Physics- HSC- Module 9.7 Astrophysics - Teaching Program

Physics

Module 9.7 Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes Astrophysics Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes 9.7 Astrophysics (28 indicative hours)

Contextual Outline

The wonders of the Universe are revealed through technological advances based on tested principles of physics. Our understanding of the cosmos draws upon models, theories and laws in our endeavour to seek explanations for the myriad of observations made by various instruments at many different wavelengths. Techniques, such as imaging, photometry, astrometry and spectroscopy, allow us to determine many of the properties and characteristics of celestial objects. Continual technical advancement has resulted in a range of devices extending from optical and radio-telescopes on Earth to orbiting telescopes, such as Hipparcos, Chandra and HST.

Explanations for events in our spectacular Universe, based on our understandings of the electromagnetic spectrum, allow for insights into the relationships between star formation and evolution (supernovae), and extreme events, such as high gravity environments of a neutron star or black hole.

This module increases students’ understanding of the nature and practice of physics and the implications of physics for society and the environment.

Concept Map Sensitivity Adaptive Optics Black Telescopes Body Interferometry Radiation Resolution Electromagnetic Emission Spectra Radiation Spectra

Absorption Magnitude Parallax Spectra Astronomical Objects parsec Astrometry Stellar Spectra Light Colour year surface temperature, Satellites Index rotational and translational velocity, HR Diagram density and chemical composition of stars Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes Astrophysics Module Plan

Module Length: 7 weeks

Focus Area Time Concept Text Summary Practical 1. Our understanding ½ 1. discuss Galileo’s of celestial utlisation of the objects telescope to identify depends upon features of the Moon. observations made from Earth or from space near the Earth ½ 2. discuss why some wavebands can be more easily detected from space 1 3. define the terms 1. (Exp 1) identify data sources, plan, choose resolution and sensitivity equipment or resources for, and perform an of telescopes. investigation to demonstrate why it is desirable for telescopes to have a large diameter objective lens or mirror in terms of both sensitivity and resolution 1 4. discuss the problems associated with ground- based astronomy in terms of resolution and absorption of radiation and atmospheric distortion. 1 5. outline methods by 2. (Act 2) gather, process and present which the resolution information on new generation optical and/or sensitivity of telescopes ground-based systems can be improved, including: – adaptive optics – interferometry - active optics. 2. Careful 1 1. define the terms measurement parallax, parsec, light of a celestial year object’s position, in the sky, (astrometry) may be used to determine its distance 1 2. explain how 1. (Act 3) solve problems and analyse trigonometric parallax information to calculate the distance to a star can be used to determine given its trigonometric parallax using d = 1/p the distance to stars 1 3. discuss the limitations 2. (Act 4) gather and process information to of trigonometric parallax determine the relative limits to trigonometric measurements parallax distance determinations using recent ground-based and space-based telescopes. Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes

Focus Area Time Concept Text Summary Practical 3. Spectroscopy is a 1 1. account for the 1. (Act 5) perform a first-hand investigation to vital tool for production of emission examine a variety of spectra produced by astronomers and absorption spectra discharge tubes, reflected sunlight, incandescent and provides and compare these with a filaments a wealth of continuous blackbody information spectrum 1 2. describe the technology needed to measure astronomical spectra 1 3. identify the general types of spectra produced by stars, emission nebulae, galaxies and quasars 1 4. describe the key features of stellar spectra and describe how this is used to classify stars 1 5. describe how spectra 3. (Act 6) analyse information to predict the can provide information surface temperature of a star from its on surface temperature, intensity/wavelength graph rotational and translational velocity, density and chemical composition of stars 4. Photometric 1 1. define absolute and measurement apparent magnitude s can be used for determining distance and comparing objects 2 2. explain how the 1. (Act 7) solve problems and analyse concept of magnitude information using: can be used to determine d M  m  5 l o g ( ) the distance to a celestial 1 0 object and I A  1 0 0 ( M B  M A ) / 5 I B to calculate the absolute or apparent magnitude of stars using data and a reference star 1 3. outline spectroscopic parallax 1 4. explain how two- 2. (Exp 8) perform an investigation to colour values (ie colour demonstrate the use of filters for photometric index, B-V) are obtained measurements. and why they are useful 1 5. describe the 3. (Act 9) identify data sources, gather, process advantages of and present information to assess the impact of photoelectrictechnologie improvements in measurement technologies on s over photographic our understanding of celestial objects methods for photometry Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes

Focus Area Time Concept Text Summary Practical 5. The study of binary 1 1. describe binary stars in 1. (Exp 10) perform an investigation to model and variable terms of the means of the light curves of eclipsing binaries using stars reveals their detection: visual, computer simulation vital eclipsing, spectroscopic information and astrometric about stars 2 2. explain the importance 2. (Act 11) solve problems and analyse of binary stars in information by applying Kepler’s Third Law: determining stellar 4 2 r 3 masses m  m  1 2 G T to calculate the mass of a star system 1 3. classify variable stars as either intrinsic or extrinsic and periodic or non-periodic 1 4. explain the importance of the period-luminosity relationship for determining the distance of Cepheids 6. Stars evolve and 2 1. describe the processes 1. (Act 12) present information by plotting eventually involved in stellar Hertzsprung-Russell diagrams for: nearby or ‘die’ formation brightest stars; stars in a young open cluster; stars in a globular cluster 2 2. outline the key stages 2. (Act 13) analyse information from a H-R in a star’s life in terms of diagram and use available evidence to determine the physical processes the characteristics of a star and its evolutionary involved stage 1 3. describe the types of nuclear reactions involved in main- sequence and post-main sequence stars 1 4. discuss the synthesis of elements in stars by fusion. 2 5. explain how the age of 3. (Act 14) present information by plotting on a a globular cluster can be H-R diagram the pathways of stars of 1, 5 and determined from its zero- 10 solar masses during their life cycle. age main sequence plot for a HR diagram 2 6.explain the concept of star death in relation to: – planetary nebula – supernovae – white dwarfs – neutron stars/pulsars – black holes Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes

HSC Physics E3: Astrophysics Experiment 1: Sensitivity and Resolution

Aim: To identify data sources, plan, choose equipment or resources for, and perform an investigation to demonstrate why it is desirable for telescopes to have a large diameter objective lens or mirror in terms of both sensitivity and resolution

You must devise a method using equipment listed below and/or any other equipment you bring in.

Equipment Available

Any equipment that is reasonable (arrange with your teacher beforehand)

You should consider the following points:  Does the experiment satisfy the aim above?  The safety of the experiment. Any safety notes need to be explicit.  Design your own result table. Have you repeated the experiment several times to validate the results and to calculate a mean?  Did you show your working?  What are some possible sources of error? How could these errors be minimised or eliminated?

HSC Physics E3: Astrophysics Activity 2: New Optical Telescopes

Aim: To gather, process and present information on new generation optical telescopes

Write a 400 word report on this issue, including relevant diagrams. A bibliography must be included and in-text referencing used. Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes

HSC Physics E3: Astrophysics Activity 3: Stellar Parallax

Aim: To solve problems and analyse information to calculate the distance to a star given its trigonometric parallax using d = 1/p

Measuring by Parallax

Stellar distances can be measured by a trigonometric method called parallax. This technique is very similar to surveying. In surveying, the distance to object O is determined by measuring the angles a and b and knowing the length of the baseline PQ.

SINE a = l / ½PQ

Since a is measured and the distance PQ is known, the perpendicular distance to O can be determined.

Parallax uses the diameter of Earth's orbit as the known distance. The angles a and b are measured when the Earth is at opposite position in its orbit (i.e. the measurements are taken 6 months apart).

The average radius of Earth's orbit is 1.5 X 108 km. This distance is also referred to as one astronomical unit A.U. As the Earth rotates about the Sun the aspect of a nearby star will appear to change by a small angle 2p. p is called the parallax of a star. As the distance to the star increases p decreases. p is so small for most stars that this method can only really be used for relatively close stars (i.e. within 100 light-years from Earth). p is measured in arcseconds where one arcsecond (1") is equal to 1/3600 th of a degree. The nearest star to Earth (excluding the Sun) is Proxima Centauri, which has a parallax of 0.765". When p = 1" the star is at a distance known as a parsec.

One parsec = 3 X 1013 km or 3.26 light-years

If the parallax angle of a star is p, then the distance to that star is equal to 1/p parsecs.

1. Calculate the distance to Proxima Centauri in parsecs and in light years.

1. Do Humphrey’s Set 75 Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes Below is a list of parallax measurements of nine of the brightest stars in the southern skies. It is you task to convert these angular measurements into distance measurement from Earth. Remember: An angle of 1" (arcsecond) = 1/3600 degree. 1 parsec = 3 X 1013 km 1 parsec = 3.26 light-years 1 A.U. = 1.5 X 108 km

Star Systematic Name Parallax Angle Distance Distance (light- Distance (A.U.) (parsecs) years) Sirius -Canis Major 0.3678”

Canopus -Carina 0.1778”

Rigil Kent -Centauri 0.7650”

Rigel ß-Orion 0.00364”

Hadar ß-Centauri 0.00762”

Betelgeuse -Orion 0.00542”

Antares -Scorpio 0.00757”

Acrux -Crus 0.01208”

Mimosa ß-Crus 0.00761”

Sol Sun 2 X 105

HSC Physics E3: Astrophysics Activity 4: Limits of Stellar Parallax

Aim: To gather and process information to determine the relative limits to trigonometric parallax distance determinations using recent ground-based and space-based telescopes.

Write a 400 word report on this issue, including relevant diagrams. A bibliography must be included and in-text referencing used. Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes

HSC Physics E3: Astrophysics Activity 5: Spectra

Aim: To process information to examine a variety of spectra produced by discharge tubes, reflected sunlight, incandescent filaments

Method On the disk supplied is the spectra produced by discharge tubes, sunlight and incandescent filaments. (in jpg format).

For each image: 1. List the features that can be found in the spectra. 2. List any elements that can be identified in the spectra. 3. Note any unusual characteristics of the spectra.

HSC Physics E3: Astrophysics Activity 6: Stellar Surface Temperature

Aim: To analyse information to calculate the surface temperature of a star from its intensity/wavelength graph

Method Attached is the intensity / wavelength graph of several spectral classes. Calculate the surface temperature of each star from this data.

HSC Physics E3: Astrophysics Activity 7: Stellar Distances

d I A M  m  5 l o g ( )  1 0 0 ( M B  M A ) / 5 Aim: To solve problems and analyse information using: 1 0 and I B to calculate the absolute or apparent magnitude of stars using data and a reference star

Method 1. Do Humphrey’s Set 74

2. Analyse the two images given for this activity:

(a) calculate the magnitude of the star from the data. (b) Use the information about its spectral class to calculate its average brightness and hence absolute magnitude. (c) Calculate the distance to the star in parsecs and light-years. Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes

HSC Physics E3: Astrophysics Experiment 8: Photometry

Aim: To perform an investigation to demonstrate why it is important to use filters for photometry

Method Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes

HSC Physics E3: Astrophysics Activity 9: Measurement Technologies

Aim: To identify data sources, gather, process and present information to assess the impact of improvements in measurement technologies on understanding of the celestial objects

Write a 400 word report on this issue, including relevant diagrams. A bibliography must be included and in-text referencing used.

HSC Physics E3: Astrophysics Experiment 10: Light Curves

Aim: To perform an investigation to model the light curves of eclipsing binaries using computer simulation

A free program is available at www.isc.tamu.edu/~astro/ebstar/ebstar.html (Mac platform) A free program is available at http://www.lsw.uni-heidelberg.de/~rwichman/Nightfall.html (Unix, Linux platform) A free program is available at http://www.physics.sfasu.edu/astro/software/EBS1A2.ZIP (Windows platform)

In any of the above programs, use the simulation to create light curves for the following situations:

1. A binary where both bodies are of equal size and luminosity. 2. A binary where one body is ten times larger than the other but at the same luminosity. 3. A binary where both bodies are of equal size but one is ten times the luminosity of the other.

HSC Physics E3: Astrophysics Activity 11: Kepler’s Third Law

4 2 r 3 m 1  m 2  Aim: To solve problems and analyse information by applying Kepler’s Third Law: G T to calculate the mass of a star system

1. Do Humphrey’s Set 72 Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes

HSC Physics E3: Astrophysics Activity 12: HR Diagrams

Aim: To present information by plotting Hertzsprung-Russell diagrams for: nearby or brightest stars; stars in a young open cluster; stars in a globular cluster

The following activity is an extract from http://geocities.com/CapeCanaveral/Hall/4180/astro/H-R_Lab.html

During the late 19th and early 20th centuries, astronomers obtained spectra and parallax distances for many stars, a powerful tool was discovered for classifying and understanding stars. Around 1911-13, Enjar Hertzsprung and Henry Norris Russell independently found that stars could be divided into three groups in a diagram plotting stellar luminosity and surface temperature. Most stars, including our Sun, lie on the main sequence. Rare but very luminous cool stars are called red giants while low luminosity hot stars are called white dwarfs. Later in the twentieth century, a full theory for the evolution of stars was developed. A star traces a complex path in the Hertzsprung-Russell diagram (H-R diagram) as its burns different nuclear fuels and evolves.

In this activity, you will construct a H-R diagram using MS Excel.

1. Getting the Data into Excel.

To enter an item in a cell, simply click at the cell and type. Use arrows to move between cells. Set up the headings as show below. You will see that the range of luminosities is so great that the diagram looks silly

Nearest Stars Name Temperature (K) Luminosity Log(Luminosity) Radius Sun 5860 1.0 Proxima Centauri 3240 0.00006 Alpha Centauri A 5860 1.6 Alpha Centauri B 5250 0.45 Barnard’s Star 3240 0.00045 Wolf 359 2640 0.00002 BD +36 2147 3580 0.0055 L 726-8A 3050 0.00006 UV Ceti 3050 0.00004 Sirius A 9230 23.5 Sirius B 9000 0.003 Ross 154 3240 0.00048 Ross 248 3050 0.00011 Epsilon Eri 4900 0.30

To obtain logs of the luminosities, go the cell next a luminosity, type =log10(C2) and the log of the luminosity (which is zero for the Sun) should then appear in the cell. To repeat this for other stars, drag the dot at the lower right corner of the cell down to the other rows. These operations can also be done in other ways eg. using the function wizard (fx icon) and Fill Down in the Edit menu.

Repeat these steps for the tables on the next page. Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes Brightest Stars Name Temperature (K) Luminosity Log(Luminosity) Radius Sun 5860 1.0 Sirius A 9230 23.5 Canopus 7700 1400 Alpha Centauri A 5860 1.6 Arcturus 4420 110 Vega 9520 50 Capella 5200 150 Rigel 11200 42000 Procyon 6440 7.2 Betelgeuse 3450 12600 Achernar 15400 200 Beta Centauri 24000 3500 Altair 7850 10 Alpha Crucis 25400 3200 Alderbaran 15400 95

Stars in a Young Open Cluster Name Temperature (K) Luminosity Log(Luminosity) Radius

Stars in a Globular Cluster Name Temperature (K) Luminosity Log(Luminosity) Radius

2. Plotting the H-R Diagram

To plot a diagram, highlight the cells to be plotted, including the labels. Open the Chart Wizard; select XY scatter plot (format 1 or 3) and the plot should appear. Follow the remaining steps and instructions to complete the graph. Astronomers historically plot the H-R diagram with temperature decreasing to the right. To do this, click on the labelled X-axis, enter the axis scale page, and reverse the order of the X-axis.

Print your H-R diagrams for the Nearest and Brightest stars. This is done by double clicking on the chart, entering the File menu, Print Preview and (if you like it) Print. On your printed chart, identify the main sequence stars, red giants and white dwarfs. Label a horizontal axis with the spectral type classifications used by astronomers. O (52000-33000 K), B (30000-11000 K), A (9500-7600 K), F (7200-6200), G (6000-5600 K), K (5200-4100 K), M (3900-2600 K)

Save your data. This will be required for the next activity.

On a separate sheet discuss the differences between the nearest and brightest stars in the H-R diagram. Can you deduce which kinds of stars are most common in the galaxy and which kinds are rare? Are the bright stars we see at night that make up the constellations mainly the common or rare types? Domremy – HSC Physics Module 9.7 Astrophysics: Student Notes

HSC Physics E3: Astrophysics Activity 13: Stellar Evolution on HR Diagrams

Aim: To analyse information from a H-R diagram and use available evidence to determine the characteristics of a star and its evolutionary stage

You will require your data from the previous activity.

1. Stellar populations and radii

Stellar surfaces are approximately “black body” emitters which obey the Stefan-Boltzmann law: Luminosity = Area X Temperature4. The shapes of stars are spheres with Area=Xradius2. We can combine these formulae to deduce the size (radii) of stars in different portions of the H-R diagram:

Radius  luminosity½ X Temperature2.

Using the Sun’s radius as a unit, estimate the radius of a selected red giant star (upper right in the H-R diagram) and a white dwarf (lower left).

2. Stellar Evolution.

Use a new part of the spreadsheet to input data showing the stages of evolution for the Sun. The table below gives the calculated solar properties during the T-Tauri (pre-main sequence), main sequence and red giant phases. The current age of the Sun is 4.6 billion years.

Evolution of the Sun Age (years) Temperature (K) Luminosity Log(Luminosity) Radius 106 4800 3 107 4800 0.3 108 5800 0.8 4.6 X 109 5800 1.0 1010 5800 1.8 1.002 X 1010 4800 3.0 1.1 X 1010 3400 350

1. Print out an H-R diagram showing the Sun’s evolution. Use a format that connects the dots. 2. What is the Sun’s radius at its most luminous point as a red giant? 3. Comment on the fate of the planets when the Sun becomes a red giant (1 A.U.  200 solar radii)

HSC Physics E3: Astrophysics Activity 13: Stellar Evolution on HR Diagrams

Aim: To present information by plotting on a H-R diagram the pathways of stars of 1, 5 and 10 solar masses during their life cycle.

On the same plot of an HR diagram, present the evolution of a 1, 5 and 10 solar mass star, fully labelling each stage and stating a nominal length of time at each stage.