Lecture Notes: Spectra Classification and Stellar Surface Temperature

Overview

• Focus on spectra classification and determining stellar surface temperatures.
• Discusses how modern spectral analysis provides an easier method to determine these temperatures compared to traditional methods.

Key Topics

Spectra Classification

• Hottest Stars: O Stars
  • Simplified spectra with fewer lines.
  • Prominent Balmer lines in A zero stars.
• Coolest Stars: M2 Stars
  • Extensive spectral lines including titanium oxide (TiO), neutral sodium (Na I), and neutral iron (Fe I).

Determining Stellar Surface Temperature

• Traditional Method: Analyzing the flux across different wavelengths to find the peak of the Planck curve.
• Modern Method: Analyzing a snapshot of the visible spectrum to determine spectral type and correlate with surface temperature.
• Importance: Faster and more efficient method using computers.

Spectral Types and Surface Temperatures

• Major Spectral Classifications: O, B, A, F, G, K, M.
  • O Stars: ~30,000 K (e.g., Mintaka in Orion)
  • B Stars: ~20,000 K
  • A Stars: ~10,000 K (e.g., Vega, Sirius)
  • G Stars: ~5,800 K (e.g., Sun, Alpha Centauri)
  • K Stars: Orange in color, include stars like Arcturus and Aldebaran.
  • M Stars: ~3,000 K, appear dull red (e.g., Betelgeuse, Barnard's Star).

Application

• Use of spectral types to understand star temperatures and characteristics.
• Example Stars:
  • Mintaka: O9 star, ~30,000 K.
  • Sirius: A1 star, ~10,000 K.
  • Sun: G2 star, similar temperature and color to Alpha Centauri.
  • Arcturus: Brightest K-type star in summer sky.
  • Betelgeuse: Famous M-type star in Orion.

Upcoming Topics

• Discussion on how a star's mass correlates with its temperature and the generation of nuclear fusion temperatures.

Conclusion

• Modern spectral analysis allows quicker and more accurate determination of stellar surface temperatures, aiding in the classification and study of stars.