Question

Recall from your homework last week that the lowest-mass stars are called "M-dwarfs", which have masses and diameters that are typically 1/5th that of the Sun.  These stars are also much cooler than the Sun.  The temperature of a typical M-dwarf star is approximately 3,000 K.  

(i) Calculate the wavelength of maximum intensity for the emission from an M-dwarf and compare it to that of the Sun (T_Sun = 5,800 K).  

(ii) Sketch the thermal spectrum of each star together on the same set of axes (wavelength on the x-axis, and relative intensity of light on the y-axis).  Make sure to label your axes, and indicate which spectrum is which.  You do not need to worry about providing correct numerical values, but your graph should be qualitatively correct.  

(iii) Use your plot to explain (a) why M-dwarfs are also commonly referred to as “red dwarfs”, and (b) why human eyes might have adapted to be sensitive to light in the visible portion of the spectrum.

Answer 1