how interstellar matter is detected 8 1 1 absorption of starlight n.
Download
Skip this Video
Loading SlideShow in 5 Seconds..
How interstellar matter is detected 8.1.1 Absorption of starlight PowerPoint Presentation
Download Presentation
How interstellar matter is detected 8.1.1 Absorption of starlight

Loading in 2 Seconds...

play fullscreen
1 / 7

How interstellar matter is detected 8.1.1 Absorption of starlight - PowerPoint PPT Presentation


  • 101 Views
  • Uploaded on

How interstellar matter is detected 8.1.1 Absorption of starlight. Byeon Jae Gyu. The Interstellar Media of Galaxies. The space between star Rarefied gas, dust particles, a magnetic field Relativistically moving electrons, protons and other atomic nuclei

loader
I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.
capcha
Download Presentation

PowerPoint Slideshow about 'How interstellar matter is detected 8.1.1 Absorption of starlight' - diem


An Image/Link below is provided (as is) to download presentation

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.


- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
the interstellar media of galaxies
The Interstellar Media of Galaxies
  • The space between star
    • Rarefied gas, dust particles, a magnetic field
    • Relativistically moving electrons, protons and other atomic nuclei
  • Interstellar medium, Interstellar matter of ISM
  • Fundamental differences between galaxies of different Hubble types
    • Until the early 1980s late-type galaxies had ISM
    • Advances in X-ray and microwave astronomy habe now demonstrated that many early-type galaxies also have rich ISM
absorption of starlight
Absorption of Starlight
  • Dust absorbs and scatters blue light more than red.
  • Interstellar dust is always associated with interstellar gas
    • Giving rise to sharp absorption lines in stellar spectra
  • Figure 8.1 Absorption by interstellar Na atoms
    • About different V-shaped features each about 0.01nm wide
    • Various features are due to difference of ~10kms-1 in the line-of-sight velocities of the clouds
    • Calcium atoms (Ca+) gives to a similar phenomenon
  • Understanding of interstellar space took a great stride forward during World War II
    • W.S Adams studies Ca+ absorption of about 300 star
absorption of starlight1
Absorption of Starlight
  • Calcium and sodium measure interstellar absorption features in optical spectra, but their line do not provide reliable of the density and temperature of the ISM
    • Hydrogen and helium dominate the ISM
    • Only a small fraction of all Na and Ca atoms are expected to be in the ionization states
  • Ultraviolet spectra are required to resolve this problem.
    • Copernicus obtained ultraviolet spectra for over 100 stars
    • International Ultraviolet Explorer (IUE) studied fainter object
absorption of starlight2
Absorption of Starlight
  • Figure 8.2 Curve of growth
    • Important tool that astronomers use to determine the value of N and thus the abundances of elements in stellar atmospheres
    • Plot (equivalent width) log(W) vs log(N) Column density N of absorbing atoms
    • Using curve of growth and a measured equivalent width, we can obtain the number of absorbing atoms
    • The Boltzmann and Saha equation are the used to convert this value in to the total number of atoms of that element lying above the photosphere
absorption of starlight3
Absorption of Starlight
  • The Curve of growth cannot be used to determine N when a line is strongly saturated
  • The general idea is to focus attention on the ‘wings’ of the line
  • Lyα transition of neutral hydrogen is possible
  • Two factors determine how far from line-center a line will extend
    • Doppler broadening
    • The line’s natural width
absorption of starlight4
Absorption of Starlight
  • Doppler broadening
    • Atoms moving at different speeds absorb photons of different energies.
    • The velocity spread of hydrogen atoms is of order 10kms-1
    • Wavelength spread Δv ≈ 0.004 nm.
  • The line’s natural width, Δn
    • The energy of the excited state is ill-determined, the wavelengths of the photons that excite the transition are uncertain too.
  • |λ – λ0| < Δv , determined by Doppler brodening.
  • |λ – λ0| > Δv , follow the readily-calculated Lorentzian profile