Reference no: EM132450727

1. Stellar Fluxes and Luminosities

An astronomer measures the apparent brightnesses (i.e. ux, or Watts/m2) of Star A and Star B to be identical. At the same time, the astronomer measures the parallax (in arcseconds) of Star A to be 4 times larger than that of Star B.

(a) Which star is further away? Express the distance to Star B in terms of the distance to Star A.

(b) Which star has a greater luminosity? Express the luminosity of Star B in terms of the luminosity of Star A.

2. The Properties of Vega

The star, Vega, has a surface temperature, TV ega = 9600 K. It also has a luminosity LV ega = 40L? (expressed in terms of the solar luminosity, L?). What is the radius of Vega, RV ega, in terms of the solar radius, R??

3. The Properties of White Dwarfs

(a) An astronomer obtains the spectrum of a white dwarf star, and determines that it peaks in the ultraviolet at = 150 nm, similar to the spectra of very luminous main-sequence stars. What is the surface temperature of the white dwarf?

(b) At the same time, the astronomer determines that the intrinsic luminosity of the white dwarf is only LWD = 0:01L? (i.e. 1% of the luminosity of the Sun). As discussed in class, the luminosity and temperature of a star can be used to infer its radius. What is the radius of the white dwarf star? Express your answer in terms of the radius of the Sun, R?, and the radius of the earth, R. (i.e., how many solar [Earth] radii is this? Or, on the other hand, what fraction of the solar [Earth] radius is this?)