facility– 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

IRS