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The Stellar Family Portrait

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The Stellar Family Portrait TEACHER SCIENCE RESOURCE CONTENT/ CURRICULUM LINK PLANET EARTH AND BEYOND – ASTRONOMICAL SYSTEMS. NATURE OF SCIENCE – UNDERSTANDING, INVESTIGATING, COMMUNICATING, PARTICIPATING STARDOME OBSERVATORY & PLANETARIUM AND CONTRIBUTING. PHYSICAL WORLD – INQUIRY AND CONCEPTS. FACTS, RESOURCES AND ACTIVITIES ON... Stellar As prerequisites to this resource we The recommend the previous resources: Star Brightness; Star Colours ; Spectroscopy; Stars (parts 1 Family Portrait , 2, and particularly 3). The Hertzsprung-Russell Diagram Just like people, stars are born, go through different life stages, and eventually die. This resource introduces the Hertzsprung-Russell diagram (HRD) which is a scatter plot of stars at every phase of the life cycle – rather like a human family portrait. A family portrait is a ‘snapshot’ in time that might have grandparents, parents, teenagers and Stars are babies. Comparing a new portrait with an old classified by two one of a generation ago, we’d find the original key properties: grandparents now absent, having been temperature and replaced by the original parents. Likewise, the luminosity. The HRD teenagers will have become parents, babies is a plot of these teenagers, and there will be a new crop of properties. babies. Some of the people will be different, but there will still be grandparents, parents, teenagers, and babies – and so it is with stars. A star’s initial mass is its DNA, The HRD, or ‘stellar family portrait’, helps us determining its understand stars and what happens as they age and eventually die. evolutionary Australia Telescope National Facility path, life span, The diagram plots stars’ (surface) and end state. temperatures against their luminosities (see star. When a star is born it enters the MS and figure). Temperature runs from right to left on spends the next 90% of its life in almost the same the x-axis and corresponds to colour and spectral On the spot. It follows that 90% of stars at any one time class (O,B,A,F,G,K, or M). Luminosity, shown HRD stars appear are MS stars. in distinct groups logarithmically on the y-axis (each step 10 times A star’s position on the MS is determined by its reflecting the different brighter than previous), represents the actual, mass: higher mass = brighter, bluer, hotter, short life stages of stars intrinsic brightness of the stars. It reveals clear (stages of stellar groupings of stars with common Lum-Temp lifespans; lower mass = dimmer, redder, cooler, evolution). correlations representing different stages of stellar long lifespans. life! These groups also align closely to 5 luminosity Once an MS star has fused all its core hydrogen into classes, from Supergiants (I) to Main Sequence (V). helium, it quickly (in stellar terms) moves to another Our Sun sits near the centre of the ‘Main Sequence (MS)’ band group, its mass determining its path (see figure). which runs from lower right to upper left. By definition, a star All stars spend proportionately much less time that fuses hydrogen into helium in its core, is a Main Sequence in each successive stage. Check out these other resources... en.wikipedia.org/wiki/Stellar_evolution atnf.csiro.au/outreach/education/senior/astrophysics/stellarevolution_postmain.html atnf.csiro.au/outreach//education/senior/cosmicengine/stars_hrdiagram.html atlasoftheuniverse.com/hr.html starinabox.lco.global/ Main sequence stars make up 90% of stars we but don’t see that many with the unaided eye. Why We need to know the intrinsic luminosities might this be? Which stars are the problem? of stars to plot them on the HRD. Discuss the factors involved in determining these correctly. Blue means bright and red means dim doesn’t it? Not always. DISCUSSION The red stars at the HRD’s top right POINTS are brilliant. How can this be? STARDOME.ORG.NZ 09 624 1246 ACTIVITY STARDOME OBSERVATORY & PLANETARIUM stellar analyses HELPS Do your own stellar analyses using the HRD. The 4 stages of stellar evolution (simplified): WHAT YOU'LL NEED 1 Main Sequence (core fusion Night Sky phone app for students (e.g.: Star Walk, Sky Safari, Stellarium, H=>He {hydrogen burning}). Google Sky) 2 Red Giants & Super Giants The HRD as per this resource (or on-line) for individual students. (inert helium-rich core, shell surrounding core fusing Large sheet of paper or whiteboard for a classroom HRD display where H=>He).. star expands, surface all results can be plotted and details shown. cools, luminosity increases due to increased surface area. WHAT TO DO 3 Horizontal Branches (core • On a clear night pick a number of prominent stars in the sky fusion He=>C&O, shell H=>He). • Identify them with your night sky app 4a Asymptotic Giant Branch • Look-up Luminosity & Temperature & Mass using the units shown on the (inert C&O core, successive HRD (Wikipedia is good) shells burn He & H).. shells > Consider ‘look-ups’ by independent parties (it’s easy to accidentally cheat) destabilise => Star ‘dies’ and • Record the stars on the attached table becomes a White Dwarf with • Plot the stars on the HRD Planetary Nebula OR Primarily from your HRD plot, and also from our resource ‘Stars (part 3 – the 4b Super Giants (successive inside stories)’ and the helps below where necessary, work out the following shells burning heavier and record your answers on the table: elements => an inert iron • Determine evolutionary stage (Main Sequence, Red Giant, Supergiant core).. eventual supernova (and branch if possible)) and cataclysmic collapse into Neutron Star or Black Hole • Deduce internal processes (fuel being used, core state, shell burning?) with supernova remnant • Determine the heaviest elements produced by end of life. • Determine star’s end state (White Dwarf? Neutron Star? Black Hole?) HIGHLY • Record your stars (and your deduced details) RECOMMENDED on the classroom HRD display. on-line activity from Las Cumbres Observatory • Compare your answers with on-line data and discuss reasons for deviations Have students go wild with this as a separate activity. They can create their own hypothetical star of a particular mass, and gathering as much information as possible from the activity, write their star’s life story for a report back to class. starinabox.lco.global/ It all ends quickly for a supergiant! Credit: Swinburne University of Technology take a photo of your activity and send it to us. we'd love to see it! [email protected] STARDOME.ORG.NZ 09 624 1246 TEMPLATE stellar analyses DATA TABLE Luminosity Stage of Internal STAR Temp (K) Elements up to End State (sols) Evolution processes Sun 1.00 5,750 MS Core H=>He C & O White Dwarf STARDOME.ORG.NZ 09 624 1246.
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