Transcript A multi-wavelength scattered light analysis of the dust grain

Dust particles and their spectra.
Review
Ge/Ay 132 Final report
Ivan Grudinin
“Dusty objects” in space
• Interstellar clouds and
protostars
• Protoplanetary disks
• Other objects and
intergalactic dust
• One of the possible
sources of cosmic
dust are the
supernovae
The most abundant dust species in space
• Total mass of the dust grains may be up to 1% of H mass.
• Silicates. Basically, the silicon atoms surrounded by the tetrahedral
arrangement of oxygen atoms. Silicates have two intense absorption
peaks at 10 and 18μm
• Carbonaceous grains and PAH (Polycyclic Aromatic Hydrocarbons)
(3.3, 6.2, 7.7, 8.6, 11.3 μm features)
• Nanodiamonds (3.47 and 3.53 μm features)
• Nano Titanium Carbide Grains (21 μm feature)
• Icy mantle may accrete onto the grain’s surface
Spectral features are taken from "Interaction of Nanoparticles with Radiation"
Aigen Li arXiv:astro-ph/0311066 v1 4 Nov 2003
Optical properties of dust grains
• Solid state spectra consist of smooth bands with shapes
depending on the environment of condensate molecules.
• Particle shapes influence polarization
• Scattering
• Absorption and radiation
• Photoluminescence
Typical spectrum of silicate grains. The mid-infrared spectrum of the
protostar Elias 29 acquired by the Short Wavelength Spectrometer
aboard Space Infrared Observatory (ISO-SWS)
Carbonaceous grains and PAHs
(Polycyclic Aromatic Hydrocarbons)
The features are bright
even far from the
illuminating stars, hence
the emission process
must be non-thermal in
nature where the
absorption of a single UV
photon by a grain can
create internal
temperatures of nearly
1000K
The 3-15 μm ISO-SWS spectrum of two post-Asymptotic Giant Branch (post
AGB) stars. IRAS 16279-4757 and the Red Rectangle, and that from the
planetary nebula NGC 7027. These UIR features arise from large aromatic
molecules that are excited by optical and UV photons.
Phonon modes and long wavelength spectra
of dust grains
• Single photon can excite single phonon in a dust grain if energy and
momentum are conserved for the photon-phonon interaction. This
process leads to absorption bands in infrared for dielectric
heteroatomic materials, or reststrahlen bands.
• Multiphonon processes have lower probabilities and also contribute
to IR absorption. In these processes, any combination of acoustic,
optical, transverse, and longitudinal phonons, which satisfies the
energy and momentum conservation conditions, can take part.
Multiphonon processes are the main source of infrared absorption in
homoatomic solids such as diamond, silicon etc..
How can we see the dust?
GG Tau circumbinary disk in scattered near IR light
To study grain growth during the planet formation
process, it is necessary to establish the properties of
dust grains in disks surrounding Myr-old
TTauri stars.
This near-infrared (H-band) image of the
disk around the binary star pair GG
Tauri A-B was obtained by Dan Potter
using the University of Hawaii's adaptive
optics system called Hokupa'a, mounted
on the Gemini North 8-meter telescope
on Mauna Kea in Hawaii on the night of
February 24, 2001.
Disk parameters: T=35K,
Inner radius is 180 au, outer is 260 au,
Distance =140pc
Binary system of 0.6 and 0.4 M(Sun)
IRAM image of GG tau circumbinary disk thermal emission
The blue, white and red contours
show the iso-intensity levels
observed at 5.5, 6.5 (systemic
velocity) and 7.5 km.s-1 in the
13CO J=2-1 lines. The
background is a false color
image of the 1.3-mm thermal
dust emission.
http://www.iram.fr/IRAMFR/ARN/apr99/node1.html
The processed 3.8 μm images of the binary system and the
dusty torus obtained with the Adaptive Optics system on
the W. M. Keck II 10m-telescope
C. McCabe 2004 arXiv:astro-ph/0401560 v1
Synthetic intensity maps from the five Monte Carlo models that were
calculated at all wavelengths
and suggest possible grain sizes in the disk.
C. McCabe 2004 arXiv:astro-ph/0401560 v1
Conclusions
• Dust grains are responsible for certain spectral features
of stars and galaxies
• Multiwavelength analysis of dust objects can reveal their
inner structure
• Dust grain formation mechanisms learned from the dust
objects can help in understanding the planet formation
processes