Think back to the lab on Spectra and Atoms and you will remember the discussion of spectral classes there. Now it is time to put the tools of spectroscopy together with what we know about the nature of stars.

Spectral Classes for Main Sequence Stars

Let's remind ourselves of what we learned about the spectra of Main Sequence stars in the Spectra and Atoms lab.

Recall that the sequence of spectral classes begins with the hottest stars, the O stars, and ends with the coolest stars, the M stars. This is summarized in the following table. The strong lines column describes the prominent line features in the spectrum. Remember that a star's classification (O, B, A, F, G, K, or M and the subdivisions 0 - 9 within, with 0 being the hot end and 9 the cool end) depends on its color and the pattern of absorption lines, both of which are determined by its temperature. In other words, all Main Sequence stars have basically the same mix of elements, but temperature controls which spectral lines you see from them.

Principal Classes and Characteristics

Principal Classes and Characteristics Class Color Temperature Strong Lines O blue-white 35,000 K ionized helium B blue-white 21,000 K neutral helium A white 10,000 K hydrogen F green-white 7,000 K ionized calcium G yellow 6,000 K ionized calcium K orange 4,500 K neutral sodium M red 3,000 K titanium oxideQuestion 7 What is the spectral type and rough temperature of Star 17 Question 8 What spectral lines are present in the spectrum of Star 1? Question 9 What is the spectral type and rough temperature of Star 2? Question 10 What spectral lines are present in the spectrum of Star 2? Relative Brightness Relative Brightness 0.8 0.6 0.4 0.2 0.8 0.6 0.4 02 Star1 4000 5000 8000 7000 8000 Wavelength (Angstroms) Star2 . . v 4000 5000 6000 7000 8000 Wavelength (Angstroms) @ = g 1 08 T 0.6 = 04 g 02 5 0 2 4000 5000 6000 7000 8000 & Wavelength (Angstroms) Question 11 What is the spectral type and rough temperature of Star 3? Question 12 What spectral lines are present in the spectrum of Star 37 Star 4 @ g1 5 08 = 08 o 04 o2 & ' L s % 4000 5000 6000 7000 8000 o Wavelength (Angstroms) Question 13 What is the spectral type and rough temperature of Star 4? Question 14 What spectral lines are present in the spectrum of Star 4? Relative Brightness 4000 5000 6000 7000 8000 Wavelength (Angstroms) Question 15 What is the spectral type and rough temperature of Star 5? Question 16 What spectral lines are present in the spectrum of Star 5