Lab3-HR-Diagram.pdf.pdf

Name: _________________________ Lab 3 – Spectral Types and The HR Diagram Types of Stars There are different classifications of stars grouped together by their properties. The table below shows several classifications and the properties that define them. Giant/Super Giant Main Sequence White Dwarfs Luminosity 10 − 10 6 ࠵? ࠵?࠵?࠵? 10 −4 − 10 6 ࠵? ࠵?࠵?࠵? 10 −4 − 1 ࠵? ࠵?࠵?࠵? Temperature 30,000 − 2,000 ࠵? 40,000 − 2,000 ࠵? 30,000 − 6,000 ࠵? Radius 10 − 1,000 ࠵? ࠵?࠵?࠵? 0.1 − 10 ࠵? ࠵?࠵?࠵? 10 2 ࠵? ࠵?࠵?࠵? Mass 0.1 − 100 ࠵? ࠵?࠵?࠵? 0.08 − 100 ࠵? ࠵?࠵?࠵? < 1.4 ࠵? ࠵?࠵?࠵? As you can see these contain big ranges that overlap, so we must use multiple properties in order to determine a star’s classification . Another method of stellar classification uses Wien’s Law: ࠵? ࠵?࠵?࠵?࠵? ∝ 1 ࠵?࠵?࠵?࠵? This states that the peak wavelength is inversely proportional to the temperature of the star. Therefore, if you know either the temperature of the star or the peak wavelength, you may gain a better understanding of the other property. Questions: 1. A star has a luminosity of 3,300 ࠵? ࠵?࠵?࠵? a temperature of 18,890 ࠵? , a radius of 4.5 ࠵? ࠵?࠵?࠵? , and a mass of 7.8 ± 0.2 ࠵? ࠵?࠵?࠵? . Based on the chart above, is this a giant/super giant, main sequence, or white dwarf star? 2. Hot stars tend to appear what color (red or blue)? Stellar Classification Stellar classifications are the classification of stars based on their spectral characteristics. They can be broken down into two categories, spectral classifications and luminosity classes. Spectral classifications use both color and spectral lines to classify the temperature of a star. There are 10 “subclasses” within each letter class, where 0 is the hottest and 9 is the coolest. O 28,000 – 50,000 K B 10,000 – 28,000 K A 7,500 – 10,000 K F 6,000 – 7,500 K G 5,000 – 6,000 K K 3,500 – 5,000 K M 2,500 – 3,500 K

Luminosity classes use the size to classify the luminosity of the star, and are added as a suffix to the spectral classification. For example Deneb is an A2Ia star. 0 or Ia + Hypergiants or extremely luminous supergiants Ia Luminous supergiants Iab Intermediate-size luminous supergiants Ib Less luminous supergiants II Bright giants III Normal giants IV Subgiants V Main-sequence stars (dwarfs) VI Subdwarfs VII White dwarfs Questions: 3. A spectral classification tells you about which property of stars? 4. What spectral class corresponds to the hottest stars? What about for the coldest stars? Hottest: __________________ Coldest: __________________ 5. Typically, there is a roman numeral at the end of a spectral class. What is that called and what does it mean?

The Hertzsprung-Russell Diagram Ejnar Hertzsprung and Henry Norris Russell independently came up with this diagram in the early 1900s. The Hertzsprung-Russell (HR) Diagram shows how temperature and luminosity are related in stars. If a star could have any temperature or luminosity, the HR Diagram would look random, but it doesn’t, we can see clear patterns. The HR Diagram isn’t always temperature and luminosity. Temperature, spectral class, color, and peak wavelength are all proportional to each other, while luminosity and absolute magnitude are proportional to each other, allowing different properties to be used on the diagram. The diagram shows the different classifications Source: https://www.eso.org/public/images/eso0728c/ discussed in previous sections. During a star’s lifetime it will travel through the HR diagram, starting a different locations and following different paths based on initial mass. Questions: 6. Briefly explain what the HR Diagram shows you. Why aren’t the poi nts evenly distributed across the whole plot? 7. What could you use to plot the HR diagram, rather than Temperature and Luminosity? X Axis: ______________________________________________________ Y Axis: ______________________________________________________

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Activities Using the reference of spectra on the last page of this packet, classify the spectral type of the following stars BD63137:_______________ Feige41:_________________ HD6111:________________ HD17647:________________ HD23733:_______________ HD24189:________________ HD27685:_______________ SAO81292:_______________

Plotting Your Own HR Diagram Go to https://en.wikipedia.org/wiki/List_of_stars_by_constellation . There is a list of constellations which are linked to pages listing all of the stars within those constellations. Pick out stars from those lists and record their name, spectral class, and absolute magnitude in the Excel spreadsheet named “Lab3template.xlsx” on Moodle. Record the information for at least 15 stars, or until the HR Diagram shows the main sequence line clearly. Normally for this lab we would be using lab computers and a program called Stellarium to gather this information. Stellarium is a free planetarium software that provides astronomical data. It is easy to use, all you have to do is click on a star and it will show the star’s information. I do not require that you download this program, you can just use the Wikipedia page, but you may use Stellarium instead if you are interested. It is available here: http://stellarium.org/ . You're going to have to do a little arithmetic to turn the spectral class into a number that Excel can plot. Take the letter at the beginning of the class. This letter corresponds to a multiple of ten as below: O = zero B = ten A = twenty F = thirty G = forty K = fifty M = sixty Add to that multiple of ten, the number directly after the letter. Example: A0 = twenty + 0 = 20 Example: G5 = forty + 5 = 45 Example: O0 = zero + 0 = 0 Example: B7 = ten + 7 = 17 This is the number that you will use for the column labeled 'Spectral Index' in the Excel Sheet. Make this calculation for all of your stars. When you are done, put your name on it, export the spreadsheet and upload it to the folder in Moodle.

Spectral Types Reference

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