The Cepheid Variable.

22 Aug
English: The oldest star of our Galaxy: HE 152...

English: The oldest star of our Galaxy: HE 1523-0901 (Photo credit: Wikipedia)

English: Diagram of how a common envelope is f...

Wireless Temperature Sensor Module uploading t...

Wireless Temperature Sensor Module uploading to emoncms via Nanode (Photo credit: Nathan Chantrell)

This ZAMS mass-luminosity table was generated ...

This ZAMS mass-luminosity table was generated using data from the isocrone calculation tool of Lionel Siess. The metallicity (Z) is 0.02 and the axis units use solar values. Note that the present-day Sun is more luminous than when it first joined the main sequence. (Photo credit: Wikipedia)

6. b) The graphs show the sensitivity of a particular brand photographic film and that of a charge coupled device, CCD, to different parts of the e.m spectrum.

The surface temperature of a star can be calculated once the wavelength of the peak of its spectrum (λmax) is known.  Use the graphs to explain why photographic film would be less suitable than CCDs for determining (λmax) for a star which radiates mainly in the visible region (400nm-700nm) of the e.m spectrum.

6b) (Answer.) The bandwidth of the film is from 350nm to 700nm whereas that of the CCD is from 300nm to 1000nm. The CCD is more suitable because the   relative sensitivity of the film is not uniform and ranges from 0.5 to a maximum of 1.0. The CCD is much better in this regard for it is uniform and close to 1 for the entire spectrum.

6c) State what happens to the hydrogen ‘burning’

6c) (Answer) The hydrogen fuses to become Helium and that is more stable.  When time will allow the star will be low in fuel and it will expand slightly.  This expansion causes the temperature to fall and the star becomes a red giant.

Why is a red giant more luminous than the main sequence star from which it originated, even though its temperature is lower?                      (1)

The luminosity depends upon the square of the radius and the 4th of the temperature.  The red giant expands more hence the radius factor plays a more important role than the temperature factor.

6d). Describe how observations of Cepheid variable stars are used to estimate the distance to nearby galaxies.

A longer time period for oscillation meant an intrinsically brighter star.  Astronomers then took this relationship and used it to determine the luminosity of variable stars at much greater distances.  From the luminosity, the distance to these stars can be determined using our expression for the radiant energy flux observed here on Earth.  Hence the estimate to the distance can be measured.

e)    Explain the meaning of the term binary system (1)

It is a star system which is made up of two stars having a common centre.

f)     At A C and E the light intensity  gets lower due to the fact that  shadow of one of the stars falling on the other.

g)    The dip at A is much smaller due to the fact that the other star is smaller. Whereas the dip at C is larger because the opposing star is larger.

h)   Estimate the orbital period of this binary.

From 2 hours to 24 hours or 22 hours.

Estimate the orbital period of this binary. (1)

i)     From B to D: 8 to 19 hours or 11 hours.

  1. Annual parallax method

tan θ = r/ d.

It is not a suitable method because it uses the parallax method hence it cannot be used for distant stars more than 650 ly.

  1. The two ways the white      dwarfs differ from the mainline stars are there is intense gravitational      pressure.  This makes it very small      in size.

Describe what happens to a star when it becomes a white dwarf?

Its strong gravitational field outweighs the fusion. And becomes very low luminous star,

  1.  40,0000K , 20,000K  10,000K, 5000K, 2500K

b) L = 1

lower left hand corner.

L= 104

They burn out quickly intense nuclear radiation.

  1.  The surface temperature could be same but      then again not for the colour is dependent upon the surface area and the      temperature.
  1. F = L/ A

Deneb has greater surface area. The luminosity is much larger,

  1.  Work it out your self.

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