Parallax question.

[lqg]

The question:

A triple stellar system, showing a parallax of 0.01 arcsecond, is composed of a binary system,

with a distance between the two stars of 0.2 AU, and a third star, at a distance of 90 AU from

the binary. This system is observed in the optical (wavelength of 55000 Angstram) with a 1 meter telescope.

a. What is the distance of this system ?

b. How many stars will actually be seen when using a space-based telescope ?

c. How many stars will be seen when using a ground-based telescope, where the typical seeing

is 1 arcsecond ?

 

 

My attempt at solution

a. Well,[latex]\theta=0.01[arcseconds][/latex]

,[latex]D=\frac{\lambda}{\theta}[/latex] where lambda is the wavelenghth given in the brackets, and D is the distance of this stellar system from earth.

 

Don't know how to do b. and c., any advice?

 

Thanks in advance.