Presentation on theme: "Dust particles and their spectra. Review Ge/Ay 132 Final report Ivan Grudinin."— Presentation transcript:
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/ 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 3-15 μm ISO-SWS spectrum of two post-Asymptotic Giant Branch (post AGB) stars. IRAS and the Red Rectangle, and that from the planetary nebula NGC These UIR features arise from large aromatic molecules that are excited by optical and UV photons. 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
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..
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, 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) How can we see the dust? GG Tau circumbinary disk in scattered near IR light
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 13 CO J =2-1 lines. The background is a false color image of the 1.3-mm thermal dust emission.
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/ 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/ 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