A star with spectral type A0 has a surface temperature of 9600 K and a radius of 2.2 RSun. How many times more luminous is this star than the Sun?  and  This star has a mass of 3.3 MSun. Using the simple approximation that we made in class, what is the main sequence lifetime of this star?

A main sequence star of mass 25 M⊙has a luminosity of approximately 80,000 L⊙. a. At what rate DOES MASS VANISH as H is fused to He in the star’s core? Note: When we say “mass vanish '' what we really mean is “gets converted into energy and leaves the star as light”. Note: approximate answer: 3.55 E14 kg/s b. At what rate is H converted into He? To do this you need to take into account that for every kg of hydrogen burned, only 0.7% gets converted into energy while the rest turns into helium. Approximate answer = 5E16 kg/s c. Assuming that only the 10% of the star’s mass in the central regions will get hot enough for fusion, calculate the main sequence lifetime of the star. Put your answer in years, and compare it to the lifetime of the Sun. It should be much, much shorter. Approximate answer: 30 million years.

A red giant star has a temperature of 3900  K and a luminosity of 13600 LSun. How many times bigger is this star than the Sun? Hint: You need the surface temperature of the sun for this problem. Use the value in the book, 5800K.

What is the total mass of a visual binary system if the average separation of the stars is 7.1 AU and their orbital period is 12 years?

12. A star with spectral type MO has a surface temperature of 3750 K and a radius of 0.63 Rsun: How many times more luminous is this star than the Sun? (if it is less luminous enter a number less than one) Answer: Submit All Answers Last Answer: 0.0923 Incorrect, tries 1/5. Hint: Use the Luminosity equation, which says that L is proportional to R^2 T^4. If you keep these as ratios compared to the sun, your L will also come out as a ratio compared to the Sun. This star has a mass of 0.4 Msun- Using the simple approximation that we made in class, what is the main sequence lifetime of this star? You may assume that the lifetime of the sun is 1010 yr. Answer: Submit All Answers Compare this to the lifetime of a MO star listed in Table 22.1 (computed using a more sophisticated approach). Is the value you calculated in the previous problem longer or shorter than what is reported in the table? (L for longer, S for shorter) (You only get one try at this problem.) Answer: Submit All Answers

Consider two stars on the main sequence, A and B. Star A has a mass of 4 M⊙. Star B has a mass of 0.8 M⊙.  By what factor is the luminosity of star A greater than the luminosity of star B?

Consider two stars on the main sequence, A and B. Star A has a mass of 6 M⊙. Star B has a mass of 0.3 M⊙.  Compute the ratio of main sequence lifetimes for the two stars, TB/TA .

The star Rigel has a radial velocity r = 20.7km s-1, parallax 700 = 4.22mas, and proper motion components la= 1.67mas yr'in right ascension and us = 0.56mas yr1 in declination. What are its total proper motion, %3D %3D %3D tangential velocity, and space motion?