Dust particles and their spectra. Review

1
Dust particles and their spectra.Review

• Ge/Ay 132 Final report
• Ivan Grudinin

2
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

3
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 grains surface

Spectral features are taken from "Interaction of
Nanoparticles with Radiation" Aigen Li
arXivastro-ph/0311066 v1 4 Nov 2003
4
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

5
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)
6
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.
7
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..

8
To study grain growth during the planet
formationprocess, it is necessary to establish
the properties of dust grains in disks
surrounding Myr-oldTTauri stars.
How can we see the dust? GG Tau circumbinary disk
in scattered near IR light
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 T35K, Inner radius is 180 au,
outer is 260 au, Distance 140pc Binary system of
0.6 and 0.4 M(Sun)
9
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
J2-1 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
10
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 arXivastro-ph/0401560 v1
11
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 arXivastro-ph/0401560 v1
12
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