Question

The star P Cygni (in the constellation Cygnus, the Swan) is surrounded by an extensive low-density atmosphere. It has a bright, continuous spectrum with many narrow, dark absorption lines and a few bright emission lines. The bright, continuous part of the spectrum is produced by:________.

a) all parts of the star, the stellar surface and the atmosphere, equally.
b) only the part of the low-density atmosphere that is between us and the surface of the star.
c) the hot, dense, opaque gas of the star's surface.
d) the hot, low-density atmosphere of the star emitting light in all directions.

Answer 1

The bright, continuous part of the spectrum of P Cygni is produced by the star's hot, low-density atmosphere emitting light in all directions.

Step-by-step explanation:

The bright, continuous part of the spectrum of the star P Cygni is produced by the hot, low-density atmosphere of the star emitting light in all directions. This is indicated by the presence of bright emission lines in the spectrum. The low-density atmosphere allows the emitted light to travel relatively unobstructed, resulting in a continuous spectrum.

Answer 2

b) only the part of the low-density atmosphere that is between us and the surface of the star.

Step-by-step explanation:

Since in the case of the stars, the photons that are received are not directly from the nucleus, but those that have traveled hundreds of thousands of years to reach the stellar atmosphere. Due to the stars are not at homogeneous temperature, density and pressure, but have gradients in different layers because of the nuclear reactions, superficial gravity or to their constant exchange of heat with their surroundings in an attempt to reach the thermodynamic equilibrium, the continuum observed in the stellar spectra comes from the inner layer of the photosphere.