Making and Using the Hertzsprung - Russell Diagram

Transcription

1 Making and Using the Hertzsprung - Russell Diagram Name The Hertzsprung-Russell Diagram is one of the main tools we use to organize data describing how stars evolve, ages of star clusters, masses of stars etc. To help you understand the diagram, you will be making your own Hertzsprung Russell (HR) diagram. The HR diagram plots temperature vs. brightness for stars. It uses logarithmic scales as laid out in the plot attached. You will be completing the scales for the axes, plotting the closest and the apparently brightest stars, and identifying the luminosity classes for stars. Your textbook has examples of this plot and what it shows. Please read about it and use it for comparison. Your diagram is the same idea, but the shape of the plot is a little different and exact values at the edges of the plot may be different. So donʼt expect your plot to look exactly the same. 1) Label the coordinates on the HR diagram. There are TWO scales for the abscissa (x coordinate) and TWO for the ordinate (y coordinate). The abscissa gets both temperature and spectral type, while the ordinate (y axis) gets both luminosity and magnitude. Follow the directions below to get the layout it correct. 1.a Label the x axis on the bottom. It shows temperatures with higher values on the left (opposite the usual but the same as in the book). The temperature scale is LOGRITHMIC. Equal amounts of space represent equal powers of 10. Label the scale with 10,000K near the middle as marked. The next vertical line to the LEFT is 20,000K. The next vertical line to the RIGHT (very close by) is 9000K. Each vertical line going to the right is 1000K less. The scale does not go down to zero or even to 1000K because there are no stars of that temperature. How can there be two coordinate labels for one axis? Because they are two different ways of telling the same information. Spectral type basically tells the surface temperature. Magnitude and luminosity both measure brightness. 1.b Label the x axis on the top with spectral types corresponding to various temperatures. s you remember, spectral types are letters and numbers characterizing the lines that are seen in the spectrum of a star. The overall system was started before people realized that the spectral lines are mainly representative of the TEMPERTURE of the star. Your textbook does describe this, so be sure to read up on it before proceeding. spectral type is specified by a letter and an rabic number (the normal kind). The letters go in the sequence OBFGKMLT going from hotter to colder. Each Spectral Surface letter is more finely divided by assigning numbers from 0 to 9 Type Temperature going from The numbers indicate surface temperatures as well; 0 K they just provide a finer subdivision than do the letter. So from hottest to coldest, the spectral types would be O0, O1, O2, O3, O4, O5, O6, O7, O8, O9, B0, B1, B2, B3, B4, B5, B6, B7, B8, B9, 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, F0, F1, F2, F3, F4, F5, F6, F7, F8, F9, G0, G1, G2, G3, G4, G5, G6, G7, G8, G9, K0, K1, K2, K3, K4, K5, K6, K7, K8, K9, M0, M1, M2, M3, M4, M5, M6, M7, M8. No doubt you have the picture. Even cooler, stars have been found. They are types L and T and have surface temperatures that go below 2000K. To relate the spectral types and temperatures, we use this table. t the top of the plot, along the horizontal axis find 40,000K and label the axis (outside the grid) with the spectral type O5. Then 05 40,000 B0 28,000 B5 15, F F G G K K M M M go to 28,000K and label the top with B0 etc. Just estimate where the labels go in cases where there is no numbered line. The right hand edge of the plot is 2000K. Hertzsprung Russell Diagram HW 1

2 t this point you should have the top and bottom of the plot labeled and there should be NO points inside the plot 2 c. The left hand y axis is the luminosity, which indicates the real brightness, in units of the solar luminosity (Sunʼs brightness). The scale is oriented so that brighter stars are toward the top. Each horizontal line corresponds to 10 times higher luminosity. Use powers of 10 times the luminosity of the Sun (eg10 3 L for 1000 times the Sunʼs luminosity). Remember 1= d. The right hand vertical scale is magnitudes. The brighter the star, the LOWER the magnitude. The scale goes to negative numbers toward the top Each small line is one magnitude difference. Label all the magnitudes. The Sun is at about magnitude 4.85, so the line for 1L is not quite lined up with the magnitude 5 mark. 2) Now it is time to plot some stars. There is data for two samples of stars attached. The stars donʼt come with temperature labels, so we use the spectral types for the x coordinate. Stars donʼt come with luminosity labels. We observe their brightness in magnitude. pparent magnitude (m) represents how bright the star appears, including the effects of its distance. bsolute magnitude (Mv) is how bright the star would appear if it were at a distance of 10 parsecs, allowing us to exclude the effect of varying distance. So plot the absolute magnitude as the y coordinate to allow comparison of the starsʼ real properties. Data for the apparently brightest (appearing) stars and the closest stars is attached. Plot all of these stars on your HR diagram. Use a different symbol for the brightest stars and the closest stars. There is no need label the individual points. 3) Once the points are plotted, the main sequence will become obvious. Sketch in the main sequence. It should go among the stars. It does not need to touch any of the star points specifically. The HR diagrams in your book show the main sequence. That will give you an idea of what direction and shape. But the plots we are using are taller and narrower than the ones in the books. So follow YOUR stars. 4) Not all stars are on the main sequence. Others are divided into Luminosity classes Ia, Ib, II, III, IV, V and white dwarfs. The main sequence is V, dwarfs. These classes depend on the radius of the stars and the evidence is both in the magnitude and the appearance of the spectral lines. Look in your textbook (Unit 58 toward the end) for a discussion of and plot of these types. There is an HR diagram with the luminosity classes marked. Sketch in the areas for luminosity classes on your HR diagram. Look carefully at the luminosity scale to decide where to put the luminosity classes. NONE of the luminosity classes crosses the main sequence. 5) Decide on the luminosity class for each of your stars based on the position of the plotted point compared with the areas for each class. Fill in the value in the rightmost column of the date tables. Do make a decision for each star. Donʼt worry about doing a perfect job in the region of O,, and B stars where the luminosity classes are very close together. The idea is to feel how this all works by doing it yourself.. Hertzsprung Russell Diagram HW 2

3 CLOSEST STRS X coord Y coord # Name Spectral Type M v bsolute Magnitude m v pparent Visual Magnitud e 1 Sun G a Centuri G a Centuri B K Barnard s Star M Wolf 359 M Lalande M Sirius Sirius B White Dwarf 9 Luyten M Luyten 726-8B M (UV Ceti) 11 Ross 154 M Ross 248 M e Eridani K Luyten789-6 M Ross 128 M Cygni K Cygni B K e Indi K Procyon F Distance in ly 20 Procyon B White Dwarf 21 S2398 M S2398 B M Groombridge 34 M Groombridge 34 M B 25 Lacaille 9352 M t Ceti G BD M L M Lacaille 8760 M Kapteyn s Star M Kruger 60 M Kruger 60 B M White dwarfs- assume that they have surface temperature 10,000K Luminosity Class (Ia, Ib, II, III, IV, V or wd) Hertzsprung Russell Diagram HW 3

4 BRIGHTEST STRS as seen from Earth # Name lternate Name X coord Y coord Spectral Type M v, bsolute Magnitude m v, pparen t Visual Magnitu de Distance (ly) 7 a Canis Sirius Majoris 33 a Carinae Canopus F Luminosity Class (Ia, Ib, II, III, IV, V or wd) 34 a Bootis rcturus K a Centauri Rigil Kentauru s G a Lyrae Vega a urigae Capella G b Orionis Rigel B a Canis Procyon F Minoris 39 a Eridanii chernar B a Orionis Betelgeu M ese 41 b Centari Hadar B B 42 a quilae ltair a Tauri ldebara K n 44 a Scorpii ntares M a Virginis Spica B b Pollux K Geminoru m 47 a Piscis Fomalha ustrinis ut 48 a Cygni Deneb b Crucis Beta B Crucis 50 a Crucis crux B Hertzsprung Russell Diagram HW 4

5 Hertzsprung Russell Diagram Spectral Type 1L 5 0 M a g n i t u d e 10-2 L Temperature Hertzsprung Russell Diagram HW 5