Spectral Classes Worksheet-1

Spectral Class Worksheet These lab activities have evolved over years of use in Clemson University’s Department of Physics and Astronomy general astronomy laboratory. Contributors include Tom Collins, Mark Leising, Neil Miller, Peter Milne, Grant Williams, Donna Mullenax, Jessica Crist, Keith Davis, Amber Porter, Lea Marcotulli, and David Connick. Please direct all questions, complaints, and corrections to David Connick (dconnic@clemson.edu) who is responsible for all errors and omissions. Worksheet Name Rico Graf III Example Stars Table 1. Stars Spectral Class Name Temperature (K) B-V Color Index (number) Absolute Magnitude (total) Distance (ly) O V918 Scorpii 36,200 +.40 yellow- white -6.18 1400 B Hadar Agena 26,200 -0.15 blue- white -7.35 390 A Muhifain 9,400 +0.01 white -1.08 130 F Sargas 10,100 +.44 yellow- white -3.26 300 G Zeta Hurculis 5,940 +0.66 yellow +2.51 35 K Menkent 4,660 +1.02 orange +.29 58.8 M Brachium 3,540 +1.63 orange-red -3.08 288 1) In which properties do you see a trend as you move down the spectral class? What is the trend? The trend that I see is that starting at the spectral class O the temperature of the stars is very hot, and the farther down you move down the spectral class the temperature decreases. Table 2. Spectral Class K or G Stars Luminosity Class Name Temperature (K) Absolute Magnitude (total) Distance (ly)

ThI Rigil Kentaurus 4990 +1.35 and +0.01 4.36 II 70 Ophiuchi 5150 +4.19 and +6.17 16.6 III 36 Ophiuchi 4990 +4.32 and +4.33 19.5 IV Alsafi 5150 +4.67 18.8 V e Eridani 5310 +4.26 19.8 2) Which property of the star determines its Luminosity Class. How is that property changing as you move from class I to class V? The property that really determines the star's luminosity class is the star's size and temperature. In this table, as you move from class I to V the temperature is the same for some stars, the magnitudes are also fairly similar. IV Spectral Class Spectra 3) Calculate the wavelength extremes for the visible spectrum of hydrogen (n 1 = 2): Ask your instructor for help with this calculation. Longest wavelength: ____6563___ Line designation (n 2 )___3____ Shortest wavelength: __4102_____ Line designation (n 2 )__6_____ V Spectral Class Ordering 4) Using the numerical designations of the absorption spectrum plots which is the simplest plot (least dips and fluctuations)? The simplest plot is plot number 1. 5) Which absorption spectrum plot is the most complex (most dips and fluctuations)? The most complex plot is plot number 7. 6) In which of the absorption spectrum plots are the hydrogen lines the strongest? The absorption spectrum that had the strongest hydrogen lines is plot number 7 7) Which of the absorption spectrum plots is from the highest temperature source? The absorption spectrum that had the highest temperature source was plot number 3 8) Which of the absorption spectrum plots is from the lowest temperature source? The absorption spectrum that had the lowest temperature was plot number 1. 9) Focus on the dips in the absorption spectrum plots due only to Hydrogen. Using the numerical designations list the spectrum from strongest (deepest) hydrogen lines to weakest (shallowest) hydrogen lines. From Highest to lowest it is plot numbers, 7,4,5,2,6,3,1

17) Hydrogen is by far the most abundant element in the atmospheres of virtually all "normal" stars. Explain how a star can have very strong lines of other low-abundance elements and only very weak lines of hydrogen. (Hint: Visible hydrogen absorption lines can occur only if the electron starts in the n = 2 orbit.) What basic condition in the star’s atmosphere (other than absence of hydrogen) could make this possible? The basic condition in the star’s atmosphere that could make this possible would be the calcium absorption lines.