* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Lecture 5
Chinese astronomy wikipedia , lookup
Space Interferometry Mission wikipedia , lookup
Constellation wikipedia , lookup
Rare Earth hypothesis wikipedia , lookup
Aries (constellation) wikipedia , lookup
Star of Bethlehem wikipedia , lookup
Dialogue Concerning the Two Chief World Systems wikipedia , lookup
Canis Minor wikipedia , lookup
Dyson sphere wikipedia , lookup
Corona Australis wikipedia , lookup
International Ultraviolet Explorer wikipedia , lookup
Auriga (constellation) wikipedia , lookup
Cassiopeia (constellation) wikipedia , lookup
Corona Borealis wikipedia , lookup
Future of an expanding universe wikipedia , lookup
Cygnus (constellation) wikipedia , lookup
Canis Major wikipedia , lookup
Observational astronomy wikipedia , lookup
Cosmic distance ladder wikipedia , lookup
H II region wikipedia , lookup
Perseus (constellation) wikipedia , lookup
Star catalogue wikipedia , lookup
Aquarius (constellation) wikipedia , lookup
Stellar classification wikipedia , lookup
Timeline of astronomy wikipedia , lookup
Stellar evolution wikipedia , lookup
Stellar kinematics wikipedia , lookup
Final part of The Nature of the Stars Chapter 19 • The iClickers are in the bookstore…please get them if you want extra credit. We will start using them next week! • You will need to register them on the web: http://www.iclicker.com/registration/index.html Questions for the class (iClicker) 1. Consider the spectral classification of stars using only the letters A B F G K M O. When these are arranged in order from coolest to hottest they would be: A. B. C. D. E. O-B-A-F-G-K-M M-K-G-F-A-B-O A-B-O-F-G-K-M M-K-G-F-O-B-A B-A-G-K-O-M-F Questions for the class (iClicker) 2. Using the Hertzsprung-Russell diagram above, determine which type of star has the following characteristics: surface temperature of 40,000 K and luminosity 100,000 times that of the Sun. A. white dwarf B. main sequence red dwarf C. red giant D. blue main sequence star Questions for the class (iClicker) 3. The ratio of the brightness of a star at two different colors, blue and visual –bv/bB- is a direct measure of what property of the star? A. distance from Earth B. surface temperature C. luminosity D. radius By carefully examining a star’s spectral lines, astronomers can determine whether that star is a main-sequence star, giant, supergiant, or white dwarf Using the H-R diagram and the inverse square law, the star’s luminosity and distance can be found without measuring its stellar parallax Just from the spectra->luminosity Classes (the higher the number the lower The luminosity) Spectroscopic Parallax (no parallax involved though!) NO MATTER HOW DISTANTE A STAR IS! Example: Star B8 V How much is its Luminosity????? Why stars have different spectral types and luminosities? Stars Masses How do we determine their masses? No direct way for an Isolated Star BUT: double stars…. Optical Double Stars (not at the same position but along the line of sight) We are looking for binaries! Visual Binaries A Binary Star System Binary Stars • Binary stars, in which two stars are held in orbit • around each other by their mutual gravitational attraction, are surprisingly common • Those that can be resolved into two distinct star images by an Earth-based telescope are called visual binaries • Each of the two stars in a binary system moves in an elliptical orbit about the center of mass of the system Some periods can be very long! Binary star systems provide crucial information about stellar masses • Binary stars are important because they allow astronomers to determine the masses of the two stars in a binary system • The masses can be computed from measurements of the orbital period and orbital dimensions of the system How do I determine a (semimajor axis)? Angular separation (convert to physical distance) For that I need to know the distance to the binary (parallax measurements or spectroscopic parallax) But still this only give me M1+M2 Center of Mass Movie….. The center of mass lies along the line connecting the two stars It can be found by plotting the separate orbits of the two stars using the background stars as reference. Comparing the relative sizes of the orbits around the center of mass yields M1/M2 We know M1+M2 M1, M2 Mass-Luminosity Relation for MainSequence Stars • Main sequence stars are stars like the Sun but with different masses • The mass-luminosity relation expresses a direct correlation between mass and luminosity for main-sequence stars • The greater the mass of a main-sequence star, the greater its luminosity (and also the greater its radius and surface temperature) (for radius: look at H-R diagram) Mass-Luminosity Relation For radius: look at H-R diagram Why Mass Control the Properties of a MainSequence Star? • Main sequence stars are same as Sun>thermonuclear reactions • Greater the Mass, greater the pressure and temperature at the Core->FASTER thermonuclear reaction->more LUMINOUS • Models of Main-Sequence Stars: for the stars to maintain equilibrium, more massive->larger radius, higher surface T (look at the HR diagram) Spectroscopy makes it possible to study binary systems in which the two stars are close together • • • • Some binaries can be detected and analyzed, even though the system may be so distant or the two stars so close together that the two star images cannot be resolved A spectrum binary appears to be a single star but has a spectrum with the absorption lines for two distinctly different spectral types A spectroscopic binary has spectral lines that shift back and forth in wavelength This is caused by the Doppler effect, as the orbits of the stars carry them first toward then away from the Earth From the Doppler Shift -> Radial Velocity Orbital Period Light curves of eclipsing binaries provide detailed information about the two stars • • An eclipsing binary is a system whose orbits are viewed nearly edge-on from the Earth, so that one star periodically eclipses the other Detailed information about the stars in an eclipsing binary can be obtained from a study of the binary’s radial velocity curve and its light curve Questions (iClicker) • 4. Absorption lines in the spectra of some binary stars are seen to change periodically from single to double lines and back again. Why is this? – A. Oscillations on the surfaces of the stars leads to Doppler-shifted lines. – B. Periodically, the magnetic field of one star produces Zeeman splitting of spectral lines in atoms of the second star. – C. The effect of the gravitational field of one star on the atoms of the second star produces spectral line shifts periodically. – D. Motion toward and away from Earth during their orbital motion results in Doppler shift of light from these stars at times and no shift when the stars are moving perpendicular to the line of sight. Light Curves of Eclipsing Binaries Light curve has a different shape due to tidal interactions Light curves can yield information about ratio of surface temperatures, The duration of an eclipse can tell astronomers about the relative sizes and their Orbits.