AST
Astrophysics of Life

# Using the hr diagram to determine distance

• Notes
• 3

This preview shows page 3. Sign up to view the full content.

Using the HR Diagram to Determine Distance: Spectroscopic “Parallax” (1) Determine temperature from color (2) Determine luminosity based on main sequence position (3) Compare luminosity with flux (apparent brightness) (4) Use inverse square law to determine distance Flux = luminosity / 4pid^2 d = sqrt[L / 4piF] What if the star doesn’t happen to lie on the main sequence? Maybe it is a red giant or white dwarf? We determine the star’s luminosity class based on its spectral line widths These lines get broader when the stellar gas is at higher densities – indicating a smaller star Stellar Masses: Visual Binary Stars With Newton’s modifications to Kepler’s laws, the period and size of the orbits yield the sum of the masses, while the relative distance of each star from the center of mass yields the ratio of the masses The ratio and sum provide each mass individually Why is mass so important? Together with the initial composition, mass defines the entire life cycle and all other properties of the star! Luminosity, radius, surface temperature, lifetime, evolutionary phases, end result . . . Example: On the main sequence: Luminosity proportional mass^2 More mass means: more gravity, more pressure on core, higher core temperatures, faster nuclear reaction rates, higher luminosities How does mass effect how long a star will live? Lifetime proportional fuel available / how fast fuel is burned So for a star: lifetime proportional mass / luminosity How long a star lives is directly related to the mass! Big stars live shorter lives, burn their fuel faster . . .
This is the end of the preview. Sign up to access the rest of the document.
• Spring '08
• Eikenberry
• Astrology, Stefan, luminosity, apparent brightness

{[ snackBarMessage ]}

### What students are saying

• As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

Kiran Temple University Fox School of Business ‘17, Course Hero Intern

• I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

Dana University of Pennsylvania ‘17, Course Hero Intern

• The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

Jill Tulane University ‘16, Course Hero Intern