Figure 2 shows optical spectra of four different stars (red line). (a) List the names of the stars in order of the surface temperature (from high to low). [5 points] (b) Make a rough estimate of the surface temperature of each star if possible. If it is not possible to infer the surface temperature, give a lower or an upper limit instead [10 points]. 1.4 1.2 Star 1 0.8 Normalized flux (A-") Normalized flux (A ') 0.6 Star 2 0.2 0.1 A(A ) -0. 3500 4000 4500 5000 5500 6000 6500 7000 7500 Wavelength(A) 3500 4000 4500 5000 6000 6500 7000 7500 Wavelength(A) 1.2 MILES 3.5 ABF Interpolation 0.8 2.5 0.6 -Normalized flux (A") Star 4 Normalized flux (A ') 1.5 Star 3 0.5 RBF Interpolation - MILES 0.2 0.3 -0.3 3500 4000 4500 5000 6000 6500 7000 7500 Wavelength(A) 3500 4000 4500 5000 5500 6000 6500 7000 7500 Wavelength(A) Figure 2: The red line in the upper panel of each figure gives stellar spectra. The x-axis gives the wavelenth in units of A, and the y-axis is the normalized flux. Cf: 1.0 A= 10- cm