Understanding Critical Features of Stars and Their Categorization
Explore the essential features of stars, such as temperature, color, spectral class, subclasses, luminosity, and more. Discover how these aspects help us categorize and understand stars better, from their temperatures to luminosity classes. Dive into the fascinating world of star classification and characteristics.
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Presentation Transcript
Learning about Stars What features are critical? What can we learn? Are there categories?
Temperature Stars are close to black body emitters Spectrum depends on temperature
Color Temperature Measure starlight through different color filters conventionally blue and yellow Color index is the difference in relative intensity Plot B V directly or match to B V of theoretical black body
Spectral Class Computers at Harvard College Observatory continued the Henry Fraper catalogue of stars to m = 9 Annie Jump Cannon classified stars by the strength of their Balmer absorption lines classes A P in descending intensity Classes correlate with temperature O, B, A, F, G, K, M in current use descending temperature
Subclasses Large temperature variations between classes Divided further into subclasses 0 9 0 is hottest, 9 is coolest So an A9 is close in temperature to a F0 The Sun is a G2 star
Temperature and Luminosity Separate of correlated?
Hertzsprung-Russell Diagram Plot absolute luminosity (M) vs temperature Bright Luminosity Dim Hot Cool Temperature
Stars within 10 pc Image: The Astrophysics Spectator
Visible Stars within 50 pc Image: The Astrophysics Spectator
H-R Groupings Most stars are main sequence top left bottom right diagonal Some are bright giants and supergiants large for their temperature Some are very hot and dim white dwarfs must be very small
Luminosity Classes Some stars are much brighter than others at the same temperature they must have much more surface area A larger star will have a less dense atmosphere Can measure pressure broadening of spectra Sharper spectra from larger stars
Luminosity Classes Classes I V Sun is a G2V star
Distance from Spectrum If we know a star s spectral class and luminosity class, we can estimate its absolute magnitude (Approximately) We can find its distance from its apparent magnitude (Approximately) This is called spectroscopic parallax
Stellar Mass Physics knows two phenomena involving mass inertia gravity We can t push a star to see how it reacts But we can watch it interact with other bodies
Binary stars Stars orbit their mutual center of mass Physics tells us that ?3 ?2 ?1+ ?2 where a is distance T is orbital period m1 and m2 are masses
Binary stars If we can find their center of mass, we learn each individual mass
Spectroscopic Binaries If the binaries eclipse each other: Can detect orbital periods and approach and recessional velocities by Doppler shift Can get information about relative sizes
