Stellar Spectrum Classification Lab Activity Directions In this exercise you will be given a table of the standard spectral classes and a number of sample spectra to be used as the accepted spectra. While they are not exactly like the actual spectra of stars, they do communicate the same information as the actual spectra. Read the following information table and accompanying notes before you begin the exercise. Type Color Approximate Surface Temperature Main Characteristics Examples O Blue > 25,000 K B Blue 11,000-25,000 A Blue 7,500-11,000 Weak H, Ionized lines of He, O and N, strong in UV. He strong in early classes, then decreasing. H strength increasing in later classes. H Balmer lines strongest early, decrease thereafter, H and K lines of CaII weak. 10 Lacertra Rigel Spica Sirius Vega F Blue to White 6,000-7,500 H lines weaker, CaII strength increasing, weak Metallic lines become noticeable. Canopus Procyon G White to Yellow 5,000-6,000 CaII lines strongest, H lines weaker, Neutral Metal Lines increasing, Molecular bands weak. Solar-type spectra. Sun Capella K Orange to Red 3,500-5,000 M Red < 3,500 H and CaII lines weak, Many neutral metal lines, Molecular bands strengthening. Weak blue continuum. Molecular bands of TiO (titanium oxide) noticeable and increasing in strength, weak metals present. Arcturus Aldebaran Betelgeuse Antares Additional notes. Metal Weak Increasing Ultraviolet Molecular Strong Decreasing Ionized Page 1 of 5
Standard Spectra: Part I The necessary atomic spectra are given on the next page. There is one to represent a typical spectrum from each of the most common atomic signatures included in the table on page one. Be advised that there is actually a wide variation within each signature so variability on placement and width of lines is left to the interpretation of the viewer. Also, not all atomic signatures in any one spectrum will always display all the characteristics of that atomic signature. In fact, there will even be some overlap between elements near one another on the periodic table. In most, if not all, cases there should always be at least one factor that clearly places the spectrum in the appropriate atomic signature. Standard Spectra: Part II The necessary Key spectra are given on the next page. There is one to represent a typical star from each of the seven spectral classes included in the table on page one. Be advised that there is actually a wide variation within each class, so variability on placement and width of lines is left to the interpretation of the viewer. Also, not all stars in any one spectral class will always display all the characteristics of that class. In fact, there will even be some overlap between classes near one another. In most, if not all cases, there should always be at least one factor that clearly places the spectrum in the appropriate class. If not, an intermediate classification like AF is given to a star in the low A to high F range. A classification such as FA would not make any sense. Note The spectra on the following page are your standards. Cut out these spectra. This will make it easier for you to identify the unknown spectra. Take care not to lose your standards or you will be unable to complete the exercise. Page 2 of 5
Atomic Spectra N O H CaII He TiO Key Spectra O B A F G K M Page 3 of 5
Exercise This exercise consists of two parts. Part one; fill in the table below using the unknown spectra (1-7) given on the following page. In each column record the atomic signature present in that specific condition. Determine the spectral classes of the unknown sample spectra using the given key spectra. Remember, they may not be exactly like the key spectra so you will have to make judgments based on the best fit to a particular accepted spectrum. Part two; complete the unknown spectra (8-14) using the data given in the table. Spectrum number Molecular Ionized Metals Weak Strong Increasing Decreasing Classification 1. 2. 3. 4. 5. 6. 7. 8. CaII N TiO N CaII CaII 9. He H H He H 10. O N O N O N 11. N CaII CaII UV N 12. TiO He UV TiO He TiO 13. O H H UV O H 14. O TiO O TiO CaII UV Page 4 of 5
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