LAB: Star Classification

Transcription

1 Name: LAB: Star Classification INTRODUCTION: Like most scientists, astronomers like to categorize the Universe around them, and stars are no exception. Here s how astronomers classify stars into different groups; let s learn a bit about star classification. Stars are classified based on the spectral characteristic of the light it s giving off. As you probably know, the light we see with our eyes is actually a mixture of colors. You can break them up into their different parts just like you can use a prism to break sunlight into all the colors of a rainbow. The rainbow that we see is actually the spectrum produced by the Sun, and it s different for different stars depending on their temperature. A cooler star will have a spectrum that has more red in it, while a hotter star will be shifted up towards the blue end of the spectrum. Astronomers classify stars by color using a series of letters: O, B, A, F, G, K and M. You can remember the sequence with the handy mnemonic, oh be a fine girl and kiss me. Under this classification, O stars are the hottest, and M stars are the coolest, with the other letters coming in between. O stars are blue, A stars are white, G stars are yellow, and M stars are red. From Star Classification by Fraser Cain on February 4, OBJECTIVE: To identify the main characteristics used to classify stars, and the four main types of stars. You will also become familiar with the use of the Hertzsprung- Russell diagram used for the classification of stars. PROCEDURE: 1. Using the data from Table 1 and the blank Hertzsprung-Russell diagram provided, plot the position of each star using its approximate temperature and luminosity. Label each star s name next to its data point on the chart. 2. Using the information provided in Table 2, and colored pencils, shade in each temperature region of your Hertzsprung-Russell diagram with the correct star color. 3. In bold letters, label the following regions of your Hertzsprung-Russell diagram: Main Sequence, Giants, Supergiants, White Dwarfs. 4. Using the information provided in Table 3, label the spectral class in the appropriate place on your Hertsprung-Russell diagram with the correct letter based on the corresponding color.

2 Table 1 - Star Temperature and Luminosity Star Temperature (ºC) Luminosity (compared to the Sun) Rigel 14,000 50,000 Betelguese 3,500 12,000 Polaris 6,500 1,000 Aldebaran 4, Barnard s Star 3, Alpha Centauri A 6,000 3 Sun 6,000 1 Procyon B 6, Sirius B 8, Sirius A 10, Vega 9, Tau Ceti 5, Alpha Centauri B 4, Regulus 12, Achernar 16,700 1,000 Spica 19, Beta Centauri 21,000 1,200 Table 2 - Star Temperature and Color Star Temperature (ºC) Star Color 2,000-3,500 Red 3,500-5,000 Orange 5,000-6,000 Yellow 6,000-7,500 White 7,500-11,000 Pale Blue-White 11,000-18,000 Blue-White 18,000-30,000 Blue Table 3 - Spectral Class and Temperature Spectral Class Temperature (ºC) O over 24,000 B 11,000-24,000 A 7,500-11,000 F 6,000-7,500 G 5,000-6,000 K 3,500-5,000 M 2,000-3,500

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4 Discussion Questions: Answer using data from the lab and in complete thoughts. 1. As a star changes color from red to blue, describe what happens to its surface temperature? 2. What two properties are used to classify stars using the Hurtzsprung-Russell diagram? 3. A main sequence star that is 10,000 times more luminous than the Sun most likely has a temperature of: 4. A main sequence star that has a luminosity of 100 is most likely to be what color? 5. A white dwarf star with a temperature of of approximately 10,000 ºC would have a luminosity of: 6. A massive star with a temperature of 20,00ºC and a luminosity of nearly 1,000,000 would be classified as what type of star? 7. What is the temperature, luminosity, and spectral class of the Sun? 8. What physical property must a star have that is low in temperature but very high in luminosity? 9. What physical property must a star have that is high in temperature but very low in luminosity?

5 Reading Comprehension Read the portion of the article on White Dwarfs below and answer the following questions based on the reading. Use complete sentences Hottest White Dwarf In Its Class ScienceDaily (Dec. 12, 2008) Astronomy & Astrophysics is publishing observations of the white dwarf KPD The team who present these observations show that this white dwarf is among the hottest stars known so far, with a temperature of 200,000º K at its surface. Stars of intermediate mass (1-8 solar masses) terminate their life as an Earth-sized white dwarf after the exhaustion of their nuclear fuel. During the transition from a nuclear-burning star to the white dwarf stage, the star becomes very hot. Many such objects with surface temperatures around Kelvin are known. Theories of stellar evolution predict that the stars can be much hotter. However, the probability of catching them in such an extremely hot state is low, because this phase is rather short-lived. Since its discovery as a faint blue star in 1985, KPD attracted much attention because observations taken with ground-based telescopes suggested that this white dwarf is very hot. In addition, it belongs to a particular class of rare white dwarfs whose atmospheres are dominated by helium. A detailed analysis had led to the conclusion that KPD has a temperature of Kelvin, which made Although theory predicted the existence of such hot white dwarfs, the star nevertheless represents a challenge to our concepts of stellar evolution because of its composition. The measured calcium abundance (1-10 times the solar value) in combination with the helium-rich nature of its atmosphere represents a chemical surface composition that is not predicted by stellar evolution models. 1. How does an intermediate mass star become a white dwarf? 2. What makes this star (KPD ) rare (2 answers)? 3. Using the H-R Diagram, what would be a likely luminosity for this star?