2 of 7 Question A2 a) Calculate the mass loss rate of the Sun M due to the solar wind flow. Assume average properties of the solar wind of number density 6 protons cm³, and a flow speed of 450 km s-1. Express your answer in units of both kg per year, and solar masses per year. b) Suppose the solar wind flow is perfectly radial. Calculate the expected rate of change of solar rotation frequency dw at the present time, based on conservation of angular momen- tum. Give your answer in units of rad s-1 y-1 (i.e., radians per second per year) and also in terms of fractional change per year, i.e., 1 du. w dt' Use a current solar rotation period of P = 25.38 days to calculate the current angular frequency of rotation w. The moment of inertia of a uniform sphere is MR². You can assume that the radius of the Sun is approximately constant, and the change in its moment of inertia due to the solar wind is only due to the mass loss. Page 3 c) By observing the rotation period of stars similar to the Sun, it is inferred that their rotation rate decreases with age such that * x age -1/2 Briefly explain how this compares with your previous result. State the implication of the observational result in terms of the action of a stellar wind. Give one possible factor that might be important to explain the observed behaviour of the rotation rate.

2 of 7 Question A2 a) Calculate the mass loss rate of the Sun M due to the solar wind flow. Assume average properties of the solar wind of number density 6 protons cm³, and a flow speed of 450 km s-1. Express your answer in units of both kg per year, and solar masses per year. b) Suppose the solar wind flow is perfectly radial. Calculate the expected rate of change of solar rotation frequency dw at the present time, based on conservation of angular momen- tum. Give your answer in units of rad s-1 y-1 (i.e., radians per second per year) and also in terms of fractional change per year, i.e., 1 du. w dt' Use a current solar rotation period of P = 25.38 days to calculate the current angular frequency of rotation w. The moment of inertia of a uniform sphere is MR². You can assume that the radius of the Sun is approximately constant, and the change in its moment of inertia due to the solar wind is only due to the mass loss. Page 3 c) By observing the rotation period of stars similar to the Sun, it is inferred that their rotation rate decreases with age such that * x age -1/2 Briefly explain how this compares with your previous result. State the implication of the observational result in terms of the action of a stellar wind. Give one possible factor that might be important to explain the observed behaviour of the rotation rate.