Stellar Spectra The spectra of stars vary, depending upon the surface temperatur

Question

Stellar Spectra The spectra of stars vary, depending upon the surface temperature of the star, and also on its luminosity. The interior layers of a star send out a continuous spectrum, and the atmosphere absorbs some wavelengths of light, leaving the absorption spectrum that we can observe. The first part of stellar classification relates to the surface temperatures of stars. There are seven main categories: O, B, A, F, G, K, and M. The categories are given in order from hottest to coldest, where type O stars are the hottest, and type M the coldest (There are a few other, lesser known, categories.) Each of these categories has subcategories within it, ranging from zero through nine. For example, our sun is a type G2 star. Example spectra for various classes of stars are shown below 06.5 B0 B6 A1 A5 FO F5 Go G5 Ko K5 Mo M5 Image from the University of Nebraska-Lincoln (http://astro.unf edu/naap/hrhr background1.html) 3. Betelgeuse is a red supergiant star that makes up Orion's right shoulder in this widely-recognized winter constellation. Betelgeuse is an M2/ ab star. Is its surface temperature warmer or colder than our sun's? 4. Rigel is Orion's left shoulder. It's actually comprised of three separate stars. One of these is Rigel A, a BB/ star. Is its surface temperature warmer or colder than our sun's?

Explanation / Answer

3. The surface temperature of Betelguese is 3500 Kelvins while that of the sun is 5778 Kelvins. Thus, surface temperature of Betelguese is colder than our sun.

4. The surface temperature of Rigel A is 11,000 Kelvins while that of our sun is 5778 Kelvins. Thus, surface temperature of RIgel A is warmer than that of our sun.

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